Time-Dependent Crack Growth in a Heat-Resistant Alloy Inconel 617

Abstract

Inconel alloys have been used extensively as heat exchange tubing materials in the power generation industry because of their excellent mechanical properties at elevated temperatures. Evaluation of the alloys for High Temperature Gas-Cooled Reactor (HTGR) applications has proved that Ni-Cr-Co alloys have good high temperature strength, creep properties and weld-ability.
In this work, the cyclic fatigue behavior and creep crack growth rate of Inconel 617 alloy were tested for analysis of time-dependent crack propagation characteristics at 650°C. Micro-structural examination was performed for observation of grain boundary carbide precipitation growth and the coalescence of intergranular microcracks that would enhance the crack propagation rate. It was observed that at higher temperatures, low fatigue frequency, and higher R-ratio (mean-stress), the effects of dynamic recovery tended to become stronger because the mobility of dislocation increased with increasing temperature. As a result, the subgrain grew to a larger size. Eventually, the influence of time-dependent processes on crack growth rate can effectively represent the overall effects on a creep ductile material at elevated temperatures.