Effects of heat treatment conditions on formation of Fe-Al alloy layer during high temperature aluminizing

Abstract

Diffusion couples of Fe2Al5 and various substrates with different carbon content, pure iron, 0.27 mass% C steel and 0.45mass% C steel were processed, and the formation of an Fe-Al alloy layer In the temperature range from 750 to 1 000°C was investigated. FeAl2, FeAl, and aluminum solid solution (αFe(All) were confirmed In the alloy layer formed by heating the diffusion couples. Voids were generated Inside the Fe2Al5 layer and near the interface between the FeAl layer and αFe(Al) layer. The layer growth of FeAl and αFe(Al) obeyed the parabolic law of the diffusion time, t1/2. However, the thickness of FeAl saturated over a diffusion time longer than 3.6 ks at 950°C because of the concentration of voids at the FeAl layer/αFe(Al) layer Interface and the disappearance of the Fe2Al5 layer. The activation energy for the formation of the FeAl layer in all kinds of the substrates was approximately 200kJ/mol In the whole temperature range and the substrate. On the other hand, the activation energies for the αFe(All) layer In the 0.27mass% C steel and the 0.45 mass% C steel were larger than that in pure iron at 750-800°C. © 2007 ISIJ.