Low Cycle Fatigue Behavior of Forged Alloy 617M

Abstract

Low cycle fatigue experiments were performed on nickel-based alloy 617M at different temperatures ranging from 300 to 1123 K. Samples were machined from a forged block of 800 mm diameter of the alloy. The alloy exhibited continuous cyclic hardening up to the macrocrack initiation followed by a rapid stress drop until the final failure at all the temperatures except 300 K, 473 K and 1123 K where saturation was observed between the initial hardening and the final stress drop. The above observations indicate the difference in the deformation mechanisms at the above temperature extremities compared to the intermediate temperature range of 573–1023 K. The extent of cyclic hardening increased initially with the strain amplitude and saturated whereas, with the increase in temperature, it increased up to 973 K followed by a reduction with further increase. Type-C serrations were observed in the temperature range of 573–1123 K. However, the serrations disappeared with progressive cycling and matrix hardening persisted and seemed to be more predominant at the later stage of cycling, resulting in cyclic hardening up to macrocrack initiation. Stress drops curves of a serrated flow were used to understand the effect of precipitates on the alloy behavior. All the samples failed in transgranular mode. The data generated was used to arrive at the fatigue design curves for the alloy.