Modern structural applications, including those used in aerospace, automobiles, consumer electronics, and industrial applications, often require materials that have differing properties. For example, a material's: strength-to-weight ratio; stiffness (how much a material deflects under a given load); ductility (the amount of plastic deformation under tensile stress a material may undergo before failure); coefficient of thermal expansion (CTE) (the rate at which a material expands due to change in temperature); thermal conductivity (the rate at which heat is transferred by conduction through the material) all factor into selecting a material for different applications. While changes to a material may provide favorable gains in one material property, it may impact other material properties.
US Publication 2016/0373154 (application Ser. No. 15/175,840, filed Jun. 7, 2016) (the '154 Publication”) describes an electronic device housing utilizing a metal matrix composite (MMC), the entirety of which is incorporated by reference herein. The '154 publication describes using a particle-reinforced aluminum alloy MMC with a reinforcement content of 55 vol. % (Al/SiC-55 p) for improved stiffness over other materials in-use. Other properties of particle-reinforced MMC are described in Karandikar et. al, Al/Al2O3MMCs AND MACROCOMPOSITES FOR ARMOR APPLICATIONS, Ceramic Engineering & Science Proceedings 34 |5| (2013) pg. 63-74, the entirely of which is incorporated by reference herein. However, further improvements are needed.
In one aspect of the disclosure, reinforced metal matrix composites are described, including, for example, a porous ceramic reinforcement having pores therein, and a metal matrix in interstitial contact with the ceramic reinforcement within the pores. In another aspect of the disclosure, a porous ceramic reinforcement is interconnected. In another aspect of the disclosure, a porous ceramic reinforcement is from about 10 percent to about 20 percent by volume of the reinforced metal matrix composite. In yet another aspect of the disclosure, the porous ceramic reinforcement is continuous from a first end of the reinforced metal matrix composite to a second end of a reinforced metal matrix composite. In another aspect of the disclosure, a size of the pores is from about 10 pores per inch (PPI) to about 50 PPI. In another aspect of the disclosure, a ceramic reinforcement has a nominal porosity of about 80%.
In one aspect of the disclosure a metal matrix comprises aluminum. In another aspect of the disclosure a porous ceramic reinforcement comprises aluminum oxide. In one aspect of the disclosure a metal matrix comprises ceramic particles. In another aspect of the disclosure, the ceramic particles comprise agglomerated aluminum oxide particles. In one particular aspect of the disclosure, agglomerated aluminum oxide particles comprise bonded aluminum oxide crystals having a diameter of from about 100 microns to about 200 microns. In another aspect of the disclosure the metal matrix comprises a metal alloy.
Disclosed herein are methods of forming a reinforced metal matrix composite. In one aspect of the disclosure, a method includes providing a porous ceramic reinforcement having pores therein, contacting the porous ceramic reinforcement with a liquid metal matrix, and solidifying the liquid metal matrix. In another aspect of the disclosure, providing a porous ceramic reinforcement includes applying a ceramic to a polymer foam and sintering the ceramic. In another aspect of the disclosure a method includes adding ceramic particles to a liquid metal matrix. In another aspect of the disclosure, the ceramic particles are added to the porous ceramic reinforcement prior the liquid metal matrix. In yet another aspect of the disclosure, ceramic particles are added to a liquid metal matrix prior to contacting the porous ceramic reinforcement with the liquid metal matrix. In a further aspect of the disclosure, ceramic particles may include agglomerated aluminum oxide particles.
Disclosed herein are methods of forming a reinforced metal matrix composite.
In one aspect of the disclosure, a porous ceramic reinforcement is interconnected. In another aspect of the disclosure, a porous ceramic reinforcement is from about 10 percent to about 20 percent by volume of a reinforced metal matrix composite. In yet another aspect of the disclosure, a porous ceramic reinforcement is continuous from a first end of the reinforced metal matrix composite to a second end of the reinforced metal matrix composite. In another aspect of the disclosure, a size of the pores is from about 10 pores per inch (PPI) to about 50 PPI. In a further aspect of the disclosure a ceramic reinforcement has a nominal porosity of about 80%. In another aspect of the disclosure, a metal matrix comprises aluminum. In another aspect of the disclosure the porous ceramic reinforcement includes aluminum oxide. In yet a further aspect of the disclosure, the disclosed methods may include machining at least one surface of the reinforced metal matrix composite.
As noted previously, many applications require materials that have differing properties. For example, many aerospace or mobile applications may call for materials having a high strength to weight ratio that are not necessary in less mobile applications. Further, applications that undergo increased shock and vibration may call for materials that are more ductile. Many types of electronic devices that are used for communication and/or entertainment purposes are relatively small; that is, configured to be hand-held, portable, or mobile devices, e.g. mobile telephone, tablets, laptops, and other wearable or hand carried devices. While needing to be sufficiently rugged to protect the complex electronics and communication components forming such a device, its outer housing (also referred to at times as a chassis, case, or shell) also needs to be relatively thin and lightweight for the comfort and convenience of the user. This is also true in other industrial environments where size and weight are a design criteria.
For example, steel is an attractive construction material for elements that require high stiffness. However, steel also has a high density, which leads to high component mass. Aluminum is can also be an attractive construction material for lightweight structural elements, since its density is significantly lower than steel. However, aluminum exhibits a very low stiffness, which leads to unwanted bending. Bending of an electronic or other sensitive device can lead to catastrophic damage. For example, there have been reports of consumer complaints regarding bending problems associated with lightweight electronic housings.
Besides the needs for lightweight, yet durable, consumer electronics housings, various commercial electronic devices (particularly, military) also derive benefits from a housing that provides the desired degree of stiffness/strength for a wide range of environmental factors, yet is lighter in weight than housings made of steel or other high-strength materials. The same is true in other industries where weight and impact resistance is a factor in the design. For example, aerospace applications (e.g., landing gear, struts, ramps, satellite components, etc.) and automotive components (e.g., connecting rods, brake calipers, pistons, piston pins, etc.).
As noted previously, the '154 publication describes using a particle-reinforced aluminum alloy MMC with a reinforcement content of 55 vol. % (Al/SiC-55 p) for improved stiffness over other materials in-use. However, such a solution also produces a relatively brittle material (low ductility). Such low ductility would typically stem from the relatively high amount of SiC content required to obtain the desired stiffness in most applications and additional silicon added to the aluminum matrix alloy to prevent unwanted Al—SiC reactions occurring between the particle reinforcement and the aluminum alloy.
Disclosed herein are reinforced metal matrix composites and methods for forming reinforced metal matrix composites suitable for structural applications where both stiffness and ductility are needed. Example disclosed reinforced metal matrix composites include a ceramic reinforcement which is porous and/or interconnected in that the ceramic components are bonded to each other. An example porous ceramic reinforcement includes ceramic structures that form pores in three dimensions such that the resulting structural material has both increased stiffness and ductility.
The porous ceramic reinforcement 102 may be any suitable ceramic having the desired bonding or structural properties. In one example, the porous ceramic reinforcement 102 is made of, or includes, aluminum oxide, for example, Al2O3. The porous ceramic reinforcement 102 may also be made entirely of aluminum oxide. Alternatively, the porous ceramic reinforcement 102 may be made from or include alumina, silicon carbide, zirconia, bonded carbon, silica (silicon oxide), titania (titanium oxide), iron oxide, an alkali, and/or combinations thereof.
The metal matrix 104 may be any appropriate metal or metal alloy suitable for the chosen porous ceramic and desired structural properties of the resulting composite. For example, in one example, metal matrix 104 may be pure aluminum or an aluminum alloy, for example 6061 aluminum (having unified numbering system (UNS) designation A96061 according to SAE International publication “Metals & Alloys in the Unified Numbering System, 13th Edition,” ISBN 978-0-7680-8421-4, which is hereby incorporated by reference in its entirety). In another example, metal matrix 104 may be an Al—Mg alloy, where the Mg promotes wetting of the alloy to the porous ceramic reinforcement 102. For example, the Al—Mg alloy could include from about 0.5 to about 10 weight percent of magnesium.
The metal matrix 104 permeates the pores of the porous ceramic reinforcement 102 such that metal matrix 104 is present interstitially within the porous ceramic reinforcement 102, e.g., within the pores of the porous ceramic reinforcement 102. As shown in
Alternatively, as shown in
Porous ceramic reinforcement 102 includes pores 110 contained or formed therein as defined by the interconnected or bonded ceramic structures 120. The ceramic structures 120 extend in different directions forming a three-dimensional lattice of ceramic structures 120 and corresponding pores 110. The example ceramic structures 120 of
Porous ceramic reinforcement 102 may also be obtained commercially, for example, as foundry filters typically used to filter flowing liquid metal. For example, filters sold commercially by ASK Chemicals under the tradenames UDICELL and EXACTFLO, specifications for which are available at: https://www.ask-chemicals.com/fileadmin/user_upload/Download_page/foundry_products_brochures/EN/Minibooklet_Filters_EN.pdf and https://www.ask-chemicals.com/products-services/filters/exactflo-filters, the entire contents of each of which are incorporated by reference herein. Another example of a material suitable for an alumina based porous ceramic reinforcement 102 is available from ASK Chemicals under the tradename Alucel-LT, which contains 17.6% SiO2, 0.32 TiO2, 81.6% Al2O3, 0.23% FeO3, and 0.24% Alkali (each percentage by weight) and having bulk density of 0.51 g/cm3 and a porosity of about 80-85% (a fraction of the volume of the voids or pores over the total volume expressed as a percentage). Other examples are available from SELEE Corporation and sold under the trade names “Ceramic Foam Filters,” “Zirconia PRZ filters” (magnesia-stabilized zirconia), and “SELEE® Advanced Ceramics® kiln fumiture.”
Further, as shown in
With reference to
Alternatively, or in addition, to utilizing a pre-liquified metal matrix 104b, metal matrix 104 may be placed in contact with the porous ceramic reinforcement 102 as a solid metal matrix 104a, for example (as shown in
Optionally, the reinforced metal matrix composites may also include particle reinforcement in addition to the reinforcement provided by porous ceramic reinforcement.
The ceramic particles 270 may be any ceramic particles known in the art, including those previously used in particle reinforced MMC. Ceramic particles 270 may also include agglomerated ceramic particles, for example agglomerated aluminum oxide particles. Agglomerated ceramic particles are bonded together ceramic crystals. Ceramic particles 270, may include for example agglomerated alumina particles having a nominal diameter of between about 10 and about 250 microns (μm), for example, about 150 μm. In one example, the ceramic particles 270 are agglomerated ceramic particles, which are unground calcined alumina particles. A photograph of an agglomerated unground calcined alumina particle with a nominal diameter of about 150 μm formed of bonded individual 20 μm crystals, is shown in
The methods described with reference to
The resulting reinforced metal matrix composite 200 may have, for example, between about 0 percent to about 35 percent by volume, for example, between about 20 percent to about 30 percent by volume, or, for example, about 25 percent by volume of the ceramic particle 270 in the metal matrix 104.
It should be noted that elements and features described with one example embodiment are applicable to other example embodiments.