Effect of grain size on the low-cycle fatigue behavior of carbon-containing high-entropy alloys

The effect of grain size on tensile and cyclic deformation behaviors of carbon-containing CoCrFeMnNi high-entropy alloys (Cantor) were investigated. Heat treatment of warm-rolled and cold-rolled specimens yielded various microstructures with average grain sizes 4 ≤ d ≤ 66 μm. The fine-grained specimens (d ≤ 15 μm) showed very similar tensile deformation behaviors. However, the prosperity of mechanical twins in the coarse-grained specimen (d ~ 66 μm) led to a strain-hardening behavior different from those of the fine-grained ones. Refining d to 10 μm by decreasing the heat-treatment temperature after warm rolling increased the strength and extended low-cycle fatigue life. However, no significant change in fatigue cycles occurred in that they could survive at similar imposed plastic strain amplitudes. Meanwhile, the cold-rolled and annealed (at 800 °C) specimen presented the finest d of ~ 4 μm with the best yield strength, but also revealed coarse carbides in the microstructure. High stress concentrations developed at the boundaries of these coarse particles severely reduced fatigue life. Thus, to increase the fatigue life in carbon-containing Cantor, thermomechanical treatment should be controlled in such a way that results in fine-grained microstructures without precipitation of coarse carbides.