Interface damage mechanism during high temperature fatigue test in SiC fiber-reinforced Ti alloy matrix composite

An experimental investigation has been made on the effect of interface wear behavior on the change of interface shear sliding stress during high temperature fatigue in a SiC (SCS-6) fiber-reinforced Ti-15-3 alloy composite. An unnotched composite was subjected to a tension-tension fatigue test in a vacuum of 2 × 10^-3 Pa at 823 K under maximum stress of 600, 780 and 960 MPa with a frequency of 2 Hz and R=0.1. The progress of interface debonding and sliding in the composite during fatigue was directly observed by scanning electron microscopy (SEM). The post-fatigued morphology of the fiber-matrix interface was observed and evaluated quantitatively using atomic force microscopy (AFM). Abrasive wear due to frictional sliding was observed near the end of a fractured fiber and the amplitude of asperity roughness at the weared interface was found to decrease with increasing of fatigue cycles. The wear behavior along the fiber shows strong dependence on the interface relative sliding length. The dominant mechanism for the reduction in the shear frictional sliding resistance along the fiber was asperity wear of outer most carbon coating layer of the fiber with the relative sliding length. The interface wear during cyclic loading results in change of load transfer potential at the interface and its leads to the increase of matrix crack initiation resistance near the fiber fracture.