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 fa tigue loading was investigated. The crack propagation patterns and dam age mechanisms under various loading conditions were characterized and compared with its uncoated composite counterparts. The results show t hat the Ag/Ta-coated composites exhibit a typical mode-I failure patte rn under both static and fatigue loading, while mixed mode-I and -II f ailure patterns were observed in the uncoated SCS-6/Ti-25-10 composite . Under fatigue loading, crack propagation was arrested at stress inte nsity 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 debondi ng, matrix cracking and fiber bridging in the crack wake were the resp onsible damage mechanisms for the Ag/Ta-coated SCS-6/Ti-25-10 composit e. Extensive interfacial debonding, crack splitting and branching, how ever, were found to be the dominant mechanisms in the uncoated SCS-6/T i-25-10 composite. Modifications of interfacial bond strength and morp hology 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 de grees C for up to 200 h.