EFFECT OF FIBER COATING ON CREEP-BEHAVIOR OF SIC FIBER-REINFORCED TITANIUM ALUMINIDE MATRIX COMPOSITES

The effect of fiber coating on the creep behavior and damage mechanism s of unnotched SCS-6 fiber-reinforced Ti3Al matrix composites under lo ngitudinal and transverse loading was investigated at 700 degrees C. S tresses ranging from 700 to 900 MPa and 200 to 400 MPa were used for l ongitudinal and transverse loading, respectively. An Ag/Ta duplex laye r was coated onto the SCS-6 fiber prior to consolidation via physical vapor deposition. The microstructure of the crept composites was exami ned to determine the creep deformation mechanisms. The creep cracking behavior of the notched composites was also studied at initial stress intensity factors, K-i, ranging from 15 to 20 MPa-m(1/2). Microstructu ral observation revealed that multiple fiber fracture (at low to mediu m stress levels), microcracking along the reaction zone/matrix interfa ce (at medium stress levels), and matrix cracking extending from the b roken fiber ends (at high stress levels) were the major damage mechani sms during quasi-steady state creep under longitudinal loading. The re sults show that the Ag/Ta duplex coating significantly improved the cr eep resistance and flexural strength of the composite under transverse loading. The Ag/Ta duplex coating was also shown to significantly pro long the creep rupture life of SiC fiber-reinforced Ti3Al composites.