Effect of Thermal Aging on High Temperature Low-Cycle Fatigue Properties of Ni-Base Superalloys for HTGR Application

Abstract

The effect of thermal aging on the high temperature low-cycle fatigue properties of Ni-base superalloys, Inconel 617 and Hastelloy XR, was studyed at High Temperature Gas-cooled Reactor (HTGR) temperatures (950-1000°C). The strain controlled low-cycle fatigue tests were conducted under a symmetrical triangular wave form for Inconel 617 at 700°C and 1000°C, and for Hastelloy XR at 950°C. Two aging conditions, namely 1000°C for 3000 hours and 700°C for 200 hours, were employed for Inconel 617. One condition of 950°C for 1000 hours was employed for Hastelloy XR.
In the both materials aged at HTGR temperatures, the low-cycle fatigue lives increased remarkably in comparison with the lives of as-received (solution heat treated) materials. This beneficial effect might be caused by the cohering and coarsening of carbide precipitates at grain boundaries. On the other hand, the fatigue life of Inconel 617 aged at 700°C was not influenced by the thermal aging.