Grain boundary mobility in metals: The current status

Current research on grain boundary mobility in metals is reviewed. For individual grain boundaries the mobility measurements on planar and curved grain boundaries as well as the dependence of grain boundary migration on orientation and impurity content are addressed. The experimental aspects of grain boundary mobility measurements are discussed. The mobility of planar tilt grain boundaries in Bi-bicrystals driven by a magnetic field strongly depends on grain boundary inclination. The mobility of the asymmetrical 90 degrees[112] tilt grain boundary even depends on the direction of motion. The effect of solute atoms on grain boundary migration cannot adequately be described by standard impurity drag theories. A more satisfactory agreement is obtained by taking an interaction of the impurities in the boundary into account. Solute atoms do not always reduce grain boundary mobility. Irrespective of the type of boundary, small amounts of Ga in Al substantially increase grain boundary mobility. Small liquid inclusions of Pb in Al exert a drag on moving boundaries, when they can move along with the boundary. There is unambiguous experimental evidence that for grain boundary mobility the logarithm of the preexponential factor changes linearly with the activation enthalpy. This is referred to as compensation effect. As a consequence, the maximum growth rate misorientation during recrystallization can depend on the annealing temperature. At high temperatures, grain boundaries with high activation enthalpy for migration are favored, while at low temperatures low Sigma coincidence boundaries dominate. The pressure dependence of grain boundary mobility provides evidence that at least [110] tilt grain boundaries in Al do migrate by a group mechanism of boundary motion. The kinetics of grain boundary systems with a triple junction are discussed in terms of a finite triple junction mobility.