Microstructural evolution in Zr3Al-based alloys during various long-time annealing treatments

The Zr3Al-based intermetallics have been considered as candidate materials for structural components in pressurized heavy water nuclear reactors due to their attractive properties. However, these alloys could not be used for structural application in the reactors because of their poor room-temperature ductility and irradiation-induced amorphization. Our recent studies of ternary addition of niobium in Zr3Al have shown some promising results. The present article reports the microstructural evolution in these alloys upon long-time annealing treatments. The formation of various phases, temperature regime of their stability, chemical composition, and volume fraction of these phases during prolonged annealing have also been studied. A pseudobinary phase diagram with varying niobium concentration has also been developed. The morphology and distribution of the Zr3Al phase have been explained on the basis long-range diffusion as the rate-controlling step.