| Popis: |
Following the experimental observations of the cubic→hexagonal transformation in silicon [P. Pirouz, R. Chaim, U. Dahmen and K.H. Westmacott, Acta metall. mater. 38 , 313 (1990)], a crystallographic analysis is presented in this paper. It is shown that the transformation is a more general mechanism of accomodating the local strain that is produced when twins in materials with a face centered cubic (f.c.c.), or diamond cubic (d.c.), structure intersect. The same crystallography describes the propagation of a secondary twinning shear into its parent crystal, leading to a hexagonal plate on a {511} plane. The habit plane and orientation relationship predicted by this model are in exact agreement with observations by high resolution electron microscopy and diffraction of hexagonal platelets in hot-indented silicon reported in Part I [P. Pirouz et al., Acta metall. mater. 38 , 313 (1990)]. This agreement suggests that the transformation originates in deformation twinning and may be considered alternatively as a stress-induced martensitic transformation, or a lattice-variant accomodation shear. |
