Mechanical and corrosion anisotropy of magnesium single crystal

Magnesium and its alloys are promising materials for medical use due to their ability to dissolve safely in the human body. However, the rate of dissolution of bioresorbable implants should be in a narrow enough range. The difficulty in ensuring this condition is that the corrosion process in magnesium alloys is influenced by many factors, including natural (single-crystal) and technological (production scheme) anisotropy. By carrying out technological operations on thermomechanical treatment, it is possible to control the process of formation of the semi-finished product texture and to create artificially a preferred orientation of crystallites in the structure of magnesium alloys and thus control their corrosion resistance. This requires precise knowledge of the relationship between corrosion processes and certain crystallographic directions, which can be most reliably obtained in experiments on single crystals. In this work, mechanical (compression and tension) and corrosion tests were carried out for the first time on the same magnesium single crystal on samples with different crystallographic orientations. The Kearns coefficients calculated from the X-ray diffraction patterns of the single crystal specimen faces by the inverse pole figure method were used as a quantitative criterion of the natural texture. The specimens were subjected to compression tests in the <0001>, <1−100> and <11−20> directions, and to tension tests in the <0001> direction. The specimen surfaces with orientations close to the (0001), (10−10), (2−1−10), and (10−11) crystallographic planes were subjected to corrosion testing. It was found that the Young’s modulus and the Kearns coefficient for the basal and pyramidal faces were 48.6 GPa and 0.81; 45.3 GPa and 0.04, respectively. The shape of the stress curves depended significantly on the sample orientation and was determined by the degree of involvement of various mechanisms in the overall plastic deformation process. The rate of corrosion in a physiological aqueous solution of 0.9 % NaCl on a 72-h basis for the (0001), (10−10), (2−1−10), and (10−11) surfaces was 0.51, 0.76, 0.71 and 0.98 mm/year, respectively. In this case, the (2−1−10) plane experienced only uniform corrosion, the (0001) plane experienced uniform corrosion with minor localised corrosion; the most intense localised corrosion is observed in the (10−10) direction, and the maximum intensity of the combination of localised and uniform corrosion is in the <10−11> direction.