Strain mapping of individual grains using diffraction contrast tomography

本研究项目的目的是通过在高能同步加速器X射线辐射光束线上使用衍射衬度断层扫描（DCT），对两种类型的多晶合金，即低间隙钢和商业纯钛（每种材料都具有非常不同的晶体结构，这对变形机制有很大影响）的塑性变形的早期阶段进行基础研究。衍射衬度层析成像是一种新型的多晶体晶粒和取向映射技术，它允许人们同时非破坏性地和在3D中表征多晶体材料中大量晶粒的晶粒形状和晶体取向。这项技术已实施在欧洲同步辐射设施（ESRF）光束线ID 19只是最近和数据分析方面的实质性进展，导致铝和钢样品中的1000个晶粒的重建。迄今为止，所有的衍射衬度层析成像工作都是在完全再结晶和未变形的材料上进行的，这是由于在使用高镶嵌性材料时，有限的对比度和扩散的衍射斑点。该项目的目的是将DCT提升到一个新的水平，使其能够测量塑性变形开始期间单个晶粒之间弹性应变的发展。这种弹性应变的发展是由于晶粒的晶体学各向异性，并可用于研究变形机制。这种测量将通过增强DCT实验过程中的扫描程序和数据分析程序的进步来实现。以这种方式记录的数据将首次提供晶粒间的应变/应力信息，这些信息可用于开发和验证晶体塑性有限元建模。

This research project will aim to undertake a fundamental study of the early stages of plastic deformation in two types of polycrystalline alloys, low interstitial steel and commercially pure titanium (each material has a very distinct crystal structure, which has a strong impact on the deformation mechanisms), by using diffraction contrast tomography (DCT) on high-energy synchrotron x-ray radiation beam lines. Diffraction contrast tomography is a novel polycrystal grain and orientation mapping technique, which allows one to simultaneously characterize nondestructively and in 3D the grain shape and crystallographic orientation of a large number of grains in a polycrystalline material. This technique has been implemented at the European Synchrotron Radiation Facility (ESRF) beamline ID19 only very recently and substantial progress in terms of data analysis has led to the reconstruction of 1000 grains in aluminum and steel samples. To date, all diffraction contrast tomography work has been on fully recrystallised and undeformed material due to the limited contrast and diffused diffraction spots when working with material of high mosaicity. The aim of this project is to take DCT to the next level enabling the measurement the development of elastic strain between individual grains during the onset of plastic deformation. This elastic strain develops due to the crystallographic anisotropy of grains and can be used to study deformation mechanisms. Such measurements will be achieved by enhancements of the scanning procedures during DCT experiments and advances in the data analysis routine. The data recorded in this way will for the first time provide grain to grain strain/stress information, which can be used to develop and validate crystal plasticity finite element modeling.