Abstract
Ultrafine-grained Si2N2O–Si3N4 composites are fabricated by hot press sintering of amorphous nanosized silicon nitride powders at 1600, 1650, and 1700°C, with nanosized Al2O3 and Y2O3 as additives. Sintered materials of increasing average grain sizes of 280, 360, and 480 nm were obtained with increasing sintering temperature. The nanoindentation hardness, microhardness and macroscopic Vickers hardness are tested using nanoindentation, microhardness tester, and macroscopic Vickers hardness tester. The hardness is found to decrease with increasing sintering temperature and average grain size. The results of the nanoindentation hardness and microhardness tests obviously reflect the effect of loading. The nanoindentation hardness is related to the ratio of the indentation maximum contact cross-sectional area A and the average grain cross-sectional area S. As the ratio of A and S decreases, the fine-grain strengthening effect becomes less evident. The comparative analysis of nanoindentation hardness and microhardness revealed that the microhardness test is considered more suitable for estimating the hardness of the ultrafine-grained Si2N2O–Si3N4 composites.
