| 1. |
- Goel, Sneha, 1993-, et al.
(författare)
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Microstructure evolution and mechanical response-based shortening of thermal post-treatment for electron beam melting (EBM) produced Alloy 718
- 2021
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Ingår i: Materials Science and Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 820
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam melting (EBM) produced Alloy 718 was subjected to thermal post-treatment involving hot isostatic pressing (HIPing) and heat treatment (HT). Subjecting the material to HIPing at 1120 °C led to significant densification. Study of microstructure evolution during HT (comprising of solution treatment and aging) showed possibility of significantly shortening the HT duration, particularly the time for two-step aging from the standard (8 h + 8 h) long cycle to possibly a shortened (4 h + 1 h) cycle. Another approach for shortening the post-treatment cycle by integrating the HIPing with HT inside the HIP vessel was also successfully implemented. The above observations were further substantiated by tensile response of the material subjected to the varied post-treatment cycles; out of all the post-treatments steps, tensile behaviour was observed to be mainly affected by the aging treatment. Further prospects for shortening the post-treatment protocol are also described, such as shortening of HIPing duration for the typical 4 h to 1 h cycle as well as possible elimination of solution treatment step from the entire post-treatment protocol specifically when prior HIPing is performed. Heat treatment with prior HIPing was found to be crucial for improving fatigue life, because subjecting EBM Alloy 718 to only HT, irrespective of the short or standard long protocol, rendered inferior fatigue response.
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| 2. |
- Goel, Sneha, et al.
(författare)
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Role of HIPing and Heat Treatment on Properties of Alloy 718 Fabricated by Electron Beam Melting
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Although additive manufacturing (AM) of difficult-to-machine materials can open new design possibilities for production of parts with complex geometries, AM builds are characterized by presence of detrimental defects like shrinkage/ gas porosity and lack-of-fusion. Microstructural inhomogeneity, anisotropy in properties and formation of undesirable phases are added concerns. Motivated by the need for investigation of appropriate thermal post-treatments to eliminate defects, and to achieve desired microstructural and mechanical properties, the influence of hot isostatic pressing (HIPing) and heat treatment on electron beam melted (EBM) Alloy 718 specimens built at different heights from the base-plate has been studied. While HIPing led to orders of magnitude reduction in defect content, conventional heat treatment without applied pressure was found to have no effect. Thermal post-treatment was found to eliminate inherent variability in phase constitution and hardness of as-built specimens. HIPing at high temperature was accompanied by grain coarsening, suggesting modification of the HIPing protocol.
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| 3. |
- Gundgire, Tejas, 1994-, et al.
(författare)
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Response of different electron beam melting produced Alloy 718 microstructures to thermal post-treatments
- 2020
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 167
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam melting (EBM) was used to produce Alloy 718 specimens with different microstructures (columnar, equiaxed and a combination thereof) by varying the process parameters. The present study aimed at assessing the response of such varying as-built microstructures to identical thermal post-treatments, which included hot isostatic pressing (HIPing) followed by heat treatment involving solution treatment and aging. The effect of these treatments on defect content, grain structure, hardness and phase constitution in the specimens was specifically analysed. Despite differences in defect content of as-built specimens with distinct microstructures, HIPing was effective in closing defects leading to samples exhibiting similar density. After HIPing, grains with equiaxed morphology or columnar grains with lower aspect ratio showed higher tendency for grain growth in comparison to the columnar grains with higher aspect ratio. The various factors affecting the stability of grains during HIPing of builds with distinct microstructures were investigated. These factors include texture, grain size, and secondary phase particles. The carbide sizes in the different as-built samples varied but were found to be largely unaffected by the post-treatments. Solution treatment following HIPing led to greater precipitation of grain boundary ÎŽ phase in regions with coarser grains than the smaller ones. After HIPing and heat treatment, all specimens exhibited similar precipitation of γ″ phase regardless of their grain morphology in the as-built condition. © 2020 The Author(s)
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