WO2005079209A2

WO2005079209A2 - Nanocrystalline material layers using cold spray

Info

Publication number: WO2005079209A2
Application number: PCT/US2004/039417
Authority: WO
Inventors: Julie M. Schoenung; George Kim; Leonardo Ajdelsztajn
Original assignee: The Regents Of The University Of California
Priority date: 2003-11-26
Filing date: 2004-11-24
Publication date: 2005-09-01
Also published as: WO2005079209A3

Abstract

This invention is a means of depositing or near-net-shape forming nanostructured metals, alloys and composites with desired hardness/strength, low porosity, and low oxidation, using a cold spray process (CSP) also known as hyperkinetic or kinetic spray. The CSP provides an efficient, fast and cost-effective means of producing such quality nanostructured deposits.

Description

CSP Methods for Producing Layers of Nanocrystalline Materials

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

60/525,387, filed November 26, 2003, and U.S. Provisional Application No. 60/577,231, filed June 23, 2004, the entire disclosures of which are hereby incorporated by reference in their entirety for all purposes.

FIELD OF INVENTION

[0002] The invention described herein relates to methods for manufacturing lightweight coatings, welds, and deposits of nanostructured materials such as aluminum, and compositions produced by said methods.

BACKGROUND

[0003] Nanostructured material is material with a microstructure the characteristic length of which is on the order of a few (typically 1-500) nanometers. Microstructure refers to the chemical composition, the arrangement of the atoms (the atomic structure), and the size of a solid in one, two, or three dimensions. Nanostructured materials have received increasing attention due to their superior physical and mechanical properties. Nanostructured ceramics are reported to exhibit unusually high ductility, whereas nanophase metals are noted to exhibit ultra-high hardness values (Suryanarayana, C, "Nanocrystalline materials," International Materials Reviews 40, 41-64 (1995), and Malow, T. R. and Koch, C. C, in Synthesis and Processing of Nanocrystalline Powder D. L. Bourell, Ed., The Minerals Metals and Materials Society, Warrendale, Pennsylvania, (1996) pp. 33). They are used in the electronic industry, telecommunication, electrical, magnetic, structural, optical, catalytic, biomedical, drug delivery, and in consumer goods.

[0004] Nanostructured materials are used as coatings and for the fabrication of bulk structures. One of the methods for the deposition of coatings is by thermally activated processes, including the "thermal spray processes" such as the High Velocity Oxy-Fuel (HNOF) process, plasma spray process, the chemical vapor condensation (CNC) process, and other combustion processes. Recent advances in HNOF include the synthesis of nanocrystalline feedstock powders suitable for HNOF thermal spraying; the development of new material systems, having the potential of producing nanocrystalline coatings with superior mechanical properties; the synthesis of nanocrystalline coatings from nanocrystalline feedstock powders; increased fundamental understanding on the formation of nanocrystalline coatings during HNOF spraying; and modeling of the HNOF process to optimize the experimental parameters. For example, a modified HNOF process has been used to fabricate dense coatings of Co/WC with remarkable properties (Kear, B. H. and Strutt, P. R., Naval Research Reviews 4, 4 (1995)).

[0005] A newer method for the deposition of coating uses the Cold Spray Process (CSP)

(U.S. Patent No. 5,302,414 to Alkhimov et al. (1994), McCune et al. "An Exploration of the Cold Gas-Dynamic Spray Method for Several Materials Systems," J. Thermal Spray Science and Technology, C.C. Berndt and S. Sampath, Ed., ASM International, 1995, pp. 1-5, and Dykhuizen et al. "Gas Dynamic Principles of Cold Spray", J. Thermal Spray Tech., 7:205 (1998)). CSP uses a supersonic gas jet (velocity of 5000 km/h) to accelerate solid fine powders (micron size) of various materials above a critical velocity at which particles impact, deform plastically and bond to the substrate to form the coating. CSP does not use plasma, combustion processes or any other thermal source, therefore, the spray environment is very clean and the material is not exposed to high temperatures. CSP has not previously been used for depositing nanocrystalline aluminum and other nanocrystalline coatings or for the production of near-net-shape bulk nanocrystalline materials.

SUMMARY

[0006] The present invention provides methods for the synthesis of fully dense nanostructured materials, such as nanostructured aluminum alloys and aluminum metal matrix composites. The compositions thus synthesized find use in the defense industry, aerospace industry, electronics industry, and in biotechnology and drug delivery, among others.

[0007] Described herein are methods for depositing at least one layer of a material having nanocrystalline grains on a substrate, said method having the steps of obtaining particles of the material, wherein the particles have nanocrystalline grains and using a cold spray process (CSP) to accelerate the particles towards the substrate, thereby depositing at least one layer of the material having nanocrystalline grains on the substrate. The method can be used to produce a coating, e.g., the substrate is usually different from the material; a weld, e.g., a joint, where the substrate is usually identical or similar to the material; or a deposit, e.g., enough layers of the material are present such that the substrate can be removed leaving behind a bulk solid, e.g., a near-net-shape bulk nanocrystalline composition.

[0008] The method can be used to create nanocrystalline layers of a wide variety of materials, e.g., pure metals and/or alloys. Examples of pure metals that can be used with the methods of the invention include, e.g., aluminum (Al), nickel (Ni), copper (Cu), and titanium (Ti). Examples of alloys that can be used with the methods of the invention include, e.g., aluminum alloy systems, nickel alloy systems, superalloys, Ni-Ti-C systems, W-C-Co systems, and MCrAlY systems, wherein M is Ni, Co, and/or Fe. In one embodiment, the material used is aluminum 5083 (Al 5083).

[0009] Alternatively, the methods can be used to create nanocrystalline layers of composite materials, e.g., a metallic matrix combined with one or more reinforcement phases. The metallic matrix can be, e.g., a pure metal or an alloy such as those described in the preceding paragraph. The reinforcement phases can be, e.g., oxides, nitrides, and/or carbides, e.g., silicon carbide (SiC), aluminum oxide (Al₂O₃), boron carbide (B₄C), and/or aluminum nitride (A1N).

[0010] A variety of substrates can be used depending on the application and final product desired. Examples of substrates that can be used include, e.g., steel, steel alloys, aluimnum, aluminum alloys, nickel, nickel alloys, superalloys, copper, silver, gold, and/or titanium. In one embodiment, the substrate is pure aluminum.

[0011] The method employs use of material particles, e.g., aluminum 5083 particles that have nanocrystalline grains. In one embodiment, the particles having nanocrystalline grains are produced using mechanical alloying techniques, e.g., using shaker type mills, attritor mills, planetary mills, ball mills, and/or rotary mills. In a further embodiment, the mechanical alloying technique is performed using attritor mills.

[0012] In another embodiment, the particles having nanocrystalline grains are produced by agglomerating nano-scale particles produced by chemical methods, e.g., through spray drying.

[0013] As described herein, the method of the invention uses material particles having nanocrystalline grains sizes in the range of 1-200 nm, 10-100 nm, and 20-40 nm. [0014] In yet another embodiment, the method employs material particles of two types: particles having nanocrystalline grains and particles without nanocrystalline grains. In one embodiment of this, the material has a reinforcement phase.

[0015] The method described and claimed herein uses a cold spray process (CSP, or

Hyperkinetic Spray Technique) to deposit the nanostructured material. CSP is performed by introducing the particles having nanocrystalline grains into a Laval nozzle through which a gas flows with a supersonic velocity. In some embodiments, the method has the additional step of heat treatment.

[0016] The claimed method produces at least one nanostructured layer with at least one of the following properties: limited oxidation, limited residual stress, limited grain growth, or a hardness exceeding that of conventional bulk alloys and coatings. In one embodiment, the method produces at least one layer having the property of a hardness exceeding that of conventional bulk alloys by a factor of 2-3. Hardness is measured using any standard microhardness test, e.g., a Vicker'.s Hardness Test.

[0017] Compositions produced by the method of the invention are also claimed and described herein. In one embodiment, the invention is a composition produced by the method having at least one layer of the material comprising nanocrystalline grains deposited on the substrate, wherein said nanocrystalline grains are 1-100 nm. Examples include nanostructured coatings and welds. In another embodiment, the invention is a composition produced by the method having at least one layer of the material comprising nanocrystalline grains, wherein said nanocrystalline grains are 1-100 nm. Examples include, e.g., a near-net-shape bulk solid.

[0018] Also claimed and described herein are compositions with properties similar to those produced by the methods described herein, e.g., nanostructured coatings, weld, and near- net-shape bulk solids, hi one embodiment, the composition is at least one layer of a material affixed to a substrate, wherein said at least one layer has nanocrystalline grains of the material and wherein said nanocrystalline grains are 1-100 nm. In another embodiment, are compositions having at least one layer of a material, wherein said at least one layer has nanocrystalline grains of the material and wherein said nanocrystalline grains are 1-100 nm. [0019] In further embodiments, the compositions of the invention have at least one of the following properties: limited oxidation, limited residual stress, limited grain growth, or a hardness exceeding that of conventional bulk alloys and coatings by a factor of 2-3.

[0020] hi another aspect, the invention provides methods for depositing at least one layer of nanocrystalline material on a substrate, where the methods comprise (a) providing metal powder and optionally a reinforcement, (b) mechanically milling at cryogenic temperatures to provide nanostructured powders, and (c) using a cold spray process to accelerate the powder towards a substrate thereby depositing at least one layer on the substrate. The metal powder can be Al, Be, Ca, Sr, Ba, Sc, N, Cr, Mn, Fe, Co, Νi, Cu, Zn, Y, Νb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, or combinations thereof, and preferably is an aluminum alloy. The reinforcement can be oxides, carbides, nitrides, borides, metals, intermetallics, or alloys. Thus, the reinforcement can be boron carbide, silicon carbide, aluminum nitride, or aluminum oxide.

[0021] In another aspect, the invention provides methods depositing at least one layer of nanocrystalline material on a substrate, the methods comprising (a) providing aluminum alloy and a reinforcement, (b) mechanically milling at a temperature of about -150 °C to about -300 °C, and (c) using a cold spray process to accelerate the powder towards a substrate thereby depositing at least one layer on the substrate. The aluminum alloy can additionally contain a metal powder such as Fe, Co, Νi, Cu, Zn, Y, Νb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, or combinations thereof. The reinforcement can be oxides, carbides, nitrides, borides, metals, intermetallics, or alloys. Thus, the reinforcement can be boron carbide, silicon carbide, aluminum nitride, or aluminum oxide.

[0022] These and other aspects of the present invention will become evident upon reference to the following detailed description, hi addition, various references are set forth herein which describe in more detail certain procedures or compositions, and are therefore incorporated by reference in their entirety.

BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic of strategies for synthesis of nanostructured materials.

[0024] Figure 2 is a schematic of a cold spray process setup. [0025] Figure 3 is an elemental mapping of the interface of nanocrystalline Al 5083 on a pure aluminum substrate.

[0026] Figure 4 are bright and dark field images of a nanocrystalline Al 5083 coating.

[0027] Figure 5 is a magnified region of a nanocrystalline Al 5083 coating, demonstrating the presence of elongated grains.

[0028] Figure 6 is a magnified region of a nanocrystalline Al 5083 coating, demonstrating twinning.

[0029] Figure 7 is a photograph of a conventional Al 5083 deposit produced using CSP.

DETAILED DESCRIPTION

I. Definitions

[0030] Unless otherwise stated, the following terms used in this application, including the specification and claims, have the definitions given below. It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. The practice of the present invention will employ, unless otherwise indicated, conventional methods of material science and physical chemistry, within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Lu L, Lai MO. Mechanical Alloying, Kluwer Academic Publishers, 1998, Boston, Massachusetts; Suryanarayana C. Progr Mater Sci 2001; 46: 1-184; Xie GQ, Ohashi O, Yoshioka T,jSong MH, Mitsuishi K, Yasuda H, Furuya K, Noda T MATERIALS TRANSACTIONS, 42 (9): 1846-1849 SEP 2001; and Cabanas-Moreno JG, Calderon HA, Umemoto M, ADVANCED STRUCTURAL MATERIALS MATERIALS SCIENCE FORUM, 442: 133-142 2003.

[0031] All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety.

[0032] The term "nanostructured material" generally refers to a material having average grain sizes on the order of nanometers. For purposes of the disclosure, nanostructured materials may include those alloys having an average grain size of 500 nanometers (nm) or less. [0033] As used herein, "cryomilling" describes the fine milling of metallic constituents at extremely low temperatures. Cryomilling takes place within a ball mill such as an attritor with metallic, ceramic, or composite balls. During milling, the mill temperature is lowered by using liquid nitrogen, liquid argon or liquid helium, hi an attritor, energy is supplied in the form of motion to the balls within the attritor, which impinge portions of the metal alloy powder within the attritor, causing repeated fracturing and welding of the metal.

[0034] As used herein, the term "powder" or "particle" are used interchangeably and encompass oxides, carbides, nitrides, borides, chalcogenides, halides, metals, intermetallics, ceramics, polymers, alloys, and combinations thereof. The term includes single metal, multi- metal, and complex compositions. Further, the terms include one-dimensional materials (fibers, tubes), two-dimensional materials (platelets, films, laminates, planar), and three- dimensional materials (spheres, cones, ovals, cylindrical, cubes, monoclinic, parallelolipids, dumbbells, hexagonal, truncated dodecahedron, irregular shaped structures, and the like).

[0035] As used herein, the terms "nanopowders" or "nanostructured powders," are used interchangeably and refer to powders having a mean grain size less than about 500 nm, preferably less than about 250 nm, or more preferably less than about 100 nm.

[0036] As used herein, the term "alloy" describes a solid comprising two or more elements, such as aluminum and a second metal selected from magnesium, lithium, silicon, titanium, and zirconium. In addition, the alloy may contain metals such as Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, or combinations thereof.

II. MODES OF CARRYING OUT THE INVENTION

[0037] Disclosed herein is the use of cold spray technology to produce nanostructured coatings, welds, and near-net-shape deposits. Included is a method of preparing nanocrystalline Al 5083 coatings and near-net-shape deposits, including optimization of the process parameters (nozzle design, powder morphology and size, gas temperature and pressure) in order to optimize the spray conditions ultimately producing porosity-free deposits, and characterization of the processed material. Also disclosed are compositions comprising at least one layer of the material comprising nanocrystalline grains of 1-100 nm.

UTILITY AND ADVANTAGES [0038] The invention is useful for lightweight applications where structural alloys or composites are used, e.g., military crafts, space/aerospace, and the automotive industries. This novel approach can be applied to high-end engineering applications where extreme working conditions are present and few suitable materials are available (aerospace industry, high performance sport applications, nuclear reactors and others), including space shuttle and satellite components, jet aircraft components, combustion engine components, gear box components, and missile components.

[0039] As described above, the cold spray process does not use plasma, combustion processes or any other thermal source. Therefore the spray environment is very clean and the material is not exposed to high temperatures. Therefore, sprayed nanocrystalline materials retain the fine grains.

[0040] This method is superior to some of the existing powder metallurgy (P/M) techniques for producing fine-grained alloys and composites components. The P/M approach consists of numerous steps to attain the final part, including powder degassing, HLPing, extruding, and machining. Using the approach described herein, the first three arduous steps of the P/M approach are eliminated.

[0041] In one aspect, the methods and processes of the invention can be used for depositing titanium anodes or anodes of its alloys for cathodic protection of reinforced concrete or steel. The reinforced concrete and structures made from the reinforced concrete may corrode in an environment where salt water may permeate therein. Most cathodic protection of steel in concrete is done with impressed current systems. Impressed current systems have the inherent need for periodic maintenance. As an alternative, the use of a zinc alloy has been proposed in a sacrificial anode method that provides long-term, stable and low- cost corrosion protection. However, a sacrificial anode formed of a zinc alloy has an exceedingly high potential (high positive), and it exhibits passivation while on concrete where the current output of the alloy anode decreases to a point where it no longer provides cathodic protection. The methods and processes of the invention provide coatings and materials of well-bonded, porous, pure titanium anodes having homogeneous structure, uniformly distributed pores, absence of cracks, superior ductility, lower electrical resistivity, greater bond strength, and little or no oxidation, thereby making them suitable for cathodic protection of reinforced concrete or steel. [0042] h another aspect, the methods and processes of the invention can be used for the manufacture of combustion engines, and parts for combustion engines, such as for use in vehicles for aerospace industry, including missile systems. For example, the combustion chamber can be coated with a metal or an alloy, such as Al, Al 5083, Ti, or Ni using the cold spray methods and processes described herein. The combustion engines thus treated provide better performance and require lower maintenance.

NANOCRYSTALLINE MATERIALS

[0043] Nanocrystalline materials are characterized by a microstructural length scale in the 1-500 nm regime. More than 50 volume percent of atoms could be associated with grain boundaries or interfacial boundaries when grain size is small enough. Thus, a significant amount of interfacial component between neighboring atoms associated with grain boundaries contributes to the physical properties of nanocrystalline materials (Birringer, R., "Nanocrystalline Materials," Mat. Sci. & Engr. Al 17, 33 (1989)). A number of techniques that are capable of producing nanocrystalline materials include gas condensation, mechanical alloying/milling, crystallization of amorphous alloys, chemical precipitation, spray conversion processing, vapor deposition, sputtering, electrodeposition, and sol-gel processing technique. Synthesis strategies for nanocrystalline materials can be divided into "bottom-up" (e.g., condensation and electrodeposition) and "top-down" (mechanical milling and severe plastic deformation), as shown in Figure 1. These techniques have several shortcomings. First, properties of nanocrystalline materials change dramatically with the presence of defects. As a result, microstructure and mechanical property data are often contradictory and difficult to interpret and predict. Second, in some cases such as inert gas condensation, it is difficult to consolidate defect-free, bulk samples due to the large surface areas involved, and their high environmental reactivity. Third, for techniques such as electrodeposition and severe plastic deformation, the critical nanoscale-sized grains are thermally unstable, unless stabilizing elements are introduced.

MILLING

[0044] Mechanical alloying is a high-energy ball milling process, in which elemental or pre-alloyed powders are welded and fractured to produce metastable materials with controlled microstructures. Today, mechanical alloying has been widely used to synthesize amorphous alloys, intermetallic compounds and nanocrystalline materials in large quantities for possible commercial use. During mechanical milling, particle welding and fracturing result in severe plastic deformation. Several factors can influence the process of mechanical alloying which include milling time, ball-to-powder charge ratio, milling environment, and the internal mechanics specific to each mill.

[0045] Cryogenic milling, often referred to as "cryomilling," is a technique in which a liquid nitrogen medium (77K) is introduced continuously to the milling process creating a slurry. The alloyed powders synthesized by this technique can be strengthened by aluminum oxy-nitride particles (2-10 nm in diameter with a mean spacing of 50-100 nm). The dispersoids are formed in-situ during cryomilling by the co-adsorption of nitrogen and oxygen onto clean aluminum surfaces. Cryogenic milling has the advantage of reducing oxygen contamination from the atmosphere and minimized heat generation during the milling process which favors fracturing over welding of ductile materials during the milling process. For example, the reported increase in thermal stability of cryomilled Fe-Al powders has been attributed in part to the formation of oxy-nitride particles during cryomilling. This reported high thermal stability is critical for consolidation of the cryomilled powder into bulk nanostructured samples.

[0046] Once the constituents of the metal or metal mixture and ceramic reinforcement are selected, powders can be cryomilled, wherein fracturing and welding of the metal particles is carried out in a very low temperature environment. Preferably the cryomilling of the metal powder takes place within an attritor. The attritor is typically a cylindrical vessel filled with a large number of metallic, ceramic, or composite spherical balls. A single fixed-axis shaft is disposed within the attritor vessel, and there are several radial arms extending from the shaft. As the shaft is turned, the arms cause the spherical balls to move about the attritor. When the attritor contains metal powder and the attritor is activated, portions of the metal powder are impinged between the metal balls as they move about the attritor. The force of the metal balls repeatedly impinges the metal particles and causes the metal particles to be continually fractured and welded together.

[0047] The milling of the powders at low temperatures imparts a high degree of plastic strain within the powder particles. During cryomilling, the repeated deformation causes a buildup of dislocation substructure within the particles. After repeated deformation, the dislocations evolve into cellular networks that become high-angle grain boundaries separating the very small grains of the metal. Grain size as small as approximately 10^" meter have been observed via electron microscopy and measured by x-ray diffraction. Structures having dimensions smaller than 10^"7 meter, such as those found in the material produced at this stage in the invented process, are commonly referred to as nanostructured.

[0048] During milling, an organic polymer, such as polyethylene glycol, polyvinyl alcohol, and the like, or organic acids, such as stearic acid, ethyl acetate, ethylene bidisteramide and dodecane may be added as one of the components to be milled with the metal powder. The addition of organic components promotes the fracturing of metal particles during milling, and prevents the severe adhesion of the metal powders onto the milling media and milling tools.

[0049] During milling, the temperature of the metal powder is preferably about -150 °C or lower, such as about -300 °C. Typically, the temperature of the metal powder is reduced by using liquified inert gases, such as liquid nitrogen (bp -196 °C), liquid argon (bp -186 °C) or liquid helium (bp —269 °C). The use of liquid gases is a convenient way to lower the temperature of the entire cryomilling system. Further, surrounding the metal powder in liquid gases limits exposure of the metal powder to oxygen or moisture. In operation, the liquid gas is placed inside the attritor, in contact with the metal particles and the attritor balls.

[0050] The operating parameters of the cryomill will depend upon the size of the attritor.

For example, a 150 liter (40 gal) attritor is preferably operated at a speed of about 100 rpm. The amount of powder added to the attritor is dependent upon the size and number of balls within the attritor vessel. For a 150 liter attritor filled with 640 kg of 0.25" diameter steel balls, up to approximately 20 kg of metal powder may be milled at any one time. Milling is continued for a time sufficient to reach an equilibrium nanostructured grain size within the metal.

[0051] After milling, the metal alloy powder is a homogenous solid solution of aluminum and the secondary metal, optionally having other added tertiary metal components and optionally having minor amounts of metallic precipitate interspersed within the alloy and optionally having ceramic reinforcements interspersed within the alloy. Grain structure within the alloy is very stable and grain size is less than 500 nm. Depending on the alloy and extent of milling the average grain size is less than about 300 nm, and preferably may be lower than about 100 nm. [0052] To produce bulk nanocrystalline samples from the cryomilled powder, a consolidation route is employed. The consolidation process involves the established approach of degassing, hot isostatic pressing (HlPing) and extrusion. Optimization of the consolidation parameters in order to achieve a fine grain structure has been extensively investigated; however, despite thermal stability, limited grain growth is unavoidable. Grain size of bulk aluminum alloys samples after consolidation varies from about 200 nm to about 900 nm depending on the processing conditions.

METALS

[0053] The methods of the present invention can be used with metals with low melting temperatures, such as Ni, Fe, Cu, Zn, and Al, and mixtures thereof, or with refractory metals, such as Ti, Nb, Mo, Ta, and W, metal matrix composites, and intermetallics. In one aspect, the metal powder to be processed is pre-alloyed powder that can be used directly in the cold spray process of the cryomilling process. In another aspect, the powder to be processed is non-alloyed powder wherein two or more different metal powders are added to the cryomill, and the cryomilling process is used to mix together the metal constituents thereby alloying the metals.

[0054] In the practice of the methods, the starting metals are preferably manipulated in a substantially oxygen-free atmosphere. For example, if the metal is aluminum, the aluminum is preferably supplied by atomizing the aluminum from an aluminum source and collecting and storing the atomized aluminum in a container under an argon or nitrogen atmosphere. The inert atmosphere prevents the surface of the aluminum particles from excessive oxidation and prevents contaminants such as moisture from reacting with the raw metal powder. Preferably, other metals that can readily oxidize are treated in the same manner as aluminum prior to milling.

[0055] The metal for use in the invention can be selected from a Group 2A metal, such as Be or Mg, and mixtures thereof, a Group 3 A metal, such as Al, and mixtures thereof, a

Group 4A metal, such Sn or Pb, and mixtures thereof, a Group V metal, such as V or Nb, and mixtures thereof, a Group VI metal including Cr, W, or Mo, and mixtures thereof, VII metal, such as, Mn, or Re, a Group VIII metal including Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, and mixtures thereof, the lanthanides, such as Ce, Eu, Er, or Yb and mixtures thereof, or transition metals such as Cu, Ag, Au, Zn, Cd, Sc, Y, or La and mixtures thereof. Specific examples of mixtures of metals, such as bimetallics, which may be employed by the present invention include Fe — Al, Al— Mg, Co— Cr, Co— W, Co— Mo, Ni— Cr, Ni— W, Ni— Mo, Ru— Cr, Ru— W, Ru— Mo, Rh— Cr, Rh— W, Rh— Mo, Pd— Cr, Pd— W, Pd— Mo, Ir— Cr, Ir— W, Pt— W, and Pt— Mo. Preferably, the metal is aluminum, iron, cobalt, nickel, titanium, copper, molybdenum, or a mixture thereof. The metal or mixture of metals can be processed to obtain the desired grain size and grain size distribution. Examples of elemental compositions include, but are not limited to, (a) precious metals such as platinum, palladium, gold, silver, rhodium, ruthenium and their alloys; (b) base and rare earth metals such as iron, nickel, manganese, cobalt, aluminum, copper, zinc, titanium, samarium, cerium, europium, erbium, and neodymium; (c) semi-metals such as boron, silicon, tin, indium, selenium, tellurium, and bismuth; (d) non- metals such as carbon, phosphorus, and halogens; and (e) alloys such as steel, shape memory alloys, aluininum alloys, manganese alloys, and superplastic alloys.

[0056] The starting metal powder can additionally be mixed with a certain amount of reinforcement, also called ceramic composition (oxide, carbide, nitride, boride, chalcogenide), or an intermetallic composition (aluminide, silicide) or an elemental composition. Examples of ceramic composition include, but are not limited to (a) simple oxides such as aluminum oxide, silicon oxide, zirconium oxide, cerium oxide, yttrium oxide, bismuth oxide, titanium oxide, iron oxide, nickel oxide, zinc oxide, molybdenum oxide, manganese oxide, magnesium oxide, calcium oxide, and tin oxide; (b) multi-metal oxides such as aluminum silicon oxide, copper zinc oxide, nickel iron oxide, magnesium aluminum oxide, calcium aluminum oxide, calcium aluminum silicon oxide, indium tin oxide, yttrium zirconium oxide, calcium cerium oxide, scandium yttrium zirconium oxide, barium titanium oxide, barium iron oxide and silver copper zinc oxide; (c) carbides such as silicon carbide, boron carbide, iron carbide, titanium carbide, zirconium carbide, hafnium carbide, molybdenum carbide, and vanadium carbide; (d) nitrides such as silicon nitride, boron nitride, iron nitride, titanium nitride, zirconium nitride, hafnium nitride, molybdenum nitride, and vanadium nitride; (e) borides such as silicon boride, iron boride, titanium diboride, zirconium boride, hafnium boride, molybdenum boride, and vanadium boride; and (f) complex ceramics such as titanium carbonitride, titanium silicon carbide, zirconium carbonitride, zirconium carboxide, titanium oxynitride, molybdenum oxynitride, and molybdenum carbonitride.

[0057] In another aspect, the starting metal powders can be mixed with some compounds other than ceramics. Such compounds may include, for instance, organometallic compounds such as metal alkoxides, as well as nitrates, carbonates, sulfates, and hydroxides. These may be in the form of a powder or a liquid.

[0058] In the case of preparing a mixture containing ceramic and metals or alloys in obtaining the sintered compact according to the present invention, there is no particular limitation on the molar equivalents for the ceramic to be added. However, the molar ratio of metals to added ceramic reinforcement is preferably 1000:1 to about 1:1, preferably about 500:1 to about 5:1, and more preferably about 100:1 to about 10:1

COLD SPRAY PROCESS

[0059] As disclosed herein, the Cold Spray Process (CSP, or Hyperkinetic Spray

Technique) represents a solution to the challenges of near-net shape spray forming of nanocrystalline metallic alloys. As described further herein, this spraying technology uses a supersonic gas jet (velocity of 5000 km/h) to accelerate solid fine powders (micron size) of various materials above a critical velocity at which particles impact, deform plastically and bond to the substrate to form the coating. Failure to accelerate the particles above the critical velocity results in the bouncing back of the latter from the substrate. Typically, copper particles accelerated at 250 m/s (below the critical velocity of copper) bounce back from the substrate and particles accelerated at 900 m/s (above copper critical velocity) bond to the substrate and build up to form a coating.

[0060] The cold spray process (CSP) can be used to spray the metals disclosed above, such as zinc, copper, aluminum, titanium, and nickel on various substrates such as tin, copper, aluminum alloys, brass, glass and tool steel, and the like. However, CSP has not yet been used to deposit material that has nanocrystalline grains to form nanocrystalline coating, welds, and deposits.

[0061] As opposed to other spraying processes, the Cold Spray Process does not involve a major heating of the carrier fluid and the driven solid particles. Although a heater is often used to pre-heat the carrier gas to temperatures near 600°C to maximize the jet velocity, the gas rapidly cools to room temperature inside the nozzle due to the quick conversion of thermal to kinetic energy. Furthermore, it is possible to circumvent the use of a heater by using a gas with low molecular weight such as helium. Consequently, the injected particles are never in contact with high temperature gas. As a result, the particles maintain solid form close to or below room temperature throughout their flight, from the injection location to the substrate. Theoretical studies on the impact dynamics have also shown that the kinetic energy of the particle is transformed into deformation and bonding energy and that very little heating of the particle occurs during the deformation/bonding process. Accordingly, Cold Spray is often referred to as a solid-state process in which high temperature transformations such as oxidation and melting are minimized. This alone represents a major advantage over all the other existing spraying techniques from the standpoint of keeping the original nanostructure and chemical composition of the powder. For the particular case of cryomilled powder, it is possible to avoid grain growth during cold spray deposition, which leads to a nanocrystalline deposit with a grain size similar to that of the cryomilled powder. Until now, tins was not possible with conventional consolidation techniques. In addition, given that the particles are not heated/melted during their flight, it becomes possible to recycle the non-deposited particles; this represents a major economic benefit over all other spraying techniques.

EQUIPMENT

[0062] The solid particles to be deposited on the substrate can be injected in a supersonic gas jet to be accelerated above the critical velocity. A high-pressure gas can be forced to flow through a de Laval (converging / diverging) nozzle, generating the high-speed jet. A simplified schematic of the process is illustrated in Figure 2. The nozzle has a geometry designed to promote the gas-particle momentum transfer and to avoid shock waves in the jet, and can be achieved by optimizing the throat/exit area ratio, the length and the interior shape of the nozzle.

[0063] The nozzle can be designed to minimize the mass flow rate to reduce the operating costs, for machining simplicity and cost effectiveness for its manufacture, for minimizing nozzle erosion and to keep the nozzle exit velocity less than about Mach 3 in order to minimize the shock wave-particle interaction in front of the substrate. The axi-symmetric cold spray nozzle preferably has a diverging length of about 150 mm to about 500 mm, preferably about 200 mm to about 330 mm, or more preferably about 250 mm to about 300 mm. The nozzle preferably has a throat diameter of about 0.1 mm to about 12 mm, preferably about 0.5 mm to about 5 mm, or more preferably about 1.2 mm to about 3 mm. Further, the nozzle preferably has an exit diameter of about 1 mm to about 20 mm, preferably about 4 mm to about 15 mm, or more preferably about 5 mm to about 9 mm. As one of skill in the art will recognize, the diverging length, the throat diameter and the exit diameter can be modified depending on the gas and the metal used in order to achieve the design requirements listed above. Thus, in one embodiment, the nozzle has a diverging length of 270 mm, a 2 mm throat diameter and an exit diameter of 7.3 mm. The predicted particle exit velocities, for particle diameters of 1, 5, 10, 15, 20, 40, 50, 60, and 100 μm are 812, 1054, 1052, 980, 918, 748, 694, 665, and 602 m/s, respectively. Thus, an optimum particle diameter between 5 and 10 μm but that any diameter between 20 and 50 μm will achieve an exit velocity over the design specification of 700 m/s. The lower exit velocities for particles of 1 μm is due to weak compression waves present in the nozzle, near the exit, that contribute to slowing these low- momentum particles. The lower exit velocities for particles over 20 μm are due to their higher mass.

[0064] A commercial powder feeder (Praxair-Model 1264) can be used to inject the particles in the nozzle. The heater can be made of a stainless steel tube connected to a power supply. By activating the power supply, the tube acts as an electrical resistance and heats up. The gas is forced through the tube and heats up by convection. It is possible to operate the system without the heater. The substrate (the piece to be coated) is mounted on a motorized plate.

NEAR-NET SHAPE SPRAY FORMING ₍

[0065] It is known that successful deposition of aluminum using the Cold Spray Process requires a higher velocity than when other metals are deposited. The critical velocity of aluminum is above 900 m s while it is around 650 m/s for copper. The higher required velocity is attributed to the oxide layer that forms around the aluminum particle that must be broken before the aluminum particle itself can deform. Furthermore, the initiation of deposition of aluminum can depend on the substrate material composition and not the substrate hardness. Initiation of deposition is much easier with a copper substrate than with a brass substrate and the initiation of deposition is much easier with a brass substrate than aluminum or carbon steel substrate where only the smallest particles achieve a good bonding. However, regardless of the substrate the growth rate of the layers is approximately the same once initial deposition has been successful. ) [0066] Accordingly, in one embodiment the substrate to be used for near net-shape spray forming using the Cold Spray technology is copper. Smaller particles reach higher velocities at the exit of the spray nozzle than larger ones, however, smaller particles also experience a larger deceleration through the shock wave present in front of the substrate and are usually tougher to inject. Larger particles can lead to a larger growth rate, once initiation is obtained but they require a longer nozzle to reach the critical velocity, due to the boundary layer and shock wave problems.

[0067] The parameters for CSP can be changed depending on the materials used and the desired final composition. Carrier gas, velocity, particle size, and temperature can be optimized for each application; such optimization is well known to one of skill in the art. For example, different carrier gases that can be used include, e.g., nitrogen (N) and/or helium (He). Velocities used can fall within the ranges of, e.g., 1-1000 m/s, 100-900 m/s, 600-900 m/s; the choice of velocity is dependent on the material used and particle size. The appropriate particle size can range between, e.g., about 1-50 μm, e.g., 20 μm or 10 μm or 5 μm, or any size in between about 1 and about 50 μm. More details on the optimization and ranges of CSP parameters are described in Example 1 below.

EXAMPLES

[0068] Below are examples of specific embodiments for carrying out the present invention. The examples are offered for illustrative purposes only, and are not intended to limit the scope of the present invention in any way. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.), but some experimental error and deviation should, of course, be allowed for.

[0069] X-ray diffraction (XRD) measurements were carried out with a Scintag XDS-

2000 diffractometer equipped with a graphite monochromator using Cu K_α radiation. A commercially available particle size analyzer (Coulter LS) was employed to determine the particle size distributions of the powders. The morphology of the powders (before and after cryomilling) and the coating microstructure were examined using a Philips XL30 FEG SEM. Prior to SEM observations, coating samples were sectioned from a transverse section and prepared by standard metallographic techniques. Backscattered electron images were obtained, and energy dispersive spectrometry (EDS) analysis was conducted on the coating samples. TEM studies on the coatings were performed using a Philips CM-12 microscope operated at 120 kV. Coating samples for TEM studies were mounted in an acrylic resin compound and sectioned in thin slices (60 nm) by a diamond knife in an MT600-XL ultramicrotome. Nickers microhardness tests were performed on the cross-section of the deposits using 300 gf of load and a dwell time of 15 s. Nanoindentation tests were performed using an MTS Nanoindenter^® XP (Berkovich indenter) on the cross-section of the cryomilled powder and the cold sprayed coating. Powder samples were prepared for nanoindentation by mixing the 5083 cryomilled powder with a conductive molding compound. The samples were then ground (1200 grit) and polished (6, 3, 1, 0.1 μm diamond slurry and 0.05 μm colloidal silica particles). The same polishing procedures were used to prepare the cross-section of the cold sprayed coating. The continuous stiffness measurement (CSM) approach was used to determine the hardness values from the nanoindentation tests.

Example 1 Method for producing a nanostructured coating

Powder processing and characterization

[0070] The first step, powder synthesis, was achieved using mechanical alloying techniques, where a conventional grain size material (micron range grain size) was reduced to a nanocrystalline grain size material. The advantage of using mechanical alloying is the capability of the process to economically produce significant quantities of nanocrystalline powders for a variety of alloy systems and composites.

[0071] Mechanical alloying is a process by which the microstructure of elemental or pre- alloyed powder particles is modified by repeated welding and fracture events. This has been observed to result in metastable microstructures including nanocrystalline grain sizes, supersaturated solid solutions and amorphization. The process is performed using an apparatus in which milling balls are continuously agitated by external vibration (shaker-type mills) or rotating impeller (attritor mills). Experimental variables affecting the final powder characteristics include shaft speed, ball size and ball to powder mass ratio.

[0072] The powders were mechanically milled in a liquid nitrogen environment

(cryomilling). The addition of cryogenic liquid media to the milling environment greatly affects the attritor milling process. The cryomilling used a modified Union Process 01 -ST attritor mill with a grinding tank capacity of 0.0057 m³. Stainless steel balls (0.635 cm in diameter) were used as the grinding media, with a typical powder-to-ball mass ratio of 1 :20. In the cryomilling experiments, liquid nitrogen was continuously fed into the mill to ensure complete immersion of the powders and to maintain it at liquid nitrogen temperature throughout the milling. After completion of the milling process, the powders were removed from the grinding tank of the attritor frame and placed in the argon-filled glove box for evaporation.

[0073] The particle size distributions of the milled powders were determined using a

Microtrac Standard Range Particle Analyzer. SEM and TEM were also used to determine agglomerate size, average grain size, and aspect ratio of the powders under different milling conditions. Contamination due to the wear of the grinding media and oxidation reactions can change the chemical composition and the phase distribution of the starting powder during mechanical alloying/milling, particularly when milling for extended periods of time. These contaminants could play an important role on the mechanical behavior and thermal stability of the nanocrystalline material, so it is important to characterize the level and type of contamination in the cryomilled powders.

Cold spray of the cryomilled powder

[0074] In the cold spray process, a gas is accelerated to a supersonic velocity in a de'Laval-type nozzle, i.e., a converging diverging nozzle. The material to be deposited is injected into a gas stream in powder form at the inlet of the nozzle, accelerated by the gas in the nozzle, and propelled toward the substrate to form the deposit. Above a certain particle velocity, which is characteristic for each respective powder material and its properties, the particles form a dense and solid adhesive coating on the substrate surface. Upon impact the particles must undergo sufficient deformation to adhere to the surface. The carrying gas can also be heated before entering the nozzle to increase gas and particles velocities. However, the gas temperature is not high enough to promote melting of the particles during flight. In comparison to other thermal spray processes, e.g., oxidation, undesirable phase transformation, loss of nanocrystalline microstructure during spray, can be avoided using the cold spray process.

[0075] Optimum particle size can be determined as follows, where a nozzle designed to accelerate particles of 20 μm diameter and smaller beyond the 900 m/s critical velocity was used. These experiments consisted of spraying different powder sizes (20μm, lOμm, 5μm) using the nozzle design parameters and testing the speed of initiation of deposition and quality of the coatings obtained. A Particle-Image-Nelocimetry (PIN) system was used to track the particle velocity on impact and find out if the critical velocity of the nanostructured powder was also 900 m/s and if the velocity changed with the powder size. The results of these experiments provide the optimum particle size to be used for the near-net-shape spray forming application.

[0076] _, A nozzle was then selected that was specific for the optimum particle size and that minimized the main gas flow rate as well as ensured that the particles were accelerated beyond the critical velocity.

[0077] The selected nozzle was used with its design operating parameters and the chosen particle size to optimize the coatings obtained by varying the stand-off distance, the feed rate and the traverse rate of the specimen.

[0078] Depending on the required properties of the final product, heat treatment can be used.

Methods of analysis

[0079] X-ray diffraction analysis was performed on the sprayed deposits for phase identification and determination of the average grain size. The microstructure was observed with a Philip XL30 FEG scanning electron microscope equipped with energy dispersive analysis. The sprayed deposit was mounted in a conductive mold that was mechanically ground to provide a polished surface. Also samples are sectioned into 3mm x 3mm samples, mechanically ground, and jet polished using a solution containing 20 % volume sulfuric acid and 80 % volume methanol for transmission electron microscopy (TEM) observations.

[0080] Miniaturized tensile samples were machined from the deposit in order to investigate its mechanical behavior. Nanoindentation and instrumented indentation techniques were also applied to interrogate the mechanical response of the deposited nanocrystalline materials.

Example 2 A Nanostructured Al 5083 Coating [0081] Aluminum 5083 powder was mechanically milled under liquid nitrogen and subsequently sprayed using hyperkinetic spray technique. The cryomilled powder was sprayed onto grit blasted Al substrates using the cold spray process. The cold spray facility consists of a spray chamber, a pressure controlled driving gas system, and a commercial powder feeder (Praxair, model 1264) linked to a carrier gas flow controller (Figure 2). The carrier gas was intentionally not heated to reduce the likelihood of grain growth. The substrate holder was motorized thereby allowing lateral movement of the substrate. The nozzle geometry has a diverging length of 270 mm, a throat diameter of 2 mm and an exit diameter of 7.3 mm. Helium at room temperature was used as the driving and carrier gas. The stagnation inlet pressure was set at 1.7 MPa, while the injection pressure was set to provide a pressure difference of 80 kPa at the injection site. One pass with a low transversal scan speed was performed to build-up the thickness of the coating on the substrate. The resulting nanocrystalline coatings were evaluated using XRD, SEM, TEM, micro- and nanoindentation. The coatings showed negligible porosity and excellent interface with the substrate material. Hyperkinetic spray technique demonstrated a great potential to spray nanocrystalline materials (low temperature and low oxidation), not only from the standpoint of coating fabrication, but also as a potential for near net-shape fabrication of bulk nanocrystalline materials.

[0082] Figure 3 shows that nanocrystalline aluminum alloy (Al 5083) powder produced by cryomilling techniques can be cold sprayed in order to produce a nanocrystalline coating with a very clean coating/substrate interface.

[0083] TEM observations show that minimal or no grain growth is observed after the spray process. The microstructures of the coating, shown in Figures 4, 5 and 6, are similar to that observed in cryomilled 5083 powders (Zhou et al. Acta Mater., 51(10): 2777 (2003)). Thus, there is no or minimal grain growth during the cold spray process.

[0084] The observed microstructures have features such as nano twins. Only recently, molecular dynamic (MD) simulations have predicted deformation twinning in nanocrystalline face-centered-cubic (fee). Al, however, deformation twin has not been observed in coarsegrained Al due to its high stacking fault energy. The deformation twins have been observed in nanocrystalline Al films produced by physical vapor deposition and on nanocrystalline Al produced by cryogenic ball milling. Therefore, the methods and processes of the invention are useful for investigating novel and not very common deformation mechanisms that have a stronger influence on the overall mechanical behavior of the material.

[0085] The hardness of the nanocrystalline Al 5083 coating was measured using the

Nicker' s Hardness Test. The results showed a 100% increase in hardness when compared to a cold sprayed coarse grained coating (using conventional atomized powder) (see Table 1). These results show that the nanocrystalline Al 5083 deposits have a great potential for structural applications where low density and high strength materials are required.

Table 1. Hardness of the conventional and nanocrystalline 5083 Al coatings

[0086] Figure 7 is a photograph of a deposit made with CSP using conventional (non- nanocrystalline) material, demonstrating the ability to spray multiple layers onto a substrate, e.g., a cube, to make bulk material.

[0087] The cold sprayed coatings using the cryomilled powder are thus characterized by an almost undetectable interface between the Al 5083 coating and the pure Al substrate, suggesting good bonding between the coating and the substrate, a coating thickness determined to be about 270 μm, the presence of nanocrystalline grains with a grain size distribution of about 10-30 nm, and a substantial increase in hardness for the nanocrystalline coating.

Example 3 A Nanostructured Ni Coating

[0088] The experimental method described in Example 2 was followed, except nickel powder was used instead of Al 5083 powder. The nanocrystalline Ni was cold spray deposited with a hardness of 605 ± 13 (HV 300g) or 5.93 Gpa. The grain size of 27 ± 7 nm was obtained by XRD, with essentially no porosity. Example 4 Cathodic protection of reinforced concrete

[0089] The experimental method described in Example 2 is followed, except titanium or titanium alloy is used instead of Al 5083 powder. The titanium or titanium alloy is cold spray processed onto reinforced concrete. The reinforced concrete thus treated allows for better current distribution to the reinforcing steel.

[0090] While the invention has been particularly shown and described with reference to a preferred embodiment and various alternate embodiments, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention. All printed patents and publications referred to in this application are hereby incorporated herein in their entirety by this reference.

Claims

We Claim:

1. A method for depositing at least one layer of a material comprising nanocrystalline grains on a substrate, said method comprising the steps of: a) obtaining particles of said material, wherein said particles comprise nanocrystalline grains; and b) using a cold spray process (CSP) to accelerate said particles towards said substrate, thereby depositing at least one layer of said material comprising nanocrystalline grains.

2. The method of claim 1 , wherein said method produces a coating, a weld, or a deposit.

3. The method of claim 1 , wherein said material is a pure metal.

4. The method of claim 3, wherein said metal is selected from the group consisting of aluminum (Al), nickel (Ni), copper (Cu), and titanium (Ti).

5. The method of claim 1 , wherein said material is an alloy.

6. The method of claim 5, wherein said alloy is selected from the group consisting of aluminum alloy systems, nickel alloy systems, superalloys, Ni-Ti-C systems, W-C-Co systems, and MCrAlY systems, wherein M is Ni, Co, and/or Fe.

7. The method of claim 5, wherein said alloy is aluminum 5083.

8. The method of claim 1, wherein said material is a composite, said composite comprising a metallic matrix and a reinforcement phase.

9. The method of claim 8, wherein said metallic matrix comprises a pure metal or an alloy.

10. The method of claim 8, wherein said reinforcement is selected from the group consisting of oxides, nitrides, and carbides.

11. The method of claim 8, wherein said reinforcement is selected from the group consisting of silicon carbide (SiC), aluminum oxide (Al₂O₃), boron carbide (B₄C), and aluminum nitride (A1N).

12. The method of claim 1, wherein said substrate comprises one or more compounds selected from the group consisting of steel, steel alloys, aluminum, aluininum alloys, nickel, nickel alloys, superalloys, copper, silver, gold, and titanium.

13. The method of claim 1, wherein said substrate comprises pure aluminum.

14. The method of claim 1 , wherein said particles comprising nanocrystalline grains are produced using mechanical alloying techniques.

15. The method of claim 14, wherein said mechanical alloying is performed using shaker type mills, attritor mills, planetary mills, ball mills, or rotary mills.

16. The method of claim 14, wherein said mechanical alloying is performed using attritor mills.

17. The method of claim 1 , wherein said particles comprising nanocrystalline grains are produced by agglomerating nano-scale particles produced by chemical methods, wherein said agglomeration is performed through spray drying.

18. The method of claim 1 , wherein said nanocrystalline grain size is 1 -200 nm.

19. The method of claim 18, wherein said nanocrystalline grain size is 10- 100 nm.

20. The method of claim 18, wherein said nanocrystalline grain size is 20-40 nm.

21. The method of claim 1 , wherein said particles of said material comprise particles comprising nanocrystalline grains and particles without nanocrystalline grains.

22. The method of claim 21 , wherein said material further comprises a reinforcement phase.

23. The method of claim 1 , wherein said CSP is performed by introducing said particles comprising nanocrystalline grains into a Laval nozzle through which a gas flows with a supersonic velocity.

24. The method of claim 1 , further comprising the step of heat treatment.

25. The method of claim 1 , wherein at least one layer comprising nanocrystalline grains comprises limited oxidation, limited residual stress, and limited grain growth.

26. The method of claim 1, wherein at least one layer comprising nanocrystalline grains comprises a hardness exceeding that of conventional bulk alloys and coatings.

27. The method of claim 26, wherein the at least one layer comprising nanocrystalline grains has a hardness exceeding that of conventional bulk alloys by a factor of 2-3.

28. A composition produced by the method of claim 1 , comprising the at least one layer of the material comprising nanocrystalline grains deposited on the substrate, wherein said nanocrystalline grains are 1-100 nm.

29. A composition produced by the method of claim 1 , comprising the at least one layer of the material comprising nanocrystalline grains, wherein said nanocrystalline grains are 1-100 nm.

30. A composition comprising at least one layer of a material affixed to a substrate, wherein said at least one layer comprises nanocrystalline grains of the material and wherein said nanocrystalline grains are 1-100 nm.

31. A composition comprising at least one layer of a material, wherein said at least one layer comprises nanocrystalline grains of the material and wherein said nanocrystalline grains are 1-100 nm.

32. The composition comprising at least one layer of a material, wherein said at least one layer comprises nanocrystalline grains of the material and wherein said nanocrystalline grains are 1-100 nm.