Ambient to high-temperature fracture toughness and cyclic fatigue behavior in Al-containing silicon carbide ceramics

Abstract

Abstract-A series of in situ toughened, Al, B and C containing, silicon carbide ceramics (ABC-SiC) has been examined with Al contents varying from 3 to 7 wt%. With increasing Al additions, the grain morphology in the as-processed microstructures varied from elongated to bimodal to equiaxed, with a change in the nature of the grain-boundary film from amorphous to partially crystalline to fully crystalline. Fracture toughness and cyclic fatigue tests on these microstructures revealed that although the 7 wt.% Al containing material (7ABC) was extremely brittle, the 3 and particularly 5 wt.% Al materials (3ABC and 5ABC, respectively) displayed excellent crack-growth resistance at both ambient (25°C) and elevated (1300°C) temperatures. Indeed, no evidence of creep damage, in the form of grain-boundary cavitation, was seen at temperatures at 1300°C or below. The enhanced toughness of the higher Al-containing materials was associated with extensive crack bridging from both interlocking grains (in 3ABC) and uncracked ligaments (in 5ABC); in contrast, the 7ABC SiC showed no such bridging, concomitant with a marked reduction in the volume fraction of elongated grains. Mechanistically, cyclic fatigue-crack growth in 3ABC and 5ABC SiC involved the progressive degradation of such bridging ligaments in the crack wake, with the difference in the degree of elastic vs. frictional bridging affecting the slope, i.e., Paris law exponent, of the crack-growth curve.

Microstructure and Properties of in Situ Toughened Silicon Carbide

“…The substantially enhanced toughness in the 5ABC-SiC was associated with extensive crack bridging from both interlocking grains, as in 3ABC-SiC, and uncracked ligaments, which only occurred in 5ABC-SiC. No toughening by crack bridging was apparent in 7ABC-SiC, concomitant with a transition from intergranular to transgranular fracture [32].…”

Effect of sintering conditions on microstructure orientation in α-SiC prepared by slip casting in a strong magnetic field

“…Many studies have reported the control of its microstructure in order to improve the sinterability, mechanical properties, etc., using many kinds of additives. [1][2][3][4][5] Several studies have reported that the sinterability and the mechanical properties of the SiC were improved by colloidal processing, 6-10 because the colloidal processing is generally able to control the dispersion of powders in a suspension and to produce a fine and dense microstructure.…”

Low temperature sintering of sub-micrometer scale SiC using spark plasma sintering

“…18) Likewise, the fracture toughness of the SiCAl 8 B 4 C 7 was believed to be improved partly due to the similar chemical composition of Al 8 B 4 C 7 with the AlBC.…”

“…Yuan et al reported that an amorphous phase composed of SiO 2 and the AlBC could be fully crystallized during cooling down and the crystallization behavior was affected by the chemical composition of the AlBC. 18) The beneficial effect of phenolic resin on the densification of the SiCAl 8 B 4 C 7 was believed to be caused by promoting the rearrangement of SiC particles. Phenolic resin pyrolized into carbon below 1200°C during sintering.…”