Mechanical and tribological properties of CrN/TiN multilayer coatings deposited by pulsed dc magnetron sputtering

Abstract

CrN/TiN multilayer coatings were deposited by pulsed dc magnetron sputtering (PDCMS) in a closed field unbalanced magnetron sputtering system. The Ti target power was maintained at 2000W while the Cr target power was varied from 70 to 1000W. As the Cr target power was increased, CrN/TiN multilayer coatings with the Cr/(Cr+Ti) ratio of 0.037–0.573 had a single phase face-centered cubic structure with a texture evolution from (111) to (220). The residual stress of the coatings increased from −1.03GPa to −5.65GPa. The hardness and the H/E* and H3/E*2 ratios of the coatings exhibited an initial increase with the increasing Cr target power, then followed by a decrease. The coating with a Cr/(Cr+Ti) ratio of 0.30 reached the highest hardness and the H/E* and H3/E*2 ratios of 31GPa, 0.0832 and 0.214, respectively. The coating also showed a dominant oxidative wear with the lowest friction coefficient and specific wear rate of 0.41 and 2.3×10−6mm3N−1m−1, respectively. The increase in the H/E* and H3/E*2 ratios led to the increase in the toughness and cohesion/adhesion strength of the coatings with the increased HF levels and critical loads (LC1, LC2 and LC3). However, the coatings with similar H/E* and H3/E*2 ratios exhibited different tribological properties due to the different critical loads LC3 resulted from the increased compressive residual stress. The improvements in toughness and cohesion/adhesion strength promoted the reduction in the crack initiation and propagation, and oxidative wear during dry sliding tests.