Effect of fiber coating on the fatigue crack initiation and multiplication of unnotched SCS-6/Ti3Al composites

The effect of fiber coating on the fatigue crack initiation and multiplication of an unnotched SCS-6 fiber-reinforced titanium aluminide (Ti3Al) matrix composite was investigated. The initiation and growth of each individual matrix crack, the evolution of matrix crack density and stiffness degradation of the composite with Ag/Ta-coated fibers were characterized quantitatively, and compared with those of the composite with uncoated fibers. The results showed that the composite with Ag/Ta-coated fibers exhibited a shorter crack initiation life, higher number of matrix cracks, and higher crack growth rate than the composite with uncoated fibers. Therefore, a higher matrix crack density and a lower residual stiffness were found in the composite with coated fibers during fatigue loading. The high interfacial cracking density and high interfacial bond strength in the Ag/Ta-coated SCS-6/Ti3Al composite is believed to be responsible for its poor fatigue damage resistance. Finally, an interface-controlled fatigue cracking model is used to predict the evolution of matrix crack density and residual stiffness of the composite under fatigue loading.