Reaction And Toughening Mechanism Of Metal-coated Sbn4Cermet Coupling Under Microwave Sintering

Silicon nitride is one of the most promising high temperaturestructural materials, because of its excellent high temperature strength,good thermal shock resistance, good resistance to creep at hightemperature, good resistance to corrosion and low density. However, theintrinsic brittleness of the Si3N4cermets limits its application. In thispaper, We have been used metal-composition and self-tougheningtechnologies to Strengthening on the Si3N4cermert. to obtain ahomogeneous metal distribution and to improve the interfacialwettability between the phase of metal and ceramic, heterogeneousprecipitation-thermal reduction process and microwave high-temperaturesintering has been used to prepare Fe-Mo-Al coated Si3N4cermetpowders.During preparation process of the powders, sinteringdensification, microstructure evolution, and its strengtheningmechanisms have been investigated. The following some important andcreative conclusions have been obtained:(1) The Fe-Mo-Al coated Si3N4cermet precursor powders weresynthesized by the heterogeneous precipitation-thermal reductionprocess. The optimal process parameters have been determined asfollows: the concentration of the Si3N4suspension is30g/L, mechanicalstirring speed is1200r/min. During the preparation process, the PHvalues of the precursor solutions are8.0in Fe-Mo-Al coated Si3N4cermet.(2)The interphase and microstructure evolution of Fe-Mo-Al coatedSi3N4cermet were studied during microwave high-temperature sintering.The results show that during the sintering process, the added Mg and Yoxides can react with Si3N4to form the glass phase of Y-Si-Mg-N-O,prompting the occurrence of phase transition of α-Si3N4to SiAlON.Metal phase and intermetallics existing in the cermet of Fe-Mo-Alcoated Si3N4are mainly consisted of FeMo、MoSi2、FeAl3compound.In addition, metal-composition and whisker self-toughening areresponsible for the toughening mechanism.(3) The effects of the microwave high-temperature sintering process on the Fe-Mo-Al coated Si3N4cermet have been investigated.Based onthe microwave properties of volumetric heating and high heating rate，roaring to1750℃for1h. The optional sintering density of the Al coatedSi3N4cermet cermet is3.29g/cm3, the flexural strength is1024MPa,fracture toughness is7.8MPa.m1/2and Vickers hardness is1550. For theFe-Mo-Al coated Si3N4cermet, the optional sintering density is3.72g/cm3, the flexural strength is903MPa, fracture toughness is10.3MPa.m1/2and Vickers hardness is1660. The mechanical properties ofthe cermet are higher than those of the Si3N4ceramic prepared by hotpressing or hot isostatic pressing.