Cluster migration in the earliest growth stages of gold films on carbon

A process has been developed for forming dense, adherent aluminized layers on Ni-Cr-type alloys. This process development was based on a previous discovery that cobalt additions of 2–20% significantly affect the morphology of aluminized coatings. To enrich the surface region of the Ni-Cr in cobalt, a layer of cobalt about (2–8) × 10^-3 mm thick is applied by physical vapor deposition, sputtering or any other suitable process. The cobalt-coated substrate is heat treated using time-temperature conditions sufficient to cause the cobalt atoms to diffuse into the substrate to the required depth prior to the second step of aluminization. The desired cobalt concentration is greater than 2 wt.% in the substrate surface.Aluminization of the substrate after surface treatment with cobalt is achieved using conventional pack cementation or any other suitable process. It is shown that the oxidation resistance of Ni-20Cr is improved when this alloy is coated with a layer of cobalt of thickness 2.5 × 10^-3mm, then heat treated for 5 h at 1160°C and finally pack aluminized.It is also shown that a duplex-aluminized physically vapor-deposited (PVD) NiCoCr coating has a significantly different morphology from a similarly aluminized PVD Ni-Cr coating.