THE USE OF ALUMINIDE DIFFUSION COATINGS TO IMPROVE CARBURIZATION RESISTANCE

摘要

Aluminide diffusion coatings have been formed on mild steel, AISI 321 stainless steel, alloy 792 and alloy 800 base materials by pack aluminizing. The aluminizing temperature employed for the four materials was adjusted to facilitate coatings on each with a common thickness between 50 and 60 mu m. A partial characterization of the aluminized materials has been performed. Differential interference contrast optical microscopy was employed to determine coating thickness and to elucidate coating microstructures. Energy-dispersive x-ray analysis was utilised to obtain a composition versus depth profile through the surface of each of the aluminized materials. The results obtained are discussed and compared to previous work. Uncoated and aluminized samples of each material have been pack carburized in air at 900 deg C. At intervals the samples were removed from the carburizing pack and their weight gain measured. Carburizing was continued for a total cumulative time of 756 hours. It was found that aluminizing had produced a distinct increase in the carburization resistance of the AISI 321 stainless steel, alloy 792 and alloy 800, but, by the end of carburizing, only a marginal increase in that of the mild steel. This is rationalized in terms of oxide layers formed on the surface of the uncoated and aluminized materials.