The Effect of Activator on Aluminizing of 304 Stainless Steel using the Halide Activated Pack Cementation Process
Authors:Michell Aranda, Christopher Calle, Armando Coronado, Shahan Kasnakjian, Mesai Loffe, Sutine Sujittosakul
Mentor:Dr. Vilupanur Ravi, Department Chair and Professor of Chemical and Materials Engineering, California State Polytechnic University Pomona
Stainless steels are frequently used in applications requiring a low cost, high strength material which can withstand high temperatures and corrosive environments. The common grades of stainless steel offer sufficient corrosion resistance under certain conditions. However, applications with harsher conditions which require more corrosion resistant materials include nuclear, coal, and biomass power plants, where stainless steel is already used extensively. To counteract this, two approaches can be taken. The first is new material selection, which can be expensive. The second option is surface modification by coatings, e.g., diffusional coatings. Diffusion coatings can be applied by processes such as halide activated pack cementation (HAPC). In HAPC, the base metal is surrounded by the “pack” - a mixture of powders including the master alloy (the coating element), a halide salt (pack activator), and an inert filler. The coating element diffuses through the surface of the base metal and forms a protective coating layer. In this project, we are investigating the effects of process parameters on coatings. In this study, Type 304 austenitic stainless steel was coated at 650°C for 9 hours under an argon atmosphere. Different activators were used to study the effects of pack composition on coating quality. The activators studied thus far include, aluminum chloride (AlCl3), ammonium chloride (NH4Cl), sodium chloride (NaCl). Microstructures of coated samples were analyzed using optical microscopy. X-ray diffraction (XRD) was used to determine the phases in the coating. Additionally, mass change, coating thickness and microhardness data will be presented and the effectiveness of the activators at 650°C will be discussed.