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Publications (10 of 69) Show all publications
Mussa, A., Krakhmalev, P. & Bergström, J. (2019). Failure analyses and wear mechanisms of rock drill rods: a case study. Engineering Failure Analysis, 102, 69-78
Open this publication in new window or tab >>Failure analyses and wear mechanisms of rock drill rods: a case study
2019 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 102, p. 69-78Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-72222 (URN)10.1016/j.engfailanal.2019.04.028 (DOI)000467804800007 ()
Available from: 2019-05-31 Created: 2019-05-31 Last updated: 2019-06-10Bibliographically approved
Vilardell, A. M., Fredriksson, G., Yadroitsev, I. & Krakhmalev, P. (2019). Fracture mechanisms in the as-built and stress-relieved laser powder bed fusion Ti6Al4V ELI alloy. Optics and Laser Technology, 109, 608-615
Open this publication in new window or tab >>Fracture mechanisms in the as-built and stress-relieved laser powder bed fusion Ti6Al4V ELI alloy
2019 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 109, p. 608-615Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Fracture analysis, Impact and fatigue properties, Laser powder bed fusion, Stress-relief treatment, Ti6A4V ELI, Aluminum alloys, Coarsening, Cracks, Ductile fracture, Fatigue testing, Fracture testing, Heat treatment, Impact testing, Microstructural evolution, Needles, Residual stresses, Stress relief, Titanium alloys, Crack propagation rate, Laser powders, Microstructural changes, Microstructural features, Optical and electron microscopies, Fatigue of materials
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-69444 (URN)10.1016/j.optlastec.2018.08.042 (DOI)000446949600074 ()2-s2.0-85053287726 (Scopus ID)
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2019-01-31Bibliographically approved
Åsberg, M., Fredriksson, G., Hatami, S., Fredriksson, W. & Krakhmalev, P. (2019). Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel. Materials Science & Engineering: A, 742, 584-589
Open this publication in new window or tab >>Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel
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2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 742, p. 584-589Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Additive manufacturing, Hot work tool steel H13, Laser powder bed fusion, Mechanical properties, Post treatment, 3D printers, Hardening, Hot isostatic pressing, Hot working, Microstructure, Porosity, Tool steel, Tools, Elongation to break, H-13 tool steels, Hot-work tool steel, Laser powders, Manufacturing technologies, Strength values, Tensile mechanical properties
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-70411 (URN)10.1016/j.msea.2018.08.046 (DOI)000457814400060 ()2-s2.0-85056673446 (Scopus ID)
Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2019-02-21Bibliographically approved
Vilardell, A. M., Krakhmalev, P., Fredriksson, G., Cabanettes, F., Sova, A., Valentin, D. & Bertrand, P. (2018). Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion. In: Procedia CIRP: . Paper presented at 10th CIRP Conference on Photonic Technologies, LANE 2018, 3 September 2018 through 6 September 2018 (pp. 49-52). Elsevier
Open this publication in new window or tab >>Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion
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2018 (English)In: 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. 

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Fatigue test, Fracture mechanisms, Laser powder bed fusion, Surface topography, Ti6Al4V alloy, Aluminum alloys, Fatigue of materials, Fatigue testing, Fracture, Scanning electron microscopy, Ternary alloys, Titanium alloys, Topography, Crack initiation and propagation, Fatigue behavior, Four point bending, Fracture surfaces, Laser powders, Manufacturing parameters, Ti-6Al-4V alloy
National Category
Physical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-70594 (URN)10.1016/j.procir.2018.08.028 (DOI)2-s2.0-85057393814 (Scopus ID)
Conference
10th CIRP Conference on Photonic Technologies, LANE 2018, 3 September 2018 through 6 September 2018
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-04-25Bibliographically approved
Krakhmalev, P., Yadroitsev, I., Baker, I. & Yadroitsava, I. (2018). Manufacturing of intermetallic Mn-46%Al by laser powder bed fusion. In: Procedia CIRP: . Paper presented at 10th CIRP Conference on Photonic Technologies, LANE 2018, 3 September 2018 through 6 September 2018 (pp. 64-67). Elsevier, 74
Open this publication in new window or tab >>Manufacturing of intermetallic Mn-46%Al by laser powder bed fusion
2018 (English)In: Procedia CIRP, Elsevier, 2018, Vol. 74, p. 64-67Conference paper, Published 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. 

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Hierarchical optimization of process parameters, Intermetallic phase, Laser Powder Bed Fusion, Mn-46 at.%Al alloys, Binary alloys, Intermetallics, Magnetic materials, Magnetism, Manganese alloys, Manufacture, Al-alloy, Chemical compositions, Hierarchical approach, Hierarchical optimization, Laser powders, Magnetic applications, Non-equilibrium phasis, Aluminum alloys
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-70595 (URN)10.1016/j.procir.2018.08.031 (DOI)2-s2.0-85057369130 (Scopus ID)
Conference
10th CIRP Conference on Photonic Technologies, LANE 2018, 3 September 2018 through 6 September 2018
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-06-13Bibliographically approved
Kazantseva, N., Krakhmalev, P., Thuvander, M., Yadroitsev, I., Vinogradova, N. & Ezhov, I. (2018). Martensitic transformations in Ti-6Al-4V (ELI) alloy manufactured by 3D Printing. Materials Characterization, 146, 101-112
Open this publication in new window or tab >>Martensitic transformations in Ti-6Al-4V (ELI) alloy manufactured by 3D Printing
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2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 146, p. 101-112Article in journal (Refereed) Published
Abstract [en]

In the present investigation, Ti-6Al-4V ELI samples were manufactured by the powder-bed fusion (PBF) process using the laser sintering (LS) technology. Microstructure, chemical and phase constitution, and mechanical properties were studied by means of the transmission electron microscopy, atom probe tomography, X-ray diffraction, nanoindentation and mechanical testing. It was found that the structure of LS samples consisted of two different variants of metastable phases, namely the hexagonal alpha' martensitic phase and small amounts of the orthorhombic alpha '' martensitic phase. The martensitic alpha'-phase was formed because of the high cooling rates of the LS method, The {10 (1) over bar2} <(1) over bar 011 > hexagonal martensite tensile twins were observed in the microstructure of the as-build alloy. Small areas with inner twinning martensitic plates, which are typical for the metastable orthor-hombic martensitic phase in titanium alloys, were identified by the transmission electron microscopy. Atom probe tomography (APT) confirmed localization of beta-stabilizing elements at interfaces, presumably at the twin or lamella boundaries. The structure and origin of the martensitic phases in 3D printed Ti-6Al-4V alloys are discussed with respect to in-situ heat treatment during manufacturing.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Material or constituting phase(s) Titanium alloys Laser sintering Metastable phases Mechanical properties
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-70951 (URN)10.1016/j.matchar.2018.09.042 (DOI)000452816700010 ()
Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2019-02-13Bibliographically approved
Krakhmalev, P., Fredriksson, G., Svensson, K., Yadroitsev, I., Yadroitsava, I., Thuvander, M. & Peng, R. (2018). Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion. Metals, 8(8), 1-18, Article ID 643.
Open this publication in new window or tab >>Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion
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2018 (English)In: Metals, ISSN 2075-4701, Vol. 8, no 8, p. 1-18, article id 643Article in journal (Refereed) Published
Abstract [en]

This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
316 L stainless steel, Cellular solidification, Electron microscopy, Laser powder bed fusion, Solidification texture, Thermal stability of microstructure
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-69224 (URN)10.3390/met8080643 (DOI)000443616400079 ()2-s2.0-85052594962 (Scopus ID)
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2019-04-26Bibliographically approved
Yadroitsev, I., Krakhmalev, P., Yadroitsava, I. & Du Plessis, A. (2018). Qualification of Ti6Al4V ELI Alloy Produced by Laser Powder Bed Fusion for Biomedical Applications. Paper presented at Annual International Solid Freeform Fabrication (SFF) Symposium / Additive Manufacturing (AM) Conference, AUG 07-09, 2017, Austin, TX. JOM: The Member Journal of TMS, 70(3), 372-377
Open this publication in new window or tab >>Qualification of Ti6Al4V ELI Alloy Produced by Laser Powder Bed Fusion for Biomedical Applications
2018 (English)In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 70, no 3, p. 372-377Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-66712 (URN)10.1007/s11837-017-2655-5 (DOI)000425324900021 ()
Conference
Annual International Solid Freeform Fabrication (SFF) Symposium / Additive Manufacturing (AM) Conference, AUG 07-09, 2017, Austin, TX
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-06-25Bibliographically approved
Krakhmalev, P., Yadroitsev, I., Yadroitsava, I. & de Smidt, O. (2017). Functionalization of Biomedical Ti6Al4V via In Situ Alloying by Cu during Laser Powder Bed Fusion Manufacturing. Materials, 10(10), Article ID 1154.
Open this publication in new window or tab >>Functionalization of Biomedical Ti6Al4V via In Situ Alloying by Cu during Laser Powder Bed Fusion Manufacturing
2017 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, no 10, article id 1154Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Basel: MDPI, 2017
Keywords
Ti6Al4V-Cu alloy; in situ alloying; microstructure and chemical homogeneity;
National Category
Materials Engineering Medical Materials
Identifiers
urn:nbn:se:kau:diva-65911 (URN)10.3390/ma10101154 (DOI)000414639000049 ()
Available from: 2018-01-25 Created: 2018-01-25 Last updated: 2018-02-26Bibliographically approved
Kinnear, A., Krakhmalev, P., Yadroitsava, I. & Yadroitsev, I. (2017). Manufacturing, microstructure and mechanical properties of selective laser melted Ti6Al4V-Cu. In: : . Paper presented at LiM 2017 "Lasers in manufacturing" conference, Munich, June 26-29, 2017. Munich: WLT German Scientific Laser Society
Open this publication in new window or tab >>Manufacturing, microstructure and mechanical properties of selective laser melted Ti6Al4V-Cu
2017 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Munich: WLT German Scientific Laser Society, 2017
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-63806 (URN)
Conference
LiM 2017 "Lasers in manufacturing" conference, Munich, June 26-29, 2017
Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2018-07-09Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9441-2502

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