Residual strain in SiC composites containing particulate MeB2

The lattice constants of dispersed particles (2H-TiB2, 2H-ZrB2, 2H-VB2 and 2H-NbB2) and the surrounding 6H-SiC matrix of the surfaces of sintered composite blocks and the corresponding pulverized powders, respectively, were evaluated by X-ray diffraction analyses. An X-ray diffraction technique applied to polished surfaces of composite blocks was found to be a useful method for analyzing such composites. The deformations of the unit cell volumes for 6H-SiC (shrinkage) and 2H-MeB2 (expansion) were respectively intensified and reduced in accordance with the increase of dispersed MeB2 particles. Both detected deformations were relaxed by a pulverizing procedure. The origin of both deformations was not any residual surface strain but the residual bulk strains which originate from a thermal expansion mismatch between the dispersed particles and the surrounding matrix. Moreover, Selsing's formulas for the residual bulk strains need to be improved to more generalized formulas.