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- Shaikh, Abdul Shaafi, 1989
(författare)
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Laser powder bed fusion processing and heat treatment of Ni-base superalloys: microstructure and properties
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nickel-base superalloys are indispensable materials for the energy and aerospace industries. The additive manufacturing (AM) of these materials by powder bed fusion – laser beam (PBF-LB) presents a valuable opportunity to improve component performance and ease manufacturing and supply chain complexity in these industries. However, only a limited number of Ni-base superalloys are currently available for PBF-LB. This is due to several challenges encountered during PBF-LB processing, including microcracking, post-process cracking, development of an AM-specific microstructure, and lack of heat treatment optimization. The aim of this thesis study is to develop better understanding of the extent of these issues in different superalloys, their causes, and potential remedies. To understand aspects of processability, the alloy Haynes® 282® was studied to assess its feasibility for manufacture by means of PBF-LB, including susceptibility to cracking. Results showed excellent processibility of Haynes® 282® by PBF-LB, allowing to reach full-density crack-free components over the wide range of energy input, while also being resistant to post-process cracking. Conventionally manufactured superalloys – cast or wrought – are currently considered as the benchmark in terms of mechanical performance. The microstructure and mechanical performance of PBF-LB processed Haynes® 282® after standard heat treatment was evaluated and compared to its wrought counterpart from the literature. PBF-LB processed Haynes® 282® showed finer grain sizes and discontinuous grain boundary carbides compared to wrought microstructure. Despite excellent room temperature tensile properties, clear anisotropy in high temperature mechanical performance of PBF-LB processed Haynes® 282® was observed, which is proposed to be addressed by heat treatment optimization. Heat treatment is a critical post processing step for any precipitation strengthened alloy, and this is especially true for PBF-LB processed superalloys. Heat treatments developed for cast or wrought alloys may not be optimal for the same alloys in PBF-LB processed form because PBF-LB processed superalloys have a starting microstructure that is very different from equivalent cast or wrought microstructures. This aspect was studied in detail by evaluation of the as-built microstructure of Inconel 939, a high γ’-fraction superalloy. No γ’ precipitates were found in the as-built microstructure, however, η phase was found at inter-dendritic regions. This secondary phase was observed to grow upon ageing, lowering the ductility of the material. This demonstrates the importance of a solution treatment for Inconel 939, regardless of γ’ in the as-built condition. Further study also aimed to optimize the ageing heat treatment steps for PBF-LB manufactured Inconel 939. This resulted in a proposed ageing heat treatment which is shorter than the one used for conventional cast Inconel 939, which also produces improved and more isotropic tensile performance. Another aspect of heat treatment in PBF-LB processing is potential contamination of an alloy from the stress relief heat treatment carried out while a part is fused to a dissimilar building platform material. This was addressed in a study on Haynes® 282® built onto a carbon steel building platform. The study showed that no large-scale change in chemical composition occurred, suggesting that steel platforms are suitable for use with Ni-base superalloys.
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| 2. |
- Shaikh, Abdul Shaafi, 1989, et al.
(författare)
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Microstructure and mechanical properties of Haynes 282 superalloy produced by laser powder bed fusion
- 2021
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Ingår i: Materials Today Communications. - : Elsevier BV. - 2352-4928. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- Ni-base superalloys are essential materials for high-temperature applications in the energy and aerospace sectors. Significant benefits in design, function, and manufacture of high-temperature components may be realized from additive manufacturing (AM) of these materials. However, because of cracking issues during AM fabrication, only a handful of materials have been tried and qualified. This article provides an initial evaluation of the processability and properties of Haynes 282 by laser-powder bed fusion (LPBF), which is a relatively new Ni-base superalloy with properties superior to those of many legacy wrought superalloys. The results demonstrated that crack-free Haynes 282 can be manufactured by means of LPBF with full density. The mechanical properties at ambient temperature exceeded the properties of the reference material in the as-built and heat-treated conditions, albeit with significant anisotropy. Mechanical properties at 800 ◦C indicated that the yield strength of heattreated Haynes 282 by LPBF was comparable to that of the reference material, however, ductility was significantly reduced. Promising stress rupture performance also indicates that Haynes 282 is an ideal candidate for adoption in additive manufacturing, especially if heat treatments can be re-designed for the additively manufactured as-built microstructure.
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| 3. |
- Shaikh, Abdul Shaafi, 1989, et al.
(författare)
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On as-built microstructure and necessity of solution treatment in additively manufactured Inconel 939
- 2023
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 66:1, s. 3-11
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Tidskriftsartikel (refereegranskat)abstract
- Increased adoption of additively manufactured superalloys has led to the consideration of revised heat treatment approaches for these materials. The rapid cooling during additive manufacturing processes has been seen to suppress gamma prime (γ′) precipitation, which has raised the possibilities for omitting the high-temperature solution treatment step that usually precedes ageing heat treatment for these alloys. In this work, the as-built microstructure of a high gamma prime fraction superalloy Inconel 939 is presented, where the absence of any γ′ precipitation is notable. However, transmission electron microscopy shows the presence of nano-sized Eta (η) phase. It is shown that the omission of solution treatment leads to the growth of the deleterious η phase upon ageing, which results in embrittlement in tensile loading. It is concluded that at least for this particular alloy the solution treatment plays a critical role in the establishment of the required microstructure and hence cannot be omitted from the heat treatment.
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| 4. |
- Shaikh, Abdul Shaafi, 1989, et al.
(författare)
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On the Additive Manufacturing of Inconel 939 - Analysis of Microstructure and ReDevelopment of Heat Treatment
- 2020
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Ingår i: Proceedings - Euro PM2020 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Inconel-939 is a Ni-base superalloy developed for service up to 850°C and is widely used in hot-sections of industrial gas turbine engines. The potential for improved hot-gas-path component design through the geometric complexity to be realized by additive manufacturing (AM) makes the processing of Inconel-939 by laser-powder bed fusion an attractive prospect. However, the complexity and length of conventional Inconel-939 heat treatment, as well as the different starting microstructure, necessitate a modified heat treatment for the AM alloy. The microstructures and mechanical properties resulting from these treatments were characterized and compared. The difference in room temperature and elevated temperature mechanical performance is discussed in light of the performance of the cast alloy and the evolution of the microstructure.
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| 5. |
- Shaikh, Abdul Shaafi, 1989, et al.
(författare)
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On the effect of building platform material on laser-powder bed fusion of a Ni-base superalloy HAYNES® 282®
- 2023
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Ingår i: European Journal of Materials. - : Informa UK Limited. - 2688-9277. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) by laser powder bed fusion (LPBF) involves melting of layers of powder onto a substrate, called a building platform. Due to cost or convenience considerations, building platform materials rarely match the LPBF material, especially for high temperature materials. To ensure tolerances in component geometries, AM components are often stress-relieved/heat-treated while still attached to the building platform. It is therefore important to understand the effect of dissimilar building platform materials on the properties of the built-up material. These effects may be particularly important for high performance materials such as Ni-base superalloys used for critical applications in the aerospace and energy industries. To investigate this effect, samples of a Ni-base superalloy HAYNES® 282® were built onto a carbon steel building platform in several configurations. The samples were removed from the building platform after heat treatment and subjected to detailed composition analysis and microstructural characterization to investigate the effect of the building platform material on the properties of the additively manufactured part. Room temperature and high temperature tensile testing were used to characterize the material. Results showed no risk of large-scale chemical composition change, or mechanical property degradation of built-up material from on-platform heat treatment.
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