CYCLIC DEFORMATION BEHAVIOR AND DAMAGE MECHANISMS OF HASTELLOY~R X SUPERALLOY UNDER FATIGUE AND CREEP-FATIGUE LOADING

摘要

The fatigue deformation behavior of a nickel-based superalloy, HASTELLOY X, was investigated at 816℃ and 927℃ in laboratory air. It was noted that at both temperatures of 816℃ and 927℃, the alloy exhibited initial cyclic hardening, followed by a saturated cyclic stress response or cyclic softening under fatigue loading condition. For creep-fatigue tests, the alloy showed either cyclic hardening or cyclic stability, which is closely related to the test temperature and the duration of the strain hold time. It was also observed that the fatigue life of the alloy considerably decreased due to the introduction of strain hold times. In addition, the fracture surfaces of the fatigued specimens were observed using scanning electron microscopy to determine the crack initiation and propagation mechanisms. The fatigue cracks was usually found to initiate in a transgranular mode, while both transgranular and intergranular crack growth mechanisms were observed.