Studies On Preparation And Tribological Behaviors Of Chromium Nitride Coatings

Filtered cathodic vacuum arc (FCVA) deposition, which presented some incomparable advantages, such as higher ionization, higher deposition rate and strong adhesion with substrate, is an excellent physical vapour deposition technology and has a widely industrial application potential.In this paper, CrN coatings have been deposited by FCVA deposition technology. The microstructure, micro-hardness, morphology and tribological properties of the coatings were characterized. The influences of deposition parameters such as partial, pressure of nitrogen, bias voltage, substrate temperature on the properties and structure of the coatings were analyzed, and the preparation technological paramteres were optimized.The tribological behaviors of reciprocating, and ball-on-disc sliding for two CrN coatings which prepared by different PVD technologies (FCVA and commercial ion plating) have been contrastively studied by CETR UMT-2 multifunctional wear tester. Base on the analyses of friction kinetics, some micro-examination means, such as scanning electron microscopy (SEM), laser Confocal scanning microscopy (LCSM), energy dispersive X-ray spectrum (EDX) and X-ray diffraction (XRD), were used to analyze the tribological characteristics under varied the test parameters of normal loads and sliding velocities. The tribo-chemical effect on wear and the wear mechanisms of the coatings were discussed in detail. Wear resistances of the two CrN coatings were compared. The main research results are as follows:1. Cr/CrN composite coatings have been deposited by filtered cathodic vacuum arc (FCVA) deposition technology, where the Cr layer played a transition role. The phase constitution of the CrN layer was composed of CrN and Cr₂N.2. During the preparation of the FCVA CrN coatings, there was only one optimal parameter for both the partial pressure of nitrogen and substrate-bias voltage. Too higher or too lower these parameters would lead to worse coating properties. The results showed that the pre-heating of the substrate was not good for improving the properties of the coating. The properties of the CrN coatings were obviously improved by adding a Cr transition layer.3. Under the reciprocating and ball-on-disc sliding test conditions, the friction coefficients in stable stage of the both types of the CrN coatings decreased with the increase of the normal loads, and increased with the decrease of the sliding velocities. The sliding wear mechanism of the both types of the CrN coatings was mainly characterized by the combination of abrasive wear and oxidation wear.4. The wear of the FCVA CrN coating was slighter and presented better wear resistance than that of the ion plating coating, which maybe were attributed to their different microstructures.5. Compared with the ion plating CrN coating, the FCVA CrN coating presented smoother, denser and continuum surface, and presented higher hardness and wear resistance, however, presented lower the bond strength. The early failure of the FCVA CrN coating under the higher normal loads was due to the poor bond strength .In general, Cr/CrN composite coatings with high hardness and good wear resistance were successively prepared by FCVA technique.