Ta addition effects on the structure, mechanical and thermal properties of sputtered Hf-Ta-C film.

Transition metal carbides (TMCs) hold great promise for protective coatings due to their excellent mechanical properties, however, developing hard yet tough TMC-based materials against harsh environment continues to be a great need but challenge, as high hardness is often obtained with toughness deterioration. Here, we focus on HfC film modification with Ta addition (10.2–26.8 at.%) using magnetron co-sputtering system, particularly, two types phase structures (cubic Hf(Ta)C single-phase solid solution and mixed phase Hf-Ta-C structure (HfC + TaC mixture), respectively) are prepared for comparison and explanation. Mechanical tests reveal that the Hf(Ta)C solid solution film exhibits the highest hardness (36 ± 0.51 GPa), which is far beyond pure HfC and TaC reference, and is nearly two times higher than the film with mixed phase of TaC and HfC. Simultaneously, excellent fracture toughness with high K f value at 3.6 MPa m1/2 can be achieved in such a solid solution film, on account of high hardness/elasticity modulus ratio. All films exhibit low friction coefficient at∼0.3 when C lubrication medium occurs, the lubrication behavior surpasses corresponding nitrides film. After high-temperature annealing at 800 °C, the Hf(Ta)C solid solution film is found to perform better in terms of thermal stability and oxidation resistance, while structural destruction and obvious oxidation occur in other reference films. We therefore give the potential advantage of solid solution structure (relative to mixed phase structure) in regulating high-performance TMC-based protective coatings, which is fundamental but very practical for other material systems. [ABSTRACT FROM AUTHOR]