Investigation on ratcheting-fatigue behavior and damage mechanism of GH4169 at 650 °C

Combined microscopy and morphology were employed to investigate the effect of ratcheting-fatigue characteristic of GH4169 superalloy. All tests were implemented on a closed-loop servo hydraulic testing machine at 650 degrees C. The cyclic deformation behaviors and damage mechanisms of nickel-based superalloy GH4169 were investigated by means of a series of symmetric and asymmetric stress-controlled tests under various stress amplitudes and mean stress levels at 650 T. The results exhibit a distinct reduction in fatigue life with the increasing of mean stress and stress amplitude. A continuous cyclic softening until final failure is observed for all the tests. Moreover, the ratcheting effect begins to operate exclusively beyond the threshold value corresponding to a stress amplitude of 600 MPa joint with a tensile mean stress of 50 MPa. A transformation in terms of cracks propagation mode from transgranular to transgranular-intergranular mixed mode has been illustrated. Meanwhile, a higher stress amplitude enhances a more intense slip trace. In addition to the damage caused by high temperature oxidation, the interaction between slip band and grain boundary is the underlying dominant factor on intergranular damage.