Twinning behavior and lattice rotation in a Mg-Gd-Y-Zr alloy under ballistic impact

The deformation microstructures of a Mg-Gd-Y-Zr alloy under ballistic impact at a velocity of 400 m.s(-1) were characterized using optical microscopy (OM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. Due to the high strain rate in the test, twinning and double twinning were prevalent in the deformation microstructure; high energy {1013} compression twins and twin-twin intersections were also readily observed. Adiabatic shear bands, the precursor of cracks, propagated along grain boundaries and through twin-rich zones. Four different lattice rotation conditions were observed in the deformation microstructure. Low angle boundaries generated by dislocations glide and dislocation arrays were partially responsible for the nonuniform orientations of the deformed grains. Some high angle boundaries formed through twinning followed by lattice rotation. Lattice rotation was also observed in unusual tension twins with misorientation angles lower than 86 degrees. Finally, the sectioned region and matrix rotated with small angles during the twin-twin intersection process. These unique twin behaviors and lattice rotations can be attributed to accommodation of severe plastic strain and maintaining compatibility between neighboring microstructures. These deformation behaviors are beneficial for materials to improve the ballistic performance. (C) 2015 Published by Elsevier B.V.