Effects of deposition temperature on the nanomechanical properties of refractory high entropy TaNbHfZr films

The refractory high-entropy TaNbHfZr films with various microstructures have been synthesized by magnetron sputtering via tuning different deposition temperature from 25 °C to 700 °C. At 25 °C, a complete amorphous structure with featureless surface morphology is formed. With the increase of deposition temperature, the precipitation of crystallites is observed at 500 °C and a nanocrystalline bcc structure high-entropy TaNbHfZr alloy film with the surface morphology of needle-like islands at 700 °C due to the significantly improved atom diffusion ability. Nanoindentation results also indicate that the hardness and reduced elastic modulus of the films are strongly dependent on their distinct microstructures. For amorphous dominated films, the hardness increases with the elevated temperature accompanied with enhanced modulus. The bcc TaNbHfZr high-entropy alloy film displays superior hardness of ∼15.3 GPa. The strengthening mechanism can be attributed to the distortion induced solid-solution strengthening and the grain boundary strengthening in the nanocrystalline microstructure. [Display omitted] •The bcc structure TaNbHfZr film was prepared at 700 °C via magnetron sputtering.•The microstructure transforms from amorphous to nanocrystalline from 25 to 700 °C.•The TaNbHfZr film deposited at 700 °C possesses a superior hardness of ∼15.3 GPa.•The strengthening mechanisms are solid-solution and grain boundary strengthening.•The lattice and modulus distortion are ∼66.7 MPa and ∼689.1 MPa, respectively.