On the role of the internal stress during non-isothermal creep life of a first generation nickel based single crystal superalloy

Non-isothermal creep tests were performed on a first generation single crystal Ni-based superalloy. These tests consist in performing one short exposure at 1200 °C during a creep test at 1050 °C. Based on the experimental results, residual creep life after the overheating can be well predicted using a continuum damage mechanics model derived from the Rabotnov–Kachanov law. It appears clearly that the behavior of the material is conditioned either by the microstructure developed before the overheating or by the overheating duration. In fact, as a striking result, an overheating performed on a microstructure with cubic γ′ precipitates or increasing the overheating duration lead to longer non-isothermal creep life. Microstructure modifications, such as γ′ precipitates rafting and dislocation network recovery at the γ/γ′ interfaces due to the overheating, modifying the internal stress σi of the material, prove to be deleterious to the non-isothermal creep life of the superalloy in the conditions investigated in this paper.