In order to reveal the microscopic mechanism which caused the plastic deformation induced by vacancy diffusion processes, the motion of a vacancy in an atomic chain was modelled and analyzed mathematically. The dynamics of the vacancy were described by using a form of diffusion equation which included essential effects upon plastic deformation: the thermal effect, the interactions of atoms, the friction of the environment and the external force. By stripping away the fluctuation of the prime motion by using a perturbation expansion, a situation could be reached in which the essential motion of the vacancy was represented by the propagation of a kink wave which responded to the external force and the temperature, although the system was described by a diffusion process. By then deriving the strain of the atomic chain, it was shown that the strain versus time behaved viscoelastically as in, for example, the Voigt model. The properties of the temperature and the applied stress coincided with well-known results for primary creep phenomena.

An Analytical Mechanism of the Vacancy Diffusion Process of an Atomic Chain and Its Effects on the Creep Properties. T.Watanabe: Materials Transactions, 2003, 44[1], 28-33