The Annealing Influence on the Mechanical Behavior of Ni45Co23Cr20Mo5Al7 Medium-Entropy Alloy

Meiling Liang; Hongmin Zhang; Peter K. Liaw; Fanchao Meng; Shuying Chen

Abstract

The influence of heat treatment on the mechanical properties of a novel Ni₄₅Co₂₃Cr₂₀Mo₅Al₇ medium-entropy alloy (MEA) has been systematically investigated. An exceptional combination of ultimate tensile strength (UTS) of approximately 1.3 GPa and ductility of approximately 13% was achieved through annealing at 850 °C for 2 h followed by aging at 780 °C for 8 h, which produces a partially recrystallized microstructure with uniformly distributed precipitates. The superior mechanical performance results from the synergistic contribution of retained deformation twins and stacking faults from cold rolling, precipitation hardening, and fine recrystallized grains. In the non-recrystallized condition annealed at 800 °C for 4 h, an extremely high UTS of approximately 1.55 GPa was obtained, attributed to the preferential segregation of Mo to deformation twins and stacking faults, which substantially increases the resistance to dislocation motion. However, this condition exhibited negligible ductility. The fully recrystallized condition achieved through annealing at 900 °C followed by aging at 780 °C resulted in a balanced combination of UTS of approximately 1.2 GPa and ductility of approximately 28%, governed by precipitation hardening and recrystallized grain size. This study demonstrates a viable heat treatment strategy for developing high-performance MEAs that overcome the conventional strength-ductility trade-off.

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