Effect Of TaC On Microstructure And Properties Of Ti(C,N)-Based Cermets

Ti（C,N）-based cermets possess high hardness,chemical stability,and oxidation resistance,which are able to partiallyreplace cemented carbides in the field of finishing.As the raw material of Ti（C,N）-based cermets,TaC is used to improve the high-temperature performances of cermets,which can reduce the performance loss of materials in a high-temperature environment and improve the cutting performances of cutting tools under actual working conditions.Therefore,two cermet systems(Ti（C,N）-xTaC-50Ni（x=0-20 wt.%）and Ti（C,N）-xTaC-WC-Mo₂C-yNi-yCo（x=0-13.96 wt.%,y=9.47-8.15 wt.%）are designed with the aid of thermodynamic calculation.The evolution processes of the core-rim structures and the effects of TaC on the microstructure,mechanical properties,and corrosion resistance of cermets are studied.The main conclusions are as follows:（1）The results of Ti（C,N）-xTaC-50Ni system show that with the increase of TaC content,the number of black core structures（Ti（C,N））decreases,while the number of white core structures increases（（Ti,Ta）（C,N）solid solution）,and a small number of rimless structures（Ti（C,N））are formed.Compared with the sample without TaC,the average grain size of the hard phase reduces from 1.97μm to 1.54μm for the sample with 20 wt.%TaC,while the hardness decreases from704HV10 to 597 HV10,and the eutectic melting point increases from1341℃to 1366℃.The white core and white rim start to form in the solid-state sintering.The formation processes of white core and white rim are different in the solid-state sintering.The white core is formed bygrain contact diffusion,while the white rim is formed bydiffusion via the binder phase.The composition of the rim phase is related to its formation temperature and is controlled bythe Gibbs free energydifference of the hard phase raw materials.With the increased formation temperature,the Ti/Ta atomic ratio of the rim phase increases.（2）The results of Ti（C,N）-xTaC-WC-Mo₂C-yNi-yCo system show that with the increase of TaC content,the number of black core structures（Ti（C,N））decreases,and the number of white core structures（（Ti,W,Mo,Ta）（C,N）solid solution）increases.With the increase of TaC content,the hardness increases from 1438 HV10 to 1519 HV10 due to the solid solution strengthening effect,while the fracture toughness decreases from 11.7 MPa·m^-1/2 to 10.5 MPa·m^-1/2 and then increases to 13.2MPa·m^-1/2.The test in 1 mol/L Na Cl solution shows that the addition of TaC contributes to improving the corrosion resistance.The samples with13.96 wt.%TaC show the lowest high-temperature wear rate(3.05×10^-5mm³/Nm)in wear tests,indicating that this sample has the best mechanical properties and oxidation resistance simultaneously.The results of high temperature oxidation experiments show that the oxidation weight gain of the samples with TaC can be reduced by35%-50%compared with the sample without TaC.Combined with the characterization of X-raydiffraction and electron probe microanalysis,it can be concluded that the main mechanism of oxidation resistance enhancement is the formation of（Ti,Ta）O₂ solid solution,which reduces the oxygen diffusion channel in the oxide layer.In this work,the effect of TaC on the mechanical properties of Ti（C,N）-based cermets and the mechanism of TaC improving the high-temperature oxidation resistance of cermets are studied,which provides an important reference for the preparation of high-performance Ti（C,N）-based cermets.34 Figures,14 Tables,117 references...