Treatment of metals for coating or activation

Abstract

Coating with high-melting metals can be simplified by alloying high-melting metal with sufficient aluminum to make low-melting alloy that is applied, bonded in place, and then subjected to the leaching out of some or most of the aluminum. The resulting surface is porous and will receive and hold top coatings. Leached surface can be pyrophoric and top coating can be exothermically combustible. Pyrophoric powder can also be coated on boron or carbon fibers or sintered with combustible particles. Carbon can be kept from contaminating diffusion-treated workpieces, by conducting diffusion treatment in retorts containing little or no carbon. Porosity can be created by subjecting workpiece to diffusion conditions in contact with depleting material such as powdered nickel or high-nickel aluminides or cobalt or high-cobalt aluminides. Aluminum particles can be electrophoretically deposited on foil and then diffused in. Leaching aluminum out with caustic is improved when a little H.sub.2 O.sub.2 is present in the caustic. Subsequent treatment of the leached surface with weak acid further improves pyrophoricity, and folding of the pyrophoric member extends its pyrophorically-generated high-temperature dwell. Resin foil containing pyrophoric particles makes effective decoy. Re-conditioning of jet engine hot section airfoils is effected with a fluoridizing treatment that can add a little chromium to the fluoridized surfaces.