Improvement of microstructure and tribological properties of titanium nitride films by optimization of substrate bias current

Abstract

Severe wear is a key factor affecting the work character and service life of the cutting tools used for dry cutting. The deposition of wear-resistant films on the cutting tools via magnetron sputtering is one of the most effective strategies, and the further improvement of the properties of the deposited films has attracted much attention. Plasma-enhanced magnetron sputtering possesses a much higher ionization rate than conventional magnetron sputtering and has been used to deposit dense hard wear-resistant film, but the influence of substrate bias current (Is) on the structure and properties of the films should be further studied. In this paper, plasma-enhanced magnetron sputtering technique was utilized to obtain an individually adjustable Is and TiN film was taken as an example to study the effects of Is on the properties of the films. It is found that the microstructure of the films is transformed from a loose columnar microstructure into a dense and featureless microstructure with increasing Is from 0.1 to 3.0 A, and the preferred growth orientation along TiN(111) is found at a high level of Is. As Is increases from 0.1 to 1.5 A, the grain size of the films is abruptly decreased, and the mechanical properties are significantly improved; but when Is further increases, the mechanical properties stay nearly unchanged. When Is is increased, the wear rate of TiN-coated samples is distinctly decreased at first, and then gradually increased. When Is is 3.0 A, the highest hardness of 38.7 GPa and lowest wear rate of 9.4 × 10–16 m3/(N•m) are obtained for the TiN-coated sample.