Protecting metals

Abstract

Diffusion chromizing of nickel-base superalloys is effected with essentially no formation of oxide or alphachrome, even in a high-volume diffusion coating pack, by use of a pack consisting essentially of, by weight, about 2 to about 3% aluminum about 3 to about 6 times as much chromium as aluminum a mixture of cobalt and nickel in a combined amount about 10 to about 20 times the amount of aluminum, the amount of cobalt being from about 1/3 to about 4/3 the amount of nickel the balance of the pack being essentially inert filler and activating material. The use of a magnesium halide activator with such pack extends the improvement to the application of heavier chromizing cases. Pack can be of fluent type, particularly where workpiece is partially masked, and masking can be colored to provide visual contrast. Metals not requiring chromizing can be aluminized and top coated with slurry of flake aluminum in aqueous solution of CrO.sub.4.sup..dbd., PO.sub.4.sup..tbd. and Mg.sup.++. Gun barrels can have their internal bores diffusion chromized with fluent pack, and quenched during the cool-down that follows the chromizing.

Dependencies are inferred from the claim text.