EFFECT OF FIBER COATING ON THE FRACTURE AND FATIGUE RESISTANCE OF SCS-6/TI3AL COMPOSITES

The effect of a Ag/Ta coating on the fracture resistance of a notched SCS-6 fiber-reinforced Ti3Al matrix composite under both static and fatigue loading was investigated. The crack propagation patterns and damage mechanisms under various loading conditions were characterized and compared with its uncoated composite counterparts. The results show that the Ag/Ta-coated composites exhibit a typical mode-I failure pattern under both static and fatigue loading, while mixed mode-I and -II failure patterns were observed in the uncoated SCS-6/Ti-25-10 composite. Under fatigue loading, crack propagation was arrested at stress intensity levels up to 34 and 45 MPa m(1/2) for Ag/Ta-coated and uncoated SCS-6/Ti-25-10 composites, respectively. Localized interfacial debonding, matrix cracking and fiber bridging in the crack wake were the responsible damage mechanisms for the Ag/Ta-coated SCS-6/Ti-25-10 composite. Extensive interfacial debonding, crack splitting and branching, however, were found to be the dominant mechanisms in the uncoated SCS-6/Ti-25-10 composite. Modifications of interfacial bond strength and morphology so as to improve the mechanical properties of the Ag/Ta-coated SCS-6/Ti-25-10 composite can be achieved by thermal exposure at 800 degrees C for up to 200 h.