Structural Insights in the β to α Phase Transformation of the U–1 wt.%Ga–0.2 wt.%Fe Alloy
Tóm tắt
β-U could be metastably retained at room temperature when alloyed with various elements such as gallium. Since iron is a common impurity, we investigated two different kinetic processes which occurs simultaneously; one is the
$$ \beta \to \alpha $$
transformation and the other is the precipitation of the U6Fe phase from the iron dilute U(Ga)–Fe alloy. Furthermore, we determined the solubility of iron and gallium solubility in quenched uranium from 800 to 720 °C (γ and β phase regions, respectively). It was shown that the
$$ \beta \to \alpha $$
phase transformation is sluggish and has a character of massive transformation. The retention from the β phase region does not fully stabilize β phase, and α phase is also formed during quenching, while the γ-quenched sample remains metastable at room temperature, and only high-temperature heat treatment transforms β to α. The precipitates found in the system are U6Fe and U2Ga3, no ternary intermetallics were detected, and the morphology of the precipitates does not depend on the heat treatment course. The gallium and iron contents found in the γ- and β-quenched samples are X
Ga = 0.72 wt% X
Fe = 0.18 wt% and X
Ga = 0.42 wt% X
Fe = 0.06 wt%, respectively. The different gallium contents in the γ and β explain the differences in the
$$ \beta \to \alpha $$
phase transformation kinetics. Quenching U–Ga alloys (above the solubility limit of gallium) from the γ region stabilizes β-U better than quenching from the β region.
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