Characterization of Superhard Ternary (Ti,Al)N Coatings Prepared by Pulsed High Energy Density Plasma

Abstract

Traditional TiN coatings cannot meet the requirements in many applications under extreme conditions because of their relatively low hardness (similar to2000Hv), high friction coefficient (>0.4), inade- quate thermal stability and insufficient corrosion. (Ti,Al)N coatings are a promising alternative to TiN coatings, which have recently been obtained by some groups. However, The deposition of coatings on ceramic substrates prepared by traditional physical vapor deposition was puzzled by low adhesions. In this work, (Ti,Al)N deposition was realized by a new technique namely pulsed high energy density plasma. The ratio of Ti and Al atoms was kept constant at 1:1, since this was known to be the best ratio for (Ti,Al)N synthesis. However, the process allows many other deposition parameters to be varied. In this study, the influences of the discharge voltage between the inner and outer electrode, the distance between the sample and the pulsed plasma gun, and the shot number of the pulsed plasma on coating formation and properties were investigated. Under the optimum deposition conditions, the adhesive strength of (Ti,Al)N coating to Si3N4 ceramic substrate was satisfactory with the critical load up to more than 80 mN. In addition, the coatings were investigated with respect to mechanical and wear behavior, including nanohardness, Young's modulus and cutting performances. The (Ti,Al)N coatings possess resulted very high values of nanohardness and Young's modulus, which are near to 40 GPa and 680 GPa, respectively. Because of the deposition of (Ti,Al)N coatings the wear resistance and edge life of the coated tools were improved dramatically evaluated by the cutting perforinances of the coated tools in turning HT250 (HB230) steel under industrial conditions. These improvements were attributed to a combination of four effects of deposition, ion implantation, quench and solid solution strengthening in terms of the structural analyses.