Patent Application
20140227125
The present invention generally relates to fabricating objects from bulk metallic glass matrix composites.
Metallic glasses, also known as amorphous alloys, embody a relatively new class of materials that is receiving much interest from the engineering and design communities. 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 glass materials 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. Importantly, the manufacture of metallic glass materials lends itself to relatively easy processing. For example, the manufacture of a metallic glass can be compatible with an injection molding process.
Nonetheless, the manufacture of metallic glasses presents challenges that limit their viability as engineering materials. In particular, metallic glasses are typically formed by raising a metallic alloy 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, and were thereby limited in the thickness with which they could be formed. Indeed, because of this limitation in thickness, metallic glasses were initially limited to applications that involved coatings. Since then, however, particular alloy compositions that are more resistant to crystallization have been developed, which can thereby form metallic glasses at much lower cooling rates, and can therefore be made to be much thicker (e.g. greater than 1 mm). These thicker metallic glasses are known as ‘bulk metallic glasses’ (“BMGs”).
In addition to the development of BMGs, ‘bulk metallic glass matrix composites’ (BMGMCs) have also been developed. BMGMCs are characterized in that they possess the amorphous structure of BMGs, but they also include crystalline phases of material within the matrix of amorphous structure. For example, the crystalline phases can exist in the form of dendrites. The crystalline phase inclusions can impart a host of favorable materials properties on the bulk material. For example, the crystalline phases can allow the material to have enhanced ductility, compared to where the material is entirely constituted of the amorphous structure.
Systems and methods in accordance with embodiments of the invention implement bulk metallic glass matrix composites in the fabrication of objects. In one embodiment, a method of fabricating an object including a bulk metallic glass matrix composite includes: forming a bulk metallic glass matrix composite composition into the shape of the object to be fabricated; and developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions that are softer than the surrounding matrix as measured by one of: the shear modulus, the elastic limit, and the hardness; where the bulk metallic glass matrix composite composition is such that the extent of the presence of the inclusions can be made to vary.
In another embodiment, the forming of the bulk metallic glass matrix composite composition is achieved using one of: a thermoplastic forming technique and a casting technique.
In yet another embodiment, the forming of the bulk metallic glass matrix composite composition is achieved using one of: die casting, injection casting, rapid capacitive discharge forming, powder injection metallurgy, and investment casting.
In still another embodiment, the non-equilibrium inclusions are developed such that they impart desired materials properties in the object to be fabricated.
In still yet another embodiment, developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions includes subjecting the bulk metallic glass matrix composite composition to an appropriate cooling rate.
In a further embodiment, subjecting the bulk metallic glass matrix composite composition to an appropriate cooling rate develops non-equilibrium inclusions in a first region of the object to be fabricated, but not in a second region of the object to be fabricated.
In a still further embodiment, the second region of the object to be fabricated is locally heat treated to develop non-equilibrium inclusions.
In a yet further embodiment, developing the bulk metallic glass matrix composite includes heat treating the formed bulk metallic glass matrix composite composition.
In a still yet further embodiment, the heat treating is annealing.
In another embodiment, the heat treating is localized to regions of the formed bulk metallic glass matrix composite composition.
In still another embodiment, the extent of the presence of the inclusions can be made to vary by thermal processing.
In yet another embodiment, the crystalline structures that are developed undergo martensitic transformation when subjected to strain beyond a predetermined threshold.
In still yet another embodiment, the bulk metallic glass matrix composite composition does not include beryllium.
In a further embodiment, the bulk metallic glass matrix composite composition is Zr48Cu47.5Al4CO0.5.
In a still further embodiment, the non-equilibrium inclusions are B2 phase inclusions.
In a yet further embodiment, the bulk metallic glass matrix composite composition is Cu47.5Zr47.5Al5.
In a still yet further embodiment, the bulk metallic glass matrix composite composition is one of: a CuZr-based composition, a TiCu-based composition, an NiTi-based composition, a CuZnAl-based composition, an FeNi-based composition, NiP-based composition, FeP-based composition, a FeNiCoAlTaB-based composition, a ZrTi-based composition, a ZrNb-based composition, an NiNb-based composition, a ZrV-based composition, a TiNB-based composition, a ZrTiTa-based composition, TiV-based composition, TiTa-based composition, a ZrTa-based composition, and a ZrCu based composition.
In another embodiment, the non-equilibrium inclusions are spherical.
In yet another embodiment, the object to be formed is a golf head casing.
In still another embodiment, a striking surface of the golf head casing is locally heat treated to develop the non-equilibrium inclusions.
Turning now to the drawings, systems and methods for implementing bulk metallic glass matrix composites in the fabrication of objects are illustrated. In many embodiments, a bulk metallic glass matrix composite composition is formed into the shape of an object to be fabricated, and the composition is developed to include non-equilibrium inclusions that are softer than the surrounding matrix (e.g. as measured by shear modulus, elastic limit, or hardness). In a number of embodiments, the formed composition is heat treated to develop the inclusions. In several embodiments, the heat treating is localized to regions where it is desired that the object be especially robust.
Although bulk metallic glasses can possess a number of advantageous materials properties that might make them suitable materials from which to fabricate some structural components from, they might not have the requisite resistance to brittle fracture and/or ductility that can allow them to implemented in many applications where a more robust material is desirable. Thus, bulk metallic glass matrix composites have been studied for their viability in applications where a more robust material would be desirable. As discussed above, BMGMCs are characterized by their crystalline inclusions that can enhance the robustness of the underlying BMG material. For example, a BMGMC can have enhanced fracture toughness, fatigue endurance, and tensile ductility compared to a base BMG. Generally, the crystalline inclusions can be understood to accommodate applied strain through, e.g. shear band arrest, martensitic transformation, twinning, etc., and thereby cause the observed enhanced materials properties. Further, it is generally understood that in order for a BMGMC to have enhanced materials properties relative to the underlying BMG, the crystalline inclusions should be soft and course.
Zr—Ti—Be BMGMC materials are an example of BMGMCs that can be made to have favorable materials properties. Zr—Ti—Be BMGMC materials typically include elastic and soft body-centered cubic crystalline dendrites. Some Zr—Ti—Be BMGMC systems are particularly distinct in that they can demonstrate tensile ductility above 1 GPa of yield stress. Nonetheless, in spite of their potentially favorable materials profile, this alloy system has some limitations that may limit its viability as an engineering material. For example, in many applications it is desirable to implement a material that is free of beryllium. Furthermore, in many Zr—Ti—Be systems, the crystalline inclusions are equilibrium phase inclusions, and as a result, the extent of the presence of the crystalline inclusions (e.g. as measured by volume fraction) is generally independent of the cooling rate (or other thermal processing) by which the BMGMC is formed. Instead, the cooling rate (or other thermal processing) impacts the overall morphology of the dendritic structures—for example, a slower cooling rate may cause a course dendritic microstructure to develop, whereas a more rapid cooling rate can cause a finer dendritic microstructure to develop. Importantly, in order to obtain a more advantageous materials profile for these systems, the dendritic structures typically must be developed to be of certain coarseness. Recall that when BMGMCs are formed into objects, they are typically heated so that they can be formed, thereafter formed into the desired shape, and subsequently cooled—the cooling rate of the BMGMC is largely a function of the geometry of the shape to be formed, e.g. a thicker geometry will cool more slowly than a thinner one. Thus, when a geometry includes varying thicknesses, the cooling rate throughout the part may be uneven—thicker portions of the geometry may cool more slowly than thinner portions. As a result, when a Zr—Ti—Be BMGMC is implemented, the microstructure can vary throughout the geometry, and the desired microstructure may appear only for a region of the geometry, whether or not it is even desired for that region of the geometry. In many instances it may be desirable for other areas of the object having such a geometry to contain the crystalline inclusions that bolster the materials properties. In general, it may be desirable to be able to more precisely control the microstructure, and thereby the materials properties, throughout the geometry.
Accordingly, in many embodiments, methods of fabricating objects are implemented that allow a more precise control of the development of the resulting microstructure, which impacts the overall material properties. For example, in many embodiments, BMGMC compositions that can be made to develop non-equilibrium phase crystalline inclusions are implemented in the fabrication of objects. The non-equilibrium phase inclusions are such that the extent of their presence (e.g. as measured by their volume fraction) can be controlled using thermal processing methods (e.g. cooling rate and annealing). In some embodiments, crystalline phases are implemented that result from primary crystallization due relatively slower cooling rate (e.g. a cooling rate slower than that required to form a monolithic glass). Additionally, in many instances the crystalline inclusions are softer than the surrounding amorphous matrix. For example, the shear modulus, the elastic limit, and/or the hardness of the crystalline inclusions can be less than that of the surrounding amorphous matrix. In this way, the BMGMC composition can be thermally processed to more precisely control the resulting microstructure, and thereby more precisely influence the materials properties. These processes are discussed in greater detail below.
Fabricating Objects from BMGMC Materials
In many embodiments, methods for fabricating objects from bulk metallic glass composite matrix materials that include non-equilibrium phase inclusions are implemented. Any suitable object may be fabricated, including objects that have geometries with varying thicknesses. For example, the casing of a golf club head can be fabricated from a BMGMC. As mentioned above, BMGMC materials can provide for a more robust materials.
A process for fabricating an object from a BMGMC using a casting technique or a thermoplastic forming technique is illustrated in
Zr48Cu47.5Al4Co0.5 is one example of a bulk metallic glass matrix composite composition that can be implemented in accordance with embodiments of the invention. This alloy can be made to form B2 phase non-equilibrium nanocrystals; it is generally understood that the B2 phase nanocrystals can accommodate strain that the bulk material is being subjected to by undergoing a martensitic transformation. In this way, the B2 phase nanocrystals can endow the bulk material with enhanced material properties. Importantly, the extent of the presence of the B2 phase can be made to vary using thermal processing techniques. For example, a formed Zr48Cu47.5Al4Co0.5 BMGMC material can be annealed to promote the development of the B2 phase. Generally, the materials properties of the bulk material can be approximated by the rule of mixtures, e.g. the greater the presence of the B2 phase nanocrystals, the more the bulk material will conform to the materials properties of the B2 phase nanocrystals. Conversely, the greater the presence of the amorphous matrix, the more the bulk material will conform to the properties of the amorphous matrix. This approximation is generally valid until the B2 crystalline phase exceeds a volume fraction of approximately 30%.
Bear in mind that although the development of B2 crystalline phases has been discussed in conjunction with a ZrCuAlCo system, B2 crystalline phases can also develop in other systems-for example TiCu alloys can develop a B2 phase. Furthermore, any BMGMC composition that can be made to form any non-equilibrium crystalline phase—not just a B2 phase—can be implemented in accordance with embodiments of the invention. Generally, any BMGMC composition that can be made to include non-equilibrium crystalline inclusions, including any of the systems discussed above, can be implemented in accordance with embodiments of the invention. For example, the BMG composition can be one of: a CuZr-based composition, a TiCu-based composition, an NiTi-based composition, a CuZnAl-based composition, an FeNi-based composition, NiP-based composition, FeP-based composition, a FeNiCoAlTaB-based composition, a ZrTi-based composition, a ZrNb-based composition, an NiNb-based composition, a ZrV-based composition, a TiNB-based composition, a ZrTiTa-based composition, TiV-based composition, TiTa-based composition, a ZrTa-based composition, and a ZrCu based composition. When a composition is referred to as being based on an element or set of elements, it is meant that those elements are present in the most amounts.
Referring back to
The process 100 further includes developing 120 the BMGMC composition to include non-equilibrium inclusions that have a shear modulus less than that of the surrounding amorphous matrix. For example, in some embodiments, the forming of the BMGMC composition into the shape of the object to be formed inherently causes the development of the non-equilibrium inclusions. In some embodiments, a base BMGMC composition is alloyed such that the formation of the BMGMC composition inherently results in the development of the non-equilibrium inclusions.
Note that the critical cooling rate to form a monolithic bulk metallic glass can be modeled by:
This equation indicates that the critical cooling rate to form a glass is a function of only the liquidus temperature, the glass transition temperature, the thermal diffusivity and the length. Glass forming ability can be defined as critical casting thickness, the critical length, Lc, where the centerline can be cooled to below Tg at the critical cooling rate. Thus, the critical casting thickness of a metallic glass can be modeled by:
If the object to be fabricated is cooled slower than the critical cooling rate or the object to be fabricated is thicker than the critical casting length, it will begin to crystallize. These principles can be utilized in implementing BMGMC compositions so that desired microstructures can be made to develop.
In some embodiments, developing 120 the BMGMC composition includes annealing the BMGMC composition until the desired microstructure is attained.
Importantly, the described heat-treating processes can be applied in localized regions of the object to be fabricated in accordance with embodiments of the invention. For instance, in many embodiments, a BMGMC composition is formed into an object to be fabricated, and a heat treatment is locally applied to locally develop the microstructure. In this way, particular regions of the object to be fabricated can be developed to be more robust.
Note that the described development 120 of non-equilibrium phase crystalline inclusions can be achieved in any suitable manner in accordance with embodiments of the invention. In many embodiments, the development is achieved using thermal processing, e.g. cooling rates and annealing stages. Additionally, as mentioned previously, the materials properties of the material can in some respects be approximated by the rule of mixtures. Thus, for example, where it is desired that the bulk material adopt a materials profile that is more akin to the crystalline structure, the microstructure can be developed accordingly. Conversely, where it is desired that the bulk material adopt a materials profile that is more akin to the amorphous structure, the microstructure can be developed accordingly. In this way, thermal processing can be used to tune the materials properties, either globally or locally.
Of course, it should be understood that the above mentioned concepts can be implemented in aggregate. For example,
In the third attempt 906, the optimal microstructure is achieved at the thickest part of the wedge-shaped object. Note that the bottom half of the wedge shaped object is entirely amorphous. If it is desired that this portion of the wedge-shaped object be developed to include crystalline phases, this portion of the object can be locally heat treated in accordance with the above-discussion. In this way, an object having varying thickness can be fabricated to include a desirable microstructure throughout its geometry.
That the geometry of the object to be fabricated can impact the cooling rate, which in turn can impact the microstructure is further expressed in
Similarly,
Referring back to
As can be inferred from the above discussion, the above-mentioned concepts can be implemented in a variety of arrangements in accordance with embodiments of the invention. Accordingly, although the present invention has been described in certain specific aspects, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that the present invention may be practiced otherwise than specifically described. Thus, embodiments of the present invention should be considered in all respects as illustrative and not restrictive.
The current application claims priority to U.S. Provisional Application No. 61/763,292, filed Feb. 11, 2013, 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 | |
|---|---|---|---|
| 61763292 | Feb 2013 | US |
