Executive Summary : | Polycrystalline Ni-base superalloys are ideal for high temperature applications due to their high temperature strength, oxidation resistance, and creep resistance. IN617 alloy, a suitable option for USC applications, has been added to the ASME Boilers and Pressure Vessel code for manufacturing components in nuclear reactors, particularly high temperature molten salt reactors. The extended in-service exposure times of these materials make it crucial to study the creep properties of IN617. IN617 alloy is composed of a family of metal-carbide inclusions and other topologically close packed (TCP) phases, including the γʹ strengthening phase. The presence of complex second phases in the alloy significantly influences its long-term stability and high temperature response. This project aims to conduct creep tests on conventionally cold-rolled IN617 at intermediate to high temperatures and applied stress. Structural investigation will be conducted to estimate the evolution of defects, particularly dislocation structure with stress and temperature and its interaction with secondary phases. Details of transmission electron microscopy (TEM)-based imaging and analyses will be performed on crept samples to understand the underlying microstructural interactions. Additional interrupted creep tests around the primary creep region will help elucidate its subdued occurrence. The structural evolution of secondary phases, which occurs both as a function of strain and temperature, adds complexity to the IN617 alloy. Finally, morphological transformations of the precipitates up to the atomic level will be determined through detailed structural and chemical characterization using TEM and 3D atom probe tomography. |