Study Of Super-hard Multi-constituent Composite Nitride Reactive Films

In this paper, (Ti,Al,Zr)N and (Cr,Ti,Al,Zr)N multi-constituent gradient film were deposited on the surface of high-speed steel substrate by multi-arc ion plating technique with (Ti-19Al-17Zr), (Ti-32Al-5Zr) alloy target and pure chromium target and controlling the flow of Ar and N2. The composition, phase structure, morphology and microstructure of the films were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Vickers indentation and scratch test were performed to measure the micro-hardness and the adhesive strength between the film and the substrate. The experiment of thermal shock was operated and the features of coatings failure were observed by optical microscope. Meanwhile, the wear resistance of the films was studied by abrasion tester at the room temperature and elevated temperature (500℃). And then worn surface morphologies were studied by optical microscope.Research showed that, (Ti,Al,Zr)N and (Cr,Ti,Al,Zr)N multi-constituent gradient supper-hard films could be deposited by using multi-arc ion plating technology and controlling the deposition process parameters (the partial pressure of Ar and N2) to control the film composition. Therefore the trend of N elements in three kinds of films from the substrate to the film surface is gradually increased. By optimizing the deposition process and film composition, the as-deposited (Ti,Al,Zr)N and (Cr,Ti,Al,Zr)N films which exhibited high micro-hardness values even up to 4000HV and very high adhesion strength super to 200N achieved the change from hard film to super hard film.It was showed that the obtained gradient films were of the TiN (Bl-NaCl) type face-centered cubic structure at different bias voltages. The surface morphologies of the gradient films showed isotropy and dense; however, there were many macro-particles (or micro-drops). By increasing the bias voltage, the drop contamination on the films decreased significantly, and then the surface morphology of the films was also improved. The cross-section morphologies revealed the typical and dense columnar structure. No evident defects were observed at the interface between the composite films and the substrates. The thickness of the gradient films was about 1.7～2.1μm at different bias voltages and decreased with increasing the bias voltage.All the thermal shock resistance of the three kinds of gradient films was superior to those of (Ti,Al)N monofilm and gradient film. During the experiment of thermal shock, the reaction product of Al2O3 and Cr2O3 at high temperature which was a high protective oxide film of denser structure and higher chemical durability could slow down the diffusion of oxygen atoms. Meanwhile the graded distribution of nitrogen could reduce the stress concentration effectively. Due to it, the thermal shock resistance of the film was improved. The degree of wear of the three kinds of films at high temperature (500℃) was more higher than that at room temperature, but the friction coefficient (0.3～0.5) is lower than that at room temperature (0.4～0.6).