Precipitates Morphology in Iron-Diluted U–Fe Alloys

The morphology of U₆Fe precipitates were investigated in the different allotropic states of uranium matrix. The morphology of γ-U is equiaxed and the characteristic size is ~65 μm. The excess dissolved iron in β-U precipitates discontinuously through a eutectoid reaction during cooling at the grain boundaries, while α-phase precipitates have a “needle-like” morphology (in many cases, aspect ratio ≫10) with a well-defined direction in the uranium matrix. This morphology may compensate for the large density differences of ~9 % between α-U and U₆Fe (~19 and ~17.4 g/cm³, respectively) and the fact that precipitation takes place at relatively low temperatures. It was shown that U₆Fe precipitates do not introduce new nucleation sites in β and α phases of uranium.