A microstructural study of fatigue fracture in titanium–molybdenum alloys

Fatigue fracture micromechanisms of Ti-15mass%Mo and -17mass%Mo alloy plates of 0.3 mm thickness have been studied by optical and electron microscopy from the microstructural point of view. Alternating plane bending fatigue tests were conducted at R=−1 and ambient temperature in vacuum (6×10−3 Pa) and in air. It was found that intergranular mode of crack propagation was more frequently observed in air than in vacuum. In vacuum, microcracking was commonly observed in the vicinity of main cracks. The Ti-15mass%Mo alloy behaved more elastically in fatigue deformation than the Ti-17mass%Mo alloy. TEM examination disclosed that dislocation loops have been retained around ω phase precipitates, which reduced the slip activities of titanium by forming a barrier against dislocation movement.