A hypothetical binary system, comprising one intermetallic compound and 2 primary solid-solution phases, was considered in order to analyze the kinetics of reactive diffusion. It was assumed that migration of the interface was controlled by volume diffusion in the neighboring phases. The growth rate of the intermetallic compound, due to reactive diffusion between the primary solid-solution phases in a semi-infinite diffusion couple at an appropriate annealing temperature, was then evaluated by using an analytical solution of the diffusion equations. The above assumption reproduced a parabolic relationship. According to the latter, the square of the thickness of the intermetallic compound increased in proportion to the annealing time. The results indicated that the most important parameters controlling the growth rate were the diffusion coefficient and the solubility range of the intermetallic compound. A change in the diffusion coefficient, by 5 orders of magnitude, resulted in variations of the proportionality coefficient of the parabolic relationship by 7 to 8 orders of magnitude; under the present initial and boundary conditions. The effect of the solubility range upon the growth rate was comparable to that of the diffusion coefficient upon the growth rate.

Analysis of Kinetics of Reactive Diffusion in a Hypothetical Binary System. M.Kajihara: Acta Materialia, 2004, 52[5], 1193-200