The cyclic creep behaviour of INCONEL alloy 718 of Ni-Iron base superalloy has been examined under the condition of square wave stress cycling tension creep test in the temperature, stress and frequency ranges of 621-677℃ (0.57-0.61 Tm), 25-87.5 Kg/㎟ (245-857.5 MPa), and 12 cpm or 0.2857 cpm, respectively. Square wave cyclic stress is chosen with the minimum stress equals to 70% of the maximum stress. Also static creep behaviour of INCONEL alloy 718 has been examined, and the relations between cyclic creep and static creep have been studied.
The observation of the stress mode changed, so-called "static-to-dynamic creep transition", was interpreted in terms of mobile dislocation density changes. Over the range of experimental conditions examined, "cyclic stress acceleration" occurs. Microstrain for cyclic creep was measured and its behaviour was investigated in the view of internal stress changes in region of primary creep.
The activation energy for static creep deformation was measured to be similar to that of interdiffusion in INCONEL alloy 718. Also the activation energies for cyclic and subsequent static creep deformation were measured and the relations among these were studied by means of effective stress differences.
The stress exponent value for cyclic and static creep is observed to be about 3.1 and 3.0, respectively.
From the above facts, it is considered that creep deformation for INCONEL alloy 718 is controlled by dislocation glide over the range of experimental conditions, and that the alloy belongs to class I alloys.
