Achieving excellent plasticity performance in non-equiatomic FCC CoCrFeNiMoMn high-entropy alloys via arc-based direct energy deposition

Abstract

High-entropy alloys (HEAs) are a relatively new class of materials with exceptional properties, offering promising applications in aerospace, nuclear industry, and hydrogen storage. Alongside alloy design and development, recent research on HEAs has focused on exploring different manufacturing processes and resulting properties. This study demonstrates the practicality of leveraging an ultra-high-frequency Tungsten Inert Gas (TIG)- heat source during directed energy deposition (DED) with dual alloy wires, to fabricate non-equiatomic CoCrFeNiMoMn HEAs for the first time. A comprehensive analysis of the microstructural evolution and mechanical properties of as-deposited HEAs and those post-heat treated based on CALPHAD methodology is detailed. The microstructural and elemental homogeneity was markedly enhanced through the application of ultra-high-frequency pulsed current (UHFPC), yielding a non-equiatomic CoCrFeNiMoMn alloy with a ductile FCC matrix in the as-deposited state. In the post-heat treatment condition, the FCC matrix underwent recrystallization and L2₁ phase precipitated at grain interiors and boundaries. These precipitates conferred significant strength to the HEA through precipitation hardening by effectively obstructing dislocation motion at incoherent interfaces, while the accompanying lattice misfit and dislocation networks further amplified the alloy's mechanical properties. The CALPHAD-guided heat treatment protocol notably elevated the performance metrics, achieving a 54.2 % enhancement in yield strength and a 42 % improvement in ultimate tensile strength, all while retaining commendable elongation. This work offers valuable insights into the potential of cost-effective TIG-based dual wire DED for the fabrication of HEAs with precisely tailored microstructures and properties, rendering them ideal for advanced applications.