R-curve analysis of solid-phase-sintered and liquid-phase-sintered silicon carbide ceramics by indentation fracture and indentation-strength-in-bending methods

The R-curve behavior of SiC ceramics was investigated from aspects of microstructure and test methods. Two groups of silicon carbide ceramics were prepared by solid-phase-sintering and liquid-phase-sintering methods. One from each, determined by systematic evaluation on microstructure and mechanical properties, was selected for. R-curve behavior study by two methods of IF and ISB. It is found that for both SSiC and LSiC, IF fracture toughness decreases while the ISB one increases with the increasing indentation load – inconsistent R-curve behaviors observed with different method. IF and ISB methods were examined on its own theoretical basis and ISB method was determined the correct method for R-curve evaluation of SSiC and LSiC. That LSiC ceramic possesses better mechanical properties than SSiC material, indicated by ISB R-curve, well matches the mechanical evaluations.