Thermodynamics and Kinetics of the Gas Phase and Pack Aluminide Coating Formation on Iron and Steel

摘要

A gas-solid diffusion model which includes the multicomponent equilibriums of the gaseous phase with the pack and the substrate, was used to study the influence of the relative rates of gas transport and solid state diffusion on the pack-aluminization process. The surface composition of the coatings and their growth rate depend on the temperature and the aluminum activity in the pack, for a given activator. Theoretical predictions for deposition in the gas phase, on substrates out of contact with the pack, can be qualitatively deduced. They agree qualitatively with the experimental results. The conditions necessary to obtain uniform coatings in the gas phase are relatively low temperature and low aluminum activity in the pack.