Abstract: In the pack diffusion coating of chromium into the surface of a superalloy, the formation of undesirable oxide inclusion is reduced when the diffusion coating pack contains at least about 3% Ni.sub.3 Al. Also the formation of alpha-chromium is reduced when the pack diffusion is carried out in a retort effectively not over five inches in height. On the other hand an alpha-chromium-rich layer at least 0.2 mil thick can be deliberately formed and the superalloy thus coated subjected to an aluminizing treatment to convert the alpha-chromium into islands that provide very high sulfidation resistance. Pack aluminizing in the presence of chromium makes a very effective aluminum- or chromium-containing top coating over platinum plated or platinum coated nickel-base superalloys. Depletion of diffusible material from workpieces heated in a powder-pack can also provide a surface on which aluminizing produces a highly impact-resistant coating.

Abstract: Diffusion coating a substrate metal with a different metal, such as aluminum and zinc, that is then chemically removed from the coated substrate, provides the residual metal with a very desirable catalytic surface. At least about a third of the removable metal can be dissolved out. Platinum wire screens activated in this way make effective exhaust catalysts for automotive engines. Chromium-rich coating for protective purposes can be applied on a superalloy, diffusion coating in a pack that in addition to the chromium to be diffused, also contains at least about 3% Ni.sub.3 Al. Also the formation of alpha-chromium is reduced when the pack diffusion is carried out in a retort effectively not over five inches in height. Pack aluminizing in the presence of chromium makes a very effective aluminum- and chromium-containing top coating over platinum plated or platinum coated nickel-base superalloys.

Abstract: Foil, wire and similar coherent bodies of catalytic metal are provided with catalytically active surfaces by diffusing a chemically removable metal such as aluminum or zinc into those surfaces and then selectively dissolving out at least about a third of the removable metal. Platinum wire screens activated in this way make effective exhaust catalysts for automotive engines.

Abstract: In the pack diffusion coating of chromium into the surface of a superalloy, the formation of undesirable oxide inclusion is reduced when the diffusion coating pack contains at least about 3% Ni.sub.3 Al. Also the formation of alpha-chromium is reduced when the pack diffusion is carried out in a retort effectively not over five inches in height. Pack aluminizing in the presence of chromium makes a very effective aluminum- and chromium-containing top coating over platinum plated or platinum coated nickel-base superalloys. Aluminized nickel can also have its aluminum attacked and at least partially removed with aqueous caustic to leave a very highly active catalytic surface. Pack diffusion can also be arranged to simultaneously provide different coatings in different locations by using different pack compositions in those locations. An aluminizing pack containing a large amount of chromium provides a thinner aluminized case than an aluminizing pack containing less chromium, or less chromium and some silicon.

Abstract: In the diffusion coating of aluminum onto brazed metal, the penetration of the aluminum into the brazing is reduced by conducting the diffusion coating with hydrated aluminum chloride, bromide or iodide as energizer, with the energizer preferably kept out of contact with the work being coated until the energizer volatilizes. This is particularly suited for aluminizing chromium-containing surfaces. Chromium diffusion coatings are less apt to form undesirable oxide inclusions when the diffusion coating is from a pack containing at least about 3% Ni.sub.3 Al. Also the formation of undesirable alpha-chromium is reduced when the pack diffusion is carried out with a retort effectively not over 5 inches in height. Pack aluminizing where the aluminizing is inhibited by the presence of chromium in the pack makes a very effective top coating over platinum plated or platinum coated nickel-base superalloys.

Abstract: Foil, wire and similar coherent bodies of catalytic metal are provided with catalytically active surfaces by diffusing a chemically removable metal such as aluminum or zinc into those surfaces and then selectively dissolving out at least about a third of the removable metal. Platinum wire screens activated in this way make effective exhaust catalysts for automotive engines.