HK1181082A - High strength alpha/beta titanium alloy fasteners and fastener stock - Google Patents

Description

High strength alpha/beta titanium alloy fasteners and fastener blanks

Inventor(s):

David J.Bryan

cross Reference to Related Applications

This application is a continuation-in-part application, filed on 23/9/2010 under the provisions of article 35, U.S. code, entitled "High Strength Alpha/Beta Titanium alloy elastomers and Fastener Stock," priority of co-pending U.S. patent application No. 12/888,699, the entire disclosure of which is incorporated herein by reference.

Technical Field

Technical Field

The present invention relates to mechanical fasteners and fastener blanks, and more particularly to fasteners and fastener blanks comprising alpha/beta titanium alloys.

Background

Titanium alloys generally have a high strength to weight ratio, are corrosion resistant, and are resistant to creep at moderately high temperatures. For these reasons, titanium alloys are used in a variety of aerospace and aeronautical applications, including, for example, landing gear members, engine mounts, and mechanical fasteners.

Reducing the weight of an aircraft can save fuel, and there is a strong need in the aerospace industry to reduce the weight of an aircraft. Titanium and titanium alloys are excellent materials for achieving weight savings in aircraft applications due to their high strength to weight ratio. Titanium alloy fasteners are currently used in less demanding aerospace applications. In certain aerospace applications, heavier iron-based and nickel-based alloy fasteners are used if the titanium alloy is not strong enough to meet the specific mechanical requirements of the particular application.

Most titanium alloy parts used in aerospace applications are made from Ti-6Al-4V titanium alloy (ASTM Grade5, UNS R56400, AMS 4965), which is an alpha/beta titanium alloy. Typical minimum specifications for small diameter Ti-6Al-4V fastener blanks, i.e., fastener blanks less than 0.5 inch (1.27 cm) in diameter, are 170ksi (1, 172 MPa) Ultimate Tensile Strength (UTS) as determined according to ASTM E8/E8M-09 ("Standard Test Methods for Testing of metallic Materials", ASTM International, 2009), and 103ksi (710 MPa) Double Shear Strength (DSS) as determined according to NASM1312-13 ("Method 13-Double Shear", Aeroscale Association-National Aeroscale Standard (Metric), 2003, 2.1.h).

Iron-based and nickel-based superalloys, such as the a286 iron-based superalloy (UNS S66286), are representative materials for aerospace fastener applications with the next level of strength. Typical minimum strength specifications for cold drawn and aged A286 metal fasteners are 180ksi (1,241 MPa) UTS and 108ksi (744 MPa) DSS.

Alloy 718 nickel-base superalloy (N07718) is the highest grade strength material used in aerospace fasteners. Typical lower specification limits for cold drawn and aged alloy 718 superalloy fasteners are 220ksi (1,517 MPa) UTS and 120ksi (827 MPa) DSS.

In addition, two beta titanium alloys currently used or considered for use as high strength fastener materials have a minimum ultimate tensile strength of 180ksi (1,241.1 MPa) and a minimum DSS of 108ksi (744.6 MPa). SPS Technologies of Jenkingtown, Pa. provides a titanium alloy fastener made from an optimized beta titanium alloy conforming to the chemical composition of Ti-3Al-8V-6Cr-4Zr-4Mo titanium alloy (AMS 4958). SPS bolts are also commercially available with diameters of up to 1 inch (2.54 cm). Alcoa Fastening Systems (AFS) have developed a high strength titanium fastener made from a titanium alloy that conforms to the nominal chemical composition of Ti-5Al-5Mo-5V-3Cr-0.5Fe titanium alloy (also referred to as Ti-5553, UNS not specified), which is a near beta titanium alloy. The AFS Ti-5553 alloy fastener is said to have a tensile strength of 190ksi (1,309 MPa), an elongation of greater than 10%, and a minimum DSS for uncoated part 113ksi (779 MPa) and 108ksi (744 MPa) for coated part.

Beta titanium alloys typically include a high alloy content and therefore component and tooling costs are higher than alpha/beta titanium alloys. Beta titanium alloys also typically have higher densities than alpha/beta titanium alloys. For example,the density of the alpha/beta titanium alloy is about 0.161lbs/in³（4.5g/cm³) And the density of the beta titanium alloy Ti-3Al-8V-6Cr-4Zr-4Mo is about 0.174lbs/in³（4.8g/cm³) The density of the near beta alloy Ti-5Al-5Mo-5V-3Cr-0.5Fe is about 0.168lbs/in³（4.7g/cm³). Fasteners made with less dense titanium alloys can further save weight for aerospace applications. Furthermore, the achievement of a bimodal microstructure in solution treated aged alpha/beta titanium alloys and the like can provide mechanical properties, e.g., high cycle fatigue, superior to that of beta titanium alloys. Beta transus temperature (T) of alpha/beta titanium alloy_β) Also higher than beta titanium alloys. For example, ATIT of titanium alloy_βAbout 1,800 DEG F (982.2 ℃), and T of Ti-5Al-5Mo-5V-3Cr-0.5Fe beta titanium alloy_βAbout 1,500 ℃ F. (815.6 ℃ C.). T of these two forms of titanium alloy_βThe difference can increase the temperature window for thermomechanical processing and heat treatment in the alpha/beta phase field of the alpha/beta titanium alloy.

As there is a continuing need to save fuel consumption by reducing aircraft weight, there is a need for improved lightweight fasteners in aerospace applications. In particular, lightweight alpha/beta titanium alloy aerospace fasteners and fastener blanks having greater strength than contemporary aerospace fasteners made from Ti-6Al-4V alpha/beta titanium alloys are advantageous.

Disclosure of Invention

In a non-limiting embodiment according to the present invention, an article selected from a titanium alloy fastener and a titanium alloy fastener blank comprises an α/β titanium alloy comprising (in weight percent): 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; titanium; and up to 0.3 total of other elements. In one non-limiting embodiment, the α/β titanium alloy fastener or fastener blank has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a double shear strength of at least 103ksi (710.2 MPa).

In another non-limiting embodiment according to the invention, an article selected from a titanium alloy fastener and a titanium alloy fastener blank comprises an α/β titanium alloy consisting essentially of (in weight percent): 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; up to 0.3 total of other elements; titanium; incidental impurities; and wherein the other elements consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 and less; and boron and yttrium, wherein the weight percent of each such element is 0.005 or less. In one non-limiting embodiment, the α/β titanium alloy fastener or fastener blank has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a double shear strength of at least 103ksi (710.2 MPa).

In another non-limiting embodiment according to the invention, a method for making a titanium alloy fastener blank comprises: providing an alpha/beta titanium alloy comprising (in weight percent): 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; titanium; and up to 0.3 total of other elements. The alpha/beta titanium alloy is hot rolled and then annealed in an annealing time of 1 hour to 2 hours and an annealing temperature of 1,200 DEG F (648.9 ℃) to 1,400 DEG F (760 ℃). After annealing, the α/β titanium alloy is air cooled and then machined to a predetermined size. The alpha/beta titanium alloy is then solution treated within a solution treatment time of 0.5 hours to 2 hours and at a solution treatment temperature of 1,500 DEG F (815.6 ℃) to 1,700 DEG F (926.7 ℃). After solution treatment, the α/β titanium alloy is cooled at a cooling rate at least equal to the air cooling rate and then aged at an aging temperature in the range of 800 ° f (426.7 ℃) to 1,000 ° f (537.8 ℃) for an aging time in the range of 4 hours to 16 hours. After the aging treatment, the titanium alloy is cooled with air. In one non-limiting embodiment, the α/β titanium alloy produced according to the foregoing method embodiments has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a double shear strength of at least 103ksi (710.2 MPa).

Brief Description of Drawings

The features and advantages of the methods described herein may be more clearly understood with reference to the following drawings, in which:

FIG. 1 is a schematic view of a non-limiting embodiment of a fastener according to the present invention;

FIG. 2 is a flow diagram of a non-limiting embodiment of a method for making a fastener and fastener blank according to the present invention;

FIG. 3 is a graph of ultimate tensile strength of fastening strips and wires made by a non-limiting embodiment according to the present invention comparing these properties with the requirements for Ti-6Al-4V titanium alloy fastening strips and wires;

FIG. 4 is a graph of the yield strength of fastening strips and wires made by a non-limiting embodiment according to the present invention comparing these properties with the requirements for Ti-6Al-4V titanium alloy fastening strips and wires; and

FIG. 5 is a graph of elongation of fastening strips and wires made by a non-limiting embodiment according to the present invention comparing these properties with the requirements for Ti-6Al-4V titanium alloy fastening strips and wires.

The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of certain non-limiting embodiments of the process of the invention.

Detailed Description

In the present non-limiting embodiment description, except in the operating examples or where otherwise indicated, all numbers expressing quantities or properties are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, all numerical parameters set forth in the following specification are approximations that may vary depending upon the desired properties of the material sought to be obtained and the method according to the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least conform to the number of reported significant digits and by applying ordinary rounding techniques.

Any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein must satisfy the following preconditions: the incorporated material should not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. Thus, where necessary, the disclosure set forth herein takes precedence over any conflicting material incorporated herein by reference. Any material, or any portion of such material, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.

Referring now to fig. 1, one aspect of the present invention is directed to an article selected from a titanium alloy fastener 10 and a titanium alloy fastener blank (not shown). In one non-limiting embodiment, the article includes an α/β titanium alloy including (in weight percent): 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; titanium; and up to 0.3 total of other elements. In a non-limiting embodiment of the invention, the other elements mentioned in the alloy composition comprise or consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese and cobalt, each in a respective maximum concentration of 0.1 wt%; and boron and yttrium, each element individually in a maximum concentration of 0.005 wt%, the sum of all other elements not exceeding 0.3 wt%. In one non-limiting embodiment, an α/β titanium article in accordance with the present invention has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a Double Shear Strength (DSS) of at least 103ksi (710.2 MPa) for a fastener having a diameter of 0.18 inches (4.57 mm) to 1.25 inches (31.8 mm). In a non-limiting embodiment of the invention, the fastener may have as small a diameter as possible. In a non-limiting embodiment, a fastener according to the present invention has an elongation of at least 10%.

In certain non-limiting embodiments, the elemental composition of the alpha/beta titanium alloy included in a fastener or fastener blank according to the present invention is included in the alloy composition disclosed in U.S. patent No. 5,980,655 ("the' 655 patent"), which is incorporated herein by reference in its entirety. The' 655 patent discloses an alloy having the composition shown in table 1 below.

TABLE 1

Alloy element	Weight percent of
		Aluminium	About 2.9 to about 5.0
Vanadium oxide	About 2.0 to about 3.0
		Iron	About 0.4 to about 2.0
Oxygen gas	Greater than 0.2 to about 0.3

Carbon (C)	About 0.005 to about 0.03
		Nitrogen is present in	About 0.001 to about 0.02
Other elements	Less than about 0.5

The commercial version of the alloy in the' 655 patent is ATIAlloys available from ATIAerospace under the name allegheny technologies of Pittsburgh, pa. The ultimate tensile strength of the alloy having the elemental composition disclosed in the' 655 patent is in the range of 130 to 133ksi (896 to 917 MPa). However, the inventors have surprisingly discovered that a significantly narrower chemical composition range can produce α/β titanium fasteners having significantly higher ultimate tensile strengths as disclosed herein. In one non-limiting embodiment, the ultimate tensile strength of the fasteners disclosed herein made from the alloy compositions disclosed herein is up to 22% greater than the UTS disclosed in the' 655 patent. Without intending to be bound by any theory of operation, it is believed that the extremely high strength fastener alloy compositions disclosed herein may result, at least in part, from aluminum and oxygen contents significantly higher than the minimum contents disclosed in the' 655 patent, which may increase the strength of the predominant alpha phase in the alpha/beta titanium alloy.

The inventors have also surprisingly found that shrinking the allowable ranges of aluminum, vanadium, iron, oxygen, carbon, and nitrogen in the fastener alloys disclosed herein relative to the alloys disclosed in the' 655 patent can reduce the variability of the mechanical properties and the variability of the beta transus temperature of the fastener alloys disclosed herein. This reduction in variability is critical to process and microstructure optimization to achieve the fine mechanical properties disclosed herein.

In another non-limiting embodiment, the titanium alloy fasteners and titanium alloy fastener blanks disclosed herein comprise a diameter of up to 0.75 inches (1.91 cm) and have an ultimate tensile strength of at least 180ksi (1,241 MPa) and a double shear strength of at least 108ksi (744.6 MPa). In one non-limiting embodiment, the ultimate tensile strength of a fastener or fastener blank according to the present invention is up to about 26% greater than the ultimate tensile strength disclosed in the' 655 patent.

Referring again to fig. 1, in accordance with another non-limiting aspect of the present invention, an article selected from the group consisting of a titanium alloy fastener 10 and a titanium alloy fastener blank (not shown) comprises an α/β titanium alloy consisting essentially of (in weight percent): 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; up to 0.3 total of other elements; the rest is titanium; and incidental impurities. In a non-limiting embodiment of the invention, the other elements mentioned in the alloy composition comprise or consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 and less; and boron and yttrium, wherein the weight percent of each such element is less than 0.005 and the sum of all other elements does not exceed 0.3 weight percent. In one non-limiting embodiment, the article has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a double shear strength of at least 103ksi (710.2 MPa).

In one non-limiting embodiment, titanium fastener and titanium alloy fastener blanks according to the present invention comprise a diameter of up to 0.75 inches (1.91 cm), an ultimate tensile strength of at least 180ksi (1,241 MPa), and a double shear strength of at least 108ksi (744.6 MPa).

The term "fastener" as used herein refers to a hardware device that mechanically connects or attaches two or more objects together. Fasteners include, but are not limited to, bolts, nuts, studs, screws, rivets, washers, and lock washers. As used herein, the term "fastener stock" refers to an article that can be processed into one or more fasteners.

Referring to FIG. 2, one non-limiting aspect of the present invention is a method 20 for making a titanium alloy fastener or fastener blank. The method includes providing (21) an α/β titanium alloy comprising (in weight percent): 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.3 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; titanium; and up to 0.3 total of other elements. In a non-limiting embodiment of the invention, the other elements mentioned in the alloy composition comprise or consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 and less; and boron and yttrium, wherein the weight percent of each such element is less than 0.005 and the sum of all other elements does not exceed 0.3 weight percent. The alpha/beta titanium alloy is hot rolled 22 at a specific temperature in the alpha/beta phase field of the alpha/beta titanium alloy. In one non-limiting embodiment, the hot rolling temperature is at least 50 ° f (27.8 ℃) below the β transus temperature of the α/β titanium alloy, but up to 600 ° f (333.3 ℃) below the β transus temperature of the α/β titanium alloy.

After hot rolling 22, the alpha/beta titanium alloy is selectively cold drawn and annealed to reduce the size without significantly altering the mechanical properties of the alpha/beta titanium alloy. In one non-limiting embodiment, the cold drawing reduces the cross-sectional area of the titanium alloy workpiece by less than 10%. Prior to cold drawing, the α/β titanium alloy may be coated with a solid lubricant, such as, but not limited to, molybdenum disulfide (MoS 2).

In one non-limiting embodiment, after hot rolling 22, the alpha/beta titanium alloy is annealed 23 and cooled 24 to provide an alpha/beta titanium alloy fastener blank. In one non-limiting embodiment, annealing 23 includes annealing the hot rolled α/β titanium alloy at a particular annealing temperature in an annealing temperature range of 1,200 ° f to 1,400 ° f (649 ℃ to 760 ℃). In another non-limiting embodiment, the annealing time is from about 1 hour to about 2 hours. In another non-limiting embodiment, annealing 23 includes annealing the hot rolled α/β titanium alloy at a temperature of about 1,275 ° f (690.6 ℃) over a period of about one hour. In one non-limiting embodiment, after annealing 23, the annealed α/β titanium alloy is cooled 24 to room or ambient temperature. In certain non-limiting embodiments, after annealing 23, the annealed α/β titanium alloy is cooled to room or ambient temperature with air or water.

After annealing 23 and cooling 24, in one non-limiting embodiment, the alpha/beta titanium alloy fastener blank is machined 25 to effective dimensions to form a fastener from the blank. Optionally, a coating may be applied to the alpha/beta titanium alloy fastener stock prior to machining. Conventional process coatings are known to those skilled in the art and need not be described in detail herein.

In one non-limiting embodiment, the processed titanium alloy fastener blank is solution treated 26 at a solution treatment temperature of 1,500 ° F (815.6 ℃) to 1,700 ° F (926.7 ℃) in a solution treatment time of 0.5 hours to 2 hours. In a specific non-limiting embodiment, the processed titanium alloy fastener blank is solution treated 26 at a solution treatment temperature of about 1610 ° f (876.7 ℃).

After solution treatment 26, the processed titanium alloy fastener blank is cooled 27. In non-limiting embodiments, cooling 27 may be achieved by air cooling, water cooling, and/or water quenching, and may be referred to as "rapid cooling. Preferably, the cooling rate during cooling 27 is equal to air cooling. In one non-limiting embodiment, cooling 27 includes a cooling rate of at least 1,000 ° f (555.6 ℃) per minute. In one non-limiting embodiment, cooling 27 comprises any cooling method known to one skilled in the art that achieves a specified cooling rate. Rapid cooling 27 serves to maintain the microstructure resulting from solution treatment 26.

In one non-limiting embodiment, the solution treated 26 and rapidly cooled 27 titanium alloy fastener is aged 28 at a specific age treatment temperature in an age treatment temperature range of about 800 ° f (426.7 ℃) to about 1,000 ° f (537.8 ℃) for a specific age treatment time in an age treatment time range of about 4 hours to about 16 hours. In a specific non-limiting embodiment, the solution treated 26 and rapidly cooled 27 titanium alloy fastener blank is aged 28 at 850 ° f (454.4 ℃) within 10 hours. In certain non-limiting embodiments, after aging treatment 28, the α/β titanium alloy fastener blank is air cooled 29 or rapidly cooled to produce the α/β titanium alloy fasteners disclosed herein.

The mechanical properties of the fastener stock prepared according to the present invention have been demonstrated to be higher than fastener stock made of Ti-6-4 titanium alloy. Thus, smaller sized fasteners made in accordance with the present invention may be used in place of Ti-6-4 fasteners in the same application. This can lead to weight savings, which is critical for aerospace applications. It has also been demonstrated that in certain applications fasteners made in accordance with the present invention can replace steel alloy fasteners of the same size and achieve weight savings critical to aerospace applications.

The following examples are intended to further describe certain non-limiting embodiments without limiting the scope of the invention. Those of ordinary skill in the art will recognize that there may be variations to the following examples that are within the scope of the present invention, which is limited only by the claims.

Example 1

Ingots were prepared from compacts made from the raw materials using the double Vacuum Arc Remelting (VAR) technique. Samples were taken from the ingots for chemical analysis, and the measured average chemical compositions of the ingots are shown in table 2. The beta transus temperature of the alloy was determined to be 1,785 ° f (973.9 ℃).

TABLE 2

Al	V	Fe	O	N	C	The rest components
							4.06	2.52	1.71	0.284	0.008	0.017	Ti and incidental impurities

Example 2

Titanium alloy ingots in several passes having a chemical composition according to the present invention were hot rolled at a hot rolling temperature of about 1,600 ° f (871.1 ℃). The hot rolled material was annealed at 1,275 ° f (690.6 ℃) for 1 hour and air cooled. The processing of the annealed material into fastener stock strips and wires having diameters in the range of about 0.25 inch (6.35 mm) to about 3.5 inches (88.9 mm). Fastener blank strips and wires were solution treated at about 1,610 ° f (876.7 ℃) for about 1 hour and water quenched. After solution treatment and water quenching, fastener blank strips and wires were aged at about 850 ° f (454.4 ℃) for about 10 hours and air cooled.

Example 3

The fastener stock strips and wires of example 2 were subjected to tensile testing at room temperature. The ultimate tensile strength of the fastener strips and wires is shown in fig. 3. The yield strength of the fastener strips and wires is shown in fig. 4, and the elongation of the fastener strips and wires is shown in fig. 5. The minimum ultimate tensile strength, yield strength and elongation required for solution treatment and aging of Ti-6Al-4V alloys in aerospace fastener applications (AMS 4965) are shown in FIGS. 3-5, respectively. As shown in FIG. 3, the ultimate tensile strength measured for fastener blank strips and wires according to the present invention significantly exceeded the indicated Ti-6Al-4V alloy gauge by about 20ksi (138 MPa) in all measured diameter sizes. Further, as shown in FIG. 5, a fastener blank having a chemical composition according to the present disclosure has an elongation range of at least 10% to about 19%.

Example 4

Tensile testing was performed on fastener blanks having a diameter of about 0.25 inch (6.35 mm), the chemical composition of example 1, and having been solution treated and aged as in example 2. The results of the tensile test are shown in table 3.

TABLE 3

The ultimate tensile strength ranges from about 196ksi to about 200ksi (1351 MPa to 1379 MPa), which is higher than the minimum requirements for the Ti-6Al-4V fastener stock 170ksi (1, 172 MPa) UTS and 103ksi (710 MPa) DSS. It was also observed that these properties conform to a well-established empirical relationship, namely DSS =0.6 XUTS.

Example 5

A tensile test was conducted on a fastener blank having a diameter of about 0.75 inch (1.91 cm), having the chemical composition of example 1, and having undergone the heat treatment of example 2. The results of the tensile test are shown in table 4.

TABLE 4

The average ultimate tensile strength of the 0.75 inch (1.91 cm) strip of fastener stock was 186ksi (1,282 MPa), meeting the minimum specifications for fasteners made from a286 iron-based superalloy. Based on the above-identified empirical relationship between DSS and UTS, it is expected that the 0.75 inch (1.91 cm) strip also meets the 108ksi (744 MPa) DSS requirements for fasteners made of a286 iron-based superalloy.

Example 6

The ingot having the chemical composition of example 1 was hot rolled, annealed, and processed as in example 2 to form a fastener blank having a diameter of about 0.75 inches (1.91 cm). And machining the fastener blank into a stud-shaped fastener by computer numerical control. The stud was solution treated and aged as in example 2 to form a non-limiting embodiment of the fastener of the invention.

Example 7

The hot rolling, annealing, and processing of example 2 was performed on the ingot having the chemical composition of example 1 to form a fastener blank having a diameter of about 1 inch (2.54 cm). The fastener blank was threaded and cut into parts having a length of about 2 inches (5.08 cm). These parts are cold forged to form a hexagon head bolt. The hex head bolt was solution treated and aged as in example 2 to form a non-limiting embodiment of a fastener according to the present invention.

Example 7

The hot rolling, annealing, and processing of example 2 was performed on the ingot having the chemical composition of example 1 to form a fastener blank having a diameter of about 1 inch (2.54 cm). The center of the fastener blank was machined to form a 0.5 inch (1.27 cm) diameter hole. The fastener blank was then cut into parts having a thickness of 0.125 inches (0.318 cm). The fastener blank was subjected to the solution treatment and aging treatment of example 2 to form a non-limiting embodiment of a fastener in the form of a washer according to the present invention.

While the invention has been described with reference to various exemplary, illustrative, and non-limiting embodiments. Those of ordinary skill in the art will recognize that various alternatives, modifications, or combinations of any of the disclosed embodiments (or portions thereof) can be made without departing from the scope of the invention, which is defined solely by the claims. Accordingly, it is contemplated and understood that the present invention includes other embodiments not specifically illustrated herein. For example, such embodiments may result from combining and/or modifying any of the disclosed steps, ingredients, components, parts, elements, features, aspects, etc., of the embodiments disclosed herein. Accordingly, the present invention is not limited by the description of the various exemplary, illustrative, and non-limiting embodiments, but is only limited by the claims. In this manner, it should be appreciated that during the prosecution of the present application, modifications may be made to the claims in order to add features to the invention as described in different ways herein.

Claims (18)

1. An article selected from a titanium alloy fastener and a titanium alloy fastener stock, the article comprising an alpha/beta titanium alloy comprising (in weight percent):

3.9 to 4.5 aluminum;

2.2 to 3.0 vanadium;

1.2 to 1.8 iron;

0.24 to 0.3 oxygen;

up to 0.08 carbon;

up to 0.05 nitrogen;

titanium; and

up to 0.3 total of other elements;

wherein the article has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a double shear strength of at least 103ksi (710.2 MPa).

2. The article of claim 1, wherein the article comprises a diameter of up to 0.75 inches (1.91 cm) and has an ultimate tensile strength of at least 180ksi (1,241 MPa) and a double shear strength of at least 108ksi (744.6 MPa).

3. The article of claim 1, wherein the other elements consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 and less; and boron and yttrium, wherein the weight percent of each such element is less than 0.005.

4. The article of claim 1 or 2, wherein the fastener comprises one of: bolts, nuts, studs, screws, washers, lock washers, and rivets.

5. An article selected from a titanium alloy fastener and a titanium alloy fastener stock, the article comprising an α/β titanium alloy consisting essentially of (in weight percent):

3.9 to 4.5 aluminum;

2.2 to 3.0 vanadium;

1.2 to 1.8 iron;

0.24 to 0.3 oxygen;

up to 0.08 carbon;

up to 0.05 nitrogen;

no more than 0.3 total of other elements;

titanium;

incidental impurities;

wherein the other elements consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 and less; and boron and yttrium, wherein the weight percent of each such element is less than 0.005; and

wherein the article has an ultimate tensile strength of at least 170ksi (1,172 MPa) and a double shear strength of at least 103ksi (710.2 MPa).

6. The article of claim 5, wherein the article comprises a diameter of up to 0.75 inches (1.91 cm) and has an ultimate tensile strength of at least 180ksi (1,241 MPa) and a double shear strength of at least 108ksi (744.6 MPa).

7. The article of claim 5 or 6, wherein the fastener comprises one of: bolts, nuts, studs, screws, washers, lock washers, and rivets.

8. A method for making a titanium alloy fastener blank, the method comprising:

providing an α/β titanium alloy comprising (in weight percent):

3.9 to 4.5 aluminum;

2.2 to 3.0 vanadium;

1.2 to 1.8 iron;

0.24 to 0.3 oxygen;

up to 0.08 carbon;

up to 0.05 nitrogen;

titanium; and

up to 0.3 total of other elements;

hot rolling the titanium alloy in an a/β phase of the titanium alloy;

annealing the titanium alloy in an annealing time of 1 hour to 2 hours and an annealing temperature of 1,200 ° F (648.9 ℃) to 1,400 ° F (760 ℃);

cooling the titanium alloy with air;

machining the titanium alloy to a predetermined size;

solution treating the titanium alloy in a solution treatment time of 0.5 hours to 2 hours and in a solution treatment range of 1,500 ° f (815.6 ℃) to 1,700 ° f (926.7 ℃);

cooling the titanium alloy at a cooling rate at least equal to the air cooling rate,

aging the titanium alloy at an aging time of 4 hours to 16 hours and an aging temperature of 800 ° F (426.7 ℃) to 1,000 ° F (537.8 ℃); and

cooling the titanium alloy with air.

9. The method of claim 8, wherein the other elements of the α/β titanium alloy consist essentially of one or more of the following elements: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 and less; and boron and yttrium, wherein the weight percent of each such element is less than 0.005.

10. The method of claim 8, wherein the hot rolling is performed at a temperature range of 50 ° F (27.8 ℃) below a beta transus temperature of the titanium alloy to 600 ° F (333.3 ℃) below the beta transus temperature of the titanium alloy.

11. The method of claim 8, further comprising, after hot rolling and before annealing the titanium alloy, cold drawing the titanium alloy to achieve a reduction in cross-sectional area of less than 10% and annealing.

12. The method of claim 11, further comprising coating the titanium alloy with a solid lubricant prior to cold drawing.

13. The method of claim 12, wherein the solid lubricant is molybdenum disulfide.

14. The method of claim 8, wherein the annealing temperature is 1,275 ° f (690.6 ℃) and the annealing time is 1 hour.

15. The method of claim 8, wherein the titanium alloy is coated prior to processing the titanium alloy.

16. The method of claim 8, wherein cooling after the solution treatment step comprises one of: air cooling, water cooling, and water quenching.

17. The method of claim 8, wherein the solution treatment temperature is 1,610 ° f (876.7 ℃) and the cooling of the titanium alloy comprises water quenching.

18. The method of claim 8, wherein aging the titanium alloy comprises aging within 10 hours and at 850 ° f (454.4 ℃).