On the biaxial thermal creep-fatigue behavior of Ni-base Alloy 617 at 950 °C

A new in-situ biaxial creep-fatigue testing system was built to study the creep-fatigue interaction of Alloy 617, a nickel base alloy with potential structural applications in the Very High Temperature Reactor, up to 70 MPa at 950 °C. The results show that creep-fatigue life of Alloy 617 is reduced with increasing hold time and the cracking mode seems to be intergranular in all creep-fatigue samples. At the microstructural level, both cellular network dislocations and slip bands were observed in the creep-fatigue tested specimens. The portion of slip bands seems to increase with increasing fatigue damage fraction. Moreover, the dislocation density increased with increasing effective stress.