Preparation, Microstructure And Properties Of Ti-Al-Zr-Cr-N Composite Hard Films Deposited By Multi-Arc Ion Plating

The TiN hard films deposited on the cutting tools of high speed steel and cemented carbide can enhance their hardness and wear resistance, which, in turn, improve the cutting performance and service life. However, high speed cutting has been the main trend in the mechanical processing field. The TiN hard films deposited cutting tools would not fulfill the function requirements of the numerical controlled processing machines, which gradually become more popular. On the other hand, the various composite techniques, namely film alloying, multilayer and gradient-layer, could improve the comprehensive quality and service life of the hard films. Therefore, the objective of this study is to achieve the better properties of TiN-based composite films by adding the different alloy elements and modifying the film structures.The two Ti-Al-Zr targets and one pure Cr target were used to prepare four types of Ti-Al-Zr-Cr-N composite hard films, namely (Ti, Al, Zr, Cr) N multi-component films, (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N bilayered films, CrN/(Ti, Al, Zr, Cr) N bilayered films and TiAlZrCr/(Ti, Al, Zr, Cr) N gradient films, on the substrates of high speed steel (W18Cr4V) and cemented carbide (WC-8%Co). The composition, morphology, roughness and microstructure of the films were analyzed by energy disperse X-ray spectroscopy (EDS), scanning electron microscopy (SEM), laser scanning Confocal optical microscopy 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. Meanwhile, the wear resistance of the films was studied by abrasion tester at the room temperature (15℃) and elevated temperature (500℃), and the worn surface morphologies were studied by SEM. Furthermore, short-term isothermal (at 600℃, 700℃, 800℃and 900℃for 4h) and long-term cyclic (at 700℃ and 800℃for 100h) high temperature oxidation behaviors of the films were studied, and the oxide scales formed on the film specimens were characterized by SEM, EDS and XRD.It was showed that the obtained Ti-Al-Zr-Cr-N composite hard films were of the TiN (B1-NaCl) type face-centered cubic structure. The compositions of the four composite films did not change too much at the other bias voltages except at -50V. The surface morphologies of the composite films were isotropy and dense; however, there were many macro-particles (or micro-drops) and pores. By increasing the bias voltage, the drop contamination on the films decreased significantly, and then the surface roughness 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 four composite films was about l¹.5|xm at the different bias voltages, and decreased with increasing the bias voltage.In the (Ti, Al, Zr, Cr) N multi-component films, the atomic ratio of (Al+Zr+Cr)/ (Ti+Al+Zr+Cr) varied from 0.44 to 0.52 on the W18Cr4V substrates, whereas it varied from 0.41 to 0.43 on the WC-8%Co substrates. When the atomic ratio approached 0.44 and 0.41, the micro-hardness of the films was improved up to 3300HV_0.01 and 3600HV_0.01, respectively. The adhesive strength between the film and the substrate was also enhanced up to 190N and 200N, respectively. The wear behavior of the films was characterized by the adhesive wear that was caused by the plastic deformation feature and the slight abrasive wear. The average values of friction coefficient varied between 0.3 and 0.5 at the room temperature and elevated temperature in the (Ti, Al, Zr, Cr) N multi-component films. The friction coefficient curves and the worn surface morphologies showed that the wear resistance was improved as the bias voltage increased. The properties of the films on the WC-8%Co substrates were better than those on the W18Cr4V substrates. Moreover, under short-term isothermal condition, the (Ti, Al, Zr, Cr) N films presented the excellent high temperature oxidation resistance on both the W18Cr4V (up to 800℃) and WC-8%Co (up to 700℃) substrates, and an oxide scale of TiO₂ was observed by XRD. On the other hand, under long-term cyclic high temperature condition, the oxidation resistant temperature of the (Ti, Al, Zr, Cr) N films was about 700℃on the W18Cr4V substrates and 600℃on the WC-8%Co substrates.The micro-hardness of the (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N bilayered films and the adhesive strength between the bilayered film and the substrate were increased remarkably with the addition of (Ti, Al, Zr) N interlayer. When the atomic ratio of (Al+Zr+Cr)/(Ti+Al+Zr+Cr) reached 0.44 on the W18Cr4V substrates and 0.40 on the WC-8%Co substrates, the micro-hardness of the films was improved up to 3450HV_0.01 and 4000HV_0.01, respectively. The adhesive strength between the film and the substrate was also enhanced to 190N and above 200N, respectively. Meanwhile, the wear resistance of the (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N bilayered films was superior to those of the (Ti, Al, Zr, Cr) N single-layered films. The average values of friction coefficient varied between 0.3 and 0.35 at the room temperature and elevated temperature in the bilayered films. Moreover, the high temperature oxidation resistance of the (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N bilayered films was improved with the addition of (Ti, Al, Zr) N interlayer according to the analysis of mass gain, morphology and microstructure of the oxide scales.In the CrN/(Ti, Al, Zr, Cr) N bilayered films, the micro-hardness values were higher than those of the (Ti, Al, Zr, Cr) N single-layered films, but lower than those of the (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N bilayered films. The CrN/(Ti, Al, Zr, Cr) N bilayered films also presented the superior adhesive strength, as compared with (Ti, Al, Zr, Cr) N and (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N films. When the atomic ratio of (Al+Zr+Cr) /(Ti+Al+Zr+Cr) reached 0.45 on the W18Cr4V substrates and 0.40 on the WC-8%Co substrates, the micro-hardness of the films was improved up to 34OOHV_0.01 and 3900HV_0.01, respectively. The adhesive strength between the film and the substrate was also enhanced up to 190N and above 200N, respectively. Meanwhile, the wear resistance of the CrN/(Ti, Al, Zr, Cr) N bilayered films was superior to those of the (Ti, Al, Zr, Cr) N single-layered films, while not as good as those of the (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N bilayered films. The average values of friction coefficient varied between 0.3 and 0.4 at the room temperature and varied between 0.3 and 0.45 at the elevated temperature in the CrN/(Ti, Al, Zr, Cr) N films. Moreover, the high temperature oxidation resistance of the CrN/(Ti, Al, Zr, Cr) N bilayered films was improved with the addition of CrN interlayer, in which the oxidation resistance temperature of the films on the WC-8%Co substrates was up to 800℃under the short-term isothermal oxidation condition.The micro-hardness and adhesive strength of the TiAlZrCr/(Ti, Al, Zr, Cr) N gradient films were higher than those of the (Ti, Al, Zr, Cr) N, (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N and CrN/(Ti, Al, Zr, Cr) N films. When the atomic ratio of (Al+Zr+Cr)/(Ti +Al+Zr+Cr) approached 0.45 on the W18Cr4V substrates and 0.39 on the WC-8%Co substrates, the micro-hardness of the gradient films was enhanced up to 3500HV_0.01 and 4000HV_0.01, respectively. The adhesive strength between the gradient film and the substrate was also enhanced up to 200N and above 200N, respectively. Meanwhile, the wear resistance of the TiAlZrCr/(Ti, Al, Zr, Cr) N gradient films was superior to those of the (Ti, Al, Zr, Cr) N, (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N and CrN/(Ti, Al, Zr, Cr) N films. The average values of friction coefficient varied between 0.25 and 0.3 at the room temperature and varied between 0.3 and 0.35 at the elevated temperature in the gradient films. Moreover, under short-term isothermal condition, the high temperature oxidation resistance of the films was excellent up to 800℃on both the W18Cr4V and WC-8%Co substrates. Under long-term cyclic high temperature condition, the oxidation resistance of the films was excellent at about 700℃on both the W18Cr4V and WC-8%Co substrates. Therefore, the high temperature oxidation resistance of the TiAlZrCr/(Ti, Al, Zr, Cr) N gradient films was obviously improved and better than those of (Ti, Al, Zr, Cr) N, (Ti, Al, Zr) N/(Ti, Al, Zr, Cr) N and CrN/(Ti, Al, Zr, Cr) N films.