Abstract : 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 masteralloys and activator salts can be identified. Codeposition of Chromium plus aluminum or Cr plus Silicon by pack cementation has yielded diffusion coatings with excellent resistance to high-temperature oxidation/corrosion for a wide range of alloy substrates.