Processing of High Performance Silicon Carbide

Abstract

Liquid phase sintering based on the dissolution-precipitation mechanism was applied to densify a 0.8 μm SiC powder with alumina (1.2 vol%)-yttria (0.9-3.3 vol%) additives. To uniformly distribute the sintering additives around the SiC particles, a heterocoagulated particle network was formed among negatively charged SiC particles, positively charged 0.2 μm alumina and yttrium ions in an aqueous suspension at pH 5. Yttrium ions were electrostatically adsorbed on the negatively charged SiC surfaces. The consolidated green compacts were highly sintered to 97-99 % of theoretical density by hot-pressing at 1950 °C. Four-point strength, fracture toughness and Weibull modulus were highly enhanced when a bimodal particle size system of SiC (75 vol% 0.8 micrometer-25 vol% 30 nanometer SiC) was sintered. The maximum strength reached 1.1 GPa. The fracture toughness was about 6 MPa•m1/2 and the Weibull modulus was 5.9. When a small amount of SiC precursor polymer was infiltrated in the green compact, the strength and Weibull modulus were further improved.

High temperature strength of silicon carbide sintered with 1 wt.% aluminum nitride and lutetium oxide

“…[24][25][26] Only a few studies have reported the successful densification of SiC ceramics with a small amount of sintering additives via liquid-phase sintering. Hirata et al 27 sintered SiC ceramics with 2.14-2.40 wt.% Al 2 O 3 -Y 2 O 3 additives by colloidal processing. Lim et al 28 In the present study, a SiC ceramic with 1 wt.% AlN-Lu 2 O 3 was fabricated by hot-pressing.…”

Electrical resistivity of silicon carbide ceramics sintered with 1 wt% aluminum nitride and rare earth oxide

“…Only a few studies reported the successful densification of SiC ceramics with a smaller amount of sintering additives via liquid-phase sintering. Hirata et al 22 sintered SiC ceramics with 2.14-2.40 wt% Al 2 O 3 -Y 2 O 3 additives by colloidal processing. Lim et al 23 was able to densify SiC ceramics with 2 wt% AlN-RE 2 O 3 (RE = Y, Er) by adding 5 wt% in situ-synthesized nano-sized SiC.…”

Particle size effect of starting SiC on processing, microstructures and mechanical properties of liquid phase-sintered SiC

“…Generally, pressureless sintering of SiC needs more sintering additives than hot-pressing to produce dense products. 11 The decreased tendency of K IC for Al 2 O 3 -Y 2 O 3 additives in the range 2d > 20 nm and K IC for K sample indicate a nearly constant K IC value for thick grain boundary.…”

“…The consolidated SiC compacts were highly densified by hot-pressing at 1850-1950 • C. [5][6][7]9 On the other hand, it was found that the infiltration of a small amount of polytitanocarbosilane (PTC, precursor of SiC fiber) into a SiC green compact with Al 2 O 3 -Y 2 O 3 additives increases the sinterability, flexural strength and fracture toughness of the hotpressed SiC and suppresses the grain growth. [10][11][12] Similarly, it has been shown that the addition of 30 nm SiC to 800 nm SiC with Al 2 O 3 -Y 2 O 3 additives decreases the grain growth and flaw size in the hot-pressed SiC, and improves the flexural strength. 9,12,13 The maximum strength was higher than 1 GPa.…”