Preparation And Performance Of TiN Coating Deposited On Cemented Carbide By HT-CVD

As one of the most important surface technologies,chemical vapor deposition has been widely used in tool industry,to improve the cutting performance and service life of drills and cutters.Cemented carbide can be suitable for coating by CVD,because of its good thermal conductivity and less detriment under high temperature.In this paper, we searched for the technical processes of TiN coating on YG6 cemented carbide by using high-temperature chemical vapor deposition.Then the optimum parameters were obtained by orthogonal experiment.And the mechanics performance, chemical composition and microstructure of TiN films were examined by OM,SEM,XRD,XPS,Scratch Test,Strength Test and Micro Hardness Test.The structural analysis of XRD showed that, besides TiN phase in coating and WC phase in substrate,the other phases such as TiC_xN_y, W₆Co₆C, multi-Ti oxide,could else be found in these diffraction patterns.It reflected that complex associate reactions were carrying on during the deposition process of TiN since chemical vapor reactions occurred.These reactions varied the chemical composition and microstructure of TiN, consequently resulting in different affections on properties. By comparing with each diffraction peak intensity of various crystallographic plane on the XRD patterns,while calculating the data for crystallograghy, CVD-TiN coating exhibited the growth towarded a preferred (220) orientation,differing from (111) favorable crystal face presented by PVD-TiN.TiO₂ ,N-O and C-O which were found in XPS analysis,further validated the results of XRD:titanium oxides originally formed on the pipe wall and lines,then inevitably been taken into the deposition region by gas flow,finally attached to the surface of TiN coating. O atoms broke up from these titanium oxides due to the high temperature, after that, rebonded with N,C atoms on the outermost layer.In addition, C atoms from substract obtained energy by the heating, acrossed the interface into TiN coating.So the Ti,N element contents were lower than C,O element contents in the outermost layer of TiN surface, owing to the both phenomena of weak oxidation and carbon diffusion.OM and SEM micrographs showed that CVD-TiN coatings were composed of columnar crystals, which refelcted on a coarse and rough surface.Calculated packing factor only reached to 70%, indicated that the coating structure had low consistency and much gapping space.The average microhardness value of 1613HV was lower than other reported research.But the cohesion value most can be 50 N,even the maximun be up to 70N. Bending strength decreased significantly about 30% - 40% after high temperature treatment.Summarized all the performance test results, the No.5 samlpe owned the highest microhardness of 2457HV than others;No. 9 sample showed its cohesion value of 70N;The bending strength of No.1 sample only decreased by 23.4%.The conclusion of orthogonal analysis stated that deposition temperature and the holding time took great impact on comprehensive performance of coating.As the holding time went go,the decarburization getting more serious,the microhardness and the bending strgenth declining more rapidly either.