Silicon Carbide and Oxide Fiber Reinforced Alumina Matrix Composites Fabricated Via Directed Metal Oxidation

Abstract

Directed metal oxidation was used to fabricate a variety of fiber-reinforced ceramic matrix composites. Reinforcements included silicon carbide and oxide based fibers. SiC f /Al 2 O 3 components successfully completed engine and rig tests with operating temperatures between 1000 and 1400• C. Replacement of ceramic grade (CG) Nicalon TM fibers with reduced oxygen containing Hi-Nicalon TM fibers resulted in enhanced properties, particularly residual strengths following elevated temperature exposure. Oxide based fibers offer the advantage of a closer coefficient of thermal expansion match with the alumina matrix. Aluminum oxide and mullite based fibers were evaluated as reinforcements. The oxide-oxide composites exhibited a significant drop in strength as test temperatures approached 1000• C. In contrast, composites reinforced with silicon carbide fibers retained over 80% of their room temperature strength and fracture toughness at temperatures as high as 1200• C in air.

Stress—strain response and thermal conductivity degradation of ceramic matrix composite fiber tows in 0—90° uni-directional and woven composites

“…A value of d ¼ 0.9 mm has been used for the thickness of the air gap and is based on examination of micrographs by Fareed. 21 The values of c ¼ 11:75 MPa for the critical interfacial shear stress, and g ¼ 20 for the Weibull index, given in Equation ( 9), have been used for the DLR-XT material; and the values of c ¼ 24:5 MPa and g ¼ 60 have been used for the HITCO material. The calibration of the parameters c and g will be addressed in a later section.…”

Uni-axial stress–strain response and thermal conductivity degradation of ceramic matrix composite fibre tows

“…where b and c are the width and height of the tow, t om is the thickness of the outer matrix material, shown in figure 9 (t om for a single-matrix material will be zero) and d is the average air gap produced by wake debonding (figure 12); a value of d = 1.0 μm has been taken as being typical of CMC composites (Fareed 2005). This value is above the critical level of 0.1 μm determined by Lu & Hutchinson (1996) for zero heat conductance.…”