The role of interfacial free energy and interface kinetics during the growth of precipitate plates and needles

An exact mathematical solution to the diffusion equation is obtained for the growth of precipitate plates from a supersaturated matrix during solid-solid phase transformations. This solution rigorously takes into account the interface curvature and the interface kinetics effects under the assumption that the shape of the advancing interface corresponds to a parabolic cylinder. Present results have been compared with those for a needle precipitate growth and it is found that, for a given supersaturation, a needle always grows faster than a plate. It is, however, shown that the variation of the diffusion coefficient with solute concentration and the presence of transformation stresses would cause a plate to grow at a higher rate when supersaturation in the matrix is increased, thereby causing the transition from needle to plate morphology.