Research On A Composite Of Mo₂FeB₂ Based Cermet

In this dissertation, the relationship among composition, manufacturing process, microstructure and properties of Mo₂FeB₂ based cermets has been systematically investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDS).In the first part of this dissertation, the development and present research situation of Mo₂FeB₂ based cermets over past 20 years have been summarized, which includes the influence of manufacturing process, composition, additive on the microstructure and properties of Mo₂FeB₂ based cermets, research achievements on phase reaction and microstructure evolution during the sintering of Mo₂FeB₂ based cermets, research progress of the grain growth inhibitors in fine grained cermets. Based on above work, the purpose and significance of the dissertation have been pointed out.The evolution of microstructure and properties of Mo₂FeB₂ based cermets had been studied. Some conclusions were drawn as follows: the L1 and L2 liquid phase were formed at 1085.7℃and 1131.0℃respectively; with the sintering temperature increasing, the content of Mo in the hard phase increased, which made the grain more anisotropic.The technique of vacuum sintering of Mo₂FeB₂ based cermets had also been studied systematically and the optimized sintering process was achieved.The influence of the individual chemical composition on the microstructure and properties of the Mo₂FeB₂ based cermets had been studied. The conclusions were obtained as follows: there were no oxygen, oxide, and graphite left in the cermets after sintering when the content of C was 0.5wt%. The cermets had better microstructure and mechanical properties when the content of Cr was 10wt%. With the content of Ni increased, the Fe based binder changed from martensite to austenite gradually. The content of Fe₂B in the cermets was suitable when the Mo/B atomic ratio was 0.89, which would reduce the melting point temperature of the liquid phase and wouldn't reduce the properties of the cermets obviously.The effect of Cr₃C₂, VC, NbC and TaC on the microstructure and properties of the cermets had also been investigated. Some conclusions were drawn as follows: Cr₃C₂ and VC remarkably reduced the wetting-ability of metal liquid phase to hard grains which would reduce the relative density of the cermets. The additions of NbC and TaC resulted in abnormal growth of some grains because they didn't disperse in the cermets uniformly.