Use of blended elemental powder mixtures for alloying in cold spray processing

Abstract

Cold spray processing is an additive manufacturing method which has been used to deposited powder materials onto a substrate through means of a supersonic gas stream in order to manufacture articles in the shape of 3D components or coatings. In conventional cold spray processing the feedstock powder and final article is the same material as the feedstock. In this method the feedstock consists of a blend individual constituents which are sprayed and subsequently heat treated in order to homogenize the constituents such that the final article is in an alloyed form. This enables the spraying of materials which previously have not been sprayable due to their poor deposition properties by utilizing the base constituents in the feedstock which individually have superior deposition properties.

Description

GOVERNMENT INTEREST

[0001] The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to the manufacturing of alloys, more particularly, to cold spray additive manufacturing alloys.BACKGROUND

[0003] Cold spray processing deposits metallic powders at supersonic speeds onto a substrate. The deposition of the metallic powders at supersonic speeds causes the metallic powders to undergo plastic deformation and form an alloy. Cold spray processing relies on plastic deformation in order for particles to deposit successfully. In high strength and high hardness particles, plastic deformation is limited or requires significantly higher amounts of energy than conventional cold spray processing systems can provide. For these reasons, high strength and high hardness materials can be unsprayable or can have very poor deposition qualities.SUMMARY OF THE INVENTION

[0004] Various deficiencies in the prior art are addressed below by the disclosed method for cold spray processing alloys.

[0005] In various aspects, a method of cold spray processing may be provided. The method of cold spray processing may include providing a substrate. The method of cold spray processing may further include preparing a feedstock powder. The feedstock powder may include a homogeneous blend of a plurality of constituents. The plurality of constituents may be configured to yield a desired alloy when heated. The method of cold spray processing may further include cold spraying the feedstock powder onto a substrate. The spraying of the feedstock powder may cause the feedstock powder to form an article on the substrate. The method may further include heating the article to a temperature sufficient to induce alloying until the plurality of constituents have alloyed for an amount of time sufficient for homogenization. The method may further include cooling the article to a room temperature causing the article to form an alloy structure.

[0006] In some embodiments, the plurality of constituents may include a plurality of pure elemental powders. In some embodiments, the plurality of constituents may include a plurality of pre-alloyed powders. In some embodiments, the plurality of constituents may include a plurality of ceramic powders. In some embodiments, the plurality of constituents may include a plurality of intermetallic powders. In still other embodiments, the plurality of constituents may include a combination of at least one pure elemental, ceramic, pre-alloyed, or intermetallic powder.

[0007] In some embodiments, the article may form a coating on the substrate. In some embodiments, the method may include alloying the coating to the substrate.

[0008] In some embodiments, the method may further include removing the article from the substrate after the cold spraying and before heating the article.

[0009] In some embodiments of the method, heating the article may include a multi-step profile.

[0010] In some embodiments of the method, heating the article may include a specific atmosphere. In some embodiments, the specific atmosphere may be a vacuum. In some embodiments, the specific atmosphere may include an inert condition. In other embodiments, the atmosphere may include a reducing condition. In still other embodiments, the atmosphere may include an oxidizing condition. In some embodiments, the atmosphere may include a carburizing condition.

[0011] In some embodiments of the method, the alloy structure may be a ceramic. In some embodiments, the substrate may include a three-dimensional shell-like structure. In some embodiments the three-dimensional shell-like structure may be one of a nose cone or rotor-blade erosion cap.

[0012] In some embodiments, the coating may form a liner for a small or large caliber gun.

[0013] In some embodiments of the method, the plurality of constituents may include 90% by weight titanium, 6% by weight aluminum, and 4% by weight vanadium.

[0014] Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.

[0016] FIG. 1 depicts a flowchart of a disclosed method.

[0017] FIG. 2 depicts an exemplary use of the disclosed method.

[0018] It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration.DETAILED DESCRIPTION OF THE INVENTION

[0019] The following description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be only for illustrative purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Additionally, the term, “or,” as used herein, refers to a non-exclusive or, unless otherwise indicated (e.g., “or else” or “or in the alternative”). Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0020] The numerous innovative teachings of the present application will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. Those skilled in the art and informed by the teachings herein will realize that the invention is also applicable to various other technical areas or embodiments, such as seismology and data fusion.

[0021] Various embodiments are directed to methods for cold spray manufacturing processes for the formation of alloyed articles or substrate coatings as well as to modifications which improve the process of cold spray additive manufacturing.

[0022] Generally speaking, the various embodiments utilize a cold spray manufacturing process to form an alloy article or an alloyed coating on a substrate. The various embodiments utilize a feedstock powder which may include pre-alloyed powders, ceramic powders, intermetallic powders or pure elemental powders.

[0023] Cold spray additive manufacturing is a solid state (no melting) method by which powder materials are deposited onto a surface and built up in a layer-wise manner to form coatings or three-dimensional components. Unlike other additive manufacturing techniques (material extrusion, binder jetting, powder bed fusion, etc.), bonding during cold spray additive manufacturing is achieved using kinetic energy by accelerating the materials to supersonic speeds through means of compressed gas. Cold spray additive manufacturing involves a feedstock which typically includes metallic powders. The metallic powders range in size between 10 μm and 100 μm. In cold spray processing, as long as the velocity of the powders is above their critical velocity (and below a rebound velocity), the metallic powders will undergo plastic deformation as they impact a substrate.

[0024] Typical feedstock materials for cold spray additive manufacturing are pure metal powders or alloy powders. As will be described, a mixture of powders with different chemistries may be utilized as the feedstock materials and are referred to as blended elemental (BE). The blended elemental feedstock has a gross chemistry of a target final material and is deposited into the desired geometry and subsequently processed via heat treatments or in-situ operation to homogenize the constituents to the gross chemistry.

[0025] Cold spraying of some pre-alloyed powders has proved difficult due to their properties such as their high strength and hardness. Due to the high strength and high hardness, it is difficult for the pre-alloyed powders to undergo plastic deformation once deposited onto a substrate. Plastic deformation of pre-alloyed powders is limited and when it occurs, it requires significantly higher amounts of energy than current cold spray systems can provide. This causes these materials to be unsprayable or have poor deposition qualities. For this reason, soft materials such as aluminum (Al) or copper (Cu) have historically been the primary materials for cold spray. However, as will be described, a mixture of soft and hard materials in the feedstock will allow for these high strength and high hardness materials to be deposited as often times the individual constituents are ductile enough to allow deposition.

[0026] Various embodiments are directed to cold spray processing methods. Cold spray processing of a feedstock powder which includes a plurality of constituents is used to manufacture an article on a substrate. The article is either removed from the substrate to act as an individual component or left on the substrate to act as a coating. The article is then heat treated to alloy the constituents such that the elements are in solution with each other and no longer present as individual particles with their original chemistry.

[0027] The constituents in the feedstock may be of any form as long as the overall chemistry is that of the desired final alloy. For example, if the desired alloy is Ti-6A1-4V, then the feedstock may include 90% by weight titanium, 6% by weight aluminum, and 4% by weight vanadium powders. The feedstock powder mixture would be sprayed and subsequently processed to allow the individual elements to diffuse and homogenize such that the cold sprayed alloy has the same chemistry characteristics on a micro level as that of the alloy produced from traditional methods.

[0028] In some embodiments, feedstock constituents may include pure elemental powders. Non-limiting examples of pure elemental powders may include aluminum, iron, titanium, nickel, boron, or yttrium. As will be appreciated, pure elemental powders may also include any metallic powder suitable to construct a desired alloy. In some embodiments, preparing the feedstock constituents may require mixing the constituents until a homogenous blend is achieved.

[0029] In some embodiments, feedstock constituents may include alloyed powders, often referred to as pre-alloyed powders. Non-limiting examples of alloyed powders may include aluminum alloy 6061, titanium alloy Ti-6Al-4V, or 1018 steel. As will be appreciated, pre-alloyed powders may also include any alloyed powder suitable to construct the desired alloy.

[0030] In some embodiments, feedstock constituents may include ceramic powders. Non-limiting examples of ceramic powders may include silicon carbide (SiC), boron nitride (B4N), or aluminum oxide (Al2O3). As will be appreciated, ceramic powders may also include any ceramic powder suitable to construct the desired alloy.

[0031] In various aspects, a method of cold spray processing may be provided. Referring to FIG. 1, the method of cold spray processing may include providing 101 a substrate. The substrate may be a three-dimensional shape that forms a shell-like structure. For instance, in some embodiments, the substrate may be a mold for a nose cone of a munition. In other embodiments, the substrate may be a mold for a nose cone of an aviation vehicle. In still other embodiments, the substrate may be a rotor blade erosion cap.

[0032] The method may further include preparing 102 a feedstock powder comprising a homogenous blend of a plurality of constituents configured to yield a desired alloy when heated. The feedstock powder may include a mixture of powders with different chemistries. The feedstock powders may have a gross chemistry of a target final material. Further, the feedstock powder may include pre-alloyed powders, such as TI-6A1-4V. The plurality of constituents may include a mixture of pure elemental powders. The pure elemental powders may be chosen such that the chemistry of the mixture of powders is that of a target alloy chemistry. For instance, if the target alloy is the titanium alloy, Ti-6A1-6V-2Sn, then the feedstock powder may contain a homogenous mixture of pure elemental powders with 86% Ti by weight, 6% Al by weight, 6% V by weight and 2% SN by weight.

[0033] The method may further include cold spraying 103 the feedstock powder onto the substrate. The spraying of the feedstock powder may cause the feedstock powder to form an article on the substrate. In some embodiments, the method may further include removing 113 the article from the substrate. For instance, if the substrate is a mold for a munitions nose cap, the article may be removed from the substrate to act as a standalone munitions nose cap. In this manner, the manufactured munitions nose cap, now having the alloy properties of heat resistivity and ductility, is able to withstand the extreme conditions of gun launched hypersonics where such properties are necessary to endure flight and survive launch. In some embodiments where the article is removed, the substrate may be reused as a mold for future cold spray manufacturing. In other embodiments, the article may remain on the substrate to act as a coating. In embodiments where the coating remains on the substrate, the coating may further be alloyed 115 to the coating by heat treatment to improve adhesion. For instance, the substrate may form a liner on a small or large caliber gun.

[0034] The method may further include heating 104 the article to a temperature sufficient to induce alloying until the plurality of constituents have alloyed for an amount of time sufficient for homogenization. As previously noted, alloyed powders exhibit poor plastic deformation qualities due to their hardness and strength. For this reason, alloyed powders are poor candidates for cold spraying because the resultant article lacks homogenous structure, characteristics, and chemistry. Heating the article will thus induce the article to alloy. Homogenization induces alloying, by reducing the chemical separation of the elements, and also increases the desired mechanical properties of the alloy, such as its hardness and strength. The heating process may include raising the temperature of the article. To raise the temperature of the article, the heating process may include one or more heating elements. In some embodiments, the heating elements may include one or more lasers. In other embodiments, the heating element may include an oven.

[0035] In some embodiments, the temperature necessary to induce alloying may depend on the plurality of feedstock constituents. For example, the plurality of feedstock constituents may include 90% by weight titanium, 6% by weight aluminum, and 4% by weight vanadium. In this example, the article may be heated to a temperature between 1000 degrees Celsius and 1500 degrees Celsius. Depending on the alloy being induced, heating temperatures may be between 100 C. and 2000 C., and for an amount of time sufficient to achieve the desired effect. In some embodiments, the time sufficient to induce alloying may depend on the plurality of feedstock constituents. Continuing with the previous example, the time necessary to induce alloying may be between 30 minutes and 6 hours.

[0036] In some embodiments, the method may include cooling 105 the article to a room temperature. In some embodiments, the cooling of the article may cause the article to form an alloy structure. In some embodiments, cooling the article may include turning off a heating element. For instance, cooling the article may include turning off a laser element or turning off an oven. In some embodiments, cooling the article may include providing a cooling element. In some embodiments, the cooling element may include a liquid. In some embodiments, the liquid may be water. In other embodiments, the cooling element may be a cooling jacket.

[0037] Referring now to FIG. 2, an example use of the cold spray processing method is shown. In this example, a cold spray means 201 is provided. The cold spray means 201 is configured to deposit a metallic powder 202. In the example use, a munitions nose cap 203 may be provided as the substrate. The munitions nose cap 203 may act as a three-dimensional shell-like structure. As seen in FIG. 2, the deposition of metal powder onto the substrate may form a coating 204 with a desired width 205. After spraying the substrate, the coating 204 may be removed by a machining process 207, such that the coating 204 and the munitions nose cap 203 are standalone articles. The munitions nose cap 203 may be reused as a mold for future cold spray processing. The removed coating 204 may then be heated and cooled 208 such that the coating 204 forms an alloy having the structure of a munitions nose cap.

[0038] Generally speaking, cold state additive manufacturing of pre-alloyed powders has presented numerous difficulties, one such issue includes the pre-alloyed powders' difficulty to undergo plastic deformation. The disclosed method overcomes this pitfall by including a heterogeneous feedstock. The heterogeneous feedstock includes individual elements which, when sprayed, contain the mechanical and target properties of a target alloy. The individual elements alone are able to undergo plastic deformation, whereas an alloyed powder would be unable to do so. However, when the individual elements are sprayed onto a substrate to form an article, the elements are able to alloy, as if the elements were part of an alloyed powder. The disclosed method also includes a heat treatment which enables the elements to diffuse and homogenize, thus creating the target alloy chemistry. As opposed to traditional heat treatments to alloys, heating the cold sprayed article further induces alloying and increases the homogeneity of the alloyed article.

[0039] The various embodiments address a number of problems associated with conventional cold spraying methods. Conventional cold spray processing is currently used to deposit coatings, and more recently as an additive manufacturing technology, and depends on the use of pre-alloyed powders in order to manufacture an alloyed article. Pre-alloyed powders are difficult to spray compared to their elemental constituents because alloys are characterized by their hardness and strength and thus are poor candidates for plastic deformation. Additionally, some high strength elements such as tungsten (W) are difficult to cold spray because of their hardness. Other pre-alloyed powders are difficult to cold spray because they often clog the spray nozzle. To overcome these hurdles, a feedstock utilizing the individual elemental constituents of an alloy is used. Cold spray additive manufacturing that utilizes blended elemental feedstocks has greater flexibility in material choices as the desired material or alloy may not always be available in powder form, but the elemental constituents typically are. Another benefit of utilizing blended elemental feedstocks with cold spray additive manufacturing is that solid state alloying prevents the formation of deleterious phases which can occur in some material systems during melt-based processing. Another such benefit may be that materials with gradients can be manufactured by varying the composition throughout the process which can produce components with directional properties, enable the bonding of dissimilar materials, or reduce the cost of components by utilizing high-cost materials only at the point of need. Furthermore, the cold spray processing that involves pre-alloyed powders may enable the manufacturing of compositionally complex alloys or high entropy alloys, such as for hypersonic uses.

[0040] Various modifications may be made to the systems, methods, apparatus, mechanisms, techniques and portions thereof described herein with respect to the various figures, such modifications being contemplated as being within the scope of the invention. For example, while a specific order of steps or arrangement of functional elements is presented in the various embodiments described herein, various other orders / arrangements of steps or functional elements may be utilized within the context of the various embodiments. Further, while modifications to embodiments may be discussed individually, various embodiments may use multiple modifications contemporaneously or in sequence, compound modifications and the like.

[0041] Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. Thus, while the foregoing is directed to various embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. As such, the appropriate scope of the invention is to be determined according to the claims.

Claims

1. A method of cold spray processing, comprising:providing a substrate;preparing a feedstock powder comprising a homogenous blend of a plurality of constituents configured to yield a desired alloy when heated;cold spraying the feedstock powder onto the substrate, the spraying of the feedstock powder causing the feedstock powder to form an article on the substrate;heating the article to a temperature sufficient to induce alloying until the plurality of constituents have alloyed for an amount of time sufficient for homogenization; andcooling the article to a room temperature causing the article to form an alloy structure.

2. The method of claim 1, wherein the plurality of constituents comprises a plurality of pre-alloyed powders.

3. The method of claim 1, wherein the plurality of constituents comprises a plurality of ceramic powders.

4. The method of claim 1, wherein the plurality of constituents comprises a plurality of intermetallic powders.

5. The method of claim 1, wherein the plurality of constituents comprises a combination of at least two pure elemental, ceramic, pre-alloyed, or intermetallic powders.

6. The method of claim 1, wherein the plurality of constituents comprises a plurality of pure elemental powders.

7. The method of claim 6, wherein the plurality of pure elemental powders comprises 90% by weight Ti, 6% by weight Al, and 4% by weight V powders.

8. The method of claim 1, wherein the article forms a coating on the substrate.

9. The method of claim 8, further comprising alloying the coating to the substrate.

10. The method of claim 8, wherein the coating forms a liner for a small or large caliber gun.

11. The method of claim 1, further comprising removing the article from the substrate after the cold spraying and before heating the article.

12. The method of claim 1, wherein heating the article includes a multi-step profile.

13. The method of claim 1, wherein heating the article includes a specific atmosphere.

14. The method of claim 13, wherein the specific atmosphere comprises a vacuum, inert, reducing, oxidizing, or carburizing condition.

15. The method of claim 1, wherein the alloy structure comprises a ceramic.

16. The method of claim 1, wherein the substrate comprises a three-dimensional shell-like structure.

17. The method of claim 16, wherein the three-dimensional shell-like structure comprises one of a nose cap or a rotor-blade erosion cap.

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