Contribution of matrix plasticity to the `frictional' sliding of debonded fibers in sapphire-reinforced TiAl matrix composites

Large-scale fiber displacement behavior, usually characterized by a `frictional' sliding stress (τ_slide), has been studied in two sapphire-reinforced TiAl systems. Experimental results from fiber pushout and reverse push-back tests indicate that the large-scale sliding behavior of debonded fibers leads to an average τ_slide-value which progressively decreases during fiber displacements. Previous studies of SCS-6 (SiC) fiber-reinforced glass and metal matrix composites have attributed decreases in τ_slide to the fracture and wear of fiber asperities. However, given a matrix in which fiber asperities do not easily wear (e.g., a TiAl alloy), SEM examination of the fiber/matrix interface indicates that matrix plasticity plays a dominant role in the decrease of τ_slide with fiber displacement. Experimental evidence suggests that the observed decrease in τ_slide can be attributed to (1) a decrease in fiber roughness perceived by the matrix due to matrix grooving and (2) a relaxation of radial clamping as a result of material removal from the interface.