Effects of whisker-like β-Si3N4 seeds on phase transformation and mechanical properties of α/β Si3N4 composites using MgSiN2 as additives

alpha/beta Si3N4 composites with beta-Si3N4 content ranging from 26% to 100% were hot-pressed with or without beta-Si3N4 seeds, using MgSiN2 as additives, and their mechanical properties were investigated. When the alpha-Si3N4 content was over 58%, the microhardness of alpha/beta Si3N4 composites was in the range of 23-24 GPa, and then the indentation hardness decreases with decreasing the content of alpha-Si3N4, whether with beta-Si3N4 seeds or not. The toughness increased with increasing elongated beta-Si3N4 grains, which improved fracture resistance by crack bridging, pull out or the crack deflection mechanism, and reached the maximum value of 7.0 MPa m(1/2) with 1 wt% beta-seeds. In comparison with alpha/beta Si3N4 composite with a similar phase.composition, the fracture strength was improved by adding beta-Si3N4 seeds because of the relatively smaller grain sizes and higher toughness. The alpha/beta Si3N4 composite with 5 wt% beta-seeds showed a high strength of 1253 MPa, a high hardness of 20.9 GPa and a toughness of 6.9 MPa m(1/2). (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.