An in-situ study on the formation mechanism of adiabatic shear band in refractory high-entropy alloys

The dynamic deformation, temperature evolution, and mechanical properties of NbTaTiV and NbTaTiVW alloys were investigated through high-speed photography, infrared temperature measurement, and the split Hopkinson pressure bar. The findings reveal that the adiabatic shear band initiated in the NbTaTiV and NbTaTiVW alloys when the temperature reaches approximately 160 °C and 115 °C, respectively. It is evident that dependence exclusively on the thermal softening effect is inadequate to activate adiabatic shear bands. Instead, microstructural softening emerges as the predominant factor influencing their formation. We assessed the adiabatic shear sensitivity of NbTaTiV and NbTaTiVW alloys from distinct perspectives. It is noteworthy that the defect density observed in the NbTaTiV alloy is considerably greater than that found in the NbTaTiVW alloy. The deformation structure of the NbTaTiV alloy predominantly consists of dislocations, deformation twins, and kink bands, whereas the NbTaTiVW alloy is deformed by dislocations and deformation twins. The kink band within the NbTaTiV alloy contributes to the delay of adiabatic shear failure. In addition, the participate phases in the NbTaTiVW alloy facilitate an increase in local dislocation density, thereby promoting adiabatic shear band failure. As a result, the energy dissipation of the adiabatic shear bands in the NbTaTiV alloy spans from 20.4 to 100.6 kJ/m², while the energy dissipation for the NbTaTiVW alloy is from 10.1 to 35.6 kJ/m². Our results and analyses contribute to formation mechanisms of shear band in refractory high-entropy alloys subjected to high strain rates.