Patent Application
20240183007
This disclosure relates to the field of extrusion of Metal Matrix Composite (MMC, or MMCs) including high conductivity MMCs.
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.
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.
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.
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.
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.
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.
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 5.8001×107 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 (<10 cm) 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
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
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.
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.
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.
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
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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.
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.
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.
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.
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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.
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.
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, Iron (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).
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 63385490 | Nov 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2023/081824 | Nov 2023 | WO |
| Child | 18437721 | US |
