Deformation twins have been observed in low-strain, plane-wave shock-loaded copper while in oblique shock loading there are microbands intermixed with deformation twins. For more complex deformation geometries such as impact cratering, microbands occur predominantly in the deformation microstructure. TEM and corresponding SAD analysis of microbands show them to be microstructurally and geometrically distinct from deformation twins, while both are coincident with {111} planes. The role of grain size, prior deformation, strain, and shear phenomena on both twinning and microband formation are presented. Deformation twins in bcc metals such as Mo and Ta are geometrically similar to microbands in fcc metals such as copper. However they are coincident with {112} planes. Nonetheless, the dislocatin mechanism specific to bcc deformation twinning may operate appropriately in fcc in a way that differentiates slip-related shear producing microbands from the linear and overlapping glide of <112>/6 partial dislocations which form microtwins in fcc metals such as copper.
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