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  • 1. Andersson, Elliot
    et al.
    Guldbrandsson, Andreas
    Värdeflödesanalys av process förframtagning av PM-pulver2023Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
  • 2.
    Andersson, Felix
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Optimization of the process-route of a Nickel-base alloy: Investigation of Sigma-phase precipitation in heat treatment2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The focus of this master’s thesis is on the heat treatment of Ni-base alloys, specifically the risk of intermetallic σ-phases during different stages of heat treatment. The alloy studied is Sanicro®28, a super-austenitic stainless steel produced by Alleima AB. The problem at hand is that the quench-annealing stage is in high demand at the manufacturing facility, and the goal is to investigate if it can be removed from the manufacturing route. During forging, the outer surface and bar-ends can reach low temperatures, posing a high risk of σ-phase precipitation. Additionally, a necklace structure with large grains surrounded by fine re-crystallization is often observed at the surface of forged superalloys/Ni-base alloys. Today, this forged structure is re-crystallized and σ-phase dissolved during the quench-annealing stage. An alternative to quench-annealing after forging is to re-heat the bar using a Car Wagon Furnace(CWF).

    The thesis includes two laboratory experiments simulating two stages of heat treatment, the CWF and induction furnaces/soaking. The samples subjected to simulated CWF treatment showed re-crystallization throughout the entire structure. Annealing in CWF removes the large grains in surface positions. The time in the CWF also showed to be sufficient to dissolve σ-phase present from forging. Samples heated to the induction furnace set temperature do not contain precipitates, while temperatures below the induction set temperature induce σ precipitation to varying degrees. The key findings of the thesis are as follows:

    • Re-heating in a CWF right after forging is enough to dissolve σ-phase at half-radius and surface locations.

    • Quench-annealing stage could be removed by changing the route to a CWF after forging.

    • If temperatures fall below the σ-maximum stability temperature during induction furnace heating cycles, σ-phase precipitation occurs.

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  • 3.
    Andersson, Sofia
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Study of Dross in Ductile Cast Iron Main Shafts2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The study of dross in ductile cast iron main shafts was performed at Global Castings Guldsmedshyttan AB and presented in this master thesis. The purpose of the study was to obtain answers to why dross defects were present in some of the foundry's casted main shafts, with the main problem located at the flange of the shaft. The chemical composition of the dross formations and which steps in the casting process that increased the dross formation were of interest. The study only included dross in main shafts manufactured at Global Castings Guldsmedshyttan AB.

    Dross particles form when elements such as Mg, Ca, Si and Mn react with O. These elements, which are highly reactive to O, are used in ductile cast irons to achieve the spheroidal graphite nodules that regulate the cast materials ductile properties. If a higher amount of dross particles has formed, the particles will start to cluster, resulting in a growing dross formation. Dross formations works as surface crack initiation points and reduces the castings fatigue strength and ductility.

    During the study it was seen that the cause of dross formations is a combination of many parameters increasing the melts exposure to O resulting in dross defects. The dross formations could be connected to worn out ladles, low melt temperatures, incorrect additions of Mg treatment, lack of an extra slag removal station and finally turbulence as the melt were poured into the mould.

    At Global Castings Guldsmedshyttan AB a greater part of the main shafts containing dross defects were a result of worn out ladles and low melt temperatures. The types of dross found in the main shaft material were mainly Mg, Ca, Si and Al which had reacted with O. S bonded with Mg and Ca was also detected in the dross formations. It was shown that the dross particles could be derived from charge material, Mg treatment and inoculation.

    To avoid dross defects the first step would be to set up an extra slag station, shorten the interval of maintenance of the ladles and to better adjust the melt temperature to the condition of the specific ladle. To minimize dross due to excess Mg a better controlled process would be recommended with an increased number of monitored manufacturing parameters.    

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  • 4.
    Andersson, Stefan
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Analysis of welding in comparable steel grades: Influence of steel grade on the welding process2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is written to examine the influence of different low carbon steel sheet materials on the GMAW welding process. During welding the properties of the base material influence the productivity of the welding process. The purpose of this thesis is to examine how the choice of material and welding speed affect the welding process and the productivity.

    A literature survey was performed to describe the welding technique and the differences in manufacturing for the sheet materials as well as the effect of alloying and welding on the sheet material. Defects in the weld and methods used to determine them are explained. Test pieces of the different sheet materials were welded with the GMAW process and examined.

    The result shows that there is a variation in the welding process regarding weld penetration. Measurements also show that welding speed and gap have little influence on the hardness of the weld and heat-affected zone and that the S355MC is more likely to suffer from a narrower toe transition radius than S355NL and S355MC Si. This and the higher area in the Y2 region for the S355MC could indicate a stronger inward flow in the weld pool during welding possibly a result of surface active agents such as oxygen and sulphur.

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  • 5.
    Bergh, Gustav
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Förslitning av fräsverktyg2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
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  • 6.
    Birgmark, Anja
    Karlstad University, Faculty of Technology and Science.
    Wear of Coater Blades2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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  • 7.
    Chantziara, Katerina
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Very HIgh Cycle Fatigue (VHCF) behavior of high strength alloys: A literature review2023Report (Other academic)
    Abstract [en]

    Very High Cycle Fatigue (VHCF) response of metallic materials is considered of significance importance, particularly for high- demanding applications. Since it is proved that most of the engineering materials do not exhibit a conventional fatigue limit, but rather display a continuously decreasing stress-life response at longer lifetimes. Consequently, the investigation of the various mechanisms are taking place during VHCF is essential. The primary object of the present effort is to explore and summarize recent developments and current status of the VHCF phenomenon in high strength alloys.

    The development of the new ultrasonic machines made the fatigue testing beyond 107 life cycles possible in a very shorter time, leading to fatigue fractures at stress levels lower than the traditionally proposed “fatigue limit”. Nowadays, a classification between Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) is commonly used. The main reasons for this specific grading are: i) the need for safe design of components and ii) the fact that the failure mechanisms are particular in each of the LCF, HCF and VHCF regimes.

    Ultrasound machines, also called piezoelectric, are resonance fatigue testing machines reducing the testing time at least 400 times compared to the conventional machines operating at frequencies up to 20 kHz.

    The crack initiation stage is one of the most investigated subjects when it comes to VHCF. Usually, the fatigue initiates from a defect (inclusion, pore, grain boundary triple points), while up to 99% of fatigue life is consumed in that stage. Different models have been proposed in the literature regarding the evolution of events that contribute to the fatigue crack initiation and growth. Proposed models are such as the ODA, the polygonization, continuous grain refinement with local plasticity, the matrix fragmentation and the NCP numerous cyclic pressing. Several studies have assessed the different models and further enriched the knowledge in the VHCF field.

    In the present literature review effort, the main VHCF mechanisms of crack initiation and growth as well as the proposed models are presented and analyzed. Moreover, the VHCF response and the recent experimental results referring to the most used engineering alloys, e.g. steels, Ti, Ni, Al and Mg alloys, are described, with a main attention to steels. The different testing parameters and the way they affect the VHCF response are also presented.

    Finally, the literature review is concluded by presenting the new challenges and directions for future work in the field, especially under the light of the new low-carbon society.

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  • 8.
    Deisenroth, David C.
    et al.
    NIST The Intelligent Systems Division, USA.
    Mekhontsev, Sergey
    NIST, Sensor Sci Div, USA.
    Lane, Brandon
    NIST The Intelligent Systems Division, USA.
    Hanssen, Leonard
    NIST, Sensor Sci Div, USA.
    Zhirnov, Ivan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). NIST, Sensor Sci Div, USA.
    Khromchenko, Vladimir
    NIST, Sensor Sci Div, USA.
    Grantham, Steven
    NIST, Sensor Sci Div, USA.
    Cardenas-Garcia, Daniel
    NIST, Sensor Sci Div, USA.;Ctr Nacl Metrol, Carretera Los Cues, MEX.
    Donmez, Alkan
    NIST The Intelligent Systems Division, USA.
    Measurement Uncertainty of Surface Temperature Distributions for Laser Powder Bed Fusion Processes2021In: Journal of research of the National Institute of Standards and Technology, ISSN 1044-677X, E-ISSN 2165-7254, Vol. 126, article id 126013Article in journal (Refereed)
    Abstract [en]

    This paper describes advances in measuring the characteristic spatial distribution of surface temperature and emissivity during laser -metal interaction under conditions relevant for laser powder bed fusion (LPBF) additive manufacturing processes. Detailed descriptions of the measurement process, results, and approaches to determining uncertainties are provided. Measurement uncertainties have complex dependencies on multiple process parameters, so the methodology is demonstrated on one set of process parameters and one material. Well-established literature values for high-purity nickel solidification temperature and emissivity at the solidification temperature were used to evaluate the predicted uncertainty of the measurements. The standard temperature measurement uncertainty is found to be approximately 0.9 % of the absolute temperature (16 degrees C), and the standard relative emissivity measurement uncertainty is found to be approximately 8 % at the solidification point of high-purity nickel, both of which are satisfactory. This paper also outlines several potential sources of test uncertainties, which may require additional experimental evaluation. The largest of these are the metal vapor and ejecta that are produced as process by-products, which can potentially affect the imaging quality, reflectometry results, and thermal signature of the process, while also affecting the process of laser power delivery. Furthermore, the current paper focuses strictly on the uncertainties of the emissivity and temperature measurement approach and therefore does not detail a variety of uncertainties associated with experimental controls that must be evaluated for future generation of reference data.

  • 9. Dzogbewu, T
    et al.
    Yadroitsev, Igor
    Central University of Technology, ZAF.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, Inna
    Central University of Technology, ZAF.
    Du Plessis, Anton
    University of Stellenbosch, ZAF.
    Optimal process parameters for in situ alloyed Ti15Mo structures by laser powder bed fusion2017In: Solid Freeform Fabrication 2017Proceedings of t he 28th Annual International Solid Freeform Fabrication Symposium–An Additive Manufacturing Conference, 2017, p. 75-96Conference paper (Refereed)
  • 10.
    Ejnermark, Sebastian
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Mjukglödgning av ett plastformsstål2012Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
  • 11.
    Ekengren, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Large and rare: An extreme values approach to estimating the distribution of large defects in high-performance steels2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The presence of different types of defects is an important reality for manufacturers and users of engineering materials. Generally, the defects are either considered to be the unwanted products of impurities in the raw materials or to have been introduced during the manufacturing process. In high-quality steel materials, such as tool steel, the defects are usually non-metallic inclusions such as oxides or sulfides.

    Traditional methods for purity control during standard manufacturing practice are usually based on the light optical microscopy scanning of polished surfaces and some statistical evaluation of the results. Yet, as the steel manufacturing process has improved, large defects have become increasingly rare. A major disadvantage of the traditional quality control methods is that the accuracy decreases proportionally to the increased rarity of the largest defects unless large areas are examined.

    However, the use of very high cycle fatigue to 109 cycles has been shown to be a powerful method to locate the largest defects in steel samples. The distribution of the located defects may then be modelled using extreme value statistics.

    This work presents new methods for determining the volume distribution of large defects in high-quality steels, based on ultrasonic fatigue and the Generalized Extreme Value (GEV) distribution. The methods have been developed and verified by extensive experimental testing, including over 400 fatigue test specimens. Further, a method for reducing the distributions into one single ranking variable has been proposed, as well as a way to estimate an ideal endurance strength at different life lengths using the observed defects and endurance limits. The methods can not only be used to discriminate between different materials made by different process routes, but also to differentiate between different batches of the same material.

    It is also shown that all modes of the GEV are to be found in different steel materials, thereby challenging a common assumption that the Gumbel distribution, a special case of the GEV, is the appropriate distribution choice when determining the distribution of defects.

    The new methods have been compared to traditional quality control methods used in common practice (surface scanning using LOM/SEM and ultrasound C-scan), and suggest a greater number of large defects present in the steel than could otherwise be detected.

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  • 12.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Estimating the volume distribution of large defects using Generalized Extreme Values2011Manuscript (preprint) (Other academic)
    Abstract [en]

    The presence of defects, such as oxides and other non-metallic inclusions, is an important factor in determining the properties of steels. Due to improvements in the manufacturing of high-quality steels, the amount of large defects has decreased and therefore it has become increasingly difficult to accurately determine their distribution using conventional methods. Previously, a method for estimating the distribution of large defects using a conversion from the Gumbel distribution has been presented. However, it has been shown that the Gumbel distribution is not always appropriate for modelling the sizes of the largest defects and that the Generalized Extreme Values (GEV) distribution should be used instead. In this work a more general method for the estimation of the total volume distribution of large defects isproposed, showing how the volume distribution may be calculated from the estimated parameters for the GEV distribution. The new method is applied to the results of a series of specimens made from high-quality tool steel tested in ultrasonic resonance fatigue. Possible methods for obtaining the confidence limits of thevolume distribution are also discussed.

  • 13.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Extreme value distributions of inclusions in six  steels2012In: Extremes, ISSN 1386-1999, E-ISSN 1572-915X, Vol. 15, p. 257-265Article in journal (Refereed)
    Abstract [en]

    There is a prevailing assumption that the largest inclusions in steel volumes follows mode I of the Generalized Extreme Values (GEV) distribution. In this work, the GEV distributions of non-metallic inclusions in six different high performance steels, of different grades and processing routes, were investigated by means of fractography of inclusions causing failure in ultrasonic fatigue testing to one billion cycles and all three modes of the GEV were found for the different steel grades. Values of the shape parameter ξ of the GEV distribution as high as 0.51 (standard deviation 0.11) were found in one steel grade. Thus, the present results show that the assumption of GEV-I (Gumbel, LEVD) distribution has to be substantiated before being used to estimate the size of the largest inclusions.

  • 14.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Influence of life length on estimated defect  distribution in a low defect steel material2011In: Proceedings of the Fifth International Conference on Very High Cycle Fatigue / [ed] C. Berger and H.-J. Christ, 2011, p. 177-182Conference paper (Refereed)
    Abstract [en]

    This paper reports on results of very high cycle fatigue tests on a steel with a relatively low number of defects per unit volume. Two series of newly designed dog-bone specimens, with low stress gradients, were tested at two constant stress levels, aiming at providing fatigue life lengths of 106–108 cycles and 107–109 cycles, respectively. Fatigue-initiating defects on the fracture surfaces were measured and the corresponding size distributions were analysed to investigate the influence of the elevated stress level needed to achieve shorter life lengths.The presented results indicate a difference between the distribution of initiating defects in the long and shorter life length test series. The main conclusion is that fixed stress level fatigue testing to life lengths around 107 cycles may be a suitable method to estimate the content of large defects in low defect steel materials, provided a suitable test specimen geometry with low stress gradients is used.

  • 15.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Assessment of strength and inclusions of Tool Steels in Very High Cycle Fatigue2009In: Proceedings of the 8th International Tooling Conference, Vol 1 / [ed] P. Beiss, C. Broeckmann, S. Franke, B. Keysselitz, Verlag Mainz, Wissenschaftsverlag , 2009Conference paper (Refereed)
    Abstract [en]

    Fatigue strength is an important material property for many tooling applications, particularly in high performance applications. The research in Very High Cycle Fatigue (VHCF) has demonstrated that the traditional fatigue limit may not be valid for many materials subjected to 107 or more load cycles. Presently, both materials data and mechanism knowledge is missing on VHCF applications, even though many components are run at these life lengths. The fatigue strength is commonly controlled by different defects initiating failure, as in well controlled laboratory experiments may be internal inclusions. In this paper VHCF experimental testing was accomplished by the use of ultrasonic fatigue testing run at 20 kHz allowing long life evaluation within reasonably short test time. Fatigue strength, failure mechanisms and inclusion content were accordingly assessed. Fatigue strength data on H13 tool steel are presented, as well as a statistical approach considering available defect distribution and load distribution in the critically stressed volume, important to both steel supplier and end-user.

  • 16.
    Glaad, Gustaf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Pressurizing of high-pressure fuel system forsingle cylinder test cell2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis covers the development of a high-pressure fuel system for compression ignitedfuels such as diesel and diesel-like fuels that will be deployed into a single cylinder test cell at AVLMTC Södertälje, Sweden. The test cell is used by AVL to conduct research and testing of new fuelsfor their customers and this new fuel system will widen the span of fuels able to be tested by theequipment.This thesis focuses on pumping and pressurizing of the fuel, ensuring that all ingoing materialsare non-corrosive in this environment and compatible with the necessary fuels and lastly a safetyanalysis of the system with respect to operator and process safety. Other aspects of the projectsuch as mass flow measurements and fuel conditioning is covered in a sister thesis Mass flowrate measurement of compression ignition fuels in high-pressure stand-alone pump unit for singlecylinder test cell written by C. Aksoy [1].The goal of this thesis project was to deliver a finished manufactured fuel system and if the timeallowed for it, also validate its performance and finally installing and incorporating it into the singlecylinder test cell. The development process started with the writing of a product specificationoutlining the requirements and request on the product in a specification of requirements matrix andrelate these to product properties of the system using a quality function deployment (QFD) matrix.This document was then used as a base for further advancement in developing concepts to solveeach product property and weighing these concepts against each other using Pugh’s matrices. Thechosen concepts were then further developed, a flow chart for the system was developed as well asfuel lines and other supporting components were analyzed and chosen.In the end the high-pressure fuel pump from Scania’s XPI fuel system were chosen as well asa pressure transducer in the HP1000 series from ESI. Within the time frame of this thesis, theproject did not end up getting finished to the degree planned, but due to time constraints werehalted before starting manufacturing of the system. Some minor component choices remained aswell as documentation such as drawings and finalizing the physical layout of the system remained.All information regarding the remaining work needed to finalize the project and deploying thesystem in the test cell were outlined and with more time, the fuel system should fulfill its purposeof allowing testing and research of compression ignited fuel to be possible in the test cell.

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  • 17.
    Gåård, Anders
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Hallbäck, Nils
    Karlstad University, Faculty of Technology and Science.
    Galling resistance and wear mechanisms - cold work tool materials sliding against carbon steel sheets2007In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 26, no 1, p. 67-72Article in journal (Refereed)
  • 18.
    Hentschel, Oliver
    et al.
    Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany;Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
    Kohlstruck, Jan
    Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
    Vetter, Johannes
    Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany;Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
    Wittmann, Alexander
    Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany;Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
    Krakhmalev, Pavel
    Department of Engineering and Physics, Karlstad University, SE-651 88 Karlstad, Sweden.
    Nikas, Dimitrios
    Department of Engineering and Physics, Karlstad University, SE-651 88 Karlstad, Sweden.
    Schmidt, Michael
    Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany;Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
    Experimental Investigations in the Processing of AISI H11 Powder Blends Enriched with Tungsten Carbide Nanoparticles for the Additive Manufacturing of Tailored Hot Working Tools in the Directed Energy Deposition (DED-LB/M)—Impact of Tungsten Carbide Nanoparticles on Microstructural and Mechanical Characteristics2024In: Metals, E-ISSN 2075-4701, Vol. 14, no 2, p. 188-188Article in journal (Refereed)
  • 19.
    Hentschel, Oliver
    et al.
    Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Fredriksson, Gunnel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Olsèn, Jon
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Selte, Aydin
    Uddeholms AB, Sverige.
    Schmidt, Michael
    Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany.
    Influence of the in-situ heat treatment during manufacturing on the microstructure and properties of DED-LB/M manufactured maraging tool steel2023In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 315, article id 117928Article in journal (Refereed)
    Abstract [en]

    Due to high productivity, additive manufacturing (AM), and especially Directed Energy Deposition using laser and metallic powder (DED-LB/M) is attractive for manufacturing tools with integrated functionalities. This investigation was dedicated to DED-LB/M manufacturing of experimental maraging tool steel, characterization of the build microstructure with advanced electron microscopy and evaluation of hardness properties. High printability and low porosity of the final builds were observed, relative density was not lower than 99.5% for specimens manufactured with 600 W and 800 W, but microstructure and properties of the build had a gradient along the height. The characteristic hardness profile and microstructure, which were dependent on the manufacturing parameters, were observed. The top layers of manufactured maraging steel samples had a structure of martensite with precipitates presumably formed during solidification. The top layers were therefore softer to the depth of the austenitization isotherm. The higher hardness was measured in the inner regions which was a result of an in-situ heat treatment that the manufactured material was subjected to during layer-by-layer manufacturing. Thermal cycles during manufacturing resulted in precipitation hardening effect in the inner regions. Scanning and transmission electron microscopy confirmed the formation film-like and round particles in the as-build material, in top and inner regions. However, the quasicrystalline nano-sized R′-phase precipitates were observed only in the inner regions. The formation of the R′-phase precipitated during manufacturing as a result of the in-situ heat treatment was discussed as a reason for higher hardness (440 – 450 HV1) measured in the inner regions. 

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  • 20.
    Hidén Rudander, Petter
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Case hardened steel plates for ballistic armour: A study of ballistic and mechanical properties of case hardened ARMOX® steel2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Protective materials are a necessity to ensure the safety of personnel or property subjected to impacts by bullets, fragments and/or explosions. To shatter an inbound projectile, the surface of the target needs to exhibit a very high hardness but also the ability to prevent crack growth and plastically deform to avoid brittle fracture. The need for a combination of hardness and toughness led to the invention of dual hard steel which can be achieved within a homogeneous plate by modification of the surface through single-sided case hardening. In this work ARMOX® 440T and ARMOX® 500T was case hardened with a case depth of 2 and 2.3 mm and shoot upon with armour piercing rounds P80 to determine the ballistic limit of the material and to compare with the reference ARMOX®. Metallographic investigation was performed together with grain size measurement and mechanical properties were tested including hardness, impact toughness, dimensional deviation and tensile strength.

    A considerable increase of the ballistic performance with 40-70 % was reached by single-sided case hardening even though an irregular failure of the diffusion barrier had led to double-sided cases in various areas. Mass efficiency also increased considerably. Especially ARMOX® 440T was suitable for the treatment since it increased by the largest relative amount despite the fact that it had a thinner case then ARMOX® 500T plates.

    The complete penetrations were caused by formation of adiabatic shear bands and lead to punching of the plates except for hits at areas with double-sided case where back spall also occurred. The backside-case also resulted in a sharp reduction in impact toughness. Crack formation in close proximity to the impact site was found in all case hardened plates perpendicular to the front surface originating from inter-granular oxides near the surface.

    All the conventionally case hardened plates deviated from the reference plate flatness. Most likely because of placement in the furnace.

    Collectively the material is not recommended to be implemented in structural components until further investigations have been made concerning multi-hit threat, heat treat optimisation to minimize dimensional changes and bending because of the formation of perpendicular cracks under tensile load.

  • 21.
    Huang, M.
    et al.
    Harbin Institute of Technology, CHN.
    Lin, Fengxiang
    Université Catholique de Louvain, BEL.
    Xie, H.
    Shanghai Institute of High Energy Applied Physics, CHN.
    Role of layered structure in ductility improvement of layered Ti-Al metal composite2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 153, p. 235-249Article in journal (Refereed)
    Abstract [en]

    Layered Ti-Al metal composite (LMC) was designed and fabricated by hot-rolling and annealing of pure Ti and Al sheets. The as-prepared composite exhibits high tensile ductility, being superior to any individual Ti or Al sheets. The stress/strain evolution and fracture behavior of the LMC were analyzed by in-situ observations during the tensile deformation. Three deformation stages of LMC were clearly observed by neutron diffraction: elastic stage, elastic-plastic stage and plastic stage. It is found that stress partitioning at the elastic-plastic deformation stage improves the strain balance of LMC, but leads to an internal stress accumulated at the interface. Additionally, a strain-transfer from Ti to adjacent Al layers relieves the strain localization of Ti layers in LMC, which improves the ductility of Ti. Both stress partitioning and strain localization of Ti layers facilitate the nucleation of cracks at a low macro strain. However, the crack propagation is constrained by layered structure. In terms of the Al layers, the constrained micro-cracks relieve the stress concentration in Al layer and improve the ductility of Al layers, so that cracking indirectly affects the plastic deformation behavior of LMC, then improving its entire ductility. This work provides a new structural strategy towards simultaneously improving strength and ductility to develop high performance LMC by structural design. © 2018 Acta Materialia Inc.

  • 22. Jansson, Andreas
    Influence of alloying content and preconditioning on gaseous ferritic nitrocarburizing of steels2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Atlas Copco rock drills AB is manufacturing and developing rock drills. These rock drills have steel components that have high requirements. To increase mechanical properties (besides material selection) the components undergoes the in-house technology surface treatment nitrocarburizing. However some material can experience a variation in result after this surface treatment. This study is performed to increase the knowledge on which parameters in the manufacturing process that are influencing on the result of this surface treatment. Several steels were studied including steel grades comparable with the low alloy steels, 50CrMo4C, 42CrMo4, 25CrMo4 and C45E but also three high alloy Cr-Mo-V tool steels with various carbon content. These steels were exposed to different external elements such as air (surface oxidation), cutting fluid and alkaline cleaning fluids to gain knowledge about how chemical composition respond to external elements regarding nitrocarburizing results. The specimens were evaluated with light optical microscopy (LOM), scanning electron microscopy (SEM) and hardness testing. The results of this study demonstrate that steels have similar behaviour as reported in literature in aspect of chemical composition; increased amount of alloying content give a harder but also thinner hardened case. External elements like cutting fluid and delay time in air (surface oxidation) decrease thickness and homogeneity of hardened case in almost all material. An alkaline cleaning process after exposure of these external elements (air, cutting fluid) would, inconsistent, decrease thickness and homogeneity even further. Adding a second step of cleaning the surface with i.e. ethanol after alkaline cleaning process could reduce the negative effect from alkaline wash. Therefore, it is recommended that the wash process at Atlas Copco will be altered to improve the result of this surface treatment by a decrement of passivation media in cleaning process.

  • 23.
    Javadzadeh Kalahroudi, Faezeh
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Chantziara, Katerina
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Sadek, Mohamed
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Lin, Fengxiang
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Maistro, Giulio
    Uddeholms AB, Sweden.
    Anantha, Krishnan Hariramabad
    Uddeholms AB, Sweden.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Grehk, Mikael
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    High-Nitrogen PM Tool Steel: A Comparison Of Microstructure And Mechanical Properties Of As-HIPed And HIPed Followed By Hot Working2022In: World PM 2022 Congress Proceedings, European Powder Metallurgy Association (EPMA) , 2022Conference paper (Other academic)
    Abstract [en]

    High-nitrogen-chromium alloyed powder metallurgy (PM) tool steels offer many attractive features including high strength and corrosion resistance. The PM route offers various advantages such as advanced alloy composition, high homogeneity, and well-defined size distribution of hard phase particles. This study presents microstructure and mechanical properties of a PM Cr-Mo-V-N alloy. The conventional manufacturing route for this alloy is hot isostatic pressing (HIP) followed by hot working. To investigate the possibility of near-net-shape manufacturing, a comprehensive comparison of the performance was made between steels produced by as-HIPed and HIPed followed by hot working. Both steel types were heat treated in the same way to obtain martensitic matrix with limited retained austenite. In the present investigation, microstructure and phase analyses were performed by X-ray diffraction and scanning electron microscopy. Mechanical tests were carried out by hardness measurements and tensile fatigue tests in the very high cycle fatigue regime using ultrasonic fatigue testing. 

  • 24.
    Karlsson, Daniel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Life and fracture in very high cycle fatigue of a high strength steel2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Classical fatigue models teach that there is an intrinsic fatigue limit for steels, representing a level of stress that is too low for regular crack growth where every cyclic load propagates a fatigue crack through the material. Modern application with extreme lifetimes has shown that fatigue will still take place in steels with stress levels well below the expected fatigue limit. This relatively new area of study has been named Very High Cycle Fatigue, or VHCF, and describes fatigue failures with a number of load cycles exceeding 107. Fractography of steels that has suffered VHCF tends to reveal an especially rough crack surface adjacent to where the fatigue crack originates, which is typically some form of defect in the bulk of the steel. This area is believed to be critical for VHCF and has been referred to in a number of ways by different studies, but will herein be called Fine Granular Area, or FGA. The aim of this study is to try and get a better understanding of VHCF. This was done by fractography analysis of test specimens of high strength tool steel that suffered fatigue failure at lifetimes ranging from about 106 cycles to 1,9x109 cycles. The lower lifetimes were achieved using hydraulic testing equipment, while the specimens in the VHCF range suffered fatigue failure in ultrasonic testing equipment allowing the application of a cyclic stress at a rate of 20 000 Hz. The resulting fracture surfaces were then investigated using a scanning electron microscope, or SEM, taking special note of the fatigue initiating defects and, in the case of VHCF, the rough area found adjacent to it. In combination with the SEM an elemental analysis of the fatigue initiating defects as well as the bulk of the material was done using energy-dispersive X-ray spectroscopy, or EDS. This was done to find out what the defects consisted of; confirming that they were slags and checking that the composition of the material of the bulk of the specimen matches what was expected. Using light optical microscopy in combination with acid etching of the surface of samples cut out of the test specimens the structure of the steel was investigated. Calculating the local stresses at the location of the fatigue initiating defect was done using FEM in combination with displacement amplitude gathered from the ultrasonic testing equipment. The data gathered was then measured and compared to that of previous studies, using models of prediction and seeing how they match the experimental results. The results suggest that the stress intensity factor at the internal slags is critical for VHCF and that with lower stress intensity factors one can expect longer lifetimes. Another observation is a relatively consistent stress intensity factor at the edge of the FGA combined with the original defect, likely signifying the transition from the creation of FGA to traditional crack propagation. There also seems to be a connection between the size of the FGA and the number of cycles to failure, with larger FGA with increasing lifetimes. The most glaring shortcoming of this study is the amount satisfactory tests conducted, and thus amount of data points, is very low due to the majority of specimens suffered failure at the threading used to connect them to the ultrasonic testing equipment at lifetimes far too low to be relevant.

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  • 25.
    Kazantseva, N. V.
    et al.
    Russian Academy of Sciences, RUS.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, I. A.
    Central University of Technology, ZAF.
    Yadroitsev, I. A.
    Central University of Technology, ZAF.
    Laser Additive 3D Printing of Titanium Alloys: Current Status, Problems, Trends2021In: Physics of metals and metallography, ISSN 0031-918X, E-ISSN 1555-6190, Vol. 122, no 1, p. 6-25Article in journal (Refereed)
    Abstract [en]

    Features of 3D printing, including laser melting of metal powders, were considered in this work. The effect of laser operation mode on the structure, residual stresses, and properties of manufactured metals was reviewed. A method for choosing process parameters using single tracks as universal for all types of metal laser 3D printers was proposed. Structural characteristics and medical requirements for biocompatible materials were presented. The biocompatible Ti-6Al-4V alloy manufactured by selective laser melting was considered.

  • 26.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Kazantseva, Natalia
    Institute of Metal Physics, Ural Branch of the Russian Academy of Science, RUS.
    Microstructure of L-PBF alloys: Chapter 8.2021In: Fundamentals of Laser Powder Bed Fusion of Metals / [ed] Igor Yadroitsev ; Ina Yadroitsava ; Eric MacDonald, Elsevier, 2021, p. 215-243Chapter in book (Refereed)
    Abstract [en]

    Laser powder bed fusion (L-PBF) of metallic alloys results in the formation of solid metallic material with microstructure different from the conventional analogs. The differences are the result of high temperature of the molten pool, high cooling rates, steep temperature gradient, thermal cycling during manufacturing, and other factors. Since the microstructure affects the physical and mechanical properties of materials and influences the performance of L-PBF parts, microstructural analysis is critical. Understanding of the formation of microstructure, therefore, is necessary to predict the final properties of the material, and it creates a strong basis for the microstructure control and manufacturing of components with tailored properties. This chapter outlines the main principles of the formation of microstructure in the L-PBF process and presents some examples of microstructures of the most common L-PBF alloys.

  • 27.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Vilardell, Anna Martin
    Nagoya University, Japan.
    Takata, Naoki
    Nagoya University, Japan.
    Structural integrity I: static mechanical properties: Chapter 132021In: Fundamentals of Laser Powder Bed Fusion of Metals / [ed] Igor Yadroitsev; Ina Yadroitsava; Anton Du Plessis; Eric MacDonald, Elsevier, 2021, p. 349-376Chapter in book (Refereed)
    Abstract [en]

    Laser powder bed fusion (L-PBF) is one of the additive manufacturing methods to produce metallic parts. The layer-by-layer manufacturing nature results in the formation of specific microstructure, achieving different properties compared to conventional analogs. In this chapter, the mechanical properties of the main classes of materials such as steels, aluminum and titanium alloys, as well as nickel-base superalloys manufactured by L-PBF are overviewed. The focus is on the static mechanical properties obtained by tensile tests as the most common standard method for the measurement of mechanical characteristics. A correlation between manufacturing, microstructure, and mechanical properties of these L-PBF materials is highlighted.

  • 28.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsev, Igor
    South Africa.
    Yadroitsava, Inna
    South Africa.
    Titanium Alloys Manufactured by In Situ Alloying During Laser Powder Bed Fusion: Additive manufacturing for medical applications2018In: Titanium Alloys Manufactured by In Situ Alloying During Laser Powder Bed Fusion: Additive manufacturing for medical applications / [ed] Jing Zhang Yeon-Gil Jung, Elsevier, 2018Chapter in book (Refereed)
  • 29.
    Kuzminova, Yulia O.
    et al.
    Skolkovo Institute of Science and Technology, Russian Federation.
    Firsov, Denis G.
    Skolkovo Institute of Science and Technology, Russian Federation.
    Shibalova, Anastasia A.
    Institute of Nanotechnology of Microelectronics of Russian Academy of Science, Russian Federation.
    Kudryavtsev, Egor A.
    Belgorod State National Research University, Russian Federation.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Klimova-Korsmik, Olga G.
    State Marine Technical University, Russian Federation.
    Shishkovsky, Igor V.
    Skolkovo Institute of Science and Technology, Russian Federation.
    Evlashin, Stanislav A.
    Skolkovo Institute of Science and Technology, Russian Federation.
    Structural and mechanical properties of the additive manufactured CrFeCoNi(Al,Ti) high-entropy alloys produced using powder blends2023In: Materialia, E-ISSN 2589-1529, Vol. 32, article id 101957Article in journal (Refereed)
    Abstract [en]

    High-entropy Alloys (HEAs) are considered prospective materials demonstrating the new approach of alloy design creating new compositions for harsh conditions. However, searching for alloy chemical composition providing the best material properties is a costly process. Additive manufacturing (AM) can be an effective technique for adjusting the alloy composition by using several initial materials. The powder bed fusion (PBF) AM process allows the printing of solid parts using powder blends. In the present study, the CrFeCoNi(Al,Ti) HEAs were printed by the PBF technique using the blends of three powders. The structural and phase investigations revealed the chemical inhomogeneity in the materials that led to the new phase formations affecting the mechanical characteristics. The high-temperature annealing at 1200 °C can be considered a post-treatment process for the printed alloys as a homogenization process while the annealing at a lower temperature of 800 °C initiates the decomposition of the initially formed f.c.c. phase. 

  • 30.
    Larsson, Karl
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Nötning av verktygsstål vid plåtformning: Inverkan på arbetsmaterialets sträckgräns och påkletningsmotstånd för verktygsstål2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In today's industry, tools are more exposed to larger forces in sheet metal forming. As materials become stronger, larger forces are also needed to achieve a geometric change of the materials. Because of this, abrasion effects in the processes have increased and one of the most common one is galling. Galling is a form of wear where both adhesive and abrasive wear occur. This means that material comes off of the host material and sticks to the tool. When material has been transferred to the tool, it no longer has the original shape and can lead to irregularities in the material to be formed. So far companies have used lubricants to minimize it. As lubricants are increasingly regulated for environmental reasons, the industry must find other solutions to the problem. One solution is to create materials that are resistant to galling through their microstructure. There is still limited knowledge in this area and the aim of this study is to compare two tool steels and investigate which of them is most resistant to galling. The tool steel Caldie and Vancron Superclean will be tested against the materials DP600 and DP1000 usually used in sheet metal forming. Where the materials have different yield strengths, this is to see if it has an impact on sheet metal forming. To decide which tool steel is most suitable for sheet metal forming, a sliding test will be produced using the SOFS method. The sliding distance will describe how quickly galling occurs and thus the better material is determined. The abrasive traces of the materials were analyzed using an electron microscope to see how galling affected the tool steel and surface material.The result showed that the Vancron Superclean was more resistant to galling, as the tool steel slid over the DP600, while no conclusion could be drawn when slipping over DP1000.

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  • 31.
    Lin, Fengxiang
    et al.
    Université catholique de Louvain, BEL.
    Zhang, Y.
    Technical University of Denmark, DNK.
    Pantleon, W.
    Technical University of Denmark, DNK.
    Juul Jensen, D.
    Technical University of Denmark, DNK.
    Importance of Non-uniform Boundary Migration for Recrystallization Kinetics2018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49, no 11, p. 5246-5258Article in journal (Refereed)
    Abstract [en]

    Recrystallization kinetics is studied by three characterization methods: post-mortem electron microscopy, in situ three-dimensional X-ray diffraction (3DXRD), and ex situ electron microscopy. Cold-rolled copper is used as a model material. The post-mortem analysis shows that the average migration velocity of unimpinged recrystallizing boundaries decreases strongly with annealing time, leading to a low Avrami exponent. For individual grains, the in situ 3DXRD measurement reveals that the growth rates decrease significantly shortly after nucleation. This is explained by the ex situ characterizations, which show that different segments of the recrystallizing boundaries migrate with significantly different velocities, and some boundaries, although unimpinged, remain stationary. This non-uniform migration of recrystallizing boundaries leads to an amoeba-like growth, and is proposed to be responsible for the decrease of the average boundary migration velocity, because the fraction of slowly moving/stationary boundaries increases during the recrystallization. Reasons for stationary boundaries are discussed based on a quantitative analysis of the local deformed microstructure. It is concluded that non-uniform boundary migration has a significant influence on recrystallization kinetics and needs to be included in recrystallization models. © 2018, The Minerals, Metals & Materials Society and ASM International.

  • 32.
    Lin, Fengxiang
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Technical University of Denmark.
    Zhang, Yubin
    Technical University of Denmark.
    Godfrey, Andrew
    Tsinghua University, China.
    Jensen, Dorte Juul
    Technical University of Denmark.
    Twinning during recrystallization and its correlation with the deformation microstructure2022In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 219, article id 114852Article in journal (Refereed)
    Abstract [en]

    The formation of annealing twins during recrystallization in a cold-rolled copper single crystal has been studied. A new method is proposed to classify annealing twins according to their orientation relationship with the surrounding deformed matrix. A statistical analysis based on the new classification method shows that during growth of a recrystallized grain, twinning occurs more frequently on twinning planes close to one of the {111} planes of the deformation microstructure, and most frequently when the {111} plane is the dominant slip plane of the deformed matrix for the present single crystal. The differences in morphology for different types of twins are discussed based on growth selection criteria. The study highlights the importance of the local deformation microstructure on the formation of annealing twins.

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  • 33.
    Lind, Sofia
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Zinklegering i åldrat och kylt tillstånd: Identifiering av parametrar som förändrar materialegenskaperna i Zamak52015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Car safety is an important issue in today's society. The easiest way to protect you when going in a car is using the seat belt. A seat belt retractor is made up of several components, one of these is called the torque tube who takes energy when the body caught by the belt in the event of collision. Seat­belts must protect passengers in the car for many years and at differ­ent temperatures. The torque tube is in this case cast in a zinc alloy called Zamak5 that changes its material properties of aged and cooled state. The goal of this work is to find the parameters that alter the material properties of Zamak5.

    Various methods were used to obtain a result on a torque tube, custom made with weakened geometry. Some of the test objects were aged and some were not aged. A pendulum test may correspond to a collision between a belt and a weight. To find the critical temperature when Zamak5 alter the material properties made the pendulum test at different temperatures to see which test objects that gave offense. The fracture surfaces were then studied under a microscope to see the parameters that caused characteristic changes.

    The results showed that the fracture was brittle. This is because the temperature has fallen below the transition temperature. The aged and cooled test object showed less strength and this is due to incoherent particles formed and folded at the grain boundaries and the critical shear plane.

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  • 34.
    Linder, Noomi
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Understanding Effects of Isothermal Heat Treatments on Microstructure of LMD-w Titanium Alloy (Ti-6242): On solution heat treated microstructure2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use and knowledge of additive manufacturing technologies are rapidly growing. It is crucial to understand the processing-structure-property relationship, which is highly discussed when trying to understand the science of a material. One commonly used material in aerospace applications is titanium alloy, lately Ti-6Al-2Sn-4Zr-2Mo (Ti-6242). This work is addressed towards a laser metal deposition wire (LMD-w) manufactured Ti-6242 built on a Ti-6Al-4V (Ti-64) base plate. 

    The microstructure of titanium alloys, like all other alloys, are highly dependent on its thermal history. It is crucial to understand the microstructural change in order to optimize the material properties. The prediction of microstructure through simulation can be improved by obtaining experimental input. Since the microstructure of an LMD-w manufactured component is different from the subtractive manufactured, the change from heat treatments are different considering the different start structures. It is therefore of interest to analyse isothermal heat treatments effect on solution heat treated microstructure of LMD-w Ti-6242, from an industrial application point of view. The objective of this work is to analyse the effect of isothermal heat treatment on microstructural changes for LMD-w Ti-6242 wall. 

    The as received state was solution heat treated according to GKN standard, isothermal treatments were additionally performed and the change was analysed with microstructural characterization. The prior beta grain size, alpha lath thickness, phase fraction and hardness have been measured. Focus has been on the Ti-6242 wall for the measurements of alpha lath thickness and phase fraction. However, an analysis of the interface and heat affected zone (HAZ) has been made as well. MIPAR, an image analysis program was used for alpha lath thickness and phase distribution measurements.

    It has been concluded that the hardness of the material increases with increasing isothermal temperature during heat treatment and that the lath thickness increases with longer holding time. An equilibrium diagram has been obtained for Ti-6242 from a solution heat treated microstructure of LMD-w between the temperatures of 700°C and 1000°C and a time-temperature-transformation diagram (TTT-diagram), in the range of 700°C-1000°C and a holding time from 30 seconds to 2 hours.

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  • 35.
    Liu, H.
    et al.
    Katholieke Universiteit Leuven, BEL.
    Lin, Fengxiang
    Université catholique de Louvain, BEL.
    Zhao, P.
    The Ohio State University, USA.
    Moelans, N.
    Katholieke Universiteit Leuven, BEL.
    Wang, Y.
    The Ohio State University, USA.
    Nie, J. F.
    Monash University, AUS.
    Formation and autocatalytic nucleation of co-zone {101¯2} deformation twins in polycrystalline Mg: A phase field simulation study2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 153, p. 86-107Article in journal (Refereed)
    Abstract [en]

    A phase-field model is developed to study the formation and autocatalytic nucleation of {101¯2} twins in polycrystalline Mg. The twins are found to nucleate most favourably in grains with the most negative interaction energy. Within such grains, the energetically most favoured nucleation site is determined by stresses concentrated near the grain boundaries that are related to the elastic anisotropy of the material. Furthermore, in a structure consisting of three lamellar grains with an incoming twin in the central grain, the simulation results show that before autocatalytic nucleation, the incoming twin often has a lenticular shape. The stress field around the tip of the incoming twin plays the major role in the autocatalytic nucleation. After a twin has nucleated in the neighbouring grain, the incoming and the outgoing twins evolve simultaneously, and the shape of the incoming twin gradually changes from lenticular to parallel-sided plate. Under the condition that the crystallographic orientation of the central grain and the applied strain remains unchanged, the driving force for twin nucleation decreases with increasing misorientation (up to 90°) across the grain boundary. It is further derived that the interaction energy values between the pre-existing stress field of the polycrystalline structure and the eigenstrain of the to-be-nucleated twin is mathematically related to the resolved shear stress of twins. © 2018 Acta Materialia Inc.

  • 36.
    Lyons, Rainey
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Cirillo, Emilio N. M.
    Sapienza University of Rome, Italy.
    Muntean, Adrian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Phase separation and morphology formation in interacting ternarymixtures under evaporation: Well-posedness and numerical simulation of a non-local evolution system2024In: Nonlinear Analysis: Real World Applications, ISSN 1468-1218, Vol. 77, article id 104039Article in journal (Refereed)
    Abstract [en]

    We study a nonlinear coupled parabolic system with non-local drift terms modeling at the continuum level the inter-species interaction within a ternary mixture that allows the evaporation of one of the species. In the absence of evaporation, the proposed system coincides with the hydrodynamic limit of a stochastic interacting particle system of Blume–Capel-type driven by the Kawasaki dynamics. Similar governing dynamics are found in models used to study morphology formation in the design of organic solar cells, thin adhesive bands, and other applications. We investigate the well-posedness of the target system and present preliminary numerical simulations which incorporate ‘from the top’ evaporation into the model. We employ a finite volumes scheme to construct approximations of the weak solution and illustrate how the evaporation process can affect the shape and connectivity of the evolving-in-time morphologies

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  • 37.
    Mussa, Abdulbaset
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Şelte, Aydın
    Uddeholm AB.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Development of a new PM tool steel for optimization of cold working of advanced high-strength steels2020In: Metals, ISSN 2075-4701, Vol. 10, no 10, article id 1326Article in journal (Refereed)
    Abstract [en]

    In the present study, Uddeholm Vancron SuperClean cold work tool steel was investigated concerning wear resistance and fatigue strength, using laboratory and semi-industrial tests. The Uddeholm Vancron SuperClean was designed with the help of ThermoCalc calculations to contain a high amount of a carbonitride phase, which was suggested to improve tribological performance of this tool steel. In order to investigate the tested steel, galling tests with a slider-on flat-surface tribotester and semi-industrial punching tests were performed on an advanced high-strength steel, CP1180HD. Uddeholm Vanadis 8 SuperClean containing only a carbide phase and Uddeholm Vancron 40 containing a mixture of carbides and carbonitrides were also tested to compare the performance of the tool steels. The microstructure and wear mechanisms were characterized with scanning electron microscopy. It was found that the carbonitrides presented in Uddeholm Vancron SuperClean improved its resistance to material transfer and galling. Semi-industrial punching tests also confirmed that Uddeholm Vancron SuperClean cold work tool steel also possesses enhanced resistance to chipping and fatigue crack nucleation, which confirms the beneficial role of the carbonitride phase in wear resistance of cold work tool steel.

  • 38.
    Ohlsson, Jonas
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Effects of different heat treatments on hardness of Grade 91 steel2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    CCI Valve Technology AB is a company located in Säffle, Sweden, that manufactures and installs bypass valves. Due to requirements outside normal standards on the valve's hardness values, some measurements have had difficulties meeting such requirements. During this thesis work, tests were carried out to determine how to overcome the difficulties. The experiments focused on five different areas that may affect the components hardness, welding method, soaking temperature during post weld heat treatment, measuring procedure, component thickness and number of heat treatment cycles. The Grade 91 steel specimens that were examined consisted of five solid cylinders and three various pipes that were welded together by using shielded metal arc welding (SMAW) or gas tungsten arc welding (GTAW). Each pipe was sawed apart into three equal parts. All specimens were hardness tested and eight of the specimens' microstructure was studied with an optical microscope. The hardness measurement instruments used, LECO V-100-C2 and GE-MIC 10, are Vickers hardness testers, one stationary and the other one portable. The measuring results contain a vast number of different hardness measurement data. From the analyzed data, the conclusions were drawn that the most suitable soaking temperature during post weld heat treatment were 750° C, that the SMAW method creates a more stable hardness profile than the GTAW method, and that one heat treatment cycle is more beneficial than two or more.

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  • 39.
    Pernefur, Emil
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Extremvärdesanalys (SEV) av högkvalitativt verktygsstål: Uppskattning av maximal inneslutningsstorlek i pulverstål2017Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    This work were requested by Uddeholms AB. Uddeholm is the worldś leading manufacturer of high performance tool steel for industrial tools. The company exists worldwide and is present in over 100 countries. One of the company’s main production processes is manufacturing powder steels with extremely high quality. In this work, one of these steels has been analyzed to evaluate the presence and distribution of non-metallic inclusions.

    Higher demands on quality and more global competition worldwide means that you always have to strive towards perfection in the manufacturing processes. Non-metallic inclusions have severe effects on the mechanical properties of steels. That's why it's of utmost importance to investigate their presence in the tool steel and especially their size. The reason for this is because it's the largest inclusions that's the most dangerous for the material.

    To obtain a statistically number of certainty of the largest of inclusions, very vast areas of steel have to be examined. Therefore a theoretical method of extrapolation is often used instead to approximate the distribution of the largest inclusions. The precision of this method is still very uncertain. Different methods of this kind of analysis do exist. The method applied in this work of degree is extreme values analysis by statistics of extreme values (SEV).

    To ensure the pre-conditions of the extreme values analysis, a large quantity of powder steel was analyzed. This was done by light-optic microscopy (LOM) and exclusively performed by Uddeholms AB at their R&D-facility (Research and development-facility) in Hagfors.

    At Karlstad Universityś test-facility specimens were subjected to ultrasonic fatigue testing at 20 kHz. The specimens derived from the same material as the ones examined in LOM. The result from the ultrasonic fatigue testing were that the largest inclusions in the material were found. This was done by applying very high cycle fatigue (VHCF).

    To calculate the maximum theoretical inclusion size, SEV was used. The extreme values analysis was performed on gathered data from both LOM and VHCF.

    All fracture surfaces from the ultrasonic fatigue testing were then examined in scanning electron microscope (SEM) at Karlstad University. In SEM, the largest inclusion in every fractured surface was identified and measured.

    The maximum real inclusion size from the fractured surfaces was then compared to the maximum theoretically calculated inclusion size from the extreme values analysis. As it turned out the real inclusion size proved to be slightly larger than the theoretical. The difference between them was found to be 3,25 µm.

    Conclusions drawn were that Uddeholms powder steel exhibits very high purity and that extreme values analysis as an analytical method is recommended. However, the analysis should be repeated to underline the chosen solution methodology.

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  • 40.
    Pinchuk, N. V.
    et al.
    Kharkiv Polytechnic Institute, Ukraine.
    Subbotina, V. V.
    Kharkiv Polytechnic Institute, Ukraine.
    Terletskyi, O. S.
    Kharkiv Polytechnic Institute, Ukraine.
    Kolupaiev, I. M.
    Kharkiv Polytechnic Institute, Ukraine.
    Tkachuk, M. M.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Kharkiv Polytechnic Institute, Ukraine.
    Hryhorieva, S. V.
    Kharkiv Polytechnic Institute, Ukraine.
    Simulation of the influence of alloying elements on the characteristics of the formation of vacuum-arc nitride coatings2023In: Functional Materials, ISSN 1027-5495, Vol. 30, no 4, p. 597-605Article in journal (Refereed)
    Abstract [en]

    An analysis of trends in the interaction of elements of the Periodic Table was carried out and the results obtained were compared with a model material (namely with a TiN coating); predictions were made for structure formation in vacuum-arc nitride coatings and modeling of the properties of the final coating depending on the composition and deposition conditions This made it possible to explain changes in structural characteristics and mechanical properties in the presence of weaker and/or stronger nitride-forming elements in nitride coatings. Under all deposition conditions and different elemental compositions, single-phase crystalline coatings were obtained. The addition of Mo to the coating increases the lattice period of TiMoN. It was es-tablished that the high-entropy coatings (TiVZrNbHf)N and (TiVZrNbHfTa)N are single-phase with an fcc lattice. The high entropy of the system prevents the formation of intermetallic com-pounds. The coatings are polycrystalline with a crystallite size of 20-23 nm. It has been estab-lished that high-entropy coatings obtained at a nitrogen atmosphere pressure of 0.26 Pa and a constant bias potential of -200 V have the highest hardness value of 53-55 GPa. The theoretical model used to analyze the characteristics of high-entropy alloys and nitride coatings based on them has been confirmed experimentally.

  • 41.
    Rashid, Lezan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Overlay welding of FeCrAl alloys2016Independent thesis Advanced level (degree of Master (Two Years)), 300 HE creditsStudent thesis
    Abstract [en]

    In this master thesis different overlay welding methods suitable for boiler application has been investigated.

    The purpose of this project is to define advantages and disadvantages for each overlay welding methods and suggest some evaluation criteria on some commercial and experimental alloys aimed for overlay welding material.

    Many components in a boiler are made of low alloy steel and the atmosphere in the furnace region can be very complex; therefore many different types of corrosion can occur. Weld overlay is a process where one or multiple layers of corrosion resistant material are applied to a base material.

    The two overlay welding methods investigated in this study were Tungsten Inert Gas welding and Metal Inert/Active Gas welding. Tests were performed with FeCrAl alloys (Kanthal A, Kanthal D and some experimental alloys). FeCrAl alloys in general are ferritic iron-based steels with a typical concentration of 20-23 wt. % chromium and ~5 wt.% aluminum.

    Different overlay welding evaluation was made; visual examination, dye penetrant inspection, macro/micro examination, side bend test and short term corrosion test (~50hours).

    Conclusion of this thesis is that MIG welding is a more productive method than TIG, but more defects such cracks and lack of fusion can be produced for MIG welding. These defects can be “fixed” if welding parameters is optimized. If repairing a certain place TIG welding is a better option. A conclusion about number of layers; one layer with MIG welding is almost as thick as three layers with TIG welding with welding wire Ø 1mm.

    Three welding evaluation that is really important is visual examination, dye penetrant testing and corrosion test in order to choose which overlay welding method is suitable in boiler application.

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    Overlay welding of FeCrAl alloys
  • 42.
    Roseen, Marcus
    Karlstad University.
    Influence of pulsing on PVD TiAlN coating microstructure and mechanical properties: Master thesis project on the impact of deposition parameters on performance and properties of PVD titanium aluminum nitride.2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis investigates the influence of pulsing on the mechanical properties of PVD TiAlN coatings. The thesis focuses on defects caused by droplets during the arc-evaporation technique by altering the duty time, which affects mechanical properties. The coatings' properties and performance depend on the microstructure and morphology, which, in turn, depend on the process parameters of the PVD process. The methodology used to analyze the coatings included microscopy techniques such as SEM and EDS. The study found that coatings produced using pulsed bias exhibited a considerably higher number of droplets, i.e. the rounded topography, than those produced using DC bias. The duty cycle of the pulsed bias may play a significant role in determining the surface characteristics of the coatings, where pulsed bias coatings with a 10% duty cycle resulted in rougher surfaces, while a 20% duty cycle resulted in smoother surfaces. The surface composition of the coatings exhibits high consistency, characterized by an even distribution of titanium and elevated concentrations of aluminum and nitrogen on droplets from both methods. A higher duty cycle also led to more cracks in the coating. 

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  • 43.
    Rådberg, Malin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics, Science, Mathematics and Engineering Education Research.
    Design of Experiment for Laser cutting in Superalloy Haynes 2822016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project aims to investigate the effect of varying different laser cutting parameters on the laser cut surface. The parameters that were varied were cutting speed, beam effect, gas pressure and focal point. The statistical method Design of Experiment was used to plan the experiments and two full factorial test plans were set up, one with argon as cooling and protective gas and one with nitrogen. Sheet metal consisting of the superalloy HAYNES ® 282 with a thickness of 2,54 mm was investigated. Samples from the material were cut with different laser cutting parameters according to the test plans. The samples were evaluated by measuring cracks, recast layer thickness, surface irregularity, burr height and distance to beam deflection point on the cut surface. The resulting data was inserted as responses into the statistical program Modde 10.1 for analysis.

    Modde 10.1 provided models of high significance for the responses of Recast layer, Tav; Recast layer, Tmax; Burrheight, max and Distance to deflection point for the argon series and Recast layer, Tav and Recast layer, Tmax for the nitrogen series.

    The results showed that both recast layer thickness and burr height decreases with increased values of cutting speed, gas pressure and focal point as well as decreased values of beam effect within the parameter window investigated. They also showed that distance to deflection point increased with increasing values of gas pressure and focal point and with decreased values of cutting speed and beam effect within the parameter window.

    The results also showed that for the samples cut with argon as cooling and assistant gas the parameters that affects the recast layer thickness the most are focal point and gas pressure, whereas for the nitrogen series it is gas pressure and beam effect. The parameter with greatest effect on burr height is the cutting speed and for the distance to deflection point it is focal point and gas pressure that have the greatest effect.

    When comparing the argon and the nitrogen series to each other it can be seen that the argon series generate less recast layer from the entry of the cut until between 60 – 80 % into the cut, after which the argon series bypasses the nitrogen series in amount of recast layer produced in the cutting process in the majority of the places measured.

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    Design of Experiment for Laser cutting in Superalloy Haynes 282
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    PÖ, examensarbete
  • 44.
    Sadek, Mohamed
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Hallbäck, Nils
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Burman, Christer
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Elvira, Roberto
    SIDENOR, ESP.
    Escauriaza, Borja
    SIDENOR, ESP.
    Fatigue Strength and Fracture Mechanisms in the Very-High-Cycle-Fatigue Regime of Automotive Steels2020In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 91, no 8, article id 2000060Article in journal (Refereed)
    Abstract [en]

    Very-high-cycle-fatigue (VHCF) strength properties are of interest to several technical applications assessed globally at different laboratories with long-life fatigue testing capabilities. Also, VHCF failure mechanisms are a scientific topic with remaining open research questions. Herein, three automotive bar grade steels are studied with respect to VHCF strength and initiation mechanisms. A microalloyed ferritic-pearlitic steel (38MnSiV5, 870 MPa tensile strength), a quenched and tempered martensitic steel (50CrV4, 1410 MPa tensile strength), and a carburizing steel (16MnCr5, 1180 MPa core structure tensile strength) are studied to reveal characteristics regarding initiation and VHCF failure mechanisms. A 20 kHz ultrasonic fatigue testing instrument is used to obtain fatigue lives up to and above 10(9) load cycles in uniaxial loading. Hour-glass specimens, smooth or notched, are tested at R = -1 and R = 0.1. Fatigue strength and stress life (SN)-diagram data are achieved, and crack initiation and growth mechanisms are studied using primarily field-emission gun-scanning electron microscopy (FEG-SEM). Fatigue strengths are explained by a modified life-dependent Murakami-expression, the Haigh diagram, and notch sensitivity. Interior and surface crack initiations by surface defects, triple points, and inclusions are found. The fine granular area (FGA) to fish-eye crack growth transition conditions are explored and schematic descriptions are given.

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  • 45.
    Sjöman, Joakim
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Cold drawing of tool steels2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Present study is a master thesis in materials engineering and has been performed at Karlstad University and at Uddeholms AB in Hagfors. Uddeholms AB has recently seen a new request from customers, of smaller dimensions of round bars than covered by Uddeholms AB’s dimension program. To get these smaller dimensions Uddeholms AB has up till now, used help from other companies to hot roll and peel the material to the desired dimension. A more efficient way could be to use a cold drawing process on these bars to the desired dimensions.

    The main objectives of this study were to find nearby companies which have suitable draw benches and to find how the material is affected by a cold drawing process. This was performed by a market investigation followed by a technical investigation. The investigated material was Uddeholm THG 2000.

    Cold drawing is an operation in which the cross section of a bar, rod or wire is reduced by pulling it through a die opening. It was soon found that in the desired dimension range the common way to perform this is from wire coil and not from straight bars. This reduced the suitable companies for the Uddeholm THG 2000 bars greatly.

    Some of the conclusions from the present study are:

    • Cold drawing of bar to bar is not the normal practice in the desired dimension range. Only three suitable companies were found to be able to perform bar to bar drawing, Boxholm Stål AB, Kiveton Park Steel and Erasteel Champagnole.
    • THG 2000 could be drawn from Ø25 mm to Ø10 mm, but this would require as many as 8-10 drawing processes, with annealing heat treatments between every second drawing process. This would not be economically efficient, but could result in an extremely fine grain size.
    • The cold drawing process of small dimensions affects the entire cross section of the material. 
    • The direct effects (hardness and internal stress) of a cold drawing operation will disappear in the quench and temper treatment, and in that aspect there are no differences between cold drawn and hot rolled material. Anyhow, indirect effects such as grain size and material distortion can affect material properties even after a quench and temper heat treatment.
  • 46.
    Subasic, Mustafa
    et al.
    KTH Royal Institute of Technology, Sweden.
    Olsson, Mårten
    KTH Royal Institute of Technology, Sweden.
    Dadbakhsh, Sasan
    KTH Royal Institute of Technology, Sweden.
    Zhao, Xiaoyu
    KTH Royal Institute of Technology, Sweden.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Mansour, Rami
    KTH Royal Institute of Technology, Sweden; Aarhus University, Denmark; DIGIT Center, Denmark .
    Fatigue strength improvement of additively manufactured 316L stainless steel with high porosity through preloading2024In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 180, article id 108077Article in journal (Refereed)
    Abstract [en]

    This work investigates the influence of a single tensile preload, applied prior to fatigue testing, on the fatigue strength of 316L stainless steel parts manufactured using laser-based powder bed fusion (PBF-LB) with a porosity of up to 4 %. The specimens were produced in both the horizontal and vertical build directions and were optionally preloaded to 85 % and 110 % of the yield strength before conducting the fatigue tests. The results indicate a clear tendency of improved fatigue life and fatigue limit with increasing overload in both cases. The fatigue limits increased by 25.8 % and 24.6 % for the horizontally and vertically built specimens, respectively. Extensive modelling and experiments confirmed that there was no significant alteration in the shape and size of the porosity before and after preloading. Therefore, the observed enhancement in fatigue performance was primarily attributed to the imposed local compressive residual stresses around the defects. 

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  • 47.
    Tofique, Muhammad Waqas
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Burman, Christer
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Hallbäck, Nils
    Karlstad University, Faculty of Technology and Science.
    Gåård, Anders
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels2016In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 7, p. 899-910Article in journal (Refereed)
    Abstract [en]

    The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic–ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R=-1. The fatigue strength is evaluated at 107, 108, and 109 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.

  • 48.
    Van Meensel, Kim
    et al.
    Katholieke Universiteit Leuven, Belgium.
    Lietaert, Karel
    Katholieke Universiteit Leuven, Belgium; 3D Systems Leuven, Belgium.
    Vrancken, Bey
    Katholieke Universiteit Leuven, Belgium.
    Dadbakhsh, Sasan
    Katholieke Universiteit Leuven, Belgium.
    Xiaopeng, Li
    Katholieke Universiteit Leuven, Belgium; University of New South Wales, Sydney, Australia.
    Kruth, Jean Pierre
    Katholieke Universiteit Leuven, Belgium.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsev, Igor
    Central University of Technology, Bloemfontein, South Africa.
    Van Humbeeck, Jan
    Katholieke Universiteit Leuven, Belgium.
    Additively manufactured metals for medical applications2018In: Additive Manufacturing: Materials, Processes, Quantifications and Applications / [ed] Jing Zhang, Yeon-Gil Jung, Kidlington, U.K.: Butterworth-Heinemann, 2018, 1, p. 261-309Chapter in book (Refereed)
  • 49.
    Vilardell, Anna M.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Fredriksson, Gunnel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Cabanettes, F
    University of Lyon, FRA.
    Sova, A
    University of Lyon, FRA.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Surface integrity factors influencing fatigue crack nucleation of laser powder bed fusion Ti6Al4V alloy2020In: Procedia CIRP / [ed] Schmidt M.,Vollertsen F.,Govekar E., Elsevier, 2020, Vol. 9, p. 222-226Conference paper (Refereed)
    Abstract [en]

    The quality of the surface influences remarkably the fatigue life of additive manufactured components. This work proposes to study the influence of surface integrity on the bending fatigue life of Ti6Al4V manufactured by laser powder bed fusion. Rectangular specimens were manufactured horizontally and the last printed layer had laser track scanning directions (α=30°,60°,90°) in relation to the specimen length. The top surface 3D-roughness average was similar for all the specimens. The specimens were studied under as-built and heat-treated conditions. A correlation between laser track scanning direction, 2D-roughness parameters, and fatigue life for as-built specimens was found. The as-built specimens with 90° and 30° direction showed the shortest and the longest fatigue life, respectively. Heat-treated specimens showed a shorter fatigue life independently of the surface roughness. This could be explained by other surface integrity factors influencing fatigue performance of the material, such as the presence of subsurface porosity and surface oxygen enrichment. © 2020 The Authors. Published by Elsevier B.V.

  • 50.
    Vilardell, Anna M.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsev, I
    Central University of Technology, ZAF.
    Yadroitsava, I
    Central University of Technology, ZAF.
    Albu, M
    Graz Ctr Electron Microscopy ZFE, AUT.
    Takata, N
    Nagoya University, JPN.
    Kobashi, M
    Nagoya University, JPN.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Kouprianoff, D
    Central University of Technology, ZAF.
    Kothleitner, G
    Graz Ctr Electron Microscopy ZFE, AUT; Graz university, AUT.
    du Plessis, A
    Stellenbosch University, ZAF;Nelson Mandela University, ZAF.
    Manufacturing and characterization of in-situ alloyed Ti6Al4V(ELI)-3 at.% Cu by laser powder bed fusion2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, p. 1-14, article id 101436Article in journal (Refereed)
    Abstract [en]

    Biofunctionalization of Ti6Al4V alloy with metallic agents like Ag or Cu is a promising approach to add antibacterial properties and thus to reduce the risk of implant failure. This research investigates the in-situ alloying of Ti6Al4V(ELI) with 3 at.% Cu powders using Laser Powder Bed Fusion (L-PBF). The morphology and geometrical characteristics of the single tracks and layers were studied. Laser powers of 170 W and 340 W, and scanning speeds ranging from 0.4 to 1.4 m/s and 0.8-2.8 m/s were implemented. Single track results showed balling effect and humping at high scanning speeds, 1.4 m/s and 1.6 m/s, for each laser powder respectively. Conversely, keyhole formation occurred at lower scanning speeds of 0.4-0.6 m/s for 170 W laser power, and below and 0.8 m/s for 340 W laser power. For both laser powers, single layers resulted in smoother surfaces at lower scanning speeds. These results were used for the development of optimal process parameters for 3D cubes with 99.9 % density. Optimal process parameters were found for 170 W and 340W laser powders at 0.7-0.9 and 1.0-1.2 m/s scanning speeds, respectively.

    In-situ alloying by L-PBF was challenging and a homogeneous distribution of Cu within the alloy was hard to achieve. The increase in laser power from 170 to 340 W resulted in small increase in homogenization. Microstructural analyses after stress-relieving treatment showed the presence of alpha' and beta phases, as well as CuTi2 intermetallic precipitates. The finer microstructure together with CuTi2 intermetallic precipitates resulted in an increase in hardness. This study demonstrates the potential for printing in-situ alloyed Ti6Al4V(ELI)- 3 at.% Cu for biomedical applications. However, further studies are required to determine the effectiveness of antibacterial properties.

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