Microstructure and High Temperature Mechanical Properties of SiC Added with AlB2-C

The microstructure of hot-pressed SiC added with AlB2-C was analyzed by the microstructural observation and elemental analysis. According with the results of such analysis, the mechanical properties at high temperature were discussed. AlB2-C mainly reacted to form Al2O3 and B4C. A minor fraction on Al-Si-(B)-C-O phase, in which O was thought to be supplied from impurity SiO2 in the raw SiC powder, was observed by transmission electron microscope. Al-C-O phase was detected as an intergranular phase. The flexural strength decreased from 60MPa at room temperature to 530MPa at 1450°C and the fracture toughness with SEPB method increased from 4.5MPa[sm middot]m1/2 at room temperature to 10.9MPa[sm middot]m1/2 at 1500°C. The intergranular phase of Al-C-O is thought to cause strength degradation because of the phase softening at high temperature. From fracture surface observation after fracture toughness test, a fibrous texture on the fracture surface was observed. Auger electron analysis revealed that the fibers were composed of Al-C-N-O. The Al-C-O intergranular phase may become a highly viscous Al-C-N-O phase during toughness test at 1500°C in N2, enhancing the crack-face bridging effect.