Grain Composition on Solid-state-sintered SiC Ceramics

doi:10.15541/jim20180072

Abstract

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).

Key words: S-SiC, grain composition, microstructure, flexural strength, fracture toughness

CLC Number:

TQ174

XING Yuan-Yuan, WU Hai-Bo, LIU Xue-Jian, HUANG Zheng-Ren. Grain Composition on Solid-state-sintered SiC Ceramics[J]. Journal of Inorganic Materials, 2018, 33(11): 1167-1172.

Figures/Tables 9

Fig. 1 Size distribution curve (a) and morphology pictures of SiC powders with different sizes D50=~0.5 µm (b) and D50= ~4.6 µm (c)

Table 1 Formula and the corresponding ratio of fine and coarse SiC powders

Formula	Ratio of coarse SiC powders/wt%	Ratio of fine SiC powders/wt%
C0	0	100
C55	55	45
C60	60	40
C65	65	35
C70	70	30
C75	75	25
C80	80	20

Fig. 2 Effects of grain composition on linear shrinkage(Rs), density(D) and relative density(RD)

Fig. 3 Effect of grain composition on the microstructures of S-SiC ceramics(a, b) C0; (c, d) C65

Fig. 4 Effect of grain composition on the grain boundaries of S-SiC ceramics (a) C0; (b) C65

Fig. 5 Effect of grain composition on the flexure strength (σf) of S-SiC ceramics

Fig. 6 Effect of grain composition on the Vickers hardness (HV) of S-SiC ceramics

Fig. 7 Effect of grain composition on the fracture toughness (KIC) of S-SiC ceramics

Fig. 8 Effect of grain composition on the fracture surfaces of S-SiC ceramics(a) C0; (b) C65

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