Isothermal and nonisothermal fatigue crack growth of nickelbase alloy MAR-M247 CC (HIP)

In this paper results from fatigue crack growth tests performed under isothermal and nonisothermal conditions are presented in the temperature range between 300 °C and 1050 °C. When correlating the results with the range of the stress intensity factor, a strong temperature dependence is observed under isothermal conditions. Under nonisothermal conditions, the results depend significantly on the phase relation between stress and temperature. In order to get a more uniform description of the fatigue crack growth results, a mechanism based model based on the cyclic crack-tip opening displacement is used. The model is extended to time dependent effects by including the time and temperature dependent creep deformation of the crack-tip opening displacement. The correlation of the fatigue crack growth results with the cyclic crack-tip opening displacement yields a significantly reduced influence of the temperature under isothermal and nonisothermal fatigue conditions. For the rather fast loading cycles, which were used under isothermal conditions, only a weak creep influence is predicted by the model.