On the effects of temperature and environment on fatigue damage processes in Ti alloys and in stainless steel

The low cycle fatigue resistance of different Ti alloys, in the temperature range 20–500°C, are presented and discussed as a function of their microstructure. The intrinsic effect of temperature and the role of environment are distinguished by comparing fatigue behaviour in air and in vacuum. Fatigue damage processes were characterized through qualitative and quantitative data on crack initiation and small crack growth. An intrinsic beneficial effect of temperature was observed in terms of cyclic plasticity. A significant effect of environment on fatigue life was noted at 300 and 500°C. In Ti alloys, this effect is mainly related to crack initiation, crack growth being weakly affected. However in some cases no difference was observed between tests performed in air and in vacuum. This behaviour is analysed by considering the role of each type of microstructural elements in the initation of the fatal crack. Similar effects of temperature and environment were obtained on a 316 L stainless steel in the range 20–600°C. In this case, environment fundamentally affects crack growth.