Nanoindentation characterization of SiC-based ceramics

Depth-sensing indentation tests were carried out on several SiC-based liquid-phase-sintered SiC ceramics characterized by different mean grain size spanning from 78 to 540 nm. The indentation tests were performed with peak loads ranging from 5 to 400mN in order to investigate the property variation with the variation of the peak load and material microstructure. The values of indentation hardness and Young's modulus were calculated according to the models developed by Oliver and Pharr (O&P) and by Cheng and Cheng (C&C). According to the O&P model, the finest grained SiC ceramics did not show the indentation size effect (ISE) which was observed in the largest grained SiC ceramics. The grain-size dependence of the indentation hardness can be described by an inverse Hall-Petch relation. With the C&C model, the correlation of the indentation hardness with the peak load and the grain size was less evident. The indentation hardness calculated by the O&P model was lower than that calculated by the C&C model and in better agreement with the values of Vickers microhardness. The O&P indentation Young's modulus was higher than the C&C indentation Young's modulus but the latter was in very good agreement with the values measured by resonant frequency. For both models, the indentation Young's modulus was almost load-independent even if a dependence on the microstructure was observed.