Effect of stress-hold and strain-hold during Creep-Fatigue Interaction of alloy 617 M

Abstract

Alloy 617 M is a Nickel based superalloy compatible for utilization in structural components of Very High Temperature Reactors (VHTR). In these complicated structural components, loading scenarios include both static and cyclic stresses at elevated temperatures. In order to understand the effect of both static and cyclic stress state on Alloy 617 M at high temperatures, Creep-Fatigue Interaction (CFI) studies with a strain amplitude of ± 0.6% and a hold/ dwell time of 60 seconds have been conducted at 600 °C, 650 °C, 700 °C, and 750 °C. At the peak tensile strain of the applied cyclic loads during CFI, the specimen was subjected to either a strain-hold (represented as εCFI) or a stress-hold (represented as σCFI) to understand their influence on mechanical behavior at elevated temperatures. This kind of testing is imminent for understanding the damage caused by both the loading scenarios. In either case of loading, with the increase in test temperature, the number of cycles to failure is reduced. However, for a given test temperature, σCFI showed lower cycles to failure compared to εCFI. Fractography studies revealed that σCFI undergoes predominant creep damage in comparison with εCFI.