Abstract: A turbine bucket assembly and turbine system are disclosed. The turbine bucket assembly includes a single-lobe joint having an integral platform, the joint having a first axial length; a segmented airfoil having a root segment extending radially outward from the platform and a tip segment coupled to the root segment, the tip segment having a second axial length, which is less than the first axial length; and a turbine wheel defining a receptacle with a geometry corresponding to the single-lobe joint and being coupled to the single-lobe joint. The tip segment includes a tip segment material, the root segment includes a root segment material, and the turbine wheel includes a turbine wheel material, the root segment material and the turbine wheel material having a lower heat resistance and a higher thermal expansion than the tip segment material.

Abstract: In some embodiments, a gamma titanium aluminide alloy consists essentially of, in atomic percent, 38 to about 50% aluminum, 1 to about 6% niobium, 0.25 to about 2% tungsten, 0.01 to about 1.5% boron, up to about 1% carbon, optionally up to about 2% chromium, optionally up to about 2% vanadium, up to about 2% manganese, and the balance titanium and incidental impurities. In some embodiments, the gamma titanium aluminide alloy forms at least a portion of a gas turbine component. In some embodiments, a gamma titanium aluminide alloy, consists essentially of, in atomic percent, about 40 to about 50% aluminum, about 1 to about 5% niobium, about 0.3 to about 1% tungsten, about 0.1 to about 0.3% boron, up to about 0.1% carbon, up to about 2% chromium, up to about 2% vanadium, up to about 2% manganese, up to about 1% molybdenum, and the balance titanium and incidental impurities.

Abstract: In some embodiments, a gamma titanium aluminide alloy consists essentially of, in atomic percent, about 38 to about 50% aluminum, about 6% niobium, about 0.25 to about 2% tungsten, optionally up to about 1.5% boron, about 0.01 to about 1.0% carbon, optionally up to about 2% chromium, optionally up to about 2% vanadium, optionally up to about 2% manganese, and the balance titanium and incidental impurities. In some embodiments, the gamma titanium aluminide alloy forms at least a portion of a gas turbine component. In some embodiments, a gamma titanium aluminide alloy, consisting essentially of, in atomic percent, about 40 to about 50% aluminum, about 3 to about 5% niobium, about 0.5 to about 1.5% tungsten, about 0.01 to about 1.5% boron, about 0.01 to about 1.0% carbon, optionally up to about 2% chromium, optionally up to about 2% vanadium, optionally up to about 2% manganese, and the balance titanium and incidental impurities.

Abstract: A turbine bucket assembly and turbine system are disclosed. The assembly includes a single-lobe joint having an integral platform, the joint having a first axial length; a non-segmented airfoil extending radially outward from the integral platform and having a tip end with a second axial length, the second axial length being less than the first axial length; and a turbine wheel having a receptacle with a geometry corresponding to the single-lobe joint and being coupled to the single-lobe joint. The joint and the non-segmented airfoil include a turbine bucket material, and the turbine wheel includes a turbine wheel material, the turbine wheel material having a lower heat resistance and a higher thermal expansion than the turbine bucket material.

Abstract: A turbine bucket assembly and turbine system are disclosed. The assembly includes a single-lobe joint having an integral platform, the joint having a first axial length; a segmented airfoil having a root segment extending radially outward from the platform and a tip segment coupled to the root segment, the tip segment having a second axial length being less than the first axial length; and a turbine wheel having a receptacle with a geometry corresponding to the single-lobe joint and being coupled to the single-lobe joint. The tip segment includes a tip segment material, the root segment includes a root segment material, and the turbine wheel includes a turbine wheel material having a lower heat resistance and a higher thermal expansion than the root segment material and the tip segment material.

Abstract: A turbine bucket assembly and turbine system are disclosed. The assembly includes a multi-lobe joint having an integral platform, the joint having a first axial length; a segmented airfoil having a root segment extending radially outward from the platform and a tip segment coupled to the root segment, the tip segment having a second axial length less than the first axial length; and a turbine wheel defining a receptacle with a geometry corresponding to the multi-lobe joint and being coupled to the multi-lobe joint. A tip segment material, a root segment material, and a turbine wheel material are selected, such that the turbine wheel material and the root segment material have a lower heat resistance and a higher thermal expansion than the tip segment material.

Abstract: A turbine bucket assembly and turbine system are disclosed. The turbine bucket assembly includes a single-lobe joint having an integral platform, the joint having a first axial length; a segmented airfoil having a root segment extending radially outward from the platform and a tip segment coupled to the root segment, the tip segment having a second axial length, which is less than the first axial length; and a turbine wheel defining a receptacle with a geometry corresponding to the single-lobe joint and being coupled to the single-lobe joint. The tip segment includes a tip segment material, the root segment includes a root segment material, and the turbine wheel includes a turbine wheel material, the root segment material and the turbine wheel material having a lower heat resistance and a higher thermal expansion than the tip segment material.

Abstract: Methods for casting a metallic material to form a component are described. The component can be a superalloy-containing turbine part, for example. The general method includes the step of pouring the metallic material, in molten form, into an investment mold; and then rapidly immersing the entire investment mold into a bath that contains a low-melting liquid coolant metal, so as to achieve substantially uniform, multi-directional heat transfer out of the molten material. The molten material that solidifies to form the component is characterized by a fine-grained, equiaxed grain structure. Related embodiments include the use of two ingots that constitute the superalloy material. One ingot includes the oxygen-reactive elements, and is prepared by a vacuum-melting technique. The other ingot includes the remainder of the elements, and can be prepared by a number of techniques, such as air-melting processes.

Abstract: A process capable of producing large metallic castings having lengths of one hundred centimeters or more and a unidirectional crystal structure substantially free of freckle defects. The process includes preheating a mold within a heating zone of a directional casting apparatus, pouring a molten metal alloy into a cavity of the mold, and then withdrawing the mold from the heating zone, through a heat shield, and into a cooling zone of the directional casting apparatus to directionally solidify the molten metal alloy within the cavity. The heating and cooling zones establish an axial thermal gradient that defines a solidification front in the molten metal alloy within the cavity. The mold is withdrawn at a withdrawal rate that, in combination with the axial thermal gradient, causes the solidification front to be substantially flat and perpendicular to the withdrawal direction.

Abstract: The invention is a class of nickel-base alloys for gas turbine applications, comprising, by weight, about 13.7 to about 14.3 percent chromium, about 5.0 to about 10.0 percent cobalt, about 3.5 to about 5.2 percent tungsten, about 2.8 to about 5.2 percent titanium, about 2.8 to about 4.6 percent aluminum, about 0.0 to about 3.5 percent tantalum, about 1.0 to about 1.7 percent molybdenum, about 0.08 to about 0.13 percent carbon, about 0.005 to about 0.02 percent boron, about 0.0 to about 1.5 percent niobium, about 0.0 to about 2.5 percent hafnium, about 0.0 to about 0.04 percent zirconium, and the balance substantially nickel. The nickel-base alloys may be provided in the form of useful articles of manufacture, and which possess a unique combination of mechanical properties, microstructural stability, resistance to localized pitting and hot corrosion in high temperature corrosive environments, and high yields during the initial forming process as well as post-forming manufacturing and repair processes.

Abstract: Nickel based alloys are provided comprising from about 7.0 weight percent (wt %) to about 12.0 wt % chromium, from about 0.1 wt % to about 5 wt % molybdenum, from about 0.2 wt % to about 4.5 wt % titanium, from about 4 wt % to about 6 wt % aluminum, from about 3 wt % to about 4.9 wt % cobalt, from about 6.0 wt % to about 9.0 wt % tungsten, from about 4.0 wt % to about 6.5 wt % tantalum, from about 0.05 wt % to about 0.6 wt % hafnium, up to about 1.0 wt % niobium, up to about 0.02 wt % boron, and up to about 0.1 wt % carbon, with the remainder being nickel and incidental impurities. The alloys may be cast, directionally solidified and heat treated to provide articles having a gamma prime fraction of greater than about 50%.

Abstract: Nickel based alloys are provided comprising from about 7.0 weight percent (wt %) to about 12.0 wt % chromium, from about 0.1 wt % to about 5 wt % molybdenum, from about 0.2 wt % to about 4.5 wt % titanium, from about 4 wt % to about 6 wt % aluminum, from about 3 wt % to about 4.9 wt % cobalt, from about 6.0 wt % to about 9.0 wt % tungsten, from about 4.0 wt % to about 6.5 wt % tantalum, from about 0.05 wt % to about 0.6 wt % hafnium, up to about 1.0 wt % niobium, up to about 0.02 wt % boron, and up to about 0.1 wt % carbon, with the remainder being nickel and incidental impurities. The alloys may be cast, directionally solidified and heat treated to provide articles having a gamma prime fraction of greater than about 50%.

Abstract: An apparatus and method for casting an alloy using a unidirectional casting technique. The apparatus includes a mold adapted to contain a molten quantity of an alloy, a primary heating zone adapted to heat the mold and the molten alloy therein to a temperature above the liquidus temperature of the alloy, a cooling zone adapted to cool the mold and molten alloy therein to a temperature below the solidus temperature of the alloy and thereby yield the unidirectionally-solidified casting, and an insulation zone between the primary heating zone and the cooling zone. The apparatus also has a secondary heating zone separated from the insulation zone by the primary heating zone. The secondary heating zone maintains the mold and the molten alloy therein at a temperature below the liquidus temperature of the alloy. The temperatures within the primary and secondary heating zones are individually set and controlled.

Abstract: An apparatus and method for casting an alloy using a unidirectional casting technique. The apparatus includes a mold adapted to contain a molten quantity of an alloy, a primary heating zone adapted to heat the mold and the molten alloy therein to a temperature above the liquidus temperature of the alloy, a cooling zone adapted to cool the mold and molten alloy therein to a temperature below the solidus temperature of the alloy and thereby yield the unidirectionally-solidified casting, and an insulation zone between the primary heating zone and the cooling zone. The apparatus also has a secondary heating zone separated from the insulation zone by the primary heating zone. The secondary heating zone maintains the mold and the molten alloy therein at a temperature below the liquidus temperature of the alloy. The temperatures within the primary and secondary heating zones are individually set and controlled.

Abstract: Nickel based alloys are provided comprising from about 7.0 weight percent (wt %) to about 12.0 wt % chromium, from about 0.1 wt % to about 5 wt % molybdenum, from about 0.2 wt % to about 4.5 wt % titanium, from about 4 wt % to about 6 wt % aluminum, from about 3 wt % to about 4.9 wt % cobalt, from about 6.0 wt % to about 9.0 wt % tungsten, from about 4.0 wt % to about 6.5 wt % tantalum, from about 0.05 wt % to about 0.6 wt % hafnium, up to about 1.0 wt % niobium, up to about 0.02 wt % boron, and up to about 0.1 wt % carbon, with the remainder being nickel and incidental impurities. The alloys may be cast, directionally solidified and heat treated to provide articles having a gamma prime fraction of greater than about 50%.

Abstract: A process capable of producing large metallic castings having lengths of one hundred centimeters or more and a unidirectional crystal structure substantially free of freckle defects. The process includes pouring a molten metal alloy into a preheated mold within a heating zone, withdrawing the mold from the heating zone, through a heat shield, and into a cooling zone to directionally solidify the molten metal alloy, and then cooling the mold to produce the casting and the unidirectional crystal structure thereof. The heat shield operates as a barrier to thermal radiation between the heating zone and the cooling zone, and the mold is withdrawn at a rate that, in combination with the heat shield, maintains a thermal gradient to solidify the molten metal alloy and form primary dendrite arms having an average spacing therebetween of about 150 to about 500 micrometers.