Mechanical properties examined by nanoindentation for selected phases relevant to the development of monolithic uranium-molybdenum metallic fuels

Nanomechanical properties, specifically the reduced modulus and hardness of several intermetallic and solid solution phases are reported to assist the development of the U-10 wt% Mo (U-10Mo) monolithic fuel system for research and test reactors. Findings from this study and reported values of mechanical properties provide data critical for understanding and predicting the structural behavior of the fuel system during fabrication and irradiation. The phases examined are products of interdiffusion and reaction between (1) the AA6061 cladding and the Zr diffusion barrier, namely (Al,Si)3Zr and Al3Zr, (2) the U-10Mo fuel and the Zr diffusion barrier, namely UZr2, Mo2Zr, and α-U, and (3) the U (or U-10Mo) and Mo, namely a mixture gradient of α- and γ-phases. The UC inclusions observed within the fuel alloy were also examined. Only phases present in thick or continuous microstructure on cross-sectioned fuel plates and diffusion couples were investigated for reduced modulus and hardness. Concentration-dependence of room-temperature reduced modulus in U solid solution with 0-10 wt% Mo was semi-quantitatively modeled based on mixture of α- and γ-phases and solid solutioning within the γ-phase.