Creep and Fatigue Behavior in Hi-Nicalon-Fiber-Reinforced Silicon Carbide Composites at High Temperatures

Monotonic tension, creep, and fatigue tests of a composite where a silicon carbide (SiC) matrix that contains glass‐forming, 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.