材料期刊网

Isothermal and thermomechanical fatigue (TMF) behaviour (including cyclic stress response and number of cycles to failure) of a Ti-5(.)6Al-4(.)8Sn-2(.)0Zr-1(.)0-Mo-0(.)32Si-0(.)8Nd (wt-%) hightemperature titanium alloy was examined. The purpose of the present investigation was to understand the effect of temperature fluctuation on the cyclic behaviour and fatigue life of this alloy and to test the suitability of lifetime prediction based on isothermal laboratory data. The results indicated that both the level of peak stress and fatigue life were decreasing with increasing test temperature from 400degreesC to 650degreesC in isothermal fatigue (IF) tests. In TMF tests run between 400degreesC and 600degreesC, the peak stresses corresponding to 600degreesC coincide well with that found in IF tests run at 600degreesC, while a slight increase in cyclic hardening was found for peak stress corresponding to 400degreesC compared to that found in a 400degreesC/IF test. This increase in cyclic hardening became more pronounced when the maximum temperature increased to 650degreesC. Fatigue life in 'out of phase' (OP) condition was found to be shorter than under an equivalent 'in phase' (IP) condition, and this gap increased with decreasing mechanical strain amplitude. The results indicate that lifetime prediction based on isothermal laboratory data may lead to non-conservative results if thermal fluctuations are present in components made of the present alloy.