Patent Description:
This disclosure is generally related to metallic components, and methods for manufacturing those components. In some specific embodiments, the disclosure is related to cast metallic articles, often formed from nickel- or cobalt-based superalloys; and related, specialized casting methods.

A number of metals and metal alloys are employed in demanding applications, in terms of strength, oxidation resistance, and/or high temperature resistance. Examples include titanium, vanadium, molybdenum, and superalloys based on nickel, cobalt, or iron. Such superalloys are especially suitable for high-temperature applications, such as, for example, gas turbine engine components of aircraft engines and power generation equipment. Very often, these components are manufactured by casting processes, such as investment-casting. While metal casting has been practiced for thousands of years, the techniques have become quite sophisticated in modern times, due in part to the high level of integrity required for cast parts such as jet engine blades.

The integrity and overall quality of the metal component is determined in part by its crystalline structure, e.g., the grain size and orientation of the grains in the component. The desired grain structure is, in turn, often dependent on the projected operating temperature of the part. As an example in the case of gas turbine components formed from various superalloys, the turbine blades in the turbine section may be exposed to extremely hot temperatures, and may have a directionally solidified (DS) columnar grain structure, or a single crystal structure, to resist high-temperature creep failure and other degrading effects.

In contrast, engine components that are subjected to lower operating temperatures often benefit from a very different grain structure. For example, gas turbine wheels and discs, while having their own set of performance requirements, often operate at temperatures much lower than those encountered within the hot gas path. In many cases, it is very desirable that these components have a fine equiaxed grain structure.

Although fine equiaxed grain structures are commonly obtained in small castings, they are relatively difficult to produce in large, complex parts, such as the gas turbine airfoils and structural components. The investment casting techniques typically produce cast components having a mixture of columnar and equiaxed grains. This is often the case for large components with thick sections (e.g., sections more than about <NUM> thick). Obtaining the desired fine-grain structure can be especially difficult if the component has a complex geometry, with a wide variation in sectional thickness.

Non-uniform grain morphology and grain size can lead to problems in the quality and performance of the cast components. In many cases (though not all), large grain size can result in low strength at a given operating temperature. Moreover, a columnar grain structure, while desirable for components operating under a specific temperature regime, can be detrimental for the lower-temperature components referenced above. Columnar grain morphology is characterized by continuous, intergranular boundaries, along which cracks and "hot tears" can sometimes develop. Also, when oriented transversely to the stress-direction during use, the columnar grain boundaries can be weak, which can in turn lead to premature failure of the component.

Alternatively, certain components may be used in ways that expose different sections of the cast component to different environments in use. In such components, it may be desirable to have different grain properties within the different sections of the component. It is currently difficult to produce components with multiple material structures in a single process. In many cases separate parts with different structures are joined to produce a structure. <CIT> relates to a method of making a cast metal turbine wheel with integral radial columnar grain blades and equiaxed grain disk. <CIT> and <CIT> relate to improved turbine wheel for jet engines and method of manufacture. <CIT> relates to a system for casting a metal article. <CIT> relates to a method and apparatus for casting directionally solidified articles.

With these general considerations in mind, new methods for casting high-performance alloys would be welcome in the art. The techniques should be especially suitable for manufacturing components that require a controlled microstructure, such as fine equiaxed grain structures or multi-type grain structure in different sections of the component. Moreover, the new developments should also be suitable for casting relatively large components having complex geometries. Furthermore, the techniques should not require substantial changes to current casting operations that would result in significant increases in manufacturing costs.

Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

A method as claimed in claim <NUM> is provided.

These and other features, aspects and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain certain principles of the invention.

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended Figs. , in which:.

In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention, as defined by the appended claims.

As alluded to previously, a number of metals and metal alloys can be cast according to embodiments of this invention. Examples include the "superalloys," a term intended to embrace iron-, cobalt-, or nickel-based alloys. The superalloys usually include one or more additional elements to enhance their high-temperature performance. Non-limiting examples of the additional elements include cobalt, chromium, aluminum, tungsten, molybdenum, rhenium, ruthenium, zirconium, carbon, titanium, tantalum, niobium, hafnium, boron, silicon, yttrium, and the rare earth metals. (Each of the base alloys may contain one or more of the other elements listed as base alloys, e.g., nickel-based alloys containing cobalt and/or iron). Other metals that can be cast according to methods described herein include titanium or titanium alloys, or stainless steel alloys.

Methods for creating a cast component from a metal material are generally provided herein, along with the resulting cast components. In particular embodiments, the method includes forming cast components with a controlled grain structure therein.

In one embodiment, methods are provided for creating a cast alloy component from a metal material. Generally, the methods involve burying a mold in a powder of ceramic material, preheating the mold to an initial mold temperature, and then pouring the molten metal material into the mold while the mold is buried within the powder. Then, the molten metal material may be allowed to cool to form a cast alloy component while the mold is buried within the powder of ceramic material.

Through this method, the resulting cast alloy component has a grain structure that is predominantly fine grains across thin and thick sections with little to no columnar grain growth. Such a finer grain structure leads to superior properties (e.g. increased fatigue life) of cast alloy components for particular applications, such as compressor blades. For example, the cast alloy component may have a grain structure that has an average grain size of about <NUM> micrometers (µm) or less, such as about <NUM> to about <NUM> (e.g., about <NUM> to about <NUM>, or about <NUM> to about <NUM>).

Without wishing to be bound by any particular theory, it is believed that the methods help achieve significantly fine grain structure across the cast alloy component by decreasing the thermal gradient within the metal material during final solidification. Without wishing to be bound by any particular theory, it is believed that the ceramic bed provides a medium into which the thermal gradient is formed, outside of the mold, to allow for more unified cooling within the mold. That is, a thermal gradient can be formed within the powder of ceramic material after poring the molten metal material into the mold, such that the thermal gradient essentially shifts from the metal material within the mold and into the ceramic powder outside of the mold. As such, the resultant grain structure within the cast alloy component has a substantially uniform grain structure across thin and thick sections with little to no columnar grain growth.

In one particular embodiment, the ceramic material of the powder is an insulating ceramic material (e.g., insulating ceramic oxides). For example, in one embodiment, the ceramic material of the powder may include alumina (e.g., tabular alumina), which has a relatively high thermal conductivity of the insulating ceramic material. Such a feature may provide a path to conduct heat throughout the powder so as to minimize any thermal gradient across the mold, keeping the metal material and the ceramic material at substantially the same temperature through the cooling process. Other insulating ceramic oxides that may be suitable for use as the ceramic material of the powder include, but are not limited to, zirconia, hafnia, titania, silica, cobalt aluminate, zircon, silica, magnesia, a rare earth oxide (e.g., yttria), or mixtures thereof.

The ceramic material of the powder generally comprises a plurality of ceramic particles (i.e., a powder of ceramic particles). In certain embodiments, the powder has relatively small sized particles (e.g., an average particle size of about <NUM> or less, preferably about <NUM> or less) such that maximum contact can be made with the exterior surfaces of the mold. In particular embodiments, the particles may have an average particle size of about <NUM> to about <NUM>.

Additionally, it is believed that the grain size may be controlled through adjusting the initial mold temperature, the material temperature of the molten material, and/or the elevated mold temperature reached after pouring the metal material therein. In one particular embodiment, the mold may be buried into a powder of ceramic material, and then the mold may be heated to the initial mold temperature. After heating to the initial mold temperature, the heat source may be disengaged, and the molten metal material may be poured into the mold while at the initial mold temperature.

The initial mold temperature is less than half of the solidus temperature of the metal material to be poured therein. As used herein, the term "solidus temperature" refers to the highest temperature at which the metal material (e.g., an alloy) is completely solid. In one embodiment, the mold temperature may be <NUM>% of the solidus temperature of the metal material or less (e.g., room temperature (e.g., <NUM>° C to <NUM>% of the solidus temperature of the metal material). For example, the mold temperature may be <NUM>% of the solidus temperature to <NUM>% of the solidus temperature of the metal material (e.g., <NUM>% to less than <NUM>% of the solidus temperature of the metal material), such as <NUM>% to <NUM>% of the solidus temperature of the metal material. When the mold temperature is less than half of the solidus temperature of the metal material, it is believed that the molten material quickly cools from its liquid phase upon being poured into the mold. As such, it is believed that the molten material may begin to crystalize while it fills the mold such that the molten metal material begins to form its grain structure upon pouring. Without wishing to be bound by any particular theory, it is believed that these grains may serve as seed sites for grain formation at the desired size. Such an embodiment may be particularly useful for components having large cavities to fill with the molten metal material.

While the molten metal is being poured into the cooler mold, it is believed, without wishing to be bound by any particular theory, that thermal energy transfers from the metal material to the mold, and then from the mold into the powder of ceramic material. That is, the metal material cools while the mold heats, which in turn causes the ceramic material surrounding the mold to heat. It is believed that the powder of ceramic material has sufficient thermal mass to absorb the heat from the metal material (through the mold), serving as a thermal sink, while providing insulation to the mold to control the cooling rate.

Generally, this controlled solidification process is allowed to occur until the metal material completely solidifies within the mold. As discussed below, the mold may then be quickly cooled, upon complete solidification of the metal material, to inhibit grain growth within the cast metal component. During the controlled solidification process, the molten material heats the mold from its initial mold temperature (i.e., the temperature of the mold when the molten material is poured therein) to an elevated mold temperature upon which the molten material is completely solidified within the mold. The elevated mold temperature may depend on a variety of factors, such as the initial mold temperature, the volume and/or temperature of the molten material at pouring, the amount and/or type of ceramic material present, the size and/or thickness of the mold, etc. For example, in certain embodiments, the elevated mold temperature may be greater than <NUM>% of the solidus temperature of the metal material (e.g., greater than <NUM>% to <NUM>% of the solidus temperature). For instance, the elevated mold temperature may be <NUM>% to <NUM>% of the solidus temperature of the metal material (e.g., <NUM>% to <NUM>% of the solidus temperature).

The mold may be made out of a ceramic material, which is independently selected from the ceramic material of the powder. For example, the mold may be formed from alumina, zirconia, hafnia, titania, silica, cobalt aluminate, zircon, silica, magnesia, a rare earth oxide, or a mixture thereof.

In certain embodiments, the molten metal material is poured into the mold near its liquidus temperature. As used herein, the term "liquidus temperature" refers to the lowest temperature at which the metal material (e.g., an alloy) is completely liquid. For example, the molten metal material is poured at a pour temperature may be about <NUM>% of the liquidus temperature to <NUM>% of the liquidus temperature of the metal material, such as about <NUM>% of the liquidus temperature to <NUM>%. When the pour temperature is at or above the liquidus temperature (e.g., <NUM>% to about <NUM>%) of the metal material, it is believed that the molten material may stay completely in the liquid phase while the mold is being filled such that the molten metal material completely fills the mold in a substantially uniform manner. Such an embodiment may be particularly useful for components having small structures through which the molten metal material fills. Alternatively, with the pour temperature is below the liquidus temperature (e.g., about <NUM>% to less than <NUM>%, such as about <NUM>% to less than <NUM>% or about <NUM>% to less than <NUM>%) of the metal material, it is believed that the molten material may begin to crystalize while it fills the mold such that the molten metal material begins to form its grain structure upon pouring. That is, crystals may form within the molten metal material, when the pour temperature is lower than the liquidus temperature, such that smaller grains already started prior to the rest of the material crystalizing. Without wishing to be bound by any particular theory, it is believed that these grains may serve as seed sites for grain formation at the desired size. Such an embodiment may be particularly useful for components having large cavities to fill with the molten metal material.

In one embodiment, the metal material may include, but is not limited to, pure metals, nickel alloys, chrome alloys, titanium, titanium alloys, magnesium, magnesium alloys, aluminum, aluminum alloys, nickel-based superalloys, cobalt-based superalloys, or mixtures thereof.

Referring to <FIG>, a mold <NUM> is generally shown having an inlet <NUM> for receiving molten metal material. A funnel portion <NUM> is connected to a center channel <NUM>, which directs the molten metal material to flow into the mold. A plurality of component cast portions <NUM> extend from the center channel <NUM> so as to form multiple components in a single casting cycle.

<FIG> shows the mold <NUM> placed into a carrier <NUM> and surrounded by a powder <NUM>. As shown, all of the component cast portions <NUM> of the mold <NUM> are completely buried in the powder <NUM> of ceramic material. However, in other embodiments, only a portion of the component cast portions <NUM> are buried within the powder <NUM> of the ceramic material. In such a method, the grain size of the cast alloy components formed within the mold will have a small grain size in the component portions buried within the powder, while the cast alloy components formed within the mold will have larger grain sizes in the component portions above the powder.

In certain embodiments, the amount of powder <NUM> that is present in the carrier <NUM> is greater, in terms of thermal mass, than the amount of metal material poured into the mold <NUM>. For example, thermal mass ratio may be defined by the volume of ceramic material to the volume of metal material within the mold. In this definition, the thermal mass ratio may be greater than <NUM>, indicating that there is more thermal mass of the powder <NUM> than the poured metal material. In particular embodiments, the thermal mass ratio may be about <NUM> or greater (e.g., about <NUM> or greater, such as about <NUM> or greater).

<FIG> shows an exemplary vacuum induction melter <NUM> that is particularly suitable for forming the cast components. In the embodiment shown, a chamber <NUM> defines a loading area <NUM> and a pouring area <NUM> separated from each other by an inner wall <NUM>. In the loading area <NUM>, the mold <NUM> may be placed on the lift <NUM>, and then lifted, while remaining buried within the powder <NUM>, into the pouring area <NUM> through an aperture <NUM> between the loading area <NUM> and the pouring area <NUM>. As shown, a valve arm <NUM> may close the aperture <NUM> in order to separate the loading area <NUM> from the pouring area <NUM>. For example, the valve arm <NUM> may pivot to close the aperture <NUM>. In other embodiments, the valve arm <NUM> may be configured to slide into place to close the aperture <NUM>.

The mold heater <NUM> may preheat the mold, while buried within the ceramic material, to the initial mold temperature, as discussed above). Additionally, a metal heater <NUM> may heat the metal material <NUM> to the pour temperature within the pouring area <NUM> (e.g., about <NUM>% of the liquidus temperature up to about <NUM>% of the liquidus temperature, as discussed above). Then, the molten metal material <NUM> may be poured into the mold <NUM> while it remains buried within the powder <NUM> of ceramic material.

In one embodiment, the chamber <NUM> may be free from oxygen during pouring of the molten metal material <NUM> so as to prevent oxidation of the metal material. In certain embodiments, a vacuum may be formed within the chamber <NUM> for pouring of the molten metal material <NUM>. For example, the chamber <NUM> may have a pressure that is less than <NUM> torr (e.g., about <NUM> torr or less). In particular embodiments, the chamber may have a pressure that is about <NUM> torr or less (e.g., about <NUM> millitorr to about <NUM> millitorr). In conditions having a pressure that is greater than <NUM> torr, it may be preferable to have an inert gas (e.g., argon) purge the chamber prior to drawing the vacuum so as to ensure that the atmosphere is substantially free from oxygen.

After pouring of the molten metal material <NUM>, the molten metal material <NUM> is cooled within the mold <NUM> while buried within the powder <NUM> of ceramic material, through thermal transfer of the thermal energy from the metal material into the mold and, subsequently into the ceramic material. In certain embodiments, cooling may begin soon after the mold <NUM> is filled with the molten metal material <NUM>. For example, upon completion of pouring, the mold <NUM> may be lowered back into the loading area <NUM> without any heating elements being used (i.e., any heating sources are disengaged). For example, the valve arm <NUM> may close the aperture <NUM> such that the loading area is isolated from the heating elements <NUM> and <NUM> in the pouring area <NUM>. As such, the metal material <NUM> may be allowed to cool within the mold <NUM> while remaining buried within the powder <NUM> of ceramic material. Once the metal material <NUM> solidifies completely within the mold <NUM> (e.g., at an elevated mold temperature), the mold <NUM> may be cooled quickly to inhibit grain growth within the cast metal component. For example, in one particular embodiment, the mold <NUM> may be removed from the powder <NUM> of ceramic material after it has completely solidified to allow the metal material <NUM> and the mold <NUM> to cool on its own.

In one embodiment, the molten material may be subjected to an overpressure (e.g., a pressure furnace) or spin casting to provide a force to drive the molten metal material into the mold. Such an overpressure may be especially useful in embodiments where the molten metal material is poured at a temperature that is less than the liquidus temperature. In embodiments where an overpressure is used, a pressure may be formed that is greater than <NUM> torr to about <NUM> torr (e.g., <NUM> torr to about <NUM> torr) within the chamber <NUM>. Such a pressure may be made with an inert gas (e.g., argon, nitrogen, etc.) so as to prevent oxidation of the cast component.

In particular embodiments, the method includes forming cast components with a controlled grain structure therein. For example, the cast component may have multiple sections, each with its own average grain structure therein resulting from the casting process that uses different environmental portions of the mold. In one embodiment, for instance, the method may be utilized to create a cast component having a first section with fine equiaxed grain structures and a second section with elongated grain structures in a single casting process.

Generally, the methods for creating such a cast component involve controlling the temperature at various areas of the mold such that different portions of the mold may have different thermal conditions (e.g. different initial temperatures) when the molten metal material is poured therein. For example, the initial temperature a first portion of the mold in a powder may be different than the initial temperature of a second portion of the mold, which may be different than the initial temperature of a third portion of the mold, etc..

In one embodiment, the methods for creating such a cast component involve surrounding a first portion of the mold in a powder of ceramic material while leaving a second portion of the mold exposed. Additional portions may be included within the mold, as desired. The mold and the powder of ceramic material may then be heated (i.e., preheating the mold), such that the first portion within the powder of ceramic material has an initial first portion temperature that is different than an initial second temperature of the second portion defined by the exposed mold. After heating, a molten metal material may be poured into the mold such that the molten metal material fills the first portion (while in contact with the powder) and the second portion. Then, the molten metal material may be allowed to cool to form a cast component. For example, the mold may be allowed to cool while the first portion of the mold is buried within the powder of ceramic material.

Through this method, the resulting cast component has a grain structure that is predominantly fine grains (e.g., with little to no columnar grain growth therein) within a first section of the cast component that corresponds with the first portion of the mold. Conversely, a second section of the cast component, corresponding to the second portion of the mold, has relatively larger grains therein (e.g., predominantly columnar grains therein). That is, the first section of the cast component may have a first average grain size that is less than a second average grain size within the second section of the cast component. Thus, an integral cast component may be formed with different properties (e.g., grain size) at different areas therein.

Referring to <FIG>, a cross-section of a casting system <NUM> is generally shown for use in the methods of creating a cast component. The casting system <NUM> includes a mold <NUM> defining a cavity <NUM> having a first portion <NUM> (i.e., a powder surrounded portion, or a "buried" portion) and a second portion <NUM> (i.e., an exposed portion), and optionally additional portions as desired. The first portion <NUM> of the mold <NUM> is surrounded by a powder of ceramic material <NUM> and the second portion of the mold <NUM> is exposed (i.e., not in contact with the powder of ceramic material <NUM>). The cavity <NUM> may further include links spanning therethrough, which result in channels within the resulting cast component (e.g., flow channels within an airfoil).

In one particular embodiment, the ceramic material of the powder is an insulating ceramic material (e.g., insulating ceramic oxides). For example, in one embodiment, the ceramic material of the powder may include alumina (e.g., tabular alumina), which has a relatively high thermal conductivity, as the insulating ceramic material. As such, the insulating ceramic material may keep the first portion <NUM> of the mold <NUM> at a lower temperature than the exposed second portion <NUM> when the molten metal material is poured into the mold <NUM>. Additionally, the insulating ceramic material may provide a path to conduct heat throughout the powder so as to minimize any thermal gradient across the first portion <NUM> of the mold <NUM>. Other insulating ceramic oxides that may be suitable for use as the ceramic material of the powder include, but are not limited to, zirconia, hafnia, titania, silica, cobalt aluminate, zircon, silica, magnesia, a rare earth oxide (e.g., yttria), or mixtures thereof.

The ceramic material of the powder generally comprises a plurality of ceramic particles (i.e., a powder of ceramic particles). In certain embodiments, the powder has relatively small sized particles (e.g., an average particle size of about <NUM> or less, preferably about <NUM> or less) such that maximum contact can be made with the exterior surfaces of the mold <NUM>. In particular embodiments, the particles may have an average particle size of about <NUM> to about <NUM>.

In contrast to the first portion <NUM>, the second portion <NUM> of the mold <NUM> is exposed to the atmosphere surrounding the mold <NUM>. That is, the second portion <NUM> is not in contact with the ceramic powder. As such, the second portion <NUM> of the mold <NUM> may be heated and cooled more quickly compared to the first portion <NUM> of the mold <NUM>.

Without wishing to be bound by any particular theory, it is believed that the grain size of the cast component <NUM> may be tailored and controlled through adjusting location of the ceramic powder <NUM>. Additionally, it is believed that the grain size of the cast component <NUM> may be further tailored and controlled through adjusting the initial mold temperature, the material temperature of the molten metal material, and/or the elevated mold temperature reached after pouring the metal material therein. In one particular embodiment, the mold <NUM> may be heated to an initial first mold temperature for the first portion <NUM> and an initial second mold temperature for the second portion <NUM>. After heating to the initial first mold temperature and second mold temperature, the heat source may be disengaged, and the molten metal material may be poured into the mold <NUM> while at the initial first mold temperature and initial second mold temperature.

In one embodiment, the initial first mold temperature is half or less of the solidus temperature of the metal material to be poured therein. As used herein, the term "solidus temperature" refers to the generally agreed upon temperature at which the material is completely solid on cooling under equilibrium conditions. In one embodiment, the initial first mold temperature may be <NUM>% of the solidus temperature of the metal material or less (e.g., room temperature of about <NUM>° C to <NUM>% of the solidus temperature of the metal material). For example, the initial first mold temperature may be <NUM>% of the solidus temperature to <NUM>% of the solidus temperature of the metal material (e.g., <NUM>% to less than <NUM>% of the solidus temperature of the metal material), such as <NUM>% to <NUM>% of the solidus temperature of the metal material. When the initial first mold temperature is half or less of the solidus temperature of the metal material, it is believed that the molten metal material quickly cools from its liquid phase upon being poured into the mold <NUM>. As such, it is believed that the molten metal material may begin to crystalize while it fills the mold such that the molten metal material begins to form its grain structure upon pouring. Without wishing to be bound by any particular theory, it is believed that these grains may serve as seed sites for grain formation at the desired size. Such an embodiment may be particularly useful for components having large cavities to fill with the molten metal material.

While the molten metal is being poured into the cooler mold, it is believed, without wishing to be bound by any particular theory, that thermal energy transfers from the metal material to the mold. In the first portion, the thermal energy transfers to the powder of ceramic material. That is, the metal material cools while the first portion of the mold heats, which in turn causes the ceramic material surrounding the mold to heat. It is believed that the powder of ceramic material has sufficient thermal mass to absorb the heat from the metal material (through the mold), serving as a thermal sink, while providing insulation to the mold to control the cooling rate. On the other hand, the thermal energy transfers to the surrounding atmosphere within the second portion of the mold.

Generally, this controlled solidification process is allowed to occur until the metal material completely solidifies within the mold. As discussed below, the mold may then be quickly cooled, upon complete solidification of the metal material, to inhibit grain growth within the first section of the cast metal component corresponding to the first portion of the mold. During the controlled solidification process, the molten metal material heats the first portion of the mold from its initial first mold temperature (i.e., the temperature of the first portion of the mold when the molten metal material is poured therein) to an elevated first mold temperature upon which the molten metal material is completely solidified within the mold. The elevated first mold temperature may depend on a variety of factors, such as the initial first mold temperature, the volume and/or temperature of the molten metal material at pouring, the amount and/or type of ceramic material present, the size and/or thickness of the mold, etc. For example, in certain embodiments, the elevated first mold temperature may be greater than <NUM>% of the solidus temperature of the metal material (e.g., greater than <NUM>% to <NUM>% of the solidus temperature). For instance, the elevated first mold temperature may be <NUM>% to <NUM>% of the solidus temperature of the metal material (e.g., <NUM>% to <NUM>% of the solidus temperature).

In certain embodiments, the amount of ceramic powder <NUM> that is present in the cavities surrounding the first portion <NUM> is greater, in terms of thermal mass, than the amount of metal material poured into the first portion <NUM>. For example, thermal mass ratio may be defined by the volume of ceramic material to the volume of metal material within the first portion <NUM> of the mold <NUM>. In this definition, the thermal mass ratio may be greater than <NUM>, indicating that there is more thermal mass of the powder than the poured metal material within the first portion <NUM>. In particular embodiments, the thermal mass ratio may be about <NUM> or greater (e.g., about <NUM> or greater, such as about <NUM> or greater).

Conversely, during the controlled solidification process, the molten metal material heats the second portion of the mold from its initial second mold temperature (i.e., the temperature of the second portion of the mold when the molten metal material is poured therein) to an elevated second mold temperature upon which the molten metal material is completely solidified within the mold. The elevated second mold temperature may depend on a variety of factors, such as the initial second mold temperature, the volume and/or temperature of the molten metal material at pouring, the amount and/or type of ceramic material present, the size and/or thickness of the mold, etc. For example, in certain embodiments, the elevated second mold temperature may be greater than <NUM>% of the solidus temperature of the metal material (e.g., greater than <NUM>% to <NUM>% of the solidus temperature). For instance, the elevated second mold temperature may be <NUM>% to <NUM>% of the solidus temperature of the metal material (e.g., <NUM>% to <NUM>% of the solidus temperature).

In particular embodiments, the mold <NUM> has a wall <NUM> surrounding a cavity <NUM> into which the molten metal material flows. The mold wall <NUM> may have a uniform or non-uniform thickness. For example, the mold wall <NUM> may have a thickness that ranges from <NUM> to <NUM> (e.g., <NUM> to <NUM>).

The mold <NUM> may be made out of a ceramic material, which is independently selected from the ceramic material of the powder. For example, the mold <NUM> may be formed from alumina, zirconia, hafnia, titania, silica, cobalt aluminate, zircon, silica, magnesia, a rare earth oxide, or a mixture thereof.

In certain embodiments, the molten metal material is poured into the mold near its liquidus temperature. As used herein, the term "liquidus temperature" refers to the lowest temperature at which the metal material (e.g., an alloy) is completely liquid. For example, the molten metal material is poured at a pour temperature that may be about <NUM>% of the liquidus temperature to <NUM>% of the liquidus temperature of the metal material, such as about <NUM>% of the liquidus temperature to <NUM>%. When the pour temperature is at or above the liquidus temperature (e.g., <NUM>% to about <NUM>%) of the metal material, it is believed that the molten metal material may stay completely in the liquid phase while the mold is being filled such that the molten metal material completely fills the mold in a substantially uniform manner. Such an embodiment may be particularly useful for components having small structures through which the molten metal material fills. Alternatively, when the pour temperature is below the liquidus temperature (e.g., about <NUM>% to less than <NUM>%, such as about <NUM>% to less than <NUM>% or about <NUM>% to less than <NUM>%) of the metal material, it is believed that the molten metal material may begin to crystalize while it fills the mold such that the molten metal material begins to form its grain structure upon pouring. That is, crystals may form within the molten metal material, when the pour temperature is lower than the liquidus temperature, such that smaller grains already started forming prior to the rest of the material crystalizing. Without wishing to be bound by any particular theory, it is believed that these grains may serve as seed sites for grain formation at the desired size. Such an embodiment may be particularly useful for components having large cavities to fill with the molten metal material.

In one embodiment, the metal material may include, but is not limited to, pure metals, nickel alloys, chrome alloys, iron alloys, titanium, titanium alloys, magnesium, magnesium alloys, aluminum, aluminum alloys, nickel-based superalloys, cobalt-based superalloys, iron-based superalloys or mixtures thereof.

Referring again to <FIG>, a supply line <NUM> is fluidly connected to the cavity <NUM> of the mold <NUM> to supply molten metal material to the cavity <NUM>. As shown, the supply line <NUM> may be formed as part of the mold <NUM> and may be connected to the cavity <NUM> at multiple inlets <NUM>. As such, the molten metal material may be simultaneously supplied into the cavity <NUM> at various multiple locations.

The mold <NUM> forms a cast component <NUM>, such as shown in <FIG> upon cooling. Generally, the first portion <NUM> of the mold <NUM> generally corresponds to a first section <NUM> (e.g., an internal section as shown) of the cast component <NUM>, and the second portion <NUM> of the mold <NUM> generally corresponds to a second section <NUM> (e.g., an outer section as shown) of the cast component <NUM>.

Without wishing to be bound by any particular theory, it is believed that the methods described herein may help achieve significantly fine grain structure within the first section of the cast component, corresponding to the first portion of the mold, by decreasing the thermal gradient within the metal material during final solidification. Without wishing to be bound by any particular theory, it is believed that the ceramic bed provides a medium into which the thermal gradient is formed surrounding the first portion, outside of the mold, to allow for more unified cooling within the first portion of the mold. That is, a thermal gradient can be formed within the powder of ceramic material around the first portion after pouring the molten metal material into the mold, such that the thermal gradient essentially shifts from the metal material within the first portion of the mold and into the ceramic powder outside of the mold. As such, the resultant grain structure within the first section of the cast component has a substantially uniform grain structure across thin and thick sections with little to no columnar grain growth.

Conversely, the second portion may include grain sizes that are larger in size than the grain sizes in the first portion. In one particular embodiment, the grain size within the second portion may have an aspect ratio (i.e., the longest measurement of the grain divided by the smallest measurement of the grain) that is relatively large compared to that of the grains in the first portion. That is, the grains within the second portion may be columnar in nature. In particular embodiments, the grains within the second portion may have an aspect ratio of <NUM> or greater (e.g., of <NUM> or greater, such as <NUM> to <NUM>). The first portion may include, in one embodiment, a single crystal grown from a starter seed crystal within the cavity <NUM> within the first portion.

In one embodiment, at least one edge of the second portion may be cooled during the solidification. Without wishing to be bound by any particular theory, it is believed that a temperature gradient may be formed within the second portion of the mold to create columnar grains extending in the direction toward the cooling source (e.g., a chiller). Referring to <FIG>, for example, a chiller <NUM> may be positioned on the outer edge <NUM> of the second portion <NUM> so as to orient the columnar grains radially in this particular embodiment of the cast component <NUM>.

In particular embodiments, the chiller <NUM> may reduce the temperature of the edge <NUM> to a temperature that is less than the initial second mold temperature of the second portion <NUM> of the mold <NUM>. For example, the chiller <NUM> may be a liquid-cooled plate (e.g., a water-cooled copper plate). The temperature of the chiller <NUM> may be controlled for the component being created by the casting process. However, in most embodiments, the chiller <NUM> has a chiller temperature that is less than the temperature of the powder <NUM>, less than the initial first mold temperature of the first portion <NUM> of the mold <NUM>, and/or less than the initial second mold temperature of the second portion <NUM> of the mold <NUM>. In particular embodiments, the chiller <NUM> has a chiller temperature that is at least <NUM>% lower than the initial second mold temperature of the second portion <NUM> of the mold <NUM>, such as at least <NUM>% lower than the initial second mold temperature of the second portion <NUM> of the mold <NUM>.

The chiller <NUM> may be engaged before pouring of the molten metal material, during pouring of the molten metal material, and/or after pouring of the molten metal material. In particular embodiments, the chiller <NUM> is engaged as the pouring of the molten metal material begins (i.e., substantially simultaneously with the introduction of the molten metal material to the mold <NUM>) and remains engaged during solidification of the molten metal material within the mold <NUM>.

For example, the cast component <NUM> may have a grain structure within the first portion <NUM> that has an average grain size of about <NUM> micrometers (µm) or less, such as about <NUM> to about <NUM> (e.g., about <NUM> to about <NUM>, or about <NUM> to about <NUM>). Additionally, the grains within the first portion <NUM> may have an average grain size and shape with a relatively low aspect ratio, such as <NUM> or less (e.g., <NUM> to <NUM>). Alternatively, the cast component <NUM> may have a grain structure within the second portion <NUM> that has a larger average grain size than the average grain size within the first portion <NUM>. The grains within the second portion <NUM> may also have an aspect ratio of <NUM> or greater, as discussed above, such that the grains within the second portion have a more columnar shape than the grains within the first portion <NUM>.

In additional embodiments, a third portion <NUM> (i.e., an intermediate portion or a transition portion) of the mold <NUM> may form a transition section <NUM> within the cast component having more grains that are larger than the grains of the first section <NUM> formed within the first portion <NUM>, but less columnar than the grains within the second section <NUM> formed within the second portion <NUM>. That is, the grains of the first section <NUM> have an average aspect ratio that is less than the average aspect ratio of the grains of the second section <NUM>.

Referring to <FIG>, the casting system <NUM> is shown within an exemplary vacuum melter <NUM> as described above. The crystal structure and grain size may also be impacted by various combinations of gating, shelling, other mold insulation (e.g. Kaowool, Fiberfrax, graphite baffles), vibration, chills, heater designs, or cooling gases (e.g. Air, Argon, Helium, Nitrogen) during the casting cycle to affect the resultant crystal structure as well.

Such control of the grain structure of the cast component allows the designer to tailor the properties of the component depending on the location (portion) of the component. For example, a finer grain structure within the first section may allow for improved strength and cyclic capability. Conversely, a more columnar grain structure within the second section may allow for improved time dependent mechanical properties (e.g., creep deformation). This type of control is particularly suitable for rotary components used, for example, in turbine engines.

While the presently disclosed methods are suitable for a variety of applications, the methods are particularly suitable for forming cast components found in high temperature environments, such as those present in gas turbine engines, for example, combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes. As stated above, the methods described herein are particularly useful for forming cast components for rotary machines, such as turbine engines. For example, a bladed disk may be formed with the first section corresponding to an internal disk area and the second section corresponding to the airfoils extending radially outwardly from the disk.

While the presently disclosed methods are suitable for a variety of applications, the methods are particularly suitable for forming cast components found in high temperature environments, such as those present in gas turbine engines, for example, combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes. <FIG> is a schematic cross-sectional view of a gas turbine engine in accordance with an exemplary embodiment of the present disclosure. More particularly, for the embodiment of <FIG>, the gas turbine engine is a high-bypass turbofan jet engine <NUM>, referred to herein as "turbofan engine <NUM>. " As shown in <FIG>, the turbofan engine <NUM> defines an axial direction A (extending parallel to a longitudinal centerline <NUM> provided for reference) and a radial direction R. In general, the turbofan <NUM> includes a fan section <NUM> and a core turbine engine <NUM> disposed downstream from the fan section <NUM>. Although described below with reference to a turbofan engine <NUM>, the present disclosure is applicable to turbomachinery in general, including turbojet, turboprop and turboshaft gas turbine engines, including industrial and marine gas turbine engines and auxiliary power units.

The exemplary core turbine engine <NUM> depicted generally includes a substantially tubular outer casing <NUM> that defines an annular inlet <NUM>. The outer casing <NUM> encases, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor <NUM> and a high pressure (HP) compressor <NUM>; a combustion section <NUM>; a turbine section including a high pressure (HP) turbine <NUM> and a low pressure (LP) turbine <NUM>; and a jet exhaust nozzle section <NUM>. A high pressure (HP) shaft or spool <NUM> drivingly connects the HP turbine <NUM> to the HP compressor <NUM>. A low pressure (LP) shaft or spool <NUM> drivingly connects the LP turbine <NUM> to the LP compressor <NUM>.

For the embodiment depicted, the fan section <NUM> includes a variable pitch fan <NUM> having a plurality of fan blades <NUM> coupled to a disk <NUM> in a spaced apart manner. As depicted, the fan blades <NUM> extend outwardly from disk <NUM> generally along the radial direction R. Each fan blade <NUM> is rotatable relative to the disk <NUM> about a pitch axis P by virtue of the fan blades <NUM> being operatively coupled to a suitable actuation member <NUM> configured to collectively vary the pitch of the fan blades <NUM> in unison. The fan blades <NUM>, disk <NUM>, and actuation member <NUM> are together rotatable about the longitudinal axis <NUM> by LP shaft <NUM> across an optional power gear box <NUM>. The power gear box <NUM> includes a plurality of gears for stepping down the rotational speed of the LP shaft <NUM> to a more efficient rotational fan speed.

Referring still to the exemplary embodiment of <FIG>, the disk <NUM> is covered by rotatable front nacelle <NUM> aerodynamically contoured to promote an airflow through the plurality of fan blades <NUM>. Additionally, the exemplary fan section <NUM> includes an annular fan casing or outer nacelle <NUM> that circumferentially surrounds the fan <NUM> and/or at least a portion of the core turbine engine <NUM>. It should be appreciated that the nacelle <NUM> may be configured to be supported relative to the core turbine engine <NUM> by a plurality of circumferentially-spaced outlet guide vanes <NUM>. Moreover, a downstream section <NUM> of the nacelle <NUM> may extend over an outer portion of the core turbine engine <NUM> so as to define a bypass airflow passage <NUM> therebetween.

During operation of the turbofan engine <NUM>, a volume of air <NUM> enters the turbofan <NUM> through an associated inlet <NUM> of the nacelle <NUM> and/or fan section <NUM>. As the volume of air <NUM> passes across the fan blades <NUM>, a first portion of the air <NUM> as indicated by arrows <NUM> is directed or routed into the bypass airflow passage <NUM> and a second portion of the air <NUM> as indicated by arrow <NUM> is directed or routed into the LP compressor <NUM>. The ratio between the first portion of air <NUM> and the second portion of air <NUM> is commonly known as a bypass ratio. The pressure of the second portion of air <NUM> is then increased as it is routed through the high pressure (HP) compressor <NUM> and into the combustion section <NUM>, where it is mixed with fuel and burned to provide combustion gases <NUM>.

The combustion gases <NUM> are routed through the HP turbine <NUM> where a portion of thermal and/or kinetic energy from the combustion gases <NUM> is extracted via sequential stages of HP turbine stator vanes <NUM> that are coupled to the outer casing <NUM> and HP turbine rotor blades <NUM> that are coupled to the HP shaft or spool <NUM>, thus causing the HP shaft or spool <NUM> to rotate, thereby supporting operation of the HP compressor <NUM>. The combustion gases <NUM> are then routed through the LP turbine <NUM> where a second portion of thermal and kinetic energy is extracted from the combustion gases <NUM> via sequential stages of LP turbine stator vanes <NUM> that are coupled to the outer casing <NUM> and LP turbine rotor blades <NUM> that are coupled to the LP shaft or spool <NUM>, thus causing the LP shaft or spool <NUM> to rotate, thereby supporting operation of the LP compressor <NUM> and/or rotation of the fan <NUM>.

The combustion gases <NUM> are subsequently routed through the jet exhaust nozzle section <NUM> of the core turbine engine <NUM> to provide propulsive thrust. Simultaneously, the pressure of the first portion of air <NUM> is substantially increased as the first portion of air <NUM> is routed through the bypass airflow passage <NUM> before it is exhausted from a fan nozzle exhaust section <NUM> of the turbofan <NUM>, also providing propulsive thrust. The HP turbine <NUM>, the LP turbine <NUM>, and the jet exhaust nozzle section <NUM> at least partially define a hot gas path <NUM> for routing the combustion gases <NUM> through the core turbine engine <NUM>.

A ceramic mold was completely buried into a powder of ceramic material. The ceramic mold was made of alumina, and the powder of ceramic material was composed of alumina. The powder of ceramic material was surrounded within a container, which was heated in a furnace at <NUM> °F (<NUM>) for <NUM> minutes in a vacuum.

Temperature sensors were placed at varying distances from the mold within the powder, and the temperature was tracked during the heating process and casting process. <FIG> shows the temperatures at various locations during the heating and casting process.

<FIG> shows an extrapolation of the temperature gradient within the ceramic powder at the initial temperature (i.e., at the time when the metal is poured into the mold).

Claim 1:
A method of creating a cast alloy component (<NUM>) from a metal material having a solidus temperature and a liquidus temperature, comprising:
burying at least a first portion (<NUM>) of a mold (<NUM>,<NUM>) in a powder (<NUM>) of ceramic material (<NUM>);
heating the mold (<NUM>) within the powder (<NUM>) of ceramic material (<NUM>) to an initial mold temperature that is <NUM>% or less of the solidus temperature of the metal material;
thereafter, pouring molten metal material into the mold (<NUM>,<NUM>) while the first portion (<NUM>) is buried in the powder (<NUM>) of ceramic material (<NUM>); and
thereafter, allowing the molten metal material to form the cast alloy component (<NUM>) within the mold (<NUM>,<NUM>) while the first portion (<NUM>) is buried within the powder (<NUM>) of ceramic material (<NUM>),
wherein the metal material is an alloy or a superalloy, wherein the mold (<NUM>,<NUM>) is constructed from a ceramic material, and wherein the ceramic material of the mold (<NUM>,<NUM>) has a different composition than the ceramic material (<NUM>) of the powder (<NUM>).