BACKGROUND

[0001] This disclosure relates to the field of extrusion of Metal Matrix Composite (MMC, or MMCs) including high conductivity MMCs.

[0002] A Metal Matrix Composite is a primary metal with fibers or particles dispersed as a second phase within a metallic matrix. The second phase material does not covalently bond with the metal, in other words, it is insoluble within the primary metal. Hereafter, the second phase is often described as a “non-metallic” or “additive”, to distinguish it from the primary metal.

[0003] There have been developments in manufacturing metals that are combined with non-metallic materials to produce new metal matrix composite (MMC) materials. Extrusion processes such as hot metal extrusion and friction extrusion have been used to combine metals, metal alloys and non-metallic materials to create MMCs. These extrusion methods fall under a broad group known as solid phase or solid state processing, hereafter referred to only as solid phase processing. Solid phase processes, including hot metal extrusion and friction extrusion, are distinguished from traditional wrought metallurgy because they operate below the melting point of the metal or metal alloy (versus fully melting the metal or metal alloy to a liquid state). Solid phase processes operate by plastically deforming the extruded metal. During solid phase processes, non-metallic materials are integrated with the metal or metal alloy while the metal or metal alloy is plasticized, thereby creating metal matrix composites that may have beneficial properties.

[0004] Solid phase processes may facilitate creation of MMCs that otherwise might not be possible by traditional molten metallurgy methods. For example, allotropes of carbon, ceramics and other non-metallic materials are insoluble in metal and are not generally combinable with metal using traditional molten metallurgy methods.

[0005] Hot metal extrusion is a metal forming process that uses a pre-heated metal billet which is placed in a chamber. The billet is generally heated above the recrystallization temperature of the metal in the billet but under the melting temperature of the metal. One side of the chamber contains a die with a desired cross section and the other side a ram that pushes the metal billet through the die. Metal plasticizes, flows through the profile of the die and, after solidification, takes the shape of the die. FIG. 1 A and 1 B illustrate a prior art billet 40. Billet 40 is a generally cylindrical rod having a length L and a diameter D. An example billet 40 could have a diameter D of between 2 inches (5.1 cm) and 6 inches (15.2 cm) and a length L of up to 3 feet (91 cm). Other processes could use a billet with different dimensions.

[0006] Friction Extrusion typically rotates the billet relative to the extrusion die in combination with an extrusion force that is applied to push the billet against the die. Alternately, either the die may be rotated against a stationary billet, or billet may be rotated against a stationary die, or the die and billet can be counter-rotated against each other. The relative motion produces frictional heat and large shear stresses that plastically deform the layer of the billet in contact with and near the die. The friction between the die and billet produces sufficient heat, so friction extrusion generally does not require preheating the billet. The plastic deformation can promote metallurgical bonds between powder particles or other finely divided precursors that can improve consolidation of the billet prior to extrusion. While Friction Extrusion heats the material at the die-billet interface, the process can be controlled to maintain the temperature below the melting point of the billet.

[0007] Various MMC materials produced by hot metal extrusion and friction extrusion have exhibited other valuable characteristics including improved mechanical properties such as increased strength relative to the material weight. Such improved mechanical properties can result in lighter weight components and/or substitution of less expensive materials to achieve similar results.

[0008] MMCs consisting of Copper (Cu) combined with Graphene (GR) have shown improved electrical conductivity compared to pure Copper. Pure Copper is used for many low to medium voltage electrical conductors and conducting electromechanical components due to its high electrical conductivity (typically 100% IACS, or 5.8001 x 10 ⁷ S/m) and desirable mechanical properties. Graphene and other forms of nano-Carbon have significantly higher electrical conductivity than Copper (up to and over 800% IACS), although with less useful mechanical properties. Using various solid-phase processes such as hot extrusion or friction extrusion, MMCs made by adding Carbon nano materials such as Carbon nano- tubes (CNT), Graphene or other nano-particle forms of Carbon to Copper have shown improved electrical conductivity compared to pure Copper, while maintaining the useful mechanical properties of Copper. Other conductive metals, when homogenously synthesized into a MMC, would likely also realize gains in conductivity. However, prior art techniques for producing MMC material with such improved electrical conductivity have not produced materials with consistent improved conductivity on a scale that would permit mass production of enhanced conductivity material. For example, using prior art methods, the addition of Graphene into Copper by friction extrusion has shown only local increases of electrical conductivity up to 105%-106% IACS, but such increased conductivity was only present in short lengths (<10cm) and was inconsistent along the length of the friction extruded wire samples. Prior art methods resulted in over 30% of the samples having lower conductivity than unmodified copper (see Table 1 and Figure 2).

Table 1 : Reference and Prior Art Cu-GR MMC

*Source: Electrical Engineer's Reference Book (Sixteenth Edition), 2003

**Source: Battelle Pacific Northwest National Lab

[0009] There is a need for improved methods of solid phase manufacturing of MMC materials that results in increased homogeneity of the characteristics of the resulting MMC material. This application focuses on billet manufacturing techniques to create pre-extrusion forms that promote such homogeneity (See Figure 1 ). There is a need for Copper-based MMC materials with enhanced conductivity that can be produced consistently, preferably at industrial scale. With the broad use of copper as an electrical conductor, even a small percentage increase in conductivity could enable a new class of more efficient conductors, thereby reducing energy waste and aiding in the fight against Greenhouse Gas (GHG) emissions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a prior art billet.

FIG. 1 B is an end view of the FIG. 1 A billet.

FIG. 2A is a side view of a prior art billet.

FIG. 2B is an end view of the FIG. 2A billet.

FIG. 3 is a side view of a prior art wire extruded from the FIG. 2A billet.

FIG. 4 is a metallographic microstructure evaluation of a Cu-Graphene wire friction-extruded from the FIG. 2A billet. The slice is tangential to the longitudinal axis of the wire.

FIG. 5 is an end view of a first billet.

FIG. 6 is an end view of a second billet.

FIG. 7 is an end view of a third billet.

FIG. 8 is an end view of a fourth billet.

FIG. 9 is an end view of a fifth billet.

FIG. 10 is an end view of a sixth billet.

FIG. 11 is a side cross-sectional view of the FIG. 10 billet.

FIG. 12 is an end view of a seventh billet.

FIG. 13 is a side cross-sectional view of the FIG. 12 billet.

FIG. 14 is an end view of an eighth billet.

FIG. 15 is a side perspective view of the FIG. 14 billet.

FIG. 16 is an end view of a ninth billet.

FIG. 17 is an end view of a tenth billet.

DETAILED DESCRIPTION OF THE DRAWINGS

[0010] For the purpose of promoting an understanding of the principles of the claimed invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the claimed invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the claimed invention as described herein are contemplated as would normally occur to one skilled in the art to which the claimed invention relates. Embodiments of the claimed invention are shown in detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present claimed invention may not be shown for the sake of clarity.

[0011] With respect to the specification and claims, it should be noted that the singular forms “a”, “an”, “the”, and the like include plural referents unless expressly discussed otherwise. As an illustration, references to “a device” or “the device” include one or more of such devices and equivalents thereof. It also should be noted that directional terms, such as “left”, “right”, “up”, “down”, “top”, “bottom”, and the like, are used herein solely for the convenience of the reader in order to aid in the reader’s understanding of the illustrated embodiments, and it is not the intent that the use of these directional terms in any manner limit the described, illustrated, and/or claimed features to a specific direction and/or orientation.

[0012] One reason to investigate MMC’s is the pursuit of enhanced conductive materials. The inventors’ experimentation was primarily with Copper, since it is the most common conductor, and also a Copper alloy, to learn if the methods could also apply to alloys. However, the methods taught herein could also apply to manufacture MMCs using other metals or alloys to achieve desirable electrical and mechanical properties. Data showing Enhanced Electrical conductivity results are described later within this application. Note that the Wiedemann-Franz principle teaches that thermal conductivity often correlates with electrical conductivity. Therefore, enhanced thermal conductivity properties, including improved Thermal Coefficient of Resistance (TCR) could also result from the methods described within this application. [0013] A potential issue identified by the Applicants in the prior art methods used to create enhanced conductive Copper-based MMC materials described above is the distribution of the non-metallic material in the billet that is extruded. One type of billet that has produced inconsistent results is shown in FIGs. 2A and 2B as billet 45. Billet 45 consists of a metallic cylinder of material sliced at a right angle to the longitudinal axis along the length of the cylinder to form several smaller cylinder segments 46. Metallic foil 48, that is coated with the non-metallic material, is positioned between adjacent cylinder segments 46 to form billet 45 in approximately the original cylindrical shape with the non-metallic material distributed along the length of the billet between each of the slices. Billet 45 is then processed using either friction extrusion or hot metal extrusion. Applicants had identified that this configuration does not adequately distribute the non-metallic material along the longitudinal length of the billet which may contribute to the resultant extruded Copper-based MMC material having varying material properties along the length of the MMC extrudate. This application teaches novel techniques for packaging the pre-materials (i.e. primary metal, plus additive), which can then promote more consistent and predictable solid phase extruded materials.

[0014] Referring to Fig. 3, a length of prior art Copper-based MMC is illustrated as wire 45’. Wire 45’ includes regions of nominal conductivity 46’, regions of enhanced (< 2% over nominal) conductivity 47 and regions of reduced conductivity 49. Referring to Fig. 4, a metallographic microstructure evaluations of a friction-extruded Cu-Graphene wire using prior art methods is illustrated. The illustrated slice is perpendicular to the longitudinal axis of the wire. The right side of the image corresponds to the center of the wire and the left side of the image corresponds to an outer edge of the wire. Note the significant variation in grain size between the center of the wire and its outer edge regions, as well as material flow lines.

[0015] In principle, both Friction Extrusion and Hot Metal Extrusion keep the temperature of the billet below the melting temperature of the metal in the billet (the non-metallic material generally has a higher melting temperature than the metal). Producing fully dense Copper-based extrudate MMC materials with either Friction Extrusion or Hot Metal Extrusion requires an extrusion ratio of at least 20:1. Extrusion ratio is defined as the ratio of the cross-sectional area of the original billet to that of the extrudate. In other examples, extrusion ratios of 80:1 or 100:1 are used. After extruding the MMC, the MMC extrudate can be further shaped and processed using known metal process including, but not limited to, hot rolling, cold rolling, annealing and drawing.

[0016] Applicants have created new billet configurations for use in either friction extrusion or hot metal extrusion that result in improved distribution of the non- metallic material along the longitudinal length of the billet and throughout the subsequent MMC extrudate.

[0017] For Copper-based MMC materials, the desired amount of non-metallic material is measured in parts per million, so the overall amount of non-metallic material can be minuscule in comparison to the amount of metallic material in the billet. For example, a desirable weight percentage of Graphene compared to Copper to produce a Copper-Graphene MMC with enhanced conductivity, could be between 10 PPM to 250 PPM.

[0018] Each of the following billets are preferably created and/or processed in an atmosphere that is non-reactive to both the metal and non-metallic materials in the billet. For many materials the primary concern is the absence of Oxygen when material is heated to reduce or eliminate any oxidation that could occur. However, preferred atmospheric conditions can vary with different materials. In the case of Copper and Graphene, a Nitrogen or Argon atmosphere can be used when materials are heated.

[0019] Referring to FIG. 5, billet 50 is illustrated. Billet 50 generally includes wires 52, coating 54 on wires 52 and jacket 56. Wires 52 are coated with coating 54 that can include the desired non-metallic material. Wires 52 are packed inside jacket 56. Wires 52 can each consist of the same metallic material or a different material can be used with different wires 52, depending on the desired MMC material. Coating 54 can be applied to every wire 52 or coating 54 can be applied to a subset of wires 52, depending on the amount of non-metallic material desired. Jacket 56 can consist of the same metallic material as wires 52 or a different material can be used, depending on the desired MMC material. Copper-Graphene MMC could be produced using Copper or Copper-Silver alloy wires that are coated with Graphene by any suitable physical or chemical deposition process. [0020] Referring to FIG. 6, an alternative embodiment of billet 50 is illustrated. Billet 50 generally includes wires 52, wires 53, coating 54 on wires 52 and/or wires 53 and jacket 56. Wires 52 and 53 have different diameters. Wires 52 and 53 can consist of the same metallic material or a different material can be used in various wires, depending on the desired MMC material. Coating 54 can be applied to every wire 52 and/or wire 53 or coating 54 can be applied to a subset of wires 52, depending on the amount of non-metallic material desired. Jacket 56 can consist of the same metallic material as wires 52 or a different material can be used, depending on the desired MMC material. Copper-Graphene MMC could be produced using Copper or Copper-Silver alloy wires that are coated with Graphene, or a mix of pure Copper and Copper-Silver alloy wires in the same or different diameters coated with Graphene using any suitable physical or chemical deposition process.

[0021] Referring to FIG. 7, billet 60 is illustrated. Billet 60 generally includes powder 62 and powder 64. Powder 62 can be a metallic material and powder 64 can be a non-metallic material. Billet 60 is formed as a cylinder by blending, pressing and, if advantageous or needed for the extrusion process chosen, sintering powders 62 and 64 together. Copper-Graphene MMC could be produced using powdered micron-sized Copper or Copper-Silver alloy and Graphene nano-platelets or any other nano-crystalline carbon in powder of flake form, for example Carbon nano-tubes.

[0022] Referring to FIG. 8, billet 70 is illustrated. Billet 70 generally includes metallic segments 72 coated with non-metallic material 74. Metallic segments 72 are pressed into the shape of billet 70. Metallic segments 72 could optionally comprise segments of metallic wire cut to length. Metallic segments 72 could have substantially uniform size, or the size could optionally vary between different metallic segments 72. In one example, metallic segments 72 are wire cut-offs that are coated with non-metallic material by processing the wire cut-offs and non-metallic material powder in a dry ball mill. Copper-Graphene MMC could be produced using Copper wire cut-offs and Graphene platelets or other carbon nano-crystalline material in powder form processed with Stainless Steel balls in the ball mill under a protective non-oxidizing atmosphere. [0023] Referring to FIG. 9, billet 80 is illustrated. Billet 80 generally includes billet quarters 82, non-metallic material 84 and optional jacket 86. Billet quarters 82 can be formed by cutting a solid metal billet twice lengthwise. Non-metallic material 84 can be a foil containing the non-metallic material placed between adjacent quarters 82 and/or non-metallic material 84 can be coated onto the cut surfaces of billet quarters 82. Optional Jacket 86 surrounds the outside of billet quarters 82. In addition, radial surface 85 may optionally be coated with a non-metallic material. Note that while billet 80 shows 2 cuts forming quarters, other cuts could be used, including, but not limited to a single cut that halves the billet, additional cuts that pass through the center of the billet that further subdivide billet 80, for example, into 6 pieces, 8 pieces or more. And additional cuts that do not all pass through the center of the billet which also future subdivide billet 80, for example into square pieces rather than pie shaped pieces. Copper-Graphene MMC could be produced using a Copper or Copper-Silver alloy billet and Copper foil coated with Graphene placed between the cut segments.

[0024] Referring to FIGs. 10 and 11 , billet 90 is illustrated. Billet 90 generally includes one or more holes 92, fill 94 and end caps 96. Billet 90 is a metallic cylinder. One or more holes 92 are drilled along the longitudinal length of billet 90. Holes 92 can be spaced apart within the volume of billet 90. Holes 92 can be positioned at varying distances from a center axis of billet 90. Holes 92 are filled with fill 94. End caps 96 retain fill 94 within holes 92. Fill 94 can be powdered material such as Graphene platelets. Fill 94 can be tamped into holes 92. End caps 96 can be metallic material that corresponds to the material of billet 90, for example, a metallic plug pressed or welded in place. Copper-Graphene MMC could be produced using a Copper or Copper-Silver alloy billet and Graphene nano-platelets, Carbon nano-tubes or other nano-crystalline carbon forms in powder form as fill.

[0025] Referring to FIGs. 12 and 13, billet 90’ is illustrated. Billet 90’ generally includes one or more holes 92, fill 94 and end caps 96. Billet 90’ is a metallic cylinder. One or more holes 92’ are drilled along the majority of the longitudinal length of billet 90’. Note that holes 92’ are not through holes. Holes 92’ can be spaced apart within the volume of billet 90’. Holes 92’ can be positioned at varying distances from a center axis of billet 90’. Holes 92’ are filled with fill 94 as described above with reference to FIGs. 10 and 11. End caps 96 retain fill 94 within holes 92’. [0026] Referring to FIGs. 14 and 15, billet 100 is illustrated. Billet 100 generally includes one or more slices 102 each containing sheet 104. Slices 102 pass through a portion of billet 100 but do not sever billet 100 into separate segments. Slices 102 may extend along the longitudinal length of billet 100. Sheet 104 can be a foil containing the non-metallic material. Copper-Graphene MMC could be produced using a Copper or Copper-Silver alloy billet and Copper foil coated with Graphene placed in the slices.

[0027] Referring to FIGs. 16 and 17, alternative embodiments of billet 100 are illustrated with different numbers and configurations of slices 102. As in FIGs. 14 and 15, each slice 102 contains a sheet 104 that contains the non-metallic material. FIG. 16 illustrates an embodiment with three slices and FIG. 17 illustrates and embodiment with seven slices. Different configurations and numbers of slices can be used to achieve a desired distribution of non-metallic material.

[0028] An enhanced conductive Copper-Graphene MMC can be made using either pure Copper or a Copper Alloy, in this case a Copper-Silver (CuAg) alloy with Ag content from 0.1 to 2.5 wt% (see Tables 2 and 3 below). Note that use of a billet prepared using the methods disclosed in this application results in Enhanced and more consistent Electrical Conductivity, and facilitates higher levels of GR additive than Prior Art referenced on Table 1 (using the same solid phase process). Graphene can take the form of Graphene nano-platelets (GNP), Copper foil coated with Graphene and Carbon nano-tubes.

Table 2: Pure Copper + GR MMC Sample prepared using method described within this application.

*Source: Electrical Engineer's Reference Book (Sixteenth Edition), 2003 **Source: NAECO, per test Method ASTM B193B-20

Table 3:- Copper-Silver Alloy + GR MMC Sample prepared using method described within this application.

Table 4: Vickers Micro-Hardness values - HV 0.1 - Plain Metals vs. MMCs

Source: NAECO, LLC (2023)

Table 5: Elongation-% per ASTM E8 for of Plain Metals vs MMCs

Source: Applied Technical Services, LLC (2023)

Table 6: Comparison of Enhanced Conductive Materials

(* MMC having minimum 2% improvement over pure metal with no additives)

[0029] Other property-enhancing nano-particles not specifically named within this application may be likewise incorporated with metals under the methods described within this patent. New property-enhancing nano-materials are under continuous development, for example: Single Layer graphene, Few Layer graphene, 3-dimensional graphene, MXenes, or similar non-metallic nano-particles. In addition to non-metallics, metallics or inter-metallics which are otherwise insoluble in the primary metal, may also be homogeneously integrated into MMCs using the techniques described within this application.

[0030] Other types of MMCs that could be produced using the methods disclosed in this paper include, but are not limited to, combinations using primary metals including, but not limited to, the common highly conductive metals: Copper (a transition metal group element)) and Copper Alloys, Aluminum (a metal group, sometimes referred to as a post-transition group, element) and Aluminum Alloys, Silver (a metal group element) and Silver alloys, lron(a transition metal group element) and Alloys/Steels, Noble Metals (a subgroup of the transition metals that includes Platinum, Palladium, Iridium, etc.), Cadmium (an alkaline earth metals group element).

[0031] While the present disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that a preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the claimed invention defined by following claims are desired to be protected.

[0032] The language used in the claims and the written description and in the above definitions is to only have its plain and ordinary meaning, except for terms explicitly defined above. Such plain and ordinary meaning is defined here as inclusive of all consistent dictionary definitions from the most recently published (on the filing date of this document) general purpose Merriam-Webster dictionary.