A thermokinetic description for grain growth in nanocrystalline materials

The kinetics and thermodynamics of normal grain growth can be linked by two open questions. Is it physically practicable to incorporate the grain boundary (GB) energy decrease with GB segregation into the parabolic kinetics of grain growth? Subsequently, how can a model for grain growth that considers the mixed effect of kinetics and thermodynamics be derived? Departing from Borisov’s equation, a qualitative description is provided to validate the incorporation of GB energy into the grain growth kinetics. Then, a thermokinetic model considering the mixed effect of solute drag and reduced GB energy is developed. Subjected to specific limitations, the thermokinetic model reduces to a purely kinetic model, a purely thermodynamic model and a model considering only grain-size-dependent solute drag. By application of the model to experimental results obtained from nanocrystalline Ni–P and oxygen-doped nickel, it has been shown that the effect of solute drag could retard but not stop the grain growth, and that the main cause of a stabilized nanocrystalline structure is not the solute drag but the reduction in GB energy.