Copper was ion plated onto a steel substrate to form a highly adherent surface coating. Electron probe examination of the copper/steel interfacial region showed that the ion-plated copper had penetrated the steel substrate to a depth of about 7–8 μ to form a graded, diffuse interface. The excellent adhesion of the coating to the substrate, which was examined by a 90° bend test and the standard Scotch Tape Test, can be attributed to the diffused interface formed by ion plating.