Patent Application
20130236352
Aspects of the present invention relate generally to nanomaterial-based composites, and more specifically, to materials and methods involving the incorporation of nanomaterials to form metal-type composites.
Material properties such as strength and ductility are important for a multitude of applications. One approach to enhancing the properties of metal-based materials involves the introduction of additional materials to metal. Recently, very small particles having dimensions in the nanometer scale have been introduced to metal-based materials.
While nanometer-scale materials (“nanomaterials”) such as nanoparticles and nanoplatelets can be useful in a variety of applications, such nanomaterials often align to grain boundaries or gather in clusters, which can limit the ability to enhance various properties of metal-based materials. For example, incorporating nanoplatelets such as graphene sheets into metal alloys can be difficult due to large surface areas, thin sheet geometry and high surface energy, which can lead to agglomerations. Moreover, nanomaterials are difficult to handle, as they tend to float to the surface of the molten metal and/or agglomerate, such that the nanomaterials do not stay dispersed in the metal. Accordingly, nanocomposite materials (e.g., a matrix to which nanomaterials have been added to improve one or more material properties) are challenging to produce in large, industrial size quantities.
These and other problems have been challenging to a variety of materials, and to methods for making those materials.
Various aspects of the present invention are directed to materials and methods involving the incorporation of nanomaterials into metal-based materials.
In accordance with various embodiments, nanomaterials such as nanoparticles and/or nanoplatelets are dispersed within a metal-based material via stirring of the material in a partially-solidified state. Viscous characteristics of the metal-based material are used to maintain the nanomaterials in a dispersed arrangement.
In various embodiments, stirring as discussed above is effected during processing as a metal-based material cools from a liquid state to a solid state, such as in an extrusion process that begins with molten metal. This approach can be carried out such that heat within the extruded metal is sufficient to facilitate stirring of the partially-solidified material (e.g., prolonging tool life), with the heat being low enough such that the extruded metal is sufficiently viscous to maintain the dispersion of the nanomaterials. In certain embodiments, ultrasonic or mechanical stirring is used to initially disperse the nanomaterials within the molten metal, with subsequent stirring in the partially-solidified state breaking up clusters or other agglomerations of the nanomaterials (e.g., as may occur while the material is still in a molten state and/or begins to cool).
In accordance with another example embodiment, nanomaterials are introduced to a metal-based material in a liquid state, and the metal-based material with nanomaterials therein are cooled from the liquid state to a viscous state (e.g., at or near a solidous temperature). The metal-based material is stirred in the viscous state to disperse the nanomaterials therein, and the metal-based material is used to maintain dispersion of the nanomaterials as the metal-based material cools. In some implementations, the metal-based material is provided in the viscous state by heating the material with an external source to the viscous state, prior to stirring.
Another example embodiment is directed to an article of manufacture including a metal-based material in a viscous state, and a plurality of nanomaterials dispersed throughout a grain structure of the metal-based material. The viscous state is a state at which the metal-based material is above its solidous temperature and at least a portion of the metal-based material is in a liquid state. In the viscous state, the metal-based material prevents substantially all of the dispersed nanomaterials from reclustering.
The above summary is not intended to describe each embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify various embodiments.
Aspects of the invention may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which.
While various embodiments of the invention are amenable to modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention including aspects defined in the claims.
Various aspects of the present invention are directed to nanomaterial-based materials and to related approaches involving the incorporation of nanomaterials in such materials, and to addressing related problems. While the present invention is not necessarily limited to such approaches, various aspects of the invention may be appreciated through a discussion of examples using this context.
In connection with various example embodiments, mechanical stirring is carried out to mix a metal-based material, and can be used to disperse nanomaterials, such as nanoparticles, nanofibers or nanoplatelets (e.g., graphene sheets) within a viscous metal-based material, using viscous characteristics of the metal-based material to maintain dispersion of the nanomaterials. Such a viscous state refers to a state occurring while the metal-based material cools from a liquid (molten) state at or above the melting temperature of the metal-based material, to a solid state below the melting temperature. Relative to the liquid state, the viscous state exhibits a higher viscosity, yet facilitates mechanical stirring relative, for example, to a solid state.
In connection with various example embodiments, it has been discovered that mechanical stirring at such an elevated material temperature facilitates dispersion yet utilizes viscous characteristics of the metal-based material to mitigate recombination/clustering with relatively low tool wear. If implemented during processing from a molten to solid state (e.g., during extrusion), these approaches can further be effected without adding heating energy via external heating and/or via friction stirring. The resulting dispersed (e.g., uniformly) nanomaterials can be used to greatly enhance mechanical properties of the resulting nanomaterials-metal composite material, such as may relate to enhanced interfacial bonding between the nanomaterials and the resulting metal matrix (e.g., metal matrix nanocomposite (MMNC)).
In a more particular example embodiment, a metal is heated above its liquidus temperature and is vibrated via ultrasonic processing. Once the metal is in a molten state, nanomaterials are fed into the molten metal during the ultrasonic processing. For example, ultrasonic processing may be used to disperse nanomaterials into molten metals using transient cavitation (with temperatures of about 5000° C., pressures of about 1000 atm) and acoustic streaming to incorporate and disperse the nanomaterials in the liquid state. The metal-nanomaterial mixture is cast into a plate, and at least a portion of the (partially cooled) plate is stirred using a rotating tool while the material is in a viscous (semi-solid) state. Multiple tools can be used, as can various tool types. In addition, these approaches can be implemented in continuous casting applications. Further processing may be carried out to provide the resulting material in sheet and/or ingot form. The figures and examples below further characterize such applications/embodiments.
As discussed above, a variety of nanomaterials such as carbon-based materials, ceramic materials and others can be dispersed in a variety of different metals and metal matrixes using approaches as described herein. Stirring of a the metal-nanomaterial combination in a viscous state facilitates the dispersion of ones of the nanoparticles that have been pushed together (e.g., by a solidification front due to repulsive Van der Waals forces between the nanoparticles and the solidification front). These approaches can be used to achieve stress-strain characteristics including yield strength, ultimate tensile strength, and elongation as relative to enhanced strength and ductility.
In one particular implementation, aluminum-based and titanium-based alloys (e.g., Al 206 with alumina (Al2O3) nanomaterials having a size of about 100-200 nm, or Al with graphene particles) can be cast using dispersion approaches discussed herein. The alpha Al2O3 can be dispersed into the Al 206 using liquid state ultrasonic processing, therein forming a liquid-state composite mixture. The Al2O3 nanomaterials may be fed, for example, into a melt of Al 206 with a double-capsulate feeding method and subsequently (initially) dispersed by ultrasonic processing.
Other approaches involve using magnesium as a metal matrix into which graphene nanoplatelets are dispersed, to form a reinforced Mg-based MMNC. Such nanoplatelets may, for example, be about 10-20 nm thick with x and y dimensions of less than about 14 μm. For instance, an automatic feeding system (feed-screw-based) can be used to feed graphene nanoplatelets into a Mg melt at about 700° C. under ultrasonic cavitation generated by a high power ultrasonic probe. After feeding, the graphene nanoplatelets are further dispersed by ultrasonic processing for 15 minutes more. The melt with graphene nanoplatelets is then cast into a plate-like viscous mold (e.g., placed in a mold/trough that holds the melt in place), to form a Mg plate (e.g., at a thickness of 6 mm) reinforced with graphene nanoplatelets, in a viscous state.
Once in a viscous state, the metal mixture/matrix as discussed in the examples above is stirred. The liquid-state mixture is then allowed to cool to a viscous state, above or at about a solidous temperature of the mixture. At such a condition, the mixture is stirred using a stirring tool in accordance with one or more approaches as discussed herein, with the heat in the mixture being substantially independent or independent from any friction-based heating via the stirring tool. Accordingly, energy from the tool is predominantly mechanical stirring, with generally little or insubstantial heating of the mixture being introduced via the stirring. In one implementation, a rotating pin with diameter of about 5 mm and length of about the thickness of the plate is inserted into the plate and traversed from side to side of the plate, using a rotating speed of about 1800 rpm and travel speed of 25 mm/min. This stirs the nanoplatelets along the travelling path in a viscous state to disperse the nanoplatelets in the Mg matrix. In one such example, Mg-based nanocomposites are reinforced with 1.2 vol. % graphene nanoplatelets to achieve a microhardness of about 66 kg/mm2 (e.g., 78% higher than the hardness of pure Mg prepared under the same condition (37 kg/mm2)).
Another example embodiment is directed to a method of forming a metal-based structure. Nanomaterials are introduced to a metal-based material in a liquid state, and the metal-based material with nanomaterials therein are provided in a viscous state at which the metal-based material is above its solidous temperature and at least a portion of the metal-based material is in a liquid state. This approach may involve, for example, cooling the metal-based material from a liquid state (e.g., during a casting process) to a solid state (e.g., at room temperature), with the viscous state being between the liquid and solid state as relative to temperature of the metal-based material. This approach may also involve, for example, heating the metal-based material after it has cooled from the liquid state to a solid state (e.g., at room temperature), to the viscous state. In the viscous state, the metal-based material is stirred in the viscous state to disperse the nanomaterials therein. These approaches can be carried out to stir the metal-based material while providing substantially no friction-based heating of the metal-based material via the stirring (i.e., the viscous state is provided via heating from a source predominantly other than any friction based heating from the stirring).
Various other embodiments are directed to an article of manufacture at a state of manufacturing as discussed herein. In one particular embodiment, an article of manufacture includes a metal-based material in a viscous state at which the metal-based material is above its solidous temperature, and at which a portion of the metal-based material is in a liquid state. The metal-based material includes a plurality of nanomaterials dispersed throughout a grain structure of the metal-based material. The metal-based material is configured and arranged to prevent substantially all of the dispersed nanomaterials from reclustering.
In certain embodiments, friction from the stirring of the partially-solidified material is also used to heat the material, which facilitates the dispersion of the nanomaterials therein. This approach involves at least some solid-state deformation of the partially-solidified material, while also using partially solidified state characteristics of the metal-based material to facilitate the dispersion of the nanomaterials. This approach can be carried out, for example, by cooling a metal mixture to at or slightly below its solidous temperature, using heat within the material but also adding some heat via the stirring.
Certain embodiments are directed to stirring a metal-based material at a partially-solidified state during solidification from a molten state to a solid state. The stirring is carried out at an elevated temperature, such as described hereinabove, and without necessarily adding nanomaterials to the metal-based material. With this approach, the resulting material (as solidified upon further cooling) exhibits desirable characteristics corresponding to the stirring of the material, while mitigating tool wear issues as may be relevant to stirring solid metal (e.g., at room temperature). In addition, various embodiments are directed to incorporating nanomaterials such as graphene nanoplatelets into a metal matrix to set or control diffusion in metals, such as for tuning one or more of creep, grain coarsening, and corrosion resistance of metals.
The materials as described herein can be implemented in one or more of a variety of applications. In some embodiments, extruded metal is manufactured and used for power-line applications. Nanomaterials mixed within a molten metal are dispersed as the metal is extruded into power lines as the extruded metal cools, using a stirring process as discussed to disperse the nanomaterials while also using viscous characteristics of the power lines to mitigate recombination (e.g., clustering) of the nanomaterials. The resulting power lines are implemented without necessarily wrapping or otherwise supporting the power lines with additional materials, as facilitated via increased strength therein as provided by the nanomaterials mixture.
In other embodiments, a resulting metal-nanomaterial matrix is used in one or more of battery applications, aluminum applications, solder and bearings. For instance, dispersed nanomaterials can lubricate bearings, which help to disperse nanomaterials that are difficult to disperse under liquid (low viscosity) conditions.
Turning now to the figures,
Various parameters as used in the dispersion may vary, depending upon the application. For example, the direction of rotation is shown by way of example as rotating clockwise with respect to an upper surface of the material 100, with advancing and retreating sides as shown. However, the tool 110 traversed in one or more directions and/or with non-linear motions throughout the material 100, to suit particular applications. In addition, a variety of metal-based materials can be used for the material 100, and a variety of nanomaterials can be dispersed therein.
As discussed above, the material 100 can be heated as part of a fabrication process, in which the heat of the process is used to set the viscous state of the material as it cools from a liquidous state to a solid state, with the stirring being effected in a viscous state in which the heat in the material is predominantly independent from the stirring. Other approaches to heating involve the use of an external heating source to bring and/or hold the material 100 above or near its solidous temperature.
The ultrasonic processing system 210 includes an ultrasonic probe 212 (e.g., made of niobium alloy C103), a booster 214 and a transducer 216. The ultrasonic probe 212 ultrasonically cavitates the molten metal 240 and disperses the nanomaterials therein. In one example, the ultrasonic processing system subjects the molten metal 240 (with nanomaterials therein) to intense transient ultrasonic cavitation, at a temperature of about 5000° C. and pressure of about 1000 atm, with strong acoustic streaming (e.g., for about 15 minutes). The molten metal 240 with mixed nanomaterials therein can then be used to form a resulting piece such as the material 100 shown in
Referring to
As discussed above, the system(s) as shown in one or all of
The various tools and approaches as shown in
In some embodiments, the process continues at block 1040, in which the metal-based material is further cooled to form a resulting structure with the nanomaterials dispersed therein. For instance, a continuous casting process can be carried out in which a metal ingot is formed with dispersion as shown in
Cooling the metal-based material at block 1020 can be carried out in a variety of manners. In some embodiments, the metal-based material is cooled from a temperature in which all the metal-based material is in a liquid state, to a temperature above a solidous temperature of the metal-based material at which at least a portion of the metal-based material is in a liquid state. In another embodiment, the metal-based material is cooled to a temperature about at a solidous temperature of the metal-based material, and in another embodiment, the metal-based material is cooled to a temperature that is within about 30 degrees Celsius below a solidous temperature of the metal-based material.
In various embodiments, the temperature and/or phase of the metal-based material is monitored/detected to determine a point at which the metal-based material has sufficient viscosity to maintain dispersion of nanoparticles, and stirring is effected at this temperature. Once dispersed, the stirring can be terminated while the metal-based material further cools, holding the nanomaterials in the dispersed state.
Various embodiments described above and shown in the figures may be implemented together and/or in other manners. One or more of the items depicted in the drawings/figures herein can also be implemented in a more separated or integrated manner, or removed and/or rendered as inoperable in certain cases, as is useful in accordance with particular applications. For example, a variety of different types of nanomaterials can be incorporated with different types of materials. In addition, one or more approaches to the incorporation of nanomaterials may be implemented in whole or part, with a variety of applications. In view of this and the description herein, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention.
This invention was made with government support under 70NANB10H003 awarded by NIST. The government has certain rights in the invention.
