Growth kinetics of intermetallic phases in U-Mo vs. Al alloy diffusion couples annealed at 550°C

This study examined the growth kinetics of intermetallic phases that develop in solid-to-solid diffusion couples assembled with U-7, 10 and 12wt.%Mo vs. Al alloys (Al, Al-2wt.%Si, Al-5wt.%Si, 4043 and 6061) after a diffusion anneal at 550°C for 24 hours. Based on interdiffusion microstructure and integrated interdiffusion coefficients, the addition of Si into the Al matrix alloy was observed to significantly reduce the growth rate of the intermetallic layer that primarily consisted of (U,Mo)Al₄ phase. Growth rate of the (U,Mo)Al₄ intermetallic layer also increases slightly with Mo content; however, it was not significant compared to the effect of alloying Si into Al alloys. Growth kinetics of (U,Mo)Al₄ intermetallic layer appear highly sensitive to composition of U-Mo fuel alloy and Al cladding alloys, and must be an important criteria in alloy development/selection for optimum fuel performance with due consideration for composition-dependent multicomponent interdiffusion.