Alkaline Earth Metal Stabilized Bulk Nanocrystalline Engineering Alloys

Abstract

A nano-structured alloy material includes a nanoparticle; a matrix phase surrounding the nanoparticle; and an alkali/alkali Earth metal (i) which is incorporated into the nanoparticle, (ii) which may also be incorporated into the matrix and therefore alter a material property of the matrix phase 120, and (iii) an interaction of the nanoparticle with the matrix phase.

Claims

1. A nano-structured alloy material comprising: a matrix phase associated with a base metal; and a dispersion of nanoparticles within the matrix phase, each nanoparticle comprising a core including an alkali/alkali Earth metal or a hydride thereof.

2. The nano-structured alloy material of claim 1, wherein the base metal comprises at least one of silver (Ag), aluminum (Al), gold (Au), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), hafnium (Hf), magnesium (Mg), molybdenum (Mo), niobium (Nb), nickel (Ni), platinum (Pt), tantalum (Ta), titanium (Ti), depleted uranium (U), vanadium (V), tungsten (W), yttrium (Y), and zirconium (Zr). The remainder of such materials may include various combinations of other periodic elements.

3. The nano-structured alloy material of claim 1, wherein the alkali/alkali Earth metal or the hydride thereof has a concentration of less than ten percent of the total composition.

4. The nano-structured alloy material of claim 1, wherein the core of each nanoparticle comprises the alkali/alkali Earth metal, barium (Ba), strontium (Sr), calcium (Ca), and magnesium (Mg), or hydrides thereof.

5. The nano-structured alloy material of claim 1, wherein the core of each nanoparticle comprises strontium (Sr) or a Sr-hydride.

6. The nano-structured alloy material of claim 1, wherein the matrix phase comprises at least fifty percent of the base metal.

7. The nano-structured alloy material of claim 1, wherein the matrix phase comprises a Group I and Group II element or hydride thereof, barium (Ba), Sr, calcium (Ca), and magnesium (Mg).

8. The nano-structured alloy material of claim 1, wherein the matrix phase comprises strontium (Sr) or a Sr-hydride.

9. The nano-structured alloy material of claim 1, wherein the matrix phase comprises a binary, ternary, or multicomponent composition in the form of a solid solution.

10. The nano-structured alloy material of claim 1, wherein the matrix phase comprises a grain size of an average diameter greater than one nm and less than ten microns.

11. The nano-structured alloy material of claim 1, wherein the nanoparticles have average diameters of less than ten nm.

12. The nano-structured alloy material of claim 1, wherein within grains of the matrix phase, an altered material property of the nanoparticle by the alkali/alkali Earth metal generates an alloy material comprising nano-structured clusters.

13. The nano-structured alloy material of claim 12, wherein the nano-structured clusters and alloy material have a particle number density greater than 10.sup.15/m.sup.3.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0008] The novel features of the disclosure are set forth in the appended claims. However, for purposes of explanation, several embodiments are illustrated in the following drawings.

[0009] FIG. 1 illustrates an example overview of one or more embodiments described herein, in which a nano-structured alloy material is generated;

[0010] FIG. 2 illustrates a flow chart of an exemplary process that synthesizes a nano-structured alloy material;

[0011] FIG. 3 illustrates a two-dimensional plot, in which grain size is indicated relative to annealing temperature for iron-based and titanium-based compounds;

[0012] FIG. 4 illustrates a two-dimensional plot, in which grain size is indicated relative to annealing temperature for aluminum-based compounds;

[0013] FIG. 5 illustrates a bar chart, in which hardness is indicated relative to annealing temperature for various substances;

[0014] FIG. 6 illustrates a bar chart, in which hardness is indicated relative to annealing temperature for various substances;

[0015] FIG. 7 illustrates a bar chart, in which hardness is indicated relative to annealing temperature for various substances;

[0016] FIG. 8A illustrates a magnified image showing grain retention for an alloy including strontium;

[0017] FIG. 8B illustrates a magnified image showing formation of nano-precipitates providing stability;

[0018] FIG. 9 illustrates a two-dimensional plot, in which stability is indicated relative to grain size for various materials;

[0019] FIG. 10 illustrates a two-dimensional plot, in which stability is indicated relative to grain size for various substances; and

[0020] FIG. 11 illustrates a two-dimensional plot, in which stability is indicated relative to grain size for various substances.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The following detailed description describes currently contemplated modes of carrying out exemplary embodiments. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of some embodiments, as the scope of the disclosure is best defined by the appended claims.

[0022] Various features are described below that can each be used independently of one another or in combination with other features. Broadly, some embodiments generally provide nanocrystalline alloys that offer stability and/or structural integrity after exposure to high temperatures.

[0023] FIG. 1 illustrates an example overview of one or more embodiments described herein, in which a nano-structured alloy material 100 is generated. One of ordinary skill in the art will recognize that the sizes (and/or relative sizes) of components, layers, regions, etc. may be distorted or exaggerated for clarity. As shown, the nano-structured alloy material 100 may include a nanoparticle 110, a matrix phase 120 surrounding the nanoparticle 110, and an alkali/alkali Earth metal 130 which may be incorporated into the nanoparticle 110, and which may also be incorporated into the matrix and therefore alter a material property of the matrix phase 120. The nanoparticle 110 may include any of a core, shape, morphology, size (e.g., greater than one nanometer (nm) and less than one hundred nm), structure, and coherency 140 of the nanoparticle 110 with respect to the matrix phase 120. The material property of the matrix phase 120 may include any of the stacking fault energy, texture, crystal structure, crystal orientation, twin spacing (e.g., twin width) , and symmetry. The interaction may include a change in a coherency 140 (e.g., how well do atoms line up) of the nanoparticle 110 with the matrix phase 120, wherein increased coherency is preferred.

[0024] The alkali/alkali Earth metal 130 may have a concentration of less than ten percent in some embodiments. In some embodiments, the alkali/alkali Earth metal 130 may include Ba, Sr, Ca, and/or Mg. The nanoparticle 110 may include any appropriate alloy 150 (e.g., alloys that include base metals such as Ag, Al, Au, Co, Cr, Cu, Fe, Hf, Mg, Mo, Nb, Ni, Pt, Ta, Ti, U (depleted), V, W, Y, and/or Zr, and/or alloys thereof) and/or oxygen (O), nitrogen (N), carbon (C), and sulfur (S).

[0025] The nano-structured alloy material 100 may include a high number density of nanoparticles 110. For example, the range of the density of nanoparticles 110 may be between 10.sup.15/m.sup.3 to 10.sup.30/m.sup.3 with a preferable density of nanoparticles 110 in the range of 10.sup.20/m.sup.3 to 10.sup.25/m.sup.3. The nanoparticle 110 may be formed by self-assembly via the decomposition of alloy 150. As one example, a dispersion of the nanoparticles 110 within the matrix phase 120 may impart a retained material strength to the nano-structured alloy material 100 of approximately one gigapascal (GPa) after having been exposed for at least one hundred hours and at a temperature greater than fifty percent of an absolute melting temperature of the nano-structured alloy material 100.

[0026] The nano-structured clusters 160 may be synthesized by adding the alkali/alkali Earth metal 130 in low concentrations, such as ten percent or less, to a base metal or alloy during initial synthesis.

[0027] The most important and efficient strengthening mechanism in alloys is to create and maintain, under service conditions, coherent interfaces between the matrix and precipitates. Successful examples of engineering alloys following this principle include age-hardenable Al alloys for automotive engines, Ni-based superalloys predominantly used in gas turbines and oxide dispersed strengthened (ODS) alloys for nuclear reactors. The clusters 160 are coherent with the matrix phase 120 and contribute to the retention of high hardness after long term extreme high temperature exposure. The clusters 160 provide a strengthening mechanism for the development of even more advanced high-performance alloys (e.g., Cu, Fe, etc.) which rely at least in part on oxide particle/clusters dispersions for high temperature applications including nuclear reactors and or turbine engines.

[0028] The alkali/alkali Earth metals 130 have an extreme affinity for oxygen and typically fall at the bottom of an Ellingham diagram and hence are very effective reducers of other metal oxides. These properties can be utilized to alter the particles/clusters in other oxide dispersed strengthen metal or alloys systems. When added to a base metal or alloy, such as one which includes nanoparticles (e.g., nanoparticle 110), the chemical potential of the alkali/alkali Earth metals 130 creates a thermodynamic driving force to seek out oxygen. In materials which utilize nanoscale oxide particle such as, for example, nanocrystalline composites and/or ODS alloys there will be a driving force to seek out and reduce these nanoscale oxide particles. In some cases, these oxide particles are less than ten nm in diameter and have a core structure where the oxygen is concentrated. The reduction of these former particles results in the creation of the new clusters 160 material which will incorporate the elements of the former oxide nanoparticle 110 and surrounding matrix phase 120. Additionally, alkali/alkali Earth metals may reduce the matrix phase 120 to form clusters 160. Accordingly, these attributes significantly increase the high temperature application space for the alloy material 100.

[0029] FIG. 2 illustrates an example process 200 for synthesizing a nano-structured alloy material, such as nano-structured alloy material 100.

[0030] As shown, process 200 may include generating (at 210) an alloy (e.g., alloy 150) via, for example, mechanical alloying which may include Alkali/Alkali-Earth metal (e.g., Earth metal 130).

[0031] As shown, process 200 may include forming (at 220) a nanoparticle (e.g., nanoparticle 110) including the Alkali/Alkali-Earth metal by self-assembly via the decomposition of an alloy such as alloy 150. Nanoparticles may also be formed via the reduction of other pre-existing oxides or similar other phases.

[0032] Process 200 may include establishing (at 230) a matrix phase surrounding the nanoparticle (e.g., matrix phase 120), through the decomposition of alloy 150. The matrix phase 120 may primarily include a composition in the form of a solid solution. The matrix phase 120 may include at least fifty percent of a base metal. Where the base metal can be one of the following including: Ag, Al, Au, Co, Cr, Cu, Fe, Hf, Mg, Mo, Nb, Ni, Pt, Ta, Ti, depleted U, V, W, Y, Zr, and/or alloys thereof. Where the remainder of the matrix phase may include various combinations of other periodic elements. The matrix phase 120 may also include any of the alkali/alkali Earth metal 130 of Group I and Group II elements or a hydride of the Group I and Group II elements.

[0033] The alkali/alkali Earth metal 130 may alter (i) a material property of the nanoparticle 110, (ii) a material property of the matrix phase 120, and (iii) an interaction of the nanoparticle 110 with the matrix phase 120. The material property of the nanoparticle 110 may include any of a core structure 170, shape, morphology, size (e.g., greater than one nm and less than one hundred nm), structure, and coherency 140 of the nanoparticle 110 with respect to the matrix phase 120. For example, the alkali/alkali Earth metal 130 may change a material structure of the nanoparticle 110 from spherical to cubic. The material property of the matrix phase 120 may include any of the stacking fault energy, texture, crystal structure, crystal orientation, twin spacing (twin width), and symmetry. The interaction may include a change in a coherency 140 (e.g., how well atoms line up) of the nanoparticle 110 with the matrix phase 120.

[0034] The alkali/alkali Earth metal 130 may have a concentration of less than ten percent. The alkali/alkali Earth metal 130 may include any of Group I and Group II elements or a hydride of the Group I and Group II elements.

[0035] The matrix phase 120 may include a grain size of an average diameter greater than one nm and less than ten microns and, within those grains, an altered material property of the nanoparticle 110 by the alkali/alkali Earth metal 130 may create clusters/alloy material 100. The nanoparticle 110 may include a core structure 170, that may include Group I and Group II elements. The clusters/alloy material 160 may include particles with diameters of less than ten nm. The clusters/alloy material 160 may include a particle number density greater than 10.sup.15/m.sup.3.

[0036] As shown, process 200 may include generating (at 240) nano-structured alloy material, such as nano-structured alloy material 100. The nano-structured alloy material 100 may include a high density of clusters 160 and associated nanoparticles 110. For example, the range of the density of nanoparticles 110 may be between 10.sup.15/m.sup.3 to 10.sup.30/m.sup.3 with a preferable density of nanoparticles 110 in the range of 10.sup.20/m.sup.3 to 10.sup.25/m.sup.3. A dispersion of the nanoparticles 110 within the matrix phase 120 may impart a retained material strength to the nano-structured alloy material 100 of approximately one GPa after having been exposed for at least one hundred hours and at temperature greater than fifty percent of an absolute melting temperature of the nano-structured alloy material 100.

[0037] Some processes for forming the binary or higher order high-density thermodynamically stable nanostructured alloy material 100 may include, for example, subjecting powder metals of the solvent to a high-energy milling process using a high-energy milling device configured to impart high impact energies to its contents. The material 100 is thermally stabilized, with the absence of substantial gross grain growth, such that the internal grain size of the matrix phase 120 is substantially suppressed to no more than about ten microns at approximately seventy-five percent of the absolute melting point temperature of the solvent metal remains substantially uniformly dispersed in the solvent metal at that temperature. For instance, a high-energy milling device may be used to subject the metallic powders to the high-energy milling process. Such a device may include, for example, a mixing vial for containing the metallic powders and a plurality of milling balls for inclusion within the mixing vial for milling the metallic powders therein.

[0038] Depending on the extent of milling operations, the range of intermixing varies from very large clusters (on the order of micro- to millimeters, containing a very large number atoms), to precipitates (nano- to micrometers, containing thousands of atoms), to particles (nanometers, containing tens of atoms), to single atoms. High energy may be imparted to the metallic system by applying high levels of kinetic or dynamic energy during the milling process where vials containing the precursor solvent and solute metals are shaken back and forth thousands of times a minute using impact milling media resulting in more than twice as many impacts a minute.

[0039] In general, mechanical milling/alloying produces nanostructured materials with grain sizes well below one hundred nm by repeated mechanical attrition of coarser grained powdered materials. Precursor powders are loaded into a steel vial and hardened steel or ceramic balls are also added. The vial then is sealed and shaken for extended periods of time. For example, the vials may be shaken one thousand sixty times a minute resulting in some two thousand one hundred twenty impacts a minute. This high-energy ball milling results in an almost complete breakdown of the initial structure of the particles. The result particles can have average particle size or agglomerate size as low as one to ten mm.

[0040] More specifically, on an atomic level, atoms can be forced into a metastable random solid solution or potentially occupy defect sites such as dislocations, triple junctions, and grain boundaries. This process is critical for setting up thermodynamic stabilization. The breakdown occurs due to the collisions of the particles with the walls of the vial and the balls. The energy deposited by the impact of the milling balls is sufficient to displace the atoms from their crystallographic positions. On a microscopic level, the particles fracture, aggregate, weld, and re-fracture causing the evolution of a heavily worked substructure in the milled powers. If more than one powder component is added into the vial, the components will be intimately mixed at an atomic level. As in mechanical alloying, this re-welding and re-fracturing continues until the elemental powders making up the initial charge are blended on the atomic level, such that either a solid solution and/or phase change results. The chemistry of the resulting alloy is comparable to the percentages of the initial elemental powders. With continued milling time, grain size reduction occurs, which eventually saturates at a minimum value that has been shown to scale inversely with melting temperature of the resultant compound. Of course, the process cycle can be interrupted to obtain intermediate grain size refinement of the powder blend and intermixing of its constituents.

[0041] The diameter, density, mass, number and/or ratio of the milling media may be altered to maintain the ball to powder mass (or weight) ratio sufficiently high so as influence the rate of breakdown, physical microstructure, and morphology of the resultant powder produced. For instance, the ball-to-powder mass ratio may be four to one, ten to one or more. To avoid cold welding and sticking to the vial and milling media, the milling process could be carried out using an additive, such as a surfactant. The additive or a surfactant may or may not be a liquid at room temperature.

[0042] The milling process may be performed at ambient or room temperature. Alternatively, the metallic powders can be continuously or semi-continuously cooled during the milling process. For instance, the milling process may be carried out using a liquid cryogen or low temperature fluid, such as liquid nitrogen. The formation of solid solutions between the constituents could be thought of as a competition between the external force of impinging balls creating finer and finer levels of intermixed alloy material via consolidation, shearing, and plastic deformation and competing processes such as diffusion-driven events such as phase separation. Thus, if mechanical milling could be performed at low enough temperatures, interdiffusion events, which are thermally activated, could all together be suppressed. As such, the likelihood of producing a solid solution is greatly enhanced. Given that the effect of the competing process is nullified, the result will be not only a much greater refinement of the grain size but also a much larger increase in the concentration of the solute in the solvent.

[0043] In some embodiments, the elemental components are brought to a sufficiently high temperature as to create a solid solution which is then quenched rapidly to produce a super-saturated solid solution of the individual constituents. For instance, the material could be manufactured in powder form by spray atomization techniques where the elemental components are brought to a sufficiently high temperature as to create a solid solution. Additionally, the elemental components might be brought to a sufficiently high temperature as to create a solid solution which is then quenched rapidly to produce a supersaturated solid solution of the individual constituents.

[0044] One of ordinary skill in the art will recognize that process 200 may be implemented in various different ways without departing from the scope of the disclosure. For instance, the elements may be implemented in a different order than shown. As another example, some embodiments may include additional elements or omit various listed elements. Elements or sets of elements may be performed iteratively and/or based on satisfaction of some performance criteria. Non-dependent elements may be performed in parallel. Elements or sets of elements may be performed continuously and/or at regular intervals.

[0045] FIG. 3 illustrates a two-dimensional plot 300, in which grain size is indicated relative to annealing temperature for iron-based and titanium-based compounds. FIG. 4 illustrates a two-dimensional plot 400, in which grain size is indicated relative to annealing temperature for aluminum-based compounds. In these examples, the alloying element X is the metal Sr, although different embodiments may utilize different elements (e.g., Ba, Ca, and Mg).

[0046] FIG. 5 illustrates a bar chart 500, in which hardness is indicated relative to annealing temperature for various substances. FIG. 6 illustrates a bar chart 600, in which hardness is indicated relative to annealing temperature for various substances. FIG. 7 illustrates a bar chart 700, in which hardness is indicated relative to annealing temperature for various substances. In these examples, the alloying element X is the metal Sr.

[0047] FIG. 8A illustrates a magnified image showing grain retention for an alloy including strontium. FIG. 8B illustrates a magnified image showing formation of nano-precipitates providing stability. As above, the alloying element is the metal Sr in these examples.

[0048] FIG. 9 illustrates a two-dimensional plot 900, in which stability is indicated relative to grain size for various materials. FIG. 10 illustrates a two-dimensional plot 1000, in which stability is indicated relative to grain size for various substances. FIG. 11 illustrates a two-dimensional plot 1100, in which stability is indicated relative to grain size for various substances. In these examples, the alloying element X is the metal Sr.

[0049] No element, act, or instruction used in the present application should be construed as critical or essential unless explicitly described as such. An instance of the use of the term and, as used herein, does not necessarily preclude the interpretation that the phrase and/or was intended in that instance. Similarly, an instance of the use of the term or, as used herein, does not necessarily preclude the interpretation that the phrase and/or was intended in that instance. Also, as used herein, the article a is intended to include one or more items and may be used interchangeably with the phrase one or more. Where only one item is intended, the terms one, single, only, or similar language is used. Further, the phrase based on is intended to mean based, at least in part, onunless explicitly stated otherwise.

[0050] The foregoing relates to illustrative details of exemplary embodiments and modifications may be made without departing from the scope of the disclosure. Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the possible implementations of the disclosure. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. For instance, although each dependent claim listed below may directly depend on only one other claim, the disclosure of the possible implementations includes each dependent claim in combination with every other claim in the claim set.