The codeposition of two or more elements in a halide-activated cementation pack is inherently difficult because of large differences in the thermodynamic stabilities for their volatile halides. However, through a computer-assisted analysis of the pack equilibria, combinations of suitable master alloys and activator salts can be identified. The codeposition of chromium plus aluminum or chromium plus silicon by pack cementation has yielded diffusion coatings with excellent resistance to high-temperature oxidation and corrosion fora wide range of alloy substrates.