Mechanical properties, thermal stability and oxidation resistance of HfC/a-C:H films deposited by HiPIMS

High power impulse magnetron sputtering (HiPIMS) technology is employed to prepare HfC/a-C:H nanocomposite films in Ar/C2H2 atmosphere. The gas flow rate is varied to modulate the carbon content and nanocomposite structure of the film. The correlations between the carbon content and nanocomposite structure and the mechanical properties, thermal stability and oxidation resistance of HfC/a-C:H films are investigated. Mechanical properties analysis revealed that the optimal hardness 34.8 GPa is obtained at the HfC/a-C:H film with C content of 63.6 at.%. The Young's modulus is related to the C-Hf* bond, which effectively toughens the film. The thermal stability of the film performs well when the annealing temperature reaches 800 degrees C and is gradually enhanced as the amorphous carbon content increases. Moreover, films with higher amorphous carbon content have greater potential for further hardening after annealing (from 31.8 to 38.4 GPa). The oxidation resistance of the film is governed by the synergistic effect of HfC grain size and amorphous carbon content. It is demonstrated that the two factors of fine grains and narrow mean grain separation are necessary to achieve enhanced oxidation resistance. These results may open up a new possible way to design other nc-MeC/a-C:H films for optimizing the toughness, thermal stability, and oxidation resistance. (C) 2020 Elsevier B.V. All rights reserved.