Microstructures and Tensile Properties of Cantor High Entropy Alloy Manufactured by Laser Powder Directed Energy Deposition

Abstract Alloys consisting of five (or more) principal elements in near equiatomic proportions are commonly called high entropy alloys (HEAs). Recent efforts to characterize the properties of these alloys have revealed interesting emergent properties. Additionally, the degrees of freedom offered by varying the number of alloying components and their compositions entails a significant design space to explore to optimize alloys for high temperature applications. In this study, gas atomized CoCrFeMnNi HEA powder was used as feedstock for laser additive manufacturing using a laser powder directed energy deposition (LP-DED) process. Samples were produced, subjected to post-printing stress relief heat treatment, and were subsequently evaluated for their microstructure, density, hardness and tensile properties. The microstructure and hardness of the LP-DED samples were compared with baseline samples produced by vacuum casting and by powder metallurgy (PM) via hot isostatic pressing (HIP). The results showed that LP-DED manufactured samples contained more porosity, had lower density, and finer but more irregularly shaped grains than the cast and PM samples. X-ray diffraction (XRD) analysis revealed that all three processes produced a uniform face-centered cubic (FCC) microstructure with no detectable secondary phases. The LP-DED samples exhibited the highest hardness after stress relief treatment, 197 HV versus 159 HV for PM/HIP and 125 HV for cast, due to the finer grain size and residual stresses. The tensile test results show that the yield strength of the LP-DED samples was equivalent to that reported for cast material although the ultimate tensile strength and ductility were lower. Anisotropic behaviour of LP-DED samples was clearly observed, with longitudinally built samples exhibiting higher yield strength and elongation than transversely built samples. Stress relief heat treatments applied to LP-DED samples reduced the tensile strength due to stress relief, but tensile elongation was unaffected.