SEDL / STP / STP1309-EB / STP11817S

Stress-Temperature-Lifetime Response of Nicalon Fiber-Reinforced Silicon Carbide (SiC) Composites in Air

Lin, H-T
Research staff member and group leader, Oak Ridge National Laboratory, Oak Ridge, TN

Becher, PF
Research staff member and group leader, Oak Ridge National Laboratory, Oak Ridge, TN

Pages: 14    Published: Jan 1997

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Abstract

Time-to-failure tests were conducted in four-point flexure and in air as a function of stress levels and temperatures to study the lifetime response of various Nicalon fiber-reinforced silicon carbide (designated as Nic/SiC) composites with a graphitic interfacial coating. The results indicated that all of the Nic/SiC composites exhibit a similar stress-dependent failure at applied stress greater than a threshold value. In this case, the lifetimes of the composites increased with decrease in both stress level and test temperature. The lifetime of the composites appeared to be relatively insensitive to the thickness of graphitic interface layer and was enhanced somewhat by the addition of oxidation inhibitors. Electron microscopy and oxidation studies indicated that the life of the Nic/SiC composites was governed by the oxidation of the graphitic interfaces and the formation of glass(es) in composites as a result of the oxidation of the fiber and matrix, as well as any inhibitor phases.