Nonuniform and directional grain growth caused by grain boundary mobility variations

Abstract

Most derivations of grain growth relations require an assumption of constant grain boundary mobility; in fact, a number of these relations cannot be derived if boundary mobility varies in space or time. Computer simulations of grain growth in which boundary mobility varies in time and/or space have been performed. When mobility varies continuously with position, grains grow with locally normal kinetics. In contrast, when the mobility profile in discontinuous, deviations from normal growth may appear near the mobility discontinuity. When the boundary mobility varies in time as well as in space, different growth morphologies can occur. Under a one-dimensional Gaussian mobility profile moving across the sample with some velocity, three growth regimes can occur. At low and high profile velocities, grain growth is equiaxed and normal. At intermediate velocities, a fully columnar grain structure forms; the width of the columnar grains evolves with normal growth kinetics.