ON THE TOUGHENING OF INTERMETALLICS WITH DUCTILE FIBERS - ROLE OF INTERFACES

The role of fiber debonding and sliding on the toughness of intemetallic composites reinforced with ductile fibers is examined. The toughness is shown to be a function of the matrix/fiber interface properties, residual stresses and the volume fraction, size and flow behavior of the fibers. Mechanical testing and in situ microstructural observations were carried out on a Ti-25at.%Ta-50at.%Al intermetallic matrix reinforced with W-3Re fibers. The fibers were coated with a thin oxide layer in order to induce debonding and prevent interdiffusion between the fiber and the matrix. The ductility, high strength and debond characteristics of coated tungsten-rhenium fibers promote a large increase in toughness. However, the mismatch in thermal expansion coefficients is the source of large residual tensile stresses in the matrix that induces spontaneous matrix cracking. Matrix cracking and composite toughness are examined as a function of the interfacial properties, residual stresses and properties of the fiber.