HK1238686B - High strength alpha/beta titanium alloy fasteners and fastener stock - Google Patents

Description

High-strength α/β titanium alloy fasteners and fastener blanks

Inventor

David J. Bryan

This application is a divisional application of the invention patent application with application date of September 7, 2011, application number 201180043325.2, and invention name “High-strength α/β titanium alloy fasteners and fastener blanks”.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application claiming priority under 35 U.S.C. § 120 to co-pending U.S. patent application Ser. No. 12/888,699, filed on Sep. 23, 2010, and entitled “High Strength Alpha/Beta Titanium Alloy Fasteners and Fastener Stock,” the entire disclosure of which is incorporated herein by reference.

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 Art

Titanium alloys typically 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 aviation applications, including, for example, landing gear components, engine mounts, and mechanical fasteners.

Reducing aircraft weight saves fuel, leading to strong demand in the aerospace industry. Titanium and titanium alloys, due to their high strength-to-weight ratio, are excellent materials for achieving weight reduction in aircraft applications. Currently, titanium alloy fasteners are used in less demanding aerospace applications. In certain aerospace applications, where titanium alloys are not strong enough to meet the specific mechanical requirements of a particular application, heavier iron- and nickel-based alloy fasteners are used.

Most titanium alloy parts used in aerospace applications are made from Ti-6Al-4V titanium alloy (ASTM Grade 5, UNSR56400, AMS 4965), which is an alpha/beta titanium alloy. Typical minimum specifications for small-diameter Ti-6Al-4V fastener stock, i.e., fastener stock with a diameter less than 0.5 inches (1.27 cm), are 170 ksi (1,172 MPa) ultimate tensile strength (UTS) determined in accordance with ASTM E8/E8M-09 (“Standard Test Methods for Tension Testing of Metallic Materials,” ASTM International, 2009), and 103 ksi (710 MPa) double shear strength (DSS) determined in accordance with NASM 1312-13 (“Method 13-Double Shear,” Aerospace Industries Association-National Aerospace Standard (Metric), February 1, 2003).

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

Alloy 718 nickel-based superalloy (N07718) is the highest strength material used in aerospace fasteners. Typical lower specification limits for cold-drawn and aged Alloy 718 superalloy fasteners are 220 ksi (1,517 MPa) UTS and 120 ksi (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 180 ksi (1,241.1 MPa) and a minimum DSS of 108 ksi (744.6 MPa). SPS Technologies of Jenkintown, Pennsylvania, provides a titanium alloy fastener made of an optimized beta titanium alloy that conforms to the chemical composition of Ti-3Al-8V-6Cr-4Zr-4Mo titanium alloy (AMS 4958). SPS bolts with diameters up to 1 inch (2.54 cm) are also commercially available. Alcoa Fastening Systems (AFS) has developed a high-strength titanium fastener made of a titanium alloy that conforms to the nominal chemical composition of Ti-5Al-5Mo-5V-3Cr-0.5Fe titanium alloy (also known as Ti-5553, UNS unspecified), which is a near-beta titanium alloy. AFS Ti-5553 alloy fasteners are said to have a tensile strength of 190 ksi (1,309 MPa), an elongation greater than 10%, and a minimum DSS of 113 ksi (779 MPa) for uncoated parts and 108 ksi (744 MPa) for coated parts.

Beta titanium alloys typically include high alloy contents, resulting in higher component and processing costs than alpha/beta titanium alloys. Beta titanium alloys also generally have higher densities than alpha/beta titanium alloys. For example, the density of ATI alpha/beta titanium alloy is approximately 0.161 lbs/ ^in³ (4.5 g/ ^cm³ ), while the density of beta titanium alloy Ti-3Al-8V-6Cr-4Zr-4Mo is approximately 0.174 lbs/ ^in³ (4.8 g/ ^cm³ ), and the density of near-beta alloy Ti-5Al-5Mo-5V-3Cr-0.5Fe is approximately 0.168 lbs/ ^in³ (4.7 g/ ^cm³ ). Fasteners made from less dense titanium alloys can further reduce weight in aerospace applications. Furthermore, the bimodal microstructure achieved in solution-treated, aged alpha/beta titanium alloys, for example, can provide mechanical properties superior to beta titanium alloys, such as high-cycle fatigue. The beta transition temperature ( _Tβ ) of alpha/beta titanium alloys is also higher than that of beta titanium alloys. For example, the _Tβ of ATI α/β titanium alloy is about 1,800°F (982.2°C), while the _Tβ of Ti-5Al-5Mo-5V-3Cr-0.5Feβ titanium alloy is about 1,500°F (815.6°C). This difference in _Tβ between these two forms of titanium alloy can increase the temperature window for thermomechanical processing and heat treatment in the α/β phase of the α/β titanium alloy.

The continued need to reduce aircraft weight to save fuel consumption has led to a need for improved lightweight fasteners for aerospace applications. Specifically, lightweight α/β titanium alloy aerospace fasteners and fastener blanks that are stronger than contemporary aerospace fasteners made from Ti-6Al-4V α/β titanium alloys are advantageous.

Summary of the Invention

In a non-limiting embodiment according to the present invention, an article selected from the group consisting of a titanium alloy fastener and a titanium alloy fastener stock comprises an alpha/beta titanium alloy comprising, by weight percentage: 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 other elements. In one non-limiting embodiment, the alpha/beta titanium alloy fastener or fastener stock has an ultimate tensile strength of at least 170 ksi (1,172 MPa) and a double shear strength of at least 103 ksi (710.2 MPa).

In another non-limiting embodiment according to the present invention, an article selected from titanium alloy fasteners and titanium alloy fastener stock comprises an alpha/beta titanium alloy consisting essentially of the following components (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 other elements; titanium; incidental impurities; and wherein the other elements consist essentially of one or more of the following: 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 alpha/beta titanium alloy fastener or fastener stock has an ultimate tensile strength of at least 170 ksi (1,172 MPa) and a double shear strength of at least 103 ksi (710.2 MPa).

In another non-limiting embodiment according to the present invention, a method for preparing a titanium alloy fastener stock comprises: providing an α/β titanium alloy comprising (by weight percentage): 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 other elements. The α/β titanium alloy is hot rolled and then annealed at an annealing temperature of 1,200°F (648.9°C) to 1,400°F (760°C) for an annealing time of 1 to 2 hours. After annealing, the α/β titanium alloy is air cooled and then machined to a predetermined size. The α/β titanium alloy is then solution treated within a solution treatment time of 0.5 to 2 hours and at a solution treatment temperature of 1,500°F (815.6°C) to 1,700°F (926.7°C). After solution treatment, the α/β titanium alloy is cooled at a cooling rate at least equal to the cooling rate of air and then aged within an aging time of 4 to 16 hours and at an aging treatment temperature of 800°F (426.7°C) to 1,000°F (537.8°C). After aging, the titanium alloy is air cooled. In one non-limiting embodiment, the α/β titanium alloy made according to the foregoing method embodiment has an ultimate tensile strength of at least 170 ksi (1,172 MPa) and a double shear strength of at least 103 ksi (710.2 MPa).

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 is a schematic diagram of a non-limiting embodiment of a fastener according to the present invention;

FIG2 is a flow chart of a non-limiting embodiment of a method for making fasteners and fastener blanks according to the present invention;

FIG3 is a graph of the ultimate tensile strength of fastening bars and wires made according to a non-limiting embodiment of the present invention, comparing these properties with the requirements of Ti-6Al-4V titanium alloy fastening bars and wires;

FIG4 is a graph of yield strength of fastening bars and wires made according to a non-limiting embodiment of the present invention, comparing these properties to the requirements of Ti-6Al-4V titanium alloy fastening bars and wires; and

5 is a graph of the elongation of fastening bars and wires made according to a non-limiting embodiment of the present invention, comparing these properties to the requirements of Ti-6Al-4V titanium alloy fastening bars 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 methods of the present invention.

DETAILED DESCRIPTION

In this non-limiting description of the embodiments, except in the operating examples or unless otherwise indicated, all numbers expressing quantities or properties are understood to be modified by "about" in any case. Therefore, unless otherwise indicated, all numerical parameters in the following description are approximate and can vary with the target material properties intended to be obtained and the methods according to the present invention. At the very least, and without intending to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed to the number of reported significant digits and using ordinary rounding techniques.

Any patent, publication, or other public material described as being incorporated herein by reference, in whole or in part, must be incorporated only to the extent that the incorporated material does not conflict with existing definitions, statements, or other public materials set forth in this disclosure. Therefore, to the extent necessary, the disclosure set forth herein takes precedence over any conflicting material incorporated herein by reference. Any material, or any portion of such material, described as being incorporated herein that conflicts with existing definitions, statements, or other public materials set forth herein will be incorporated only to the extent that there is no conflict between the incorporated material and the existing public materials.

Referring now to FIG1 , one aspect of the present invention relates to an article selected from the group consisting of a titanium alloy fastener 10 and a titanium alloy fastener stock (not shown). In one non-limiting embodiment, the article comprises 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% other elements combined. In a non-limiting embodiment of the invention, the other elements mentioned in the alloy composition include or consist essentially of one or more of the following: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, each at a maximum concentration of 0.1% by weight; and boron and yttrium, each at a maximum concentration of 0.005% by weight, with the sum of all other elements not exceeding 0.3% by weight. In one non-limiting embodiment, for a fastener having a diameter between 0.18 inches (4.57 mm) and 1.25 inches (31.8 mm), an alpha/beta titanium article according to the present invention has an ultimate tensile strength of at least 170 ksi (1,172 MPa) and a double shear strength (DSS) of at least 103 ksi (710.2 MPa). In a non-limiting embodiment of the present invention, the fastener can have a diameter as small 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 the fastener or fastener blank according to the present invention is encompassed by the alloy compositions 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

A commercial version of the alloy of the '655 patent is the ATI alloy, available from ATI Aerospace, a subsidiary of Allegheny Technologies of Pittsburgh, Pennsylvania. Alloys having the elemental compositions disclosed in the '655 patent have ultimate tensile strengths ranging from 130 to 133 ksi (896 to 917 MPa). However, the inventors surprisingly discovered that alpha/beta titanium fasteners made with the significantly narrower chemical composition range of the present invention can exhibit the significantly higher ultimate tensile strengths disclosed herein. In one non-limiting embodiment, the ultimate tensile strength of fasteners made from the disclosed alloy compositions 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 levels disclosed in the '655 patent, which can enhance the strength of the dominant alpha phase in the alpha/beta titanium alloy.

The present inventors have also surprisingly discovered that narrowing the permissible ranges of aluminum, vanadium, iron, oxygen, carbon, and nitrogen in the fastener alloys disclosed herein relative to the alloys disclosed in the '655 patent reduces the variability in the mechanical properties and beta transus temperature of the fastener alloys disclosed herein. This reduction in variability is crucial for process and microstructural optimization to achieve the superior mechanical properties disclosed herein.

In another non-limiting embodiment, the titanium alloy fasteners and titanium alloy fastener stock disclosed herein comprise a diameter of up to 0.75 inches (1.91 cm) and have an ultimate tensile strength of at least 180 ksi (1,241 MPa) and a double shear strength of at least 108 ksi (744.6 MPa). In one non-limiting embodiment, the ultimate tensile strength of a fastener or fastener stock 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 stock (not shown) comprises an alpha/beta titanium alloy consisting essentially of the following components (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 other elements in total; the remainder being titanium; and incidental impurities. In a non-limiting embodiment of the present invention, the other elements mentioned in the alloy composition include or consist essentially of one or more of the following: tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, wherein the weight percent of each such element is 0.1 or 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 170 ksi (1,172 MPa) and a double shear strength of at least 103 ksi (710.2 MPa).

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

As used herein, the term "fastener" 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 FIG2 , one non-limiting aspect of the present invention is a method 20 for preparing a titanium alloy fastener or fastener stock. The method comprises providing (21) 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 other elements. In a non-limiting embodiment of the present invention, the other elements mentioned in the alloy composition include or consist essentially of one or more of the following: 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 α/β titanium alloy is hot rolled 22 at a specific temperature in the α/β phase field of the α/β titanium alloy. In one non-limiting embodiment, the hot rolling temperature is at least 50°F (27.8°C) below the β transus temperature of the α/β titanium alloy, but no more than 600°F (333.3°C) below the β transus temperature of the α/β titanium alloy.

After hot rolling 22, the α/β titanium alloy is optionally cold drawn and annealed to reduce the size without significantly changing the mechanical properties of the α/β titanium alloy. In one non-limiting embodiment, 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 ( _MoS2 ).

In one non-limiting embodiment, after hot rolling 22, the α/β titanium alloy is annealed 23 and cooled 24 to provide an α/β titanium alloy fastener stock. In one non-limiting embodiment, annealing 23 includes annealing the hot-rolled α/β titanium alloy at a specific annealing temperature in the annealing temperature range of 1,200°F to 1,400°F (649°C to 760°C). 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°C) for about one hour. In one non-limiting embodiment, after annealing 23, the annealed α/β titanium alloy is cooled 24 to room temperature or ambient temperature. In a specific non-limiting embodiment, after annealing 23, the annealed α/β titanium alloy is cooled to room temperature or ambient temperature using air or water.

After annealing 23 and cooling 24, in one non-limiting embodiment, the α/β titanium alloy fastener stock is machined 25 to effective dimensions for forming fasteners from the stock. Optionally, a coating can be applied to the α/β titanium alloy fastener stock prior to machining. Conventional machining 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 stock is solution treated 26 at a solution treatment temperature of 1,500°F (815.6°C) to 1,700°F (926.7°C) for a solution treatment time of 0.5 hours to 2 hours. In a specific non-limiting embodiment, the processed titanium alloy fastener stock is solution treated 26 at a solution treatment temperature of approximately 1610°F (876.7°C).

After solution treatment 26, the processed titanium alloy fastener blank is cooled 27. In a non-limiting embodiment, cooling 27 can be achieved by air cooling, water cooling and/or water quenching, and can be referred to as "rapid cooling". Preferably, the cooling rate during cooling 27 is equal to air cooling. In a non-limiting embodiment, cooling 27 includes a cooling rate of at least 1,000°F (555.6°C) per minute. In a non-limiting embodiment, cooling 27 includes any cooling method known to those skilled in the art to achieve a specified cooling rate. Rapid cooling 27 is used to maintain the microstructure obtained by solution treatment 26.

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

Fastener blanks prepared according to the present invention have been shown to have superior mechanical properties to those made from Ti-6-4 titanium alloy. Consequently, smaller fasteners made according to the present invention can be used to replace Ti-6-4 fasteners in the same application. This can result in weight savings, which is crucial for aerospace applications. Fasteners made according to the present invention have also been shown to be able to replace similarly sized steel alloy fasteners in certain applications, achieving the weight savings that are crucial for aerospace applications.

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

Example 1

Ingots were prepared from compacts made from the raw materials using a double vacuum arc remelting (VAR) technique. Samples were taken from the ingots for chemical analysis, and the measured average chemical composition of the ingots is shown in Table 2. The beta transus temperature of the alloy was determined to be 1,785°F (973.9°C).

Table 2

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

Example 2

Several heats of titanium alloy ingots having a chemical composition according to the present invention were hot rolled at a hot rolling temperature of approximately 1,600°F (871.1°C). The hot rolled material was annealed at 1,275°F (690.6°C) for 1 hour and air cooled. The annealed material was processed into fastener stock bars and wires having diameters ranging from approximately 0.25 inches (6.35 mm) to approximately 3.5 inches (88.9 mm). The fastener stock bars and wires were solution treated at approximately 1,610°F (876.7°C) for approximately 1 hour and water quenched. Following solution treatment and water quenching, the fastener stock bars and wires were aged at approximately 850°F (454.4°C) for approximately 10 hours and air cooled.

Example 3

Tensile testing was performed on the fastener stock, strips, and wires of Example 2 at room temperature. The ultimate tensile strength of the fastener stock and wires is shown in FIG3 . The yield strength of the fastener stock and wires is shown in FIG4 , and the elongation of the fastener stock and wires is shown in FIG5 . The minimum ultimate tensile strength, yield strength, and elongation required for solution-treated and aged Ti-6Al-4V alloys for aerospace fastener applications (AMS 4965) are shown in FIG3 through FIG5 , respectively. As shown in FIG3 , the ultimate tensile strength measured for the fastener stock, strips, and wires according to the present invention significantly exceeds the specified Ti-6Al-4V alloy specification by approximately 20 ksi (138 MPa) across all measured diameters. Furthermore, as shown in FIG5 , the fastener stock having a chemical composition according to the present invention exhibits an elongation range of at least 10% to about 19%.

Example 4

Tensile testing was performed on fastener blanks having a diameter of approximately 0.25 inches (6.35 mm), the chemical composition of Example 1, and the solution treatment and aging treatment of Example 2. The results of the tensile testing are shown in Table 3.

Table 3

The ultimate tensile strength ranges from about 196 ksi to about 200 ksi (1351 MPa to 1379 MPa), exceeding the minimum requirements of 170 ksi (1,172 MPa) UTS and 103 ksi (710 MPa) DSS for Ti-6Al-4V fastener stock. It was also observed that these properties conform to the recognized empirical relationship of DSS = 0.6 x UTS.

Example 5

Tensile testing was performed on fastener blanks having a diameter of approximately 0.75 inches (1.91 cm), having the chemical composition of Example 1, and having been heat treated as in Example 2. The results of the tensile testing are shown in Table 4.

Table 4

The average ultimate tensile strength of the 0.75-inch (1.91 cm) fastener stock bar is 186 ksi (1,282 MPa), meeting the minimum specification for fasteners made from the A286 iron-based superalloy. Based on the recognized empirical relationship between DSS and UTS mentioned above, it is expected that the 0.75-inch (1.91 cm) bar will also meet the 108 ksi (744 MPa) DSS requirement for fasteners made from the 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 approximately 0.75 inches (1.91 cm). The fastener blank was computer numerically controlled machined into a fastener in the shape of a stud. The stud was solution treated and aged as in Example 2 to form a non-limiting embodiment of the fastener of the present invention.

Example 7

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 approximately 1 inch (2.54 cm). The fastener blank was threaded and cut into parts having a length of approximately 2 inches (5.08 cm). These parts were cold forged to form hexagonal head bolts. The hexagonal head bolts were 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 ingot having the chemical composition of Example 1 was hot rolled, annealed, and machined as in Example 2 to form a fastener blank having a diameter of approximately 1 inch (2.54 cm). The center of the fastener blank was machined to form a hole having a diameter of 0.5 inches (1.27 cm). The fastener blank was then cut into parts having a thickness of 0.125 inches (0.318 cm). The fastener blank was solution treated and aged as in Example 2 to form a non-limiting embodiment of a fastener in the form of a washer according to the present invention.

Although the present invention has been described with reference to various exemplary, illustrative and non-limiting embodiments. However, those skilled in the art will recognize that various alternatives, modifications or combinations of any disclosed embodiment (or a portion of these embodiments) can be derived without departing from the scope of the present invention, and the scope of the present invention is limited only by the claims. Therefore, it is expected and understood that the present invention includes other embodiments not explicitly described herein. For example, such embodiments can be obtained by combining and/or modifying any disclosed steps, ingredients, components, parts, elements, features, aspects, etc. of the embodiments disclosed herein. Therefore, the present invention is not limited to the description of the various exemplary, illustrative and non-limiting embodiments, but is limited only by the claims. In this way, it should be understood that during the execution of this patent application, the claims can be modified to add features to the present invention described in different ways herein.

Claims (4)

1. An article selected from titanium alloy fasteners and titanium alloy fastener blanks, said article comprising an α/β titanium alloy that has undergone hot rolling, solution treatment, and aging treatment, wherein said α/β titanium alloy comprises, by weight percentage: Aluminum of 3.9 to 4.5; Vanadium of 2.2 to 3.0; Iron content of 1.2 to 1.8; 0.24 to 0.3% oxygen; Up to 0.08 carbon atoms; Up to 0.05% nitrogen; Other elements totaling up to 0.3, wherein the other elements totaling up to 0.3 include one or more of the following: Boron and yttrium, each less than 0.005; Tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, each not exceeding 0.10; and Balance of titanium and associated impurities; The article described herein has an ultimate tensile strength of at least 180 ksi (1,241 MPa) and a double shear strength of at least 108 ksi (744.6 MPa). The titanium alloy is prepared by a method comprising the following steps: The titanium alloy is hot-rolled in the α/β phase; The titanium alloy is annealed within an annealing time of 1 to 2 hours and at an annealing temperature of 1,200℉ (648.9℃) to 1,400℉ (760℃). The titanium alloy was cooled with air. The titanium alloy is processed to a predetermined size; The titanium alloy was solution treated within a solution treatment time of 0.5 to 2 hours and a solution treatment range of 1,500℉ (815.6℃) to 1,700℉ (926.7℃). The titanium alloy was cooled at a cooling rate of at least 1,000°F (555.6°C) per minute. The titanium alloy was aged for a period of 4 to 16 hours and at an aging temperature of 800℉ (426.7℃) to 1,000℉ (537.8℃); and The titanium alloy is cooled with air. 2. The article of claim 1, wherein the article of claim 1 comprises a diameter of up to 0.75 inches (1.91 cm). 3. The article of claim 1 or 2, wherein the fastener comprises one of the following: bolt, nut, stud, screw, washer, locking washer, and rivet. 4. The article of claim 1, wherein the article has an ultimate tensile strength of at least 196 ksi (1351 MPa).