Abstract: Methods of protecting a metallic substrate from corrosion include introducing an aqueous or powder-form composition including at least one corrosion inhibitor into a crevice that traverses one or more layers covering the metallic substrate to deliver the composition via the crevice into contact with a surface of the metallic substrate. The corrosion inhibitors present in the composition bond to the surface of the metallic substrate, resulting in formation of a film on the surface of the metallic substrate. This film protects the surface of the metallic substrate against corrosion.

Abstract: A superalloy has a composition of, in weight percent, from about 16.0 percent to about 22.4 percent cobalt, from about 6.6 percent to about 14.3 percent chromium, from about 1.4 percent to about 3.5 percent tantalum, from about 1.9 percent to about 4.0 percent tungsten, from about 1.9 percent to about 3.9 percent molybdenum, from about 0.03 percent to about 0.10 percent zirconium, from about 0.9 percent to about 3.0 percent niobium, from about 2.4 percent to about 4.6 percent titanium, from about 2.6 percent to about 4.8 percent aluminum, from 0 to about 2.5 percent rhenium, from about 0.02 percent to about 0.10 percent carbon, from about 0.02 percent to about 0.10 percent boron, balance nickel and minor amounts of impurities. The superalloy is advantageously utilized in aircraft gas turbine disks.

Abstract: A .gamma.' precipitation strengthened nickel-base superalloy provided in powder metal or cast and wrought form and alloyed to minimize nucleation tendencies and control grain growth. The superalloy includes a fine dispersion of a second phase in sufficient amounts to prevent critical grain growth in the superalloy when the superalloy is subjected to temperatures above its .gamma.' solvus temperature. The superalloy preferably contains at least about 0.030 weight percent carbon or about 27 to about 2000 ppm yttrium in order to produce a volume fraction of the second phase which is sufficient to cover a minimum of about 10 percent of the grain boundary area.

Abstract: A method is provided for reducing the tendency for thermally induced porosity within a .gamma.' precipitation strengthened nickel-base superalloy which has been processed to obtain a uniform and coarse grain microstructure. This method is particularly useful for forming components such as gas turbine compressor and turbine disk assemblies in which optimal mechanical properties, such as low cycle fatigue and creep resistance, are necessary for operating at elevated temperatures within a gas turbine engine. The method generally entails alloying a .gamma.' precipitation strengthened nickel-base superalloy to have a boron content of not more than about 0.02 weight percent, and then forming a billet by melting an ingot of the superalloy in an argon gas atmosphere and atomizing the molten superalloy using argon gas. The above atomizing technique encompasses both powder metallurgy and spray forming processes.

Abstract: A method is provided for obtaining uniform grain growth within .gamma.' precipitation strengthened nickel-base superalloys provided in powder metal or cast and wrought form. The method includes alloying the nickel-base superalloy to contain a minimum calculated amount of carbon which, when finely dispersed within the alloy using suitable processing methods, yields a sufficient amount of carbide phase which restricts the grain boundary motion of the alloy during supersolvus heat treatment. When appropriately processed, the grains are not permitted to grow randomly during supersolvus heat treatment, making possible a microstructure whose grain size is uniform, having a grain size range of about 2 to about 3 ASTM units and being substantially free of random grain growth in excess of about 2 ASTM units coarser than the desired grain size range.

Abstract: A method is provided for obtaining a uniform grain size on the order of about ASTM 5 or coarser in at least a portion of an article formed from a .gamma.' precipitation strengthened nickel-base superalloy. The method comprises forming an article by: providing a billet, preheating the billet above 2000.degree. F. for at least 0.5 hours, working at least a portion to near-net shape at working conditions including a first strain rate of less than about 0.01 per second and at a subsolvus temperature at or near the recrystallization temperature, supersolvus heating to form a grain size in the portion of at least 5 ASTM, and cooling to reprecipitate .gamma.' within the article. The method can be utilized to form a .gamma.' precipitation strengthened nickel-base superalloy article whose grain size varies uniformly between portions thereof, so as to yield a desirable microstructure and property gradient in the article in accordance with the in-service temperature and stress-state gradient experienced by the article.

Abstract: A method is provided for obtaining uniform grain growth within .gamma.' precipitation strengthened nickel-base superalloys. The method includes forming a billet having a very fine grain size in order to achieve optimum superplasticity of the superalloy during forging. The article is then heated to a pre-working hold temperature in a manner which prevents coarsening of the microstructure and a loss of superplasticity. The article is then worked, such as by forging, at a temperature below the .gamma.' solvus temperature of the alloy, so as to maintain local strain rates within the article below a critical strain rate for random grain growth, and so as to maintain the strain rate gradient throughout the article below a critical upper limit. After working, the article is subjected to annealing at a temperature which is less than the .gamma.' solvus temperature of the alloy, and for a duration which is sufficient to remove accumulated metallurgical strain in the article.