Abstract: A nickel-based superalloy known by the designation "718" and having a typical composition comprising, in percentages by weight, Cr 19, Fe 18, Nb 5, and the remainder Ni, is subjected, after the usual thermo-mechanical and heat treatment steps, to an additional annealing step wherein the temperature and duration are selected from the following range as desired:800.degree. C. for between 5 and 30 hours;750.degree. C. for between 25 and 70 hours; and700.degree. C. for between 100 and 300 hours.This leads to a definite improvement in the behaviour of parts made from the superalloy, in terms of fatigue cracking, when used at temperatures over 650.degree. C.

Abstract: A vacuum centrifugally cast combustion liner suitable for use in a gas turbine engine operating at temperatures ranging from ambient up to about 1700.degree. F. is provided. The combustion liner is formed by centrifugally vacuum casting a precipitation hardened nickel-based superalloy having controlled, low amounts of aluminum and titanium. The combustion liner is characterized by a homogeneous grain structure having enhanced strength and creep resistance particularly at elevated temperatures. In addition, the preferred elemental composition, particularly the relatively small amounts of aluminum and titanium, enhance the weldability and overall manufacturability of the combustion liner.

Abstract: A method for obtaining a product from pre-alloyed powders in which the powders are subjected to compaction treatment. The powders are first subjected to pre-treatment under low pressure (or without pressure) at a temperature such that segregating materials precipitate out in stable phases.

Abstract: Superalloy articles are made more oxidation resistant by a process which includes heat treating the article in the presence of foreign chemical species, at a temperature at which the foreign chemical species reacts with and modifies any oxide film present on the article surface. The heat treatment is best carried out at a temperature above the gamma prime solvus temperature of the article and below the incipient melting temperature of the article. Alternatively, the heat treatment may be carried out within the range defined by the incipient melting temperature of the article and about 150.degree. C. below the incipient melting temperature of the article. At such temperatures the foreign chemical species reacts with and modifies the oxide film on the article surface. Sulfur is then able to diffuse through such modified film, and a more oxidation resistant component is produced.

Abstract: Superalloy articles are made more oxidation resistant by a process which includes heating the article in an environment having a reduced pressure of inert gas and a low partial pressure of oxygen to a temperature at which the sulfur in the article diffuses out. The heat treatment is best carried out at a temperature within the range defined by the incipient melting temperature of the article and about 150.degree. C. below the incipient melting temperature of the article. Alternatively, the heat treatment may be carried out at a temperature above the gamma prime solvus temperature of the article and below the incipient melting temperature of the article. At such temperatures, sulfur readily diffuses out of the article, and a more oxidation resistant component is produced.

Abstract: Nickel base superalloys which contain niobium (columbium) to promote gamma double prime strengthening are improved by replacing the niobium with tantalum on an atom-for-atom basis and then heat treating the new alloy at temperatures in excess of those conventionally used for superalloys which include niobium. The resultant tantalum-bearing alloys are found to exhibit increased strength and greater phase stability than corresponding niobium-bearing alloys.

Abstract: A nickel-based alloy useful in the manufacture of a glass fibre centrifuge of which the composition consists essentially of the following elements expressed as percentage by weight:______________________________________ Cr 27.5-29.5% W 6.5-7.8% C 0.69-0.73% Fe 7-10% ______________________________________the remainder substantially being nickel and having in its crystalline structure M.sub.23 C.sub.6 type carbides, M being chromium, at least one equivalent metal, or combination thereof, the M.sub.23 C.sub.6 carbides being substantially secondary.

Abstract: Nickel base superalloy articles, especially gas turbine disks, are provided with substantially enhanced resistance to crack growth through a specific heat treatment. The heat treatment employs a true solution treatment step followed by a subsolvus solution treatment step, followed by at least one aging step. The effect of this series of heat treatment steps is to provide a microstructure having an optimum arrangement of gamma prime particles, with respect to both size and location. Reductions in crack growth rates of several hundred percent relative to prior art heat treatments are achieved.

Abstract: A method and apparatus for heat-treating nickel base superalloy articles to provide different properties in different regions of the article. An initially fine grain microstructure is heated such that a portion of the article is held above the .gamma.' solvus temperature long enough to provide a coarse grain microstructure while the remainder of the article remains below the .gamma.' solvus temperature and retains the fine grain microstructure. The coarse grain microstructure provides a reduced rate of fatigue crack growth rate while the fine grain microstructure retains good tensile properties. The invention is particularly applicable to the fabrication of turbine disks for gas turbine engines.

Abstract: Superalloy castings having large variations in section thickness are heat treated using a cyclic stress relief procedure, with the temperature being cycled between about 50.degree. F. (28.degree. C.) and 150.degree. F. (83.degree. C.) below the second phase particle solvus temperature, to relieve the residual stresses incurred during cooling within the mold following casting, followed by a solution cycle at a temperature about 25.degree. F. (14.degree. C.) below the second phase particle solvus temperature to dissolve some or all of the second phase particles.

Abstract: A nickel base superalloy capable of being made into a single crystal article is provided with high temperature strength and improved stability by limiting the Presence of an undesirable SRZ constituent. Significant to the control of formation of such undesirable constituents is the control of the amount of Re in the alloy in combination with elements such as Al, Cr, Ta, Mo, Co and W. A solution heat treatment is provided for additional control.

Abstract: A method for preparing a heat-treated article made of a superalloy, such as a turbine disk preform, includes furnishing an article made of a superalloy that is prone to quench cracking, usually after forging the article, and thereafter covering at least a portion of the article with a quench cladding having a thickness of at least about 1/8 inch so that the quench cladding is in direct thermal contact with the article. The quench cladding may be conveniently applied to the article by thermal spraying, which produces direct thermal contact between the quench cladding and the article, or by placing the article into the envelope of the quench cladding material and hot isostatically pressing to achieve a direct thermal contact between the envelope and the article. After the quench cladding is in place, the clad article is heated to elevated temperature and quenched from the elevated temperature to a lower temperature, and the envelope is removed.

Abstract: A method of increasing intergranular stress corrosion cracking resistance of Alloy 718 in water reactor environments is described where the alloy is heat treated at a high solution annealing temperature to dissolve grain boundary precipitates formed during thermomechanical processing. A water quenching step is advantageously employed following the high solution annealing. The alloy is then aged at two separate temperatures and finally air cooled to room temperature.

Abstract: Nickel base superalloys which contain niobium (columbium) to promote gamma double prime strengthening are improved by replacing the niobium with tantalum on an atom-for-atom basis and then heat treating the new alloy at temperatures in excess of those conventionally used for superalloys which include niobium. The resultant tantalum-bearing alloys are found to exhibit increased strength and greater phase stability than corresponding niobium-bearing alloys.

Abstract: Process for the production of longitudinally-directed coarse-grained columnar crystals in an oxide-dispersion-hardened nickel-based superalloy which is difficult to recrystallize, starting from a warm-kneaded fine-grained structural status, by heating to a preheating temperature T.sub.pre, which is below the minimum recrystallization temperature T.sub.rec min necessary for the material and is at least at the solution annealing temperature of the carbides in the .gamma.-matrix, keeping at T.sub.pre for 5 min to 6 h, for the purpose of isothermal annealing, and immediately heating to recrystallization temperature T.sub.rec at 10.degree. to 40.degree. C./min without prior cooling, and cooling to room temperature.

Abstract: One form of an improved cast, hollow, columnar grain nickel base alloy article is provided with outstanding elevated temperature stability as represented by oxidation resistance, an improved combination of longitudinal and transverse stress rupture properties, and a thin wall of less than about 0.035 inch, substantially free of cracks. Described is a heat treatment in combination with an alloy for providing such an article.

Abstract: A process for identificaiton, evaluation and removal of microshrinkage of investment cast superalloy parts and parts produced by the process. Parts free of deleterious microshrinkage capable of longer life at existing stress levels or use at higher alternating stresses are produced by first subjecting the parts to hot isostatic pressing to eliminate nonsurface connected subsurface microshrinkage. Next, in order to expose near-surface microshrinkage microscopically connected to the surface, the parts are immersed in an acid solution for a time sufficient to uniformly remove at least about 0.005 inches of the original as cast surface. The exposed microshrinkage is evaluated for acceptability or removal by standard nondestructive techniques, such as liquid penetration evaluation.

Abstract: A nickel-based superalloy consisting essentially of, in weight percent, from about 4 to about 5 percent chromium, from about 11 to about 14 percent cobalt, from about 4 to about 8 percent tungsten, from about 6 to about 10 percent tantalum, from about 5 to about 7 percent aluminum, from about 5.5 to about 8 percent rhenium, from about 0 to about 0.50 percent hafnium, from about 0 to about 0.07 percent carbon, from 0 to about 0.01 percent boron, from 0 to about 0.030 percent yttrium, from 0 to about 6 percent ruthenium, from 0 to about 1 percent molybdenum, from 0 to about 1 percent niobium, and the balance essentially nickel. Articles made from the superalloy of the invention are especially useful when cast as single crystal airfoils for use in advanced gas turbine engines.

Abstract: Improved, creep-stress rupture and hold-time fatigue resistant nickel base alloys for use at elevated temperatures are disclosed. The alloys consists essentially of, in weight percent, 10.9 to 12.9% Co; 11.8 to 13.8% Cr; 4.6 to 5.6% Mo; 2.1 to 3.1% Al; 4.4 to 5.4% Ti; 1.1 to 2.1% Nb; 0.005 to 0.025% B; 0.01 to 0.06% C; 0 to 0.6% Zr; 0.1 to 0.3% Hf; balance nickel. The article is characterized by a microstructure having an average grain size of from about 20 to 40 microns, with carbides, borides, and 0.3 to 0.4 micron-sized coarse gamma prime located at the grain boundaries, and 30 nanometer-sized fine gamma prime uniformly distributed throughout the grains. The alloys are suitable for use as turbine disks in gas turbine engines of the type used in jet engines, or for use as rim sections of dual alloy turbine disks for advanced turbine engines and are capable of operation at temperatures up to about 1500.degree. F. A method for achieving the desired properties in such turbine disks is also disclosed.