On the diffusion of solute during the eutectoid and eutectic transformations, part I

Abstract

The boundary value problem is formulated for the solute distributions during the constant-velocity, lamellar eutectoid and eutectic transformations. The boundary condition on the transformation interface, assumed planar, is shown to be of a non-homogeneous Cauchy type with variable coefficients. An exact solution is obtained for negligible diffusion in the transformed phase by employing Fourier analysis in the calculation of coefficients in the general solution. The eutectoid solute distribution is obtained for phase diagrams exhibiting a specified symmetry in liquidus and solidus slopes. A solute distribution for the eutectic transformation is obtained which is valid to first order in the Peclet number. This solution is shown to differ markedly from previously reported solutions obtained with approximate boundary conditions. The limitations of approximate methods are discussed. Finally, the solute distribution for a dilute ternary constituent in a binary eutectic is derived by similar methods.