Super-hard and tough Ta1-xWxCy films deposited by magnetron sputtering

Abstract In order to achieve hard, tough and super wear resistant film, Ta1-xWxCy films with various W contents were deposited by DC magnetron sputtering and their structural evolution and mechanical properties were investigated. Ta1-xWxCy films show the structures of fcc-NaCl solid solution and nanocomposite, which depended on the W contents. Doping W atoms induces the amorphous carbon (a-C) precipitated at the grain boundary. The structure of Ta1-xWxCy film changes from the single solid solution to a nanocomposite structure, which consists of Ta(W)C nanocrystalline with C vacancies and small amount of a-C. Ta0.69W0.31C0.75 film shows superior mechanical properties with ultra-high hardness of 43.9 GPa and enhanced toughness (KIC) of 3.95 MPa·m1/2, which is attributed to the synergistic effect of solid solution strengthening, composite structure strengthening and toughening related to the interaction of valence electrons. Both low average friction coefficient of 0.28 and wear rate of 1.12 × 10−6 mm3/N·m is obtained from the Ta0.69W0.31C0.75 film, which is consistent well with its super mechanical properties. In this study, the fracture toughness is not directional related to H/E and H3/E2 for the nanocomposite coating.