Hold-Time Effects on Low-Cycle-Fatigue Behavior of Hastelloy X Superalloy at High Temperatures

Abstract

Total strain-controlled low-cycle-fatigue tests with and without hold times were performed at temperatures ranging from 816C to 982C in a laboratory air on a nickel-based superalloy, HASTELLOY X. The influence of hold times on the cyclicstress response and fatigue life was studied. At the temperatures considered, the alloy exhibited initial cyclic hardening, followed by a saturated cyclic-stress response or cyclic softening under low-cycle fatigue without hold times. For low-cycle-fatigue tests with hold times, however, the alloy showed cyclic hardening, cyclic stability, or cyclic softening, which is closely related to the test temperature and the duration of the hold time. It was also observed that the low-cycle-fatigue life of the alloy considerably decreased due to the introduction of strain hold times. Generally, a longer hold time would result in a greater reduction in the fatigue life. For the tests without hold times, the test temperature seems to have little influence on the fatigue life of the alloy at the test temperatures from 816C to 927C. However, when the test temperature increased to 982C, the fatigue life clearly shortened. In addition, the fracture surfaces of the fatigued specimens were observed, using scanningelectron microscopy, to determine the crack initiation and propagation modes. The fatigue life was predicted by the frequency-modified tensile-hysteresis-energy method. The predicted lives were found to be in good agreement with the experiment results.