强流脉冲电子束贫铀表面抛光与强化机理研究

Uranium, due to its specific nuclear properties, is widely used in applications such as national defense，nuclear energy and precision physics experiments. However, uranium is highly reactive due to its extremely low standard electropotential, impurities and elements segragation during metallugical processing of uranium. These factors combined facilitate corrosion and the decrease of surface strength of uranium in service. On the other hand,modern precision physics experiments pose requirement of a highly flat surface of uranium sample. However, the preparation of such flat surface nowadays mainly depending on old-fashion metallurgical polishing. Thus, there exist urgent demands of development of new surface polishing and strengthening techniques and also a thorough understanding of the mechanisms implied..High current pulsed electron beam technique，as an emergent powerful tool for surface modification of materials, is drawing more and more attention. This proposal focuses on exploring of the technique and mechanisms of polishing and strengthening uranium surface via high current pulsed electron beam irradiation. The surface unflatness (including microcracks and geometry roughness) can be removed by tuning the energy deposited onto uranium surface through adjusting high current pulsed electron beam parameters. Meanwhile, mechanisms resulting in improved surface properties could be generated through thorough understanding of the changes in the microstructure and compositions within the irradiation affected layer.

金属铀因其独特核性能使之广泛应用于国防、核能和精密物理实验等领域。但铀化学性质十分活泼，冶金过程中也容易形成夹杂和元素偏析，使得铀在使用过程极易发生腐蚀和表面强度的下降。另一方面，精密物理实验对材料表面平整度提出了较高要求，目前制备手段主要还停留在人工抛光的阶段。因此，开展贫铀表面抛光与强化的相关研究十分有意义。强流脉冲电子束作为一种新兴的表面改性技术手段，其在金属材料表面抛光化的作用正受到人们日益关注。本项目在考虑强流脉冲电子束与贫铀相互作用的基础上，进行贫铀强流脉冲电子束处理的理论模拟工作，深入探讨相关的抛光与强化机理：结合实验研究强流入射束能量参数与贫铀表面微观不平整之间的关系，例如去除附着残留物、控制表面微裂纹和几何粗糙度等，深入认知铀材料表面抛光机理；通过实验研究处理样品表层组织、成分等因素与表面性能之间的关系，深入认识表面强化的机理。

本项目通过分析强流脉冲电子束与贫铀材料的相互作用过程建立了热力耦合模型。通过大量文献调研获得了贫铀的热物理、力学性能参数。通过计算采用脉冲电子束加速电压27kV，脉冲持续时间2μs和能量密度3J/cm2等参数分别对500#砂纸和机加态样品分别进行了10次、20次和30次强流脉冲电子束表面处理。获得的贫铀原始样品晶粒大小在数百微米量级。处理后，样品表面仍然呈现alpha单相贫铀。但由于贫铀在空气或水汽气氛的高反应活性，表面生成了较复杂的铀氧化物。处理后样品的表面砂纸磨痕和机加纹理基本消失，且机加后的表面呈现龟裂状态。表面粗糙度分析表明两种表面状态的样品处理后的粗糙度呈现先降后升的规律，10次脉冲处理后样品表面粗糙度最低。研究表明强流脉冲电子束诱发的表面熔坑喷发及表面反复重熔机制实现了不同表面状态的低碳贫铀样品表面抛光效果。