TRANSVERSE STRENGTHS AND FAILURE MECHANISMS IN TI3AL MATRIX COMPOSITES

Transverse mechanical properties have been measured, and damage mechan isms identified, in three Ti3Al matrix composites with different inter face compositions and residual stress states. Two of the composites co ntained SiC fibers with weak interfaces. Large improvements in transve rse strength and rupture strain were found in one of these composites, in which brittle reaction products in the matrix around the fibers ha d been avoided by coating the fibers with Ag and Ta before consolidati on. The third composite contained sapphire fibers that were strongly b onded to the matrix. Different damage mechanisms were observed in the strongly and weakly bonded composites. Insight into the damage mechani sms and their dependence on residual stress fields and interface prope rties is gained from comparison of the observations with analytical so lutions of elastic stresses. The conditions for optimum transverse pro perties are discussed; the results indicate that strong interfacial bo nding does not necessarily lead to optimum transverse strength of the composite.