Nucleation and growth of second phase precipitates under non-isothermal conditions

Abstract

The Langer-Schwartz equations for precipitation are formulated to calculate nucleation, growth and coarsening of second phase precipitates under non-isothermal situations. A field-theoretic steady-state nucleation rate model is used in the analysis. The field-theoretic nucleation rate is compared with the classical nucleation rate relation derived from the Fokker-Planck equation. This integrated model is used to simulate a bcc-to-hcp phase quenching and subsequent annealing in the hcp phase of a dilute zirconium alloy, where the mean precipitate size, number density and the degree of supersaturation are calculated as a function of time. The influence of cooling rate on the aforementioned parameters is evaluated. A lower cooling rate results in larger precipitates with a smaller number density in concordance with observations.