The present application claims priority to U.S. Provisional Application Ser. No. 62/746,988 filed Oct. 17, 2018, the contents of which is hereby incorporated by reference in their entry
The present invention relates to Nb-based refractory alloys and processes of making and using same.
Nb-based refractory alloys currently used in some high-temperature structural applications contain expensive and dense alloying elements. For example, C-103, which is one of the most commonly used medium-strength Nb alloys, contains (by atomic percent) 5.4 Hf, 0.3 Ta, 0.3 W, 0.7 Zr, 2.0 Ti, and remaining Nb; and a high strength C-3009 contains 19.2 Hf, 5.6 W and remaining Nb. Such metals as Hf, Ta and Zr are expensive, costing approximately $1200, $290 and $150 per kilogram, respectively, and Hf, W and Ta have high density of, respectively, 13.21, 16.65 and 19.25 g/cm3. Moreover, these alloys have poor oxidation resistance above 600° C. and thus require oxidation resistive coatings. There has been extensive efforts put forth to solve the above mention problems including research on Nb alloys containing Si, which main goal is to improve both high temperature strength and oxidation resistance; however, Nb—Si alloys are generally brittle at temperatures ≤1000° C. and they have not found practical use yet. Refractory complex concentrated alloys (RCCAs) or refractory high entropy alloys (RHEAs) are another promising direction of research but such research has yet to result in a Nb-based refractory alloy that is known to solve the aforementioned problems.
In view of the foregoing, Applicants invented Nb-based refractory alloys that are less expensive and less dense than current Nb-based refractory alloys, yet which have similar or better ductility, high temperature strengths and oxidation resistance when compared to current Nb-based refractory alloys. Furthermore, Applicants' Nb-based refractory alloys typically continue to be compatible with current oxidation resistive coating systems that are employed to improve the oxidation resistance of Nb-based refractory alloys. Applicants disclose their improved Nb-based refractory alloys herein.
The present invention relates to Nb-based refractory alloys that are less expensive and less dense than current Nb-based refractory alloys, yet which have similar or better ductility, high temperature strengths and oxidation resistance when compared to current Nb-based refractory alloys. Such Nb-based refractory alloys typically continue to be compatible with current coating systems for Nb-based refractory alloys. Such Nb-based refractory alloys are disclosed herein.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration.
Definitions
Unless specifically stated otherwise, as used herein, the terms “a”, “an” and “the” mean “at least one”.
As used herein, the terms “include”, “includes” and “including” are meant to be non-limiting.
Unless otherwise noted, all component or composition levels are in reference to the active portion of that component or composition, and are exclusive of impurities, for example, residual solvents or by-products, which may be present in commercially available sources of such components or compositions.
All percentages and ratios are calculated by weight unless otherwise indicated. All percentages and ratios are calculated based on the total composition unless otherwise indicated.
It should be understood that every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.
Detailed Description of the Invention
Nb—Mo—Ti-Based Refractory Alloys
Applicants disclose a Nb—Mo—Ti alloy comprising Nb, about 4 atomic percent to about 35 atomic percent Mo, preferably about 8 atomic percent to about 30 atomic percent Mo, more preferably about 15 atomic percent to about 25 atomic percent Mo, and about 5 atomic percent to about 35 atomic percent Ti, preferably about 10 atomic percent to about 25 atomic percent Ti, more preferably about 15 atomic percent to about 25 atomic percent Ti. For purposes of this specification, headings are not considered paragraphs and thus this paragraph is Paragraph 0027 of the present specification. The individual number of each paragraph above and below this paragraph can be determined by reference to this paragraph's number.
The Nb—Mo—Ti alloy of Paragraph 0027 wherein Nb is the balance of said Nb—Mo—Ti alloy.
The Nb—Mo—Ti alloy of Paragraph 0027, said Nb—Mo—Ti alloy comprising an elemental alloy addition selected from the group consisting of Cr, Fe, W, Zr, C, N, O and mixtures thereof.
The Nb—Mo—Ti alloy of Paragraph 0029 wherein at least one of said elemental alloy additions is present at the following level:
The Nb—Mo—Ti alloy of Paragraph 0029 comprising two, three, four, five, six or seven of said elemental alloy additions.
The Nb—Mo—Ti alloy of Paragraphs 0030 through 0031, said Nb—Mo—Ti alloy comprising a total of no more than about 20 atomic percent of combined Cr, Fe, W, Zr elemental alloy additions. Exceeding 20 atomic percent of these elements in some embodiments may cause brittleness.
The Nb—Mo—Ti alloy of Paragraphs 0027 through 0032 in which elemental impurities are present in a total amount not exceeding about 2 atomic percent, preferably a total amount not exceeding about 1 atomic percent, more preferably a total amount not exceeding about 0.5 atomic percent.
The Nb—Mo—Ti alloy of Paragraph 0033 in which said elemental impurities are any elements not recited by Paragraphs 0027 through 0030.
An article comprising a Nb—Mo—Ti alloy according to any of Paragraphs 0027 through 0034, said article being selected from the group consisting of aircraft, spacecraft, munition, ship, vehicle, thermal protection system, and power generation system; preferably said article comprises a nuclear reactor, engine, an airframe that comprises said Nb—Mo—Ti alloy.
The Nb—Mo—Ti alloys containing 30 at. % to 91 at. % Nb, 4 at. % to 35 at. % Mo, 5 at. % to 35 at. % Ti are single-phase body center cubic (BCC) structures over a wide temperature range.
Process of Making Nb—Mo—Ti-Based Refractory Alloys
The alloys can be made using different processing methods, which may include, but are not limited to, mixing, melting, casting, powder metallurgy making and processing, cold and hot working, heat treatment and/or thermo-mechanical treatment. The alloys can be used in the form of cast products, powder metallurgy products including additive manufacturing, worked (rolled, forged, extruded, etc.) products, in the as-produced, annealed or heat treated conditions.
Compression rectangular test specimens with the dimensions of 4.6 mm×4.6 mm×7.6 mm were electric discharge machined (EDM) from larger pieces of alloy material and their surfaces were polished with a 400 grit SiC paper. The specimens were compression deformed along the longest direction at different temperatures and a rams speed of 0.0076 mm/s. The room temperature tests were conducted in air and high temperature tests were conducted in a 10−5 Torr vacuum.
Oxidation test specimens were electric discharge machined (EDM) from larger pieces of alloy material. Uncoated oxidation samples were sectioned into a rectangular geometries measuring 4.6 mm×4.6 mm×7.4 mm. Samples intended for coating and subsequent oxidation were sectioned into disks with 9.5 mm diameter and 3.2 mm thickness. In all cases, recast layers were removed using coarse grinding paper, followed by standard metallographic techniques up to a 600 grit finish and finally cleaned in isopropanol. Commercial R512E slurry coatings were applied to the “disk” specimens by a commercial vendor using standard techniques developed for coating commercial C103 alloys. All subsequent oxidation tests (coated and uncoated specimens) were conducted using a thermogravimetric analyzer (TGA) using bottled air for reaction gas and ultra-high purity argon for the balance gas. Specimens were heated under inert atmosphere and then subsequently oxidized in air at 1200° C. Only data captured during the oxidation regime (in air) is represented here.
The following examples illustrate particular properties and advantages of some of the embodiments of the present invention. Furthermore, these are examples of reduction to practice of the present invention and confirmation that the principles described in the present invention are therefore valid but should not be construed as in any way limiting the scope of the invention.
While the alloys of the present invention can be made by a number of methods, to prove the concept, seven Nb alloys, which composition (in at. %) is shown in Table 1 were produced by vacuum arc melting. The density of the produced alloys, which do not contain W, is in the range from 7.70 g/cm3 for alloy M4 to 8.03 g/cm3 for alloys M3 and M3Fe, which is considerably smaller than the density of commercial alloys C103 (8.86 g/cm3) or C-3009 (10.3 g/cm3). The density of MW1 (8.94 g/cm3), which contains W, is higher than that of C103 but smaller that the density of C-3009. Vickers Hardness of all the produced alloys are higher than the Vickers hardness of C1-3 or C-3009 (Table 1).
In the temperature range of 20° C. to 1200° C. the alloys are ductile and can be forged or rolled. The yield strength values are given in Table 2 and compared with the properties of commercial alloys C-103 and C-3009. All produced alloys are stronger than C-103 in the temperature range from 20° C. to 1200° C. All the produced alloys are stronger than C-3009 at room temperature. The alloys M4, MW1, M2Fe and M3Fe are also stronger than C-3009 at 800° C. and 1000° C., and the alloy MW1 is also stronger than C-3009 at 1200° C.
Table 2. Yield strength (in MPa) of the selected alloys and commercial alloys C-103 and C-3009 at different temperatures.
The specific yield strength values (yield strength divided by the alloy density) of the selected alloys at different temperatures are shown in Table 3. The specific strength values of commercial alloys C103 and C-3009 are also shown for comparison. All the produced alloys have the specific yield strength values much higher than C103. In the temperature range from room temperature to 1000° C., the specific strengths of alloys M4, MW1, M2Fe and M3Fe are higher than the specific strengths of C-3009. At 1200° C., the specific strength of M4 and MW1 are higher than the specific strengths of C-3009. Table 3. Specific yield strength (in MPa/cm3/g) of the selected alloys and commercial alloys C-103 and C-3009 at different temperatures.
Commercial R512E slurry coating integration on Nb-15Mo-20Ti-3Fe alloy (M3F), as compared to commercial C103 alloy is shown in
Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.
While the present invention has been illustrated by a description of one or more embodiments thereof and while these embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
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