R-curve behavior of layered silicon carbide ceramics with surface fine microstructure

By adjusting the α : β SiC phase ratios in the individual starting powders, a layered SiC consisting of surface and inner layers with distinctively different microstructures are produced by hot-pressing and subsequent annealing. The surface layer consisted of relatively fine, equiaxed α-SiC grains, designed for high strength, while the inner layer consisted of elongated α-SiC grains, designed for high toughness. By virtue of the common SiC phase and the same sintering aids (Al₂O₃-Y₂O₃), the interlayer interfaces are chemically compatible and strongly bonded. R-curve behavior of the layered SiC was measured and compared with the related monolithic materials. The layered SiC showed better damage tolerance than monolithic materials and stronger R-curve behavior than surface layer. This superior performance of layered SiC ceramics was attributed to the contribution of both high strength of the surface layer for small flaws and high toughness of the inner layer for larger flaws.