Microstructural evolution of as-cast Th–U alloys

• As-cast Th–U alloy microstructures vary from single phase to biphasic.
• Uranium is present as spheroids (<1 μm), islands (∼7 μm) in high thorium Th–U alloys.
• Uranium forms continuous, interpenetrating network in intermediate alloy compositions.
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• Th–96U eutectic colonies and comparatively lower hardness.
• Substantial grain refinement seen in high thorium Th–U alloys.
• Hardness of Th–U alloys increases steeply up to ∼10.7 wt.% uranium alloying.

Microstructural evolution of as-cast (arc-melted) microstructures of selected compositions of Th–U alloys is investigated. Characterizations are done using XRD, optical microscopy, SEM, TEM and hardness measurement. Microstructures vary from single phase to biphasic with increase in uranium content in thorium. Uranium is present as spheroids (<1 μm) or islands (∼7 μm) in high thorium (<10.7 wt.% U) alloys. With further increase in uranium content it forms an interconnected network of uranium rich phase and gets interspersed with similar network of thorium rich phase. High uranium Th–U alloys has dendrites of thorium dispersed in uranium rich phase. Grain size refinement of thorium rich phase is effective up to ≤10.7 wt.% uranium addition. Hardness of Th–U alloys increases with increase in uranium content. Comparatively lower hardness observed in Th–96U is due to presence of softer eutectic colonies in the microstructures. High thorium alloys have potentials for being utilized as dispersion type fuel with fissile uranium spread in thorium matrix.