Kinetics of Fe2Al5 phase formation on 4130 steel by Al pack cementation and its oxidation resistance

Abstract

Aluminide coatings were developed on low alloy AISI 4130 steel in the temperature range of 500~700 °C by pack cementation method. A Fe2Al5 phase was produced on the surface of the steel samples. The coating layer showed a single and a uniform structure. The growth kinetics of the coating layer exhibited a diffusional growth. The activation energy for formation of Fe2Al5 was estimated to be 53.7 kJ mol−1. Oxidation tests were carried out for both the aluminized and the bare steels in the temperature range of 500~700 °C. In the case of the coated specimens, the upper region of the aluminide layer was converted to an Al2O3 layer. The oxidation resistance tests showed that the presence of Fe2Al5 layer increased the oxidation resistance of AISI 4130 steels via formation of the Al2O3 layer. The coated specimen exhibited an increased oxidation resistance by about two orders. The kinetics of the coating layer has also been discussed in terms of microstructural observations and estimation of the corresponding parameters.