The Effects of Processing Time on the Microstructure and Composition of Plasma Pack-Aluminized and -Oxidized Surface Layers on Low Carbon Steel

Low carbon steel was plasma pack aluminized at 973 K (700 °C) for 5, 10, and 15 minutes in vacuum of 15 mbar. A paste of aluminum was packed around the samples, and the process was carried out in glow discharge of argon gas in one step without further diffusion processes. The aluminized samples were oxidized at 973 K (700 °C) and 15 mbar for 60 minutes in synthetic air. The aluminized and oxidized layers were characterized for iron-aluminum intermetallic phases, local composition, morphology, and hardness of the phases. At 973 K (700 °C) after 5-, 10-, and 15-minute treatments, FeAl₃ and Fe₂Al₅ intermetallic compounds were observed in the surface layers. After 60-minute oxidation, Fe₃Al and FeAl compounds appeared at the interface between the compound layers and the oxide scale. Oxidation products were mainly Al₂O₃ and a few amounts of Fe₃O₄ and Fe₂O₃. The thicknesses of the compound layers on the samples were up to 350 μm. The maximum hardness of the aluminized layers was 980 HV0.5.