Formation and modelling of aluminide coatings on iron by a fluidised bed CVD process

Aluminide coatings have been deposited on ARMCO iron and an iron–chromium alloy (15 at.% Cr) by a fluidised-bed chemical vapour deposition (FBCVD) process at 1000 °C with the use of FeAl donor powder and an NH4Cl activator. Examination of the coated samples by means of optical microscopy, SEM and microanalysis has shown the formation of dense and homogeneous coatings consisting of an FeAl outer phase and an α-solid solution inner phase. A simplified process model based on the diffusion equations of aluminium in pure iron, considering the intermetallic compounds according to the FeAl phase diagram, has been derived. The model yields the aluminium composition profiles as a function of time for particular process conditions and can be used for evaluation of the coating growth rate and morphology during aluminisation.