Rapid phase transformation under local non-equilibrium diffusion conditions

Abstract

Phase transformation with a moving interface occurs under far from local equilibrium conditions when the interface moves with sufficiently high velocity. This deviation cannot be adequately described by the classical irreversible thermodynamics with diffusion equation of parabolic type because it assumes local equilibrium hypothesis. The local non-equilibrium diffusion model has been developed to take into account the deviation from local equilibrium during binary alloy solidification using the hyperbolic diffusion equation. The model introduces a finite propagation velocity of concentration disturbances in the bulk liquid V _D as the characteristic diffusion parameter and predicts a sharp transition from diffusion controlled to diffusionless and partitionless solidification at V = V _D due to the deviation from local equilibrium. This review does not intend to be extensive, but rather to illustrate the main advances of the local non-equilibrium diffusion approach in rapid alloy solidification. Applications of the local non-equilibrium model to other phase transformation processes such as solid–solid transformation, colloidal and multicomponent alloy solidification have been briefly discussed. The parallels and possible combinations of the model with molecular dynamics, phase field, phase field crystal and cellular automata methods have been considered.

Keywords:

• Phase transformation
• Rapid alloy solidification
• Solid state transformation
• Colloidal solidification
• Local non-equilibrium
• Hyperbolic diffusion
• Diffusionless solidification
• Partition coefficient
• Solute trapping