ON THE COMPOSITION PROFILE IN THE MATRIX PHASE WITHIN A DISCONTINUOUSPRECIPITATION COLONY

A modification to Cahn's solution for the solute distribution profile in the solute depleted matrix (alpha) within a discontinuous precipita te (DP) colony is presented. The proposed modification is based on the premises that (a) the average solute content in the alpha phase follo wing DP approaches the metastable solvus instead of the equilibrium so lvus, and (b) the reaction front migrates in discrete steps of ''stop' ' and ''go'', as proposed by Gust and evidenced by Abdou. The modified model fits the experimentally determined composition profile better f or DP in an Al-22 at.% Zn alloy than that obtained from Cahn's origina l formulation.