On Melt Growth and Microstructure Characterization of Magnesium Bicrystals

Oriented magnesium bicrystals with a 45 degrees 101 over bar 0 asymmetrical tilt boundary were produced by directional solidification in a vertical Bridgman furnace. Employing a partition in the cylindrical mold led to unwanted crystallization on the contact surface with the growing interface, disrupting the desired growth conditions for the boundary. A modified setup with seed crystals placed side by side in a conical mold addressed the former issue and enabled the production of high-quality 56 mm x null 34 mm bicrystals. Due to the asymmetrical character of the boundary, the adjacent growing crystals witnessed unequal growth rates, with the basal-oriented crystal dominating the growth process. Plane strain compression experiments were carried out on bicrystalline samples extracted from the prepared bicrystal. The panoramic orientation mapping of large areas of several mm2 revealed low-angle boundaries (5 degrees misorientation) associated with the curved segments of the original asymmetrical tilt boundary. It also depicted heterogeneous lattice rotation near the grain boundaries.