Grain Boundary Mechanics -- New Approaches to Microstructure Control

Abstract

The reaction of grain boundaries to mechanical stresses is reviewed. Results of in-situ experiments on planar, symmetrical tilt grain boundaries with different tilt axes ((112), (111), (100)) under the influence of an external mechanical stress field will be presented. It was found that the motion of planar grain boundaries can be induced by an imposed external stress irrespective of the angle of misorientation i.e., irrespective whether the grain boundary was a low or high angle grain boundary. The observed activation enthalpies of the stress induced grain boundary motion allow conclusions on the migration mechanism. The motion of planar low and high angle grain boundaries under the influence of a mechanical stress field can be attributed to the movement of the grain boundary dislocations which comprise the structure of the boundary. A sharp transition between low and high angle grain boundaries was observed for different tilt axes. Also an influence of the mechanical stress on grain growth was investigated. The fact that boundaries can also be moved by mechanical forces sheds new light on microstructure evolution during elevated temperature deformation.