Heat treatment effects on SiC fiber

The Wright Laboratory Materials Directorate at Wright-Patterson AFB has been spearheading the development and evaluation of a new class of metal matrix composites based upon continuous SiC fiber reinforcement of orthorhombic phase containing titanium aluminide matrices. These composites (O TMCs) will be subjected to thermal exposures during primary and secondary component processing, and possibly also during heat treatments to optimize matrix-dominated mechanical performance. Such thermal excursions must not degrade the SiC fiber reinforcement, hence compromising resulting composite properties. Therefore, the effects of heat treatment on the room temperature tensile strength of continuous SiC fibers were studied. The fibers examined included: Trimarc 1®, SCS-6, Ultra SCS and an experimental large diameter version of Ultra SCS. The fibers were heat treated below and above the beta solvus temperature of the orthorhombic matrix alloy utilized for this study, Ti-22Al-23Nb (at%). The fibers were evaluated for ambient temperature tensile strength in the following conditions: (1) as-received: (2) heat treated in vacuum; and (3) consolidated into Ti-22Al-23Nb, heat treated in vacuum, and chemically extracted. Fiber microstructure and fracture analysis was accomplished via secondary scanning electron microscopy (SEM). Chemical reactions between fiber core and the SiC, and between the SiC fiber and the Ti-22Al-23Nb matrix, were also studied by SEM.