铀基高熵合金相结构稳定性及强韧机制的原位中子衍射研究

Metallic nuclear fuel is the main fuel for nuclear energy devices such as fusion-fission hybrid reactors and fast neutron reactors. Uranium-based high-entropy alloys are expected to be an important candidate for commercial nuclear fuels due to their unique advantages in phase structure, mechanical properties and radiation resistance. In this project, based on UTiNbMoCr (biphasic solid solution), UTiZrNbMo (single phase solid solution) and UTiZrNbCr (solid solution + gap compound) three typical phase structure uranium-based high-entropy alloy system, by using machine learning and EMTO-CPA method, the alloy composition will be firstly optimized. Then, several alloy ingots and mechanical tensile specimens with uniform composition and compact structure will be prepared. The samples will be comprehensively analyzed by XRD, AES, FIB and TEM, combined with in-situ neutron diffraction technique to monitor the response parameters of alloy microstructure during in-situ temperature change and force-heat composite loading, in order to determine the temperature evolution and toughness of alloy phase structure. Based on theoretical and experimental researches, the intrinsic relationship among "alloy composition-temperature-microstructure and mechanical properties" will be constructed, and the phase structure stability and strengthen-toughness deformation mechanism of uranium high entropy alloy are also explored. All results obtained from this project will provides theoretical and technical supports for the full design of novel uranium high entropy alloys in advanced nuclear reactor in future.

金属型核燃料是聚变-裂变混合堆和快中子堆等核能装置的主要燃料，铀基高熵合金因其在相结构、力学性能稳定和耐辐照等方面的独特优势，成为未来先进商用核燃料的重要候选材料。本项目拟以UTiNbMoCr（双相固溶）、UTiZrNbMo（单相固溶）和UTiZrNbCr（固溶+间隙化合物）三种典型相结构铀基高熵合金体系为基础，采用机器学习、EMTO-CPA方法对合金成分进行优化设计，并制备出合金母锭和力学拉伸试样；综合利用XRD、AES、FIB和TEM等手段对样品进行精细结构表征；结合原位中子衍射技术，监测原位变温及力-热复合加载过程中合金微观结构的响应参数，确定合金相结构的温度演变规律和强韧化主控变形机制；综合理论和实验研究结果，构建“合金组分-温度-组织结构与力学性能”间的内在联系，获得铀基高熵合金相结构稳定性和高温强韧化变形机制，为铀基高熵合金在未来先进燃料材料领域的应用提供理论基础和技术支撑。

金属型核燃料是聚变-裂变混合堆和快中子堆等核能装置的主要燃料，铀基高熵合金因其在相结构、力学性能稳定和耐辐照等方面的独特优势，成为未来先进商用核燃料的重要候选材料。本项目以UTiNbMoCr（双相固溶）、UTiZrNbMo（单相固溶）和UTiZrNbCr（固溶+间隙化合物）三种典型相结构铀基高熵合金体系为基础，采用半经验公式、机器学习、EMTO-CPA方法对合金成分进行优化设计，并制备出系列合金母锭和力学拉伸试样，指出有效构型熵是影响铀基高熵合金相稳定性的重要因素；综合利用XRD、OM、DSC、FIB和TEM等手段对样品进行精细结构表征，指出铀基高熵合金满足二元固溶体合金H-R形成准则，晶格扭曲是影响单/双相的形成重要因素，单相高熵合金力学性能优于双相高熵合金，且双相高熵合金中的脆性BCC相的存在会严重恶化高熵合金的力学性能；结合原位中子衍射技术，首次监测到原位变温及原位加载过程中合金微观结构的响应参数，确定了合金相结构的温度演变规律，证实富铀高熵合金DSC测量中的吸热峰是γ相过饱和固溶体的分解导致的，而在原位压缩过程中铀基高熵合金强韧化主控变形机制是位错滑移，在加载过程中(110)、(002)、(112)三个晶面的点阵应变呈现明显各向异性，在初始弹性阶段，上述三个晶面的响应也呈明显各向异性，(002)晶面对应的弹性模量最小（或最软），三个晶面点阵应变在约1.1GPa时出现拐点现象，即在高于该应力区，随着应力增大，点阵应变反而区域减小。对于典型的UNbHf合金应力低于0.8GPa时，ρ值基本在1.4×10^14~1.9×10^14 m-2范围内变化、起伏较小；而应力约1.4GPa时，位错密度增大至4倍左右。综合理论和实验研究结果，揭示了“合金组分-温度-组织结构与力学性能”间的内在联系，获得了铀基高熵合金相结构稳定性和强韧化变形机制，为铀基高熵合金在未来先进燃料材料领域的应用提供理论基础和技术支撑。