Interstitial carbon content effect on the microstructure and mechanical properties of additively manufactured NiCoCr medium-entropy alloy

초록

In this study, we manufactured the NiCoCr medium-entropy alloy (MEA) for the first time with controlled interstitial C content of 0.25 at% and 0.75 at% (0.25 C MEA and 0.75 C MEA) using a powder bed fusion-type additive manufacturing (AM) process. Moreover, we investigated the effect of interstitial C content on the microstructure, room temperature tensile properties and deformation behavior of MEA. The initial microstructure shows that both AM-built interstitial C-doped MEAs had a heterogeneous grain structure and epitaxial growth grains along the building direction. The analysis of electron channeling contrast images showed a large amount of nano-sized precipitates (in-situ precipitates) distributed at the sub-structure boundaries formed by a dislocation network, and a large number of stacking faults were simultaneously observed inside the sub-structure. The fraction of in-situ precipitates was higher in 0.75 C MEA than in 0.25 C MEA. A room temperature tensile test measured yield strengths (YS) of 747.5 MPa for 0.25 C MEA and 832.2 MPa for 0.75 C MEA, indicating the highest properties among additively manufactured MEAs reported to date. Considering the strengthening mechanisms, we compared the microstructural characteristics that affected YS, and identified that in-situ precipitates and high-dislocation density were major strengthening factors. On the other hand, deformation twin, which improves strain hardening rate and ductility was observed in both alloys. Based on the above results, we discuss the correlation of microstructure, mechanical properties, and deformation mechanism of AM-built interstitial NiCoCr MEA.(c) 2022 Elsevier B.V. All rights reserved.

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