| Alloy 22 is a Ni-Cr-Mo-W corrosion-resistant metal alloy. Its durability and mechanical properties can be linked to subsequent formations of secondary phase during processing and welding. The Yucca Mountain Repository intends to use Alloy 22 as an integral component of the waste package canisters to ultimately house spent nuclear fuels and high-level waste. This research studies the microstructural formations of phases along with their stability and variability in Alloy 22. Microstructural characterization was performed using light optical, scanning electron, and transmission electron microscopy along with measurements from grain size, phase fraction, and hardness. Results show light optical micrographs with a distinct increase in secondary phase formations in the temperature range of 650°C to 850° C with durations of 60 minutes up to 60,000 minutes. Energy-dispersive x-ray spectroscopy indicated the presence of the mu-phase, as predicted from the Ni-Cr-Mo ternary phase-diagram. The results in this work validate earlier studies reported in the literature with a reasonable level of confidence. The long-term metallurgical stability of Alloy 22 is dependent on the dissolution of its secondary phases and its study is important to establish additional criteria before it is put in service. |
