Molecular theory of plastic deformation

Abstract

In order to elucidate the plastic deformation of solids, the following assumptions were made: (1) the plastic deformation of solids is classified into two main types, the one which is caused by dislocation movement and the other caused by grain boundary movement is also expressed by a parallel connection of various kinds of Maxwell grain boundary movement is also expressed by a parallel connection of various kinds of Maxwell grain boundary flow units; the parallel connection in each type of movements indicates that all the flow units on each shear surface flow with the same shear rate, (3) the latter model for grain boundary movement is connected in series to the former for dislocation movement, this means physically that the applied stress distributes homogeneously in the flow system while the total strain rate distributes heterogeneously on the two types of shear planes (dislocation or grain boundary shear plane), (4) the movement of dislocation flow units and grain boundary units becomes possible when the atoms or molecules near the obstacles, which hinder the movement of flow units, diffuse away from the obstacles. Using the above assumptions in conjuction with the theory of rate processes, generalized equations of shear stress and shear rate for plastic deformation were derived. In this paper, four cases important in practice were considered. The authors`` theory was applied to plastic deformation of ceramics, metals, alloys and single crystals. For polycrystalline substance, the flow mechanisms due to dislocation movement and grain boundary movement appear together or separately according to the experimental conditions whereas for single crystals, only the mechanism of dislocation movement appears. The parameters appearing in the flow eauations $(\alpha_{d1},1/\beta_{d1})$ and $(\alpha_{gj}/x_{gj},1/\beta_{gj})$ (j=1 or 2) and the activation enthalpies $\triangle{H}_{k1}^{\neq}$ (k = d or g) were determined \& tabulated. Here, the subscript dl indicates t...