Tuning the mechanical properties of CrCoFeMnNi high entropy alloy via cold spray additive manufacturing associated with heat treatment

Abstract

The CoCrFeMnNi high entropy alloy (HEA) is the most studied HEA because of its excellent combination of strength and ductility. However, despite the advantage of CoCrFeMnNi HEA, its application is limited owing to its low yield strength. In this study, an emerging cold spray additive manufacturing technique was applied to fabricate a bulk CrCoFeMnNi high entropy alloy to improve the yield strength of CrCoFeMnNi. The paper presented an experimental investigation of the microstructure and mechanical properties of the as-sprayed and heat-treated CrCoFeMnNi high entropy alloy samples under compressive loading conditions at different strain rates. The microstructural analysis of the as-sprayed samples exhibited undeformed particles, numerous refined grains, and an interparticle incomplete interface. Post-heat treatment was applied to tune inter-particle bonding and ductility. Quasi-static compression tests (at 0.001 s−1) and dynamic impact tests (up to 3900 s−1) were carried out on the as-sprayed and heat-treated samples along the printing direction (vertical samples) and perpendicular to the printing direction (horizontal samples). The extraordinary mechanical properties of the as-sprayed vertical samples reached a yield strength of ∼ 1036.6 MPa and an ultimate compressive strength of ∼ 1117.8 MPa at a strain deformation of 10.1%. The as-sprayed horizontal samples had a yield strength of ∼ 1033.1 MPa and an ultimate compressive strength of ∼ 1102 MPa at a strain of 5.6%. Thus, the as-sprayed (vertical and horizontal) samples showed mechanical anisotropic properties. Further, the as-sprayed samples showed brittle behavior. However, as-sprayed samples exhibit high ductility, up to 70%, and high plastic deformation after heat treatment. The deformation mechanism of as-sprayed and heat-treated samples is dominated by deformation twinning. This work showed excellent yield and ultimate compressive strength compared to other CrCoFeMnNi high entropy alloy manufacturing methods.