Deformation Mechanisms: Atomic Transfer Flow

Abstract

In this category of deformation mechanisms we are concerned with processes in which individual atoms or small groups of associated atoms are removed from certain interfaces or discontinuities within the structure of the body (sources) and are transferred to other interfaces or discontinuities (sinks) in such a way that the overall shape of the body is changed, that is, the body undergoes macroscopic strain. The sources and sinks may be dislocation cores, planar crystal defects, grain boundaries or free internal or external surfaces, and the transfer may take place by a variety of mechanisms, including solid state diffusion (intra- or intergranular) and transfer via a fluid phase (in case of a porous or partially melted body). The overall kinetics may be controlled by the kinetics of the transfer process or by the kinetics of the detachment and re-attachment processes. We have used the term “atomic transfer flow” in introducing this class of mechanisms in order to emphasize that the transfer occurs more or less atom by atom rather than by the movement of relatively large blocks of atoms; however, the term “diffusion creep” is commonly used in the same sense, especially when it is wished to emphasize diffusion as the transfer process or as being rate controlling.