Patent ID: 7163718

Claim:
A process for forming diffusion aluminide coatings on an uncoated portion of a surface of a substrate, without interdiffusing a sufficient amount of aluminum into a coating layer to adversely affect the coating growth potential or mechanical properties of said coating layer, comprising the steps of: providing a metal substrate comprising an external surface and an internal passage therein defined by an internal surface, at least a portion of the external surface of the substrate being coated, but at least a portion of the internal surface being uncoated, with a coating layer selected from the group consisting of β-NiAl-base, MCrAlX, a line-of sight diffusion aluminide, a non-line-of-sight diffusion aluminide, a pack diffusion aluminide, and a slurry diffusion aluminide on said substrate, wherein the substrate is a gas turbine airfoil, and wherein the internal passage is a plurality of internal cooling passages which extend through an interior of the airfoil; cleaning the external surface of the substrate; subjecting the metal substrate to an aluminum vapor phase deposition process performed using a fluorine-containing activator selected from the group consisting of AlF 3 , CrF 3 , NH 4 F, and combinations thereof, at a rate in the range of about 0.036 mols of fluorine per ft 3 /hr of transport gas to about 0.18 mols of fluorine per ft 3 /hr of transport gas, at a temperature in the range of about 1350° F. to about 1925° F., using a transport gas selected from the group consisting of argon, nitrogen, hydrogen, and combinations thereof, the transport gas being provided at a flow rate in the range of about 20 ft 3 /hr to about 120 ft 3 /hr for a period of time in the range of about 2 hours to about 10 hours; and cooling the substrate.