Mechanical characterization of U – 9Mo – 3Zr and U – 3Mo – 9Zr alloys

Abstract

U – 9Mo – 3Zr and U – 3Mo – 9Zr alloys were characterized, through hardness and simple bending tests, at different processing stages designed to produce nuclear reactor monolithic fuel elements. Hardness evolution in the U – 9Mo – 3Zr alloys can be understood based on the evolution of γ matrix composition due to precipitation. Hardness evolution in U – 3Mo – 9Zr is more complex and involves the competing roles of both matrix metastable states and its composition evolution. Both alloys show a ductile micromechanism in fracture, presenting dimples at the fracture surface which are affected by size and distribution of Laves precipitates. In the macroscopic scale ductility is limited in both alloys, but U – 3Mo – 9Zr show some residual plastic deformation probably associated with a γ° → α″ stress-induced martensitic transformation. The results are discussed also concerning the potential interaction of U – Mo monolithic fuels and Zr-rich cladding.