Effect Of WC Content On The Microstructure And Tribological Properties Of Ti(C,N)-based Cermets

The combination of high thermal conductivity,red hardness,and wear resistance makes Ti（C,N）-based cermets a candidate cutting tool material that is widely used in industrial production.As the carbides with the best wettability improvement between ceramic phase and binder,WC has become an essential additive in industrial production.However,the effect of WC content on the gradient structure and high-temperature tribological properties of Ti（C,N）-based cermets remains to be studied.This paper focuses on the effect of WC content on the gradient structure of Ti（C,N）-WC-Ni cermet and the tribological properties of Ti（C,N）-WC-Mo₂C-Ta C-Ni/Co cermet.The influence of WC content on the cermet gradient structure was studied,and the thermodynamic mechanism of the influence of WC content on the cermet gradient structure was analyzed.Effects of WC content changes at different temperatures on the tribological properties of cermets.The main research contents and results of this paper are as follows:（1）Combined with thermodynamic calculation,the WC content was designed to study the influence of WC content on the gradient structure of cermets.The diffusion behavior of WC in sintering was amplified by adding only one kind of WC carbide to eliminate the influence of other carbides and increase the proportion of the binder in cermets.The results show that the addition of WC makes Ti（C,N）thermodynamically unstable,leading to the denitrification of Ti（C,N）.After the denitrification of cermet,a gradient of nitrogen concentration gradually decreases from inside to outside,and the formation of the gradient of nitrogen concentration causes the change of the solubility of W in the Ti-W-C-N system.After the content of WC reaches supersaturation（20 wt.%）,a multi-layer structure is formed in cermet:the WC precipitation region with the elliptic center,WC dissolution region around the elliptic center,and the near-surface is composed of W-rich（Ti,W）（C,N）solid solution.（2）Ti（C,N）-WC-Mo₂C-Ta C-Ni/Co cermet designed regarding the WC content of the Ti（C,N）-WC-Ni system in this paper and combined with thermodynamic calculations can effectively avoid harmful phases,such as the carbon deficient phase and graphite phase,and only（Ti,M）（C,N）（M=W,Ta,Mo）and（Ni,Co）binder exist in the cermets.According to the content of M in（Ti,M）（C,N）,the core/rim structures in the ceramic phase can be divided into the white-core and the white-rim with high M content,and the gray-rim,the black-core with low M content.With the increase of WC content,the number of white-core structures increases,and the increase of the number of the white-core with high hardness makes the hardness of WC composite cermets increase with the increase of WC content（increase by about 10%）.The toughness decreases of cermets with the increase of WC content（reduced by about 20%）,which is mainly related to a large amount of W in the solid solution of the binder.（3）The influence of WC content on tribological properties of Ti（C,N）-WC-Mo₂C-Ta C-Ni/Co cermets at different temperatures was studied and analyzed.The results show that the friction and wear behavior at 25℃is mainly affected by the hardness of the cermets.The higher the hardness is,the stronger the wear resistance is（reduced by about 86%）.When the temperature was increased to 400℃,the toughness of cermets and the formation of an oxide friction layer dominated the wear behavior of cermets.The higher the toughness,the lower the friction coefficient,and the more oxide tribolayer,the less wear（reduced by about 97%）.When the experimental temperature reaches 750℃,the formation degree of the oxide tribolayer determines the friction and wear behavior of cermets.Only the formation of a complete and uniform oxide friction layer can effectively reduce the wear amount（reduced by about 78%）.TEM and Raman spectra showed that the oxide friction layer was mainly composed of WO₃and Ti O₂.