Zhang Hongjia, Sui Tan, Salvati Enrico, Daisenberger Dominik, Lunt Alexander J G, Fong Kai Soon, Song Xu, Korsunsky Alexander M
Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK.
Department of Mechanical Engineering Sciences, University of Surrey, Guildford GU2 7XH, UK.
Materials (Basel). 2018 Mar 15;11(3):427. doi: 10.3390/ma11030427.
High energy 2D X-ray powder diffraction experiments are widely used for lattice strain measurement. The 2D to 1D conversion of diffraction patterns is a necessary step used to prepare the data for full pattern refinement, but is inefficient when only peak centre position information is required for lattice strain evaluation. The multi-step conversion process is likely to lead to increased errors associated with the 'caking' (radial binning) or fitting procedures. A new method is proposed here that relies on direct Digital Image Correlation analysis of 2D X-ray powder diffraction patterns (XRD-DIC, for short). As an example of using XRD-DIC, residual strain values along the central line in a Mg AZ31B alloy bar after 3-point bending are calculated by using both XRD-DIC and the conventional 'caking' with fitting procedures. Comparison of the results for strain values in different azimuthal angles demonstrates excellent agreement between the two methods. The principal strains and directions are calculated using multiple direction strain data, leading to full in-plane strain evaluation. It is therefore concluded that XRD-DIC provides a reliable and robust method for strain evaluation from 2D powder diffraction data. The XRD-DIC approach simplifies the analysis process by skipping 2D to 1D conversion, and opens new possibilities for robust 2D powder diffraction data analysis for full in-plane strain evaluation.
高能二维X射线粉末衍射实验广泛用于晶格应变测量。衍射图谱从二维到一维的转换是为全图谱精修准备数据的必要步骤，但在晶格应变评估仅需要峰中心位置信息时效率较低。多步骤转换过程可能会导致与“结块”（径向分箱）或拟合程序相关的误差增加。本文提出了一种新方法，该方法依赖于对二维X射线粉末衍射图谱进行直接数字图像相关分析（简称为XRD-DIC）。作为使用XRD-DIC的一个例子，通过使用XRD-DIC和传统的带拟合程序的“结块”方法，计算了Mg AZ31B合金棒在三点弯曲后沿中心线的残余应变值。不同方位角应变值结果的比较表明两种方法之间具有极好的一致性。使用多个方向的应变数据计算主应变和主方向，从而实现平面内全应变评估。因此得出结论，XRD-DIC为从二维粉末衍射数据进行应变评估提供了一种可靠且稳健的方法。XRD-DIC方法通过跳过二维到一维的转换简化了分析过程，并为用于平面内全应变评估的稳健二维粉末衍射数据分析开辟了新的可能性。
