Abstract
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.
Highlights
X-ray powder diffraction (XRD) is a widely used experimental technique that finds extensive application in materials engineering [1,2,3,4,5,6,7,8,9,10]
The major advantage of using Digital Image Correlation (DIC) to analyse 2D X-ray powder diffraction patterns (Debye-Scherrer rings) is that it can avoid the necessity of 2D to 1D conversion and fitting
The accuracy of XRD-DIC technique can be validated by comparison with the results of the conventional ConFit analysis
Summary
X-ray powder diffraction (XRD) is a widely used experimental technique that finds extensive application in materials engineering [1,2,3,4,5,6,7,8,9,10]. Conventional data analysis is a multi-stage process which involves three main steps: calibration, conversion of the 2D pattern(s) into a 1D profile(s), and Gaussian fitting for peak centre determination to calculate strain values. They can arise when collecting diffraction pattern from the positioning of a standard calibration sample, or in the subsequent calculation that involves data reduction and manipulation Useful Gaussian peak fitting demands continuity and symmetry of peaks, which require high quality Debye-Scherrer rings with high intensity and good uniformity This is not always possible due to the nature of texture introduced in the processed sample or the lack of sufficient grain sampling by the beam (within the gauge volume). XRD-DIC utilises DIC technique to analyse 2D XRD patterns directly, without 2D to
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