Effect of Strain Waveform on Low-Cycle Fatigue Properties of Inconel 625 Alloy

The low-cycle fatigue tests for the Inconel 625 alloy were performed at 650 C under three strain waveforms including triangular waveform as well as two sawtooth waveforms with slow-tension followed by fast-compression and fast-tension followed by slow-compression. And the low cycle fatigue deformation and fracture behaviors of the alloy under different strain waveforms were investigated. The results show that the Inconel 625 alloy exhibits the cyclic hardening at different strain waveforms and applied total strain amplitudes from 0.3% to 0.7%. When two sawtooth waveforms are adopted, the fatigue life of the alloy will shorten due to the introduction of either tensile or compressive creep strain component. In addition, the relation between the plastic or elastic strain amplitudes and fatigue life as well as between the cyclic stress amplitude and plastic strain amplitude exhibits a single slope linear behavior. The observations on the fatigue fracture surfaces reveal that under three strain waveforms, the fatigue cracks initiate and propagate in a transgranular mode.