High strain rate sensitivity and nanoscratch properties of the nano-sized crystalline/amorphous Ti-Zr-Hf-Co-Ni-Cu high-entropy metallic glass thin film fabricated by magnetron sputtering

Abstract

Catering for the development of microelectromechanical systems and micro actuators, the high-entropy conception is introduced into the metallic glass thin films to enhance the mechanical and thermal properties. Ti-Zr-Hf-Co-Ni-Cu high-entropy metallic glass thin films which exhibit promising application prospects are deposited at substrate bias voltages of 0 V, −50 V, and −100 V on the Si substrates coated with ∼150 μm SiO₂ by high-vacuum direct-current magnetron sputtering system in this work. The effects of substrate bias voltage on topographies, crystallinity, fracture behavior, mechanical properties, strain rate sensitivity, nanoscratch properties of thin films are investigated. With the substrate bias voltage increasing from 0 V to −100 V, the roughness of thin film decreases from 2.96 ± 0.03 nm to 0.63 ± 0.03 nm due to the densification and renucleation process. It is also the lowest roughness that has ever been reported in the Ti-Zr-Hf-Co-Ni-Cu high-entropy metallic glass thin films. All elements are distributed uniformly at the micrometer scale on the surfaces of all thin films, and the contents of each element are equal. All the thin films exhibit nanometer-sized crystalline/amorphous bi-phase nanostructures. With the increase of substrate bias voltage, the cross-sectional morphology changes from brittle cleavage character to plastic dimple structures, possibly related to the increased crystallinity. With the increasing substrate bias voltage, the elastic modulus and hardness both increase from 93.8 ± 0.2 GPa to 100.2 ± 0.2 GPa and from 6.4 ± 0.02 GPa to 7.0 ± 0.03 GPa, respectively. A significant strain rate sensitivity of ∼0.1 is discovered in all the thin films. Furthermore, the nanoscratch test shows that the largest critical stress to date for interface separation are discovered in these thin films, which show an enhancement from 5.7 N to 6.7 N with an increase of substrate bias from 0 V to −100 V, suggesting an improvement of bonding strength between the thin film and substrate.