Study On High Temperature Oxidation Resistance Of Ti(C,N)-based Cermet

In this paper,Ti(C_x,N_y)solid solution is used as the main ceramic hard phase,Ni,Co as the metal binding phase,and secondary carbides such as WC,Mo₂C and TaC are added.Vacuum sintering and partial pressure sintering are used to prepare A series of Ti(C,N)-based cermets,using scanning electron microscope(SEM),energy spectrometer(EDS),X-ray diffractometer(XRD)and other analytical methods to characterize the microstructure of the cermet,using universal testing The mechanical properties of cermets have been evaluated by testing equipment such as machine and Vickers hardness tester.Using static air constant temperature oxidation method,the effect of different carbon to nitrogen ratios on the oxidation resistance of Ti(C_x,N_y)solid solution and the high temperature oxidation resistance and oxidation mechanism of cermets with different transition metal carbides were studied.In this paper,Ti(C,N)solid solution powders were subjected to isothermal oxidation and non-isothermal oxidation.Through TG-DSC thermal analysis,oxidation kinetic analysis and phase analysis,the effect of carbon to nitrogen ratio on the oxidation behavior of Ti(C,N)powder was studied.The experimental content includes non-isothermal oxidation of Ti(C,N)powder heated from room temperature to 1000?1200?in O₂air flow,and isothermal oxidation in 650?standing air.The results show that in the non-isothermal oxidation process of Ti(C,N)powder,the oxidation process can be divided into two stages or three stages.In the first oxidation stage,denitrification is dominant,and in the second oxidation stage,decarburization is dominant,Ti(C_0.5,N_0.5)powder shows the best oxidation resistance.In the isothermal oxidation of 650?,the oxidation of Ti(C,N)powder follows the random nucleation kinetic model.Ti(C_0.7,N_0.3)has the smallest first-order rate constant and shows the best oxidation resistance.The solid product of initial oxidation is anatase structure Ti O₂,and gradually transforms to rutile structure Ti O₂ as the oxidation time extends.Secondly,on the basis of exploring the oxidation resistance of cermets with different carbon to nitrogen ratios,the high temperature oxidation resistance and oxidation mechanism of cermets with different Mo₂C and TaC transition metal carbides were studied.The results showed that as the carbon to nitrogen ratio increases,the resistance Enhanced oxidation;the presence of Ta in the cermet will reduce the solubility and transmission of oxygen in the hard phase and the binder phase,thereby inhibiting the oxidation of the cermet,and at the same time accelerating the formation of nickel titanate in the cermet.The entry of atoms has played a very important role.With the increase of Ta content,the oxidation resistance of Ti(C,N)-based cermets is greatly improved;With the increase of Mo content,the oxidation resistance gradually increases;during the oxidation process of Ti(C,N)-based cermets,the oxidation kinetics curve is quasi-parabolic,the initial oxidation rate is relatively fast,and titanium is gradually formed as the oxidation progresses.A kind of stable and uniform oxide layer,such as acid salt and cobalt acid,hinders the entry of oxygen atoms,thereby playing an anti-oxidation effect.The entire oxidation process is accompanied by the migration of Co and Ni elements and the two-dimensional oxidation between the basic oxides.A series of complicated reactions such as secondary reactions.Finally,the effects of partial pressure sintering process and WC content on the oxidation resistance of Ti(C,N)-based cermets were studied,and the experiments of solid phase vacuum,low argon sintering and liquid phase nitrogen sintering were carried out.The effects of partial pressure sintering process and WC content on physical and mechanical properties,microstructure and oxidation resistance were studied.The results show that the nitrogen sintering in the solid phase has a significant effect on the final nitrogen content of the cermet,thereby affecting the alloy composition,microstructure and various properties.Compared with the vacuum sintering process,in the liquid phase sintering at 1350?1 490?,the atmosphere sintering is carried out with 1300Pa N₂ gas,which can inhibit the loss of N element and significantly enhance its performance.The results show that the comprehensive mechanical properties are best when the WC content is 25%;when the addition amount is higher than 25%,the core ring structure will be broken and the mechanics will be significantly reduced;The oxidation resistance gradually decreases with the addition of WC;under partial pressure sintering,the flexural strength and hardness are better than those of vacuum sintering;nitrogen partial pressure sintering has the strongest oxidation resistance,mainly due to its increase in nitrogen partial pressure suppression After the decomposition of Ti(C,N),the nitrogen element in the material increases,and the oxidation resistance increases.