Elastic–plastic analysis of ultrafine-grained Si2N2O–Si3N4 composites by nanoindentation and finite element simulation

Ultrafine-grained Si2N2O–Si3N4 composites are fabricated by hot-press sintering of amorphous nano-sized silicon nitride powders at 1600, 1650, and 1700 °C with nano-sized Al2O3 and Y2O3 as additives. Sintered materials of increasing average grain sizes of 280, 360, and 480 nm were obtained with increasing sintering temperature. Hardness and elastic modulus are tested by nanoindentation. Finite element simulations of the nanoindentation are performed to study the elastic and plastic mechanical properties based on the elastic modulus and P–h curve that were obtained through the nanoindentation tests. A theoretical method is proposed for calculating the stress–strain relationship of brittle ceramic materials based on the experimental nanoindentation data. Several relevant coefficients in the theoretical calculation formula are determined by comparing the calculation and simulation results.