Fe–Al/Al2O3 composite coating on Reduced Activation Ferritic/
Martensitic (RAFM) steel is considered as the reference tritium permeation
barrier coating in future fusion reactors. In our previous
work [1,2] the iron aluminide coating on CLAM (a Chinese RAFM
steel) was prepared by pack cementation and subsequent heat
treatment process. A surface Fe2Al5 layer was formed on CLAM
substrate by pack cementation process with Fe2Al5 donor powder
and NH4Cl activator. Heat treatments were carried out at 980 C
(CLAM steel solution treatment temperature) in order to allow
the phase transformation of Fe2Al5 to the phase with lower aluminum
content. After heat treatment at 980 C, Fe2Al5 scale is completely
transformed into the a-Fe(Al) solid solution at which the
FeAl2 and FeAl phase consecutively occur [3,4].
Control of the surface Al concentration is one of the most
important issues. In this paper, the composition and structure of
iron aluminide coating were systematically studied. A predictive
model was developed to describe the phase transformation of
Fe2Al5 as a function of processing parameters. The Wagner’s
equation is used to calculate the interdiffusion coefficients of the
FeAl and a-Fe(Al) phase based on the Al content profiles.