Abstract: A method of forming an aluminum silicon diffusion coating on a surface of an alloy product utilizes a diffusion mixture containing by weight 1% to 5% aluminum, 0.5% to 5% silicon, 0.5% to 3% ammonium halide activator and the balance an inert filler. The product to be coated is placed in a retort with the diffusion mixture covering the product surfaces to be coated. Upon heating aluminum and silicon will diffuse onto the product surfaces forming the aluminum and silicon diffusion coating.

Abstract: Chromium, silicon, aluminum, and optionally manganese are diffused onto the surface of a high temperature alloy product, to provide a coating having improved resistance to carburization and catalytic coke formation and smoother surfaces for high temperature hydrocarbon environments. Preferably, a first layer of chromium or chromium and silicon is deposited and diffusion heat-treated and covered by the second layer of aluminum or aluminum-silicon. The inner layer contains a minimum of 8 weight percent chromium above that contained in the substrate alloy. The outer layer contains a minimum of 20 weight percent aluminum at the coating surface. The coating system is then aged to yield the improved coating that has 60 to 90 weight percent chromium at the surface. Each layer or the combination of layers is diffusion heat treated to cause a diffusion depth ranging from 0.006 inch (0.1524 millimeter) to 0.030 inch (0.762 millimeter) with targeted 0.012 inch (0.3048 millimeter) to 0.015 inch (0.3810 millimeter).

Abstract: A method of aluminum diffusion coating the surface of an iron-, nickel-, cobalt-, or titanium-base alloy product begins with cleaning and providing an anchor profile on the surface of the product, followed by depositing with an appropriate thermal spray method at least 4 mils (0.1016 millimeters) thickness of a minimum 85 wt. % aluminum alloy, which can also contain up to 12 wt. % silicon. A MCrAlX-type coating layer is also thermally sprayed on the substrate surface before the aluminum alloy is sprayed. The thermal sprayed products are heat treated in a sealed retort at a temperature of between 900.degree. F. and 1200.degree. F. (482.degree. C. and 649.degree. C.) and then maintained at that temperature for a period of at least one hour to ensure the formation of a strong metallurgical bond between the aluminum alloy layer and the product. The retort temperature is then elevated to between 1400.degree. F. and 2000.degree. F. (760.degree. C. and 1093.degree. C.) and held at that temperature for between 0.

Abstract: A method of diffusion coating a surface of an alloy product containing at least 5 wt. % iron with a chromium-silicon coating uses a dual activator containing a fluoride salt and a chloride salt, at least one of those salts particularly being ammonium chloride or another ammonium halide salt. The pack mix contain at least 20% chromium and a chromium to silicon ratio of at least 10 to 1. The workpiece is heated to at least 2050.degree. F. to obtain a coating of at least 10 mils which contains at least 30% chromium. Upon heating the ammonium salt will form a reducing environment containing molecular hydrogen. The presence of molecular hydrogen speeds up the chemical reactions by an additional reduction reaction to create the surface coating which enables the coating reactions to occur shorter hold times.

Abstract: The inner surface of ethylene furnace tubes is diffusion coated with a sufficient amount of chromium or chromium and silicon to form a first coating having a thickness of at least two mils. This coating is then cleaned, neutralized, and grit blasted. Then a second coating of a sufficient amount of aluminum or aluminum and silicon is diffused onto the first coating to form a total coating thickness of at least five mils. The surface of the second coating is cleaned and polished to remove the nickel and iron-rich overlay which is present as a result of the coating process and to provide a smooth uniform surface. When ethelyene is produced using furnace tubes which are coated in this manner less coking occurs.