The morphology and growth kinetics of discontinuous precipitates were studied, at temperatures ranging from 383 to 583K, by means of optical and scanning electron microscopy. It was found that the precipitate phase had a lamellar morphology, and maintained a statistically constant interlamellar spacing during isothermal growth. The interlamellar spacing increased with increasing temperature. The isothermal growth kinetics, measured in terms of reaction-front migration rate, were fastest at 523K. The upper temperature limit for the occurrence of reactions in the alloy was predicted to be 643K. A detailed kinetic analysis of the experimental data, using several analytical models, confirmed that discontinuous precipitation in this system was a boundary diffusion controlled reaction. This permitted the grain boundary chemical diffusivity of Cu in Zn-rich alloys to be deduced. The activation energies which were estimated here ranged from 65 to 86kJ/mol within the above temperature range. These values compared well with published data.

I.Manna, J.N.Jha, S.K.Pabi: Journal of Materials Science, 1995, 30[6], 1449-54