Transient Growth of Second Phases during Solution Treatment

The study shows experimentally that, in the initial stages of a solution treatment process, an unstable phase may grow prior to dissolving if the diffusion flux in the unstable phase is larger than that in the stable matrix. The effect was demonstrated using diffusion couples fabricated from thin, multiple layers of alpha and beta brass such that the mean compositions of the couples relative to the alpha-beta phase equilibrium would result in solution of the beta phase. Since at the diffusion temperature of 870C the interdiffusion coefficient of the beta phase is about twenty times that of th alpha phase, the initial beta phase flux was much greater than that of the alpha phase. (Author) Prepared in cooperation with Carnegie-Mellon Univ., Pittsburgh Pa., Dept of Metallurgy and Materials Science. and General Electric Co., Philadelphia, Pa. Re-Entry and Environmental Systems Div. Includes errata sheet dated 3 Aug 72.