Fatigue Resistant Ti3A1 Composites

Abstract : Measurements of interfacial properties and residual stresses in Tl3 Al/SiC composites with and without ductile Ag/Ta layers are presented as the first step in determining the role of the ductile layers in the fatigue of these composites. In the composite without ductile layers, debonding and fiber sliding occurred along the interface between the outer surface of the fiber and the layer of reaction products. In the composite with Ag/Ta layers, debonding and sliding occurred within the SCS-6 layers that form the outer part of the fiber, with a higher frictional stress resisting sliding (100 MPa c.f. 66 MPa). Fatigue crack growth measurements indicated only minor differences in growth rates in the two composites in a given environment, but both composites exhibited much larger growth rates in air than in vacuum. High resolution crack opening displacement measurements are used to assess relative bridging effects. To avoid the limitation imposed by the presence of weak SCS-6 layers on the SIC fibers, a composite composed of sapphire fibers In matrix of Ti3Al with an interfacial layer of Ta was fabricated. In situ observations during transverse loading Indicated that the interfacial bonding was sufficiently strong that interfacial debonding or plasticity did not affect transverse properties.... Titanium aluminide composites, Interface properties, Transverse failure.