Vacancy generation in deformed thin metal

Kiritani found that vacancy clusters of large number density form in f.c.c, thin metal of 100 nm thickness deformed to their fracture. In the present work, a computer simulation of deformation of thin metal is carried out to investigate how vacancies of high concentration generate during a deformati on of thin specimens of Al and Cu. A crystal of 4000 atoms whose size is (1 0a(0) x 10a(0) x 10a(0)) is elongated to z-axes. Two modes of simulation ar e carried out. In the mode 1, surface which are normal to x-axes and y-axes are kept free, In the mode 2, the periodic boundary condition is applied f or all surfaces. The mode 2 is equivalent to the deformation of bull; Metal . In the simulation of mode 1, the tilting of (1 1 0) atom row initiates on the surface. A tilting of rows to the same direction expands on a (1 1 1) plane and arrives to other side of surface. Dislocations do not form during the tilting. The tilting of atom rows occurs due to easy movement of atoms on surface responding to stress. In highly deformed thin metal, the tiltin g of atom rows occurs on multi-layers of parallel planes. Subsequently a ti lted row split into two rows. A new row initiates by moving an atom on surf ace to the interstitial position, A transportation of atoms from the normal row to the new row occurs during deformation, which contributes to the red uction of thickness. Vacancies of high concentration are not generated in t he case of the mode 1 deformation. In the simulation of the mode 2, the for mation of domain in which atom rows tilt to the same direction occurs. At t he domain boundary ordered array of atom rows becomes disordered in an inst ant and grows to a small crack of vacancy cluster. The formation process of vacancy clusters which were observed in deformed thin metal is due to the combination of the processes of the modes 1 and 2. (C) 1999 Elsevier Scienc e B.V. All rights reserved.