Microstructure And Tribological Properties Of CrN/W₂N Multilayere And Ti/a-C Composite Films Deposited By Magnetron Sputtering

Compared with single-layered films, nano-multilayered ones often have various special performances, such as higher hardness, adhesive strength and toughness, more excellent thermal statebility, lower friction coefficient and higher wear resistance. Also, amorphous carbon (a-C) films have excellent tribological property, duing to the formation of transfer graphite-like layer during the wear test, so they have extensive applications as anti-wear materials.In this present work, CrN/W₂N multilayers with different modulated periods and amorphous carbon (a-C) films with different Ti concentration were fabricated through DC magnetron sputtering. The microstructure, surface and cross-sectional morphologies of the as-deposited films were investigated by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Raman spectscopy and scanning electron microscopy (SEM). The hardness and elastic modulus was measured by nanoindentation testing. The adhesion and tribological properties were evaluated using scratch tests and a conventional ball-on-disk tribometer, respectively. The effects of modulated periods of CrN/W₂N multilayers and Ti concentration of a-C films on the mechanical and tribological properties were further investigated.The modulated period has an influence on the hardness, adhesion and tribological properties of CrN/W₂N multilayers. It is shown that the hardness and elastic modulus increase gradually with decreasing the modulated period. Besides the crystals inside the film, the high density of interfaces, different lattice constants and crystalline orientation all make the dislocation be blocked, so the hardness is improved. For the CrN/W₂N multilayer film with a bilayer period of 15 nm, both the hardness and elastic modulus achieve to maximum values, approximately 29.2 GPa and 376 GPa respectively. Also this kind of film shows the best adhesion and tribological properties.For the a-C films, the pure one has the highest hardness and elastic modulus, 53 GPa and 289 GPa respectively. With the increase of Ti concentration, the values of hardness and elastic modulus decrease. However, the adhesive strength is improved. During the wear test, the asperities on the surface between film and counterpart come into intimate contact and interaction, to make recrystallization and reorientation happened, which results in the formation of a transfer graphite-like layer. The single-orientation sliding made the direction of the transfer layer corresponding with the surface of film, making the friction reduced. The a-C film has low friction and high wear resistance owing to the formation of transfer graphite-like layer. The a-C film with 3.1 at.% Ti had the lowest friction coefficient, 0.125. With increasing the performed load, the friction coefficient decreases gradually.