Fokker-Planck equation for the particle size distribution function in KJMA transformations

Abstract

The Fokker-Planck (FP) equation has been derived for describing the temporal evolution of the particle size probability density function (PDF) for KJMA (Kolmogorov-Johnson-Mehl-Avrami) transformations. The classical case of transformations with constant rates of both nucleation and growth, in 3D space, has been considered. Integration of the equation shows that the PDF is given by the superposition of one-parameter Gamma distributions with time dependent mean size given by the KJMA theory. The asymptotic behavior of the FP solution offers a demonstration of the conjecture, previously proposed by Pineda et al [E. Pineda, P. Bruna, D. Crespo, Phys. Rev. E 70 (2004) 066119], according to which the set of nuclei formed at the same time are Gamma-distributed, with parameter depending on nucleus birth time. Computer simulations of the transformation with constant nucleation and growth rates, do show that the temporal evolution of the PDF, in the volume domain, is in good agreement with the Johnson-Mehl PDF. The approach based on the FP equations provides a particle size PDF that exhibits such behavior.

22 pages; 7 figures

References in corpus (3)

• Numerical model of solid phase transformations governed by nucleation and growth. Microstructure development during isothermal crystallization
• Cell size distribution in a random tessellation of space governed by the Kolmogorov-Johnson-Mehl-Avrami model: Grain size distribution in crystallization
• Cell-size distribution and scaling in a one-dimensional KJMA lattice model with continuous nucleation