3-11. Synchrotron-based, in situ, real time, multiscale X-ray diagnostic techniques for investigating deformation and damage of materials

Lei Lu¹, Sheng-Nian Luo^1,2,*

1. School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031

2. The Peac Institute of Multiscale Sciences, Chengdu, Sichuan, 610031

Abstract: Learning from biological genetic engineering technology, “Materials Genome Engineering” investigates the relationship between material structure and performance, and prepares new materials with specific properties through structural regulation, so as to shorten the research and development cycles of new materials and lower the corresponding costs. For the current material science research, it is indispensable to efficiently establish the link between material structure and performance. Multiscale synchrotron-based X-ray diagnostic techniques with excellent spatial and temporal resolutions, establish a one-to-one correspondence between macroscale-mesoscale-microscale deformation and time, which provides a high-throughput characterization capability for evaluating material service behavior and building a database on material structure and performance. In this paper, multiscale X-ray diagnostic techniques including fast computed tomography (CT) with in-situ loading and multi-field material test system (MTS) are presented; such techniques can realize in situ, real time measurements on macroscale stress-strain curves, mesoscale displacement and strain fields, and microscale lattice deformation for deformation and damage of magnesium, titanium and other engineering materials under coupled multi-fields. High-throughput characterization of macroscale-mesoscale-microscale deformation and damage, reveals the deformation and damage mechanisms of materials at different spatial scales and their connections, providing a physical basis for the design and preparation of new materials.

A miniature MTS fixed to an air-bearing rotary stage is utilized to load the specimen. In the meantime, high-flux X-rays are applied for imaging. The transmitted X-rays impinge on the scintillator and recorded by high-speed cameras, realizing fast CT with in-situ loading. The macroscale stress-strain curve is obtained by strain/stress gauges. X-ray imaging sequences obtained at different strains are processed by a rapid reconstruction code to achieve three-dimensional (3D) image sequences of microstructure evolution. Then 3D displacement and strain fields are obtained by processing the 3D imaging sequences with digital volume correlation method. 3D deformation and damage of an aeronautical foam are studied. The homogeneity of 3D strain field is accurately measured, and the nucleation and growth of local deformation bands are investigated.

An MTS with coupled multi-fields is utilized to load the specimen under high/low temperature environment, and X-ray imaging and diffraction measurements are applied. The transmitted and scattered X-rays are incident on imaging and diffraction scintillators and recorded by high-speed cameras to achieve simultaneous in-situ X-ray phase contrast imaging and diffraction measurements. A size-variable X-ray slit is designed for large field-of-view imaging and small field-of-view diffraction, maintaining a large imaging field while improving the quality of X-ray diffraction data. The macroscale stress-strain curve is obtained by strain/stress gauge. The X-ray imaging sequences are processed by digital image correlation to obtain mesoscale displacement and strain fields, and X-ray diffraction data are analyzed to quantify the microscale lattice deformation or phase transition; in addition, we develop a GPU-accelerated atom-based polychromatic diffraction (GAPD) simulation code to help experimental design and data analysis. The tensile deformation parallel to normal direction and compressive deformation perpendicular to the normal direction of a rolled magnesium alloy are investigated. Microscale X-ray diffraction results indicate massive deformation twins are activated for both cases, while the growth rate of compression-induced twins is higher than that of tension-induced twins. Mesoscale strain fields show twin-induced delocalization occurs at lower strain under compression than tensile loading. Macroscale stress-strain curves exhibits tension-compression asymmetry.

Keywords: High-throughput; Multiscale; X-ray; Material test system; Computed tomography

Figure Schematic of the multiscale diagnostic techniques for fast CT with in situ loading (left) and multi-field coupling MTS (right).

原位加载快速CT（左）和多场耦合MTS（右）多尺度诊断平台

材料变形损伤的同步辐射X射线多尺度原位实时诊断技术

卢磊¹，罗胜年^1,2,*

1. 西南交通大学材料科学与工程学院，成都 610031

2. 顶峰多尺度科学研究所，成都 610031

摘要：“材料基因工程”借鉴生物学上的基因工程技术，探究材料结构与性能之间的关系，并通过调控结构制备出具有特定性能的新型材料，从而缩短新型材料的研发周期，降低研发成本。如何高效建立材料结构与性能之间的联系成为当前材料科学研究中不可或缺的一部分。同步辐射X射线多尺度诊断技术，以其优异的时空分辨率实现了宏观-细观-微观变形与时间演化的一一对应，为评估材料服役行为及建立材料结构-性能数据库提供了一种高通量表征方法。本文详细介绍了原位加载快速计算机断层扫描(computed tomography, CT)和多场耦合材料试验机(material test system, MTS)多尺度诊断技术，实现了多场耦合下镁/钛等新型工程材料变形损伤过程中宏观应力应变、细观位移场应变场和微观组织结构演化的原位实时测量。宏观-细观-微观尺度变形损伤的高通量表征，揭示了不同空间尺度下新型工程材料的变形损伤机制并建立联系，为新型材料设计与制备提供物理基础。

原位加载快速CT多尺度诊断技术采用高通量X射线照射微型MTS加载下的新型工程材料，微型MTS固定在高精度气浮转台上并且随之快速转动，透射X射线经闪烁体转化为可见光后被高速相机记录。不同应变下的X射线成像序列经快速重构程序处理得到微观组织结构演化的三维图像序列，三维图像序列经数字体相关方法处理得到细观尺度的三维位移场和应变场，应力计提供宏观尺度的应力-应变曲线。利用该方法开展了航空泡沫材料的三维变形与损伤研究，准确测算三维应变场的均匀性，获得航空泡沫材料的局部变形带成核与演化规律。

多场耦合MTS多尺度诊断技术采用高光通量X射线照射高/低温MTS加载下的新型工程材料，透射和散射X射线经闪烁体转化为可见光后被高速相机记录，分别实现X射线相衬成像和衍射原位测量。实验设计一种狭缝尺寸可动态调节的X射线快门，同时实现了大光斑X射线相衬成像和小光斑X射线衍射，在提升X射线衍射数据质量的同时保持了较大的X射线相衬成像视场。应力计提供宏观尺度的应力-应变曲线，X射线成像序列经数字图像相关方法处理得到细观尺度的位移场和应变场；运用基于原子构型的超大规模图形处理器加速X射线衍射模拟程序GAPD分析X射线衍射数据，用以量化微观晶格尺度的变形或相变。利用上述方法探究镁合金板材平行轧面法向的拉伸变形和垂直轧面法向的压缩变形，微观尺度X射线衍射表明二者均激发出大量孪晶且压缩诱导的孪生速率明显高于拉伸诱导孪生速率，细观尺度上压缩加载下的应变场去局域化过程先于拉伸加载结束，宏观尺度上应力-应变曲线表现为拉压不对称变形。

关键词：高通量；多尺度；X射线；材料试验机；CT