The enhancement of fracture toughness and tribological properties of the titanium nitride films by doping yttrium

In this paper, yttrium was incorporated into titanium nitride matrix to deposit TiYON films using a reactive magnetron sputtering system and the microstructure, mechanical and tribological properties were investigated. The results showed that solid solution face centered cubic (fcc) TiYN was the major phase of the film when the yttrium content was < 7.8 at.%. When the yttrium content was further increased, the film exhibited mixed phases of fcc-TiYN and amorphous yttrium oxide, this induced grain refinement and appearance of lots of grain boundaries. Hardness of the films first rose from 21 GPa at 0 at.% Y to 26 GPa at 10.2 at.% Y, and remained stable as the yttrium content was above 10.2 at.%. The hardness was influenced by the amorphous yttrium oxide phase, solid solution strengthening, grain boundaries and residual stress. Between 0 at.% to 7.8 at.% of yttrium, the fracture toughness (KIC) rose slowly, KIC rose sharply to 0.85 MPa.m1/2 as the yttrium content was 10.2 at.% due to the formation of amorphous yttrium oxide phase, it rose slowly again with a further increase in yttrium content. For the film at < 7.8 at.% Y, average friction coefficient (μ) and wear rate were influenced by the load significantly and there was an obvious rise in their values with an increase in load. A further increase in yttrium content in the films, improved the tribological properties, μ and wear rate were almost independent on the load. Fracture toughness enhancement attributed to the improved load capacity and tribological properties.