The Research On The Strengthening And Toughening Process And Mechanical Properties Of Ti(C,N)-based Cermets

Ti(C,N)-based cermets are an important class of engineering structure ceramic materialdue to its excellent high temperature mechanical properties, which has wide developmentspace and can be used in aerospace industry, machinery processing, petroleum chemicalindustry, geological exploration and so on. However, because of the common defect oftraditional ceramics, the application of Ti(C,N)-based cermets is limited for its lowobdurability. Therefore, the research on the strengthening and toughening of Ti(C,N)-basedcermets is very necessary. On the based of previous work of our research group,Ti(C,N)-based cermets were successfully prepared by vacuum sintering, the relationshipamong raw materials formula, sintering process, microstructure and mechanical properties ofTi(C,N)-based cermets were systematically studied.The effects of the sintering process and metal binding phase Ni/Co ratio on themicrostructure and mechanical properties of Ti(C,N)-based cermets were studied. The resultsshow that when soaking at1220℃for2h and sintering at1450℃for50min, themicrostructure of typical “core-rim” is observed in the Ti(C,N)-based cermets with metalbinding phase of10%Ni5%Co, which is compact and distributed homogeneously, the densityand relative density are5.91g/cm3and95.6%, respectively. Compared with sample of nosoaking process, microhardness, bending strength and fracture toughness were by19.1%,153.9%and18.4%. Intergranular fracture is the main crack propagation mode, with a few ofthe transgranular fracture, and more dimples and tearing ridges appear in the fracture surface.The effects of the sintering process and rare earth Y2O3content on the microstructure andmechanical properties of Ti(C,N)-based cermets were studied. The results show that themicrostructure of Ti(C,N)-based cermets is compact, greatly refined and distributedhomogeneously for sintering at1500℃for50min, the density and relative density are 5.79g/cm3and94.4%. The crack propagation is mainly mixed fracture of intergranular andtransgranular formation, and fracture surface shows more small dimples uniform distributionwhich caused by hard phase particles pulled off, left hard phase particles attached to thearborous dendritic matrix, compact structure and good phase interface are observed.Ti(C,N)-based cermets achieve the best mechanical properties at the rare earth Y2O3contentof0.8wt%, microhardness, bending strength and fracture toughness increased respectively by7.9%,45.8%and6.1%compared to the previous. However, the brittle and hard intermetalliccompound can be formed due to enrichment of excessive Y2O3, which has an adverse effecton strengthening and toughening of Ti(C,N)-based cermets.The effects of the sintering process and carbon fiber content on the microstructure andmechanical properties of Ti(C,N)-based cermets were studied. The results show that themicrostructure of Ti(C,N)-based cermets is compact, greatly refined and distributedhomogeneously for sintering at1500℃for50min, good phase interface, moderate thicknessof rim phase and mixed type of fracture morphology are observed. The mechanical propertiesof Ti(C,N)-based cermets improve with the increase of sintering temperature, but theembedded rare earth Y2O3has no effect on the microstructure and mechanical properties ofTi(C,N)-based cermets. The density of Ti(C,N)-based cermets was reduced with addition ofcarbon fiber, but which did not change the structure characteristics of Ti(C,N) based cermets,crack propagation mode change gradually from transgranular fracture into intergranularfracture, crack path transform gradually from straight to flexuous, fracture morphology showsteep characteristics of plastic fracture, toughening mechanism: fiber pull-out, fiber fracture,fiber bridging and metal binder phase bridging. Ti(C,N)-based cermets achieve the bestmechanical properties at the carbon fiber content of4wt%, fracture toughness increases by22.1%with no strength reduction.