Structure And Properties Of CrN/TiN Superlattice Coatings Deposited By The Combined Deep Oscillation Magnetron Sputtering

Deep oscillation magnetron sputtering (DOMS) is a novel high power impulse magnetron sputtering technique, which offers large voltage oscillation packets to generate a stable high-power discharge plasma with high ionization, high density and deposition rate under virtually arc-free conditions to significantly improve the properties of the coatings. CrN/TiN superlattice coatings were deposited by the combined DOMS and pulsed dc magnetron sputtering (PDCMS) in a closed field unbalanced magnetron sputtering system. The composition and micro structure of coatings were characterized using electron probe micro-analysis, X-ray diffraction, scan electron microscopy and transmission electron microscopy. The mechanical and tribo logical properties of the coatings were analysised using nanoindenter, Rockwell C, scratch test and ball-on-disc tribometer. The thermal stability of the coatings was investigated after anealing at 200-900? in air using a resistance furnace. Anode polarization test in 3.5 wt.% NaCl aqueous solution was used to evaluate the corrosion resistance of the coatings.CrN/TiN superlattice coatings has been deposited by a PDCMS technique at the frequency of 100 kHz, pulse period of 1.0 ?s, nittrogen flow rate ratio (fN2) of 40%, Cr target power (PCr) of 70-1000 W, Ti target power (PTi) of 2000 W, working pressure (Pw) of 0.67 Pa, and negative substrate bias (Vs) of -60 V. The thickness of coatings and modulated period (A) ranged from 2 to 2.5?m and from 4.4 to 8.2 nm, respectively. The substrate materials were Si(100), AISI 304L stainless steel (SS) and WC-6%Co certented carbon. The Cr/(Cr+Ti) ratio of 0.037-0.573, the texture evolution from (111) to (220) and single face-centred cubic phase structured with a nano-columnar were obtained. The residual stress was of -0.81--7.36 GPa. The hardness (H), and the H/E* and H3/E*2 ratios were 12.4-33.2 GPa,0.0436-0.0832 and 0.0237-0.214, respectively. The coatings at ?=5.8 nm showed the highest H, the H/E* and H3/E*2 ratios and a lower residual stress, resulting in the highest LC1,LC2 and LC3 of 10.8 N, 10.8 N and 20.3 N, high thermal stability up to 700?. The improvement in wear resistance of CrN/TiN superlattice coatings were obtained with the lowest the coefficient of friction (COF) of 0.41 and the lowest specific wear rate (WR) of 2.3×10-6mm3N-1m-1. Correspondingly, the coatings showed increased corrosion resistance with corrosion potential of (Ecorr) of -40 mV(SCE) and passive current density (Icorr) of 10-2?Acm-2 in 3.5 wt.% NaCl aqueous solutions. The decreasing number and size of pits were detected on corroded surface.CrN/TiN superlattice coatings deposited by the combined DOMS+PDCMS techniques at the frequency of 100 kHz, pulse-on time of 2 ?s and pulse-off time of 40 ?s,fN2=40%, PCr=300-1000 W, Pw=0.67 Pa and Vs=-60 V. The thickness and A ranged from 2 to 3 ?m and from 4.9 to 10.2 nm. The substrate materials were Si(100), AISI 304L SS, IN 718 and WC-6%Co. The coatings with the Cr/(Cr+Ti) ratio of 0.177-0.496 showed a single face-centred cubic phase with a strong (111)-texture and dense nano-columnar structure. The residual stress ranged from-0.72 GPa to-6.8 GPa. H, and the H/E* and H3/E*2 ratios were 17-37.3 GPa,0.058-0.094 and 0.057-0.316, respectively. The coating at A=6.3 nm with deposited on WC-6%Co rearched LC1 of 41 N, LC2 and LC3 were higher than 50 N, due to the highest H/E* and H3/E*2 ratios, lower residual stress and high substrate hardness, The dominating scratch adhesion failure mode changed from buckling failure to slight elastic-plastic deformation. Cooperative deformation between the substarte with high hardness and the coatings with high the H/E* and H3/E*2 ratios inhibited crack initiation and propagation of low stressed coatings, resulting in the increased adhesion.CrN/TiN superlattice coatings deposited by the combined DOMS+PDCMS techniques showed an increase in wear resistance with COF and WR of 0.27-1.17 and 0.2-11 X 10-6mm3N-1m-1, respectively. The coating with smaller A and low stress deposited on a hard substrate showed a dominating oxidative wear, resulting in the significant improvement in wear resistance. During the dry sliding test, the coatings surffered cyclical contact stress. The high LC1 reflecting high elastic strain to failure and plastic deformation resistance reduced the contact tangential force, resulting in the decrease in COF. The high LC2 and LC3 reflecting cracks propagation resistance reduced the cracking and delamination to inhibit the occourence of abrasion wear, resulting in the decrease in WR. The coatings at A=6.3 nm deposited on AISI 304L SS substrate had the thermal stability up to 800? without the formation of TiO2 and Cr2O3 phases. Correspondingly, the coating with smooth corroded surface showed excellent corrosion resistance in 3.5 wt.%NaCl aqueous solution with Ecorr of-6.5 mV(SCE) and Icorr of 10-3 ?Acm-2. As compared with the coatings deposited by a PDCMS technique, the coatings deposited by the combined DOMS+PDCMS techniques showed higher mechanical properties, endurable wear resistance and antifriction properties and corrosion resistance due to the improved architecture.