Enhancing the impact performance of TaNbHfZr high-entropy alloy film by interface strengthening and stress dispersion: Microstructure and mechanism

The sandwich-structured TaNbHfZr refractory high-entropy alloy film (RHEAF) was fabricated by magnetron sputtering. Nano-impact was utilized to extract the local mechanical response of the film with severe localized strain due to the high instantaneous strain rate (ISR). Analysis on dynamic hardness (H_D) and toughness of TaNbHfZr film was carried out quantitatively. The plasticity absorption ability in nano-impact is higher indicated by the increased plastic work (W_p) with increasing acceleration force (AF). The decreased H_D is attributed to the contribution of the energy to the fracture at higher AF. Through TEM observation, the dynamic response is confirmed by thickness reduction in nano-impact. Cracks occur where the stress reaches its maximum in the middle layer, near the middle-bottom boundary, serving as the primary energy-storage mechanism in the sandwich-structured TaNbHfZr film. Furthermore, the rate-controlling response can be attributed to the dislocation motion at varing loading rates. This phenomenon is confirmed by FEM simulation. Here, the equiaxed grains within the middle layer mitigate further catastrophic damage by absorbing the localized and concentrated stress through rotation or grain boundary sliding. Consequently, the film was strengthened and stabilized due to the effective stress dispersion and existence of interface in the sandwich structure.