A Re-Visit to the Haigh Diagram with the Effect of Creep Damage on the High Cycle Fatigue Behavior of Alloy 617M

The present work is aimed at a re-evaluation of the Haigh diagram incorporating the effect of creep on HCF. HCF testing was carried out at 973 K with varying mean stress (crm) and alternating stress (cra) to generate the Haigh diagram. The influence of creep on HCF was investigated by imposing periodic holds at crm during the course of HCF cycling. Under such HCF-creep interaction tests, specimens were found to fail for certain cra-crm combinations that resulted in run-outs in the absence of superimposed creep holds, leading to a deviation in the Haigh diagram. Such deviation was more prominent with an increase in the crm (increase in R) and the hold time. The test results obtained are correlated with microscopic and fracture surface analysis to understand the mechanism of crack initiation and propagation, as well as the role of precipitation under HCF-creep interaction.