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Abstract Wire arc additive manufacturing (WAAM) is an efficient technique for producing medium to large‐size components, due to its accessibility and sustainability in fabricating large‐scale parts with high deposition rates, employing low‐cost and simple equipment, and achieving high material efficiency. Consequently, WAAM has garnered attention across various industrial sectors and experienced significant growth, particularly over the last decade, as it addresses and mitigates challenges within production markets. One of the primary limitations of WAAM is its thermal history during the process, which directly influences grain formation and microstructure heterogeneity in the resulting part. Understanding the thermal cycle of the WAAM process is thus crucial for process improvement. Typically, fabricating a part using WAAM results in a microstructure with three distinct zones along the build direction: an upper zone (thin surface layer) with fine grains, a middle zone dominated by undesirably long and large columnar grains covering more than 90% of the produced part, and a lower zone with smaller to intermediate columnar grains closer to the substrate material. These zones arise from variations in cooling rates, with the middle zone exhibiting the lowest cooling rate due to 2D conduction heat transfer. Consequently, producing a component with a microstructure comprising three different zones, with a high fraction of large and long columnar grains, significantly impacts the final mechanical properties. Therefore, controlling the size and formation of these grain zones plays a key role in improving WAAM. The aim of this work is to investigate the formation of undesired columnar grains in austenitic stainless steel 316L during WAAM and propose a simple hybrid technique by combining WAAM with a hot forging process (with or without interlayer cooling time). This approach targets the disruption of the solidification pattern of columnar grain growth during deposition progression and aims to enhance the microstructure of WAAM components.
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Effect of Homogenization on the Microstructure and Magnetic Properties of Direct Laser-Deposited Magnetocaloric Ni43Co7Mn39Sn11
Abstract Transitioning current cooling and refrigeration technologies to solid-state cooling leveraging the magnetocaloric effect would improve efficiency and eliminate a harmful influence on the environment. Employing additive manufacturing as a production method would increase geometrical freedom and allow designed channels and porosity in heat exchangers made from magnetocaloric materials, to increase surface area for heat transfer via a fluid. This study is the first to demonstrate a successful deposition of the Ni43Co7Mn39Sn11 magnetocaloric material by direct laser deposition. Samples were defined as either properly- or overbuilt, and representative ones were characterized for microstructural features before and after homogenization heat treatment, as well as magnetic behavior and constituent phases. As-built microstructures consisted of dendrites, columnar grains, and elongated cells, with a mix of both austenite and 7M martensite phases. Homogenization increased the fraction of 7M martensite, and encouraged distinct equiaxed and columnar grains, eliminating dendrites and cellular structures. The increased fraction of the weak magnetic martensitic phase also resulted in a strong reduction of the saturation magnetization. Some differences in structure and performance may be related to an energy density difference causing higher Mn loss in the properly built sample, with a lower powder-to-energy input ratio. As a whole, it is found that direct laser deposition (DLD) additive manufacturing of Ni-Mn-based magnetocaloric material is very promising, since representative transformation, phase state, and magnetic properties have been achieved in this study.
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- Award ID(s):
- 1808082
- PAR ID:
- 10159799
- Date Published:
- Journal Name:
- Journal of Manufacturing Science and Engineering
- Volume:
- 142
- Issue:
- 7
- ISSN:
- 1087-1357
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Wire arc additive manufacturing (WAAM) is an effective technique for producing medium to large-size components, due to its convenience and sustainability in fabricating large-scale parts with high deposition rates, employing low-cost and simple equipment, and attaining high material efficiency. Thus, WAAM attracts different industrial sectors and has experienced great growth, particularly over the last decade to overcome production market’s challenges. Consequently, fabricating parts in WAAM, mostly resulted in heterogeneity in microstructure of three different zones towards the buildup direction due to different cooling rates; upper zone (thin surface layer of fine grains), middle zone (undesired large columnar grains covers 90% of the produced part), and lower zone (intermediate columnar grains close to substrate material). Accordingly, producing parts consisting of different zones affects the final component's mechanical properties. Therefore, controlling the formation of these zones is a key role in improving WAAM technique. Altering torch motion and cooling rates were found to be effective methods to control the homogeneity of the final component in WAAM.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1115/1.4046900
