Preparation of fine-grained silicon-nitride ceramics and their characterization by depth-sensing indentation tests

Both pressureless-sintered and dense, fine-grained silicon nitride ceramics were produced from mechanochemically activated nitride-based precursors. Scanning Electron Microscopy (SEM), Transmition Electron Microscopy (TEM), X-Ray Diffraction (XRD) and an ultra-low load microhardness tester were used to characterize these ceramics. Depth-sensing indentation (DSI) tests in the range of 200-1800 mN were performed on the silicon nitride ceramic to determine dynamic hardness (HD) and reduced elastic modulus (Er) values. These values were deduced by analyzing the unloading segments of the DSI curves. It was found that both Hd and Er exhibits a significant indentation load dependence. Nix-Gao (NG) model was used to analyze the dynamic hardness data in the calculation of the load independent hardness value