Aluminization of high purity iron and stainless steel by powder liquid coating

Powder liquid coating is investigated metallographically as an aluminization technique for high-purity iron [Acta Mater., in press] and stainless steel. In this process, Fe2Al5 forms initially during heat treatment, with c axis preferentially aligned with the sample normal. In Fe–18mass%Cr alloy, Cr exhibits almost the same concentration profile as Fe except for the temporary formation of a Cr5Al8 network in the early stage of heat treatment. Fe–25Cr–18Ni alloy forms a thinner aluminized layer compared to the other substrates, and contains an Al–Ni-rich layer and spherical precipitates (ordered B2). The diffusion of Al and Ni in the system (B2/bcc/fcc) is simulated using a new formulation of the diffusion equation for the ternary Fe–Al–Ni system taking the concentration-dependent interdiffusion coefficient into account. The bcc layer is found to be predominantly in a steady state due to the large interdiffusion coefficients, and characteristic uphill diffusion of Al in the B2 layer is attributed to the existence of Ni.