Research On The Manufacturing Process And Oxidation Of Fine Grain Mo₂FeB₂-based Cermet

Mo2FeB2-based cermets has a high strength, toughness and lower costs of raw powders. Hence,Mo2FeB2-based cermets has a broad application prospect in manufacturing In this dissertation, therelationships among composition, preparation process, two-step sinstering, grain growth inhibitormicrostructure and mechanical properties of Mo2FeB2-based cermets had been systematicallyinvestigated by different X-ray diffraction(XRD), scanning electron microscopy(SEM), energydispersive X-ray analysis(EDS). And then, the oxidation behavior and oxidation mechanism at hightemperature of Mo2FeB2-based cermets has been studied.In the first part of this dissertation, the development and present research situation ofMo2FeB2-based cermets over past20years have been summarized, which includes the influence ofmanufacturing process, composition, additive on the microstructure and properties of Mo2FeB2-basedcermets, phase reaction and microstructure evolution during the sintering of Mo2FeB2-based cermets,research progress of grain growth inhibitors in fine grained cermets. In addition, high temperatureoxidation of materials and research test methods are summarized.The process of two-step sintering for Mo2FeB2-based cermets has been studied. The first stepshould be keep30minutes at1160℃, full density was achieved after holding at the second step attemperatures around1080℃for20h. The final grain size is1.21μm, the high TRS of about2039.5MPa and hardness of90.2HRA was obtioned.The characteristic of phase transformation and microstructure evolution of Mo2FeB2-basedcermets has been studied. The hard phase Mo2FeB2was produced in the compact prior to liquidformation by the reaction Mo and Fe2B. A sufficiently high starting density should be obtained duringthe first step, full density was achieved after holding at the second temperature for20h, during whichthere was no grain growth.The influence of two kinds of grain growth inhibitors on the microstructure and properties of theMo2FeB2-based cermets in two step sintering process has been studied. The conclusions wereobiained as follows: No remarkable decrease of grains size occurred with Cr3C2addition. VC haseffective in inhibiting grain growth. The cermets had better microstructure and mechanical propertieswhen the content of VC was0.4wt%, the high TRS of about2295.2MPa and hardness of90.5HRAwas obtioned.The oxidation behavior and oxidation mechanism at high temperature of Mo2FeB2-based cermethave also been investigated. At temperature of750℃in the air, the oxidation weight grain in unit area of Mo2FeB2-based cermets was25.17×10-4g·cm-2, and the oxidation rate constant was7.88×10-5mg2·cm-4·h-1after100h oxidation. The high temperature oxidation behavior of cermetfollows the parabolic law.