A feasibility study of full‐field X‐ray orientation microscopy at the onset of deformation twinning. Issue 2 (18th March 2016)

• Record Type: Journal Article
• Authors: Viganò, Nicola; Nervo, Laura; Valzania, Lorenzo; Singh, Gaurav; Preuss, Michael; Batenburg, Kees Joost; Ludwig, Wolfgang
• Is Part Of: Journal of applied crystallography. Volume 49:Issue 2(2016)
• Page Start: 544
• Page End: 555
• Publication Date: 2016-03-18
• Subjects: X‐ray orientation microscopy -- full‐field imaging -- grain microstructure -- deformation twinning; Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S1600576716002302
• Languages: English
• ISSNs: 0021-8898

Abstract

Abstract : In this article, the adaptation of a previously introduced six‐dimensional grain reconstruction framework to the case of deformation twinning in metallic alloys is described. The optimized procedure enables the detection and three‐dimensional reconstruction of twin lamellae down to micrometre thickness and more accurate reconstruction of orientation maps at moderate levels of plastic deformation. Abstract : Three‐dimensional X‐ray orientation microscopy based on X‐ray full‐field imaging techniques such as diffraction contrast tomography is a challenging task when it comes to materials displaying non‐negligible intragranular orientation spread and/or intricate grain microstructures as a result of plastic deformation and deformation twinning. As shown in this article, the optimization of the experimental conditions and a number of modifications of the data analysis routines enable detection and three‐dimensional reconstruction of twin lamellae down to micrometre thickness, as well as more accurate three‐dimensional reconstruction of grains displaying intragranular orientation spreads of up to a few degrees. The reconstruction of spatially resolved orientation maps becomes possible through the use of a recently introduced six‐dimensional reconstruction framework, which has been further extended in order to enable simultaneous reconstruction of parent and twin orientations and to account for the finite impulse response of the X‐ray imaging detector. The simultaneous reconstruction of disjoint orientation domains requires appropriate scaling of the scattering intensities based on structure and Lorentz factors and yields three‐dimensional reconstructions with comparable density values for all the grains. This in turn enables the use of a global intensity‐guided assembly procedure and avoids problems related to the single‐grain thresholding procedure used previously. Last but not least, carrying out a systematic search over the list of known twin variants (forward modelling) for each of the indexed parent grains, it is possible to identify additional twins which have been left undetected at the previous stage of grain indexing based on diffraction spot peak positions. The enhanced procedure has been tested on a 1% deformed specimen made from a Ti–4% Al alloy and the result has been cross‐validated against a two‐dimensional electron backscatter diffraction orientation map acquired on one of the lateral sample surfaces.