Research On The Preparation And The Properties Of Ti (C, N)-Ni-Cr Cermets

Cermets are structural materials composed of ceramic hard phases and metallic binding phases.They are incorporated with the advantages of both metals and ceramics. The were prepared by vacuum sintering at high temperature using TiC and TiN powders as the ceramic hard phases and Ni and Cr powders as the metallic binding phases in this paper.The result shows that the Ti(C,N) -Ni-Cr cermets could be densified at a properly selected sintering temperature.Those with higher content of metals could be given the microstructure characteristic of Ti(C,N) ceramic particles uniformly distributed in the continuous NiCr alloy phases.Cermets with metal content of 10%and 15%have a relatively large porosity,the samples sintered at 1450℃are more dense than those at 1400℃resulted from the lower viscousity and better wettability to ceramic phases of metals at the higher sintering temperature.Cermets with higher density and higher content of metals have the higher bending strength with the muximum bending strenth of 635 MPa.The hardness of the samples was increased with the increasing of the relative density but decreased by the increased metal content.Samples with metal content of 20%and 25%have higher fracture toughness through the transgranular and intergranular fracture.The passitive oxidation at 800℃of the cermets had been discovered as the formation of an oxidize dense layer,helpful to the oxidation resistance.The mass gaining during the oxidation process was increased with the elevated oxidizing temperature and with the increased porosity of sample.Oxidation resistance of the cermets is better than that of cemented carbide.Samples with metal content of 20%and 25%have a good oxidation resistance.To the expousing to air at 1000℃for 10h with respectively unit area oxidation mass gain of 22.6mg/cm² and 20.5mg/cm².The oxidized layer was composed of rutile, NiTiO₃,NiCrO₄,and Ni₅TiO₇,no Cr₂O₃ can be found.Rutile formed at 1000℃was columnar and long strip,while that formed at 1200℃become coarse.