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 degrees C during a creep test at 1050 degrees 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 gamma' precipitates or increasing the overheating duration lead to longer non-isothermal creep life. Microstructure modifications, such as gamma' precipitates rafting and dislocation network recovery at the gamma/gamma' interfaces due to the overheating, modifying the internal stress sigma(i) of the material, prove to be deleterious to the non-isothermal creep life of the superalloy in the conditions investigated in this paper. (C) 2009 Elsevier B.V. All rights reserved.