NONUNIFORM AND DIRECTIONAL GRAIN-GROWTH CAUSED BY GRAIN-BOUNDARY MOBILITY VARIATIONS

Most derivations of grain growth relations require an assumption of co nstant grain boundary mobility; in fact, a number of these relations c annot be derived if boundary mobility varies in space or time. Compute r simulations of grain growth in which boundary mobility varies in tim e 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 gro wth may appear near the mobility discontinuity. When the boundary mobi lity varies in lime as well as in space, different growth morphologies can occur. Under a one-dimensional Gaussian mobility profile moving a cross the sample with some velocity, three growth regimes can occur. A t 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.