Protective coating

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PCT No. PCT/GB95/01745 Sec. 371 Date May 16, 1996 Sec. 102(e) Date May 16, 1996 PCT Filed Jul. 24, 1995 PCT Pub. No. WO96/03535 PCT Pub. Date Feb. 8, 1996A method producing a coating on a substrate by aluminizing, chromizing or siliconizing the substrate, and depositing on the coated substrate by electrolytic or electroless deposition a metal matrix M1 from a bath containing particles of CrAlM2 to co-deposit the particles with the matrix as M1CrAlM2, where M1 is Ni, Co or Fe or two or all of these elements and M2 is Y, Si, Ti, Hf, Ga, Nb, Mn, Pt, a rare earth element or two or more of these elements. Preferably, the method includes platinum aluminizing of the substrate. Heat treatments may be incorporated before and after deposition of the M1CrAlM2. The deposition of the M1CrAlM2 is carried out at a current density of less than 5 mA per square centimeter. Preferably, the deposition forms a M1CrAlM2 layer less than 50 microns thick, and occurs at a bath loading of less than 40 grams per liter of the particles. In a preferred embodiment, the particle size distribution in the plating bath is 25 percent between 15 and 12 microns, 45 percent between 12 and 10 microns and 30 percent less than 10 microns. The method is particularly useful for coating a gas turbine part.