Combustion Synthesis, Microstructure And Properties Of MoSi₂/Al₂O₃Composites

MoSi2-based composites is the hotspot of high-temperature structure materials.The paper designed two kinds of synthetic methods that in stu synthesis and directcompositing, and prepared MoSi2/xvol.%Al2O3composites by self-propagatinghigh-temperature synthesis(SHS) on the basis of the research at home and abroad. Thedense materials were prepared by the vacuum hot-pressing sintering. In the process of combustion,the combustion mode, combustion temperature, the phase component and structure morphology ofcombustion products were studied. The effect of the composition and the different sinteringtemperature on the density, microstructure, resistivity, hardness, bending strength and fracturetoughness was researched. In addition, the strengthening and toughening mechanism wasdiscussed.The results of X ray diffraction analyses shown that the MoSi2/xvol.%Al2O3composites was prepared successfully. For the in stu synthesis, the combustion modechanged from unsteady burning to steady burning with the increase of the percentageof Al2O3, as the same time, the time of combustion reaction decreased, and thecombustion temperature increased. For the direct compositing, the combustion modeall was unsteady burning. The time of combustion reaction increased, and thecombustion temperature decreased.The densities of the composites prepared by vacuum hot-pressing sintering wereall over95%, and the densities increased with the rising of the sintering temperaturein the same content. The resistivity decreased with the rising of the sinteringtemperature, and increased with the increased of the percentage of compositing Al2O3.The results of XRD, SEM and EDS shown that the composites were comprised of thegray phase of MoSi2, the white phase of Mo5Si3and the black phase of Al2O3.The following conclusions can be drawn from the results of mechanicalproperties.1) For MoSi2/xvol.%Al2O3composites prepared by the in stu synthesis,when the percentage of compositing Al2O3was5%and10%, the sinteringtemperature was1300℃and1400℃, the performance of composites had beenimproved, and when the sintering temperature was1500℃and1600℃, only thefracture toughness had been improved. When the percentage of compositing Al2O3was15%, the performance had not been improved. When the sintering temperaturewas1400℃, MoSi2/5vol.%Al2O3had the best performance, the bending strength andfracture toughness improved by the percentage of32.4%and36.4%respectively compared with the pure MoSi2. In addition, the performance of MoSi2/xvol.%Al2O3added excess of Al powder were all improved, the bending strength and fracturetoughness of MoSi2/10vol.%Al2O3composite improved by the percentage of28.6%and56.3%respectively.2) For MoSi2/xvol.%Al2O3and Mo(Si0.95Al0.05)2/xvol.%Al2O3composites prepared by the direct compositing, the performance had been improvedobviously, and when the percentage of compositing Al2O3was5%, the performancewas better, the bending strength and fracture toughness of MoSi2/5vol.%Al2O3composites improved by the percentage of45.2%and39.2%respectively, the bendingstrength and fracture toughness of Mo(Si0.95Al0.05)2/5vol.%Al2O3compositesimproved by the percentage of45.2%and39.2%respectively. The strengtheningmechanism was fine crystal reinforcing and dispersion strengthening, and thetoughening mechanism was crack deflection and crack bridging.