WO2008140638A2 - Ultrasonic consolidated nanostructured materials and methods of manufacturing same - Google Patents

Abstract

A method for manufacturing a dense consolidated volume of a nanostructured material is provided. The method includes providing a plurality of portions formed from a high strain deformation process and having a nano-sized grain structure therein. One surface of each portion may then be contacted against a surface of another portion. Thereafter, ultrasonic vibrations may be applied along at least one of the portions to permit the contacting surfaces to bond with one another without substantially melting the portions, so as to form a consolidated volume. A bulk ultrasonically consolidated nanostructured material or mass is also provided.

Description

ULTRASONIC CONSOLIDATED NANOSTRUCTURED MATERIALS AND METHODS OF MANUFACTURING SAME

TECHNICAL FIELD

[0001] The present invention relates to consolidated nanostructured materials and methods of manufacturing such materials, and more particularly, to ultrasonic consolidated nanostructured materials and methods of manufacturing ultrasonically consolidated nanostructured materials.

GOVERNMENT CONTRACT

[0002] Research in connection with the subject matter of this application was conducted through the support of the Federal Government under (1) contract FA8651-05-C-0120, a Phase II SBIR with the Air Force Research Laboratory entitled: "High Performance Nanostructured Tantalum for Warhead Applications" and (2) contract NSF0637989, a Phase I STTR with the National Science Foundation entitled: "Novel Consolidated Method for Nanostructured Metals". The United States Government may have certain rights in this invention.

BACKGROUND ART

[0003] Manufacturing industries constantly require advancement in materials in order to extend functionality, increase efficiency, mitigate environmental impact, and a host of other compelling reasons. One critical measure of advancement is the strength-to- weight ratio of the materials. As such, significant research has been carried out to address this issue.

[0004] Over the past decade, nanotechnology has emerged as a promising route to provide materials that may satisfy the most demanding requirements. Broadly, nanotechnology is based on controlling various features at the submicrometer level, and may provide a new paradigm that can be applied to a broad range of scientific and engineering disciplines. For materials, it has been established that extending microstructural refinement down to the range of nanometers can cause a change in the characteristics of the material, which can often result in significant property improvements. This is because reduction or structural refinement of intrinsic grain size can generally result in a material with relatively harder and stronger properties. For instance, the work of Gleiter and others showed that materials made by consolidating nanocrystalline powders have novel attributes that may not typically be found in conventional materials having grain sizes on the order of micrometers or tens or hundreds of micrometers. H. Gleiter, Nanocrystalline Materials, Progress in Materials Science, 33, pp 223-315 (1989); R. W. Siegel, Creating Nanophase Materials, Scientific American, pp 74-79 (Dec. 1996).

[0005] It is also believed that nanostructured solids or materials made from nanocrystalline materials may have improved strength, ductility, hardness, formability, and resistance to crack propagation. Furthermore, nanostructured material have been observed to possess interesting chemical, optical, magnetic and electrical properties. Nanotechnology has opened the door to an entirely new class of advanced materials, and nanostructured materials may hold significant potential for a broad range of commercial as well as military applications.

[0006] However, achieving the full potential of nanostructured materials in bulk components has been hampered by high production costs and a lack of processing knowledge base. Indeed, the lack of even small bulk test specimens having well characterized nanostructured grains has limited systematic studies of structure-property relationships, let alone development of bulk components. Furthermore, the particles or materials that can be produced generally suffer from agglomeration and contamination. As such, the prospects for economical high volume production of components are currently generally poor.

[0007] In particular, when forming bulk materials from consolidating nanostructured metals, alloys, and/or composites produce with, for example, particles made from chemical precipitation or other techniques, certain critical issues must be addressed: [0008] 1) Purity - as with any engineering material, impurities in the source or starting materials will impact the properties of the end product;

[0009] 2) Oxidation - since the particles or powders are substantially small, resulting in relatively large surface areas, the particles can be highly sensitive to oxygen and/or moisture, which can lead to oxide formation; and

[00010] 3) Densification - the particles or powders need be in a state that allows full densification during consolidation, since the nanosized powders can consist of hard agglomerates, which typically have poor packing characteristics and which may not consolidate well, that can yield bulk forms with low density, and poor performance characteristics.

[00011 ] Currently, a wide variety of consolidation techniques are known in

Powder Metallurgy (PM). Such techniques include cold uniaxial pressing, cold isostatic pressing, sintering, hot isostatic pressing, hot forging, and metal injection molding. However, such consolidation techniques have not been proven successful for nanomaterials. In particular, the issue of porosity and density, both of which need to be minimized within the bulk consolidated nanostructured materials (i.e., consolidated mass), such as metals, remain when employing currently available techniques. The presence of residual porosity in the consolidated material, for example, can affect material properties, including strength.

[00012] In addition, when producing dense products from feedstock having nanoparticulates or nanostructured materials, the use of known Powder Metallurgy consolidation techniques can result in significant grain growth that can reduce or eliminate the benefits associated with nanomaterials. Furthermore, when PM techniques are adapted to mitigate grain growth, these techniques can lead to the production of materials that may be far from the theoretical maximum density of the materials, such that the benefits (e.g., strength) of nanostructuring may be diminished in the bulk material.

[00013] Accordingly, it would be desirable to provide a method for making nanostructured feedstock materials having reduced grain size with increased hardness and strength, and which can subsequently be consolidated to manufacture substantially fully dense nanostructured bulk materials with minimal porosity, so that the benefits associated with nanostructured materials, such as extended functionality and increased efficiency, can be realized.

SUMMARY OF THE INVENTION

[00014] The present invention provides, in one embodiment, a method for manufacturing bulk, consolidated volumes of nanostructured materials. In particular, the method includes initially machining at least one source or starting material using a high strain deformation process to generate a plurality of feedstock materials or portions having a nano-sized grain structure therein. In an embodiment, each feedstock portion may have an average Vickers hardness ranging up to over about 300 percent of that of the source material. Additionally, the feedstock portions and may be provided with various geometric shapes, including fragments, chips, particles, strips, foils, platetlets, sheets, or continuous rolls. Next, a surface of one feedstock portion may be made to contact against a surface of another feedstock portion. Thereafter, ultrasonic vibrations may be applied along at least one of the feedstock portions to permit the contacting surfaces to bond with one another without substantially melting the feedstock portions, so as to form a consolidated volume.

[00015] In another embodiment, the present invention provides a method for manufacturing a consolidated volume of nanostructured materials that includes initially providing a plurality of extended or elongated feedstock portions, such as strips, formed from a high strain deformation process and having a nano- sized grain structure therein. In an embodiment, the strips may be the same or different in nanostructured materials. Next, a surface of one feedstock portion may be contacted against a surface of another feedstock portion. Thereafter, ultrasonic vibrations may be applied along at least one of the feedstock portions to permit the contacting surfaces to bond with one another without substantially heating the portions to cause re-crystallization, so as to form a consolidated volume. [00016] In a further embodiment, the present invention provides a method for manufacturing a consolidated volume of nanostructured materials that includes initially providing a continuous feed of a material formed from a high strain deformation process and having a nano-sized grain structure therein, the material having an outer surface and an inner surface. Next, the material may be wrapped about a central axis, so that its inner surface makes contact along its outer surface. Thereafter, ultrasonic vibrations may be applied along the outer surface of the material as the material is being wrapped about the central axis to permit, where contact is made between the inner surface and the outer surface, to bond with one another without substantially melting the material, so as to form a consolidated volume.

[00017] In another embodiment, the present invention provides a method for manufacturing a nanostructured portion. The method includes initially providing a source material made having an predefined hardness and from which the nanostructured portion can be manufactured. Next, the source material may be subject to a high strain deformation process. Thereafter, at least one portion having a nano-sized grain structure and a Vickers hardness ranging up to over about 300 percent above the predefined hardness of the source material may be generated. The portion having a nano-sized grain structure can be of various geometric shapes, including fragments, chips, particles, strips, foils, platelets, ribbons, wires, filaments, sheets, elongated foils or substantially continuous rolls

[00018] In a further embodiment, the present invention provides a nanostructured material. The nanostructured material includes a body portion having a top side and a bottom side. The nanostructured material also includes a continuous strip made from a source material and wound about itself to provide the body portion. In an embodiment, the strip includes a nano-sized grain structure therein, and a Vickers hardness ranging up to over about 300 percent above the predefined hardness of a source material. The roll further includes a width extending from the top side to the bottom side. In an embodiment, the continuous roll may include an ultrasonic bond between layers of adjacent wound strip.

[00019] In yet another embodiment of the present invention, there is provided an ultrasonically consolidated volume of a nanostructured material. The material, in an embodiment, includes a plurality of feedstock portions formed from a high strain deformation process and having a nano-sized grain structure therein. The mass also includes a bond securely positioned between adjacent feedstock portions. In one embodiment, the bond may be provided with minimal melting characteristics on each of the feedstock portions.

BRIEF DESCRIPTION OF DRAWINGS

[00020] Figure 1 illustrates a cutting system for use in connection with a Large

Strain Extrusion Machining process for generating an elongated nanostructured strip in accordance with an embodiment of the present invention. [00021] Figure 2 shows a detailed illustration of an extrusion die for use in connection with the cutting system of Figure 1. [00022] Figures 3A-E illustrate a number of nanostructured strip samples produced in accordance with various embodiments of the present invention. [00023] Figure 4 illustrates various locations on a nanostructured strip that can be measured for hardness in accordance with an embodiment of the present invention. [00024] Figure 5 illustrates variation in hardness level due to changes in the cutting speed of the system in Fig. 1. [00025] Figures 6A-C illustrate examples of hardness distributions across the width of a nanostructured strip at different cutting speeds. [00026] Figure 7 illustrates temperature measurements for the cutting tool and nanostructured strips extruded in accordance with one embodiment of the present invention. [00027] Figure 8 illustrates a consolidated mass of metal foils that have been ultrasonically welded together over half the length. [00028] Figure 9 illustrates a substantially dense consolidated nanostructured mass produced in accordance with an embodiment of the present invention. [00029] Figures lOA-C illustrate various ways in which strips of nanostructured materials can be ultra-sonically welded to build-up a bulk form. [00030] Figures 1 IA-D illustrate the addition of ductile structures to nanostructured materials to reduce tensile failure of the resulting mass. [00031] Figures 12A-B illustrates the continuous production of nanostructured foil, subsequent collection on a spool, and ultrasonically welded to increase the size of the resulting mass.

DESCRIPTION OF SPECIFIC EMBODIMENTS

[00032] The present invention provides, in one embodiment, a method for manufacturing a bulk volume or mass of nanostructured material from consolidating feedstock portions having nano-sized grain structures therein. The feedstock portions can be generated from a variety of materials, including metals, metal alloys, composites, or ceramics, among others. In addition, the feedstock portions from which the bulk, consolidated volumes can be formed, in an embodiment, can be in a variety of geometric shapes. As examples, the feedstock portions can be any of fragments, chips, particles, ribbons, wires, filaments, sheets, platelets, elongated foils, continuous rolls or any other geometric shapes.

[00033] Such a bulk, consolidated nanostructured mass, for instance, can enable a variety of applications that can benefit by the enhanced properties resulting from the nanostructured feedstock material having, for instance, nanosized grains. In particular, it is known that the hardness and strength of a material, such as metal, generally increases with reduced grain size. To that end, the increase in hardness and/or strength-to-weight ratio, for instance, can extend, among other things, the useful range of operation of the nanostructured material, such as a metal and its alloys, in structural applications in a variety of industries. High Velocity Deformation (HVD)

A. HVD Process

[00034] In accordance with one embodiment, the method for manufacturing a bulk, consolidated nanostructured mass includes initially generating, from a source or starting material, feedstock portions having nanometer sized grains or crystals. In an embodiment, generation of these nanostructured portions involves employing a high strain deformation process, such as, a high velocity deformation (HVD) process, similar to that disclosed in U.S. Patent No. 6,706,324, which patent is hereby incorporated by reference. It should be understood that the terms "feedstock portion(s)", "nanostructured material(s)", or "nanostructured portion(s)" hereinafter can be used interchangeably to mean substantially the same thing.

[00035] In general, a high velocity deformation process uses standard machining techniques, such as milling, lathing, or grinding to remove portions from a source or starting material. The removed portions (i.e., chips or fragments) having a nano-sized grain structure therein can subsequently be used as feedstock for forming a bulk, consolidated nanostructured mass.

[00036] Under certain conditions, the angle of a cutting tool used, its penetration depth into the starting material, and the cutting velocity, can cause the portions removed from the source or starting material to undergo severe plastic deformation. In accordance with one embodiment of the present invention, the cutting angle employed for HVD may range from about -20° to about 20°, whereas the depth of cut may range from about 0.0005 inches to about 0.125 inches, and the feed rate may range from about 0.0005 inches per minute to about 0.125 inches per minute, while the cutting velocity may range from about 800 rpm to about 1800 rpm. The HVD process employed by the present invention, in an embodiment, can refine the grain or crystalline size of the removed portions to the nanometer length scale. The resulting removed portions having nanometer sized grains or crystals, typically in the range of from about 50 nanometers (nm) to about 500 nm, can be referred to as nanostructured. [00037] The intrinsic properties of nanostructured materials, in one embodiment, can differ from that of their conventional counterparts. For example, the hardness of the nanostructured metals of the present invention can be up to about 300 percent or more of conventional metals. As hardness can be correlated to strength, and in turn strength can be correlated to wear resistance, the nanostructured materials or portions of the present invention can offer means to enhance these properties without substantially adding mass or the need to add a coating etc. Furthermore, the nanostructured materials of the present invention can be provided with a toughness necessary to subsequently yield ductilely, while minimizing, for example, fragmentation.

[00038] It should be appreciated that although described in connection with machining, the manufacturing of the nanostructured materials or portions of the present invention can be accomplished using other approaches. In particular, nanostructured portions can be manufactured in accordance with the present invention by, for example, equal channel angular extrusion (ECAE), cryogenic ball-milling, and spray deposition, among others, or a combination of any of the mentioned approaches.

B. Materials for HVD

[00039] The source or starting material for use in connection with the HVD process of the present invention, in one embodiment, may need to address a spectrum of characteristics, and preferably include those materials that can provide the generated nanostructured portions with one of increased strength, ductility, hardness, formability, resistance to crack propagation or a combination thereof. In addition, the source or starting material may need to provide the generated nanostructured portions with the capacity to be consolidated (i.e., welded) under imposed fabrication conditions into a specific suitably designed structure. Furthermore, the source or starting material may need to provide nanostructured portions that, once consolidated into a suitable designed structure, be capable of satisfactory performance for an intended purpose. [00040] Examples of appropriate materials may include metals, metal alloys, composites, or ceramics, among others. In an embodiment, metals that can be used include Al, Be, Cu, Ge, Au, Fe, Mg, Mo, Ni, Pd, Pt, Si, Ag, Ta, Sn, Ti, W, Zr, their alloys, steel, stainless steel, or a combination thereof.

C. Results

[00041] Tables 1-3 below contain hardness data of various HVD processed samples and their associated processing conditions, in accordance with various embodiments of the present invention.

[00042] Table 1 illustrates hardness data taken of samples from annealed tantalum vs. as-drawn tantalum, at various indicated feed rates, and tool speeds. Although tantalum (Ta) was employed, it should be appreciated that the HVD process employed by the present invention may be used to machine any of the materials provided above.

Table 1. Vickers hardness of HVD processed Ta.

3/16" dia.; tests; (5) -NI

[00043] In machining Ta, it was noted that there were certain unique challenges with the HVD process due to the combination of high strength and ductility of Ta. Nevertheless, the process employed by the present invention can permit successful high velocity deformation processing of Ta. The resulting HVD- processed fragments, as noted, can be in various geometric shapes, including chips, fragments, particles, platelets, foils etc.

[00044] For Run 7, as illustrated in Table 1 , a climbing cut technique was used, whereas for all others Runs a conventional cut technique was employed. Despite this and various other processing conditions or parameters, the HVD process of the present invention can routinely process a bulk Ta starting material having a Vickers hardness of about 90, for annealed Ta, and about 140, for as-drawn Ta, that can result in nanostructured portions having a Vickers hardness ranging from about 200 to about 300. This is an enhancement on the order of up to about 300 percent or more over the bulk starting material.

[00045] For Runs 5, 6, 1 1, and 12, the same source or starting material was HVD processed using a grinding wheel with the resulting product being fine particulates. It should be noted that these samples of fine particulates were generally too small to have standard Vickers hardness testing. As a result, a nano-indentation technique was employed. The nano-indentation technique utilized is a standard technique employed by the industry, and is known to those skilled in the art.

[00046] Alternatively, materials characterization testing, such as transmission electron microscopy, can be employed to definitively demonstrate the quality of the nanostructuring process. However, such a test can be costly and time consuming. For the process of the present invention, since it is known that grain refinement in materials, including metals, can lead to an increase in strength and hardness, a more readily performed and less time consuming standard micro- or nano-indentation hardness test can be utilized as an indicator of grain refinement.

[00047] To benchmark the nano-indentation test with the Vickers test, certain relevant samples had their nano-indentation hardness tested. As shown in Table 2, for each Run, the results indicated that the samples of fine particulates also had a significant increase in hardness in comparison to the hardness of the • source or starting material (see "% vs. Bulk" column). Table 2. Nano-Indentation Results

D. HVD under Cryogenic Conditions

[00048] In accordance with one embodiment of the present invention, and as indicated above, the HVD process can be performed under cryogenic conditions. To determine whether cryogenic conditions have any effect on the resulting fragments, the HVD process was performed with cryogenically cooled Ta (i.e., Ta that have been immersed in liquid nitrogen prior to machining) as a starting material. In embodiment, the cryogenically cooled Ta may be cooled to within a temperature range of from about 0° C to about -200° C. The hardness of the resulting Ta fragments was subsequently assessed.

[00049] Table 3 illustrates Vickers hardness data taken on cryogenically cooled

Ta . Interestingly, although the data indicated that the pre-cooled Ta had a slight improvement only in one test (Test 8), for the most part, pre-cooled Ta did not result in a harder material. This result may indicated that the grain refinement was likely inhibited by the cryogenic conditions. Table 3. Hardness of H VD Ta

Large Strain Extrusion Machining (LSEM)

A. Apparatus and Process

[00050] In accordance with another embodiment of the present invention, another method for manufacturing a bulk, consolidated nanostructured mass may initially employ the generation of the nanostructured materials or portions using another high strain deformation process, such as Large Strain Extrusion Machining (LSEM) process, prior to consolidation. The LSEM process may be considered a subset of the HVD process. The nanostructured materials or portions generated by LSEM, rather than exhibiting chip-like shapes, such as those associated with HVD, tend to be elongated and/or continuous strips.

[00051] The LSEM process of the present invention, in various aspects, may be similar to the HVD process described above. In particular, LSEM can exert a substantially large amount of strain on the source or starting material that can lead to severe plastic deformation of the source or starting material in order to generate and refine the grain or crystalline size of the removed portion to the nanometer length scale. One difference, however, is that the LSEM process of the present invention uses a cutting system that includes, among other things, an extrusion component or die designed to maintain structural continuity of the removed portion, so that an elongated and/or continuous strip of nanostructured material can be generated for subsequent consolidation into a bulk nanostructured mass. [00052] As illustrated in Fig. 1, there is shown a cutting system 10 having a support body 11 to which a workpiece 12 (i.e., source or starting material) may be attached. The workpiece 12, in an embodiment, may be affixed to the support body 11 in such a manner so as to permit the workpiece 12 to rotate about an axis X. To securely affixed the workpiece 12 to the support body 11, the workpiece 12 may be provided with a plurality of apertures 13 through each of which a securing mechanism (not shown), such as a screw or a bolt, may be extended and tightened into the support body 11. Of course, other securing mechanisms and designs known in the industry may be employed to secure the workpiece 12 to the support body 11.

[00053] The cutting system 10 may also include an extrusion die 14 designed to generate from the workpiece 12 an extended and/or continuous strip 15 of nanostructured material. The extrusion die 14, as shown in Fig. 2, may include a cutter 21 having a cutting edge 22 positioned substantially against the workpiece 12. In an embodiment, the cutter 21 may be designed to have a relatively fixed position during cutting, so as to minimize or prohibit movement of cutting edge 22 relative to a rotating workpiece 12. The cutting edge 22, in one embodiment, may be placed at such an angle, so as to cut into and exert a substantially large amount of strain on surface 121 of the workpiece 12, as the workpiece 12 rotates by and against cutter 21. In an embodiment, the cutting angle, depth and force exerted by the cutting edge 22 of cutter 21 may be varied or adjusted to any desired level, and should be sufficient such that an extended and/or continuous strip 15 of nanostructured material can be generated from the workpiece 12. It should be appreciated that since the cutter 21 needs to cut into the workpiece 12, which can be made from substantially hard materials, cutter 21 may be made from any substantially solid, hard material that can allow a sufficiently sharp cutting edge 22 to be maintained. Examples of a material from which the cutter 21 may be made includes, metal or metal alloys, such as Tool Steel, Cobalt, Tungsten-Cobalt, Tungsten-Cobalt Carbide, Carbide, Cubic Boron Nitride etc., or any other material capable of cutting into the hard workpiece 12. [00054] Still looking at Fig. 2, the extrusion die 14 may also include a constraint piece or mechanism 23 positioned above the cutter 21. By placing the constraint mechanism 23 in such a position, the constraint mechanism 23, together with the cutter 21, can act to control the thickness of the strip 15 being extruded from workpiece 12. In an embodiment, the constraint mechanism 23 includes a constraining edge 24 designed to permit placement substantially flush against surface 121. The constraining edge 24 may also be designed to have a relatively fixed position during cutting, so as to minimize or prohibit movement of constraining edge 24 relative to a rotating workpiece 12 and cutter 21. It should be appreciated that the placement of constraining edge 24 of mechanism 23 relative to the placement of cutting edge 22 of cutter 21, as illustrated in Fig. 2, can be used to control depth t at which the cutting edge 22 may penetrate into workpiece 12. To that end, the thickness of strip 15 generated from workpiece 12 may be controlled.

[00055] Furthermore, due to its placement relative to the cutter 21, the constraint mechanism 23 may also act to guide the extruded strip 15 away from the surface of workpiece 12 during extrusion. To guide the strip 15 away from the workpiece 12, the constraint mechanism 23 and the cutter 21 may be designed so that a channel 16 (see Fig. 1) may exist between the constraint mechanism 23 and cutter 21 when the two are positioned against one another.

[00056] It should be noted that the design of the extrusion die 14 can be such that the angle of the cutter 21, the penetration depth t of the cutter 21 into the workpiece 12, the rate of spin of the workpiece 12 and hence the cutting velocity, as well as the feed rate of the workpiece 12 to the cutter 21, can be varied and set to a desired range or rate. In addition, as the workpiece 12 becomes smaller during extrusion of strip 15, i.e., diameter D of workpiece 12 becomes smaller as strip 15 is generated, extrusion die 14 can be designed to move toward axis X of workpiece 12 to continuously generate strip 15. Movement of extrusion die 14 toward axis X may be provided by, for instance, in one embodiment, a stepper motor. Moreover, in accordance with an embodiment of the invention, extrusion die 14 may be designed to move toward axis X at a substantially controlled rate, so as to maintain a substantially uniform penetration depth t, thereby allowing strip 15 to be generated with a substantially uniform thickness.

B. Materials for LSEM

[00057] The source or starting material for use in connection with the LSEM process of the present invention, in one embodiment of the invention, may need to address a spectrum of characteristics, similar to the material used in connection with the HVD process described above. The material preferably includes those that can provide the generated nano structured fragments with one of increased strength, ductility, hardness, formability, resistance to crack propagation or a combination thereof. In addition, the source or starting material may need to provide the generated nanostructured fragments with the capacity to be consolidated (i.e., welded) under imposed fabrication conditions into specific suitably designed structure. Furthermore, the source or starting material may need to provide nanostructured fragments that, once consolidated into a suitable designed structure, be capable of satisfactory performance for an intended purpose.

[00058] Examples of appropriate materials may include metals, metal alloys, composites, or ceramics, among others. In an embodiment, metals that can be used include Al, Be, Cu, Ge, Au, Fe, Mg, Mo, Ni, Pd, Pt, Si, Ag, Ta, Sn, Ti, W, Zr, their alloys, steel, stainless steel, or a combination thereof.

C. Results and Parameters

[00059] The cutting system 10 of the present invention can be used in connection with the LSEM process to produce elongated or substantially continuous strips or foils with a variety of shear strain rates relative to the thickness ratio (λ) of the strips. This thickness ratio may be the thickness of the foil (tc) produced divided by the penetration depth t (i.e., depth of the cut), that is, λ = XcIt. By varying the thickness ratio, the LSEM process can allow for the ability to produce strips with different material properties, ranging from a relatively high shear strain strip (i.e., unconstrained strip) to a relatively low shear strain strip (i.e., constrained strip).

[00060] In one embodiment, nanostructured strips of various widths were generated using the LSEM process of the present invention to understand the effects of various parameters on the resulting nanostructured strips. The strips were generated from aluminum, and in particular, Al 6061, having width sizes of about 0.25 inches, about 0.5 inches, and about 1.0 inch.

[00061] In particular, a disc of Al 6061 metal was mounted on the support body

11 of cutting system 10, and secured thereto with a series of bolts through apertures 13. The extrusion die 14 having cutter 21 and constraint mechanism 23 was affixed to the cutting system 10 against the surface of the Al 6061 disc. The extrusion die 14 was positioned such that the constraining edge 24 of constraint mechanism 23 was placed over the cutting edge 22 of cutter 21, as illustrated in Fig. 2, at a predetermined angle t. The 0.25 in. wide strip, 0.5 in. wide strip, and 1.0 in. wide strip were generated with different thicknesses by varying the RPM of the cutting system 10 and thus the cutting rate, the angle of the cutting edge 22, as well as the height of the constraining edge 24. Figures 3A-E illustrate the various nanostructured strip samples produced, ranging from a non-uniform strips to a substantially smooth, straight strip.

[00062] Although Aluminum (Al) was employed, it should be appreciated that the LSEM process employed by the present invention may be used to extrude any of the materials provided above.

Thickness of Nanostructured Strips

[00063] In connection with one embodiment of the present invention, the cutting edge angle of cutter 21 can set at angles ranging from -20° to about 20°. The restraining edge of restraint mechanism 23 was also set at different heights. Of course, cutting edge angles and restraint heights different from those indicated here can be employed depending on the desired outcome (e.g., thickness) for the nanostructured strip. As can be seen in Table 4, the thickness of the resulting nanostructured strips can be affected by the cutting edge angle and the restraint height.

Table 4

[00064] In addition to the cutting edge angle and restraint height, another variable that can affect the thickness of the resulting nanostructured strip may be the cutting speed employed. Moreover, it should be appreciated that even if the cutting angle and restraint height remain the same, varying the cutting speed can affect the thickness of the resulting nanostructured strip. In an embodiment, the cutting speed can be set to a range of from about 10 m/min to about 200 m/min. It is observed that at a slower cutting speed, for instance, 25 m/min, a slightly thicker strip may be produced in comparison to a strip produced at a relatively faster speed, for instance, 200 m/min.

Grain Size and Hardness of Nanostructured Strips

[00065] Hardness values were measured directly on the nanostructured strips generated by the LSEM process of the present invention. One property that relates to hardness may be the mean grain (i.e., crystal) size in the extruded nanostructured strip. A useful measurement tool for determining the mean grain size is Electron Back-Scattered Diffraction (EBSD). In general, EBSD can be used to obtain information on the grain size distribution and orientation on the nanostructured strip. [00066] In one example, EBSD results for an LSEM extruded aluminum strip obtained from data reduction software of the diffraction images, indicate that the LSEM extruded strip had an average crystal size of about 9.8 μm. This is approximately an order of magnitude smaller than the average crystal size of about 82 μm of the starting material.

[00067] However EBSD is a relatively expensive process and was limited to only a few select samples.

[00068] Another useful indicator of grain refinement is hardness. Hardness testing can be performed at different locations on a nanostructured strip by a standard micro- or nano-indentation hardness testing device. Figure 4 illustrates various locations on a nanostructured strip that can be measured for hardness. The average hardness then can be determined along with the distribution of hardnesses across the width of the strip.

[00069] In an example, when the 13 selected locations on the Al 6061 LSEM strip shown in Figure 4 were tested for hardness, it was noted that there was a marked increase in hardness across the width of the strip when compared to the hardness of the source or starting material. In particular, it was noted that although the hardness of the starting material was about 107 Vickers, the average hardness of the LSEM strip was about 128 Vickers, with a maximum average hardness recorded at about 138 Vickers and a maximum single point hardness being about 145 Vickers. This represents an average increase in hardness of about 20 percent over starting material. In certain situations, the hardness can be increased up to three times over that of the source or starting material.

[00070] In general, the LSEM process of the present invention can result in a nanostructured strip with an increased hardness. However, along with the increase in hardness, the nanostructured strip may also experience an increase in tensile strength .

[00071] In another example, five 1.00 in X 0.016 in Al 6061 LSEM strips were tested for hardness and tensile strength. The results indicated that the average tensile strength increased by about 13 percent over that of the source or starting material, as well as an increase of about 20 percent in the overall yield strength over that of the source or starting material. Table 5 illustrates the tensile properties of the five strips tested.

Table 5

TENSILE PROPERTIES

The samples were machined to a width of 0.16 inches; gauge length was 1.00 inch. Yield strength was determined by the 0.2% olfset method. Crosshead speed was 0.02 m./miα to yield and 0.2 ta/rnin. to fracture.

Method in accordance with ASTM E 8-04,

[00072] It has also been observed that varying certain parameters during the

LSEM process can enhance the relative hardness of the resulting nanostructured strip. For instance, by increasing the surface speed of the source or starting material being machined and thus increasing the cutting speed of the cutting system 10, the hardness value of the resulting nanostructured strip changes. As can be seen in Fig. 5, at a slower cutting speed, for example, between 25 m/min and 100 m/min, the nanostructured strip produced tend to have a higher hardness value than the nanostructured strip produced at a higher cutting speed of about 200 m/min. This may be due to the fact that at a slower cutting speed, a relatively larger strain is put on the source or starting material during the deformation process, resulting in a strip with smaller crystal size, and thus a higher level of hardness.

[00073] In addition, varying the cutting speed can lead to a change in hardness distribution across the width of the resulting nanostructured strip. Figures 6A-C illustrate examples of hardness distributions across the width of a nanostructured strip at different cutting speeds (e.g., from 25 m/min to 100 m/min to 200 m/min.) In particular, by using the hardness values obtained across the width of the strip and the location at which each hardness value was obtained relative to an adjacent location, a map of hardness can be generated, such as that seen in Figures 6A-C, better visualize the effects of the various LSEM parameters.

[00074] As can be seen in Fig. 6A, a surface speed of about 25 m/min resulted in hardness values ranging from about 120-140 as depicted by regions A and B. On the other hand, as shown in Fig. 6C, a speed of about 200 m/min resulted in hardness values ranging from 90-100 as depicted by region C. It is believed that this variation in hardness may be due to extreme plastic deformation and the amount of heat being generated on the extruded nanostructured strip at relatively high speed. In general, the faster the surface speed, the more heat will be generated from the friction between the extruded nanostructed strip and the cutter and constraint mechanism of the extrusion die. This excessive heat can lead to softening of the extruded nanostructured strip, thus affecting it hardness. Furthermore, the excessive heat, once at a certain temperature, can lead to re- crystallization within the nanostructured strip. Re-crystallization, in particular, can also decrease the hardness of the nanostructured strip. It should be noted that also visible in the topographies in Figs. 6A-B is the difference in hardness from the center to the edges of the strip.

Integrity and Consistency of Nanostructured Strips

[00075] It was observed that with LSEM processing using the system 10 of the present invention, extrusion of nanostructured strips having a relatively wide width can increase dynamic frictional forces during extrusion, resulting in an increase in temperature of the strips. This increase in temperature, as mentioned above, can be due to the cutting edge 22 and constraint edge 24 contacting the surface 121 of workpiece 12. If not appropriately monitored, the increase when reached a certain temperature can lead to re-crystallization of the nano-sized grains in the strip and affect the integrity and hardness of the nanostructured strip. The re-crystallization temperature, as can be appreciated, can vary depending on the material being extruded. [00076] Figure 7 illustrates the temperature measurements for the cutter 21 and an extruded nanostructured strip from Al 6061 during an LSEM process of the present invention. Temperature measurements for the cutter 21 were obtained from two thermocouples inserted into the cutter 21 at a distance of 4 mm away from the cutting edge 22 and 8 mm away from the cutting edge 22. Temperature measurements for the extruded nanostructured strip were obtained from Infra-Red Detectors directed to the top surface of the extruded nanostructured strip.

[00077] As shown, the temperature of the cutting edge and cutter can increase quickly over a short period of time. From the temperature data recorded with the thermocouples in the cutter 21 and through a Finite Element Analysis, the theoretical temperature at the cutting edge exceeded 300° C. As a note, the re- crystallization temperature of Al is about 315° C. On the other hand, the temperature of the strip being extruded, although not as high as that of the cutting edge, it can be assumed that the temperature gradient between the cutting edge and the extruded strip at the interface point (i.e., juncture) is about 0° C. In other words, at the interface point, the temperature of the extruded strip likely approximates that of the cutting edge.

[00078] Thus, if not monitored, it has been determined that the re-crystallization temperature of Al (i.e., 315° C), such as AL 6061, would be reached in less than about 90 seconds during a continuous LSEM process. To minimize any effect on the integrity of the resulting nanostructured strip, in one embodiment of the present invention, the temperature of the strip during extrusion should be kept to below the re-crystallization temperature of the material being extruded. In accordance with an embodiment, a machine coolant may be used with the system 10 to maintain and stabilize the operating temperature during the continuous LSEM process well below the re-crystallization temperature of the material being extruded. An example of such a coolant can be a 20:1 mixture of water to mineral oil.

[00079] Alternatively, the operating temperature may be maintained and stabilized below the re-crystallization temperature of the material being extruded by employing a cryogenic cooling process. In particular, the use of cryogenic cooling can reduce frictional forces between the extruded nanostructured strip and the extrusion die, namely the cutter and constraint mechanism, to maintain the operating temperature in check. The use of cryogenic cooling can also eliminate residues, such as oil, on the starting material (i.e., workpiece) and the extruded nanostructured strip. The use of the water/mineral oil mixture as a coolant may result, in certain instances, in oil residues being deposited on the extruded nanostructured strip. By eliminating such residues, the quality of the extruded strip can be improved.

[00080] Thus, in addition to the width of the strip and frictional forces applied to the strip, the temperature of the extrusion die 14, including that of the cutter 21, temperature of the strip, as well as the amount of power employed by the cutting system 10, among others, can potentially jeopardize the integrity of the nanostructured strip, as well as its consistency during production by LSEM processing. Moreover, the thinner the extruded nanostructured strip relative to the depth of the cut (i.e., the smaller the thickness ration), the higher the frictional forces may be, and thus the more heat that will be generated. To that end, cutting system 10 can be design to have a feedback system to monitor and control variables that can affect the temperature of the nanostructured strip being extruded to maintain the temperature to that below the re-crystallization temperature of the material being extruded.

Consolidating

[00081] Once the nanostructured portions, such as those created by the HVD process, or nanostructured strips, such as those created by the LSEM process, have been generated, they can be placed against one another and, in one embodiment, ultrasonically bonded to one another. Ultrasonic bonding, welding, or consolidation is a method known in the art. An example of such is disclosed in U.S. Patent No. 6,519,500, which patent is hereby incorporated herein by reference. Although known, it should be appreciated that such a method has. yet to be employed in the bonding of nanostructured materials, either those generated by HVD processing or LSEM processing. Ultrasonic consolidation generally involves contacting the surfaces of the materials to be bonded, applying a pressure against the surfaces, and subsequently moving these surfaces horizontally with respect to one another at ultrasonic frequencies until the surfaces are bonded to one another. In an embodiment where metallic nanostructured portions are used, the surfaces of the portions to be bonded may initially be placed against one another and may be pressed together with an applied force. Next, an ultrasonic frequency may be applied in an oscillatory motion within the contacting plane between the surfaces. In one embodiment, the ultrasonic frequency may include a static normal force and an oscillating shearing (i.e., tangential) force. This oscillating shearing force may be a high-frequency ultrasonic acoustic vibration. The application of the ultrasonic frequency thereafter can cause small scale plastic deformation at the interface between the portions to be bonded and generate factional forces that act to break up and/or remove, for instance, oxide layers and/or contaminants between the portions. Upon contact, sufficiently smooth pure metals can migrate from one surface toward the opposite surface to produce a substantially strong solid-state bond between the nanostructured portions, so as to form a consolidated volume. In certain situations, some of the metal may diffuse across the weld area and re-crystallize into a fine grain structure. While some heat is generated, the temperatures generated during ultrasonic consolidation typically may not be sufficiently hot to melt the contacting surfaces of the portions, as in traditional welding, or permit substantial re-crystallization that can affect the integrity of the nanostructured portions. In an embodiment, the temperature generated in the weld zone typically range between about 30 percent to about 50 percent of the melting point of the joined portions. This is an important feature of ultrasonic consolidation, especially in regards to nanostructured metals. In particular, with minimal heat generated, grain growth (i.e., re-crystallization) can be mitigated, and only a thin layer near the contact surface is joined by the ultrasonic vibration, while the remainder of the adjoining fragments remain unaffected. In this way nanostructured metals are expected to remain nanostructured in whole or in part through the ultrasonic welding process. [00083] In contrast, when producing dense products from nanostructured feedstock material using known Powder Metallurgy consolidation techniques, significant grain growth occurs that reduces or eliminates the benefits associated with nanostructuring. Furthermore, when PM techniques are adapted to mitigate grain growth, these techniques can result in materials far from their theoretical maximum density, such that the benefits (e.g., strength) of nanostructuring are not realized in the bulk material.

[00084] In accordance with one embodiment, an ultrasonic generator or power supply may receive main grid electricity at a low frequency, preferably in the range of 50 to 60 Hz, and at a low voltage of 120V or 240 V AC. The ultrasonic generator then converts the input to an output at a higher voltage, preferably having a frequency in the range of 15 to 60 kHz. A useful working frequency may be about 20 kHz, which is above the normal range of human hearing of about 18 kHz. Systems employing higher frequencies of 40 kHz to 60 kHz with lower amplitude vibrations may be employed for fragile materials, such as very thin foils, wires of very small diameter, or substrates which can easily be damaged.

[00085] The high frequency output of the generator may thereafter be transmitted to a transducer or converter, which converts the signal to mechanical vibratory energy at similar ultrasonic frequencies. State-of-the art transducers operate on piezoelectric principles and incorporate discs or rings made of piezoelectric material, such as piezoelectric ceramic crystals, which are compressed between two metal sections. An advanced generator features automatic tuning adjustment in relation to the transducer so that a constant amplitude of vibration can be maintained during the operation of the welding unit.

[00086] The peak-to-peak amplitude of the vibration, in an embodiment, may be about 20 microns (0.0008 in.) for a typical 20 kHz transducer and about 9 microns (0.00035 in.) for a 40 kHz transducer. If a different amplitude is required, a booster may be attached to the transducer. In such an embodiment, the vibratory energy of the transducer is transmitted to the booster, which decreases or increases the amplitude of the ultrasonic waves. The waves are then transmitted to a horn, which is a custom-made acoustic tool that comes in contact with the nanostructured portions to be consolidated. The horn is also known as a sonotrode or head unit. The horn may be designed as a tool-holder carrying a tool bit, or it may be provided in one integrated piece incorporating specific geometric features. For ultrasonic welding of metals, the sonotrode is preferably made of tool steel, and it may be manufactured as a unitary component. On the other hand, for ultrasonic welding of, for example, plastics, the sonotrode may be made from aluminum or titanium.

[00087] The nanostructure portions to be consolidated, in an embodiment, may be held under pressure between the contact surface of the sonotrode and a substrate or anvil. The contacting surfaces of the sonotrode and anvil may be roughened to provide a secure grip. Pneumatically operated jaws or other fixtures are used to insert and remove the parts to be welded, typically in conjunction with automated feeding mechanisms and automated positioning controllers.

[00088] Table 6 provides an optimum set of parameters for ultrasonic welding of a nanostructured Al strip (6061T6).

Table 6

[00089] As can be seen in Table 6, the optimum set of ultrasonic welding parameters were adjusted to provide a substantially dense volume of consolidated nanostructured mass or material with substantially minimal amount of porosity from those parameters applied to the other nanostructured Al strips (ND 6061). In particular, the weld amplitude and force in the optimum set were increased, while the weld velocity was decreased to form secure bonds between the nanostructured Al strips. The welding parameters for the ND 6061, as can be seen, resulted in substantially non-secure bonding.

Advantages

[00090] Ultrasonic consolidation or welding, as applied to the nanostructured materials of the present invention can minimize the presence of porosity within the materials, so as to provide fully dense bulk, consolidated nanostructured mass. Minimizing porosity of the bulk, consolidted nanostructured mass can be desirable, as large pores can contribute to fracture in certain applications. As such, using ultrasonics consolidation can make it easier to control and reduce porosity.

[00091] Moreover, as the nanostructured materials of the present invention, for instance, nanostructured metals, such as Al or Ta, can be formed into essentially planar morphologies, for example, fragments, strips, platelets, foils, or continuous rolls, ultrasonic welding can consolidate these materials into bulk forms for subsequent applications. Key advantages can be that the generated nanostructured material, either by HVD or LSEM, can remain intact either in whole or part, and that a substantially dense mass can be fabricated as a result. In certain embodiments, similar or different nanostructured materials can be consolidated to form a bulk volume of a nanstructured mass. Furthermore, as the HVD and LSEM processes tend to align the grain structure within individual nanostructured portions, these portions can be consolidated into preferred bulk grain alignment patterns or fiber texture. In an embodiment, a strong and substantially homogenous fiber texture may be advantageous when it comes to mitigating high strain rate failure in polycrystalline Ta or Al.

[00092] In accordance with another embodiment, relatively ductile metallic layers, mesh, or other structures can be added or incorporated with the nanostructured fragments during the consolidation process. These layers of either the same annealed metal or another more ductile metal, such as copper, can act as a type of buffer during large tensile stresses. This can be analogous to how rebar reduces the amount of cracks in cement during use. The ductile metal can, in an embodiment, be added either in a layered fashion throughout the solid or all on one surface. Moreover, it should be appreciated that ductile material can be added at those locations that may experience enhanced stress to ensure ductile behavior when needed.

Example 1 :

[00093] Figure 8 illustrates a structure 80 made from nanostructured (aluminum) foils 81 that has been ultrasonically welded together over half its length. In this example, multiple strips of foil 81 have been ultrasonically welded together to form a solid structure 81 approximately 5 millimeters (mm) in thickness. The unwelded half of the 32 strips of foil 81 are shown as being fanned out to clearly contrast the two sections of the structure 80. This is a relatively simple piece and much more complex geometries may be generated should it be desired.

Example 2:

[00094] Figure 9 illustrates a structure 90 made from approximately twenty (20)

1 in. wide nanostructures strips layered on top of one another and ultrasonically welded together. The resulting substantially dense structure 90 has dimensions of 1 in. wide X 4 in. long X 0.25 in. thick.

Example 3 :

[00095] In accordance with another embodiment of the present invention, 1 to 2 inch wide strips of foil may be sequentially consolidated to one another. Specifically, as the foil is set on top of the surface of the foil before it, pressure and ultrasonic vibration may be applied. The surfaces of the foil strips may rub against one another, removing oxides (i.e., cleans them), and allowing the surfaces to join atomically. Pure metal-metal surface contact can naturally form a metallic bond.

[00096] For example, as depicted in Fig. 1OA, a 5 inch diameter disk 100, or any other geometric shape, can be fabricated by sequential consolidation of several parallel strips 101. As illustrated, the strips 101 may be laid down as parallel chords and welded progressively. Additional thickness can be had by applying more layers of strips 101 on top of one another. The larger surface area bond between vertically stacked strips 101 (i.e., those on top of one another) can be inherently stronger than the smaller surface area bond between horizontally positioned strips 101 (i.e., those next to one another). In order to prevent seams where the strips 101 horizontally contact each other through the thickness of the part, these layers can be put down at an angle to each other, or overlapping. Once consolidated, disk 100 may be formed by trimming excess material into the shape of the disk 100, such as by laser cutting or conventional milling. Of course, any other geometric shapes can be formed in a similar manner from the consolidated strips 101.

[00097] Furthermore, as the HVD or LSEM process may align the grain structure within individual piece, these foil strips 101 can be consolidated into preferred bulk grain alignment patterns or fiber texture. A strong and homogenous fiber texture may be advantageous to mitigating high strain rate failure.

[00098] In Fig. 1OB the nanostructured strip 101 may be provided which is sufficiently wide to permit subsequent formation of, disk 100 or any other geometric shape. The use of a single material strip 101 can avoid intra-plane welding of a plurality of strips, such as strips 101 in Fig. 1OA. The thickness of disk 100 or the particular geometric shape may controlled by the number of layers of strip 101 welded on top of one another. Unlike Fig. 1OA, no special tooling would even be required, as multiple passes of the ultrasonic welding head can be used to sweep over the area to be joined. Once the desired thickness has been reached, the disk 100 or any other geometric shape may be cut-out from the strip 101.

[00099] Fig. 1OC depicts a disk 100 being formed from continuous addition of a nanostructured strip 101 to its outer surface 102. The thickness of the disk 100 may be controlled by the width W of the continuous strip 101, and the diameter D of the disk 100 may be controlled by amount of addition of nanostructured strip 101 to its outer surface 102. The advantage here may be that unlike the method as in Fig. 1OA, there exist substantially no weak seams as the welding occurs across the width of the strip 101 as it is added. [000100] In one embodiment of the present invention, the ultrasonic welding of the strip 101 in Figs. lOA-C may take place in an inert atmosphere, so as to mitigate oxidation of the metals and facilitate the welding process.

Example 4:

[000101] Fig. 11 illustrates another embodiment and variation of a structure 110 that can be formed in accordance with an embodiment of the present invention. In Figs. 1 IA and 1 IB, a composite material may be made by alternating layers of annealed, ductile material 111 (such as copper) with a hardened nanostructured base material 112. This could be advantageous because the toughness of the composite material 110 would be increased over that of the base material without changing other material properties, such as electrical or thermal conductivity. Moreover, if the layers of hardened and unhardened material are altered in a precise manner, for example, one layer of hardened material for every 5 layers of unhardened material, the material could be engineered to have very specific toughness values depending on the average affect. This approach may be applied to various metals or other materials to reduce high strain-rate fracture or in other soft metals or materials that need more stiffness.

[000102] In a further embodiment of the present invention, and as depicted in

Figs. 11C and 1 ID, increased toughness and/or ductility of a material can be had by adding ductile layers or specifically placed reinforcements in a more brittle material. For example, layers of copper could be added to either or both surfaces of a base plate made from nanostructured materials, or copper wire or mesh 113 could be added in between layers 114 of base plates made from nanostructured materials, or copper layers 115 could be added to the circumference of the nanostructured plate 116. To that end, it should be appreciated that fragments of different nanostructured materials can be consolidated with one another. Example 5:

[000103] Figures 12A and B illustrate another embodiment of the present invention using continuous production. A continuous nanostructured foil or roll 120, such as Al or Ta, may be produced, such as by lathing a bar 121 (i.e., starting material) with tool 122. The foil 120 may initially be fed to a rotating uptake spool 123 and ultrasonically consolidated on top of itself or on top of another material already put down by, for instance, an ultrasonic roller head 124. In other words, the foil 120 may be wrapped about a central axis, so that its inner surface 1201 makes contact along its outer surface 1202. In this way, as the foil 120 continues to be wrapped about the central axis (i.e., as additive material increases about disc 126), the diameter of the disc 126 (i.e., bulk product) increases. The thickness of the bulk product can be determined by the width of the foil 120.

Applications

[000104] In general, nanostructured materials have increased hardness, strength, and toughness compared to their conventional counterparts. In addition, these nanostructured materials may be substantially corrosion resistant. Thus nanostructured materials can be used to improve the properties and/or reduce the size or mass of material required. Applications can be ubiquitous and can include structural components or products made of solids. For example, load bearing construction (beams, levers, etc.); machinery, engine, and motor components; vehicle exteriors (automotive panels, aircraft skins, etc.); and other applications where advanced properties are beneficial can employ ultrasonic welding to consolidate the nanostructured materials of the present invention into bulk solids.

[000105] Furthermore, as nanostructuring and ultrasonic welding can enhance the value of the material, practical applications will be ones in which value will be of a cost benefit. For instance, the transportation industry, especially aerospace and automotive, constantly seeks to improve both safety (through stronger materials) and energy efficiency (through lighter materials), and can benefit by the use of this technology, for example in body parts and load bearing components of airplanes and cars. Police agencies and the military can also find benefit in this technology in advanced armor applications.

[000106] For example, Explosively Formed Penetrators (EFPs) can be an important component of the modern military arsenal. Generally, EFP devices are conventional weapons, coupled with traditional chemical energy systems (i.e., high explosives). Based on their designs, EFP devices are capable of penetrating many inches (even feet) of armor. As such, these EFP devices can easily destroy tanks and other battlefield equipment, as well as other protected assets, including ships and bunkers.

[000107] Needless to say, high performance can be of critical concern to designers of these devices. Moreover, continued improvement of these devices requires availability of advanced materials that can perform under severe conditions. Specifically, when used as liners, for instance, Explosively Formed Penetrators can undergo extreme plastic deformation when fired, changing from a pre-fired thin dome/cone, to a fully accelerated spear-headed or carrot shaped projectile. In general, the formation of Explosively Formed Penetrators involves strains up to 300% at strain rates on the order of 104/s. The structure and material properties of the liner formed from EFPs, therefore, are of paramount importance. As a result, processing conditions must be carefully controlled in order to achieve lot-to-lot reproducibility.

[000108] When considering a material for Explosively Formed Penetrator liners, such a material needs to have a density that is relatively high, while having relatively good ductility. Accordingly, traditional industrial high-density tungsten (S. G. = 19.2), for instance, may not be suitable as it may be too brittle. Gold may perform well as an EFP liner. However, cost considerations can make gold impractical. Other materials, such as depleted uranium (DU), may also perform well, but may not be the materials of choice for a variety of reasons.

[000109] Currently, most EFP liners are made from oxygen-free high-conductivity

(OFHC) copper because the material performs well, has good repeatability, and can be manufactured at reasonable costs. However, OFHC copper can be a practical compromise, and can suffer from limited performance because of its low density. To that end, developers continue to explore for a better choice. Among the materials being considered for future liners, tantalum may be a good choice because of its relatively high density (S. G. = 16.7) and relatively good ductility. Furthermore, the performance of tantalum as an EFP liner has been demonstrated. Pappu, S. and Murr, L. E., "Hydrocode and Microstructural Analysis of Explosively Formed Penetrators," J. Mater. Sci., 37:233 (2002); McWilliams, T., Baker, E.L., Ng, K. W., Vuong, T., andMazeski, R.P., "High Spin Armor Piercing Warheads Development with Molybdenum and Tantalum Liners," 2002 International Infantry & Small Arms Conference, Atlantic City, NJ, May (2002).

[000110] In addition to necessary improvements in lot-to-lot variability, improved material properties, such as strain to failure ductility, improved ductility at high strain rates, and texture (grain or crystallite size distribution) may be sought for the next generation of EFP liners. Development of such materials and low cost manufacturing methods of same need to be pursued, so that next generation EFP devices can be realized. However, with the requirements of high-performance, low-cost, and environmentally friendly manufacturing processes, the development of these EFP materials can be a challenge.

[000111] Moreover, EFP liners can be an extremely demanding application due to the combination of high total strain (-300%) and strain rate (~100/s). When a projectile is formed from the EFP liner, any large inhomogeneity can result in catastrophic failure of the projectile immediately after charge detonation, and can severely reduce its effectiveness. Residual porosity in the EFP liner, impurities, or large crystals can further act as nucleation sites for cracks, and a rapid propagation of these cracks can result in premature faults. Presently, high quality nanostructured Ta liners have not been produced.

[000112] While the invention has been described in connection with the specific embodiments thereof, it will be understood that it is capable of further modification. Furthermore, this application is intended to cover any variations, uses, or adaptations of the invention, including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains.

Claims

What is claimed is:

1. A method for manufacturing a consolidated volume of nanostructured materials, the method comprising: machining at least one source material using a high strain deformation process to generate a plurality feedstock portions having a nano-sized grain structure therein; contacting a surface of one portion against a surface of another portion; and applying ultrasonic vibrations along at least one of the portions to permit the contacting surfaces to bond with one another without substantially melting the portions thereat, so as to form a consolidated volume of nanostructured materials.

2. A method as set forth in claim 1, wherein, in the step of machining, the high strain deformation process is a high velocity deformation process.

3. A method as set forth in claim 1, wherein, in the step of machining, the high strain deformation process is a large strain extrusion machining process.

4. A method as set forth in claim 1, wherein, in the step of machining, the source material that can provide the generated feedstock portions with one of increased strength, ductility, hardness, formability, resistance to crack propagation, or a combination thereof.

5. A method as set forth in claim 4, wherein, in the step of machining, the source material can be one of metal, metal alloys, composites, ceramics, or a combination thereof.

6. A method as set forth in claim 4, wherein, in the step of machining, the source material can be one of Al, Be, Cu, Ge, Au, Fe, Mg, Mo, Ni, Pd, Pt, Si, Ag, Ta, Sn, Ti, W, Zr, their alloys, steel, stainless steel, or a combination thereof.

7. A method as set forth in claim 1, wherein, in the step of machining, the feedstock portions have a Vickers hardness ranging up to over about 300 percent of that of the source material.

8. A method as set forth in claim 7, wherein, in the step of machining, the hardness of the feedstock portions can be controlled by varying machining parameters.

9. A method as set forth in claim 1 , wherein, in the step of machining, the feedstock portions can be of various geometric shapes, including fragments, chips, particles, strips, foils, platelets, ribbons, wires, filaments, sheets, elongated foils or substantially continuous rolls.

10. A method as set forth in claim 1, wherein, in the step of machining, the feedstock portions are different in nanostructured materials.

11. A method as set forth in claim 1 , wherein step of machining includes cryogenic cooling.

12. A method as set forth in claim 1, wherein the step of applying includes maintaining the bonding temperature at a temperature that can minimize grain growth within the feedstock portions.

13. A method for manufacturing a consolidated volume of nanostructured materials, the method comprising: providing a plurality of extended or elongated feedstock portions formed from a high strain deformation process and having a nano-sized grain structure therein; contacting a surface of one elongated portions against a surface of another elongated portion; and applying ultrasonic vibrations along at least one of the portions to permit the contacting surfaces to bond with one another without substantially melting the portions, so as to form a consolidated volume of nanostructured materials.

14. A method as set forth in claim 13, wherein, in the step of providing, the high strain deformation process can be one of a high velocity deformation process or a large strain extrusion machining process.

15. A method as set forth in claim 13, wherein the step of providing includes extruding the elongated feedstock portions from a source material by large strain extrusion machining with the use of an extrusion die.

16. A method as set forth in claim 13, wherein, in the step of providing, the feedstock portions can be one of metal, metal alloys, composites, ceramics, or a combination thereof that have relatively high strength, ductility, hardness, formability, resistance to crack propagation, or a combination thereof.

17. A method as set forth in claim 16, wherein, in the step of providing, the feedstock portions can be one of Al, Be, Cu, Ge, Au, Fe, Mg, Mo, Ni, Pd, Pt, Si, Ag, Ta, Sn, Ti, W, Zr, their alloys, steel, stainless steel, or a combination thereof.

18. A method as set forth in claim 13, wherein, in the step of providing, the feedstock portions have a Vickers hardness ranging up to over about 300 percent of that of a source material from which the portions are made.

19. A method as set forth in claim 13, wherein, in the step of providing, the feedstock portions are different in nanostructured materials.

20. A method as set forth in claim 13, wherein the step of applying includes maintaining the bonding temperature at a temperature that can minimize grain growth within the feedstock portions.

21. A method as set forth in claim 13, further including placing adjacent a feedstock portion a layer of a material having different properties from that of the feedstock portion.

22. A method for manufacturing a consolidated volume of nanostructured materials, the method comprising: providing a substantially continuous feed of a material formed from a high strain deformation process and having a nano-sized grain structure therein, the material having an outer surface and an inner surface; wrapping the material about a central axis, so that its inner surface makes contact along its outer surface; and applying ultrasonic vibrations along the outer surface of the material as the material is being wrapped about the central axis to permit, where contact is made between the inner surface and the outer surface, to bond with one another without substantially melting the material, so as to form a consolidated volume.

23. A method as set forth in claim 22, wherein, in the step of providing, the high strain deformation process can be one of a high velocity deformation process or a large strain extrusion machining process.

24. A method as set forth in claim 22, wherein the step of providing includes extruding the substantially continuous feed from a source material by large strain extrusion machining with the use of an extrusion die.

25. A method as set forth in claim 24, wherein the step of extruding includes maintaining the extruded continuous feed, at an interface with the extrusion die, at a temperature which can minimize grain growth in the continuous feed.

26. A method as set forth in claim 25, wherein the step of maintaining includes cryogenic cooling.

27. A method as set forth in claim 22, wherein, in the step of providing, the continuous feed can be one of metal, metal alloys, composites, ceramics, or a combination thereof that have relatively high strength, ductility, hardness, formability, resistance to crack propagation, or a combination thereof.

28. A method as set forth in claim 22, wherein, in the step of providing, the continuous feed has a Vickers hardness ranging up to over about 300 percent of that of a source material from which the continuous feed is made.

29. A method as set forth in claim 22, wherein the step of applying includes maintaining a bonding temperature at a level that can minimize grain growth within the wrapped material.

30. A method as set forth in claim 22, further including placing, adjacent a layer of the wrapped continuous feed material, a material having different properties from that of the continuous feed material.

31. A method of manufacturing a nanostructured portion, the method comprising: providing a source material having an predefined hardness; subjecting the source material to a high strain deformation process; and generating, from the high strain deformation, at least one portion having a nano- sized grain structure therein and a Vickers hardness ranging up to over about 300 percent above the predefined hardness of the source material.

32. A method as set forth in claim 31 , wherein, in the step of providing, the source material can be one of Al, Be, Cu, Ge, Au, Fe, Mg, Mo, Ni, Pd, Pt, Si, Ag, Ta, Sn, Ti, W, Zr, their alloys, steel, stainless steel, or a combination thereof.

33. A method as set forth in claim 31 , wherein, in the step of subjecting, the high strain deformation process is a high velocity deformation process.

34. A method as set forth in claim 31 , wherein, in the step of subjecting, the high strain deformation process is a large strain extrusion machining process.

35. A method as set forth in claim 31 , wherein, in the step of generating, the portion having a nano-sized grain structure can be of various geometric shapes, including fragments, chips, particles, strips, foils, platelets, ribbons, wires, filaments, sheets, elongated foils or substantially continuous rolls.

36. A nanostructured material comprising: a body portion having a top side and a bottom side; a continuous strip made from a source material and wound about itself to provide the body portion, the strip having a nano-sized grain structure therein, and a Vickers hardness ranging up to over about 300 percent above a predefined hardness of a source material; and a width extending from the top side to the bottom side of the portion.

37. A nanostructured material as set forth in claim 36, further having an ultrasonic bond positioned between layers of adjacently wound strip.

38. A nanostructured material as set forth in claim 36, further including, adjacent to a layer of the wound strip, a layer of a material having properties different from that of the wound strip.

39. An ultrasonic consolidated nanostructured material comprising: a plurality of feedstock portions formed from a source material using a high strain deformation process, and having a nano-sized grain structure therein; a bond, generated from ultrasonic consolidation, securely placed between adjacent portions to maintain the position of the portions relative to one another; wherein the bond is provided with minimal melting characteristics on each of the portion.

40. A nanostructured material as set forth in claim 39, wherein the feedstock portions have Vickers hardness ranging up to over about 300 percent above a predefined hardness of a source material.

40. A nanostructured material as set forth in claim 37, further including, adjacent to a feedstock portion, a layer of a material having properties different from that of the feedstock portion.