Influence of the C content on the mechanical and tribological properties of the TiCN coatings deposited by LAFAD technique

Abstract

TiCN coatings with different C content were deposited using a large area filtered arc deposition (LAFAD) technique from Ti targets in a mixture of N 2 and CH 4 gases. Scanning electron microscopy (SEM), nano-indentation, and pin-on-disc tribometer were used to characterize the cross-sectional microstructure, hardness, modulus, wear rate, and friction coefficient of the TiCN coatings. The increase in the CH 4 fraction in the gases leads to a continuous increase in the deposition rate of the TiCN coatings as well as an increase in the defect density in the coatings. Nano-indentation results indicate that with an increase of the C content in the coatings, the hardness and elastic modulus increase to a maximum at a C content of 2.8 at.%, then decreases rapidly, which results from the increase in the defect density in the coatings. Tribological test results show that when tested against Al 2O 3 balls, there is no significant change in the friction coefficient (0.78–0.88) of the TiCN coatings with a C content of below 4.6 at.%, but the friction coefficient decreases rapidly to 0.21 with a further increase in the C content to 9.3 at.%. In addition, with increasing C content in the coatings from 0 to 9.3 at.%, the wear rate decreases remarkably from 2.5 × 10 −6 mm 3/Nm to 5.3 × 10 −7 mm 3/Nm. The low friction coefficient and the formation of a transfer layer correspond to the low wear rate for the TiCN coatings with high C content.