Grain Boundary Engineering and Related Topics

Abstract

Grain boundaries play a fondamental role in the plastic deformation of polycrystalline materials. There are two levels of study on the effect of grain boundaries, The first one concerns with the microscopic effect of grain boundaries on the dislocations during plastic deformation, and the second one deals with the macroscopic effect of boundaries on the bulk mechanical properties. In the early stages of deformation, the grain boundary regions are strained more than the grain interior. The grain boundaries are not only effective barriers to dislocation slip, but also act as sinks and sources of dislocations. The localized stress produced by dislocation pile up at grain boundaries will initiate multislip in the vicinity of the grain boundary to accommodate the shape change between differentially deforming grains. These dislocations are called geometrically necessary dislocations as distinct from the statistically stored dislocations[1] which result from homogeneous deformation. The existence of such a zone of misfit of the order of the spacing between the slip bands has been put forward by Hauser and Chalmers[2] to explain the macroscopic influence of grain boundaries on the flow stress in terms of the Hall-Petch relation as described in Sec. 6.4.2.