Patent Application
20140141164
The present invention generally regards layers of metallic glass-based materials, and techniques for fabricating such layers.
Metallic glasses, also known as amorphous metals, have generated much interest for their potential as robust engineering materials. Metallic glasses are characterized by their disordered atomic-scale structure in spite of their metallic constituent elements—i.e. whereas conventional metallic materials typically possess a highly ordered atomic structure, metallic glasses are characterized by their disordered atomic structure. Notably, metallic glasses typically possess a number of useful material properties that can allow them to be implemented as highly effective engineering materials. For example, metallic glasses are generally much harder than conventional metals, and are generally tougher than ceramic materials. They are also relatively corrosion resistant, and, unlike conventional glass, they can have good electrical conductivity.
Nonetheless, the manufacture and implementation of metallic glasses present challenges that limit their viability as engineering materials. In particular, metallic glasses are typically formed by raising a metallic glass above its melting temperature, and rapidly cooling the melt to solidify it in a way such that its crystallization is avoided, thereby forming the metallic glass. The first metallic glasses required extraordinary cooling rates, e.g. on the order of 106 K/s, to avoid crystallization, and were thereby limited in the thickness with which they could be formed because thicker parts could not be cooled as quickly. Indeed, because of this limitation in thickness, metallic glasses were initially largely limited to applications that involved coatings. Since then, however, metallic glass compositions that have lower critical cooling rates have been developed that have enabled a broader implementation of metallic glass materials. Nonetheless, implementing metallic glass coatings remains a viable technique for harnessing the advantages that metallic glasses can offer. Accordingly, the present state of the art can benefit from improved techniques for implementing layers of metallic glass.
Systems and methods in accordance with embodiments of the invention implement layers of metallic glass-based materials. In one embodiment, a method of fabricating a layer of a metallic glass includes: applying a coating layer of liquid phase metallic glass to an object, the coating layer being applied in a sufficient quantity such that the surface tension of the liquid phase metallic glass causes the coating layer to have a smooth surface; where the metallic glass has a critical cooling rate less than 1000 K/s; and cooling the coating layer of liquid phase metallic glass to form a layer of solid phase metallic glass.
In another embodiment, the thickness of the coating layer is greater than 50 micrometers.
In yet another embodiment, the thickness of the coating layer is greater than 1 mm.
In still another embodiment, the thickness of the coating layer is thinner than the plastic zone size of the metallic glass.
In still yet another embodiment, the object includes one of aluminum, titanium, steel, cobalt, graphite, quartz, silicon carbide, and mixtures thereof.
In a further embodiment, the metallic glass is a composition that has a glass forming ability such that it can be readily cast in to parts having a thickness greater than approximately 1 mm.
In a yet further embodiment, the metallic glass is a composition that has a glass forming ability such that it can be readily cast in to parts having a thickness greater than approximately 3 mm.
In a still yet further embodiment, the metallic glass is one of: Cu40Zr40Al7Be10Nb3, Cu45Zr45Al5Y2Nb3, Cu42.5Zr42.5Al7Be5Nb3, Cu41.5Zr41.5Al7Be7Nb3, Cu41.5Zr41.5Al7Be7Cr3, Cu44Zr44Al5Ni3Be4, Cu46.5Zr46.5Al7, Cu43Zr43Al7Ag7, Cu41.5Zr41.5Al7Be10, Cu44Zr44Al7Be5, Cu43Zr43Al7Be7, Cu44Zr44Al7Ni5, Cu40Zr40Al10Be10, Cu41Zr40Al7Be7Co5, Cu42Zr41Al7Be7Co3, Cu47.5Zr48Al4Co0.5, Cu47Zr46Al5Y2, Cu50Zr50, Ti33.18Zr30.51Ni5.33Be22.88Cu8.1, Ti40Zr25Be30Cr5, Ti40Zr25Ni8Cu9Be18, Ti45Zr16Ni9Cu10Be20, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr52.5Ti5Cu17.9Ni14.6Al10, Zr58.5Nb2.5Cu15.6Ni12.8Al10.3, Zr55Cu30Al10Ni5, Zr65Cu17.5Al7.5Ni10, ZrAlCo, Zr36.6Ti31.4Nb7Cu5.9Be19.1, Zr35Ti30Cu8.25Be26.75, and mixtures thereof.
In another embodiment, cooling the coating layer includes subjecting the liquid phase metallic glass to cooling gases.
In yet another embodiment, cooling the coating layer includes allowing the coating layer to cool via thermal conduction.
In still another embodiment, the method of fabricating a layer of metallic glass further includes spinning the coating layer of liquid phase metallic glass to eliminate excess liquid phase metallic glass.
In still yet another embodiment, the object has a lower melting temperature than the metallic glass, and where the cooling is done with such rapidity that thermal energy from the coating layer does not have time to diffuse from the coating layer to the object to thereby melt it.
In a further embodiment, the object is the interior of a pipe.
In a yet further embodiment, the application of a coating of liquid phase metallic glass to an object and the cooling of the coating layer of liquid phase metallic glass occur in an inert environment to discourage contamination of the layer of metallic glass.
In a still further embodiment, the inert environment is effectuated by substantially immersing the object in one of argon, helium, neon, nitrogen, and mixtures thereof.
In a still yet further embodiment, the application of a coating layer of liquid phase metallic glass to an object includes one of: immersing at least a portion of the object in a bath of the liquid phase metallic glass; and pouring the liquid phase metallic glass over at least a portion of the object.
In another embodiment, the object is one of: a laptop case, an electronic case, a mirror, sheet metal, a metal foam, a graphite parts, a part made from refractory metals, an aluminum part, a pyrolyzed polymer part, a titanium part, a steel part, a knife, a gear, a golf club, a baseball bat, a watch, jewelry, a metal tool, and a biomedical implant.
In still another embodiment, a forming tool is used to form the coated layer of liquid phase metallic glass.
In yet another embodiment, the forming tool is a rolling wheel.
In a further embodiment, the method of fabricating a layer of metallic glass further includes separating the layer of solid phase metallic glass from the object.
Turning now to the drawings, systems and methods for implementing layers of metallic glass-based materials are illustrated. For the purposes of this patent application, the term ‘metallic glass’ shall be interpreted to be inclusive of ‘metallic glass composites’, except where otherwise noted. Metallic glass composites are characterized in that they possess the amorphous structure of metallic glasses, but they also include crystalline phases of material within the matrix of the amorphous structure. Crystalline phases can allow a material to have enhanced ductility, compared to where the material is entirely constituted of the amorphous structure. Many techniques can be used to implement layers of metallic glass, e.g. metallic glass coatings on objects. However, many of the techniques that have been used thus far exhibit a number of shortcomings. For example, thermal spraying techniques have been used to implement metallic glass coatings. Thermal spraying techniques generally regard spraying heated material onto an object to establish a coating. In some thermal spraying techniques, metallic glass in a powdered form of micrometer sized particles is sprayed onto the object to be coated. In other thermal spraying techniques, metallic glass in a wire form is heated to a molten state and thereby applied to the object to be coated. However, these thermal spraying techniques are limited insofar as they usually result in a coating that has a very rough surface finish; in many instances it is desirable for the coating to have a smooth finish. Moreover, thermal spraying techniques generally can be fairly time-consuming. Additionally, these techniques may be fairly expensive to implement because the feedstock, e.g. the metallic glass in powdered form, can be costly.
Sputtering techniques and chemical vapor deposition techniques have also been used to implement metallic glass coatings; but these techniques can have their own shortcomings. For example, sputtering techniques and chemical vapor deposition techniques generally regard a layer by layer deposition of material on an atomic scale. With this being the case, such processes can be extremely slow. Moreover, the thickness of the coating layer can be substantially limited, in many cases less than 10 micrometers.
Notably, in the context of implementing metallic glass layers, these techniques have been applied with an extensive focus on ensuring a fast cooling rate to facilitate the formation of the solid phase metallic glass. However, metallic glass alloy compositions have now been developed that have critical cooling rates sufficiently low such that parts having thicknesses on the order of millimeters can readily be developed, e.g. by casting processes. These metallic alloy compositions are generally known as ‘bulk metallic glasses’ (BMGs). Such materials that have an amorphous structure but also include crystalline phases within the amorphous matrix are known as ‘bulk metallic glass matrix composites’ (BMGMCs).
Accordingly, the inventor of the instant application has observed that the development of metallic glasses having lower critical cooling rates, and thereby greater glass forming ability, can enable the development of more robust and advantageous techniques for developing layers of metallic glass. Thus, in many embodiments of the invention, a liquid phase metallic glass—the metallic glass having a relatively low critical cooling rate—is applied to an object in relatively substantial volumes, and the liquid phase metallic glass is thereafter allowed to cool to form the layer of solid phase metallic glass. The layer of solid phase metallic glass can form in spite of the fact that a relatively substantial volume of liquid phase metallic glass is used to coat the object, because the metallic glass has a relatively low critical cooling rate.
Processes for fabricating metallic glass layers are now discussed in greater detail below.
In many embodiments of the invention, liquid phase metallic glass is applied to an object in relatively substantial volumes, and is thereafter allowed to cool to form a solid phase metallic glass layer. In many embodiments, the metallic glass has a relatively low critical cooling rate, and the liquid phase metallic glass is cooled at a rate that can allow a solid phase metallic glass layer to form. In some embodiments, the quantity of liquid phase metallic glass that is applied is such that the surface tension of the liquid phase metallic glass causes the coating layer to have a smooth surface. In many embodiments, the quantity of liquid phase metallic glass that is applied is such that the thickness of the coating layer is greater than approximately 50 micrometers.
A process for implementing a layer of metallic glass where a liquid phase metallic glass is applied in a sufficient quantity such that the surface tension of the metallic glass in its liquid phase causes the coating layer to have a smooth surface in accordance with embodiments of the invention is illustrated in
Of course, it should be noted that although
Note that this technique can further take advantage of the fact that certain metallic glass alloys, especially bulk metallic glasses, have excellent wetting characteristics. For example, many bulk metallic glasses have excellent wetting characteristics with respect to aluminum, titanium, steel, cobalt, graphite, quartz and silicon-carbide. Accordingly, in many embodiments of the invention, the object that is the subject of the application of the liquid phase metallic glass includes one of: aluminum, titanium, steel, cobalt, graphite, quartz, silicon-carbide, and mixtures thereof.
In many embodiments, the metallic glass has a relatively low critical cooling rate. A ‘critical cooling rate’ refers to how fast a liquid phase metallic glass must be cooled in order to form the corresponding solid phase metallic glass, i.e., in an amorphous crystalline structure. The critical cooling rate of a metallic glass is associated with its ‘glass forming ability,’ a term that references a measure as to how easy it is to form a solid phase metallic glass. It is desirable to use a metallic glass having a low critical cooling rate in conjunction with embodiments of the invention because relatively substantial volumes of liquid phase metallic glass are used to coat the object in many embodiments, e.g. a sufficient quantity such that a smooth coating layer surface can result. Thus, with these substantial volumes, it can become difficult to ensure a sufficiently high cooling rate such that a solid phase metallic glass can result using conventional cooling processes. However, by using a metallic glass composition that has a relatively low critical cooling rate, a solid phase metallic glass layer can form in spite of the volume of the liquid phase metallic glass applied. In many embodiments, the critical cooling rate of the metallic glass alloy is less than approximately 1000 K/s. Of course although a particular threshold value is referenced, any suitable metallic glass can be implemented in accordance with embodiments of the invention.
Additionally, although the critical cooling rate can be used as a measure of glass forming ability in accordance with embodiments of the invention, any suitable measure of glass forming ability can be used. For instance, the thickness of a part that can be readily formed from a metallic glass using standard casting procedures can be used to judge the metallic glass's glass forming ability. Accordingly, in many embodiments, a metallic glass is used that can readily be cast in to parts having a thickness of greater than approximately 1 mm. Again, although a particular threshold value is referenced, any suitable metallic glass can be implemented in accordance with embodiments of the invention. For example, in some embodiments a metallic glass is used that can be readily cast in to parts that have a thickness greater than approximately 3 mm.
Suitable metallic glasses include copper-zirconium based metallic glasses, titanium-based metallic glasses, iron-based metallic glasses, nickel-based metallic glasses, and zirconium based metallic glasses. In many embodiments, the metallic glass is one of: Cu40Zr40Al7Be10Nb3, Cu45Zr45Al5Y2Nb3, Cu42.5Zr42.5Al7Be5Nb3, Cu41.5Zr41.5Al7Be7Nb3, Cu41.5Zr41.5Al7Be7Cr3, Cu44Zr44Al5Ni3Be4, Cu46.5Zr46.5Al73, Cu43Zr43Al7Ag7, Cu41.5Zr41.5Al7Be10, Cu44Zr44Al7Be5, Cu43Zr43Al7Be7, Cu44Zr44Al7Ni5, Cu40Zr40Al10Be10, Cu41Zr40Al7Be7Co3, Cu42Zr41Al7Be7Co3, Cu47.5Zr48Al4Co0.5, Cu47Zr46Al5Y2, Cu50Zr50, Ti33.18Zr30.51Ni5.33Be22.88Cu8.1, Ti40Zr25Be30Cr5, Ti40Zr25Ni8Cu9Be18, Ti45Zr16Ni9Cu10Be20, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr52.5Ti5Cu7.9Ni14.6Al10, Zr58.5Nb2.5Cu15.6Ni12.8Al10.3, Zr55Cu30Al10Ni5, Zr65Cu17.5Al7.5Ni10, ZrAlCo, Zr36.6Ti31.4Nb7Cu5.9Be19.1, Zr35Ti30Cu8.25Be26.75, and mixtures thereof. These alloys have demonstrated sufficient glass forming ability. Of course, although several metallic glass alloys are listed, embodiments in accordance with the instant invention are not limited to using these alloys. Indeed, any suitable metallic glass can be used in accordance with embodiments of the invention.
The layer of liquid phase metallic glass is then cooled (104) to form the solid phase metallic glass layer. This generally requires a cooling rate faster than the critical cooling rate. Any suitable technique can be used to cool the layer of liquid phase metallic glass. For example, the metallic glass layer can be spun to facilitate cooling by convection. Spinning the liquid phase metallic glass has the additional advantage of getting rid of excess liquid, which can inhibit the quality of the surface finish. Indeed, in many embodiments, the layer of liquid phase metallic glass is spun primarily to get rid of excess liquid; separate cooling mechanisms can then be relied on to facilitate the cooling of the layer. Cooling gases may also be used to cool the liquid phase metallic glass. In some embodiments, the cooling of the liquid phase metallic glass layer occurs largely by thermal conduction, e.g. through object that was coated. Of course, although certain techniques for cooling the liquid phase cooling layer are mentioned, it should of course be understood that any suitable technique(s) for cooling the liquid phase metallic glass layer can be implemented in accordance with embodiments of the invention.
In many embodiments, the application of the liquid phase metallic glass and its cooling is done with such rapidity, that even where the object that is coated with liquid phase metallic glass has a lower melting point than the metallic glass, a metallic glass layer can still be developed on the object, i.e. the liquid phase metallic glass does not melt the object. In particular, liquid phase metallic glass can be applied to the object in relatively substantial volumes and cooled all prior to the thermal energy diffusing through the coated object to melt it.
Importantly, the formation of layers of metallic glass can be highly sensitive to the development of oxide layers or other contamination that can adversely impact the final material properties. In particular, many of the above listed CuZr-based alloys, Ti-based alloys, and Zr-based alloys are sensitive in this manner. Thus, in many embodiments, the application of liquid phase metallic glass and its cooling occurs in an inert environment. For instance, the application of the liquid layer and its cooling can occur in a chamber that is substantially filled with one of: argon, helium, neon, nitrogen and/or mixtures thereof (argon, helium, neon, and nitrogen being relatively inert elements).
The ability to develop metallic glass layers using relatively substantial volumes of liquid phase metallic glass can offer many advantages. For example, using relatively substantial volumes of liquid phase metallic glass can allow thicker layers of metallic glass to form, which can provide for greater structural integrity. Indeed, where a part is coated in a metallic glass layer, if the metallic glass layer is sufficiently thick, the part with the coated layer can perform in many ways as if it were entirely constituted from the metallic glass.
Additionally, as can be inferred from above, using relatively substantial volumes of liquid phase metallic glass can allow for the final layer of metallic glass to have a smooth finish, which in many instances can be desirable. For example, smooth finishes generally provide for appealing aesthetics. Moreover, smooth surface finishes can also be used to facilitate laminar flow, e.g. where the inside of a pipe that is to facilitate the transportation of liquid has a smooth finish. Furthermore, the smooth layer of metallic glass can be used to mask the rough surface of the object that was coated.
Techniques for applying liquid phase metallic glass are now discussed below.
Liquid phase metallic glass can be applied to objects in many ways in accordance with embodiments of the invention. For example, an object can be dipped into a bath of liquid phase metallic glass in accordance with embodiments of the invention. A system for dipping an object in a bath of liquid phase metallic glass in an inert environment to form a layer of metallic glass in accordance with embodiments of the invention is illustrated in
As can be inferred, dipping the object 304 (or at least a portion of it) in the bath of liquid phase metallic glass 310 is sufficient to apply a relatively substantial volume of liquid phase metallic glass to the object, e.g. such that a smooth coating layer can develop.
As stated previously, the layer of liquid phase metallic glass can be spun to facilitate the cooling and/or to eliminate excess material.
It should of course be understood that any suitable metallic glass can be used, and that any suitable technique for cooling can be used in accordance with embodiments of the invention. For example, it is not necessary to use a source of cooing gases to cool the layer of metallic glass. The layer of metallic glass can be cooled simply by thermal conduction for instance.
Generally, these dipping techniques can be substantially advantageous in many respects; for example, they can provide for an efficient and economical way of developing a smooth metallic glass coating. Pouring techniques can also be used to develop layers of metallic glass, and this is now discussed below.
Liquid phase metallic glass can also be poured over an object to develop a layer of metallic glass in accordance with embodiments of the invention. A system for pouring liquid phase metallic glass over an object develop a layer of metallic glass is illustrated in
The above described techniques can be used to effectively and efficiently implement metallic glass coatings, which can possess favorable materials properties. For example, metallic glasses can be developed to possess corrosion resistance, wear resistance, and sufficient resistance to brittle failure, and otherwise favorable structural properties. Additionally, as mentioned above, techniques in accordance with embodiments of the instant invention can implement metallic glass coating layers that have a smooth surface, which can be aesthetically appealing and/or utilitarian. Thus, in many embodiments of the invention, objects are coated with metallic glass layers to enhance the functionality of the object. For example, in many embodiments, electronic casings are coated with metallic glass layers using any of the above described techniques.
A system for developing a metallic glass coating for a phone casing in accordance with embodiments of the invention is illustrated in
Of course it should be understood that although the coating of a phone casing has been described above, any suitable object can be coated using the techniques described herein in accordance with embodiments of the invention. For example, metallic glass coating layers can be deposited on any of the following objects in accordance with embodiments of the invention: laptop case, electronic case, a mirror, sheet metal, metal foams, graphite parts, parts made from refractory metals, aluminum parts, pyrolyzed polymer parts, titanium parts, steel parts, knives, gears, golf clubs, baseball bats, watches, jewelry, miscellaneous metal tools, biomedical implants, etc. Generally, any suitable objects can take advantage of the above-described techniques for developing metallic glass layers. Note that biomedical are especially well-suited for the techniques described herein as they can take advantage of the hardness and corrosion resistance that metallic glasses can offer, as well as their resistance to corrosion. Resistance to corrosion is particularly important in biomedical applications because of the potential for corrosion fatigue, which can result from corrosive biological environments. Accordingly, biomedical parts can be fabricated from metal, coated with metallic glass; in this way, the metallic glass can provide resistance to corrosion, while the underlying metal can be sufficiently resistant to corrosion fatigue. Additionally, porous foams are also well suited for the dipping techniques described above, which can enable a substantial portion of the exposed surfaces within a porous foam to be sufficiently coated.
Of course it should be understood that the application of relatively substantial volumes of liquid phase metallic glass to an object can be instituted in ways other than those corresponding to the dipping or pouring techniques described above in accordance with embodiments of the invention. For instance, spraying techniques can be implemented.
A system for coating the inside of a pipe with a metallic glass layer using a spraying technique in accordance with embodiments of the invention is illustrated in
It should of course be understood that although several techniques have been discussed above with respect to developing metallic glass coating layers, by applying relatively substantial volumes of liquid phase metallic glass, any number of techniques can be used to do so in accordance with embodiments of the invention. In essence, the above-descriptions are meant to be illustrative and not comprehensive. Additionally, although much of the above-discussion has been focused on developing metallic glass coating layers, free-standing metallic glass layers can also be developed in accordance with embodiments of the invention and this is now discussed.
In many embodiments, free standing sheets of metallic glass layers are fabricated by depositing relatively substantial volumes of liquid phase metallic glass onto a substrate, e.g. such that a smooth coating layer can develop, allowing the liquid phase metallic glass to cool and thereby form a solid phase layer of metallic glass, and separating the solid phase metallic glass from the substrate layer. A system for fabricating free-standing sheets of metallic glass is illustrated in
In many embodiments of the invention, forming techniques are introduced into processes for fabricating metallic glass layers. For example, rolling wheels can be used. A rolling wheel used to form a free standing sheet in accordance with embodiments of the invention is illustrated in
The current application claims priority to U.S. Provisional Application No. 61/727,362, filed Nov. 16, 2012, the disclosure of which is incorporated herein by reference.
The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 U.S.C. 202) in which the Contractor has elected to retain title.
| Number | Date | Country | |
|---|---|---|---|
| 61727362 | Nov 2012 | US |
