铀基包晶合金的液态热物理性质与组织形成机理研究

As one of the promising candidates for research and test reactors, U-based alloy fuels have received much attention due to their high uranium density. Thus, it is essential to investigate the phase selection, microstructure evolution, mechanical properties of U-based alloy fuels. The typical U-Al/Si/Mo peritectic alloy fuels are chosen as the study objects in the present project. The thermophysical properties of liquid U-based peritectic alloy fuels are investigated by molecular dynamics simulations, which provide the indispensable original data for the dynamic analysis of rapid solidification. Rapid solidification of U-based peritectic alloy fuels are accomplished by melt spinning technique. The microstructures, mechanical properties of samples solidified at different cooling rates are investigated. Moreover, the orientation relationship and high-resolution structure at the phase boundary of the primary and peritectic phases are analyzed by EBSD and TEM, respectively. Based on the above results, the mechanism of competitive nucleation between the primary and peritectic phases are discussed. This project may cast light for the development of high-performance U-based alloy fuels.

铀基合金燃料是下一代高性能研究试验堆的首选燃料，对其制备过程中的相选择、微观组织控制和应用性能等关键科学问题进行研究具有重要意义。本项目以研究试验堆用U-Al/Si/Mo二元包晶型合金燃料为研究对象，采用分子动力学方法在宽广的温度范围内计算液态铀基包晶型合金的热物理性质，为其快速凝固理论研究提供必不可少的基础数据。利用单辊急冷技术实现铀基包晶型合金的快速凝固，研究凝固组织随冷却速率的演变规律，确定发生相选择的动力学条件，阐明初生相与包晶相竞争形核机制，探明初生相与包晶相两相取向关系以及相界面高分辨结构，建立样品的力学性能与冷却速率的关系；为开发新型铀基合金燃料奠定理论基础。

铀基合金燃料是下一代高性能研究试验堆的首选燃料，对其液态热物理性质及其制备过程中的相选择、微观组织控制等关键科学问题的研究具有重要意义。本项目采用分子动力学方法对液态U-Al/Si合金体系的热物理性质与温度和成分的依赖关系进行了理论模拟，模拟内容包括熔点、密度、热膨胀系数、比热、扩散系数和过剩体积等，阐明了热物理性质随合金温度和成分的变化规律；为铀基合金快速凝固理论研究和开发新型核燃料提供必不可少的基础热力学数据。此外，还在宽广的温度范围内对液态U和U-Al合金的局域结构进行研究，揭示了熔体中的化学短程有序和拓扑短程有序特征；探索了局域结构随温度的演变规律，建立了液相结构与结晶相结构的内在联系，研究了局域团簇结构对晶体形核、相稳定性的作用机制。制备了不同冷却速率的铀基包晶合金样品，对其凝固组织、力学性能进行表征，研究了初生相与包晶相竞争形核与生长机制。

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