Abstract: Compositional requirements and processing improvements are disclosed which improve the hydrogen embrittlement resistance and the fatigue resistance in air of nickel base single crystal articles. The compositional requirements enlarge the difference between the &ggr;′ solvus temperature and the incipient melting temperature, thus enabling the solution of &ggr;/&ggr;′ eutectic islands without causing incipient melting, while hot isostatic pressing and careful melt practice eliminate porosity and carbides, borides and nitrides, all of which act as crack initiation sites.

Abstract: Layered ceramic coatings in which some layers contain porosity as described as are methods for producing such coatings. The different layers have different compositions and/or are applied under different conditions. As applied, some of the layers have a Zone I structure and some have a Zone II/III type structure (as defined by Movchan). Heat treatment can be used to increase the porosity in the Zone I structure layers.

Abstract: Pest-resistant molybdenum disilicide alloys containing rhenium. The addition of rhenium results in the formation of a thin protective oxide layer that suppresses pesting disintegration.

Abstract: A high strength dispersion strengthened aluminum alloy comprising an aluminum solid solution matrix strengthened by a dispersion of particles based on the compound Al3X, where Al3X has an L12 structure, is described. Various alloying elements are employed to modify the lattice parameter of the matrix and/or the particles so that the matrix and particles have similar lattice parameters. The alloy is produced by rapid solidification from the melt.

Abstract: A metallic coating containing hard carbide particles is described. The coating is applied by an HVOF process using powder particles whose size ranges from about 15 to about 44 microns. The carbide particles are held in a 80% nickel-20% chromium matrix. The coating has a reduced tensile compressive stress relative to similar plasma sprayed coatings and exhibits a high strain to cracking value.

Abstract: The invention is a process for removing ceramic thermal barrier layers from gas turbine engine hardware. A combination of chemical and mechanical steps are used to remove the thermal barrier coating from the substrate without removing the bond coat from the substrate. The process leaves the bond coat on the substrate in condition to receive a repair ceramic thermal barrier coating. The process includes a caustic solution treatment in an autoclave under controlled conditions followed by a mechanical abrasion process.

Abstract: A new family of ceramic materials is identified having particular utility as thermal insulating or thermal barrier coatings on metallic substrates. The ceramic materials have a pyrochlore structure and are typified by the composition A.sub.2 B.sub.2 O.sub.7 where A and B are various ions and O is oxygen. A may have a positive charge of 3.sup.+ or 2.sup.+ and B may have a positive charge of 4.sup.+ or 5.sup.30. These materials are characterized by having chemical stability, thermal stability and thermal insulating properties superior to those of currently used thermal barrier ceramics. An example pyrochlore material is lanthanum zirconate.

Abstract: Layered ceramic coatings in which some layers contain porosity as described as are methods for producing such coatings. The different layers have different compositions and/or are applied under different conditions. As applied, some of the layers have a Zone I structure and some have a Zone II/III type structure (as defined by Movchan). Heat treatment can be used to increase the porosity in the Zone I structure layers.

Abstract: Improved compositions for fabricating nickel superalloy single crystal articles are described. The compositions are characterized by the substantial absence of carbon, boron, zirconium and vanadium and intentional additions of cobalt. The cobalt additions increase the stability of the compositions and provide enhanced heat treatability. Single crystal articles of these compositions have utility as gas turbine engine components.

Abstract: Internal hot corrosion which occurs in hollow uncooled gas turbine engine components is reduced by increasing the oxygen potential of the gas which fills the hollow portion of the component. In particular, blades and vanes which operate in conditions where there is a pressure differential across the component have deliberate venting holes introduced in a sealing structure at one end of the component to permit gas flow through the hollow portion of the component.

Abstract: Columnar grain and single crystal nickel base superalloys are heat treated to provide a damage tolerant microstructure. The microstructure contains large, irregularly shaped "barrier" .gamma.' particles interspersed in an ordered array of smaller cuboidal .gamma.' particles in a .gamma. phase matrix. The barrier particles interrupt the progression of cracks through the microstructure. The invention process includes solutioning the .gamma.' phase, cooling slowly to a temperature about 50.degree. F. to 150.degree. F. (28.degree. C. to 83.degree. C.) below the .gamma.' solvus temperature, further cooling at a rate of at least about 100.degree. F. (56.degree. C.) per minute to less than 1000.degree. F. (538.degree. C.), reheating to 1975.degree. F. to 2000.degree. F. (1079.degree. C. to 1093.degree. C.) and holding for about four to six hours, cooling at 100.degree. F. (56.degree. C.) per minute to less than 1000.degree. F. (538.degree. C.), and heating to 1600.degree. F..+-.25.degree. F. (871.degree. C..+-.14.

Abstract: A two dimensional convergent/divergent exhaust nozzle for a gas turbine engine where a first flap is stationary and a second flap is variable. The flaps have an integrated convergent/divergent design to reduce the number of exhaust nozzle components, increasing engine maintainability and simplifying the exhaust nozzle control system. The design allows fluidic vectoring to be incorporated into the exhaust nozzle by injecting high pressure air into the exhaust stream.

Abstract: A process for producing a fine grain forged superalloy article having a high yield strength at intermediate temperatures. A preferred starting composition comprises, by weight, 15% Cr, 13.6% Co, 4.1% Mo, 4.6% Ti, 2.2% Al, 0.01% C, 0.007% B, 0.07% Zr, balance Ni. This material is forged at a temperature above the gamma prime solvus and at a true strain of at least 0.5. Alternately, the material may be forged below the gamma prime solvus temperature with intermediate super solvus anneals. The overaged material is then worked at a temperature below the gamma prime solvus. The resultant fine grain material is then heat treated or can be further isothermally forged prior to heat treatment to produce complex shapes.

Abstract: A thermal barrier coating for high temperature applications has improved resistance to heat flow. The coating comprises a large number of these (nanometer scale) layers separated by interfaces which are effective in retarding heat flow. The coating material will typically be oxide based ceramics and the coating has particular applications in gas turbine engines.

Abstract: Variable polarity welding is used to repair coated articles, particularly gas turbine engine components. The variable polarity welding process is found to remove the coating during the welding process. This permits the elimination of costly steps which would otherwise be needed in the repair process.

Abstract: A method of forming diffusion holes in a super alloy article by electrical discharge machining by the steps of (a) inserting onto an electrical discharge machine a multiple piece electrode with at least one tooth with respectively at least one movable elongated rod wherein each rod is positioned through each tooth and secured to the tooth, and (b) advancing the multiple piece electrode during electrical discharge machining longitudinally into the super alloy article so that the rod forms a hole with a metering section in the super alloy article of about 0.010 inches in diameter at a depth in excess of about 0.250 inches and the tooth forms a diffused area, with an angle of about 10 degrees, at one end of the hole.

Abstract: A cyclic heat treatment for eliminating the tendency of moderately deformed superalloys to recrystallize is described. The superalloys are subjected to a temperature cycle including a period at a high temperature and a period at a low temperature. The resultant heat treated articles are resistant to recrystallization at temperatures above the gamma prime solvus temperature.

Abstract: Molybdenum disilicide base materials and methods for producing them are described. Mixtures of MoSi.sub.2 powder and other powders including SiO.sub.2, Si.sub.3 N.sub.4, SiC and Mo.sub.5 Si.sub.3 are plasma sprayed. Another embodiment which involves oxidation of MoSi.sub.2 is also disclosed. The resistant materials have particular utility as coatings for Nb alloys.

Abstract: Methods for improving the erosion resistance of composite airfoils are disclosed as are the resultant structures. Wire mesh materials are coated with an erosion-resistant coating, formed to the shape of the airfoil leading edge, and molded into the leading edge during airfoil fabrication.

Abstract: A method for reducing the tendencies of small holes to become packed with particulate material during pack cooling. An organic substance is used to wholly or partially fill small holes prior to placing the part in the packed cooling material. The organic material decomposes during the packed cooling process.