Microstructure changes caused by annealing of U-Pu-Zr alloys

Thermally induced microstructural changes in five uranium-plutonium-zirconium alloys (38U-22Pu-40Zr, 49U-19Pu-32Zr, 33U-27Pu-40Zr, 19U-41Pu-40Zr, and 20U-12Pu-68Zr, compositions in at%) were examined by comparing as-cast alloys with alloys that had been annealed at 500 °C for 168 h using scanning electron microscopy. All of the as-cast and annealed alloys had high-Zr inclusions not predicted from currently available phase diagrams. Microstructures in all alloys except U-12Pu-68Zr demonstrate increasing development of irregularly shaped polygons with high-actinide, low-Zr boundaries as a result of annealing.