Abstract
UNS S30400 austenitic stainless steel was coated by pack aluminizing at 650, 750 and 8500C under an inert atmosphere. Six different activators were used in this study: sodium chloride, ammonium chloride, aluminum chloride, sodium fluoride, aluminum fluoride and sodium hexafluoroaluminate (cryolite). Microstructures of the coatings were obtained using optical and scanning electron microscopy. Microhardness values measured from the outer surface of the coated sample into the substrate were found to be directly related to the aluminum concentration. An inverse relationship was found between activator boiling point and coating thickness. Coating thickness also increased with increasing process temperature for all activators. The thermodynamic stability of the activators was found to have an effect on the coating thickness.
