more than one element being applied in more than one step

Full Title

Solid state diffusion of only non-metal elements into metallic material surfaces (diffusion of silicon C23C10/00); Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals (C23C14/00 takes precedence) > using solids, e.g. powders, pastes (using liquid suspensions of solids C23C8/40) > more than one element being applied in more than one step