Influence of Solutes on the Mobility of Tilt Boundaries

Grain boundaries have a profound effect on the strength of metals and alloys. Material properties,can be changed significantly by boundary migration. Studies of grain boundary mobility in matrices of poly- and single-crystals under the conditions of a difference in stored energy across the moving boundary have provided only limited advances towards understanding the behavior of grain boundaries. Primarily, this has been due to uncertainties in the magnitude of the force acting on the boundary during its motion. This difficulty has been avoided by examining boundary motion in wedge-shaped bicrystals in which the boundary migrates under the driving force of its own interfacial energy. The driving force per unit area of the boundary is simply related, in this case, to the specific interfacial energy and to the distance between the boundary and the tip of the wedge. Results of an investigation of the velocities of pure tilt boundaries in zonerefined aluminum and dilute aluminum-magnesium alloy bicrystals of preselected orientations have been presented. The effects of varying driving force and solute concentration on thermally activated boundary motion will be discussed in relation to the postulates of current theories.