Tribological characteristics of Ti-Si-N films deposited by unbalanced DC magnetron sputtering

Abstract

Ti-Si-N thin films were deposited onto silicon (100) and AlSl M2 high-speed steel (HSS) substrates by reactive unbalanced DC magnetron sputtering in order to study the tribological properties and their correlation with the coating microstructure. The emphasis of this research was focused on the adhesion properties, friction behavior and wear resistance of Ti-Si-N coatings, using a combination of Rockwell-C adhesion tests, scratch tests, and pin-on-disc wear tests. In addition, the wear rates of Ti-Si-N coatings sliding against a tungsten carbide (WC) ball were ranked by wear performance and related to their hardness, microstructures, and wear mechanisms. With addition of silicon, better adhesion strength quality and higher critical load of Ti-Si-N coatings were obtained. The best adhesion performance (critical load beyond 80 N) was observed at a silicon content of 9%. In addition, results from dry sliding pin-on-disc tests indicated that Ti-Si-N coatings showed stable friction behavior and enhanced wear resistance compared with TiN and Si 3 N 4 coatings deposited at the same conditions. Friction behavior of Ti-Si-N coatings can reflect the complete transition from the initial break-in behavior to a steady state, post break-in roughness referred to as equilibrium roughness. Crystallographic reorientation can produce a reduction in the effective shear stress in the near-surface region and a reduction of friction. Wear rates of Ti-Si-N coatings were compared and found to be in the range 10 −16 −10 −15 m 3 /Nm. The Ti 0.28 Si 0.14 N 0.58 even shows 5 times higher wear resistance when compared with that of TiN coating. The surface morphology of the wear scars after tribological tests was analyzed by optical and scanning electron microscopes (SEM) in order to identify the main failure modes. The elemental compositions of the films were determined by energy dispersive X-ray analysis (EDX). The crystallography and surface textures were measured by X-ray diffraction (XRD). In addition, the surface roughness and morphology of the films were investigated by atomic force microscopy (AFM) in contact mode. The better tribological performance of Ti-Si-N coatings is due to improved surface morphology, microstructure, better adhesion properties, and their enhanced hardness and faster elastic recovery.