Patent Grant
10494698
The present disclosure relates to metallic alloys, and more particularly to the production of zirconium based alloy feedstock.
Certain alloys comprising zirconium (Zr) may require high purity of the alloy chemistry to achieve desired properties. For example, bulk metallic glass (BMG) alloys that incorporate Zr, e.g., those that incorporate little or no beryllium (Be), may be formed using high purity Zr crystal bar feedstock. Other high performance crystalline alloys that include Zr may also rely upon high purity Zr cystal bar feedstock for their production. High purity alloys that comprise Zr may be expensive to produce due to, among other things, the expense of the high purity Zr crystal bar feedstock.
BMGs are a family of materials that, when cooled at rates generally less than 100° C./s, form an amorphous (or non-crystalline) microstructure with thicknesses in the range of 0.1 to 10 mm or greater. BMGs may have unique and novel properties given their lack of long-range order and absence of crystalline structure. BMG alloys may have exceptional strength, high elasticity, limited plasticity, good corrosion and wear resistance, and high hardness relative to their crystalline counterparts. From a processing perspective, the alloys also offer unique possibilities. BMG alloys may have melting temperatures far below their constituent elements, allowing for permanent mold casting processes and other processing such as thermoplastic forming, which are not possible with many conventional alloy systems.
The present inventors have observed a need for improved approaches for producing Zr based alloys, including BMGs, at lower cost. Exemplary approaches described herein may address such needs.
These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings.
In one example, a method of preparing a Zr-based metallic alloy comprises heating Zr sponge comprising Zr and multiple contaminants in a sponge structure in a processing chamber with an electron-beam-heating apparatus or an arc-melting apparatus under a desired pressure condition to release volatile contaminants from the Zr sponge; introducing a purge gas into the processing chamber and permitting the purge gas to intermingle with at least some of the released volatile contaminants; evacuating the processing chamber to extract at least some of the purge gas and released volatile contaminants; repeating said heating of the Zr sponge, said introducing a purge gas, and said evacuating the processing chamber release and evacuate additional volatile contaminants from the Zr sponge to provide a processed Zr sponge with enhanced purity; melting the processed Zr sponge with multiple other alloy constituents to provide a Zr-based metallic alloy.
In an example, the Zr-based metallic alloy may comprise Zr, Ti, Cu, Ni, and Be. In an example, the Zr-based metallic alloy may comprise Zr, Ti, Cu, Ni, and Al. In an example, the Zr-based metallic alloy may comprise Zr, Cu, Ni, Al, and Nb.
In an example, the method may comprise cooling the Zr-based metallic alloy so that it solidifies as a bulk metallic glass.
In an example, the Zr-based metallic alloy may be substantially amorphous in structure.
In an example, the volatile contaminants may comprise Mg and Cl.
In an example, the method may comprise gettering oxygen with a getter during the heating the Zr sponge. The getter may comprise a Ti getter.
In an example, a mass of the Zr sponge heated in a given heating operation may be in the range of 5 kg to 50 kg.
In an example, the purge gas comprises an inert gas, such as argon, helium or nitrogen, or combinations thereof.
In an example, the desired pressure condition may comprise a vacuum condition. The vacuum condition may be provided with the addition of an inert gas into the processing chamber.
In an example, the heating of the Zr sponge may comprise melting the Zr sponge.
In an example, the heating of the Zr sponge under a desired pressure condition may comprise heating under a vacuum condition, wherein the method may further comprise additionally heating the Zr sponge material under an overpressure condition in the presence of an inert gas.
These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings.
BMG alloys generally contain combinations of three or more different elements, and some of the best BMG alloy forming systems contain four or five or more elements. Often, the elements are quite different from one another (early or late transition metal, metalloid, etc.) and form deep eutectic systems. This suggests that the thermodynamically disparate elements are more stable as a molten solution than in a solid-state. It is believed that the elements in such molten solutions encounter difficulty arranging into a crystal structure during solidification, and this allows the alloy to remain as an undercooled liquid and eventually a metallic glass. The best glass forming alloys generally have the slowest critical cooling rates, and this allows for a wider processing window for robust processing and production. Many good glass forming alloys (those with slow critical cooling rates) contain the metallic element Be, or metalloids such as P or B. Other good glass forming alloys may incorporate Zr, such as: Zr—Ti—Cu—Ni—Be BMGs, such as described in U.S. Pat. No. 5,288,344, Zr—Cu—Al—Ni BMGs and Zr—Cu—Al—Ni—Nb BMGs, such as described in U.S. Pat. Nos. 6,592,689 and 7,070,665, Zr—(Ni, Cu, Fe, Co, Mn)—Al BMGs, such as described in U.S. Pat. No. 5,032,196, and Zr-based alloys described in U.S. Patent Application Publication No. 2011/0163509. Other Zr based BMG alloys include those disclosed in the following patent documents: U.S. Pat. Nos. 8,333,850, 8,308,877, 8,221,561, 8,034,200, 7,591,910, 7,368,023, 7,300,529, 7,153,376, 7,070,665, 6,896,750, 6,805,758, 6,692,590, 6,682,611, 6,592,689, 6,521,058, 6,231,697, 5,735,975; U.S. Patent Application Publication Nos. 20120305142, 20120298264, 2012022278, 20120073706, 20110308671, 20110100514, 20110097237, 20090202386, 20090139612, 20080190521; and International Patent Application Publication No. WO2011159596. The entire contents of each of the foregoing patent documents listed in this paragraph are incorporated herein by reference in their entirety.
Besides the unique combinations of alloying elements, BMG alloys may require tight alloy composition, contaminant, and inclusion control to maintain high glass forming ability. Oxygen, carbon, and nitrogen are usually unfavorable for glass forming ability. It is believed that these elements may enhance nucleation of a solid phase during cooling from the liquid state to below the glass transition temperature. Other elements that promote formation of stable solid phases (e.g., Fe contaminants in Zr-based VITRELOY ® alloys) are also detrimental. Production of alloys that achieve the desired chemistry while avoiding contaminants is a manufacturing challenge.
The present disclosure relates to approaches for preparing metallic alloys that contain Zr as a constituent, including BMG alloys, crystalline alloys and feedstock alloys (precursor alloys for making other alloys). High purity Zr feedstock is generally very expensive because it is produced by a slow process and limited to a small number of global suppliers. Prices of high purity Zr feedstock can be volatile because of the limited number of producers and consumers. Non-Be or low-Be containing Zr-based BMG alloys may require high purity input materials; generally with oxygen levels of less than 1000 ppm; and often less than 500 ppm. There are few zirconium metal sources which have sufficiently high purity (for example; low concentrations of Fe; Hf; and Sn) for making sufficient quality bulk metallic glass alloy and feedstock alloy. One source of Zr is Zr sponge, which is readily available and can have low levels of metallic impurities and oxygen less than <1000 ppm. However; Zr sponge is made with the Kroll process involving reduction of ZrCl4 using Mg, leaving some residual Mg and MgCl2 in the sponge. These volatile compounds are detrimental to formation of BMG alloys and other Zr based alloys that require high purity. The present disclosure addresses, among other things, the processing and use of Zr sponge to yield Zr metal of sufficiently high purity for use in producing Zr alloys and feedstock that require high purity.
In some examples of preparing alloys using Zr sponge, an intermediate processing step (refining step) may be carried out on Zr sponge, e.g., arc melting or electron beam melting, to drive off volatile Mg and Cl containing compounds present in the Zr sponge. The cost of the Zr sponge with such added processing steps may be lower than the cost of comparable high purity Zr crystal bar. Furthermore, in some examples, during the refining step, it is possible to add other BMG alloying elements to create a master feedstock alloy (e.g. Zr—Cu; Zr—Cu—Ni; Zr—Ti; etc.) for use in preparing the ultimate desired Zr alloy. In some examples, when producing an alloy such as a BMG alloy, the refined sponge; or the refined sponge master alloy, may be combined with another Zr source such as crystal bar to further decrease oxygen levels in the resulting alloy, e.g., BMG alloy.
Further exemplary details will now be described further with reference to
Power is applied from the arc melter electrode 232A to the Zr sponge 202 by controlling power from an arc-melter power supply (e.g., a conventional welding power supply) to provide sufficient heating of the Zr sponge to drive contaminating compounds from the Zr sponge, e.g., volatile Mg and Cl compounds. The level of the applied power and duration of the refining step will depend upon the size of the Zr sponge charge being refined and may be determined by straightforward testing trials, which may include chemical analysis by conventional methods to verify the sufficiency of the purity of the processed Zr following the refining step. If it is determined that any contaminants exceed desired levels, further refinement may be carried out, and/or the resulting Zr may be additionally remelted with an amount of high purity Zr crystal bar to dilute the concentration of contaminants in the refined Zr metal. In some examples, the Zr sponge may be heated to a fully molten state. A titanium getter 210 may also be included to absorb oxygen or other contaminants that be liberated during the refining step. In some examples, the refined Zr metal may be directly cast from the molten state into a Zr ingot of a particular shape using a mold at another region of the water cooled hearth.
In another example,
Power is applied from the electron beam source 232B to the Zr sponge 202 by controlling power from an electron-beam power supply to provide sufficient heating of the Zr sponge to drive contaminating compounds from the Zr sponge, e.g., volatile Mg and Cl compounds. The level of the applied power and duration of the refining step will depend upon the size of the Zr sponge charge being refined and may be determined by straightforward testing trials, which may include chemical analysis to verify the sufficiency of the purity of the processed Zr following the refining step. If it is determined that any contaminants exceed desired levels, further refinement may be carried out, and/or the resulting Zr may be additionally remelted with an amount of high purity Zr crystal bar to dilute the concentration of contaminants in the refined Zr metal. In some examples, the Zr sponge may be heated to a fully molten state. In some examples, the refined Zr metal may be directly cast from the molten state into a Zr ingot of a particular shape using a mold at another region of the water cooled hearth.
A vacuum valve 322 connected to a port of the vacuum chamber 312 is connected to a vacuum system to evacuate the chamber 312 and maintain a desired level of vacuum in the chamber 312. A valve 324 is connected to a port on the vacuum chamber 312 to permit gas, e.g., inert gas such as argon, helium, nitrogen, etc., to be fed into the chamber 212 to provide a source of gas, if desired, e.g., to purge the chamber of contaminants through alternating evacuation and back filling with inert gas. One or more pressure sensors 326 may be provided for measuring the pressure in the vacuum chamber 312. Any suitable combination of gas flow controllers, pressure sensors, vacuum pumps and associated vacuum plumbing may be utilized to control the vacuum/pressure conditions and gaseous environment of the vacuum chamber 312, e.g., in the range of one bar to several bars or more, (e.g., about 2, 3, 4 or 5 bars, 6-10 bars, or more) wherein one bar is atmospheric pressure (760 Torr) to sub-ambient pressures less than atmospheric pressure (e.g., a few hundred Torr to 10−6 Torr), including low vacuums (e.g., 10−2-10−6 Torr, or below, for instance). One or more temperature sensors 334 (e.g., thermocouple or optical pyrometer, etc.) for measuring the temperature of the crucible 330 or alloy being melted may be provided. A Ti getter 310 may also be included to absorb oxygen or other ambient contaminants during the melting to prevent them from contaminating the alloy under formation. In one example, a molten pre-alloy, e.g., of Zr—Cu or some other alloy may be formed, and then that pre alloy may be further alloyed with other constituents in the desired amounts to provide the desired composition for the alloy. The heating and melting may be carried out in an inert atmosphere at a pressure of less than, equal to, or greater than 1 bar, e.g., several bars or more of Argon or other inert gas.
Thereafter, the melt may be cooled (step 408), e.g., by pouring the melt into a desired mold, thereby forming a Zr based metallic alloy, which may be an initial alloy, e.g., feedstock for another alloy, or a final alloy. The composition of the initial alloy may be measured if desired. A determination can be made on what, if any, additional constituent(s) should be added and in what amount(s) to bring the alloy to the desired composition.
At step 410 further alloying may be carried out with other constituents, if desired, e.g., to obtain the desired alloy composition. The Zr-based alloy may then be cast (step 412) into individual ingots (also called slugs or charges) of the desired size and desired composition. The result is many ingots or slugs of desired size, shape and composition. This step can be carried out in a different chamber/furnace system than that used for the prior heating/melting, or in the same chamber/furnace system used for the prior heating/melting but with a different crucible/heater arrangement, for instance. For example, this step can be carried out, if desired, in hot isostatic press (HIP) apparatus, or pressurized furnace apparatus.
The cooling during the casting step 412 can be done at any desired rate. For instance, the cooling could be carried out slowly, such that the resulting ingots or slugs have a crystalline or partially crystalline structure, in which case they may be used as charges for later remelting and casting at a sufficient cooling rate into BMG materials or parts. Alternatively, the cooling at step 412 may be carried out sufficiently quickly by suitable quenching, e.g., water quenching, so that the resulting ingots or slugs will already have a BMG structure, i.e., are cooled directly to an amorphous state. These ingots or slugs can then be used for further molding processes into BMG parts.
Alternatively, the casting at step 412 can be carried out in a vacuum controlled counter gravity casting apparatus, such that the melt can be cast into any suitable counter-gravity-casting mold with less turbulence and potentially greater control of the casting process. In this case, the cooling can be carried out slowly or quickly such as described above to obtain resulting ingots of either crystalline or BMG structure. In any of these options, the choice of suitable temperatures, heating times and pressures can be determined from experimental testing and/or modeling.
The above described approaches may have benefits over conventional approaches for forming BMG alloys containing Zr. For example, the approaches described herein permit Zr sponge to be utilized for alloying, following a refinement process to enhance its purity, in place of high purity Zr crystal bar. Such Zr-based alloys may be made less expensively and with greater options for sources for the starting Zr material.
While the present invention has been described in terms of exemplary embodiments, it will be understood by those skilled in the art that various modifications can be made thereto without departing from the scope of the invention as set forth in the claims.
This application is a continuation of U.S. patent application Ser. No. 14/872,425, filed Oct. 1, 2015, now U.S. Pat. No. 9,938,605, which further claims the benefit of U.S. Provisional Patent Application No. 62/058,648, filed Oct. 1, 2014. The foregoing related applications, in their entirety, are incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 14872425 | Oct 2015 | US |
| Child | 15938894 | US |
