The Rate-Temperature Dependent Compressive Mechanical Behavior and Deformation Mechanism of CrCoNiSi_0.3 Medium Entropy Alloy

The CrCoNiSi_0.3 medium entropy alloy exhibits excellent synergistic mechanical behavior of strength and toughness under quasi-static loading. However, the influences of temperature and strain rate on the mechanical behavior of the alloy urgently need to be studied. Through the split Hopkinson pressure bar (SHPB), dynamic compression experiments at room temperature (20 ℃) with strain rates ranging from 1776 s⁻¹ to 5196 s⁻¹ and quasi-static compression experiments at high temperatures (from 20 ℃ to 1000 ℃) were carried out on the CrCoNiSi_0.3 medium entropy alloy. The strain rate and temperature-dependent mechanical behavior and deformation mechanism of the CrCoNiSi_0.3 medium entropy alloy were systematically investigated. The results show that under dynamic loading, the yield strength of the CrCoNiSi_0.3 medium entropy alloy increases with the increase of the strain rate, exhibiting a high strain rate sensitivity. This is attributed to the comprehensive mechanism of stacking faults, deformation twins, and the phase transformation from face-centered cubic to hexagonal close packed, which increase as the strain rate increases. The average work hardening rate increases slightly at first with the increase of the strain rate. When the strain rate reaches about 5196 s⁻¹, the average work hardening rate decreases due to the formation of shear bands. As the temperature rises, the compressive yield stress and work hardening ability of the alloy gradually decrease. However, there is still no work softening phenomenon at a temperature of 1000 ℃. Due to the high density of stacking faults and dislocation locks in the alloy at 600 ℃, it shows almost the same yield strength and flow stress as at 400 ℃. Aiming at the mechanical behavior that the strain hardening shows a decrease with the increase of the strain rate, a strain hardening function was introduced into the model, and a modified Johnson-Cook constitutive model was established, which can predict the mechanical behavior of the CrCoNiSi_0.3 medium entropy alloy quite well.