Influence Of Matrix Density On The Composition,Microstructure And Properties Of The MoSi₂-RSiC Composites

MoSi₂-RSiC composites with three-dimensional interpenetrating network structure was prepared by MoSi₂ high temperature melt infiltration method where RSiC worked as a matrix. With this special structure the composites combined the excellent high temperature mechanical properties, creep resistant, heat conduction etc of RSiC and the outstanding electrical and thermal conductivity, high temperature oxidation resistance of MoSi₂. The composites would be widely used as high temperature structural materials in aeronautics and high temperature heat material in industrial area. The previous studies shown that the density of RSiC matrix had important effect to the compose, microstructure and properties of MoSi₂-RSiC composites. So this text had studied the influence of density to the microstructure,mechanical properties; electrical and thermal properties of RSiC and discussed the relevant electric transmission mechanism. On this basis, the MoSi₂-RSiC composites were prepared by direct melt infiltration process; impregnation and pyrolysis?PIP? of polycarbosilane?PCS? and direct melt infiltration composite process?MI?;impregnation and pyrolysis?PIP? of phenolic resin?PF? and direct melt infiltration composite process?MI?; impregnation and PF-PIP-MoSi₂-Si-Ti alloy activated melting infiltration?AAMI? composite process. The influence of density on the microsturcure,mechanical properties, volume resistivity and thermal conductivity of the MoSi₂-RSiC composite were studied.?1? With the increase of matrix material's density, the porosity, volume resistivity and thermal conductivity of RSiC reduced, and the bending strength and elasticity modulus of RSiC increased. The porosity, bending strength, elasticity modulus,coefficient of expansion, volume resistivity of 2.6 g ×cm-3 RSiC were 17.3% ? 95.1MPa ? 84.2 GPa ? 4.23×10-6/? ? 4.8 ?·cm respectively. The heat conductivity coefficient of 2.6 g × cm-3 RSiC decreased from 173.7 W/?m·K?-1?20 ?? to 22.2W/?m·K?-1?1300??. At the same temperature, the higher density RSiC had the bigger thermal conductivity.?2? MoSi₂-RSiC composites with 3-D interpenetrated network structure was obtained by the direct melt infiltration process. The major components were SiC and MoSi₂, as well as a little Mo5Si3 and Mo4.8Si3C0.6. With the increase of matrix material's density the porosity,volume resistivity reduced and the bending strength,elasticity modulus of MoSi₂-RSiC increased, the bending strength, elasticity modulus,and volume resistivity were 108.7MPa and 173.2 GPa, and 60.9 m?·cm respectively.The topology resistivity value had a similar variation trend with the experiment value.?3?MoSi₂-RSiC composites with 3-D interpenetrated network structure was obtained by PCS-PIP-MI, PF-PIP-MI. The major components were SiC and MoSi₂, as well as a little Mo5Si3 and Mo4.8Si3C0.6. Compared with the direct melt infiltration process, composites obtained by PCS-PIP-MI, PF-PIP-MI possessed a good interface associativity and had a higher bending strength. Composite made by the 2.3 g ×cm-3RSiC, PF-PIP-MI process had the highest bending strength and elasticity modulus,127.1 Mpa?128.9GPa, respectively. Compared with the matrix, the volume resistivity of MoSi₂-RSiC composites decreased significantly. The volume resistivity of the composites made by the 2.3 g×cm-3 RSiC, PCS-PIP-MI process was 37.45 m?·cm.?4?MoSi₂-RSiC composites with 3-D interpenetrated network structure were obtained by PF-PIP-AAMI at a low temperature. The major components were SiC and MoSi₂, Ti C. The bending strength, elasticity modulus, and volume resistivity of MoSi₂-RSiC composites made at 1900 ?, thermal insulation for 60 minutes,m?MoSi₂?:m?Ti?m?Si?=48.2:30.3:21.5,were 116.7 MPa, 157.4 GPa and 158.3 m?·cm...