Ti(C,N)-based Metal Ceramic Study On Preparation And Its Anti-oxidation Performance

Ti(C,N)-based cermets have high hardness,high strength as well as high wear resistance,high toughness and excellent high temperature oxidation resistance,and are widely used in the industrial mould industry.In this paper,Ti(C,N)-based cermets were prepared by vacuum sintering.The relationship between the preparation process,microstructure and mechanical properties of Ti(C,N)-based cermets was investigated by metallographic microscopy,scanning electron microscopy(SEM),X-ray diffractometer,tensile testing machine and microhardness tester.The behaviour of alloying elements on the high temperature oxidation resistance of metal ceramics and the oxidation mechanism were studied by static air constant temperature oxidation.In this paper,the effects of different sintering processes on the organisation of Ti(C,N)-based cermets and their properties were first investigated.The results show that when the solid phase sintering temperature is 1240°C,the liquid phase sintering temperature is1490°C and the liquid phase holding time is 60 min,the Ti(C,N)-based cermets have a typical core-ring structure with a thin outer ring and a complete inner ring structure,and the comprehensive mechanical properties are relatively good,with a flexural strength of 2141MPa,a Rockwell hardness of 87.9 HRA,and a fracture toughness of 10.54 MNm^-3/2.The effect of Cr,Cr₃C₂ and Nb C on the oxidation behaviour of Ti(C,N)-based cermets was investigated.The results show that the addition of Cr can generate Ni Cr₂O₄ in the oxide layer as well as the transition layer,which is dense and can relatively well prevent the diffusion of oxygen ions to the inside and metal cations to the outside,thus preventing the oxidation process from taking place.The addition of Cr₃C₂ and Nb C tends to form a large number of holes in the oxide or transition layer,causing the oxide film to peel off and the oxidation resistance to be relatively poor.The oxidation kinetic curves of Cr-containing ceramics are logarithmic,while those of Cr₃C₂ and Nb C-containing ceramics are parabolic.The oxygen partial pressure of the oxidation products of the relevant components in Ti(C,N)-based cermets was calculated at 900°C.The results showed that the stability of the oxides was Cr₂O₃>Nb₂O₅>Ti O₂>Ni O,and Cr₂O₃ and Nb₂O₅ were dense hexagonal lattice types with high densities,which could prevent further oxidation from occurring.However,with the increase of oxidation time,Nb₂O₅ reacts with Ni O to form Ni Ti₂Nb₇,which promotes the formation of Ni Mo O₄ and Ni WO₃,while Ni Mo O₄ and Ni WO₃ volatilise to form a large number of holes in the oxide layer and accelerate oxidation instead.The oxidation cross-section of Ti(C,N)-based cermets consists of an oxide film,a transition layer and a substrate,the main components of the oxide film are Ni WO₃ and Ni Mo O₄,the transition layer is Ti O₂ and the interior is the substrate.content increases,the thickness of the oxide film increases,hindering the diffusion of oxygen and metal elements,and the oxidation rate decreases,which is controlled by the concentration of oxygen ions and metal cations.As the oxidation time increases,the oxide layer or transition layer forms a large number of holes and the oxide film falls off.