| 1. |
- Hentschel, Oliver, et al.
(författare)
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Influence of the in-situ heat treatment during manufacturing on the microstructure and properties of DED-LB/M manufactured maraging tool steel
- 2023
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 315
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 2. |
- Krakhmalev, Pavel, 1973-, et al.
(författare)
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Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion
- 2020
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 772
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to density the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is nececcary, and development of new post processing regimes guaranteeing the best performance of the material is required.
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| 3. |
- Vilardell, Anna M., et al.
(författare)
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Surface integrity factors influencing fatigue crack nucleation of laser powder bed fusion Ti6Al4V alloy
- 2020
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Ingår i: Procedia CIRP. - : Elsevier. - 2212-8271. ; , s. 222-226
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Konferensbidrag (refereegranskat)abstract
- 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.
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