Preparation And Characterization Of MoSi2 Matrix Composite Materials By In-situ Reaction Sintering

Due to the higher melting point, outstanding high-temperature oxidation resistance, stable electrical resistance, plastic deformation at high temperature and good compatibility with many reinforcements, the MoSi₂ and MoSi₂ based composites have great potential in application and have been given increasingly interest in recent years. The MoSi₂ and MoSi₂ matrix composites had been successfully prepared by in-situ pressureless reaction sintering and microwave reactive sintering in this paper. Then the mechanical properties at room-temperature were determined by Vickers indentation. The microstructure, surface micrograph and phase composition were investigated by means of SEM, microprobe, XRD. The frictional and wear properties of SiC-WSi₂/MoSi₂ matrix composite which was sintered by in situ was further examined by using XP-5 type friction and wear tester, and the wear mechanism was discussed. The results are shown as follows:1. SiC/MoSi₂,WSi₂/MoSi₂ and SiC-WSi₂/MoSi₂ composites with different volume fraction were successfully prepared by in-situ pressureless reaction sintering. The mechanical properties of composites have a greater increase than that of pure MoSi₂ specimens, When the volume fraction of SiC increases to 10%, the bending strength and fracture toughness of SiC/MoSi₂ composite reach the highest value of 274·5MPa and 5.5MPa·m1/2 ,respectively, which are approximately 40.7% and 30.7% higher than MoSi₂ matrix which sintered by hot-pressing. When the volume fraction of WSi₂ increases to 20%, the flexural strength, Vickers hardness and fracture toughness of WSi₂/MoSi₂ composite reach the highest value of 301.6MPa,10.26GPa and 7.87MPa·m1/2, which increased about 54.7%,16.1% and 86.9% as compared to MoSi₂ matrix which sintered by hot-pressing.The mechanical properties of SiC-WSi₂/MoSi₂ composites material are not as good as expected, its hardness and fracture toughness reach to 7.997GPa and 6.534MPa·m1/2. The strengthen mechanism of the composites were fine-grain strengthening, dispersion strengthening, the second-phase particles and solid solution strengthening. The sequence of the contribution to toughening is as follows: fine-grain toughening, crack deflection and the second-phase particles.2. The results showed that the composite materials can achieve the best mechanical properties at 1400oC , the bending strength, hardness and toughness of 10% SiC-containing SiCp/MoSi₂ composite materials are 270.6MPa, 8.36GPa and 8.96MPa·m^1/2 which sintered by microwave at 1400oC. The bending strength, hardness and toughness of SiC-WSi₂/MoSi₂ composites (MSWC3) were 200MPa, 8.916GPa and 9.269MPa·m^1/2. Compared with the MoSi₂ matrix materials synthesized by other methods, the mechanical properties of MoSi₂ matrix materials synthesized by microwave sintering had a marked improvement and increase. MoSi₂ matrix had been successfully reinforced by SiC and WSi₂, through fine-grain strengthening, the second-phase dispersion strengthening, solid solution strengthening and crack deflecting.3. SiCp-WSi₂/MoSi₂ composite material had good abrasion resistance. When the rotational speed is constant, the friction coefficient droped gradually and the wear rate tended to increase with the increase of load. The main wear mechanism of MoSi₂ matrix composites were oxidation and adhesive. When the load is constant, the rotational speed has a certain influence on the friction coefficient and wear rate of composite materials, the friction coefficient and wear rate increase at first and then reduced, at last them maintain a certain level; as the speed increases, wear mechanism of composite materials are mainly fatigue wear and adhesive wear.