Effect of substrate bias current on structure and properties of CrNx films deposited by plasma enhanced magnetron sputtering

Abstract

In order to further improve the mechanical properties of CrN films, the influence of substrate bias current on the microstructure and properties of the CrNx films deposited by plasma enhanced magnetron sputtering was studied by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, 3D profiler, nano indenter, and ball-on-disk tribometer. With the increase of substrate bias current, the microstructure of the films is transformed from a dendritic structure into a super dense columnar structure, and the phase composition is evolved from Cr → Cr + Cr2N → pure Cr2N. When the substrate bias current is >1.5 A, the preferred orientation is transformed from Cr2N(111) to Cr2N(300) with increasing substrate bias current. The surface roughness of the films is decreased from 27.3 to 18.7 nm as the substrate bias current is increased from 0.1 to 1.5 A, but the surface roughness remains nearly unchanged when the substrate bias current exceeds 1.5 A. The hardness and effective Young's modulus of the films are obviously increased with increasing the substrate bias current from 0.1 to 3.0 A, while they are almost independent of the substrate bias current when the substrate bias current is no less than 3.0 A. The lowest friction coefficient of 0.43 is obtained when the substrate bias current is 4.5 A. When the substrate bias current is increased, the wear rate of CrN-coated samples is first increased and then decreased, and the lowest wear rates is 4.6 × 10−16 m3/(N·m) when the substrate bias current is 6.0 A.