Research On Oxidation Resistant Properties Of TiN Hard Films

In this paper,we investigated major properties and oxidation mechanism of TiN. TiN films were prepared by hollow cathode discharge ion plating apparatus(XH-830) which was improved by XiHua University,on ZK1 powder metallurgy,and treated by air oxidation.The microstructure,chemical composition and mechanics performance of the TiN films were examined by OM,SEM,XRD,XPS,Scratch Test and Micro Hardness Test.OM and SEM showed that,the average thickness of TiN films was approximate 5μm and the surface morphology of TiN was typical island structure.Whole films owned well compacted structure and no disfigurement,also had well cohesion and markedly columnar grain.The surface grains were growing with the increasing of oxidation temperature.Above 650℃,there was cracking-off phenomena.XRD results indicated that,the rigid films(TiN) settled from ZK1 oriented obviously in(111) crystal plane by hollow cathode discharge ion plating apparatus (XH-830) and the average orientation degree was 80%.The film released TiO₂ at 550℃,and the gas increased greatly with the increasing temperature.XPS results suggested that,TiN could react with O₂ and generated TiN_xO_y.TiO₂ and TiO_0.73.The contents of TiO₂ and TiO_0.73 increased,TiN_xO_y decreased with the oxidized temperature,and the peak of TiN disappeared.Furthermore,according to crystallography and thermodynamics,it's easy to bond together for the atoms of Ti and O,when the atom of O entered into TiN crystal cell,only a little activation energy could change to TiO₂ of rutile structure,and change to TiN_xO_y with lack of oxygen.The structure of TiN film was composed of complicated oxidations,most of N existed with N-O bond in the film and a few exist with N₂.Scratch Test and Microhardness Test showed that,the average micro hardness of TiN films was 2388HV,and the cohesion of TiN coating and substrate was 85N. With the increasing of oxidation temperature and content of TiO₂,the micro hardness and cohesion were decreasing sharply.In the high temperature,fasting formation, low micro hardness and bad compacted structure of TiO₂ was mainly reason that due to invalidation of TiN.