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 m icroscopy from the microstructural point of view. Alternating plane be nding fatigue tests were conducted at R= -1 and ambient temperature in vacuum (6 x 10(-3) Pa) and in air. It was found that intergranular mo de of crack propagation was more frequently observed in air than in va cuum. In vacuum, microcracking was commonly observed in the vicinity o f main cracks. The Ti-15mass%Mo alloy behaved more elastically in fati gue deformation than the Ti-17mass%Mo alloy. TEM examination disclosed that dislocation loops have been retained around omega phase precipit ates, which reduced the slip activities of titanium by forming a barri er against dislocation movement. (C) 1998 Elsevier Science S.A. All ri ghts reserved.