Effects of Heat Treatment Conditions on Formation of Fe-Al Alloy Layer during High Temperature Aluminizing

摘要

Diffusion couples of Fe_2Al_5 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℃ was investigated. FeAl_2, FeAl, and aluminum solid solution (αFe(Al)) were confirmed in the alloy layer formed by heating the diffusion couples. Voids were generated inside the Fe_2Al_5 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, t~(1/2). However, the thickness of FeAl saturated over a diffusion time longer than 3.6 ks at 950℃ because of the concentration of voids at the FeAl layer/αFe(Al) layer interface and the disappearance of the Fe_2Al_5 layer. The activation energy for the formation of the FeAl layer in all kinds of the substrates was approximately 200 kJ/mol in the whole temperature range and the substrate. On the other hand, the activation energies for the αFe(Al) layer in the 0.27 mass% C steel and the 0.45 mass% C steel were larger than that in pure iron at 750-800℃.