ClaNG: Classical Nucleation and Growth (model)
Definition:A statistical model for precipitation kinetics that can simultaneously describe the nucleation, growth, and dissolution of spherical precipitates which is equilibrium phases during annealing.
Explanation:The presence and evolution of precipitates during sheet production decisively affect the physical mechanisms that operate during microstructural evolution, and thus, influence microstructure development. This is particularly evident during heat treatments where the microstructural evolution is determined by the motion of crystal defects, such as dislocations (in the case of recovery) and grain boundaries (in the case of recrystallization (→RX) and grain growth), whose motions can be hindered by the precipitates. The strength and nature of the interaction between the migrating crystal defect and the precipitate depend strongly on its volume fraction, size and type. The ClaNG model is capable of describing the precipitation kinetics of equilibrium phases, and hence, determining these important parameters as a function of time, temperature and alloy composition. The calculation of the chemical driving force is performed with the Calphad approach using commercial databases that are incrementally linked with the precipitation model. Grain boundary and pipe diffusion are considered by means of a mean-field approach. For more detailed investigations, the model is able to simulate local diffusion fluxes on a spatial grid by explicitly solving the Cahn-Hilliard equation, for instance, in the vicinity of existing precipitates.
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Copper (Cu) concentration profile in the vicinity of Al2CuMg precipitates in a commercial Al alloy
SFB-Link:Precipitation of second phase particles in the Fe-Mn-Al-C system (e.g. κ-carbides) can have a significant influence on nucleation and grain boundary movement during a heat treatment. The ClaNG model allows to simulate the formation of these precipitates, which can be implemented in both RX and grain growth simulations.
References:Schneider, M.; Gottstein, G.; Lochte, L.; Hirsch, J.: A Statistical Model for Precipitation-Applications to Commercial Al-Mn-Mg-Fe-Si Alloys, Materials Science Forum, 396-402 (2002), 637-642