INTERFACIAL SHEAR-STRENGTH OF CAST AND DIRECTIONALLY SOLIDIFIED NIAL-SAPPHIRE FIBER COMPOSITES

The feasibility of fabricating intermetallic NiAl-sapphire fiber compo sites by casting and zone directional solidification-has been examined . The fiber-matrix interfacial shear strengths measured using a fiber push-out technique in both cast and directionally solidified composite s are greater than the strengths reported for composites fabricated by powder cloth process using organic binders. Microscopic examination o f fibers extracted from cast, directionally solidified (DS), and therm ally cycled composites, and the high values of interfacial shear stren gths suggest that the fiber-matrix interface does not degrade due to c asting and directional solidification. Sapphire fibers do not pin grai n boundaries during directional solidification, suggesting that this t echnique can be used to fabricate sapphire fiber reinforced NiAl compo sites with single crystal matrices.