Simulation of recrystallization in polycrystalline materials

The microstructure evolution plays an important role in the process of static recrystallization occurring during heat treatment following plastic deformation. The process is affected by the deformation energy stored in the material and the temperature of the heat treatment of finite duration. Key parameters are the density and spatial distribution of nucleation sites in the initial polycrystalline microstructure. Similarly, key modelling assumptions are the distribution of the moving speed of the recrystallization front, and whether nucleation is site-saturated or continuous.
The simulations are done on three-dimensional rectangular subblocks using the principles of the Monte Carlo Potts model. The effect of the previous deformation was defined by the elongated shape of grains in the initial microstructure. The nucleation happens with a defined probability for internal cells, surfaces and edges on the grain boundaries, and triple junctions. Outer surfaces are defined as either periodic or rigid boundary conditions. Continuous nucleation is defined as a constant generation possibility on each unrecrystallized cell over time.
The JMAK (Johnson–Mehl–Avrami–Kolmogorov) theory describes recrystallization kinetics using a shape exponent and a scale parameter. An important result is finding the relation between the coefficients in the general JMAK model, and the parameters of the current simulation with various initial assumptions. Simulations with site-saturated nucleation precisely reproduce the JMAK model with three-dimensional growth, while continuous nucleation causes higher exponents, similarly to the theoretical values.
The developed model can simulate the static recrystallization of the crystalline materials, with a good correlation with measured recrystallization fraction from measured hardnesses. A further aim is taking into consideration the effect of the grain boundary misorientation and the orientations of the grains on the nucleation process.
Supported by the EKÖP-25 University Excellence Scholarship Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.