Isothermal low cycle fatigue of titanium matrix composites

Ceramic fibre reinforcement has been suggested as a means to improve the resistance of a titanium alloy to mechanical fatigue. Low cycle fatigue tests at room and elevated (600 degrees C) temperature were conducted on specimens, fabricated by DLR, a part of them heat treated at 700 degrees C/2000h. In comparison with results described in the literature the tested material showed an increase of stress of nearly 30% at the same fatigue life. An investigation of metallographically polished specimens gave a first insight in the damage mechanisms. Defects at the surface of the specimens and the brittle reaction zone at the fibre/matrix interface acted as points of crack initiation. The crack propagation mainly depended on fibre bridging mechanisms, stress level in the matrix, microstructure of the matrix and properties of the fibre/matrix interface.