Deformation Behavior of Magnesium Single Crystals Compressed Along [0001]
Jie Geng (Brown University), Sharvan Kumar (Brown University), Matthew Chisholm (Materials Science and Technology Division, Oak Ridge National Laboratory ), Raj Mishra (GM Research and Development Center, Warren, Michigan, 48090), Anil Sachdev (GM Research and Development Center, Warren, Michigan, 48090)
Plasticity at Different Length Scales
Mon 9:00 - 10:30
CIT 219
When compressed along the c-axis at room temperature, magnesium single crystals support high stress (around 250-300 MPa) prior to fracture; the associated plastic strain is however less than one percent with high associated work hardening. Fracture in compression is often on an inclined plane suggestive of shear failure. Negligible strain rate sensitivity is noted at room temperature in the strain rate range of 1×10-6 to 1×10-4 s-1. The deformed microstructure has been examined by conventional transmission electron microscopy (TEM) using bright field and weak-beam dark field techniques as well as high resolution TEM. The {10-11} compression twin, which is favored by c-axis compression, was seldom observed. Slip was found to be the dominant deformation mode. Three types of dislocations, i.e. < a >, < c+a >, and < c >, were observed. In addition, a high density of < c+a > dislocation loops were formed during compression. Some of the loops appeared dissociated in the weak beam dark field mode. The screw < c+a > dislocations are more mobile than the edge < c+a > dislocations and can double cross slip between first- and second-order pyramidal planes. TEM observations suggest that the < c+a > dislocation can dissociate to < c > and < a > dislocations and the latter can further extended on the basal plane.