The monotonic tension, creep, and fatigue behavior of an enhanced SiC/SiC composite was investigated at a temperature of 1300°C in air and argon. The improved creep and fatigue resistances were determined and compared to those of the standard SiC/SiC composite. The effects of additives (glass-forming, boron-based particulates) in the matrix on the creep and environmental resistance of the enhanced SiC/SiC composite were discussed. Crack propagation in the matrix of the enhanced SiC/SiC composite was different from that in the standard SiC/SiC composite. The filling of the glassy phases in the cracks prohibited the diffusion of oxygen from the environment. As a result, creep and fatigue properties in the enhanced SiC/SiC composite in air at high temperatures was improved.

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Monotonic tension, creep, and fatigue tests of a composite where a silicon carbide (SiC) matrix that contains glassforming, boron-based particulates has been reinforced with Hi-Nicalon™ fiber (Hi-Nicalon™/SiC) were conducted in air at 1300°C, and creep tests also were conducted in argon at 1300°C. The ultimate tensile strength (UTS) of the Hi-Nicalon™/SiC composite was similar to that of a SiC composite where a pure SiC matrix is reinforced with Nicalon™ fiber (standard SiC/SiC) and a SiC composite where a matrix of glass-forming, boron-based particulates is reinforced with Nicalon™ fiber (enhanced SiC/SiC); however, the strains at UTS of the Hi-Nicalon™/SiC composite and the enhanced SiC/SiC composite were much larger than that of the standard SiC/SiC composite. The Young's modulus of the Hi-Nicalon™/SiC composite was ∼140 GPa, which is higher than that of the enhanced SiC/ SiC composite (90 GPa) and lower than that of the standard SiC/SiC composite (200 GPa) at a temperature of 1300°C. The minimum strain rates of cyclic creep (fatigue) were lower than those of static creep. The time to rupture under creep loads was slightly shorter than that under fatigue loads at a given maximum stress. The creep strain rates of the Hi-Nicalon™/SiC composite in air were lower than those in argon. Consequently, the time to rupture at a given stress in air was longer than in argon. The creep and fatigue resistance of the Hi-Nicalon™/SiC composite both were similar to that of the enhanced SiC/SiC composite but were much better than that of the standard SiC/SiC composite in air. However, in argon, the standard SiC/SiC composite had the lowest creep rate, whereas the enhanced SiC/SiC composite had the highest creep rate. The time to rupture of the standard SiC/SiC composite was the shortest and the Hi-Nicalon™/SiC composite had the longest life.