Zr基非晶合金耐中子辐照性的微观机理研究

China has largely developed its own nuclear industry since the begging of the 21 century to satisfy the demand for more energy. It is very important to run the nuclear reactors efficiently and safely. So far, various crystalline alloys are largely applied in the reactors, serving as nuclear materials. However, these alloys suffer from the neutron radiation during the long-term service that their structures are destroyed at the micro-, meso- and macroscopic-scales, resulting in the failure of their properties. The essential reason for this phenomenon is that there is a conflict between the random motion of the excited atoms induced by neutron radiation and the long-range ordering in the crystalline alloys. This conflict is supposed to be avoided in amorphous alloys, because such glassy materials have no long-range orderings at all. In other words, the amorphous alloys are expected to have perfect resistance of the neutron radiation. In this proposal, the Zr-based amorphous alloys will be selected as the prototype to research their resistance of the neutron radiation. The state-of-the-art synchrotron radiation-based experiments coupled with simulations will be applied to build the structural models of the selected Zr-based amorphous alloys. The combination of the particle transport technique and the molecular dynamics calculation will be carried out to simulate the effect of materials radiated by the neutrons, from which the structural evolution of the models can be probed. In particular, the initiation, spread and annihilation of the defects caused by the radiation-excited atoms will be focused on. Understanding the mechanism of the resistance of neutron radiation in amorphous alloys is expected, which may guide the development and preparation of nuclear materials with high resistance of neutron radiation in alloy systems.

目前，我国核能发展方兴未艾，核反应堆的安全和高效运行至关重要。核反应堆多选用各种晶态合金材料作为部件材料，但在经受长期中子辐照后均存在微观、介观甚至宏观结构变异以及性能失效等问题，从而影响部件材料甚至反应堆的服役寿命。该现象的根本原因在于受辐照激发原子的随机迁移性与晶体内部结构的有序性之间存在矛盾。而作为新型的合金类材料，非晶合金具有类似玻璃的无序态结构特征，上述矛盾可望得以弱化甚至避免，从而可能具有良好的耐辐照性。本申请课题拟选用Zr基非晶合金材料，利用同步辐射技术对其进行结构标定和建模，再利用粒子输运技术模拟中子辐照条件，在分子动力学的计算框架下（可加入温度和压力等势场），研究结构模型的微观原子结构演化，重点探索受辐照激发原子引起的微观缺陷的萌生、发展与变化，从而揭示其耐中子辐照能力与形成机制。本工作立足于利用结构调控的研究思路，可望为新型耐中子辐照的合金材料的制备和筛选提供理论依据。

本项目关注Zr基非晶合金对中子辐照的结构响应，以评判非晶合金在中子辐照环境下的结构稳定性，主要研究内容和成果如下：.一、判定了Zr基非晶合金的耐辐照结构稳定性。对非晶合金样品进行了快中子辐照实验，对比未辐照样品，进行结构测试，发现两者结构信息差异不大，且辐照后样品保持完全非晶，证实非晶合金样品在中子辐照后结构稳定，不发生非晶到晶体的结构相变，主要表现为非晶结构自身的轻微精细结构变化。.二、研究了辐照后Zr基非晶合金的结构演化。发现非晶合金在辐照后到结构稳定存在几个中间过程：级联效应阶段、缺陷湮灭阶段、自由体积重分布阶段和结构弛豫稳定阶段，与晶体既有相同级联效应阶段，又存在独特或有差异的过程。充分表明非晶合金的辐照结构自修复具有独特性。.三、研究了非晶合金辐照结构耐辐照的微观机制。发现非晶合金经中子辐照后，产生类空位缺陷，其极不稳定，迅速被邻近原子协同挤压而湮灭，同时自由体积因此而增多增大，但带来结构不稳定和能量不平衡问题，因此自由体积自发进行重排重分布，在细化自由体积的同时通过扩散趋向均匀分布于非晶体内，即为结构自修复与弛豫过程。最终达到结构稳定和能量平衡，保持非晶结构，与未辐照结构非常相似。这表明，非晶合金具有优异的耐中子辐照结构稳定性。.四、研究了元素选择对非晶合金辐照结构变化的影响。发现Zr元素的特征信息在辐照后的变化较明显，而Cu、Ni元素等相对不明显。表明这三种元素中，辐致结构变化主要围绕Zr元素发生，即元素选择对提高非晶合金的辐照结构稳定性具有重要参考价值，这是晶体材料选择耐辐照材料所不具备的。.我们的研究成果表明，非晶合金具有优异的耐中子辐照稳定性，能高效地自修复辐照结构缺陷，保持其非晶结构的稳定。并且辐致结构变化具有元素依赖性，即我们可以通过调控合金体系或成分，以筛选具有优异耐中子辐照的非晶合金材料。本研究为耐中子辐照新型材料的研发工作提供了一种思路和初步尝试，具有重要的科研价值。