Abstract
The Ni-base IN100 super alloy, developed as a heat-resistant material for gas turbines, is subject to complex thermal and mechanical histories during a typical cycle of operation; i.e., the material is used under conditions of creep-fatigue interaction. To maintain operational safety and minimize maintenance costs, it is necessary to clarify the characteristics of fracture life, taking into account the effect of both creep and fatigue interaction on fracture lifespan. In this paper, an in situ observational testing method under the conditions of creep-fatigue interaction was conducted using IN100, and the effects of cycle- and time-dependent crack growth on the fracture life tf were investigated from the experimental relationship between the inverse value of fracture life 1⁄tf and the load frequency f. So far it has been difficult to comprehend the characteristics of the load frequency of the fracture life under creep and fatigue interaction, since the characteristics indicate nonlinear fluctuations depending on stress, stress holding time, material properties and temperature. In this research, creep ductility, stress holding time tH and temperature T were found to be unified as promoting factors of time dependent crack growth. Finally, the multiple effects of creep and fatigue on fracture life tf were clarified.
