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  • 51.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Ström, E.
    Li, C.
    Microstructure and properties stability of Al-alloyed MoSi2 matrix composites2004In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 12, no 2, p. 225-233Article in journal (Refereed)
  • 52.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Ström, E.
    Sundberg, M.
    Li, C.
    Microstructure, hardness and indentation toughness of C40 Mo(Si,Al)2/ZrO2 composites prepared by SPS of MA powders2003In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 48, no 6, p. 725-729Article in journal (Refereed)
  • 53.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Ström, E.
    Sundberg, M.
    Li, C.
    Microstructure, hardness and indentation toughness of high-temperature C40 Mo(Si,Al)2/SiC composites prepared by SPS of MA powders2003In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 57, no 22-23, p. 3387-3391Article in journal (Refereed)
  • 54.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Ström, E.
    Sundberg, M.
    Li, C.
    Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites, Materials Science and Engineering A, Volume 360, Issues 1-2, Pages 207-213, 20032003Article in journal (Refereed)
  • 55.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Sukumaran, J.
    Gåård, Anders
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Effect of microstructure on edge wear mechanisms in WC-Co2007In: International Journal of Refractory Metals and Hard Materials, ISSN 0958-0611, Vol. 25, no 2, p. 171-178Article in journal (Refereed)
    Abstract [en]

    Edge wear of nano to coarse WC–Co grades was investigated under two-body abrasion conditions using SiC abrasive at 2 and 15 N loads. With the fine abrasive utilized, a transition from homogeneous plowing in submicron grades to inhomogeneous grains pullout in coarse hardmetals was observed at the beginning stages. At final stages, plowing was detected in all the grades. When using the coarse abrasive, for all grades, flaking at the beginning and plowing at the final stages occurred. The performed numerical finite element simulation of the microstructural mechanical response showed good agreement to experimental results and was discussed in relation to the operative wear mechanisms observed. The found results demonstrated a remarkable influence of microstructure and abrasive size on the heterogeneous to homogeneous wear mechanisms transition at initial stages

  • 56.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Sukumaran, J.
    Gåård, Anders
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    How hardmetals react to wear: Nano is not always the best2007In: Metal Powder Report, ISSN 0026-0657, E-ISSN 1873-4065, Vol. 62, no 2, p. 30-35Article in journal (Refereed)
  • 57.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, Inna
    Central University of Technology, Free State, South Africa.
    Fredriksson, Gunnel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsev, Igor
    Central University of Technology, Free State, South Africa.
    Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks2017In: South African Journal of Industrial Engineering, ISSN 1012-277X, E-ISSN 2224-7890, Vol. 28, no 1, p. 12-19Article in journal (Refereed)
    Abstract [en]

    To remove residual stresses, an as-built SLM object is usually posttreated. This treatment can affect the microstructure, changing the final mechanical characteristics. This investigation is focused on the microstructural characterisation of 316L austenitic stainless steel in as-built and annealed conditions. The SLM microstructure was relatively stable up to 900°C, when cell boundaries start to disappear. At higher temperatures, an insignificant grain coarsening was detected. These microstructural changes caused a gradual drop in the hardness. The obtained result is background for the future development of post-treatment regimens to achieve a high level in the final mechanical properties of SLM objects.

  • 58.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, Inna
    Central University of Technology, South Africa.
    Fredriksson, Gunnel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsev, Igor
    Central University of Technology, South Africa.
    Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks2015In: Additive Manufacturing Transforming ideas into business: RAPDASA Rapid Product Development Association of South Africa, 16th Annual International Conference 4-6 November 2015, Roodevallei, Pretoria, South Africa, Pretoria: University , 2015, p. 91-Conference paper (Refereed)
  • 59.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, Inna
    Central University of Technology, South Africa.
    Fredriksson, Gunnel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsev, Igor
    Central University of Technology, South Africa.
    Microstructure of SLM manufactured 316L and 420 grades stainless steels2014In: PROCEEDINGS 15th Annual International Conference 6 November – 7 November 2014 Stellenbosch, South Africa / [ed] Dimitrov, Dimitar; Becker, Thorsten, Stellenbosch: Stellenbosch University , 2014Conference paper (Refereed)
  • 60.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsev, I.
    Univ Lyon, Ecole Natl Ingn St Etienne ENISE, DIPI Lab, F-42023 St Etienne, France..
    Microstructure and properties of intermetallic composite coatings fabricated by selective laser melting of Ti-SiC powder mixtures2014In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 46, p. 147-155Article in journal (Refereed)
    Abstract [en]

    Transition metal silicides and carbides are attractive advanced materials possessing unique combinations of physical and mechanical properties. However, conventional synthesis of bulk intermetallics is a challenging task because of their high melting point. In the present research, titanium carbides and silicides composites were fabricated on the titanium substrate by a selective laser melting (SLM) of Ti -(20,30,40 wt.%)SiC powder mixtures by an Ytterbium fiber laser with 1.075 mu m wavelength, operating at 50 W power, with the laser scanning speed of 120 mm/s. Phase analysis of the fabricated coatings showed that the initial powders remelted and new multiphase structures containing TiCx, Ti5Si3C5, TiSi2 and SIC phases in situ formed. Investigation of the microstructure revealed two main types of inhomogeneities in the composites, (i) SiC particles at the interlayer interfaces and, (ii) chemical segregation of the elements in the central areas of the tracks. It was suggested and experimentally proven that an increase in laser power to 80 W was an efficient way to improve the laser penetration depth and the mass transport in the liquid phase, and therefore, to fabricate more homogeneous composite. The SLM Ti (20,30,40 wt.%)SiC composites demonstrated high hardness (11-17 GPa) and high abrasive wear resistance (3.99 x 10(-7)-9.51 x 10(-7) g/Nm) properties, promising for the applications involving abrasive wear. (C) 2013 Elsevier Ltd. All rights reserved.

  • 61.
    Krakhmalev, Pavel
    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, Free State, South Africa.
    Baker, I.
    Thayer School of Engineering, USA.
    Yadroitsava, I.
    Central University of Technology, Free State, South Africa.
    Manufacturing of intermetallic Mn-46%Al by laser powder bed fusion2018In: Procedia CIRP, Elsevier, 2018, Vol. 74, p. 64-67Conference paper (Refereed)
    Abstract [en]

    Laser powder bed fusion (LPBF) provides an excellent opportunity to use custom powders for complex objects without extensive machining. This opportunity is attractive for brittle and hard intermetallics, but is challenging due to cracking, anisotropy, and the formation of non-equilibrium phases. The present investigation is focused on a development of the process parameters for pre-alloyed Mn-46 at.%Al gas atomized intermetallic powder, which is a promising magnetic material. A hierarchical approach involving optimization of the process parameters for a single track, a single layer, and then a 3D specimen was applied. The manufacturing of single tracks was performed at scanning speeds of 0.06-3.4 m/s and laser powers of 50-350 W. Test parameters guaranteeing stable single track with constant width and height, and sufficient remelting depth were selected for further manufacturing. Surface morphology, chemical composition, crack density and distribution, and the microstructures in the final materials were investigated. It was shown that the consists mostly of the ε-phase with some amounts of equilibrium γ2 and β phases and the ferromagnetic τ-phase. The presence of the ε-phase shows a potential to use heat treatment to form τ-phase magnetic phase in AM Mn-46 at.%Al. Future investigations will clarify the applicability of LPBF to manufacture Mn-46%Al for magnetic applications. 

  • 62.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013), Science, Mathematics and Engineering Education Research.
    Yadroitsev, Igor
    Yadroitsava, Ina
    de Smidt, Olga
    Functionalization of Biomedical Ti6Al4V via In Situ Alloying by Cu during Laser Powder Bed Fusion Manufacturing2017In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, no 10, article id 1154Article in journal (Refereed)
    Abstract [en]

    The modern medical industry successfully utilizes Laser Powder Bed Fusion (LPBF) to manufacture complex custom implants. Ti6Al4V is one of the most commonly used biocompatible alloys. In surgery practice, infection at the bone-implant interface is one of the key reasons for implant failure. Therefore, advanced implants with biocompatibility and antibacterial properties are required. Modification of Ti alloy with Cu, which in small concentrations is a proven non-toxic antibacterial agent, is an attractive way to manufacture implants with embedded antibacterial functionality. The possibility of achieving alloying in situ, during manufacturing, is a unique option of the LPBF technology. It provides unique opportunities to manufacture customized implant shapes and design new alloys. Nevertheless, optimal process parameters need to be established for the in situ alloyed materials to form dense parts with required mechanical properties. This research is dedicated to an investigation of Ti6Al4V (ELI)-1 at % Cu material, manufactured by LPBF from a mixture of Ti6Al4V (ELI) and pure Cu powders. The effect of process parameters on surface roughness, chemical composition and distribution of Cu was investigated. Chemical homogeneity was discussed in relation to differences in the viscosity and density of molten Cu and Ti6Al4V. Microstructure, mechanical properties, and fracture behavior of as-built 3D samples were analyzed and discussed. Pilot antibacterial functionalization testing of Ti6Al4V (ELI) in situ alloyed with 1 at % Cu showed promising results and notable reduction in the growth of pure cultures of Escherichia coli and Staphylococcus aureus.

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  • 63.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yi, D.
    Nyborg, L.
    Preparation of nanocrystalline/amorphous structure in soft magnetic Fe-based alloys by mechanical alloying, 22nd Risoe International Symposium on Materials Science2001Conference paper (Refereed)
  • 64.
    Lindvall, Fredrik W.
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Tool steel and contact geometry influence on galling initiation in lubricated sliding on carbon steel sheets2009In: Proceedings of the 8th International Tooling Conference, Vol 1, 2009, p. 189-198Conference paper (Refereed)
    Abstract [en]

    In sheet metal forming operations, sliding contact may cause adhesive wear of sheet materials with transfer of worn material to the tool surface, a wear damage process named galling. It results in loss of product quality, process performance and tool lifetime. The industrial experience of the optimal combination of sheet metal grades, tool steel grades, tool geometry and lubrication to increase the tool performance is not clearly understood. Accordingly, simulation of wear of sheet metal forming operation in laboratory conditions in order to quantify tendency of a tool material to galling is not a trivial problem neither. In the present study two tool steel grades, an ESR made 8%Cr cold work tool steel and a superior PM made high speed steel, were tested with different test tool geometries to obtain different contact pressure conditions. A slider on flat sheet (SOFS) test equipment was utilized, where a disc made of tool steel was slid along lubricated carbon steel sheets of different strengths. The sliding tool discs were prepared so that one elliptical and two linear contacts were simulated, in order to study their influence on distance to galling initiation. Normal and friction force data were collected, galling initiation was detected by analysis of the friction curve and verified by SEM and OP analysis of the tool surfaces and sheet sliding tracks. It was found that under selected test conditions, galling initiation was remarkably dependent on tool material as well as geometry.

  • 65.
    Lindvall, Fredrik W.
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Bay, Niels
    Department of Mechanical Engineering, Technical University of Denmark.
    The effect of grinding and polishing procedure of tool steels in sheet metal forming2010In: ICTPM 2010, 2010, p. 603-612Conference paper (Refereed)
    Abstract [en]

    The surface finish of tools in sheet metal forming has a large influence on the performance of the forming tool. Galling, concern of wear in sheet metal forming, is a severe form of adhesive wear where sheet material is transferred on to the tool surface. By polishing the tools to a fine surface finish, material pick-up has traditionally been reduced, but some surface preparations withstand adhesive wear better. To investigate the effect on galling performance of different surface preparations lubricated tests have been performed using a strip reduction rig. Two different tool materials, Vancron 40 and Vanadis 6 and up to ten different grinding and polishing treatments were tested against AISI 316 stainless steel. The tests showed that an optimum surface preparation might be found at the transition between abrasive and adhesive wear.

  • 66.
    Lindvall, Fredrik W.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester2013In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 56, no 6, p. 1137-1145Article in journal (Refereed)
    Abstract [en]

    One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation.Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets.The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact.Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.

  • 67.
    Medvedeva, Anna
    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. Karlstad University, Faculty of Technology and Science, Materials Science.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Andersson, Jörgen
    Research and Development, Uddeholm Tooling AB.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Stress relaxation resistance of tool steels for tool holder applications2009In: Proceedings of the 8th International Tooling Conference, 2-4 June, Aachen, Germany, 2009, 2009, p. 697-712Conference paper (Refereed)
  • 68.
    Medvedeva, Anna
    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. Karlstad University, Faculty of Technology and Science, Materials Science.
    Gunnarsson, Staffan
    Research and Development, Uddeholm Tooling AB.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Thermally activated relaxation behaviour of shot peened tool steels for cutting tool body application2011In: materials science and engineering A: Structural Materials: Properties, Microstructures and Processing, ISSN 0921-5093, Vol. 528, no 3, p. 1773-1779Article, review/survey (Other academic)
  • 69.
    Medvedeva, Anna
    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. Karlstad University, Faculty of Technology and Science, Materials Science.
    Gunnarsson, Staffan
    Research and Development, Uddeholms Tooling AB.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Nordh, Lars Göran
    Research and Development, Uddeholm Tooling AB.
    Influence of nickel content on machinability of a hot-work tool steel in prehardened condition2011In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, no 2, p. 706-715Article in journal (Refereed)
    Abstract [en]

    In the present study, the influence of nickel content on the machinability of a prehardened hot-work tool steel was investigated. The machinability with varying nickel content from 1 to 5 wt% was characterized in end milling and drilling by evaluating tool life, cutting forces, and tool/chip interface temperature.

    Nickel content showed to have a positive effect on the machinability of the hot-work tool steel; with increasing nickel content in the steel, the longer tool life was reached in end milling and drilling operations. Machining the higher nickel containing steels generated lower cutting forces and tool/workpiece interface temperature. In addition, less adhesive wear and built-up edge formation were observed on the tools.

    The difference in the steel machinability was discussed in terms of their microstructure and mechanical properties. Increasing nickel content tends to decrease the carbon in the martensite and to retain a fine distribution of small primary carbides. It resulted in a reduction in yield strength with increasing nickel content related to the cutting force reduction and machinability improvement.

  • 70.
    Moletsane, M G
    et al.
    Cent Univ Technol, Dept Mech & Mech Engn, Bloemfontein, Free State, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Kazantseva, N
    Urals Branch Acad Sci, Inst Met Phys, Ekaterinburg, Russia.
    du Plessis, Anton
    Univ Stellenbosch, CT Scanner Facil, Stellenbosch, South Africa.
    Yadroitsava, I
    Cent Univ Technol, Dept Mech & Mech Engn, Bloemfontein, Free State, South Africa.
    Yadroitsev, I
    Cent Univ Technol, Dept Mech & Mech Engn, Bloemfontein, Free State, South Africa.
    Tensile properties and microstructure of direct metal laser-sintered TI6AL4V (ELI) alloy2016In: South African Journal of Industrial Engineering, ISSN 1012-277X, E-ISSN 2224-7890, Vol. 27, no 3, p. 110-121Article in journal (Refereed)
    Abstract [en]

    Direct metal laser sintering (DMLS) is an additive manufacturing technology used to melt metal powder by high laser power to produce customised parts, light-weight structures, or other complex objects. During DMLS, powder is melted and solidified track-by-track and layer-by-layer; thus, building direction can influence the mechanical properties of DMLS parts. The mechanical properties and microstructure of material produced by DMLS can depend on the powder properties, process parameters, scanning strategy, and building geometry. In this study, the microstructure, tensile properties, and porosity of DMLS Ti6Al4V (ELI) horizontal samples were analysed. Defect analysis by CT scans in pre-strained samples was used to detect the crack formation mechanism during tensile testing of as-built and heat-treated samples. The mechanical properties of the samples before and after stress relieving are discussed. 

  • 71.
    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).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Failure analyses and wear mechanisms of rock drill rods: a case study2019In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 102, p. 69-78Article in journal (Refereed)
    Abstract [en]

    Rock drill rod failure is a big concern for the mining industry. The tough conditions required to break down rock material into small pieces subject rock drill components to high mechanical stresses and corrosion that lead to the failure of the drill rods. This paper describes a detailed examination of rock drill rods failed during field operations. The drill rods were manufactured from a high strength, hardened and tempered steel 22NiCrMo12-5F, carburized for better surface performance. The examination was carried out by means of light optical microscopy and scanning electron microscope. Microhardness profiles were performed for the studied rods. The focus of the present case study was to characterize the failure mechanisms and surface damages of the failed drill rods. The examined drill rods failed due to the initiation and propagation of fatigue microcracks at the outer surface of the thread. Surface cracks propagated to a certain crack length until the fracture toughness of the drill rod was exceeded and the final failure occurred. Multiple short cracks were observed on the fracture surface of the failed rods. The observed cracks propagated perpendicularly to the impacting direction towards the inner surface of the rods. Two different crack initiation mechanisms were observed in the present study, crack initiation from pits and crack initiation from severe plastic surface deformation. Sliding and abrasive wear damage, severe plastic deformation and pitting corrosion were observed on the threaded portion of the rods. Sliding wear was the most common wear damage mechanism observed in the thread joint. Pitting corrosion and severe plastic deformation, made the worn surface susceptible to crack initiation.

  • 72.
    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).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Sliding wear and fatigue cracking damage mechanisms in reciprocal and unidirectional sliding of high-strength steels in dry contact2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 444, article id 203119Article in journal (Refereed)
    Abstract [en]

    Rock drill components operate under tough contact conditions during rock drilling. Reciprocal and unidirectional motion under high contact stresses are the common contact conditions between interconnected components. It will result in component damage and often the observed surface damage of rock drill tools is due to wear and fatigue cracks. Nevertheless, the effects of the properties and structure of the mating materials on tribological performance, is not fully understood. The present study is dedicated to simulation and investigation of the wear mechanisms observed in reciprocal and unidirectional sliding of high strength steels for rock drill components. A high strength martensitic steel, 22NiCrMo12–F, commonly used in rock drills was tested in self-mating contact. Wear mechanisms were investigated by means of electron microscopy and wear damage was quantified by a 3D optical interferometer. Total damage, as a result of adhesive wear, severe plastic deformation and nucleation and propagation of fatigue cracks, was discussed in relation to test conditions and material properties. It was observed that the coefficient of friction decreased with increasing normal load. Moreover, the results showed that the type of motion had a significant influence on the worn volume and crack nucleation of the specimens in sliding contact. In addition, the reciprocal motion resulted in higher wear than unidirectional motion under the same test conditions.

  • 73. Svenningsson, R
    et al.
    Bergström, Jens
    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.
    Tool life in sliding wear on high strength stainless steel sheets (poster WOM 2007)2007Other (Other (popular science, discussion, etc.))
  • 74.
    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)
  • 75.
    van Zyl, Ian
    et al.
    Cent Univ Technol, Dept Mech & Mechatron Engn, Bloemfontein, Free State, South Africa.
    Moletsane, M
    Cent Univ Technol, Dept Mech & Mechatron Engn, Bloemfontein, Free State, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, I
    Cent Univ Technol, Dept Mech & Mechatron Engn, Bloemfontein, Free State, South Africa.
    Yadroitsev, I
    Cent Univ Technol, Dept Mech & Mechatron Engn, Bloemfontein, Free State, South Africa.
    Validation of miniaturised tensile testing on DMLS TI6AL4V (ELI) specimens2016In: South African Journal of Industrial Engineering, ISSN 1012-277X, E-ISSN 2224-7890, Vol. 27, no 3, p. 192-200Article in journal (Refereed)
    Abstract [en]

    Direct metal laser sintering (DMLS) is a relatively new technology that is developing rapidly. Since DMLS material is created by melting/solidifying tracks and layers from powder, even building geometry can influence the mechanical properties. To certify a material, the testing specimens must be designed and manufactured according to the appropriate standards. Miniaturised tensile DMLS samples could be a good alternative for express quality control, and could reduce the cost of DMLS-specific testing. In this study, as-built and stress-relieved miniaturised tensile DMLS Ti6Al4V (ELI) specimens with different surface qualities were investigated. The fracture surfaces and mechanical properties of the mini-tensile specimens were analysed and compared with standard full-sized specimens also manufactured by DMLS. The obtained data showed the applicability of mini-tensile tests for the express analysis of DMLS objects if a correction factor is applied for the calculation of the load-bearing cross-section of the specimen. 

  • 76. Vilardell, A. M.
    et al.
    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).
    Cabanettes, F.
    University of Lyon.
    Sova, A.
    University of Lyon.
    Valentin, D.
    University of Lyon.
    Bertrand, P.
    University of Lyon.
    Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion2018In: Procedia CIRP, Elsevier, 2018, p. 49-52Conference paper (Refereed)
    Abstract [en]

    This article deals with the understanding of the influence of surface topography on fatigue behavior of Ti6Al4V alloy specimens produced by laser powder bed fusion (LPBF). The same laser parameters and scan strategy were used for all specimens, giving a sample density higher than 99.5 %. Two different surface topographies were obtained by using the top and side surfaces of the specimens. The surface topography and morphology were investigated by optical surface profilometry and focus variation microscopy. Four-point bending fatigue test was performed on specimens with top and side surfaces as the highest stressed surface respectively. Machined specimens were used as reference. The features of the fracture surface, such as crack initiation and propagation, were analyzed by focus variation and scanning electron microscopy (SEM). Both, fatigue results and fracture surface investigations, were correlated and discussed in relation to surface topography and microstructure, as well as manufacturing parameters. 

  • 77.
    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).
    Yadroitsev, I.
    Cent Univ Technol Free State, Dept Mech & Mechatron Engn, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Fracture mechanisms in the as-built and stress-relieved laser powder bed fusion Ti6Al4V ELI alloy2019In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 109, p. 608-615Article in journal (Refereed)
    Abstract [en]

    The influence of a stress-relief treatment on impact and fatigue properties of Ti6Al4V ELI samples manufactured by laser powder bed fusion was analyzed. The heat treatment resulted in removal of residual stresses, coarsening of needles and formation of precipitations between needles. In both, impact and fatigue tests, crack development was correlated to microstructural features. Fracture analysis was carried out by means of optical and electron microscopy to reveal the influence of microstructure on crack development. Ductile fracture was the dominating fracture mode at impact testing. Pore formation and coalescence were the main crack formation mechanisms. The microstructural changes led to a decrease in impact toughness after heat treatment. Presumably, this was a result of the precipitations between needles. Fatigue results showed multiple crack nucleation at the surface in both, as-built and stress-relieved material. The crack propagation rate was slightly higher and the crack was less deflected in the stress-relieved material due to the stress relief and coarsening of the microstructure.

  • 78.
    Yadoitsev, Igor
    et al.
    Central University of Technology, Free State, Department of Mechanical and Mechatronic Engineering, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsava, Ina
    Central University of Technology, Free State, Department of Mechanical and Mechatronic Engineering, South Africa.
    Hierarchical design principles of selective laser melting for high quality metallic objects2015In: Additive manufacturing, ISSN 2214-8604, Vol. 7, p. 45-56Article in journal (Refereed)
  • 79.
    Yadroitsev, I
    et al.
    Université de Lyon, Ecole Nationale d’Ingénieurs de Saint-Etienne, Saint-Etienne, France.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsava, I
    Université de Lyon, Ecole Nationale d’Ingénieurs de Saint-Etienne, Saint-Etienne, France.
    Selective laser melting of Ti6Al4V alloy for biomedical applications: Temperature monitoring and microstructural evolution2014In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 583, p. 404-409Article in journal (Refereed)
  • 80.
    Yadroitsev, I.
    et al.
    Cent Univ Technol, Dept Mech & Mechatron Engn, ZA-9300 Bloemfontein, Free State, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, I.
    Cent Univ Technol, Dept Mech & Mechatron Engn, ZA-9300 Bloemfontein, Free State, South Africa.
    Du Plessis, A.
    Univ Stellenbosch, CT Scanner Facil, ZA-7602 Stellenbosch, South Africa.
    Qualification of Ti6Al4V ELI Alloy Produced by Laser Powder Bed Fusion for Biomedical Applications2018In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 70, no 3, p. 372-377Article in journal (Refereed)
    Abstract [en]

    Rectangular Ti6Al4V extralow interstitials (ELI) samples were manufactured by laser powder bed fusion (LPBF) in vertical and horizontal orientations relative to the build platform and subjected to various heat treatments. Detailed analyses of porosity, microstructure, residual stress, tensile properties, fatigue, and fracture surfaces were performed based on x-ray micro-computed tomography, scanning electron microscopy, and x-ray diffraction methods. The types of fracture and the tensile fracture mechanisms of the LPBF Ti6Al4V ELI alloy were also studied. Detailed analysis of the microstructure and the corresponding mechanical properties were compared against standard specifications for conventional Ti6Al4V alloy for use in surgical implant applications. Conclusions regarding the mechanical properties and heat treatment of LPBF Ti6Al4V ELI for biomedical applications are made.

  • 81.
    Yadroitsev, I
    et al.
    Université de Lyon, France.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Yadroitsava, I
    Université de , France.
    Johansson, S
    Linköpings universitet.
    Smurov, I
    Université de Lyon.
    Energy input effect on morphology and microstructure of selective laser melting single track from metallic powder2013In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 4, p. 606-613Article in journal (Refereed)
  • 82.
    Yadroitsev, Igor
    et al.
    South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Yadroitsava, I.
    South Africa.
    A systematic approach to manufacturing parts with desired properties by selective laser melting2015In: Materials Science and Technology Conference and Exhibition 2015, MS and T 2015, Association for Iron and Steel Technology, AISTECH , 2015, Vol. 1, p. 121-128Conference paper (Refereed)
    Abstract [en]

    Selective laser melting (SLM) is becoming a powerful additive manufacturing technology for different industries: automotive, medical, chemical, aerospace, etc. The extension of applications requires a wide spectrum of powder materials with specific properties. To produce parts with tailored properties by SLM, optimal process-parameters and scanning strategies have to be used for different powders. Numerical simulation allows the estimation of temperature distribution during laser melting and prediction the final microstructures and properties of SLM object. A hierarchical approach, including systematic analysis of SLM parameters necessary to control the final product quality on every level - track, layer, 3D object is suggested and discussed. A series of single tracks, layers and 3D objects were manufactured from metal powders to validate a proposed algorithm. The efficiency of the approach was illustrated by the manufacturing of fully dense samples from AISI 420 stainless steel.

  • 83. Yadroitsev, Igov
    et al.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Yadroitsava, Inna
    Titanium Alloys Manufactured by In Situ Alloying During Laser Powder Bed Fusion2017In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 69, no 12, p. 2725-2730Article in journal (Refereed)
    Abstract [en]

    This work is focused on the investigation and understanding of in situ processes in Ti-15%Mo and Ti6Al4V-1.38%Cu alloys by laser powder bed fusion (LPBF). In both materials, Mo and Cu were introduced as elemental powders into the precursor powder mixture. The effect of process parameters, i.e., energy input on surface morphology and homogeneity, was investigated. The importance of different thermophysical properties of blended powders is also discussed. The chemical composition of phases and phase distribution in sintered materials were investigated by means of scanning electron microscopy. The mechanical properties of in situ alloyed as-built LPBF specimens were determined. The results obtained developed knowledge that is important for understanding the in situ alloying process during LPBF, and they create a base for synthesizing new materials.

  • 84.
    Yadroitsev, Igov
    et al.
    Department of Mechanical and Mechatronic Engineering, Bloemfontein, Central University of Technology, Free State, South Africa.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Yadroitsava, Inna
    Department of Mechanical and Mechatronic Engineering, Bloemfontein, Central University of Technology, Free State, South Africa.
    Du Plessis, Anton
    University of Stellenbosch.
    Qualification of DMLS Ti6Al4V (ELI) alloy for biomedical applications2017In: Proceedings of the 28th Annual International Solid Freedom Fabrication symposium – an Additive Manufacturing conference 2017 / [ed] David L. Bourell, Richard H. Crawford, Carolyn C. Seepersad, Joseph J. Beaman & Scott Fish, Austin: University of Texas , 2017Conference paper (Refereed)
  • 85.
    Åsberg, Mikael
    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).
    Hatami, Sepehr
    Swerea IVF AB.
    Fredriksson, Wendy
    Bodycote Hot Isostatic Pressing.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 742, p. 584-589Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.

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