Detailed electrical and mechanical retention characteristics of MoSi2-RSiC composites exhibiting three-dimensional (3D) interpenetrated network structure during long-term high-temperature oxidation process

MoSi2-RSiC composites were prepared via a combination of precursor impregnation pyrolysis and high-temperature melt infiltration, in which re-crystallized silicon carbide (RSiC) was used as matrix. The composition, microstructure, oxidation resistance, electrical and mechanical retention characteristics of the composites during long-term high-temperature oxidation process were studied. SEM images revealed that dense MoSi2-RSiC composites exhibiting three-dimensional (3D) interpenetrated network structure were obtained. XRD patterns confirmed that the primary compositions of the composites were 6H-SiC and hexagonal MoSi2, as well as a small amount of Mo4.8Si3C0.6. The weight gain rate of the MoSi2-RSiC composites was about 50% lower than that of RSiC, indicating that the MoSi2-RSiC composites possess improved oxidation resistance, which was mainly attributed to the acute decrease in porosity of the composites and the oxidation only occurred on the surface of it. The electrical properties of the MoSi2-RSiC composites decreased slightly and then reached a flat with the increase in oxidation time, suggesting that the MoSi2-RSiC composites possessed an excellent electrical retention characteristic. The calculated infactor I of the modified mixture value indicated that the interface combination played a more important role than that of interpenetrated network structure on the electrical retention characteristic of the composites. The composites oxidized for 50 h achieved the maximal flexural strength and elastic modulus, and values were 132.38 MPa (flexural strength) and 335.45 GPa (elastic modulus) for MoSi2-RSiC-2, respectively, exhibiting 31.30% and 27.7% improvement compared with their initial values. The mechanical properties of MoSi2-RSiC composites were higher than their original values even after 100 h of oxidation. This phenomenon can be due to the dense 3D interpenetrated network structure of the composites, in which oxidation reaction only occurred on the external surface.