Effects of bias voltage and discharge current on mechanical properties of TiN film deposited by DC magnetron sputtering

The effects of bias voltage and discharge current on the mechanical properties of TiN films deposited on carbon steel JIS S45C by reactive dc magnetron sputtering are investigated. The residual stress, hardness, toughness and adhesive strength are examined by X-ray diffraction method, nano-indentation test, indentation fracture method and scratch test, respectively. The films are revealed to exhibit high compressive residual stress that increases with the bias voltage and discharge current. The hardness also increases with the bias voltage and discharge current, whereas the adhesive strength decreases and the toughness increases only with increasing bias voltage. The variation of these properties correlates well with the variation in residual stress, regardless of changes in coating conditions. These properties are considered to depend mainly on the residual stress. The width of the X-ray diffraction peak also increased with bias voltage and discharge current, and correlated well with the change in residual stress. It was confirmed that the residual stress was generated by bombardment with high-energy ions during the coating process, and it was concluded that increasing the bias voltage and discharge current had the same effect to enhance the ion bombardment. Based on these findings, the ion bombardment is considered to be the dominant mechanism governing the mechanical properties of TiN films.