October 4-9, 2015
For magnesium and some other hexagonal-close-packed metals, twinning on the plane is a common mode of plastic deformation. Recently, we have used in situ transmission electron microscopy (TEM) to monitor the deformation of submicron-sized single-crystal magnesium, in quantitative compression and tension tests (B-Y. Liu et al., Nature Commun. 2014). We have observed the reorientation of the parent lattice to a “twin” lattice, producing an orientational relationship akin to that of the conventional twinning. However, aberration-corrected TEM observations reveal that the boundary between the parent lattice and the “twin” lattice is composed of many segments of semi-coherent basal-prismatic (B-P) interfaces, instead of the twinning plane. Both TEM and molecular dynamics simulations suggest that the migration of this boundary is accomplished by B-P interfaces undergoing basal-prismatic transformation, in addition to the migration of the boundary of the extension twin. This deformation mode mimics conventional deformation twinning, but is distinct from the latter. It is a form of boundary motion coupled to stresses, but produces plastic strain that is not simple shear. The basal-prismatic transformation appears to be important under deformation conditions when the availability and/or mobility of twinning dislocations/disconnections are limited. As such, this new twist in lattice reorientation accompanying deformation twinning enriches the known repertoire of plasticity mechanisms.
Evan Ma, Bo-Yu Liu, and Zhi Shan, "Boundary motion coupled with tensile and compressive deformation: TEM observation of twinning-like lattice reorientation in Mg micropillars" in "Nanomechanical Testing in Materials Research and Development V", Dr. Marc Legros, CEMES-CNRS, France Eds, ECI Symposium Series, (2015). http://dc.engconfintl.org/nanomechtest_v/28