Ultra-high strain-rate strengthening in ductile refractory high entropy alloys upon dynamic loading

The mechanical properties and strain-rate strengthening mechanism of single-phase TiZrHfNbTaMox (x = 0.25, 0.5, and 0.75) refractory high entropy alloys (RHEAs) upon dynamic loading are investigated. Dynamic compression with varying strain rates of 2100-6000 s(-1) at room temperature are performed by the split-Hopkinson pressure bar (SHPB), and the dynamic yielding strength is about 1.3 times of the quasi-static one. Positive strain-rate sensitivity (SRS) on the yielding strength is available, and the work-hardening is weakened but the yielding strength is improved with increasing strain rates due to the adiabatic heating upon dynamic loadings and the dislocation movement resistance, respectively. Considering the adiabatic temperature rise converted by plastic deformation work at high strain rates, the flow behavior is characterized by employing the modified Johnson-Cook model. A semi-empirical Zerilli-Armstrong constitutive model is proposed to predict yielding strengths at various strain rate.