Study On Thermal Shock Resistance And High Temperature Oxidation Resistance Of The Ti(C,N)-Based Cermets

A series of component differents Ti(C,N)-based cermets were prepared by vacuum sintering technology.The microstructure and mechanical properties of different component cermets were analyzed by the scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffraction(XRD),and tested by universal testing machine,Vickers hardness tester,etc.The effect of different C/N ratio and adding different transition metal carbides of Ti(C,N)-based cermets on the thermal shock resistance was investigated by an indentation-quenching method,and the high temperature oxidation behavior and oxidation mechanism were studied by high temperature oxidation in the static air.The influences of carbon content and sintering temperature on the microstructure and mechanical properties of Ti(C,N)-based cermets have been studied in the first part of the paper.The results were obtained as follows:the metallurgy reaction during the sintering process is facilitated when increasing the carbon content and sintering temperature,the volume fraction of black core in hard phase with“black core-grey rim”structure decrease,the volume fraction of rim phase increases,the volume fraction of binder phase decreases,and the microstructure exhibits the trend of uniformity.The effect of the carbon content on the transverse rupture strength(TRS)is more significant,however the carbon content has less effect on the Vicker hardness(HV)and fracture toughness(K_IC),HV and K_IC of the cermets slightly increase with the increase of the carbon content.TRS of the cermets maintains a constant level when sintered at the range of 1440^oC to 1500^oC.HV of the cermets declines with the increase of sintering temperature.The fracture toughness(K_IC)of the cermets is significantly improved when sintered at 1520^oC,so the crack propagation resistance is elevated.The influences of different C/N ratio and adding different transition metal carbides of Ti(C,N)-based cermets on the thermal shock resistance have been studied.The results show that the thermal shock resistance of the different C/N ratio of Ti(C,N)-based cermets is more better with the increase of carbon content and decrease of nitrogen content.For adding different transition metal carbide of Ti(C,N)-based cermets,adding Nb C and Ta C can effectively improve the thermal shock resistance of cermets,however adding VC and Cr₃C₂ are not good for the thermal shock resistance.The critical stress fracture theory has been used to evaluate the thermal shock resistance of Ti(C,N)-based cermets,and the calculation result and experimental results presented perfectly,the consequence suggests that physical properties and mechanical properties of ceramic materials is available to predict thermal shock resistance of Ti(C,N)-based cermets.The effect of different C/N ratio and adding different transition metal carbides of Ti(C,N)-based cermets on high temperature oxidation behavior and oxidation mechanism have also been studied.The results indicate that:nitrogen content increased and carbon content decreased is helpful to enhance the oxidation resistance for different C/N ratio of Ti(C,N)-based cermets.The addition of Nb C and Ta C can effectively inhibited the diffusion of oxygen atoms to substrate,thus achieving the oxidation resistance.The addition of VC and Cr₃C₂ has little effect on the oxidation resistance.The oxidation kinetics curve of Ti(C,N)-based cermets is a quasi-parabolic type.The initial oxidation rate was faster,and the oxidation rate increased gradually with the extension of oxidation time.The oxidation film of cermets can be divided into four areas:the outermost aera rich in elements of Ni,Co,the secondary outer area was full of Ti O₂,phase structure damage area and oxygen dissolution area.The oxygen content decreased from the outermost area to substrate.