Schaeffer, Jon C. | Engineering Papers

NASA NTRS2003

Preparation of low-sulfur platinum and platinum aluminide layers in thermal barrier coatings

A method for preparing a coated nickel-base superalloy article reduces the sulfur content of the surface region of the metallic coating layers to low levels, thereby improving the adhesion of the coating layers to the article. The method includes depositing a first layer of platinum overlying the surface of a substrate, depositing a second layer of aluminum over the platinum, and final desulfurizing the article by heating the article to elevated temperature, preferably in hydrogen, and removing a small amount of material from the surface that was exposed during the step of heating. A ceramic layer may be deposited over the desulfurized article. The article may also be similarly desulfurized at other points in the fabrication procedure.

Spitsberg, Irene T.↗

NASA NTRS1997

Design for Oxidation Resistance

Alloys intended for use in high-temperature environment rely on the formation of a continuous, compact, slow-growing oxide layer for oxidation and hot corrosion resistance. To be protective, this oxide layer must be chemically, thermodynamically stable. Successful alloy design for oxidative environment is best achieved by developing alloys that are capable of forming adherent scales of either alumina (Al2O3), chromia (Cr2O3), or silica (SiO2). In this article, emphasis has been placed on the issue related to high-temperature oxidation of superalloys used in gas turbine engine application. Despite the complexity of these alloys, optimal performance has been associated with protective alumina scale formation. As will be described below, both compositional makeup and protective coatings play key role in providing oxidation protection. Other high-temperature materials described include nickel and titanium aluminide intermetallics, refractory metal, and ceramics.

Smialek, James L.↗