Grain Composition on Solid-state-sintered SiC Ceramics

Abstract

Strengthening and toughening of dense solid-state-sintered SiC (S-SiC) ceramics was achieved by grain composition of coarse and fine SiC powder, whose median particle sizes were ~4.6 μm and ~0.5 μm, respectively. The fraction effects of coarse SiC powder on densification, microstructures, and mechanical properties of S-SiC ceramics were systematically investigated. High relative densities (higher than 98.3%) were successfully acquired for the S-SiC samples with the fraction of coarse powder less than 75wt%. The linear sintering shrinkage of SiC samples sharply decreased with increasing fraction of coarse powder, with the minimum fraction as low as 14.5%. Moreover, the coarse SiC powder significantly suppressed abnormal grain growth in S-SiC ceramics by Zener pining of grain boundaries. As a result, SiC grains became smaller and equiaxial, which was beneficial for obtaining high flexural strength for S-SiC ceramic. Meanwhile, the introduction of coarse SiC powder induced fracture mode transfer S-SiC ceramic from transgranular type to transgranular-intergranular mixture type, resulting in improved fracture toughness. The S-SiC ceramic added with 65wt% coarse powder achieved an increase of 14.0% in flexural strength ((440±35) MPa) and 17.1% in fracture toughness ((4.92±0.24) MPa•m 1/2 ).