Effect of annealing treatment on microstructural and mechanical properties of a hot-forged FeCrCuMn2Ni2 high-entropy alloy

Abstract

The present study prepared an as-cast ingot of a FeCrCuMn2Ni2 high-entropy alloy using vacuum induction melting process, followed by hot forging at 650–750 °C. The samples were then annealed at temperatures between 600 and 1100 °C for 2 h, and were characterized in terms of their microstructural features and mechanical properties. No phase transformation was observed for the hot-forged and annealed samples. Compared to the as-cast state, the hot-forged sample exhibited higher compressive yield strength and hardness, but lower compressive strain. This behavior can be due to the precipitation of hard σ-phase with an average size of 0.55 µm during hot forging. It was further observed that the precipitates dissolved, when the temperature exceeded 1000 °C, resulting in discontinuous static recrystallization with an average grain size of 15.9 µm. Annealing between 600 and 800 °C decreased the compressive yield strength and compressive strain, which could be attributed to σ-precipitates morphological change and their growth up to an average size of 1.34 µm. On the other hand, when the annealing temperature increased above 800 °C, the compressive yield strength decreased and compressive strain increased. This behavior was attributed to the dissolution of a large amount of σ-precipitates, growth of the residual σ-precipitates, and softening of the alloy. Findings further revealed a decrease in the hardening capacity value of annealed samples in the range of 600–800 °C, resulting from the formation of σ-precipitates. In contrast, the hardening capacity value of the alloy increased with the annealing temperature, due to the grains size increase at higher temperatures.