Iron Aluminide Coating of Structural Steel by Mechanical Alloying Followed by Annealing

Abstract

Iron aluminide coating of structural steel by mechanical alloying (MA) followed by annealing was examined. As starting materials, stabilized Al powders containing fat, fat-free Al powders and pure Fe powders were used. Stabilized Al-25 at% Fe powder deposited on the steel substrate from the early stage of MA and formed the coating layer. The mixing and the refinement of Al rich and Fe rich phases in the coating layer were promoted by the suppression of cold welding due to the presence of fat in the coating layer, resulting in the formation of coating layer with fine and homogeneous microstructure. In annealing for 7.2 ks after MA, Fe2Al5 was formed at 673 K, Fe2Al5 and FeAl were formed at 873 K and Fe2Al5, FeAl and Fe3Al were formed at1073 K, respectively. Thus, the formation temperature of FeAl was lower than that of the conventional hot dip coating or pack cementation. This is because interdiffusion between the steel substrate and the coating layer is enhanced by the refinement of microstructure of coating layer due to MA. By coupling annealing to MA, it is possible to improve embrittlement of iron aluminide coating layer.