Observations of Twinning and Detwinning in Magnesium Alloy by Synchrotron Radiation DCT and EBSD

Abstract

Recently, three-dimensional grain mapping techniques for polycrystalline materials called X-ray diffraction contrast tomography (DCT) have received considerable attention. DCT can simultaneously provide information on the three-dimensional grain arrangement of a sample, such as the shapes, locations, and crystallographic orientations of grains, together with the misorientation of grains. In the present study, the twinning and the detwinning in tension and compression loading in a magnesium alloy was observed by the DCT using ultra-bright synchrotron radiation X-ray, and the electron backscatter diffraction (EBSD) analysis. The shape of each grain in a polycrystalline magnesium alloy was successfully reconstructed and misorientation of each crystallographic plane was successfully measured by DCT. With increasing applied compression stress, the average value of the misorientation was decreased, while it is usually increased with plastic strain for materials without twinning. The value of misorientation increased with unloading process, indicating that the twinning was occurred under the compressive applied stress. The shape of diffraction spots of some grains also shows the twinning under the compressive stress and the detwining under the following tensile stress. The EBSD analysis of specimen surface also shows that the twinning was occurred under the compressive applied stress, and the following applied tension stress brought detwinning.