Dynamic behavior and microstructure characterization of TaNbHfZrTi high-entropy alloy at a wide range of strain rates and temperatures

The TaNbHfZrTi refractory high-entropy alloy (RHEA) is suction casted by vacuum arc melting furnace. The mechanical behavior of the TaNbHfZrTi RHEA is systematically investigated through material testing machine and Split Hopkinson Pressure Bar (SHPB) system at strain rate up to 2600s-1 and temperatures from 77K to 873K. Significant increases in the yield strength and interesting changes in strain rate sensitivity at high strain rates and high temperatures are observed. During the dynamic tests, the strain rate sensitivity rises from ~5 to ~76 with the temperature increases from 293K to 673K, demonstrating that high temperature has a significant influence on the strain rate effect of the TaNbHfZrTi RHEA. The comprehensive analysis of electron backscatter diffraction (EBSD) and Kernel Average Misorientation (KAM) technique shows that the pronounced homogeneous deformation microstructures exist in the sample even at the true strain of about 0.34, only very short adiabatic shear band (ASB) initiates. The fracture morphology investigated by scanning electron microscopy (SEM) indicates both ductile and brittle fracture behavior of the TaNbHfZrTi RHEA at 77K. The improved Johnson-Cook (J-C) model is proposed to describe the deformation behavior, in which both strain rate hardening and temperature softening terms are expressed as a function of strain and strain rate, respectively.