Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
• • 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
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
• • 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
  • F01D5/02—Blade-carrying members, e.g. rotors
• • 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
  • F01D5/30—Fixing blades to rotors; Blade roots ; Blade spacers
  • F01D5/3007—Fixing blades to rotors; Blade roots ; Blade spacers of axial insertion type
• • 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
  • F01D5/34—Rotor-blade aggregates of unitary construction, e.g. formed of sheet laminae
• • 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
  • F05D2230/25—Manufacture essentially without removing material by forging
• • 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
  • F05D2230/40—Heat treatment

Definitions

• the present invention generally relates to components that are produced by forging processes and then heat treated to obtain desirable microstructures. More particularly, this invention is directed to a method for avoiding quench cracking in highly alloyed nickel-base alloys, for example, of the type used to form rotating components of a turbomachine, whose processing includes heat treatment parameters capable of obtaining optimal microstructures.
• Components within the combustor and turbine sections of a gas turbine engine are often formed of superalloy materials in order to achieve acceptable mechanical properties while at elevated temperatures resulting from the hot combustion gases produced in the combustor.
• Higher compressor exit temperatures in modern high pressure ratio gas turbine engines can also necessitate the use of high performance superalloys for compressor components, including blades, spools, disks (wheels) and other components.
• Suitable alloy compositions and microstructures for a given component are dependent on the particular temperatures, stresses, and other conditions to which the component is subjected.
• rotating hardware such as turbine disks and compressor spools and disks are typically formed of alloys that must undergo carefully controlled forging, heat treatments, and surface treatments to produce a controlled grain structure and desirable mechanical properties.
• alloys used in these applications include gamma prime ( ⁇ ') precipitation-strengthened nickel-base superalloys containing chromium, tungsten, molybdenum, rhenium and/or cobalt as principal elements that combine with nickel to form the gamma ( ⁇ ) matrix, and contain aluminum, titanium, tantalum, niobium, and/or vanadium as principal elements that combine with nickel to form the gamma prime precipitate strengthening phase, principally Ni 3 (Al,Ti).
• gamma prime nickel-base superalloys include Rene 88DT (R88DT; U.S. Patent No. 4,957,567) and Rene 104 (R104; U.S.
• Patent No. 6,521,175) as well as certain nickel-base superalloys commercially available under the trademarks Inconel®, Nimonic®, and Udimet®.
• R88DT has a composition of, by weight, about 15.0-17.0% chromium, about 12.0-14.0%) cobalt, about 3.5-4.5%) molybdenum, about 3.5-4.5%) tungsten, about 1.5-2.5% aluminum, about 3.2-4.2% titanium, about 0.5.0-1.0% niobium, about 0.010-0.060% carbon, about 0.010-0.060% zirconium, about 0.010-0.040% boron, about 0.0-0.3% hafnium, about 0.0-0.01 vanadium, and about 0.0-0.01 yttrium, the balance nickel and incidental impurities.
• R104 has a nominal composition of, by weight, about 16.0-22.4% cobalt, about 6.6-14.3% chromium, about 2.6-4.8% aluminum, about 2.4-4.6% titanium, about 1.4-3.5% tantalum, about 0.9-3.0% niobium, about 1.9-4.0% tungsten, about 1.9-3.9%) molybdenum, about 0.0-2.5%) rhenium, about 0.02-0.10%) carbon, about 0.02-0.10% boron, about 0.03-0.10% zirconium, the balance nickel and incidental impurities.
• Disks and other critical gas turbine engine components are often forged from billets produced by powder metallurgy (P/M), conventional cast and wrought processing, and spraycast or nucleated casting forming techniques.
• Forging is typically performed on billets having a fine-grained microstructure that promotes formability, after which a heat treatment is often performed to cause uniform grain growth (coarsening) to optimize properties.
• This heat treatment is performed at a supersolvus temperature, in other words, above the solvus temperature at which the gamma prime precipitates of the alloy enter into solid solution.
• the forging is then cooled according to a specific cooling process to obtain desired precipitate strengthened microstructures within the disk.
• a turbine disk 10 of a type known in the art is represented in FIG. 1.
• the disk 10 generally includes an outer rim 12, a central hub or bore 14, and a web 16 between the rim 12 and bore 14.
• the rim 12 is configured for the attachment of turbine blades (not shown) in accordance with known practice.
• a bore hole 18 in the form of a through-hole is centrally located in the bore 14 for mounting the disk 10 on a shaft, and therefore the axis of the bore hole 18 coincides with the axis of rotation of the disk 10.
• the disk 10 is a unitary forging and representative of turbine disks used in aircraft engines, including but not limited to high-bypass gas turbine engines such as the GE90® and GEnx® commercial engines manufactured by the General Electric Company.
• the bore 14 and web 16 of the turbine disk 10 (as well as those of compressor spools and disks) generally have lower operating temperatures than the rim 12. It is therefore permissible and often desirable that the bore 14 have different properties than the rim 12. Depending on the particular alloy or alloys used, optimal microstructures for the rim 12, bore 14 and web 16 can also differ. For example, a relatively fine grain size is often optimal for the bore 14 and web 16 to promote tensile strength, burst strength, and resistance to low cycle fatigue (LCF), while a coarser grain size is often optimal in the rim 12 to promote creep, stress-rupture, and crack growth resistance, for example, low dwell (hold-time) fatigue crack growth rates (DFCGR) at high temperatures.
• DFCGR low dwell (hold-time) fatigue crack growth rates
• disks have been proposed that are formed of multiple alloys and/or have different microstructures within the rim and bore.
• U.S. Patent Nos. 4,820,358, 5,527,020, 5,527,402 and 6,478,896 disclose dual heat treatment techniques capable of producing single-piece, constant-composition disks having coarser grains within the rim and finer grains with the bore as a result of performing heat treatments at different temperatures on the rim and bore, thereby obtaining the different grain structures and resulting different properties.
• the present invention provides processes for heat treating components to have regions with desirable microstructures, and components produced by such processes.
• Nonlimiting examples include rotating components of turbomachines, including turbine disks of gas turbine engines.
• a process is provided for heat treating a component formed of an alloy.
• the process includes manipulating uniaxial strain test data of the alloy using a triaxiality factor to determine an equivalent multiaxial stress state. Conditions are then applied to the multiaxial stress state to identify a cooling path for the component.
• the cooling path includes boundaries for heat treatment temperatures and cooling rates that do not exceed predetermined stresses or strains and/or avoid predetermined residual stress patterns in the alloy.
• the component is then heated to a heat treatment temperature and quenched according to the cooling path identified in the applying step.
• a process for heat treating a turbine disk of a gas turbine engine.
• the process includes manipulating uniaxial strain test data on a precipitation-strengthened alloy using a triaxiality factor to determine an equivalent multiaxial stress state.
• the turbine disk is formed of the precipitation-strengthened alloy.
• Conditions are then applied to the multiaxial stress state to identify a cooling path for the turbine disk.
• the cooling path comprises boundaries for heat treatment temperatures and cooling rates that do not exceed predetermined stresses or strains and/or avoid predetermined residual stress patterns in the precipitation-strengthened alloy.
• the turbine disk is then heated to a heat treatment temperature and quenched according to the cooling path identified in the applying step.
• a technical effect of the invention is the ability to produce a component from a Ni-base composition that has a high gamma prime content and under forging conditions, high temperature heat treatments and quench rates that, in combination, are capable of achieving desirable undistorted geometries, microstructures, and high temperature properties.
• FIG. 1 is a perspective view of a turbine disk of a type used in gas turbine engines.
• FIG. 2 outlines steps performed within a method according to an embodiment of the present invention.
• FIG. 3 contains two graphs that relate uniaxial fracture strain data, temperature, and location (relative to the surface of a forging) to the triaxiality factor employed by the present invention to predict quench cracking.
• the rim 12, bore 14 and web 16 are all formed of the same alloy.
• Preferred alloys are strengthened with a precipitation phase that can be solutioned during processing of the alloys.
• preferred alloys are gamma prime precipitation-strengthened nickel-base alloys, and particular alloys can be chosen on the basis of the operating conditions to which the final product will be subjected.
• suitable materials include the aforementioned gamma prime nickel-base superalloys R88DT and R104, as well as certain nickel-base superalloys commercially available under the trademarks Inconel®, Nimonic®, and Udimet®.
• Ni-base compositions that have high gamma prime contents, for example, about 30 volume percent and above, and more preferably, about 42 volume percent and above, and most preferably about 49 volume percent and above with a solvus temperature higher than about 2100°F (about 1150°C), which include R88DT and R104.
• the invention involves forging processes, heat treatments, and quench rates capable of producing different grain sizes and optimal precipitate size and size distribution in different locations of the final product, with grain sizes in specific locations being tailored for the service conditions at those locations.
• a preform can be initially forged at relatively high strain rates to generate a fine-grained structure within at least a portion of the resulting forged profile, after which the profile undergoes a heat treatment and quench to cause or promote the generation of different grain sizes in different locations of the disk 10.
• the heat treatment can be a supersolvus heat treatment to dissolve the gamma prime precipitates and cause recrystallization and grain growth that occurs as a result of plastic strain retained within the forged profile from the preceding forging process, after which the quench is performed following a suitable cooling path to achieve a desired grain size and form a desired size and size distribution of gamma prime precipitates.
• the term cooling path refers to a process involving any number of heat treatment temperatures, hold times, and quench rates performed in a specific order so as to obtain a desired microstructure in a component.
• Forging preforms can be produced by a variety of known processes, including billets produced by powder metallurgy (P/M), conventional cast and wrought processing, and spraycast or nucleated casting forming techniques. Preforms will typically have a fine grain size, for example, an average grain size of about ASTM 10 or finer, to promote forgeability.
• the preform can be forged at a temperature, strain level and strain rates that will promote desired grain sizes, for example, finer grains within the portion of the profile that will eventually define the bore 14 of the disk 10.
• the strain level in the preform is preferably sufficiently high to cause recrystallization and grain growth during a subsequent heat treatment, which is preferably carried out to obtain a microstructure having desirable characteristics.
• the final heat treatment is preferably performed at a supersolvus (solution) heat treatment temperature, in other words, at a temperature higher than the solvus temperature of the alloy.
• a supersolvus (solution) heat treatment temperature in other words, at a temperature higher than the solvus temperature of the alloy.
• gamma prime precipitates within the profile dissolve, which permits recrystallization and grain growth to occur.
• the profile is cooled according a predetermined cooling path. For example, the profile may be initially cooled slowly to reduce plastic strain built up in the profile to avoid the quench cracking. This brief period of slow cooling will likely have little impact on the desired precipitation, due to the undercooling of the precipitation kinetics.
• the desired microstructure and quench cracking limits are balanced.
• a more rapid quench may be used.
• the cooling path (dependent on time and temperature) likely includes multiple cooling rates and times.
• the quench rate is typically limited to avoid quench cracking.
• Advanced P/M disks formed of Ni-base alloys that are highly alloyed to contain a high gamma prime content are known to be particularly susceptible to quench cracking.
• Typical measures taken to avoid quench cracking have posed significant limits on the chemistry, gamma prime content, and properties of Ni-base alloys.
• Prior attempts to predict quench cracking based on the use of uniaxial strain-to-crack or stress-to-crack criteria have not faithfully accounted for the complicated multi-dimensional strain or stress states that exist within the geometries of disks and other components produced by forging and other high-deformation processes.
• the present invention identifies the triaxiality effect as a critical addition to the quench crack analysis in conjunction with previously developed cooling rate sensitive strain-to-crack criteria.
• Quench cracking criteria utilizing this principle have the potential for allowing highly-alloyed Ni-base alloys to be quenched without cracking, while also achieving refined microstructures capable of promoting desirable properties, such as those required for disks and other rotating hardware of turbomachines.
• the present invention makes use of a method of modeling a realistic strain-to-crack value caused by the triaxiality of the stress and strain state in a forging, in conjunction with uniaxial tests and finite element modeling (FEM) of the forging.
• FEM finite element modeling
• the model corrects for the reduction of ductility by triaxiality that would result from a purely uniaxial analysis.
• heat treatment process windows and equipment can be designed to achieve specific and more optimal microstructures and properties within certain locations of a forging.
• the modeling method involves first obtaining data with uniaxial strain tests relating to the material of the desired component.
• tensile tests may be performed on a Ni-based alloy of interest having a similar microstructure to the desired component, for example, fine grains near the bore 14 of the disk 10.
• the tensile tests are performed at various temperatures to determine the uniaxial fracture strain of the alloy at the tested temperatures.
• the results of the tensile tests may be compiled in a table of values listing the maximum uniaxial strain (dependent on temperature and cooling rate) achieved with the alloy without necking or voiding, which can then be used to predict whether or not quench cracking might occur as a result of a particular heat treatment condition.
• ductile fracture is strongly dependent on triaxiality, which is the ratio of hydrostatic and equivalent stresses.
• the resulting triaxiality-based strain-to-crack values (8f) are believed to address the ductility reduction in the material, or the decrease in the strain level at failure, due to multiaxial loading effects. Therefore, these values are believed to more accurately predict quench cracking within the alloy under given heat treatment conditions, including temperatures and cooling rates.
• the uniaxial strain-to-crack test data (s u ) provide fracture strain for an equivalent multiaxial stress state (8f).
• ductile fracture strain under any multi-stress state can be related to a measurable uniaxial fracture strain for specific heat treatment temperatures and cooling rates. These resulting values represent specific stresses or strains and/or specific residual stress patterns that should be avoided in the alloy in order to avoid quench cracking.
• FIG. 3 contains two graphs that relate uniaxial fracture strain data, temperature, and location (relative to the surface of a forging) to the triaxiality factor (F T ) employed by the present invention to predict quench cracking.
• Graph A represents the relationship between a ratio of actual fracture strain, uniaxial fracture strain, and triaxiality. This relationship was verified by U notch tests using nickel-base superalloy specimens that were evaluated during investigations leading to the present invention.
• point one (PI) is a position level with a surface of the specimen and the other points (P2-P6) are positioned incrementally 0.05 inches (about 1.27 mm) away from the surface and PI .
• conditions are applied to the resulting triaxiality-based strain-to-crack values computed with the two equations above using the triaxiality factor to identify boundaries for heat treatment parameters that avoid strain values that would cause quench cracking.
• This may be accomplished by imputing the data into a FEM-based heat treatment model to compute the dynamic triaxiality under quench conditions, by which the locus of fracture strain close to the surface under the quench conditions are mapped out. Any total effective strain in the vicinity of the surface that exceeds the triaxiality corrected fracture strain computed by FEM is predicted to result in a quench crack. This information is used to identify boundaries of the potential heat treatment (quench cooling rates) parameters that avoid strain values that would cause quench cracking.
• the identified boundaries for the heat treatment parameters may be further validated by performing quenching tests on subscale coupons and full scale production parts with various quench media.
• the disk heat treatments (cooling path) can be designed to achieve the highest cooling rate possible for improved properties while avoiding quench cracking, for example, by controlling the heat treat delay transfer time and the localized ramped gas cooling. More particularly, and corresponding to the fourth and fifth steps identified in FIG. 2, a preform of the alloy used as the basis for the preceding steps is then forged and heat treated at or approaching the boundaries for the strain rate values and heat treatment parameters that avoid quench cracking that were identified in the preceding steps.
• strain rates and heat treatment conditions can be selected to optimize strain rates or heat treatment conditions (including temperatures and cooling rates), depending on the particular microstructure (for example, grain sizes) and properties desired for the forging following heat treatment. With these additional steps, the method of this invention has been experimentally validated in production trials on gas turbine disks.

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• 2012
  • 2012-12-20 US US13/721,984 patent/US20130167979A1/en not_active Abandoned
  • 2012-12-21 CN CN201280065599.6A patent/CN104136635B/zh not_active Expired - Fee Related
  • 2012-12-21 CA CA2860214A patent/CA2860214A1/en not_active Abandoned
  • 2012-12-21 EP EP12818739.0A patent/EP2798093A1/en not_active Ceased
  • 2012-12-21 JP JP2014550389A patent/JP6105626B2/ja not_active Expired - Fee Related
  • 2012-12-21 WO PCT/US2012/071122 patent/WO2013101692A1/en active Application Filing
  • 2012-12-21 BR BR112014016065A patent/BR112014016065A2/pt not_active Application Discontinuation

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