Electron Backscatter Diffraction Mapping of Microstructural Evolution of Pure Magnesium during Creep

To provide new insight into microstructural development during creep, sequential electron backscatter diffraction (EBSD) orientation maps were obtained from fixed surface areas during interrupted creep tests of extruded pure magnesium. Samples were tested under two distinctly different conditions, i.e., low-temperature power-law creep and high-temperature power-law creep. Three aspects of microstructural evolution during creep were observed. In both specimens, transient creep was marked by the elimination of tension twins formed during the extrusion process. As steady-state creep rates were obtained, both specimens exhibited an ever-decreasing contribution by basal slip accompanied by an ever-increasing contribution by prismatic slip. In the low-temperature specimen, prismatic slip was manifested by the formation of a network of new fine subgrains along original grain boundaries, resulting in a bimodal grain size distribution. However, the high-temperature specimen developed linear prismatic slip lines while maintaining its original grain size.