Patent Grant
11951528
The present disclosure generally relates to techniques and systems for forming superalloy components.
Hot forging may be used to form alloy components. During hot forging, an alloy component may be heated at or above a forging temperature to soften the component and worked to change a shape of the alloy component. As a result of forging, the alloy component may have a non-homogeneous microstructure caused by the forging temperature and the forces exerted on the alloy component during forging.
The disclosure describes example systems and techniques for controlling microstructure of an alloy substrate by controlling temperature during forging and using multiple forging stages with different die to control formation of grain boundary phases of the superalloy, and components formed by such example systems and techniques.
In some examples, the disclosure describes an example method that includes heating a substrate to within a forging temperature range. The substrate includes a nickel-based superalloy, and the forging temperature range is below an eta phase solvus temperature of the substrate. The method includes applying a plurality of die forging stages to the substrate to form a component preform. The method includes maintaining the substrate within the forging temperature range during application of the plurality of die forging stages and cooling the component preform after completing the plurality of die forging stages.
In some examples, the disclosure describes a system including a plurality of sequential forging dies configured to form a component preform from a substrate. The substrate includes an alloy or superalloy. The system includes a forging press configured to apply the plurality of sequential forging dies in a plurality of die forging stages. The system includes a heat source configured to heat the substrate to within a forging temperature range and maintain the substrate within the forging temperature range during application of the plurality of die forging stages. The forging temperature range is below a transition temperature of the substrate. The system may include a cooling source configured to cool the component preform after completing the plurality of die forging stages, such as if geometry of the component requires.
In some examples, the disclosure describes a component including a nickel-based superalloy. A high stress portion of the component includes a relatively low delta phase region in which a volume fraction of a delta phase in the relatively low delta phase region is less than about 80% of an average volume fraction of the delta phase in the component.
The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
The disclosure describes example systems and techniques for controlling microstructure of a nickel-based superalloy by controlling temperature during hot forging and using multiple die forging stages to refine grain size and control formation of grain boundary phases of the superalloy, and components formed by such example systems and techniques.
High temperature components of gas turbine engines, such as high pressure discs and impellers, may be formed from precipitation-hardened nickel-based superalloys. The microstructure of such superalloys may be designed to increase strength, low cycle fatigue performance, and/or resistance to fatigue crack growth and creep deformation. Nickel-based superalloys may be alloyed with refractory elements and heat-treated to precipitate a high volume fraction of strengthening phases, such as gamma prime (γ′) and double prime (γ″) phases, in an austenitic face centered cubic (fcc) matrix. For example, a nickel-based superalloy that includes various combinations of niobium, titanium, and/or aluminum may be strengthened by a gamma prime phase (Ni3Ti or Ni3Al) and/or a gamma double prime (Ni3Nb) phase. Nickel-based superalloys may also be hot forged under high loads and at high temperatures to refine grains, such as by recrystallization and grain growth. In these various ways, a microstructure of nickel-based superalloys may be refined and controlled to produce improved mechanical properties.
At certain processing conditions, nickel-based superalloys may also precipitate other phases, primarily at grain boundaries (i.e., grain boundary phases, though precipitation may occur at twin boundaries or between boundaries), which do not contribute to the strength of the superalloys. For example, a nickel-based superalloy containing niobium, titanium, and/or aluminum, such as 718Plus (718+), may form a delta phase (Ni3Nb) or an eta phase (Ni3Ti and/or Ni3Al0.5Nb0.5) when maintained at sub-solvus temperatures below the solvus temperature of the grain boundary phases and above the solvus temperatures of the strengthening phases, such as illustrated in
In addition to temperature, other processing conditions, such as strain, may increase formation of the grain boundary phases. For example, an increase in residual strain during forging may correspond to an increase in precipitation of the eta phase. Strain or cold work modifies the alignment of the crystal structure of the many grains that make up the microstructure creating a preferred alignment or crystallographic texture. These highly aligned textures often enhance precipitation of secondary phases. Likewise, the alignment or texture tends to encourage the secondary growth in certain orientations thus creating alignment of the secondary phase precipitates. Residual stress also encourages or enhances the rate of nucleation and growth of these secondary phases. Therefore, a highly cold/warm worked structure (such as a forging done well into the subsolvus region) tends to have a high degree of crystallographic texture as well as the potential to have higher residual stresses. These conditions will tend to encourage precipitation and growth of aligned secondary phases such as eta and delta.
The grain boundary phases may have different crystal structures, such as orthorhombic for the delta phase or hexagonal closed pack for the eta phase, than the crystal structures of the matrix or strengthening phases (e.g., gamma, gamma prime, and gamma double prime phases), and a relatively large volume fraction of the grain boundary phases may result in degradation of mechanical properties, such as ductility, of the superalloy substrate. For example, nickel-based superalloy substrates subject to relatively high loads during thermomechanical processing, and thereby incurring large amounts of residual strain, may be particularly susceptible to formation of the eta phase. A component machined from a component preform having a relatively high volume fraction of grain boundary phases may have lower strength, ductility, and/or creep resistance than a component formed from a superalloy substrate having relatively low volume fraction of grain boundary phases.
According to examples described herein, an alloy component preform, such as a nickel-based superalloy component preform, may include a relatively uniform microstructure (i.e., grain boundary sizes) with a low volume fraction of grain boundary phases, such as the delta and/or eta phases. A nickel-based superalloy substrate may be heated to within a forging temperature range and subjected to multiple die forging stages to refine the grain size of the substrate and shape the substrate into a component preform from which a component may be machined. This forging temperature range may be at or below one or more grain boundary phase solvus temperatures and above intermediate temperatures at which transformation kinetics of the grain boundary phases may be relatively high. The superalloy substrate may be maintained within this forging temperature range during and between the multiple die forging stages to reduce precipitation of the grain boundary phases and quickly cooled to a low temperature to reduce precipitation and/or transformation of the delta and eta phases from the strengthening phases. In this way, the resulting component preform may include relatively uniform grain size and a relatively low volume fraction of the delta and/or eta phase.
In some examples, a nickel-based superalloy component preform may include a reduced volume fraction of delta and eta phases in particular portions or regions of the component preform. During forging, particular portions of the superalloy substrate may be maintained at relatively high forging temperatures to reduce formation of grain boundary phases, such as the delta and eta phases described above. The plurality of die forging stages applied to the superalloy substrate may be configured to refine the grain size through relatively high strain, while also forming the component preform to include low grain boundary phase regions at predetermined volumes within the component preform. When processing a component from the component preform, portions of the component that undergo higher and/or repeated stresses during operation, such as a bore of an impeller, may include the relatively low grain boundary phase regions of the component preform, while portions of the component that undergo lower stresses during operation, such as a rim of the impeller, may include relatively higher grain boundary phase regions. In this way, the microstructure of the component may be selectively controlled to provide improved mechanical properties to regions under higher amounts of stress.
The component preform may be formed from a superalloy substrate that includes a precipitation-hardened nickel-based superalloy. The precipitation-hardened nickel-based superalloy may include any alloy with a primary constituent (i.e., greater wt. % than any other constituent) of nickel forming a gamma phase face centered cubic (fcc) matrix and one or more alloying elements configured to precipitate one or more strengthening fcc phases. In some examples, the nickel-based superalloy may be a nickel-chromium-iron-based (NiCrFe) superalloy having a relatively high strength and corrosion resistance. In addition to nickel, the nickel-based superalloys may include other elements configured to reside in the gamma phase matrix including, but not limited to, cobalt, iron, chromium, molybdenum, tungsten, and other elements having a relatively similar atomic radii to nickel.
In addition to gamma phase components, the nickel-based superalloy substrate includes one or more components configured to precipitate one or more strengthening phases. For example, components having a relatively large atomic radii compared to nickel may encourage precipitation of relatively ordered phases, such as gamma prime (e.g., Ni3Ti or Ni3Al) and/or gamma double prime (e.g., Ni3Nb) phases. As described above, the gamma prime and/or gamma double prime phases may be configured to increase strength, low cycle fatigue performance, resistance to fatigue crack growth and creep deformation, and/or ductility of the superalloy substrate, in addition to other advantageous mechanical properties. In some examples, the nickel-based superalloy may include at least one of niobium, aluminum, titanium, and/or tantalum. In some examples, a relative concentration of aluminum to titanium may be selected to reduce precipitation of the delta and eta phases, such as by having a relatively high ratio of aluminum to titanium and/or including an aluminum and titanium concentration greater than about 3 wt. %. In some examples, the superalloy substrate may include between about 4 wt. % and about 8 wt. % niobium, between about 0.4 wt. % and about 2.6 wt. % aluminum, and between about 0.4 wt. % and about 1.4 wt. % titanium.
In some examples, the superalloy substrate may include other components selected to improve one or more properties of the superalloy substrate. As one example, the superalloy substrate may include chromium to increase resistance to oxidation and corrosion. In some examples, the superalloy substrate may include less than about 15 wt. % to reduce combination with refractory elements in the alloy and formation of topologically close-packed (TCP) phases. In some examples, the superalloy substrate may include cobalt to lower a gamma prime solvus and a stacking fault energy, which may aid in processability, creep rupture strength, and, at some temperatures, fatigue strength. In some examples, the superalloy substrate may include less than about 20 wt. % cobalt to reduce formation of grain boundary phases. In some examples, molybdenum and tungsten may act as solid solution strengtheners for both the gamma and gamma prime phases. In some examples, the superalloy substrate may include boron, carbon, and/or zirconium to strengthen the grain boundaries by forming nonmetallic particles at the grain boundaries and/or counteract the deleterious effects of grain impurity segregates like sulfur and oxygen by acting as a diffusion barrier. In some examples, the superalloy substrate may include hafnium and silicon to improve dwell fatigue and environmental resistance, respectively.
In some examples, the superalloy substrate may have a composition including between about 12 wt. % and about 20 wt. % chromium, between about 6 wt. % and about 14 wt. % iron, between about 5 wt. % and about 12 wt. % cobalt, between about 4 wt. % and about 8 wt. % niobium, less than about 6 wt. % tungsten, less than about 4 wt. % molybdenum, between about 0.6 wt. % and about 2.6 wt. % aluminum, between about 0.4 wt. % and about 1.4 wt. % titanium, less than about 0.1 wt. % carbon, between about 0.003 wt. % and about 0.03 wt. % phosphorus, and between about 0.003 and about 0.015 wt. % boron.
In some examples, the superalloy substrate may include Inconel 718Plus and/or alloy variants relatively similar in composition that are prone to form delta and eta phases. For example, the superalloy substrate may have a composition including between about 17 wt. % and about 21 wt. % chromium, between about 8 wt. % and about 10 wt. % iron, between about 8 wt. % and about 10 wt. % cobalt, between about 5.2 wt. % and about 5.8 wt. % niobium, between about 0.8 wt. % about 1.4 wt. % tungsten, between about 2.5 wt. % and about 3.1 wt. % molybdenum, between about 1.2 wt. % and about 1.7 wt. % aluminum, between about 0.5 wt. % and about 1 wt. % titanium, between about 0.01 wt. % and about 0.05 wt. % carbon, between about 0.004 wt. % and about 0.02 wt. % phosphorus, between about 0.003 and about 0.008 wt. % boron, less than about 0.35 wt. % manganese, less than about 0.35 wt. % silicon, less than about 0.0025 wt. % sulfur, less than about 0.3 wt. % copper, and less than about 0.0005 wt. % lead.
The method of
In some examples, and without being limited to any particular theory, grain refinement of the superalloy substrate may be achieved, at least partially, by precipitating a relatively small, distributed delta phase under high strain. These fine, precipitated delta phases may inhibit grain growth during recrystallization to obtain relatively fine, uniform grains, as will be described further below. The forging temperature range may be high enough to reduce tonnage for producing relatively high strain through the superalloy substrate, such as within about 100° C. of a delta solvus temperature.
In some examples, the forging temperature may be selected to reduce formation of one or more grain boundary phases of the superalloy. As explained above, in addition to forming strengthening phases at elevated temperatures, the strengthening phase formers may form other phases, such as the delta phases and eta phases. These phases may be incoherent with the gamma prime and double prime phases of the superalloy or may form relatively large grain boundaries. Formation of these phases may be related to particular temperatures or for particular amounts of time. For example, in an Inconel 718 substrate, a gamma double prime phase of Ni3Nb may transform to a delta phase, thereby reducing a strength of the substrate, while in an Inconel 718Plus substrate, a gamma prime phase of Ni3(Al/Ti) may transform to an eta phase. These transformations may be more likely at relatively intermediate temperatures.
As one example,
To reduce formation of the grain boundary phases of the substrate, such as the eta phase, the forging temperature range is configured to be below the eta phase solvus temperature of the substrate. This forging temperature range may be sufficiently high to enable grain refinement of the superalloy substrate through application of a plurality of die forging stages, as will be discussed further below, as well as limit precipitation of the grain boundary phases during grain refinement. In some examples, the eta phase solvus temperature is between about 980° C. and about 1010° C., such as about 990° C. However, the eta phase solvus temperature may vary depending on a composition of the superalloy substrate. In some examples, the forging temperature range is within about 100° C. of the eta solvus temperature. In some examples, the forging temperature range is between about 925° C. to about 950° C.
The method of
In some examples, the plurality of die forging stages may be configured to refine a microstructure (e.g., grain size, shape, or distribution) of the superalloy substrate with reduced variability (i.e., increased uniformity). For example, the plurality of die forging stages may be configured to produce adequate strain through a cross-section of the component preform, such that a microstructure resulting from grain refinement is relatively uniform. A relatively uniform microstructure may include a grain size across the component preform that is within about 5 ASTM grain size units, such as within about 3 ASTM grain size units.
In some examples, the plurality of die forging stages may be configured to refine the microstructure of the superalloy substrate along at least two axes. Without being limited to any particular theory, application of high amounts of strain along an axis may cause delta and/or eta phase precipitates to change morphology (e.g., through deformation and/or dissolution breakage) to a more refined and/or distributed morphology. For example, eta phase precipitates may become mobile and align with forging flow perpendicular to application of a load, resulting in a finer morphology. As another example, delta phase precipitates may break up and form coarser, more distributed precipitates.
To produce grains that are refined in more than one direction, the plurality of die forging stages may be configured to apply a load along more than one axes. For example, during a first forging stage, such as a pancake forging stage or other stage configured to reduce a cross-section of the superalloy substrate in one or more directions and/or increase a cross-section of the substrate in another direction, a load may be applied along a first axis, such as a z-axis, such that local forging flow may be primarily along an x-y plane. In subsequent forging stages, such as a closed die forging stage or other forging stage configured to shape the superalloy substrate, a load may be applied along a second or third axis, such as an x-axis and/or y-axis, such that local forging flow may be primarily along planes other than an x-y plane. In this way, the plurality of die forging stages may refine the microstructure of the superalloy substrate along multiple axes through refinement of one or more grain boundary phases.
The method of
In some examples, particular portions of the superalloy substrate may be maintained at relatively high temperatures compared to other portions of the superalloy substrate. For example, a portion of the superalloy substrate may be maintained at the relatively high temperature to reduce a volume fraction of one or more boundary phases at the portions of the superalloy substrate (i.e., low grain boundary phase regions, such as a relatively low delta phase region or a relatively low eta phase region). In some examples, a volume fraction of a delta or eta phase in a relatively low delta phase region or relatively low eta phase region may be less than about 80% of an average volume fraction of the respective delta phase or eta phase in the superalloy substrate.
The method of
In some examples, the method of
In examples in which the component preform includes a relatively low gain boundary phase region, the component preform may be processed such that a high stress portion of the component is at least partially positioned within the relatively low grain boundary phase region. For example, a relatively low delta phase region may higher ductility or other mechanical properties than a relatively high delta phase region, such that portions of a component that are more subject to failure due to higher stresses may be machined into the relatively low delta phase region or regions.
Component preforms manufactured from the method described in
System 30 includes a plurality of sequential forging dies 34. The plurality of forging dies 34 may be configured to form a component preform from substrate 32. As explained in
System 30 includes a forging press 40. Forging press 40 may be configured to apply a load to the plurality of sequential forging dies 34 in a plurality of die forging stages. For example, forging press 40 may be configured, in combination with the plurality of sequential forging dies 34, to produce sufficient strain in substrate 32 to refine a microstructure of substrate 32.
System 30 includes a heat source 36. Heat source 36 may be configured to heat substrate 32 to within a forging temperature range and maintain substrate 32 within the forging temperature range during application of the plurality of die forging stages. The forging temperature range is below an eta phase solvus temperature of the substrate. A variety of heat sources may be used including, but not limited to, die heating, adiabatic heating, and the like. In some examples, heat source 36 is a die heat source. For example, heat source 36 may include one or more heating elements in thermal contact with the plurality of sequential forging dies 34 and configured to heat substrate 32. While not shown, system 30 may include a furnace or other enclosure configured to provide an inert atmosphere. System 30 includes a cooling source 38 configured to cool the component preform formed from substrate 32. A variety of cooling sources may be used including, but not limited to air cooling, and the like.
System 30 includes controller 42. Controller 42 may be communicatively coupled to heat source 36, cooling source 38, and forging press 40. Controller 42 may include or may be one or more processors or processing circuitry, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some examples, the functionality of computing device 40 may be provided within dedicated hardware and/or software modules.
Controller 42 may be configured to control operation of system 30, including, for example, each of heat source 36, cooling source 38, and forging press 40 to implement the method of
In general, the plurality of die forging stages described in
Referring to
Referring to
Referring to
Referring to
In some examples, second forging stage 60 may be configured such that processing conditions corresponding to a relatively low volume fraction of grain boundary phases, such as relatively high temperature, may be maintained in an overlapping region between first forging stage 50 and second forging stage 60. For example, low grain boundary phase region 68 of second forging stage 60 may at least partially overlap with low grain boundary phase region 58 of first forging stage 50.
Referring to
Referring to
While
Rather than use a single die forging stage, which may create the varied strain across a component preform as illustrated in
The relatively high strain of impeller preform 94 may assist in creating a refined microstructure, such as evidenced by a relatively low and/or uniform grain size.
As explained above, a microstructure of the superalloy may be influenced by grain size and precipitation of grain boundary phases. Precipitation of grain boundary phases, such as the eta phase, may be reduced by maintaining relatively high temperature during the plurality of die forging stages.
A volume fraction of delta phase that forms in a component preform may be related to a temperature of the component preform and the strain of the component preform. However, as illustrated in
While
Various examples have been described. These and other examples are within the scope of the following claims.
This application claims the benefit of U.S. Provisional Application Ser. No. 63/068,137 filed Aug. 20, 2020, the entire contents of which is incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20220055093 A1 | Feb 2022 | US |
| Number | Date | Country | |
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| 63068137 | Aug 2020 | US |
