Computer simulations of the deformation of thin metal samples were carried out in order to investigate how high concentrations of vacancies were generated during deformation. A crystal of 4000 atoms was elongated along the z-axis, and 2 types of simulation were used. In one type, the surfaces which were normal to the x- and y-axes were kept free. In the other type, a periodic boundary condition was applied to all of the surfaces. The second type was equivalent to the deformation of bulk metal. In type-1 simulations, tilting of <110> atom-rows began at the surface. Tilting of other rows in the same direction spread on a (111) plane and reached the opposite surface. Dislocations did not form during tilting. The tilting of atomic rows occurred due to the easy movement of surface atoms in response to stress. In highly-deformed thin metal, the tilting of atomic rows occurred on multi-layers of parallel planes. A tilted row then split into 2 rows. A new row initiated by moving a surface atom to an interstitial position. Transportation of atoms from the normal row to the new row occurred during deformation, and this contributed to the reduction in thickness. High concentrations of vacancies were not generated in the case of type-1 deformation. In type-2 simulations, the formation of a domain in which atomic rows tilted in the same direction occurred. At the domain boundary, the ordered array of atomic rows became disordered in an instant, and grew into a small crack of vacancy clusters. It was concluded that the formation of the vacancy clusters which were observed in deformed thin metal was due to a combination of type-1 and type-2 processes.

Vacancy Generation in Deformed Thin Metal. Y.Shimomura, K.Sugio, M.Kiritani: Computational Materials Science, 1999, 14[1-4], 97-102