Effect of Temperature on Tensile Properties of CrCoNi Medium-Entropy Alloy at High Strain Rate

Medium-entropy alloys (MEAs) have shown broad prospects in extreme environmental applications, such as aircraft landing gears and actuators, due to their excellent low-temperature mechanical properties. However, as the temperature rises to room temperature or above, the comprehensive mechanical properties significantly decrease, which has become a bottleneck limiting its application. For this purpose, in this work, the gradient twin structures for MEAs are designed, and the mechanical response is investigated under the combined effects of microstructure design, temperature effects, and strain rate effects from multiple angles. On this basis, combined with the study of tensile mechanical behavior over a wide range of temperature range and different strain rates, the strengthening mechanism of MEAs in gradient twin structures under strain rate temperature coupling conditions is elucidated. It proves that the surface plastic deformation (SPD) process has a significant effect on improving the mechanical properties, especially the yield strength, of CrCoNi MEA. The gradient structure enhances the strain rate sensitivity of CrCoNi MEA at room temperature, while reducing its value at high temperatures. For uniform coarse-grained MEAs, an increase in temperature significantly reduces the strain hardening ability, while for gradient-structured MEAs, an increase in temperature results in a greater difference in strain hardening ability at different strain rates.