EP3122495A2 - Article for use in high stress environments having multiple grain structures - Google Patents

Article for use in high stress environments having multiple grain structures

Info

Publication number
EP3122495A2
EP3122495A2 EP15717716.3A EP15717716A EP3122495A2 EP 3122495 A2 EP3122495 A2 EP 3122495A2 EP 15717716 A EP15717716 A EP 15717716A EP 3122495 A2 EP3122495 A2 EP 3122495A2
Authority
EP
European Patent Office
Prior art keywords
weight percent
metal
cooling
mold
metal alloy
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP15717716.3A
Other languages
German (de)
French (fr)
Inventor
Yan Cui
Ganjiang Feng
Srikanth Chandrudu Kottilingam
Matthew Joseph LAYLOCK
Dechao Lin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Publication of EP3122495A2 publication Critical patent/EP3122495A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
    • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
    • B22D21/025—Casting heavy metals with high melting point, i.e. 1000 - 1600 degrees C, e.g. Co 1490 degrees C, Ni 1450 degrees C, Mn 1240 degrees C, Cu 1083 degrees C
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
    • B22D27/045—Directionally solidified castings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D30/00—Cooling castings, not restricted to casting processes covered by a single main group
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
    • C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F01D5/14—Form or construction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D9/00—Stators
    • F01D9/02—Nozzles; Nozzle boxes; Stator blades; Guide conduits, e.g. individual nozzles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2230/00—Manufacture
    • F05D2230/20—Manufacture essentially without removing material
    • F05D2230/21—Manufacture essentially without removing material by casting
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft

Definitions

  • the subject matter disclosed herein relates to an article for use in high stress environments and the method of manufacturing the same. More particularly, the subject matter relates to enhancing durability of articles used in the hot section of a turbine.
  • Articles exposed to high temperature environments can experience stress cracking due to localized stress within the article.
  • This localized stress can be caused by a temperature gradient within a material which can lead to different rates of expansion. Portions of the material can expand more rapidly and can induce a tension force on adjacent areas. If not mitigated a stress crack can propagate through the article and result in failure of the article, such as creep, thermal fatigue, and the like.
  • a method of forming an article can comprise: heating a metal to form a molten metal having a metal temperature; heating a mold to a mold temperature greater than or equal to the metal temperature; introducing the molten metal to the mold; cooling a first portion of the molten metal while maintaining a second portion of the molten metal at the metal temperature, wherein the first portion has a first side and a second side, wherein the second side is opposite the first side and adjacent to the second portion, and wherein the cooling comprises progressively cooling the first portion from the first side to the second side such that a solidification interface progresses from the first side to the second side; and cooling the remainder of the molten metal from multiple directions after the first portion is cooled to less than or equal to a crystallization temperature.
  • a part for a turbine can comprise: a base having a base wall and an attachment, where the attachment is configured for mechanical attachment turbine component; an airfoil extending from the base wall; wherein the part comprises a first portion comprising the base and a first section of the airfoil and a second portion comprising a second section of the airfoil, wherein the first portion comprises a metal having directionally solidified grains and the second portion comprises the metal having equiaxed grains, and wherein a longest dimension of the directionally solidified grains extend parallel to an expected tensile stress in the part when the part is in use.
  • FIG. 1 is an illustration of a cross-section of a metal part being molded.
  • FIG. 2 is an illustration of a cross-section of metal part being cast having directionally solidified (DS) grains.
  • FIG. 3 is an illustration of a cross-section of a metal part in a mold having a hybrid grain structure.
  • FIG. 4 is an illustration of a metal part used in a turbine having an airfoil affixed between two walls.
  • a turbine part can include a blade and/or vane having an airfoil section.
  • the turbine part can be exposed to high temperature fluid flow. This flow can cause high thermal stress in some areas of the turbine part, at least partially due to thermal gradients imposed on the part by the high temperature fluids flowing along a surface of the part.
  • the turbine part can include hollow portions, cavities, or passages, such that it can be cooled using various methods to reduce the temperature gradients within the part thereby reducing the magnitude of internal stress within the part.
  • Such cooling methods can include internal cooling methods (e.g., convection cooling, impingement cooling, and the like) or external cooling methods (e.g. film cooling, effusion cooling, transpiration cooling, pin fin cooling and the like).
  • the turbine part can be cast from metal, such as metal alloys. Superalloys can be used to enhance the durability of these parts.
  • Solid phase metals and metal alloys can have microscopic crystal structures. These microscopic crystals, also referred to as grains, can form microstructures within the volume of the solid metal. These grain structures impart particular properties to the metal, such as structural properties including tensile strength, ultimate strength, hardness, ductility, and the like.
  • metal turbine parts having hybrid grain structures, such as two or more different grain structures in different areas of the part, and methods for forming these structures.
  • a metal in the manufacture of turbine parts a metal can be molded into a selected part shape, for example, in a casting process.
  • a metal can be heated to a melt temperature, e.g. a temperature sufficient to melt the metal and form a homogeneous metal mixture, wherein a homogeneous metal mixture has a single phase microstructure.
  • a melt temperature e.g. a temperature sufficient to melt the metal and form a homogeneous metal mixture, wherein a homogeneous metal mixture has a single phase microstructure.
  • the composition can be uniform.
  • the melt temperature can vary depending on the composition of the metal chosen for the casting.
  • the melt temperature can be greater than the melting temperature of a metal component of a metal alloy, such that the metal can form a homogeneous mixture.
  • the melt temperature can be greater than or equal to 2300 °F (1260 °C), for example, 2500 °F (1371 °C) - 3000 °F (1649 °C), or, 2600 °F (1427 °C) - 2800 °F (1538 °C).
  • the mold can be heated to a temperature equal to or greater than the melt temperature, such that the molten metal can flow into and fill the mold cavity without solidifying.
  • the mold can be heated by placing the mold in a furnace or other suitable heat source.
  • the furnace can maintain the temperature of the mold at or above the melt temperature.
  • the mold can include electrical heating elements for providing additional heating and/or for controlling temperatures along portions of the mold surfaces.
  • a surface of the mold can be cooled to solidify an adjacent volume of the molten metal. While a portion of the molten metal is cooled along this cooling surface, the temperature of the remainder of the molten metal can be maintained above the melt temperature. In this way a temperature gradient can be established in the molten metal.
  • the temperature gradient can be established along a single linear dimension of the molten metal. This gradient can be maintained by controlling the mold cavity surface temperatures along a dimension of the mold and the temperature of the cooling surface. The direction that thermal energy flows out of the molten metal can be controlled by the established temperature gradient. Thermal energy can be removed along a plane adjacent to the cooling surface such that heat flux out of the metal is through the plane.
  • the molten metal As a volume of the molten metal cools below its solidification temperature it can form a layer of solidified metal adjacent to the cooling surface.
  • the solidified metal can act as a thermal conductor to remove heat from molten metal adjacent to the solidified layer, bridging the distance between the cooling surface and a solidification interface (e.g. surface along which both molten and solidified phases abut). In this way, the solidification interface can incrementally move from the cooling surface through the mold cavity volume. Controlling the flow of thermal energy during the cooling process can allow a directionally solidified (DS) grain structure to be established in the solidified metal.
  • DS directionally solidified
  • Such a grain structure can have metal crystals, or grains, adjacent to one another that include a coordinated orientation.
  • These grains can share a common axial dimension (e.g., longest dimension), such that the longest dimension of each grain extends parallel to a common axis.
  • the direction of the axial dimension of these DS grains can be perpendicular to the plane from which thermal energy is extracted during cooling.
  • the direction of the axial dimension of the DS grains can be parallel to the direction from which heat was removed from a surface of the metal.
  • the DS grains can grow along a dimension by maintaining the direction that thermal energy is removed from the metal as it solidifies, e.g., by maintaining a selected temperature gradient.
  • the temperature throughout the metal within the mold cavity can be controlled by controlling the amount of energy flowing into the metal from a heat source, such as a furnace, and the amount of energy that is removed from a cooling surface, such as a chill plate.
  • the cooling rate of the metal can be controlled by adjusting the amount of energy removed from the cooling surface. By controlling the rate of energy removal, the molten metal can be cooled incrementally, e.g., progressively, from the cooling surface.
  • the specific rate of energy removal is readily determinable based upon the particular part such as the part design, wall thickness, and materials.
  • Controlling the cooling rate of a metal casting can impart enhanced structural characteristics to the part.
  • such processes can be time consuming and can extend the processing time for cast parts.
  • the processing time can be reduced in comparison to if the cast part were formed having a DS microstructure throughout. In this way, the part can have desired structural characteristics wherein greater structural integrity is located in higher stress areas of the part, while processing time is reduced.
  • Progressive cooling can allow for the formation of directional solidified grains having axes perpendicular to the cooling surface.
  • the solidification interface can move along the dimension of the temperature gradient from the cooling surface as the adjacent metal cools into the solid DS grains.
  • a portion e.g., a volume
  • the mold can be removed from a heat source and the remaining molten metal can be allowed to cool along multiple surfaces, not just from the cooling surface. In this way the remaining metal can cool quickly in comparison to the portion of the metal that is cooled to form a DS grain structure.
  • Such cooling can form equiaxed grains in the remaining metal as energy is drawn through multiple surfaces of the mold cavity.
  • the metal grain growth in this equiaxed section can occur in multiple directions, along multiple dimensions.
  • the portion of the metal part that is manufactured to have a DS grains can be selected to be any portion of the metal part.
  • the portion of a part formed having DS grains in this way can include up to 60% of the total volume of the part, for example, 10% to 50%, or 25% to 50%.
  • the volume of the metal part which is cooled to form DS grains can be selected to include portions of the part that will see the highest stress when the part is in use.
  • the portions of a part that experience the highest stress can be determined empirically or analytically. These stresses can occur at least partially as a result of the gas temperature impinging the surface of the part and centrifugal forces acting on the part due to rotation about the turbine shaft.
  • a portion of an airfoil adjacent to the outside wall, or outer shroud can have the highest stress.
  • the outer shroud and an adjacent portion of the airfoil can be formed having a DS grain structure to enhance the durability of the part in this area.
  • the DS grains can be oriented such that the longest dimension of the grains can be parallel with an expected tensile load when the part is in use.
  • the DS grains can be oriented such that the longest dimension of the grains can be parallel to the airfoil length, L, (extending in the 1-axis in the attached figures).
  • the DS grain orientation can contribute enhanced tensile strength to the part such that the tensile strength of the part can exceed the tensile stress acting on the part when the part is in use (i.e. during operation of the turbine).
  • the DS grain structure can be formed in selected volumes of a part.
  • a cooling surface of a mold can control heat flux from the molten metal along a direction parallel to the surface of the leading edge of an airfoil.
  • the DS grain structure (e.g., in the area to the left of line 84 in FIG. 4) can be formed to a depth from the leading edge (see depth D in FIG. 4), perpendicular to the surface of the leading edge, such as by withdrawing the heat in the direction of arrows 82.
  • the selected volume of a part that includes DS grains can include a high stress region of the part as determined empirically or analytically.
  • FIG. 1 is an illustration of a cross-section of a metal part 10 being cast in a mold 14.
  • a metal 2 can be held in a holder 4, such as a crucible, within a furnace 6.
  • the furnace 6 can provide thermal energy 8 for melting the metal 2 and/or for heating the mold 14.
  • the thermal energy 8 of the furnace 6 can be used to maintain the metal 2 in a homogeneous molten state 20 (depicted as wavy lines).
  • the metal 2 can be introduced, e.g. flowed by gravity, into the mold cavity 12 via a passage 22 and a mold inlet 24. Any suitable method can be used for introducing the metal 2 to a mold cavity 12, e.g., pressure assisted pumping and/or vacuum assisted pulling.
  • the mold can be filled to a desired volume with the metal 2.
  • a cooling fluid can be introduced to a cooling plate 30.
  • a cooling plate 30 can provide a cooling surface 32.
  • the cooling surface can create a heat flux 34 which extracts thermal energy from the metal 2.
  • the cooling surface 32 can extract thermal energy from the metal 2 along a single dimension, e.g. along the 1-axis dimension.
  • FIG. 2 is an illustration of a cross-section of metal part 10 being cast having directionally solidified (DS) grains 42 (depicted as parallel straight lines in the 1-axis dimension).
  • the DS grains 42 can grow from the cooling plate 30 in a direction orthogonal to the cooling surface 32, opposite the direction the heat flux 34 through the cooling surface 32.
  • the axial dimension (e.g., longest dimension) of the DS grains 42 can have a coordinated orientation throughout the DS portion of the metal, such that the axis of the grains extend parallel to a common axis (e.g., 1-axis) which is orthogonal to the cooling surface 32.
  • a common axis e.g., 1-axis
  • the DS grains 42 can form while the remainder of the metal 2 is kept in a homogeneous molten phase 20, such as while the remainder is heated by the furnace 6. This can establish a solidification interface 38 where the molten metal abuts the solidified metal phase.
  • the solidification interface 38 can progress incrementally from the cooling surface 32 in a direction opposite the heat flux 34 through the cooling surface 32.
  • the mold 14 can be withdrawn from the furnace progressively along a direction 50 as the adjacent DS grains 42 are formed incrementally along the solidification interface 38 in microscopic layers. In this way a portion of the metal can remain in a molten homogeneous phase 20 (depicted as wavy lines) while another portion is solidified into DS grains 42 such that the solidification interface 38 advances in a direction opposite the heat flux 34.
  • FIG. 3 is an illustration of a cross-section of a metal part 10 in a mold 14 having a hybrid grain structure after solidification of the metal 2 is complete.
  • the metal part 10 can include a base 26 and an airfoil 70.
  • the base 26 can be configured to mechanically attach to a turbine component, such as a shroud, shaft, base of an adjacent part, a platform, and the like. Such attachment can be non-permanent, such that the metal part 10 can be repaired ex-situ (e.g., from outside the turbine) or replaced without damaging surrounding components.
  • the metal part 10 can be cooled first by the heat flux 34 along a first dimension (1-axis dimension) induced by a cooling surface 32 of the cooling plate 30.
  • the heat flux 34 can remove thermal energy from the metal 2 in a single direction parallel to the heat flux 34 through the cooling surface 32.
  • the remainder of the homogeneous molten metal 20 within the mold 14 can be kept at a temperature greater than or equal to the melt temperature of the metal 2 such that a temperature gradient can be established in the 1-axis dimension.
  • the solidification interface 38 advances to a predetermined position (e.g., a distance from the cooling surface 32) the mold 14 can be removed from the furnace 6 to stop the formation of DS grains 42.
  • the solidification interface 38 can be allowed to progress from a first side 55, abuting the cooling surface 32, to a second side 57 to define a first portion 56 having DS grains 42.
  • the first portion 56 can include a first section 76 of an airfoil 70.
  • a second portion 58 can be defined by the remainder of the homogeneous molten metal 20 after the first portion 56 is formed.
  • the second portion 58 can include a second section 78 of the airfoil 70.
  • the second portion 78 can be cooled by multiple heat fluxes 36 in multiple directions through multiple surfaces.
  • the homogeneous molten metal 20 can solidify having equiaxed grains 44 (depicted as cross-hatched lines) where the axial direction of the individual grains do not form having a coordinated orientation, or parallel to a common axis.
  • the cooling rate during formation of equiaxed grains 44 can be more rapid than during formation of DS grains 42.
  • the cooling rate during formation of equiaxed grains 44 can be increased by forcing cooling fluid through the mold 14 and/or along surfaces of the mold 14.
  • the metal 2 can be quenched with any suitable quenchant, such as air, oil, water, and the like.
  • FIG. 4 is an illustration of a metal part 60 used in a turbine having an airfoil 70 affixed to inside wall 62 and an outside wall 64.
  • the airfoil can have a length, L, extending in an 1-axis dimension away from the inside wall 62, a leading edge 72 and a trailing edge 74.
  • the metal part 60 can have a high stress region 80.
  • the high stress region 80 can be in an area of the leading edge 72 adjacent to the outside wall 64.
  • the metal part 60 can be cast having a hybrid grain structure where a first portion 56, having a first side 55 and a second side 57, includes DS grains 42, and a second portion 58 includes equiaxed grains 44.
  • the first side 55 can be opposite the second side 57.
  • the first portion 56 can include the high stress region 80.
  • the first portion 56 can include a first section of the air foil 76 and the outside wall 64.
  • the second section portion 58 can include a second section of the air foil 78 and the inside wall 62.
  • the second side 57 of the first portion 56 can be adjacent to the second portion 58.
  • the location of the solidification interface 38 just before the metal part 60 was cooled in multiple directions can determine a boundary between portions of the part having DS grains 42 and portions of the metal part 60 having equiaxed grains 44.
  • the casted part can include hollow sections. Hollow sections can allow for cooling fluid to pass through the part to cool the part during operation. Hollow section can reduce the mass of the part.
  • a part for a turbine can include a turbine blade having an airfoil portion and a base portion.
  • a part for a turbine can include a vane having a central airfoil portion and two shroud portions (e.g. an inner shroud, or base, and an outer shroud).
  • the inner shroud can be considered to be equivalent to the base portion of a turbine blade.
  • the base portions can include a mechanical attachment for securing the part to a component of the turbine, such that the part and the component are in mechanical communication.
  • a base of a part can attach to a turbine component which can include a shroud, a shaft, a base of an adjacent part, a platform, and the like.
  • Turbine parts can be exposed to high stress environments.
  • the high stress can be a result, at least in part, of hot fluid flowing along a surface of the part and creating a temperature gradient within the part.
  • temperature gradients can lead to high internal stress within a part and can result in stress cracking at a surface of the part.
  • a metal alloy can include any metal and/or metalloid.
  • the metal alloy can include aluminum (Al), boron (B), carbon (C), cobalt (Co), chromium (Cr), hafnium (Hi), iron (Fe), nickel (Ni), niobium (Nb), rhenium (Re), tantalum (Ta), titanium (Ti), tungsten (W), and zirconium (Zr), and combinations comprising at least one of the foregoing, such as a nickel based superalloys (e.g., an alloy comprising Ni, Cr, and Co, or an alloy comprising Ni, Cr, Co, Al, Ti, B, Zr, .
  • a nickel based superalloys e.g., an alloy comprising Ni, Cr, and Co, or an alloy comprising Ni, Cr, Co, Al, Ti, B, Zr, .
  • the metal alloy can include Hastelloy, Inconel alloys ("IN"), Waspaloy, Rene alloys, such as GTDlll, GTD222, GTD262, Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, IN 706, Nimonic 263, or a combination comprising at least one of the foregoing.
  • the composition of these elements in a metal alloy can vary significantly.
  • the composition of a metal alloy can have the following weight percent (wt ) ranges:
  • Al 0 wt% - 6.0 wt , e.g., greater than 0 wt% to 6.0 wt , or 0.5 wt% to 4.5 wt ;
  • Co 0 wt% - 20 wt , e.g., greater than 0 wt% to 20 wt , or 2.0 wt% to 18.0 wt ;
  • Hf 0 wt - 1.5 wt , e.g., greater than 0 wt to 1.5 wt , or 0.1 wt to 1.0 wt ;
  • Fe 0 wt % - 19 wt , e.g., greater than 0 wt to 19 wt , or 5.0 wt to 15.0 wt ;
  • Nb 0 wt% - 5 wt , e.g., greater than 0 wt% to 5.0 wt , or 1.0 wt% to 4.0 wt ;
  • Re 0 wt% - 3 wt , e.g., greater than 0 wt% to 3.0 wt , or 0.05 wt% to 2.5 wt ;
  • Ta 0 wt% - 7.5 wt , e.g., greater than 0 wt% to 7.5 wt , or 1.0 wt% to 6.5 wt ;
  • Ti 0 wt% - 5 wt , e.g., greater than 0 wt% to 5.0 wt , or 0.05 wt% to 4.0 wt ;
  • W 0 wt% - 12.5 wt%, e.g., greater than 0 wt% to 12.5 wt , or 2.0 wt% to 10 wt ;
  • Zr 0 wt - 0.1 wt , e.g., greater than 0 wt to 0.1 wt , or 0.05 wt to 0.1 wt .
  • Materials having DS grain structures can exhibit enhanced creep strain resistance in comparison to equiaxed grain structures.
  • a metal alloy having a DS grain structure can withstand a creep strain of up to 12 times that of an equiaxed grain structure prior to fracture and endure creep strain for up to 85% longer.
  • the present application provides many advantages over parts, e.g., turbine parts such as air foils and blades. Since the part comprises DS grains in areas of higher stress, these areas are strengthened (for example as compared to a part with only equiaxed grains). As a result, the material options for the part is expanded and weldable materials, which were previously insufficient to provide the desired mechanical properties, can be employed while still attaining the desired properties.
  • Embodiment 1 A method of forming an article comprising: heating a metal to form a molten metal having a metal temperature; heating a mold to a mold temperature greater than or equal to the metal temperature; introducing the molten metal to the mold; cooling a first portion of the molten metal while maintaining a second portion of the molten metal at the metal temperature, wherein the first portion has a first side and a second side, wherein the second side is opposite the first side and adjacent to the second portion, and wherein the cooling comprises progressively cooling the first portion from the first side to the second side such that a solidification interface progresses from the first side to the second side; and cooling the remainder of the molten metal from multiple directions after the first portion is cooled to less than or equal to a crystallization temperature.
  • Embodiment 2 The method of Embodiment 1, wherein cooling the remainder of the molten metal further comprises cooling the molten metal from all mold surfaces.
  • Embodiment 3 The method of any of Embodiments 1-2, wherein a volume of the first portion is greater than or equal 20 % of a total volume of the article.
  • Embodiment 4 The method of any of Embodiments 1-3, comprising determining a higher stress area of the article.
  • Embodiment 5 The method of Embodiment 4, wherein the higher stress area is within the first portion.
  • Embodiment 6 A part for a turbine made by the method of any of Embodiments 1-5.
  • Embodiment 7 A part for a turbine comprising: a base having a base wall and an attachment; an airfoil extending from the base wall; wherein the part comprises a first portion comprising the base and a first section of the airfoil and a second portion comprising a second section of the airfoil, wherein the first portion comprises a metal having directionally solidified grains and the second portion comprises the metal having equiaxed grains.
  • Embodiment 8 The part of Embodiment 7, comprising a shroud having a shroud wall, wherein the airfoil extends between the base and the shroud wall, and wherein the second portion further comprises the shroud.
  • Embodiment 9 The part of any of Embodiments 7-8, wherein the first portion comprises a first portion volume and wherein the first portion volume is less than or equal to 60 % of a total volume of the part.
  • Embodiment 10 The part of any of Embodiments 7-9, wherein the metal comprises GTD111, GTD222, GTD262, Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing.
  • Embodiment 11 The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 7.5 to 9.0 weight percent Cr, 9.5 to 10.5 weight percent Co, 5.0 to 6.0 weight percent Al, 0.50 to 1.5 weight percent Ti, 0.2 to 1 weight percent Mo, 2 to 4 weight percent Ta, 9 to 11 weight percent W, 1 to 2 weight percent Hf, 0.025 to 0.075 weight percent Zr, 0.010 to 0.020 weight percent B, 0.10 to 0.20 weight percent C, and the balance Ni (e.g., wherein the metal comprises 8.1 weight percent Cr, 10 weight percent Co, 5.5 weight percent Al, 1 weight percent Ti, 0.6 weight percent Mo, 3 weight percent Ta, 10 weight percent W, 1.5 weight percent Hf, 0.05 weight percent Zr, 0.015 weight percent B, 0.16 weight percent C, and the balance Ni).
  • the metal comprises 7.5 to 9.0 weight percent Cr, 9.5 to 10.5 weight percent Co, 5.0 to 6.0 weight percent Al, 0.50 to 1.5 weight percent Ti
  • Embodiment 12 The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 13 to 15 weight percent Cr, 9 to 10 weight percent Co, 2 to 4 weight percent Al, 4 to 6 weight percent Ti, 1 to 3 weight percent Mo, 2 to 4 weight percent Ta, 3 to 5 weight percent W, 0.01 to 0.03 weight percent Zr, 0.008 to 0.02 weight percent B, 0.050 to 0.20 weight percent C, and the balance Ni (e.g., wherein the metal comprises 14 weight percent Cr, 9.5 weight percent Co, 3 weight percent Al, 4.9 weight percent Ti, 1.6 weight percent Mo, 2.8 weight percent Ta, 3.8 weight percent W, 0.02 weight percent Zr, 0.012 weight percent B, 0.10 weight percent C, and the balance Ni).
  • the metal comprises 13 to 15 weight percent Cr, 9 to 10 weight percent Co, 2 to 4 weight percent Al, 4 to 6 weight percent Ti, 1 to 3 weight percent Mo, 2 to 4 weight percent Ta, 3 to 5 weight percent W, 0.01 to 0.03 weight percent
  • Embodiment 13 The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 19 to 25 weight percent Cr, 12 to 21 weight percent Co, 1.5 to 3.5 weight percent Al, 1.0 to 3.9 weight percent Ti, 0.050 to 3.0 weight percent Ta, 0.050 to 3.5 weight percent W, 0.0050 to 0.050 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, 0.05 to 2 weight percent Nb, and the balance Ni (e.g., wherein the metal comprises 22.5 weight percent Cr, 19 weight percent Co, 1.2 weight percent Al, 2.3 weight percent Ti, 1 weight percent Ta, 2 weight percent W, 0.012 weight percent Zr, 0.005 weight percent B, 0.10 weight percent C, 0.8 weight percent Nb, and the balance Ni).
  • the metal comprises 22.5 weight percent Cr, 19 weight percent Co, 1.2 weight percent Al, 2.3 weight percent Ti, 1 weight percent Ta, 2 weight percent W, 0.012 weight percent Zr,
  • Embodiment 14 The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 15.5 to 17.5 weight percent Cr, 7 to 9 weight percent Co, 1 to 5 weight percent Al, 2.5 to 6.0 weight percent Ti, 0.50 to 3.0 weight percent Mo, 0.70 to 3.0 weight percent Ta, 0.050 to 3.5 weight percent W, 0.0050 to 0.15 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, 0.05 to 2 weight percent Nb, and the balance Ni (wherein the metal comprises 16 weight percent Cr, 8.5 weight percent Co, 3.5 weight percent Al, 3.5 weight percent Ti, 1.7 weight percent Mo, 1.7 weight percent Ta, 2.5 weight percent W, 0.05 to 0.1 weight percent Zr, 0.01 weight percent B, 0.09 to 0.17 weight percent C, 0.8 weight percent Nb, and the balance Ni).
  • the metal comprises 16 weight percent Cr, 8.5 weight percent Co, 3.5 weight percent Al, 3.5 weight percent Ti, 1.7 weight percent Mo
  • Embodiment 15 The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 13 to 15 weight percent Cr, 7.0 to 11 weight percent Co, 1 to 5 weight percent Al, 2.5 to 6.0 weight percent Ti, 3.1 to 6 weight percent Mo, 2 to 6 weight percent W, 0.0050 to 0.15 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, and the balance Ni (wherein the metal comprises 14 weight percent Cr, 9.5 weight percent Co, 3 weight percent Al, 5 weight percent Ti, 4 weight percent Mo, 4 weight percent W, 0.03 weight percent Zr, 0.015 weight percent B, 0.16 weight percent C, and the balance Ni).
  • Embodiment 16 The part of any of Embodiments 7-15, wherein a longest dimension of the directionally solidified grains extend parallel to an expected tensile stress in the part when the part is in use.
  • Embodiment 17 The part of any of Embodiments 7-16, where the attachment is configured for mechanical attachment turbine component.
  • Embodiment 18 The part of any of Embodiments 7-10, wherein the part is not weldable.
  • Embodiment 19 The part of Embodiment 18, wherein the metal comprises Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing.
  • Embodiment 20 The part of Embodiment 18, wherein the metal comprises IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing.
  • Embodiment 21 The part of any of Embodiments 7-10, wherein the part is weldable.
  • Embodiment 22 The part of Embodiment 21, wherein the metal comprises GTDl ll, GTD222, GTD262, IN X-750, Waspaloy, Nimonic 263, or a combination comprising at least one of the foregoing.
  • Embodiment 23 The part of Embodiment 21, wherein the metal comprises GTDl ll, GTD222, GTD262, or a combination comprising at least one of the foregoing.
  • Embodiment 24 The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises greater than 0 wt to 6.0 wt% Al; greater than 0 wt% to 0.06 wt% B; greater than 0 wt% to 2.0 wt% C; greater than 0 wt% to 20 wt% Co; 5 wt% - 22.5 wt% Cr; greater than 0 wt% to 19 wt Fe; greater than 0 wt to 5.0 wt Nb; and optionally Re, Ta, Ti, W, and/or Zn; balance Ni.
  • the metal alloy comprises greater than 0 wt to 6.0 wt% Al; greater than 0 wt% to 0.06 wt% B; greater than 0 wt% to 2.0 wt% C; greater than 0 wt% to 20 wt% Co; 5 wt% - 22.5 wt% Cr; greater than
  • the weldability of a metal alloy can be characterized by the amount of the gamma prime phase that it contains. These materials can also be characterized by the relationship between the weight percent of aluminum to the weight percent of titanium in the alloy. It has been found that the following relationship establishes a region of a YAI versus ⁇ ⁇ graph for a metal alloys that can be considered weldable using conventional fusion welding techniques, such as arc welding, oxy-fuel welding, electric resistance welding, laser beam welding, electron beam welding, and thermite welding:
  • YAI is the weight percent of aluminum of the alloy
  • ⁇ ⁇ is the weight percent of the titanium of the alloy.

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Abstract

A method of forming an article can comprise heating a metal to form a molten metal having a metal temperature; heating a mold to a mold temperature greater than or equal to the metal temperature; introducing the molten metal to the mold; cooling a first portion of the molten metal while maintaining a second portion of the molten metal at the metal temperature, wherein the first portion has a first side and a second side, wherein the second side is opposite the first side and adjacent to the second portion, and wherein the cooling comprises progressively cooling the first portion from the first side to the second side such that a solidification interface progresses from the first side to the second side; and cooling the remainder of the molten metal from multiple directions after the first portion is cooled to less than or equal to a crystallization temperature.

Description

ARTICLE FOR USE IN HIGH STRESS ENVIRONMENTS HAVING MULTIPLE
GRAIN STRUCTURES
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Application Serial No. 61/971,109, filed March 27, 2014, the content of which is hereby incorporated in its entirety.
BACKGROUND OF THE INVENTION
[0002] The subject matter disclosed herein relates to an article for use in high stress environments and the method of manufacturing the same. More particularly, the subject matter relates to enhancing durability of articles used in the hot section of a turbine.
[0003] Articles exposed to high temperature environments can experience stress cracking due to localized stress within the article. This localized stress can be caused by a temperature gradient within a material which can lead to different rates of expansion. Portions of the material can expand more rapidly and can induce a tension force on adjacent areas. If not mitigated a stress crack can propagate through the article and result in failure of the article, such as creep, thermal fatigue, and the like.
[0004] Welding a cracked article can offer a temporary repair. Such repair can allow the article to be returned to service operation for a period of time. However, repairs of this kind can be disruptive and can be expensive. For example, repair of a power generating gas turbine can force the turbine offline, or repair of a jet engine can force an aircraft to stay grounded while the repair is performed. As a result, manufacturers desire longer lasting components that can reduce the frequency of stress induced cracking and lengthen the time between repairs.
[0005] Superalloys can be used in the manufacture of these articles to reduce the likelihood of stress cracking. These materials can offer superior mechanical properties in comparison to other metal alloys. However, even these materials can be subject to stress induced cracking and can require periodic repair. These high strength alloys can have poor weldability which can make repair by welding difficult and can thereby make the component unrepairable. Thus there is a need in the art for articles having enhanced durability in high stress environments that can operate over longer intervals without repair or that can be welded.
BRIEF DESCRIPTION OF THE INVENTION
[0006] According to one aspect of the invention, a method of forming an article can comprise: heating a metal to form a molten metal having a metal temperature; heating a mold to a mold temperature greater than or equal to the metal temperature; introducing the molten metal to the mold; cooling a first portion of the molten metal while maintaining a second portion of the molten metal at the metal temperature, wherein the first portion has a first side and a second side, wherein the second side is opposite the first side and adjacent to the second portion, and wherein the cooling comprises progressively cooling the first portion from the first side to the second side such that a solidification interface progresses from the first side to the second side; and cooling the remainder of the molten metal from multiple directions after the first portion is cooled to less than or equal to a crystallization temperature.
[0007] According to another aspect of the invention, a part for a turbine can comprise: a base having a base wall and an attachment, where the attachment is configured for mechanical attachment turbine component; an airfoil extending from the base wall; wherein the part comprises a first portion comprising the base and a first section of the airfoil and a second portion comprising a second section of the airfoil, wherein the first portion comprises a metal having directionally solidified grains and the second portion comprises the metal having equiaxed grains, and wherein a longest dimension of the directionally solidified grains extend parallel to an expected tensile stress in the part when the part is in use.
[0008] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWING
[0009] The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
[0010] FIG. 1 is an illustration of a cross-section of a metal part being molded.
[0011] FIG. 2 is an illustration of a cross-section of metal part being cast having directionally solidified (DS) grains.
[0012] FIG. 3 is an illustration of a cross-section of a metal part in a mold having a hybrid grain structure.
[0013] FIG. 4 is an illustration of a metal part used in a turbine having an airfoil affixed between two walls.
[0014] The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0015] A turbine part can include a blade and/or vane having an airfoil section. The turbine part can be exposed to high temperature fluid flow. This flow can cause high thermal stress in some areas of the turbine part, at least partially due to thermal gradients imposed on the part by the high temperature fluids flowing along a surface of the part. The turbine part can include hollow portions, cavities, or passages, such that it can be cooled using various methods to reduce the temperature gradients within the part thereby reducing the magnitude of internal stress within the part. Such cooling methods can include internal cooling methods (e.g., convection cooling, impingement cooling, and the like) or external cooling methods (e.g. film cooling, effusion cooling, transpiration cooling, pin fin cooling and the like). [0016] The turbine part can be cast from metal, such as metal alloys. Superalloys can be used to enhance the durability of these parts. Solid phase metals and metal alloys can have microscopic crystal structures. These microscopic crystals, also referred to as grains, can form microstructures within the volume of the solid metal. These grain structures impart particular properties to the metal, such as structural properties including tensile strength, ultimate strength, hardness, ductility, and the like. Disclosed herein are metal turbine parts having hybrid grain structures, such as two or more different grain structures in different areas of the part, and methods for forming these structures.
[0017] In the manufacture of turbine parts a metal can be molded into a selected part shape, for example, in a casting process. In such a process a metal can be heated to a melt temperature, e.g. a temperature sufficient to melt the metal and form a homogeneous metal mixture, wherein a homogeneous metal mixture has a single phase microstructure. For example, in a homogeneous metal mixture the composition can be uniform. The melt temperature can vary depending on the composition of the metal chosen for the casting. The melt temperature can be greater than the melting temperature of a metal component of a metal alloy, such that the metal can form a homogeneous mixture. The melt temperature can be greater than or equal to 2300 °F (1260 °C), for example, 2500 °F (1371 °C) - 3000 °F (1649 °C), or, 2600 °F (1427 °C) - 2800 °F (1538 °C).
[0018] The mold can be heated to a temperature equal to or greater than the melt temperature, such that the molten metal can flow into and fill the mold cavity without solidifying. The mold can be heated by placing the mold in a furnace or other suitable heat source. The furnace can maintain the temperature of the mold at or above the melt temperature. Optionally, the mold can include electrical heating elements for providing additional heating and/or for controlling temperatures along portions of the mold surfaces.
[0019] A surface of the mold can be cooled to solidify an adjacent volume of the molten metal. While a portion of the molten metal is cooled along this cooling surface, the temperature of the remainder of the molten metal can be maintained above the melt temperature. In this way a temperature gradient can be established in the molten metal. The temperature gradient can be established along a single linear dimension of the molten metal. This gradient can be maintained by controlling the mold cavity surface temperatures along a dimension of the mold and the temperature of the cooling surface. The direction that thermal energy flows out of the molten metal can be controlled by the established temperature gradient. Thermal energy can be removed along a plane adjacent to the cooling surface such that heat flux out of the metal is through the plane.
[0020] As a volume of the molten metal cools below its solidification temperature it can form a layer of solidified metal adjacent to the cooling surface. The solidified metal can act as a thermal conductor to remove heat from molten metal adjacent to the solidified layer, bridging the distance between the cooling surface and a solidification interface (e.g. surface along which both molten and solidified phases abut). In this way, the solidification interface can incrementally move from the cooling surface through the mold cavity volume. Controlling the flow of thermal energy during the cooling process can allow a directionally solidified (DS) grain structure to be established in the solidified metal. Such a grain structure can have metal crystals, or grains, adjacent to one another that include a coordinated orientation. These grains can share a common axial dimension (e.g., longest dimension), such that the longest dimension of each grain extends parallel to a common axis. The direction of the axial dimension of these DS grains can be perpendicular to the plane from which thermal energy is extracted during cooling. The direction of the axial dimension of the DS grains can be parallel to the direction from which heat was removed from a surface of the metal.
[0021] The DS grains can grow along a dimension by maintaining the direction that thermal energy is removed from the metal as it solidifies, e.g., by maintaining a selected temperature gradient. The temperature throughout the metal within the mold cavity can be controlled by controlling the amount of energy flowing into the metal from a heat source, such as a furnace, and the amount of energy that is removed from a cooling surface, such as a chill plate. The cooling rate of the metal can be controlled by adjusting the amount of energy removed from the cooling surface. By controlling the rate of energy removal, the molten metal can be cooled incrementally, e.g., progressively, from the cooling surface. The specific rate of energy removal is readily determinable based upon the particular part such as the part design, wall thickness, and materials.
[0022] Controlling the cooling rate of a metal casting can impart enhanced structural characteristics to the part. However, such processes can be time consuming and can extend the processing time for cast parts. By forming a DS microstructure in a cast metal part in a selected region(s) the processing time can be reduced in comparison to if the cast part were formed having a DS microstructure throughout. In this way, the part can have desired structural characteristics wherein greater structural integrity is located in higher stress areas of the part, while processing time is reduced.
[0023] Progressive cooling can allow for the formation of directional solidified grains having axes perpendicular to the cooling surface. The solidification interface can move along the dimension of the temperature gradient from the cooling surface as the adjacent metal cools into the solid DS grains. Once a portion (e.g., a volume) of the metal has been cooled, the mold can be removed from a heat source and the remaining molten metal can be allowed to cool along multiple surfaces, not just from the cooling surface. In this way the remaining metal can cool quickly in comparison to the portion of the metal that is cooled to form a DS grain structure. Such cooling can form equiaxed grains in the remaining metal as energy is drawn through multiple surfaces of the mold cavity. The metal grain growth in this equiaxed section can occur in multiple directions, along multiple dimensions.
[0024] The portion of the metal part that is manufactured to have a DS grains, (e.g., having a DS grain structure), can be selected to be any portion of the metal part. The portion of a part formed having DS grains in this way can include up to 60% of the total volume of the part, for example, 10% to 50%, or 25% to 50%.
[0025] The volume of the metal part which is cooled to form DS grains can be selected to include portions of the part that will see the highest stress when the part is in use. The portions of a part that experience the highest stress can be determined empirically or analytically. These stresses can occur at least partially as a result of the gas temperature impinging the surface of the part and centrifugal forces acting on the part due to rotation about the turbine shaft. For example, a portion of an airfoil adjacent to the outside wall, or outer shroud, can have the highest stress. Thus, the outer shroud and an adjacent portion of the airfoil can be formed having a DS grain structure to enhance the durability of the part in this area. The DS grains can be oriented such that the longest dimension of the grains can be parallel with an expected tensile load when the part is in use. The DS grains can be oriented such that the longest dimension of the grains can be parallel to the airfoil length, L, (extending in the 1-axis in the attached figures). The DS grain orientation can contribute enhanced tensile strength to the part such that the tensile strength of the part can exceed the tensile stress acting on the part when the part is in use (i.e. during operation of the turbine).
[0026] The DS grain structure can be formed in selected volumes of a part. For example, a cooling surface of a mold can control heat flux from the molten metal along a direction parallel to the surface of the leading edge of an airfoil. The DS grain structure (e.g., in the area to the left of line 84 in FIG. 4) can be formed to a depth from the leading edge (see depth D in FIG. 4), perpendicular to the surface of the leading edge, such as by withdrawing the heat in the direction of arrows 82. The selected volume of a part that includes DS grains can include a high stress region of the part as determined empirically or analytically.
[0027] FIG. 1 is an illustration of a cross-section of a metal part 10 being cast in a mold 14. A metal 2 can be held in a holder 4, such as a crucible, within a furnace 6. The furnace 6 can provide thermal energy 8 for melting the metal 2 and/or for heating the mold 14. The thermal energy 8 of the furnace 6 can be used to maintain the metal 2 in a homogeneous molten state 20 (depicted as wavy lines). Once molten, the metal 2 can be introduced, e.g. flowed by gravity, into the mold cavity 12 via a passage 22 and a mold inlet 24. Any suitable method can be used for introducing the metal 2 to a mold cavity 12, e.g., pressure assisted pumping and/or vacuum assisted pulling. The mold can be filled to a desired volume with the metal 2. A cooling fluid can be introduced to a cooling plate 30. A cooling plate 30 can provide a cooling surface 32. The cooling surface can create a heat flux 34 which extracts thermal energy from the metal 2. The cooling surface 32 can extract thermal energy from the metal 2 along a single dimension, e.g. along the 1-axis dimension.
[0028] FIG. 2 is an illustration of a cross-section of metal part 10 being cast having directionally solidified (DS) grains 42 (depicted as parallel straight lines in the 1-axis dimension). The DS grains 42 can grow from the cooling plate 30 in a direction orthogonal to the cooling surface 32, opposite the direction the heat flux 34 through the cooling surface 32. The axial dimension (e.g., longest dimension) of the DS grains 42 can have a coordinated orientation throughout the DS portion of the metal, such that the axis of the grains extend parallel to a common axis (e.g., 1-axis) which is orthogonal to the cooling surface 32. The DS grains 42 can form while the remainder of the metal 2 is kept in a homogeneous molten phase 20, such as while the remainder is heated by the furnace 6. This can establish a solidification interface 38 where the molten metal abuts the solidified metal phase. The solidification interface 38 can progress incrementally from the cooling surface 32 in a direction opposite the heat flux 34 through the cooling surface 32. For example, the mold 14 can be withdrawn from the furnace progressively along a direction 50 as the adjacent DS grains 42 are formed incrementally along the solidification interface 38 in microscopic layers. In this way a portion of the metal can remain in a molten homogeneous phase 20 (depicted as wavy lines) while another portion is solidified into DS grains 42 such that the solidification interface 38 advances in a direction opposite the heat flux 34.
[0029] FIG. 3 is an illustration of a cross-section of a metal part 10 in a mold 14 having a hybrid grain structure after solidification of the metal 2 is complete. The metal part 10 can include a base 26 and an airfoil 70. The base 26 can be configured to mechanically attach to a turbine component, such as a shroud, shaft, base of an adjacent part, a platform, and the like. Such attachment can be non-permanent, such that the metal part 10 can be repaired ex-situ (e.g., from outside the turbine) or replaced without damaging surrounding components.
[0030] The metal part 10 can be cooled first by the heat flux 34 along a first dimension (1-axis dimension) induced by a cooling surface 32 of the cooling plate 30. The heat flux 34 can remove thermal energy from the metal 2 in a single direction parallel to the heat flux 34 through the cooling surface 32. The remainder of the homogeneous molten metal 20 within the mold 14 can be kept at a temperature greater than or equal to the melt temperature of the metal 2 such that a temperature gradient can be established in the 1-axis dimension. Once the solidification interface 38 advances to a predetermined position (e.g., a distance from the cooling surface 32) the mold 14 can be removed from the furnace 6 to stop the formation of DS grains 42. The solidification interface 38 can be allowed to progress from a first side 55, abuting the cooling surface 32, to a second side 57 to define a first portion 56 having DS grains 42. The first portion 56 can include a first section 76 of an airfoil 70.
[0031] Once a first portion 56 having DS grains 42 has been solidified the remainder of the homogeneous molten metal 20 within the mold 14 can be cooled. A second portion 58 can be defined by the remainder of the homogeneous molten metal 20 after the first portion 56 is formed. The second portion 58 can include a second section 78 of the airfoil 70. The second portion 78 can be cooled by multiple heat fluxes 36 in multiple directions through multiple surfaces. During cooling of this type, where a single temperature gradient is not maintained, the homogeneous molten metal 20 can solidify having equiaxed grains 44 (depicted as cross-hatched lines) where the axial direction of the individual grains do not form having a coordinated orientation, or parallel to a common axis. The cooling rate during formation of equiaxed grains 44 can be more rapid than during formation of DS grains 42. The cooling rate during formation of equiaxed grains 44 can be increased by forcing cooling fluid through the mold 14 and/or along surfaces of the mold 14. During the formation of equiaxed grains 44 the metal 2 can be quenched with any suitable quenchant, such as air, oil, water, and the like.
[0032] FIG. 4 is an illustration of a metal part 60 used in a turbine having an airfoil 70 affixed to inside wall 62 and an outside wall 64. The airfoil can have a length, L, extending in an 1-axis dimension away from the inside wall 62, a leading edge 72 and a trailing edge 74. The metal part 60 can have a high stress region 80. The high stress region 80 can be in an area of the leading edge 72 adjacent to the outside wall 64. The metal part 60 can be cast having a hybrid grain structure where a first portion 56, having a first side 55 and a second side 57, includes DS grains 42, and a second portion 58 includes equiaxed grains 44. The first side 55 can be opposite the second side 57. The first portion 56 can include the high stress region 80. The first portion 56 can include a first section of the air foil 76 and the outside wall 64. The second section portion 58 can include a second section of the air foil 78 and the inside wall 62. The second side 57 of the first portion 56 can be adjacent to the second portion 58. The location of the solidification interface 38 just before the metal part 60 was cooled in multiple directions can determine a boundary between portions of the part having DS grains 42 and portions of the metal part 60 having equiaxed grains 44. Once the part is case having the hybrid grain structure
[0033] The casted part can include hollow sections. Hollow sections can allow for cooling fluid to pass through the part to cool the part during operation. Hollow section can reduce the mass of the part.
[0034] A part for a turbine can include a turbine blade having an airfoil portion and a base portion. A part for a turbine can include a vane having a central airfoil portion and two shroud portions (e.g. an inner shroud, or base, and an outer shroud). The inner shroud can be considered to be equivalent to the base portion of a turbine blade. The base portions can include a mechanical attachment for securing the part to a component of the turbine, such that the part and the component are in mechanical communication. A base of a part can attach to a turbine component which can include a shroud, a shaft, a base of an adjacent part, a platform, and the like.
[0035] Turbine parts can be exposed to high stress environments. The high stress can be a result, at least in part, of hot fluid flowing along a surface of the part and creating a temperature gradient within the part. Thus, temperature gradients can lead to high internal stress within a part and can result in stress cracking at a surface of the part.
[0036] A metal alloy can include any metal and/or metalloid. The metal alloy can include aluminum (Al), boron (B), carbon (C), cobalt (Co), chromium (Cr), hafnium (Hi), iron (Fe), nickel (Ni), niobium (Nb), rhenium (Re), tantalum (Ta), titanium (Ti), tungsten (W), and zirconium (Zr), and combinations comprising at least one of the foregoing, such as a nickel based superalloys (e.g., an alloy comprising Ni, Cr, and Co, or an alloy comprising Ni, Cr, Co, Al, Ti, B, Zr, . Some examples of the metal alloy can include Hastelloy, Inconel alloys ("IN"), Waspaloy, Rene alloys, such as GTDlll, GTD222, GTD262, Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, IN 706, Nimonic 263, or a combination comprising at least one of the foregoing. The composition of these elements in a metal alloy can vary significantly. For example, the composition of a metal alloy can have the following weight percent (wt ) ranges:
Al: 0 wt% - 6.0 wt , e.g., greater than 0 wt% to 6.0 wt , or 0.5 wt% to 4.5 wt ;
B: 0 wt - 0.06 wt , e.g., greater than 0 wt to 0.06 wt , or 0.01 wt to 0.05 wt ;
C: 0 wt - 0.2 wt , e.g., greater than 0 wt to 2.0 wt , or 0.05 wt to 0.15 wt ;
Co: 0 wt% - 20 wt , e.g., greater than 0 wt% to 20 wt , or 2.0 wt% to 18.0 wt ;
Cr: 5 wt - 22.5 wt , or 8 wt to 18 wt ;
Hf: 0 wt - 1.5 wt , e.g., greater than 0 wt to 1.5 wt , or 0.1 wt to 1.0 wt ;
Fe: 0 wt % - 19 wt , e.g., greater than 0 wt to 19 wt , or 5.0 wt to 15.0 wt ;
Ni: 40 wt - 85 wt , e.g., 45 wt to 80 wt , or 50 wt to 80 wt ;
Nb: 0 wt% - 5 wt , e.g., greater than 0 wt% to 5.0 wt , or 1.0 wt% to 4.0 wt ;
Re: 0 wt% - 3 wt , e.g., greater than 0 wt% to 3.0 wt , or 0.05 wt% to 2.5 wt ;
Ta: 0 wt% - 7.5 wt , e.g., greater than 0 wt% to 7.5 wt , or 1.0 wt% to 6.5 wt ;
Ti: 0 wt% - 5 wt , e.g., greater than 0 wt% to 5.0 wt , or 0.05 wt% to 4.0 wt ; W: 0 wt% - 12.5 wt%, e.g., greater than 0 wt% to 12.5 wt , or 2.0 wt% to 10 wt ;
Zr: 0 wt - 0.1 wt , e.g., greater than 0 wt to 0.1 wt , or 0.05 wt to 0.1 wt .
[0037] Materials having DS grain structures can exhibit enhanced creep strain resistance in comparison to equiaxed grain structures. For example, a metal alloy having a DS grain structure can withstand a creep strain of up to 12 times that of an equiaxed grain structure prior to fracture and endure creep strain for up to 85% longer.
[0038] The present application provides many advantages over parts, e.g., turbine parts such as air foils and blades. Since the part comprises DS grains in areas of higher stress, these areas are strengthened (for example as compared to a part with only equiaxed grains). As a result, the material options for the part is expanded and weldable materials, which were previously insufficient to provide the desired mechanical properties, can be employed while still attaining the desired properties.
[0039] Set forth below are some embodiments of the method for forming the article and the articles disclosed herein
[0040] Embodiment 1: A method of forming an article comprising: heating a metal to form a molten metal having a metal temperature; heating a mold to a mold temperature greater than or equal to the metal temperature; introducing the molten metal to the mold; cooling a first portion of the molten metal while maintaining a second portion of the molten metal at the metal temperature, wherein the first portion has a first side and a second side, wherein the second side is opposite the first side and adjacent to the second portion, and wherein the cooling comprises progressively cooling the first portion from the first side to the second side such that a solidification interface progresses from the first side to the second side; and cooling the remainder of the molten metal from multiple directions after the first portion is cooled to less than or equal to a crystallization temperature. [0041] Embodiment 2: The method of Embodiment 1, wherein cooling the remainder of the molten metal further comprises cooling the molten metal from all mold surfaces.
[0042] Embodiment 3: The method of any of Embodiments 1-2, wherein a volume of the first portion is greater than or equal 20 % of a total volume of the article.
[0043] Embodiment 4: The method of any of Embodiments 1-3, comprising determining a higher stress area of the article.
[0044] Embodiment 5: The method of Embodiment 4, wherein the higher stress area is within the first portion.
[0045] Embodiment 6: A part for a turbine made by the method of any of Embodiments 1-5.
[0046] Embodiment 7: A part for a turbine comprising: a base having a base wall and an attachment; an airfoil extending from the base wall; wherein the part comprises a first portion comprising the base and a first section of the airfoil and a second portion comprising a second section of the airfoil, wherein the first portion comprises a metal having directionally solidified grains and the second portion comprises the metal having equiaxed grains.
[0047] Embodiment 8: The part of Embodiment 7, comprising a shroud having a shroud wall, wherein the airfoil extends between the base and the shroud wall, and wherein the second portion further comprises the shroud.
[0048] Embodiment 9: The part of any of Embodiments 7-8, wherein the first portion comprises a first portion volume and wherein the first portion volume is less than or equal to 60 % of a total volume of the part.
[0049] Embodiment 10: The part of any of Embodiments 7-9, wherein the metal comprises GTD111, GTD222, GTD262, Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing. [0050] Embodiment 11: The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 7.5 to 9.0 weight percent Cr, 9.5 to 10.5 weight percent Co, 5.0 to 6.0 weight percent Al, 0.50 to 1.5 weight percent Ti, 0.2 to 1 weight percent Mo, 2 to 4 weight percent Ta, 9 to 11 weight percent W, 1 to 2 weight percent Hf, 0.025 to 0.075 weight percent Zr, 0.010 to 0.020 weight percent B, 0.10 to 0.20 weight percent C, and the balance Ni (e.g., wherein the metal comprises 8.1 weight percent Cr, 10 weight percent Co, 5.5 weight percent Al, 1 weight percent Ti, 0.6 weight percent Mo, 3 weight percent Ta, 10 weight percent W, 1.5 weight percent Hf, 0.05 weight percent Zr, 0.015 weight percent B, 0.16 weight percent C, and the balance Ni).
[0051] Embodiment 12: The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 13 to 15 weight percent Cr, 9 to 10 weight percent Co, 2 to 4 weight percent Al, 4 to 6 weight percent Ti, 1 to 3 weight percent Mo, 2 to 4 weight percent Ta, 3 to 5 weight percent W, 0.01 to 0.03 weight percent Zr, 0.008 to 0.02 weight percent B, 0.050 to 0.20 weight percent C, and the balance Ni (e.g., wherein the metal comprises 14 weight percent Cr, 9.5 weight percent Co, 3 weight percent Al, 4.9 weight percent Ti, 1.6 weight percent Mo, 2.8 weight percent Ta, 3.8 weight percent W, 0.02 weight percent Zr, 0.012 weight percent B, 0.10 weight percent C, and the balance Ni).
[0052] Embodiment 13: The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 19 to 25 weight percent Cr, 12 to 21 weight percent Co, 1.5 to 3.5 weight percent Al, 1.0 to 3.9 weight percent Ti, 0.050 to 3.0 weight percent Ta, 0.050 to 3.5 weight percent W, 0.0050 to 0.050 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, 0.05 to 2 weight percent Nb, and the balance Ni (e.g., wherein the metal comprises 22.5 weight percent Cr, 19 weight percent Co, 1.2 weight percent Al, 2.3 weight percent Ti, 1 weight percent Ta, 2 weight percent W, 0.012 weight percent Zr, 0.005 weight percent B, 0.10 weight percent C, 0.8 weight percent Nb, and the balance Ni).
[0053] Embodiment 14: The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 15.5 to 17.5 weight percent Cr, 7 to 9 weight percent Co, 1 to 5 weight percent Al, 2.5 to 6.0 weight percent Ti, 0.50 to 3.0 weight percent Mo, 0.70 to 3.0 weight percent Ta, 0.050 to 3.5 weight percent W, 0.0050 to 0.15 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, 0.05 to 2 weight percent Nb, and the balance Ni (wherein the metal comprises 16 weight percent Cr, 8.5 weight percent Co, 3.5 weight percent Al, 3.5 weight percent Ti, 1.7 weight percent Mo, 1.7 weight percent Ta, 2.5 weight percent W, 0.05 to 0.1 weight percent Zr, 0.01 weight percent B, 0.09 to 0.17 weight percent C, 0.8 weight percent Nb, and the balance Ni).
[0054] Embodiment 15: The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises 13 to 15 weight percent Cr, 7.0 to 11 weight percent Co, 1 to 5 weight percent Al, 2.5 to 6.0 weight percent Ti, 3.1 to 6 weight percent Mo, 2 to 6 weight percent W, 0.0050 to 0.15 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, and the balance Ni (wherein the metal comprises 14 weight percent Cr, 9.5 weight percent Co, 3 weight percent Al, 5 weight percent Ti, 4 weight percent Mo, 4 weight percent W, 0.03 weight percent Zr, 0.015 weight percent B, 0.16 weight percent C, and the balance Ni).
[0055] Embodiment 16: The part of any of Embodiments 7-15, wherein a longest dimension of the directionally solidified grains extend parallel to an expected tensile stress in the part when the part is in use.
[0056] Embodiment 17: The part of any of Embodiments 7-16, where the attachment is configured for mechanical attachment turbine component.
[0057] Embodiment 18: The part of any of Embodiments 7-10, wherein the part is not weldable.
[0058] Embodiment 19: The part of Embodiment 18, wherein the metal comprises Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing. [0059] Embodiment 20: The part of Embodiment 18, wherein the metal comprises IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing.
[0060] Embodiment 21: The part of any of Embodiments 7-10, wherein the part is weldable.
[0061] Embodiment 22: The part of Embodiment 21, wherein the metal comprises GTDl ll, GTD222, GTD262, IN X-750, Waspaloy, Nimonic 263, or a combination comprising at least one of the foregoing.
[0062] Embodiment 23: The part of Embodiment 21, wherein the metal comprises GTDl ll, GTD222, GTD262, or a combination comprising at least one of the foregoing.
[0063] Embodiment 24: The part of any of Embodiments 7-9, wherein the metal is a metal alloy, and wherein the metal alloy comprises greater than 0 wt to 6.0 wt% Al; greater than 0 wt% to 0.06 wt% B; greater than 0 wt% to 2.0 wt% C; greater than 0 wt% to 20 wt% Co; 5 wt% - 22.5 wt% Cr; greater than 0 wt% to 19 wt Fe; greater than 0 wt to 5.0 wt Nb; and optionally Re, Ta, Ti, W, and/or Zn; balance Ni.
[0064] The weldability of a metal alloy can be characterized by the amount of the gamma prime phase that it contains. These materials can also be characterized by the relationship between the weight percent of aluminum to the weight percent of titanium in the alloy. It has been found that the following relationship establishes a region of a YAI versus Χχί graph for a metal alloys that can be considered weldable using conventional fusion welding techniques, such as arc welding, oxy-fuel welding, electric resistance welding, laser beam welding, electron beam welding, and thermite welding:
YAi < -0.5XTi + 3, [1]
wherein, YAI is the weight percent of aluminum of the alloy, and Χχί is the weight percent of the titanium of the alloy. [0065] As used herein, metal alloys having compositions that can satisfy the relation of [1] can be considered weldable. As used herein, metal alloys having compositions that do not satisfy the relation of [1] can be considered not weldable.
[0066] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

CLAIMS:
1. A method of forming an article comprising:
heating a metal to form a molten metal having a metal temperature;
heating a mold to a mold temperature greater than or equal to the metal temperature;
introducing the molten metal to the mold;
cooling a first portion of the molten metal while maintaining a second portion of the molten metal at the metal temperature, wherein the first portion has a first side and a second side, wherein the second side is opposite the first side and adjacent to the second portion, and wherein the cooling comprises progressively cooling the first portion from the first side to the second side such that a solidification interface progresses from the first side to the second side; and
cooling the remainder of the molten metal from multiple directions after the first portion is cooled to less than or equal to a crystallization temperature.
2. The method of Claim 1, wherein cooling the remainder of the molten metal further comprises cooling the molten metal from all mold surfaces.
3. The method of Claim 1, wherein a volume of the first portion is greater than or equal 20 % of a total volume of the article.
4. The method of Claim 1, comprising determining a higher stress area of the article.
5. The method of Claim 4, wherein the higher stress area is within the first portion.
6. A part for a turbine made by the method of Claim 1.
7. A part for a turbine comprising:
a base having a base wall and an attachment;
an airfoil extending from the base wall;
wherein the part comprises a first portion comprising the base and a first section of the airfoil and a second portion comprising a second section of the airfoil, wherein the first portion comprises a metal having directionally solidified grains and the second portion comprises the metal having equiaxed grains.
8. The part of Claim 7, comprising a shroud having a shroud wall, wherein the airfoil extends between the base and the shroud wall, and wherein the second portion further comprises the shroud.
9. The part of Claim 7, wherein the first portion comprises a first portion volume and wherein the first portion volume is less than or equal to 60 % of a total volume of the part.
10. The part of Claim 7, wherein the metal is a metal alloy, and wherein the metal alloy comprises GTD111, GTD222, GTD262, Mar M247, IN 738, Rene 80, IN 939, Rene N2, Rene 108, or a combination comprising at least one of the foregoing.
11. The part of Claim 7, wherein the metal is a metal alloy, and wherein the metal alloy comprises 7.5 to 9.0 weight percent Cr, 9.5 to 10.5 weight percent Co, 5.0 to 6.0 weight percent Al, 0.50 to 1.5 weight percent Ti, 0.2 to 1 weight percent Mo, 2 to 4 weight percent Ta, 9 to 11 weight percent W, 1 to 2 weight percent Hf , 0.025 to 0.075 weight percent Zr, 0.010 to 0.020 weight percent B, 0.10 to 0.20 weight percent C, and the balance Ni.
12. The part of Claim 7, wherein the metal is a metal alloy, and wherein the metal alloy comprises 13 to 15 weight percent Cr, 9 to 10 weight percent Co, 2 to 4 weight percent Al, 4 to 6 weight percent Ti, 1 to 3 weight percent Mo, 2 to 4 weight percent Ta, 3 to 5 weight percent W, 0.01 to 0.03 weight percent Zr, 0.008 to 0.02 weight percent B, 0.050 to 0.20 weight percent C, and the balance Ni.
13. The part of Claim 7, wherein the metal is a metal alloy, and wherein the metal alloy comprises 19 to 25 weight percent Cr, 12 to 21 weight percent Co, 1.5 to 3.5 weight percent Al, 1.0 to 3.9 weight percent Ti, 0.050 to 3.0 weight percent Ta, 0.050 to 3.5 weight percent W, 0.0050 to 0.050 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, 0.05 to 2 weight percent Nb, and the balance Ni.
14. The part of Claim 7, wherein the metal is a metal alloy, and wherein the metal alloy comprises 15.5 to 17.5 weight percent Cr, 7 to 9 weight percent Co, 1 to 5 weight percent Al, 2.5 to 6.0 weight percent Ti, 0.50 to 3.0 weight percent Mo, 0.70 to 3.0 weight percent Ta, 0.050 to 3.5 weight percent W, 0.0050 to 0.15 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, 0.05 to 2 weight percent Nb, and the balance Ni.
15. The part of Claim 7, wherein the metal is a metal alloy, and wherein the metal alloy comprises 13 to 15 weight percent Cr, 7.0 to 11 weight percent Co, 1 to 5 weight percent Al, 2.5 to 6.0 weight percent Ti, 3.1 to 6 weight percent Mo, 2 to 6 weight percent W, 0.0050 to 0.15 weight percent Zr, 0.0010 to 0.060 weight percent B, 0.050 to 0.20 weight percent C, and the balance Ni.
EP15717716.3A 2014-03-27 2015-03-27 Article for use in high stress environments having multiple grain structures Withdrawn EP3122495A2 (en)

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