Method for Manufacturing an Article from a Consolidated Metallic Powder Composition

The present application relates generally to the field of metallurgy and, more specifically, to methods for manufacturing articles from metallic powder compositions.

Traditionally, wrought metallic products, including, but not limited to, plates, bars, billets, and sheets, are manufactured through a process that involves the melting or in some cases, double or triple melting, of cast ingots. The resulting precursor materials are then processed into their final form via a sequence of lengthy, energy-intensive thermo-mechanical conversion processes. These processes may include operations such as rolling and forming. This conventional method of processing large cast ingots requires a significant amount of time, energy, and skilled labor to produce material of a quality that is acceptable for use in demanding industries, such as the aerospace industry.

Powder metallurgy techniques have been introduced as alternatives that can circumvent some of these intensive processing steps, thereby making the production of high-performance metallic materials more affordable. These techniques typically involve the consolidation of loose metal powder into stock shapes, such as bars and plates, or near-net-shape parts or preforms using methods like cold isostatic pressing and sintering or hot isostatic pressing.

However, even with the advantages offered by powder metallurgy, these techniques have their own set of challenges. One significant drawback is the relatively high cost associated with achieving a nearly fully dense and durable product. This cost factor is driven by the need to eliminate porosity, which can compromise the mechanical properties of the final product. Another significant drawback is the presence of powder particle boundaries (PPBs) in consolidated powder metallurgy products, which can have a number of detrimental effects. Mitigation of PPBs typically requires additional treatments to the produced articles.

Therefore, while powder metallurgy offers several advantages over traditional ingot-based methods, it also necessitates the development of more efficient and cost-effective methods for producing high-quality wrought metallic products from metallic powder compositions.

Accordingly, those skilled in the art continue with research and development in the field of metallurgy.

Disclosed are methods for manufacturing articles from metallic powder compositions.

In one example, the disclosed method for manufacturing an article includes consolidating a metallic powder composition into a consolidated preform, applying a supersolidus heat treatment to the consolidated preform during or after consolidating the metallic powder composition to yield a heat treated preform, and reducing a cross-sectional area of the heat treated preform by thermo-mechanical processing to yield a processed preform.

In another example, the disclosed method for manufacturing an article includes consolidating a metallic powder composition into a consolidated preform, applying a supersolidus heat treatment to the consolidated preform during or after consolidating the metallic powder composition to yield a heat treated preform, and reducing a cross-sectional area of the heat treated preform by at least one of a cogging process and a rotary incremental forming process to yield a processed preform.

Also disclosed are wrought metallic articles manufactured according to the disclosed methods.

Other examples of the disclosed methods and wrought metallic articles manufactured according to the disclosed methods will become apparent from the following detailed description, the accompanying drawings and the appended claims.

The method of the present description is a process for manufacturing metallic articles from metallic powder compositions. Referring to, the method () includes, at block (), consolidating a metallic powder composition into a consolidated preform, at block (), applying a supersolidus heat treatment to the consolidated preform during or after consolidating the metallic powder composition to yield a heat treated preform, and, at block (), reducing a cross-sectional area of the heat treated preform by thermo-mechanical processing to yield a processed preform.

The metallic powder composition serves as the foundational material in the manufacturing process, and its formulation determines the final article's mechanical, thermal, and chemical properties. The formulation of the metallic powder composition can be selected to meet particular requirements such as strength, durability, corrosion resistance, tolerance to high temperatures, and manufacturability.

The metallic powder composition can, for example, include an alloy, an intermetallic, a metal-matrix composite, or combinations thereof. An alloy is a combination of two or more metals or a metal and a nonmetal, which may have distinct properties from its constituent elements. An intermetallic is a compound of two or more metals that has a stoichiometry and crystal structure different from those of the pure metals. A metal-matrix composite includes a material having a metal matrix embedded with reinforcing materials, such as another metal, a ceramic, or an intermetallic, which can improve the properties of the metal matrix. The metallic powder composition can include of any of these materials or combinations thereof, depending on the desired characteristics and applications of the final article. For example, the metallic powder can comprise of an alloy and an intermetallic, an intermetallic and a metal-matrix composite, an alloy and a metal-matrix composite, or a mixture of all three.

The metallic powder composition may have a uniform composition, or the metallic powder composition may have a blended composition in which the metallic powder composition comprises, for example, a blend of a first metallic powder component having a first composition with a second metallic powder component having a second composition to yield the metallic powder composition. For a uniform composition, the metallic powder can have a substantially consistent and homogeneous chemical composition throughout. For a blended composition, the metallic powder composition can be formed by mixing two or more different metallic powders, each having a distinct chemical composition, to create a new blended metallic powder composition upon consolidation. The blended composition can also be used to introduce additional elements or phases into the metallic powder, such as alloying elements, intermetallics, ceramics, or metal-matrix composites, to modify the formulation of the final article.

Specific examples of the metallic powder composition include an aluminum alloy, a metal-matrix composite comprising aluminum, a titanium alloy, a metal-matrix composite comprising titanium, a superalloy, an iron alloy, a metal-matrix composite comprising iron, a nickel alloy, a metal-matrix composite comprising nickel, a cobalt alloy, a metal-matrix composite comprising cobalt, a refractory metal alloy, a metal-matrix composite comprising a refractory metal, a copper alloy, a metal-matrix composite comprising copper, a precious-metal alloy, a metal-matrix composite comprising a precious metal, a zirconium alloy, a metal-matrix composite comprising zirconium, a hafnium alloy, a metal-matrix composite comprising hafnium, a rare-earth-metal alloy, a metal-matrix composite comprising a rare-earth metal, a magnesium alloy, a metal-matrix composite comprising magnesium, a steel, a metal-matrix composite comprising steel, an intermetallic, a complex concentrated alloy, a metal-matrix composite comprising a complex concentrated alloy, a high-entropy alloy, a metal-matrix composite comprising a high-entropy alloy, a medium-entropy alloy, a metal-matrix composite comprising a medium-entropy alloy, a multicomponent alloy, a metal-matrix composite comprising a multicomponent alloy, or combinations thereof. Each example of the metallic powder composition, whether an alloy, a metal-matrix composite, or an intermetallic, brings distinct properties that may be significant for the intended use of the final article. For instance, aluminum alloys and metal-matrix composites containing aluminum may be chosen for their lightweight and high corrosion resistance, whereas titanium alloys and their composites can offer high strength-to-weight ratios. The formulation of these various metallic powders allows for the production of components that meet the demands of various specific environments and applications.

In a specific example, the metallic powder composition may include a nickel alloy. A nickel alloy, specifically for the manufacturing of nickel-based superalloys, may be selected due to their properties which make them desirable for demanding applications. Nickel superalloys may be used for their resistance to thermal creep deformation, excellent mechanical strength, and stability across a wide range of temperatures, making them suitable for use in high-temperature, high-stress environments. The methods of the present description are particularly relevant for addressing challenges that occur during processing of powder metallurgy nickel-based superalloys into wrought products. Products created from powder metallurgy, specifically those based on nickel alloys, need to exhibit a certain level of ductility. Ductility refers to the ability of the material to deform under tensile stress, which is important for the subsequent processing of the consolidated preforms into final shapes or forms. Historically, it has been challenging to process nickel-based products, initially produced via standard consolidation techniques, into additional forms or shapes. These challenges arise from the inherent material properties of such nickel alloys, including high melting points and tendencies to retain prior particle boundaries throughout subsequent processes. These properties can complicate further shaping or machining of the consolidated preforms. The methods of the present description address such challenges though applying a supersolidus heat treatment to the consolidated nickel-based alloys during or after consolidating the metallic powder composition, and reducing a cross-sectional area of the heat treated preform by thermo-mechanical processing as further explained below.

The form of the metallic powder composition is not limited and may include, for example, granular particles, spherical particles, spheroidal particles, fines, chips, flakes, and combinations thereof. The form of the metallic powder composition may depend on various factors, such as the method of production, the desired properties, and the intended application of the final product. For example, granular particles have irregular shapes and sizes, which may affect the packing density and flowability of the powder. Spherical or spheroidal particles have more uniform shapes and sizes, which may improve the packing density and flowability of the powder. Fines are very small particles that may have high surface area and reactivity, which may influence the sintering and consolidation behavior of the powder. Chips and flakes are thin and elongated particles that may have high aspect ratios and low density, which may affect the orientation and alignment of the powder during consolidation. Combinations of different forms of metallic powder may also be used to achieve a desired mixture of characteristics, such as density, strength, ductility, and conductivity. The form of the metallic powder composition may be controlled or modified by various techniques, such as atomization, milling, crushing, sieving, screening, blending, coating, or doping.

The metallic powder composition can be produced by any suitable method. Some examples of methods for producing metallic powder are atomization, mechanical milling, electrolysis, chemical reduction, thermal decomposition, or gas-phase synthesis. Each of these methods has advantages and disadvantages in terms of the cost, efficiency, quality, and properties of the resulting metallic powder. The choice of the method for producing metallic powder may depend on various factors, such as the type and composition of the metallic powder, the desired particle size and shape, the intended application and performance of the final product, and the availability and accessibility of equipment and materials. One of the common methods for producing metallic powder is atomization, which involves melting a metal or alloy and then spraying it into a stream of gas or liquid to break it into fine droplets that solidify into powder particles. Atomization can be performed using different techniques, such as gas atomization, water atomization, centrifugal atomization, or plasma atomization, depending on the type of metal, the desired particle size and shape, and the cost and efficiency of the process. Atomization can produce metallic powders with various characteristics, such as high purity, low oxygen content, uniform particle size distribution, and spherical or spheroidal morphology. Atomization can also be used to produce pre-alloyed powders, which are powders that contain more than one metallic element in a homogeneous phase, or composite powders, which are powders that contain more than one phase, such as metal matrix composites or metal-ceramic composites.

The consolidation of the metallic powder can include, but is not limited to pressing the metallic powder composition, isostatic pressing the metallic powder composition, hot pressing the metallic powder composition, hot isostatic pressing the metallic powder composition, vacuum hot pressing the metallic powder composition, cold pressing the metallic powder composition, cold isostatic pressing the metallic powder composition, sintering the metallic powder composition, cold isostatic pressing and sintering the metallic powder composition, sintering the metallic powder composition, spark plasma sintering the metallic powder composition, high strain rate densification, and combinations thereof.

Pressing involves compressing the metallic powder, such as in a die or a mold under a mechanical force, which reduces the porosity and increases the density of the powder. Pressing can be done at room temperature (cold pressing) or at elevated temperature (hot pressing). Cold pressing can produce products with high dimensional accuracy and low residual stress, but may require higher pressure and result in lower density and strength than hot pressing. Hot pressing can produce products with higher density and strength, but can resulting oxidation or other changes in the powder. Pressing can also be combined with sintering, which is a heat treatment that enhances the bonding between the powder particles.

Isostatic pressing involves compressing the metallic powder in a flexible container under a uniform pressure from a fluid or a gas, which can be applied at room temperature (cold isostatic pressing) or at elevated temperature (hot isostatic pressing). Isostatic pressing can produce products with high density and isotropic properties, as well as complex shapes and large sizes.

Vacuum hot pressing is a method of producing metallic products from powder. It involves applying high pressure and temperature to the powder in a vacuum environment, which can prevent it from oxidizing or getting otherwise contaminated. This method can result in products that have high density, homogeneity, and properties such as hardness, creep resistance, and dimensional stability. It can also be used to consolidate powders that are difficult to process, such as refractory or intermetallic materials, or to create products that have different compositions or functions in different layers, such as metal matrix composites or functionally graded materials.

Sintering involves heating the metallic powder near its melting point, which causes diffusion and bonding between the powder particles. Sintering can be performed in a furnace, a vacuum, or an inert atmosphere, depending on the type and composition of the metallic powder. Sintering can produce products with high density and strength, as well as improved mechanical, electrical, and thermal properties. However, sintering may also cause grain growth, shrinkage, and distortion of the powder, as well as oxidation or contamination from the surrounding environment.

Cold Isostatic Pressing followed by Sintering (CIP+Sinter) involves compressing the metallic powder in mold at high pressure and low temperature, which results in a green compact with uniform density and shape. The green compact is then sintered in a furnace to achieve full densification and bonding between the powder particles. CIP+Sinter can produce products with complex geometries and fine details, as well as good dimensional accuracy and surface finish. CIP+Sinter can also improve the mechanical, electrical, and thermal properties of the products, as well as reduce the porosity and defects in the powder.

Spark plasma sintering involves applying a pulsed electric current through the metallic powder, which generates heat and pressure simultaneously. Spark plasma sintering can produce products with high density and fine microstructure, as well as enhanced properties such as hardness, wear resistance, and corrosion resistance. Spark plasma sintering can also reduce the processing time and temperature, as well as prevent oxidation and contamination of the powder.

High strain rate densification involves subjecting the metallic powder to a high strain rate deformation, such as explosive compaction, shock loading, or dynamic forging. High strain rate densification can produce products with high density and refined microstructure, as well as improved properties such as ductility, toughness, and fatigue resistance. High strain rate densification can also enable the consolidation of hard-to-deform or reactive powders, as well as the synthesis of novel materials such as nanocrystalline or amorphous metals.

One of the challenges of powder metallurgy is to obtain a homogeneous and defect-free microstructure of the consolidated metallic powder composition. However, during the consolidation process, inhomogeneities may occur at the interfaces between the individual particles of the metallic powder, resulting in prior particle boundaries, or PPBs. PPBs can be formed from various sources, such as oxides, carbides, nitrides, or other impurities that are present on the surface of the powder particles, or from the incomplete diffusion of atoms across the interfaces. PPBs can have negative effects on the properties and subsequent processability of the consolidated metallic powder composition, such as reducing the strength, ductility, and fracture toughness, increasing the susceptibility to corrosion and fatigue cracking, or limiting the grain growth and recrystallization during heat treatment.

Supersolidus heat treatment is a process where the preform is heated above the solidus temperature of the metallic powder composition, but below the liquidus temperature (i.e., to a supersolidus temperature). This allows for partial melting of the preform during or after consolidation. Supersolidus heat treatment can eliminate the prior particle boundaries or a portion thereof and improve the homogeneity of the consolidated metallic powder composition. The elimination of PPB by supersolidus heat treatment involves the formation and migration of liquid phases at the prior particle boundaries formed at interfaces between the pre-existing powder particles before consolidation. The liquid phases can dissolve and transport the impurities or segregations that cause the PPBs. Supersolidus heat treatment can improve the homogeneity of the consolidated metallic powder composition by reducing the chemical and structural gradients across the particle boundaries, and enhancing the coherency and continuity of the microstructure.

The supersolidus heat treatment can be applied during or after consolidating the metallic powder composition. For example, the supersolidus heat treatment can be applied during a consolidation processes such as hot pressing or sintering, or the supersolidus heat treatment can be applied after any of the consolidation processes.

Kirkendall voids are pores that can form in the diffusion zone of a solid-state bond between two metals with different diffusion rates. They are caused by the faster diffusion of one metal species relative to another, creating vacancies that coalesce into voids. Kirkendall voids can weaken the bond strength and reduce the fatigue resistance of the resulting article.

One of the features of the present method is that it does not require a fully dense preform before the thermo-mechanical process. The relative density of the heat-treated preform, following the supersolidus heat treatment, can be lower than the maximum density of the respective material, such as 99.9 percent relative density or lower, 99.5 percent or lower, 99 percent or lower, 98 percent or lower, 97 percent or lower, 96 percent or lower, 95 percent or lower, 90 percent or lower, 85 percent or lower, or 80 percent or lower. The low relative density can be as a result of the consolidation process, kirkendall voids, or a combination thereof. The low relative density following the supersolidus heat treatment differentiates the present method from traditional methods which typically attempt to maximize the relative density at each step of the process. In contrast, the present method allows for a less-than-fully-dense preform, alleviating the need for energy- and time-intensive processes to reduce the relative density, and the method relies upon the thermo-mechanical processing to densify the preform.

After the supersolidus heat treatment, the preform is subjected to a thermo-mechanical processing (TMP) step, in which the cross-sectional area of the preform is reduced by applying mechanical forces at an elevated temperature. The TMP step can improve the microstructure and mechanical properties of the article, as well as reduce the porosity and increase the relative density. The TMP step can be performed by various methods, such as cogging, rotary incremental forming, or a combination thereof. These processes can achieve a substantial reduction of the cross-sectional area and result in a near-net-shape or net-shape article.

Cogging is a process where the supersolidus heat treated preform undergoes a series of compressive blows, which reduce its cross-sectional area and extend its length. This step is typically conducted through the use of forging presses or hammers and involves successive forging sequences. Such sequences can contribute to reducing the centerline porosity in the preform. The cogging operation applies global deformation, providing densification and shape to the preform. This process achieves significant objectives: on a macro-scale, it reduces the overall cross-sectional area of the preform. Simultaneously, the application of high pressures and deformation aids in breaking up and reducing the centerline porosity within the preform, as the spaces between particles are forced to close. This process results in densification of the material and refines the microstructure, enhancing the mechanical properties of the final product.

The method may also employ a rotary incremental forming process to refine the heat treated preform further. This process involves a tool that progressively and locally deforms the preform in a rotational manner, causing further reduction in its cross-sectional area. This process can be executed in several passes, each pass gradually changing the shape and size of the preform. Unlike cogging, which applies global deformation, rotary incremental forming induces localized plastic deformation at the contact point between the tool and the preform. This localized deformation effectively closes up surface pores, thereby reducing the surface porosity of the preform. The cumulative effect of the rotary incremental forming process is further densification of the surface of the preform and a refined surface microstructure. Both effects contribute to the improved properties of the final wrought metallic article. The process not only leads to further densification but also assists in achieving a better surface finish in the final metallic article.

The cogging process and the rotary incremental forming process can be conducted together in any order. The combination of these two processes together can provide a systematic reduction of porosity in the preform. While cogging primarily targets the centerline porosity, rotary incremental forming effectively reduces surface porosity. This dual approach ensures that the entire body of the preform, from the center to the surface, can be densified. This feature of the present method contributes to efficient manufacturing of a wrought metallic article with excellent mechanical properties, regardless of the order of the processes.

Cogging, as a metalworking process, is a versatile operation that can be performed in several ways, such as through open die forging, upsetting, pancaking, or billeting. These are all sub-processes that can be classified under the broader cogging process. Open die forging involves deforming the preform between two dies that do not completely enclose the material. The dies hammer or press the preform, reducing its cross-sectional area and lengthening it. This process allows for large reductions in cross-section and is particularly effective at reducing centerline porosity in the preform. Upsetting forging is a process where a preform is placed vertically, and force is applied to the top and bottom surfaces, decreasing its height. Pancaking is a similar process to upsetting but is used to describe a specific instance where the preform is deformed into a flatter shape. This can help to close centerline porosity and increase the density of the material. Billeting is another forging operation that aims to create a billet, a long, usually rectangular or cylindrical, piece of metal with a standardized cross-sectional size. This is achieved by deforming the preform through a series of hammer or press blows, reducing its cross-sectional area and lengthening it. Each of these processes can be used in the cogging step of the described method, depending on the specific requirements of the metallic article being manufactured. The key principle behind all these processes is the application of force to deform the preform, reducing its cross-sectional area and enhancing its densification. The choice between open die forging, upsetting, pancaking, and billeting would be made based on the desired final shape and size of the metallic article, as well as the specific properties of the metallic powder composition.

In the process of reducing the cross-sectional area of the heat treated preform via the cogging process, the approach may be staged or progressive, involving multiple forging passes each reducing the cross-sectional area by a different degree.

The cross-sectional area of the heat treated preform may be reduced via an initial forming pass of the cogging process that results in a modest reduction of the cross-sectional area. This initial pass can often be considered a ‘softening’ or ‘conditioning’ stage, where the preform is prepared for more significant deformation in subsequent stages. This initial pass does not significantly alter the dimensions of the preform, perhaps reducing the cross-sectional area by no more than 2 percent, 1.5 percent, or even as little as 1 percent. Despite this modest dimensional change, the initial forming pass plays a role in initiating the closure of centerline porosity in the preform, without damaging or fracturing the preform.

After the initial forming pass, further reduction of the decreased cross-sectional area of the preform is achieved via one or more subsequent forming passes of the cogging process. The subsequent pass reduces the cross-sectional area by a greater percentage than the initial forming pass. This could be a reduction of at least 2 percent, 3 percent, 5 percent, or in some cases even 10 percent or more. These subsequent forming passes continue to close up the centerline porosity and further densify the preform, while also beginning to shape the preform closer to the final desired shape of the metallic article.

In some instances, the method can include additional forming passes that progressively reduce the cross-sectional area. For example, a second subsequent forming pass can reduce the further-decreased cross-sectional area of the preform by at least 6 percent, or in another example, at least 10 percent. Each of these passes serves to further refine and shape the preform, enhancing densification and improving the microstructure and mechanical properties of the final product.

This staged, progressive approach to the cogging process allows for a controlled and efficient method of transforming the preform into the final metallic article, minimizing the risk of damage or fracture to the preform, and enhancing the properties and quality of the final product.

In an example, the step of reducing the cross-sectional area of the preform via at least one forming pass of a cogging process may include: reducing the cross-sectional area of the preform via an initial forming pass of a cogging process so that the preform has a decreased cross-sectional area; and reducing the decreased cross-sectional area of the preform via a subsequent forming pass of the cogging process by a greater percentage than that, by which the cross-sectional area of the preform was reduced during the initial forming pass. The amount/magnitude by which the initial forming pass of the cogging process reduces the cross-sectional area of the preform may be sufficient to close centerline porosity of the preform without damaging the preform.

In an example, the initial forming pass of the cogging process may reduce the cross-sectional area of the preform by at most 2 percent. In another example, the initial forming pass of the cogging process may reduce the cross-sectional area of the preform by at most 1.5 percent. In another example, the initial forming pass of the cogging process may reduce the cross-sectional area of the preform by at most 1 percent.

In an example, the subsequent forming pass of the cogging process may reduce the decreased cross-sectional area of the preform by at least 2 percent. In another example, the subsequent forming pass of the cogging process may reduce the decreased cross-sectional area of the preform by at least 3 percent. In another example, the subsequent forming pass of the cogging process may reduce the decreased cross-sectional area of the preform by at least 5 percent. In another example, the subsequent forming pass of the cogging process may reduce the decreased cross-sectional area of the preform by at least 10 percent.

In a specific example, the subsequent forming pass of the cogging process reduces the decreased cross-sectional area of the preform by at least 3 percent so that the preform has a further-decreased cross-sectional area, and a second subsequent forming pass of the cogging process reduces the further-decreased cross-sectional area of the preform by at least 6 percent.

In another specific example, the subsequent forming pass of the cogging process reduces the decreased cross-sectional area of the preform by at least 5 percent so that the preform has a further-decreased cross-sectional area, and a second subsequent forming pass of the cogging process reduces the further-decreased cross-sectional area of the preform by at least 10 percent.

The cogging process is performed at a temperature conducive to effective and efficient deformation. This temperature, known as the cogging-process temperature, is selected taking into account several factors, including the type of metallic powder used to form the preform, the extent of deformation desired, and the planned sequence of forming operations.

The cogging-process temperature is chosen relative to the solidus temperature of the metallic powder composition. This is done to ensure that the preform remains in a solid state during the cogging process, while still being sufficiently malleable for effective deformation. The elevated temperature also aids in the densification process and assists in the closure of porosity.

In general, the cogging-process temperature may typically be at most 95 percent of the solidus temperature (in degrees Kelvin) of the metallic powder composition. This ensures the preform remains solid and workable without melting. However, the cogging-process temperature could be set within a range lower than this maximum, based on the specific requirements of the cogging process and the final metallic article.