Interfaces and fatigue damage in a metastable beta titanium matrix composite

The results of a systematic study of the effects of interfacial microstructure on fatigue damage in a metastable β Ti---15V---3Cr---3Al---3Sn/SiC (SCS-9) composite are presented. Interfacial microstructure is controlled by heat treatment in the β phase field of the matrix, which promotes coarsening of the fiber-matrix interface without significant changes in the metastable β matrix microstructure (grain size). The effects of interfacial microstructure on debone and friction strengths are also discussed using results from fiber push-out tests. Fatigue damage initiation and propagation mechanisms are elucidated via optical/scanning electron microscopy and acoustic emission analysis of specimens that were deformed to failure in incremental cyclic loading steps. The effects of cyclic deformation on matrix hardness and composite modulus are also examined prior to the presentation of a fracture mechanics (micromechanics) approach for the prediction of fatigue life, and the effects of crack-tip shielding via bridging mechanisms. The paper highlights the potential for the development of accurate life prediction methodologies that are based on experimental observations of damage in titanium matrix composites. It also illustrates the need for multidisciplinary mechanics and materials approaches in the study of composite behavior.