原位同步辐射掠入射XRD/XAFS研究镍基合金辐照层的微观变形行为

The intrinsic relationship between radiation damage defects and mechanical properties of nuclear alloy materials is always a basic issue in the field of nuclear materials. Ion irradiation is always used to study the irradiation damage effects instead of neutron irradiation. However, it is a challenge to reveal the mechanical properties of ion irradiated metals directly due to a very thin damage layer (less than a dozen micrometers). XRD analysis is only sensitive to long-range order structure, can describe the change of Lattice constant, however can hardly describe the fine structure of materials. XAFS (X-ray absorption fine structure) technique is a sensitive tool for probing the local structure of materials because of its sensitivity to the short-range order and atomic species surrounding the absorbing atoms. And grazing incidence XRD and XAFS can study the microstructure of radiation damage layers from tens of nanometers to a dozen micrometers. To establish the structural change of Nickel-based alloy by irradiation, a combined study of the long-range and short-range structure will be carried out using in situ grazing incidence XRD and XAFS techniques. So，this project intends to study the microstructure and the evolution of the radiation damage layer during tension and reveal the micro-mechanism of the mechanical properties by in situ grazing incident XRD and XAFS.

核能用合金的辐照损伤缺陷与其力学性能之间的内在相关性一直是核材料领域关键基础的问题。人们常采用离子辐照模拟中子辐照研究金属材料的辐照损伤行为，然而，由于离子辐照损伤层很薄（小于十几微米），使直接揭示合金被辐照后的力学性能成为难题。同步X 射线衍射（XRD）可以描述合金晶格常数的变化，同步辐射X射线吸收精细结构谱(XAFS)可对合金中特定元素的缺陷结构进行表征。掠入射XRD和XAFS 可以研究几十纳米到十几微米辐照损伤层的微观缺陷，并且上海光源同步实验XRD和XAFS线站可实现原位拉伸和掠入射测试的组合。因此本项目联合原位掠入射XRD和XAFS 来研究镍基合金在离子辐照后其损伤层的微观结构及其在原位拉伸变形过程中的演化规律，从微观结构演化入手，揭示辐照损伤层力学性能的微观机制。

核能用合金的辐照损伤缺陷与其力学性能之间的内在相关性一直是核材料领域关键基础的问题。在熔盐反应堆中，中子辐照嬗变产物He引起的高温辐照脆化/肿胀将导致合金力学性能劣化、构件使用寿命缩短，成为了限制熔融盐反应堆发展的瓶颈之一。本项目采用同步辐射XAFS和SAXS来研究镍基合金辐照后原子尺度上和纳米尺度上的微观缺陷，通过同步辐射XAFS和SAXS，实现对合金辐照后从原子级别到纳米级别缺陷量化表征。通过同步辐射XAFS发现He辐照对Cr的原子局域结构影响最大，辐照后Cr-Ni配位数减小，Cr周围产生空位，Cr更活泼更易与熔盐中的氧化性杂质反应, 生成Cr-O键, 形成Cr2O3, 而生成的Cr2O3极易溶解在熔盐里，促进了合金的腐蚀。采用原位拉伸XRD发现合金的晶格应变减小与合金辐照硬化成比率, He辐照损伤层屈服强度下降了20Mpa，提供一种测试合金辐照后硬度变化及屈服强度的方法。同时采用原位高能XRD研究发现镍基合金中小尺寸碳化物可以通过载荷转移,提升其屈服强度和塑性，而大尺寸的碳化物由于其位错障碍，容易导致其脆性断裂。基于同步辐射研究镍基合金的成果，指导并制备出更耐辐照，且力学性能更优异的NiMo-Y2O3镍基合金。