中子衍射在核电工程材料中的应用

中子衍射为工程材料组织结构、微观缺陷、残余应力等材料特性的精确测量、分析与表征提供了独天得厚的科研保障,是工程材料制备工艺的优化、工程构件的安全维护、以及关键工程设备的长寿命设计、安全评价以及延寿论证工作的理想工具。概述了中子衍射测量的基本原理,回顾了中子衍射技术在核电结构焊接应力工程与延寿技术,焊接热处理工艺辅助优化等方面的应用,最后根据中子衍射工程谱仪的特点,展望了此技术在材料研究领域的未来前景。     

中子衍射技术测量残余应力的研究进展

随着我国中子大科学装置技术的发展和进步,中子衍射技术已广泛应用于航空、航天、核电、汽车等各领域.本文介绍中子衍射残余应力测量原理及相关基础知识,与其他深部应力测试结果进行对比,中子衍射具有高穿透力,是无损获得材料及工程部件内部三维应力的最有效方法,尤其适用于局域位置的应力测量,在工程部件残余应力测试与分析,揭示制造加工...     

材料热处理中子散射研究

作为新一代微观结构表征技术，中子散射正广泛应用于材料科学、物质科学、生物科学等诸多学科领域。本文仅就其在钢铁热处理领域的应用作一简要综述，包括热膨胀／收缩特性、扩散转变、马氏体转变、回复与再结晶，还涉及奥氏体预变形对铁素体转变的影响、马氏体BCT晶体结构在回火过程中的轴比变化、热应力与相变残余应力等，指出在新一代中子源建成后中子衍射技术将得到进一步广泛应用和快速发展。     

利用中子衍射法和轮廓法测定GH4169圆盘残余应力

分别采用中子衍射法和轮廓法对服役态GH4169合金圆盘工件内部残余应力分布特征进行表征。两种测试技术的机理完全不同,测量结果互相对比验证后,确定出较高可信度的残余应力测量结果。首先利用飞行时间中子衍射技术准确表征了GH4169合金圆盘完全热处理后轴向、径向和周向的应力,其量级约为-300~300 MPa,以周向和径向残余应力为主,沿轮廓呈“外压内拉”特征分布;利用轮廓法测量沿直径截面周向残余应力的二维分布图,切割截面周向残余应力呈现明显的“外拉内压”式分布特征的残余应力,残余应力量级约为-300~250 MPa量级。合金盘厚度中心截面上,中子衍射法与轮廓法的测试结果从趋势和绝对数值上基本一致,测试结果可信度高。     

利用中子衍射法和轮廓法测定GH4169圆盘残余应力

分别采用中子衍射法和轮廓法对服役态GH4169合金圆盘工件内部残余应力分布特征进行表征。两种测试技术的机理完全不同，测量结果互相对比验证后，确定出较高可信度的残余应力测量结果。首先利用飞行时间中子衍射技术准确表征了GH4169合金圆盘完全热处理后轴向、径向和周向的应力，其量级约为-300~300 MPa，以周向和径向残余应力为主，沿轮廓呈“外压内拉”特征分布；利用轮廓法测量沿直径截面周向残余应力的二维分布图，切割截面周向残余应力呈现明显的“外拉内压”式分布特征的残余应力，残余应力量级约为-300~250 MPa量级。合金盘厚度中心截面上，中子衍射法与轮廓法的测试结果从趋势和绝对数值上基本一致，测试结果可信度高。     

中子衍射在残余应力分析中的应用

中子衍射应力测量原理基于布拉格方程,通过取样测量体积内样品晶格的晶面间距进行精确表征,获取材料微观晶格的形变信息,可以实现晶体材料深层内部弹性应变的直接无损测量.测量值通常与样品测量位置和外加温度或力学载荷相关,用于评估实际部件整体结构和变形参数.本研究介绍中子衍射的基本原理,辊压法调控搅拌摩擦焊的残余应力和变形、管道...     

航空材料组织与残余应力评价对中子散射与同步辐射技术的需求

航空材料是航空装备发展的基础，航空材料及其构件从研发、制造、服役、维修到重大事故（故障）的失效分析等全寿命周期中，检测与表征技术起着关键性作用。本研究以问题与需求为导向，结合具体案例，阐述了航空材料及其构件在新材料研发、构件制造、产品服役与可靠性评估、重大事故（故障）的失效分析中，现有检测手段存在如不能无损地开展构件内部组织结构、残余应力等表征与评价方面的不足，以及航空材料在组织结构、残余应力等表征与评价中对于中子散射和同步辐射大科学装置技术的迫切需求，提出了发展航空中子应力谱仪、加强中子散射与同步辐射技术在航空材料中的技术开发与应用研究等建议。     

中子无损表征技术及其在失效分析中的应用

材料或部件在加工及服役过程中产生的残余应力、缺陷、织构和纳米析出相,成为影响服役性能及使用安全的重要因素。由于中子具有对特定材料深穿透性强、对较轻元素及同位素敏感的特性,使其成为无损表征的重要手段。通过列举中子散射及中子成像技术在材料及部件内部的残余应力、织构、纳米析出相和缺陷的典型应用示例,证明中子无损表征技术在材料失效分析中具有独特的优势,是改善加工工艺及延长服役寿命的重要支撑手段。     

中子反射及其在界面腐蚀研究中的应用

中子反射是一种先进的界面和薄膜材料表征手段。其技术特点使之能在众多研究领域，包括界面氧化腐蚀等工业相关领域，发挥积极作用。文章简要介绍中子反射技术，综述其在界面腐蚀研究中的应用，分析和展望相关研究的前景。     

中子衍射残余应力无损测量与谱仪研发

简要介绍了中子衍射残余应力无损测量方法和位于中国先进研究堆旁的国内第一台致力于深度、三维、无损中子衍射残余应力测量谱仪的研发,即将为国内的广大用户提供材料科学和工程应用方面的研究和实验平台。     

Combining neutron diffraction and imaging for residual strain measurements in a single crystal turbine blade

Neutron diffraction is a technique often used for the non-destructive characterization of residual stresses in engineering materials and components. Measuring stresses within partially hollow objects with complex internal geometry however is challenging due to the difficulties of accurately placing the measurement gage volume in relation to the internal structures. In this study this difficulty is overcome combining surface metrology and neutron tomography to guide the neutron diffraction measurements. Using this technique the triaxial residual strain variations across the airfoil in a single crystal nickel-based superalloy turbine blade have been measured.     

Application of Neutron Scattering in Earth Sciences

The unique properties of neutron interaction with materials have long been applied to the study of geological materials, with Shull and Smart using them in 1949 to determine the antiferromagnetic structure of manganosite (MnO). Neutron diffraction provides an accurate method for crystal structure determination of hydrous phases, particularly ices, and investigations of cation ordering of elements that are adjacent in the Periodic Table, such as Al–Si in feldspars and zeolites. Both elastic and inelastic scattering have been used to determine the properties of fluids that are present in many sedimentary rocks, including shales that are often saturated with brines or hydrocarbons. Due to minimal absorption and deep sample penetration, neutron scattering has become a favorite tool for crystallographic preferred orientation (texture) analysis of rocks as well as destruction-free three-dimensional (3D) tomographic characterization of microstructures.     

Advanced Postirradiation Characterization of Nuclear Fuels Using Pulsed Neutrons

Methods for postirradiation characterization of bulk (cm³) irradiated materials or even spent nuclear fuels are sparse due to their extremely radioactive nature. While several methods exist to characterize smaller volumes (<?1 mm³) of such samples, selecting these volumes from larger samples is challenging. X-ray-based methods are prohibitive due to the strong γ-radiation from the sample flooding the detectors. Neutron-based methods available in the proximity of irradiation reactors allow for thermal neutron radiography or computed tomography using a small reactor source, but one cannot assess isotope distributions or microstructural features such as phases, texture, or strain from diffraction measurements due to flux limitations. We present herein a pathway to provide pulsed neutron characterization of bulk irradiated samples using time-of-flight neutron diffraction for microstructural characterization and energy-resolved neutron imaging for assessment of isotopic densities and distributions. Ultimately, laser-driven pulsed neutron sources may allow deployment of these techniques pool-side at irradiation reactors.

     

Neutron diffraction studies of permanent magnetic materials

Neutron diffraction technology as an advanced material research technique has special advantages in studying magnetic materials compared to the conventional techniques such as X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).In this review,the applications of neutron diffraction technology on permanent magnetic materials were briefly reviewed:(1) the determination of the crystal structure and magnetic structure of the typical permanent magnet material,(2) in situ neutron diffraction study of the crystal structure evolution of the permanent magnets,and(3) phase transition in permanent magnetic materials.     

Materials science applications of inelastic neutron scattering

Inelastic neutron scattering measures the dynamical processes in materials, as opposed to spatial arrangements of atoms. A neutron diffraction pattern is obtained from measurements of the momentum transfer between the neutron and the sample. Inelastic neutron scattering includes the additional dimension of energy. This paper explains concepts, describes instrumentation, and gives a few materials applications for inelastic neutron scattering.     

Orientation stress field analysis in polycrystalline bcc steel using neutron diffraction

We propose a methodology associating texture determinations and strains measurements by neutron diffraction in order to analyse the stress fields within families of crystallites with the same crystallographic orientation in polycrystalline materials. This stress analysis method allows an intermediate approach between a local and a global scale characterization within the bulk of massive samples, and appears promising for coupling with modelling methods due to the statistically representative informations it provides. We report here its application to characterize in situ the mechanical behaviour under uniaxial tension of a low alloyed 16MND5 bainitic steel used for nuclear reactor pressure vessels. It appears that the selected investigated phases exhibit very different mechanical responses. A large plastic deformation heterogeneity is observed.     

The application of neutron diffraction to engineering problems

After more than two decades of extensive development, neutron diffraction has become an essential research tool for the study of mechanical behavior in materials. This article will focus on how information obtained from the diffraction peak position and width is used to answer important questions concerning the mechanical behavior of materials. The principle of strain measurements is described, and the concept of strain mapping is introduced. Examples are presented to illustrate the application of neutron diffraction to engineering problems, and new research opportunities are discussed that will be enabled by the next generation of instruments.