The role of copper incorporation on the microstructure, mechanical and tribological properties of TiBN-Cu films by reactive magnetron sputtering

Abstract

An experimental study was conducted on a series of Ti-B-N-Cu films via magnetron sputtering of titanium, boron and copper targets. This study aims at assessing the microstructure, mechanical and tribological properties of the Ti-B-N-Cu films by varying the concentration of copper. The deposited film revealed a face-centred cubic TiN structure with a (111) preferred orientation, and its grain size decreased with increasing content of copper. More so, the film exhibited the highest hardness and elastic modulus values of ∼33.2 GPa and ∼288.8 GPa respectively when the content of copper in the film was 1.8 at.% which also coincides with the best wear resistance value of the films. The initial increase in hardness is due to grain refinement and an increase in compressive residual stress in the film. Even though the incorporation of copper improved the high-temperature coefficient of friction, the wear rate deteriorates as the content of copper and temperature increases. The presence of tribo-oxides and copper within the wear track acted as a lubricating medium for the reduction of the coefficient of friction whiles the reduced hardness of the films as the copper content in increased resulted in the increased wear rate. Also, the wear rate of the films with the same copper content increases as the test temperature increases from RT to 700 °C. Hence caution must be taken when applying copper doped films for high temperature wear resistance operations.