MICROALLOYING OF NIOBIUM ALLOYS

FIELD

[0001]The present disclosure is directed to methods for preparing a refractory alloy from a niobium base alloy and methods for recycling a niobium base alloy.

BACKGROUND

[0002]Niobium-containing alloys have a wide ranges of uses, including in aerospace and energy industries. In these industries, it is typically desirable that the niobium alloy have refractory properties (e.g., is able to withstand high heat and maintain consistent physical properties under strain). However, niobium and other metals used in the alloys for such applications (e.g., hafnium, tantalum, tungsten, etc.) are generally in limited supply and/or are expensive.

[0003]There is currently an inability to effectively recycle niobium alloys, due to problematic oxygen formation during the recycling processes. This inability to effectively recycle niobium alloys further contributes to the supply and cost problems associated with these alloys.

[0004]Therefore, a need exits for a method of forming a refractory alloy by recycling a niobium base alloy. Still further, a need exists for a method of preparing a refractory alloy from a niobium base alloy, wherein the refractory alloy exhibits improved properties (e.g., creep resistance, ductility, toughness, etc.) as compared to the niobium base alloy.

BRIEF SUMMARY

[0005]One aspect of the present disclosure is directed to a method of preparing a refractory alloy. The method comprises microalloying a niobium base alloy with one or more reactive element selected from the group consisting of Sc, Y, Er, Gd, Ce or combinations thereof, to form an intermediate alloy; and adding carbon to the intermediate alloy to form the refractory alloy. The niobium base alloy optionally further comprises Hf, Ti, Mo, V, Zr, W, Ta, or combinations thereof.

[0006]Further aspects of the present disclosure are directed to a method of preparing a recycled alloy. The method comprises microalloying a niobium base alloy with one or more reactive element selected from the group consisting of Sc, Y, Er, Gd, Ce or combinations thereof, to form an intermediate alloy; and adding carbon to the intermediate alloy to form the recycled alloy. The niobium base alloy optionally further comprises Hf, Ti, Mo, V, Zr, W, Ta, or combinations thereof In certain aspects, the niobium base alloy comprises from about 0 wt % to about 25 wt % Hf; from about 0.5 wt % to about 2.5 wt % Ti; from about 0 wt % to about 5 wt % Mo; from about 0 wt % to about 5 wt % V; from about 0 wt % to about 1 wt % Zr; from about 0 wt % to about 15 wt % W; and the remainder Nb together with unavoidable impurities.

[0007]Additional aspects of the present disclosure are directed to the refractory alloy and/or recycled alloy prepared by the described methods.

[0008]Other objects and features will be in part apparent and in part pointed out hereinafter.

DETAILED DESCRIPTION

[0009]Niobium-containing alloys present significant problems when attempting to recycle or repurpose the alloy. Their reactive nature and the high processing temperatures typically associated with recycling processes result in the accumulation of significant interstitial components.

[0010]One problem previously encountered when attempting to recycle or improve niobium alloys was the presence of oxygen in the niobium base alloy. For example, problems are encountered when interstitial oxygen forms in the niobium alloy matrix during recycling.

[0011]Niobium alloys typically collect this oxygen during machining, additive manufacturing, or other processing. The presence of oxygen results in a niobium alloy having a propensity towards embrittlement. Niobium alloys are considerably less tolerant to the presence of interstitial impurities (e.g., oxygen) as compared to titanium or zirconium alloys. When the niobium alloy is present as a metal powder, the high surface area to volume ratio further exacerbates these issues. For example, it has been reported that the allowable upper limit of oxygen for the niobium alloy C-103 is only 0.03 wt %. In contrast, the allowable upper limit of oxygen for the alloy Ti-6Al-4V is 0.2 wt % and for Grade 4 commercial purity titanium is 0.4 wt %.

[0012]Niobium-containing alloys that are presently known to tolerate higher interstitial oxygen concentrations contain a significant concentration of other high value or rare components, that make the recycling and use of the alloy more expensive and difficult. It has been previously reported that niobium alloys containing a high concentration of Hf (e.g., 30 wt % in WC-3009) dissolve the oxygen to form stable oxides and allow for a much higher tolerance of oxygen in the alloy as compared to traditional niobium alloys. For example, niobium alloys WC-3009 and FS-85 may tolerate three times to five times more interstitial oxygen than other commercial niobium alloys. However, WC-3009 and FS-85 rely on high concentrations of Hf or Ta in the alloy in order to neutralize the interstitial oxygen. The presence of Hf or Ta in such a high concentration may present issues for the economic viability of the alloy and the recycling processes.

[0013]The inventors of the present disclosure have discovered methods that allow for the effective recycling a niobium base alloy, wherein the niobium base alloy is microalloyed with one or more reactive elements to remove oxygen from the niobium base alloy. In certain embodiments, the method utilizes a niobium base alloy that does not contain a high concentration of rare or prohibitively expensive materials, such as Hf or Ta in an amount of more than 25 wt % or 28 wt %. This not only allows for a more economical process as compared to high concentration Hf or Ta alloys, but also allows for the incorporation of carbon to further strengthen and improve the physical properties of the resulting recycled or refractory alloy (as discussed in further detail below).

[0014]In one embodiment, the method of the present disclosure comprises preparing a refractory alloy. The method comprises microalloying a niobium base alloy with one or more reactive element selected from the group consisting of Sc, Y, Er, Gd, Ce or combinations thereof, to form an intermediate alloy; and adding carbon to the intermediate alloy to form the refractory alloy. In some embodiments, the niobium base alloy optionally further comprises Hf, Ti, Mo, V, Zr, W, Ta, or combinations thereof.

[0015]In an additional embodiment, the method is directed to recycling a niobium base alloy. The method comprises microalloying a niobium base alloy with one or more reactive element selected from the group consisting of Sc, Y, Er, Gd, Ce or combinations thereof, to form an intermediate alloy; and adding carbon to the intermediate alloy to form the recycled alloy. In some embodiments, the niobium base alloy optionally further comprises Hf, Ti, Mo, V, Zr, W, Ta, or combinations thereof.

[0016]Although discussion herein may be directed to methods of preparing a refractory alloy, it will be understood by those skilled in the art that this disclosure is equally applicable to methods for recycling a niobium alloy for non-refractory applications (i.e. preparing an improved/recycled alloy from a niobium base alloy, wherein the improved/recycled alloy may not have the physical properties typically exhibited by a refractory alloy).

[0017]The alloys described herein (e.g., niobium base alloy, intermediate alloy, refractory alloy, recycled alloy) may be in any suitable form. For example, in certain embodiments, the alloy may be in the form of a powder.

[0018]As used herein, “niobium base alloy” is intended to reference any suitable alloy comprising niobium.

[0019]In certain embodiments, the niobium base alloy comprises niobium and one or more additional element selected from the group consisting of Hf, Ti, Mo, V, Zr, W, Ta, or combinations thereof. In other embodiments, the niobium base alloy comprises niobium and one or more additional element selected from the group consisting of Hf, Ti, Mo, V, Zr, and combinations thereof. For example, in one embodiment the niobium base alloy comprises Hf, Ti, and Nb. In another embodiment, the niobium base alloy comprises Hf, Ti, Zr, and Nb. In further embodiments, the niobium base alloy comprises Hf, Mo, V, Zr, and Nb. In other embodiments, the niobium base alloy comprises Hf, W, Zr, and Nb.

[0020]Although the niobium base alloy may comprise one or more additional elements, it is one object of the present disclosure to provide a method for the recycling/processing of a niobium base alloy in order to prepare a suitable recycled/refractory alloy, wherein the niobium base alloy is a lower cost niobium alloy. For example, a niobium alloy that does not contain a high concentration of Hf. These methods not only result in considerable reduction in formulation costs, they also reduce the risk associated with sourcing alloys containing highly strategic/high value components.

[0021]In one embodiment, the niobium base alloy comprises from about 0 wt % to about 30 wt %, from about 0 wt % to about 25 wt %, from about 1 wt % to about 25 wt %, from about 2 wt % to about 25 wt %, from about 3 wt % to about 25 wt %, from about 4 wt % to about 25 wt %, from about 5 wt % to about 25 wt %, from about 6 wt % to about 25 wt %, from about 7 wt % to about 25 wt %, from about 8 wt % to about 25 wt %, from about 9 wt % to about 25 wt %, from about 10 wt % to about 25 wt %, from about 11 wt % to about 25 wt %, from about 12 wt % to about 25 wt %, from about 13 wt % to about 25 wt %, from about 14 wt % to about 25 wt %, or from about 15 wt % to about 25 wt % Hf. In other embodiments, the niobium base alloy may comprise from about 10 wt % to about 15 wt % Hf. In still further embodiments, the niobium base alloy may comprise about 15 wt % or less, about 10 wt % or less, about 5 wt % or less, about 4 wt % or less, about 3 wt % or less, about 2 wt % or less, or about 1 wt % or less Hf.

[0022]In some embodiments, the niobium base alloy comprises from about 0 wt % to about 5 wt %, from about 0 wt % to about 4 wt %, from about 0 wt % to about 3 wt %, from about 0 wt % to about 2.5 wt %, from about 0.5 wt % to about 2.5 wt %, from about 1 wt % to about 2.5 wt %, or from about 1 wt % to about 2 wt % Ti.

[0023]In further embodiments, the niobium base alloy comprises from about 0 wt % to about 10 wt %, from about 0 wt % to about 7.5 wt %, or from about 0 wt % to about 5 wt % Mo. In other embodiments, the niobium base alloy may comprise from about 1 wt % to about 7.5 wt %, from about 2 wt % to about 7.5 wt %, from about 3 wt % to about 7.5 wt %, from about 4 wt % to about 7.5 wt %, from about 4 wt % to about 7 wt %, or from about 4 wt % to about 6 wt % Mo.

[0024]In additional embodiments, the niobium base alloy comprises from about 0 wt % to about 10 wt %, from about 0 wt % to about 7.5 wt %, or from about 0 wt % to about 5 wt % V. In other embodiments, the niobium base alloy may comprise from about 1 wt % to about 7.5 wt %, from about 2 wt % to about 7.5 wt %, from about 3 wt % to about 7.5 wt %, from about 4 wt % to about 7.5 wt %, from about 4 wt % to about 7 wt %, or from about 4 wt % to about 6 wt % V.

[0025]In still further embodiments, the niobium base alloy comprises from about 0 wt % to about 5 wt %, from about 0 wt % to about 4 wt %, from about 0 wt % to about 3 wt %, from about 0 wt % to about 2 wt %, or from about 0 wt % to about 1 wt % Zr. In other embodiments, the niobium base alloy may comprise from about 0.1 wt % to about 5 wt %, from about 0.1 wt % to about 4 wt %, from about 0.1 wt % to about 3 wt %, from about 0.1 wt % to about 2 wt %, from about 0.2 wt % to about 2 wt %, from about 0.3 wt % to about 2 wt %, from about 0.4 wt % to about 2 wt %, from about 0.5 wt % to about 2 wt %, or from about 0.5 wt % to about 1.5 wt % Zr.

[0026]In other embodiments, the niobium base alloy comprises from about 0 wt % to about 15 wt %, from about 0 wt % to about 10 wt %, from about 0 wt % to about 7.5 wt %, or from about 0 wt % to about 5 wt % W.

[0027]In additional embodiments, the niobium base alloy comprises from about 0 wt % to about 15 wt %, from about 0 wt % to about 10 wt %, from about 0 wt % to about 7.5 wt %, or from about 0 wt % to about 5 wt % Ta.

[0028]In one embodiment, the niobium base alloy comprises: from about 0 wt % to about 25 wt % Hf; from about 0.5 wt % to about 2.5 wt % Ti; from about 0 wt % to about 5 wt % Mo; from about 0 wt % to about 5 wt % V; from about 0 wt % to about 1 wt % Zr; and the remainder Nb together with unavoidable impurities.

[0029]In another embodiment, the niobium base alloy comprises: from about 5 wt % to about 25 wt % Hf; from about 0.75 wt % to about 2 wt % Ti; from about 0 wt % to about 5 wt % Mo; from about 0 wt % to about 5 wt % V; from about 0 wt % to about 1 wt % Zr; and the remainder Nb together with unavoidable impurities.

[0030]In an additional embodiment, the niobium base alloy comprises: from about 0 wt % to about 25 wt % Hf; from about 0 wt % to about 15 wt % W; from about 0.5 wt % to about 2.5 wt % Ti; from about 0 wt % to about 5 wt % Mo; from about 0 wt % to about 5 wt % V; from about 0 wt % to about 1 wt % Zr; and the remainder Nb together with unavoidable impurities.

[0031]In still further embodiments, the niobium base alloy is selected from the group consisting of C-103, Nb-1Zr, PWC-11, Cb752, and Cb129Y. In one embodiment, the niobium base alloy is C-103.

[0032]In additional embodiments, the niobium base alloy may comprise one or more unavoidable impurities or additional materials selected from the group consisting of Al, Cr, Si, B, and Fe. For example, in one embodiment, the niobium base alloy comprises Hf, Ti, Nb, Al, and Si. In another embodiment, the niobium base alloy comprises Hf, Ti, Zr, Nb, Al, and Si.

[0033]In various embodiments, the niobium base alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Al.

[0034]In some embodiments, the niobium base alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Cr.

[0035]In additional embodiments, the niobium base alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Si.

[0036]In further embodiments, the niobium base alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of B.

[0037]In various embodiments, the niobium base alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Fe.

[0038]In some embodiments, the niobium base alloy comprises a total concentration of unavoidable impurities or additional materials of less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, or less than about 0.1 wt %. For example, in one embodiments, the niobium base alloy has a total concentration of Al, Cr, Si, B, and Fe of less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, or less than about 0.1 wt %.

[0039]Certain methods of the present disclosure are directed to microalloying a niobium base alloy with one or more reactive element to form an intermediate alloy. Processing of a niobium base alloy typically increase the interstitial oxygen content of the base alloy. The reactive element (e.g., Er or Y) combines with oxygen in the niobium base alloy to form finely dispersed in-situ stable reactive elemental oxides (e.g., Er₂O₃ or Y₂O₃). By controlling the amount of the one or more reactive element microalloyed with the niobium base alloy, it is possible to remove interstitial oxygen formed during the processing and allow formation of an intermediate alloy (and refractory alloy) maintaining suitable toughness and ductility. The intermediate alloy and resulting refractory alloy of this method may also exhibit improved creep resistance via oxide dispersion strengthening (as discussed in greater detail below).

[0040]Microalloying a niobium base alloy with one or more reactive element, as described herein, also reduces the need to use excessive levels of other additives. This in turn reduces the tendency of the alloy to form excessive levels of harmful intermetallic compounds that can reduce malleability.

[0041]Discussion herein related to the removal of oxygen from the niobium base alloy or deoxidation of the niobium base alloy should be understood to mean removal of the interstitial oxygen from the niobium base alloy. As described herein, oxygen may be present in the system after microalloying with one or more reactive element. However, the oxygen will have transformed from an interstitial part of the niobium base alloy, to being an oxide of the one or more reactive elements. For example, microalloying a niobium base alloy with Er removes interstitial oxygen from the niobium base alloy and forms an intermediate alloy comprising Er₂O₃.

[0042]Effective deoxidation of a niobium alloy requires use of a reactive element that has a Gibbs free energy of formation below that of niobium. As many niobium base alloys also comprise Hf, it may be desirable to select a reactive element with a Gibbs free energy below that of Hf.

[0043]In certain embodiments, the one or more reactive element may comprise rare earth metals with a Gibbs free energy for forming oxides lower than that of Hf. Certain of these elements may have Gibbs free energies below that of Hf, but nonetheless may not be suited for use in alloys subjected to extreme conditions (e.g., space or hypersonic flight). For example, Ce and La are suitable reactive elements for use in the described methods of recycling and adding carbon to a niobium base alloy. These reactive elements act to form elemental oxides and remove interstitial oxygen from the niobium base alloy as described elsewhere herein, and may form a useful recycled alloy. Recycled alloys comprising Ce or La oxides may not be suitable for use in extreme or high temperature conditions (e.g., >2,500° F.) due to their lower melting point.

[0044]Nevertheless, Ce or La containing alloys may allow for improved machinability of super conducting Nb alloys or may be used in chemical processes that require lower temperatures than traditional aerospace application. Therefore, those skilled in the art will understand that rare earth metals with a Gibbs free energy for forming oxides lower than that of Hf may be used as the reactive element of the microalloying step, but that the specific selection of the rare earth metal may be dependent on the intended use of the resulting alloy.

[0045]The inventors have discovered that Sc, Y, Er, and Gd are particularly well suited for microalloying with a niobium base alloy to remove oxygen and form small stable oxide particles. Ce has also been determined to be a suitable reactive element for certain applications.

[0046]In some embodiments, the one or more reactive element is selected from the group consisting of Sc, Y, Er, Gd, Ce, or combinations thereof. In other embodiments, the one or more reactive element is selected from the group consisting of Sc, Y, Er, Gd, or combinations thereof. In other embodiments, the one or more reactive element is selected from the group consisting of Y, Er, Gd, Ce, or combinations thereof.

[0047]The amount of the one or more reactive element used in microalloying is important to the resulting intermediate alloy and refractory alloy. The amount should be selected such that sufficient oxygen is removed to allow for recycling and further use of the niobium base alloy and also to allow for the addition of carbon (as discussed in greater detail below) to increase the strength and creep resistance of the refractory alloy. Excessive amounts of the one or more reactive element may result in brittle alloys or unacceptably lower the melting point of the formed alloy. However, sufficient reactive element should be present to allow for full deoxidation in the microalloying step and further steps of the method that may produce oxygen.

[0048]In certain embodiments, the one or more reactive element is used in an amount slightly higher than the stoichiometric amount required to remove the interstitial oxygen from the niobium base alloy. In some embodiments, the one or more reactive element is supplied to the microalloying step in an amount 1.2 to 2 times the stoichiometric amount required for that reactive element oxide. For example, in a microalloying step wherein the one or more reactive element is Er, 1.2 to 2 times the stoichiometric amount of Er required to deoxygenate the niobium base alloy is used in the microalloying step. In some embodiments, the one or more reactive element is supplied to the microalloying step in an amount of from about 1.1 to about 10, from about 1.1 to about 9, from about 1.1 to about 8, from about 1.1 to about 7, from about 1.1 to about 6, from about 1.2 to about 6, from about 1.4 to about 6, from about 1.6 to about 6, from about 1.8 to about 6, from about 2 to about 6, from about 3 to about 6, or from about 3 to about 5 times the stoichiometric amount required to deoxygenate the niobium base alloy.

[0049]The addition of microalloying reactive elements slightly above the stoichiometric levels allows for deoxidization of the niobium base alloy and also the deoxidation of the intermediate alloy and/or refractory alloy during further processing. Due to the stoichiometric excess, oxygen present in these further processing steps would thus form stable oxides instead of interstitial strengthening, ductility reducing components.

[0050]As the one or more reactive element is used in an excess stoichiometric amount in relation to the interstitial oxygen, the amount of reactive element used in the method may be quantified based on the amount of such elements present in the final refractory alloy product.

[0051]In one embodiment, the refractory alloy comprises from about 0 wt % to about 0.15 wt %, from about 0.01 wt % to about 0.14 wt %, from about 0.01 wt % to about 0.13 wt %, from about 0.01 wt % to about 0.12 wt %, from about 0.01 wt % to about 0.11 wt %, from about 0.01 wt % to about 0.1 wt %, from about 0.02 wt % to about 0.1 wt %, from about 0.02 wt % to about 0.09 wt %, from about 0.02 wt % to about 0.08 wt %, from about 0.03 wt % to about 0.08 wt %, from about 0.03 wt % to about 0.07 wt %, from about 0.03 wt % to about 0.06 wt %, or from about 0.04 wt % to about 0.06 wt % of each of the one or more reactive elements. For example, the refractory alloy may comprise the above concentrations of Sc, the above concentrations of Y, the above concentrations of Er, the above concentrations of Gd, and/or the above concentrations of Ce.

[0052]In certain embodiments, the refractory alloy may comprise from about 0 wt % to about 0.1 wt %, from about 0.01 wt % to about 0.1 wt %, from about 0.01 wt % to about 0.09 wt %, from about 0.01 wt % to about 0.08 wt %, from about 0.02 wt % to about 0.08 wt %, from about 0.02 wt % to about 0.07 wt %, from about 0.02 wt % to about 0.06 wt %, or from about 0.03 wt % to about 0.05 wt % of Ce.

[0053]In embodiments wherein the method comprises a combination of two or more reactive elements selected from the group consisting of Sc, Y, Er, Gd, Ce, the total concentration of reactive elements in the refractory alloy may be less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, or less than about 0.1 wt %. For example, from about 0.01 wt % to about 0.5 wt %, from about 0.02 wt % to about 0.5 wt %, from about 0.03 wt % to about 0.5 wt %, from about 0.04 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.4 wt %, from about 0.05 wt % to about 0.3 wt %, from about 0.06 wt % to about 0.3 wt %, from about 0.07 wt % to about 0.3 wt %, from about 0.07 wt % to about 0.25 wt %, from about 0.08 wt % to about 0.25 wt %, from about 0.09 wt % to about 0.25 wt %, from about 0.1 wt % to about 0.25 wt %, from about 0.12 wt % to about 0.25 wt %, from about 0.14 wt % to about 0.25 wt %, from about 0.16 wt % to about 0.25 wt %, from about 0.18 wt % to about 0.25 wt %, or from about 0.2 wt % to about 0.25 wt %.

[0054]In some embodiments, the microalloying step may further comprise the intentional addition of Al, Cr, Si, B, Fe, or combinations thereof. In other embodiments, the microalloying step may further comprise the intentional addition of Al, Cr, Si, B, Fe, W, or combinations thereof. Without being bound to the theory, it is believed that the purposeful microalloying addition of Al, Cr, Si, B, Fe, W, or combinations thereof may slightly reduce the solidus and liquidus temperatures of the resulting alloy. This reduction in solidus and liquidus temperature promotes better interparticle bonding and the formation of minute intermetallic hardening compounds. The amount of Al, Cr, Si, B, Fe, W, or combinations thereof introduced in the microalloying step may similarly be quantified based on the amount of such elements present in the final refractory alloy product.

[0055]In one embodiment, the refractory alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Al.

[0056]In another embodiment, the refractory alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Cr.

[0057]In further embodiments, the refractory alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Si.

[0058]In additional embodiments, the refractory alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of B.

[0059]In still further embodiments, the refractory alloy comprises about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of Fe.

[0060]In other embodiments, the refractory alloy comprises about 15 wt % or less, about 10 wt % or less, about 7.5 wt % or less, about 5 wt % or less, about 1 wt % or less, about 0.1 wt % or less, about 0.075 wt % or less, about 0.05 wt % or less, about 0.0025 wt % or less, or about 0.01 wt % or less of W.

[0061]In some embodiments, the total concentration of Al, Cr, Si, B, and Fe in the refractory alloy is less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, or less than about 0.1 wt %. In additional embodiments, the total concentration of Al, Cr, Si, B, Fe, and W in the refractory alloy is less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, or less than about 0.1 wt %. In other embodiments, the total concentration of Al, Cr, Si, B, and Fe in the refractory alloy is from about 0.01 wt % to about 0.5 wt %, from about 0.02 wt % to about 0.5 wt %, from about 0.03 wt % to about 0.5 wt %, from about 0.04 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.4 wt %, from about 0.05 wt % to about 0.3 wt %, from about 0.05 wt % to about 0.2 wt %, or from about 0.05 wt % to about 0.1 wt %. In further embodiments, the total concentration of Al, Cr, Si, B, Fe, and W in the refractory alloy is from about 0.01 wt % to about 0.5 wt %, from about 0.02 wt % to about 0.5 wt %, from about 0.03 wt % to about 0.5 wt %, from about 0.04 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.4 wt %, from about 0.05 wt % to about 0.3 wt %, from about 0.05 wt % to about 0.2 wt %, or from about 0.05 wt % to about 0.1 wt %.

[0062]As noted above, microalloying a niobium base alloy and one or more reactive element allows for the removal of oxygen from the niobium base alloy. Interstitial nitrogen may also be removed from the niobium base alloy in a similar manner. The removal of interstitial oxygen and/or nitrogen improves the ductility of the alloy (i.e. the intermediate alloy exhibits greater ductility than the niobium base alloy). For example, in embodiments wherein Ce is present as the one or more reactive element, Ce may react with nitrogen present in the alloy to form CeN dispersoids. In other embodiments, the niobium base alloy may comprise nitride formers (e.g., Nb, Zr, Hf, Ti, Ta, etc.) that also act to remove interstitial elements, counteract the reduction in toughness and ductility, and form in-situ nitride dispersoids. These nitride formers are highly reactive to nitrogen and preferentially combine with nitrogen to reduce the interstitial levels of nitrogen in the niobium alloy. Excessive interstitial nitrogen may otherwise embrittle the niobium base alloy.

[0063]The inventors have also discovered that carbon can be successful added to the intermediate alloy when interstitial oxygen/nitrogen has been removed. Surprisingly, the inventors have discovered that the addition of carbon to this intermediate alloy does not result in any appreciable reduction in the ductility or toughness of the final alloy. That is, carbon can be added to the intermediate alloy while still resulting in a refractory alloy that exhibits acceptable ductility and toughness. In certain embodiments, the intermediate alloy contains strong carbide formers (e.g., Nb, Zr, Ti, V, or Hf) which allow for an increase in the overall creep resistance of the alloy when combined with carbon.

[0064]In certain embodiments, it is important to microalloy the one or more reactive element with the niobium base alloy before the addition of carbon. Without being bound by the theory, it is believed that the elimination/reduction of dissolved interstitial oxygen via deoxidation with one or more reactive element (i.e. the microalloying step) results in higher ductility of the intermediate alloy, which in turn allows for carbon to be effectively added to the intermediate alloy to improve the alloy strength without undue embrittlement. It is also believed that the addition of carbon to a deoxidized intermediate alloy allows for the formation of in-situ carbides that increase the creep resistance.

[0065]The addition of carbon to achieve these properties presents further cost savings. As explained above, the present process may be conducted with a niobium base alloy that does not contain a high percentage of expensive, hard to obtain or strategic alloying elements such as Hf, Ta or W. Thus, the methods disclosed herein offer an inexpensive way to increased creep strength.

[0066]Carbon may be added to the intermediate alloy by any known method. For example, vacuum arc addition, plasma melting, electron beam melting, or laser melting.

[0067]In certain embodiments, carbon is added to the intermediate alloy in an amount such that the refractory alloy has a carbon content of from about 0.01 wt % to about 1 wt %, from about 0.01 wt % to about 0.9 wt %, from about 0.01 wt % to about 0.8 wt %, from about 0.01 wt % to about 0.7 wt %, from about 0.01 wt % to about 0.6 wt %, from about 0.01 wt % to about 0.5 wt %, from about 0.02 wt % to about 0.5 wt %, from about 0.03 wt % to about 0.5 wt %, from about 0.04 wt % to about 0.5 wt %, from about 0.04 wt % to about 0.4 wt %, from about 0.04 wt % to about 0.3 wt %, from about 0.04 wt % to about 0.2 wt %, from about 0.05 wt % to about 0.2 wt %, from about 0.06 wt % to about 0.2 wt %, from about 0.07 wt % to about 0.2 wt %, from about 0.08 wt % to about 0.2 wt %, from about 0.08 wt % to about 0.19 wt %, from about 0.08 wt % to about 0.18 wt %, from about 0.08 wt % to about 0.16 wt %, from about 0.08 wt % to about 0.15 wt %, from about 0.09 wt % to about 0.15 wt %, or from about 0.1 wt % to about 0.15 wt %.

[0068]As explained in further detail above, microalloying the niobium base alloy with one or more reactive elements removes interstitial oxygen in the niobium base alloy to form finely dispersed in-situ stable reactive elemental oxides (e.g., Er₂O₃ or Y₂O₃). This transformation is important to achieving the desired properties of the resulting refractory alloy. Therefore, in certain embodiments, it is desirable to achieve a reduced oxygen content or interstitial oxygen content of the intermediate alloy and/or refractory alloy. In other embodiments it is important to achieve a specific total concentration or interstitial concentration of carbon, oxygen, and nitrogen in the intermediate and/or refractory alloy.

[0069]In some embodiments, the interstitial oxygen content of the intermediate alloy is less than the interstitial oxygen content of the niobium base alloy. In other embodiments, the oxygen content of the intermediate alloy is less than the oxygen content of the niobium base alloy.

[0070]In certain embodiments of the present method, the intermediate alloy has an interstitial oxygen content of about 0.1 wt % or less, about 0.09 wt % or less, about 0.08 wt % or less, about 0.07 wt % or less, about 0.06 wt % or less, about 0.05 wt % or less, about 0.04 wt % or less, about 0.03 wt % or less, about 0.02 wt % or less, about 0.01 wt % or less, or about 0.005 wt % or less.

[0071]In various embodiments of the present method, the intermediate alloy has an oxygen content of about 0.1 wt % or less, about 0.09 wt % or less, about 0.08 wt % or less, about 0.07 wt % or less, about 0.06 wt % or less, about 0.05 wt % or less, about 0.04 wt % or less, about 0.03 wt % or less, about 0.02 wt % or less, about 0.01 wt % or less, or about 0.005 wt % or less.

[0072]In some embodiments, the interstitial oxygen content of the refractory alloy is less than the interstitial oxygen content of the niobium base alloy. In other embodiments, the oxygen content of the refractory alloy is less than the oxygen content of the niobium base alloy.

[0073]In certain embodiments of the present method, the refractory alloy has an interstitial oxygen content of about 0.1 wt % or less, about 0.09 wt % or less, about 0.08 wt % or less, about 0.07 wt % or less, about 0.06 wt % or less, about 0.05 wt % or less, about 0.04 wt % or less, about 0.03 wt % or less, about 0.02 wt % or less, about 0.01 wt % or less, or about 0.005 wt % or less.

[0074]In various embodiments of the present method, the refractory alloy has an oxygen content of about 0.1 wt % or less, about 0.09 wt % or less, about 0.08 wt % or less, about 0.07 wt % or less, about 0.06 wt % or less, about 0.05 wt % or less, about 0.04 wt % or less, about 0.03 wt % or less, about 0.02 wt % or less, about 0.01 wt % or less, or about 0.005 wt % or less.

[0075]In some embodiments, the total concentration of interstitial carbon, oxygen, and nitrogen in the refractory alloy is less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, less than about 0.1 wt %, or less than about 0.05 wt %.

[0076]For example, in one embodiment, the total concentration of interstitial carbon, oxygen, and nitrogen in the refractory alloy is from about 0.05 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.4 wt %, from about 0.05 wt % to about 0.3 wt %, from about 0.075 wt % to about 0.3 wt %, or from about 0.1 wt % to about 0.3 wt %.

[0077]In some embodiments, the total concentration of carbon, oxygen, and nitrogen in the refractory alloy is less than about 0.5 wt %, less than about 0.4 wt %, less than about 0.3 wt %, less than about 0.2 wt %, less than about 0.1 wt %, or less than about 0.05 wt %. For example, in one embodiment, the total concentration of carbon, oxygen, and nitrogen in the refractory alloy is from about 0.05 wt % to about 0.5 wt %, from about 0.05 wt % to about 0.4 wt %, from about 0.05 wt % to about 0.3 wt %, from about 0.075 wt % to about 0.3 wt %, or from about 0.1 wt % to about 0.3 wt %.

[0078]Certain exemplary, non-limiting, embodiments of refractory alloys prepared according to the methods described herein are set forth below.

[0079]In one embodiment, the refractory alloy comprises Hf, Ti, Nb, Y, Gd, and C. For example, Nb-10Hf-1Ti-0.15C-0.05Y-0.1Gd.

[0080]In another embodiment, the refractory alloy comprises Hf, Ti, Nb, Al, Si, Er, and C. For example, Nb-10Hf-1.5Ti-0.10C-0.10Er-0.15Al-0.05Si.

[0081]In a further embodiment, the refractory alloy comprises Hf, Mo, V, Zr, Nb, Sc, and C. For example, Nb-10Hf-5Mo-5V-1Zr-0.08C-0.08Sc.

[0082]In some embodiments, the refractory alloy comprises Hf, W, Zr, Nb, Y, and Er. For example, Nb-5Hf-10W-1Zr-0.10C-0.08Y-0.05Er.

[0083]In an additional embodiment, the refractory alloy comprises Hf, Ti, Zr, Nb, Al, Si, Er, and C. For example, Nb-12Hf-1Ti-1Zr-0.10C-0.08Er-0.15Al-0.08Y-0.1Si.

[0084]Certain further embodiments of the present disclosure are directed to the formation of products using the refractory alloy prepared by the methods described herein. For example, aerospace, propulsion, defense, etc. materials or components prepared from the refractory alloy described herein.

[0085]In various embodiments, the refractory alloy may be in a suitable form for manufacturing or processing. For example, the refractory alloy may be in the form of a powder. Small particle sizes have been found to limit the size and reduce the distance between oxide, carbide, and/or nitride dispersoids that may be present, which may be desirable for certain applications.

[0086]In some embodiments, the refractory alloy described herein may be subjected to additive manufacturing processes (e.g., cold spray, laser bed fusion, direct energy deposition).

[0087]Refractory alloys prepared in accordance with the described methods, having interstitial oxygen removed, may unexpectedly undergo oxide dispersion hardening when used in such additive manufacturing processes. This results in improved products over those prepared by other refractory alloys. For example, such alloys which have undergone oxide dispersion hardening may exhibit improved tensile and creep resistance at elevated temperatures.

[0088]Without being bound by the theory, it is believed that refractory alloys formed by the methods disclosed herein provide improved benefits when used in additive manufacturing processes. Cold spray processes are typically performed below the solidus and liquidus temperatures of the alloy. Similarly, laser powder bed fusion creates a small solidification pool, such that the solidification rate and post-solidification rate are very high. In both of these processes, the segregation of oxides formed during the additive manufacturing process is limited. This lack of segregation advantageously allows for oxide dispersion strengthening of the alloy, and thus an increase in the creep resistance.

[0089]Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

[0090]When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0091]In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

[0092]As various changes could be made in the above alloys, methods, and products without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.