US20120076686A1

US20120076686A1 - High strength alpha/beta titanium alloy

Info

Publication number: US20120076686A1
Application number: US13/108,045
Authority: US
Inventors: David J. Bryan; John V. Mantione; Thomas D. Bayha
Original assignee: ATI Properties LLC
Current assignee: ATI Properties LLC
Priority date: 2010-09-23
Filing date: 2011-05-16
Publication date: 2012-03-29
Also published as: TW201224163A; BR112013005248B1; JP6104164B2; RU2616676C2; MX2013002312A; CA2809035A1; WO2012039929A1; PE20131367A1; KR20130099001A; KR20180049165A; MX368806B; IL224802A; CN103097559A; EP2619340A1; KR20190040094A; TW201708555A; AU2011305924A1; AU2011305924B2; JP2013539822A; BR112013005248A2

Abstract

An alpha/beta titanium alloy comprising, in percent by weight based on total alloy weight: 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; up to 0.015 hydrogen ; titanium; and up to a total of 0.30 of other elements. A non-limiting embodiment of the alpha/beta titanium alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, exhibits a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa), exhibits an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa), and exhibits a ductility in the range of 12 to 30 percent elongation.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application claiming priority under 35 U.S.C. §120 from co-pending U.S. patent application Ser. No. 12/903,851, filed on Oct. 13, 2010, and entitled “High Strength Alpha/Beta Titanium Alloy Fasteners and Fastener Stock, which is a continuation-in-part application claiming priority under 35 U.S.C. §120 from 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 disclosures of application Ser. Nos. 12/903,851 and 12/888,699 are hereby incorporated by reference herein.

BACKGROUND OF THE TECHNOLOGY

1. Field of the Technology
The present disclosure relates to high strength and ductile alpha/beta titanium alloys.
2. Description of the Background of the Technology
Titanium alloys typically exhibit 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 aerospace, aeronautic, defense, marine, and automotive applications including, for example, landing gear members, engine frames, ballistic armor, hulls, and mechanical fasteners.
Reducing the weight of an aircraft or other moving vehicle results in fuel savings. Thus, for example, there is a strong drive in the aerospace industry to reduce aircraft weight. Titanium and titanium alloys are attractive materials for achieving weight reduction in aircraft applications because of their high strength-to-weight ratio. Most titanium alloy parts used in aerospace applications are made from Ti-6Al-4V alloy (ASTM Grade 5; UNS R56400; AMS 4928, AMS 4911), which is an alpha/beta titanium alloy.
Ti-6Al-4V alloy is one of the most common titanium-based manufactured materials, estimated to account for over 50% of the total titanium-based materials market. Ti-6Al-4V alloy is used in a number of applications that benefit from the alloy's advantageous combination of light weight, corrosion resistance, and high strength at low to moderate temperatures. For example, Ti-6Al-4V alloy is used to produce aircraft engine components, aircraft structural components, fasteners, high-performance automotive components, components for medical devices, sports equipment, components for marine applications, and components for chemical processing equipment.
Ti-6Al-4V alloy mill products are generally used in either a mill annealed condition or in a solution treated and aged (STA) condition. As used herein, the “mill-annealed condition” refers to the condition of a titanium alloy after a “mill-annealing” heat treatment in which a workpiece is annealed at an elevated temperature (e.g., 1200-1500° F./649-816° C.) for about 1-8 hours and cooled in still air. A mill-annealing heat treatment is performed after a workpiece is hot worked in the α+β phase field. Round bar of Ti-6Al-4V alloy having a diameter of about 2 to 4 inches (5.08 to 10.16 cm) in a mill-annealed condition has a minimum specified ultimate tensile strength of 130 ksi (896 MPa) and a minimum specified yield strength of 120 ksi (827 MPa), at room temperature. Mill annealed Ti-6Al-4V plate is often produced to specification AMS 4911, whereas mill annealed Ti-6Al-4V bar is often produced to specification AMS 4928.
U.S. Pat. No. 5,980,655 (“the '655 patent”), which is hereby incorporated herein by reference in its entirety, discloses an alpha/beta titanium alloy that comprises, in weight percentages, from 2.90 to 5.00 aluminum, from 2.00 to 3.00 vanadium, from 0.40 to 2.00 iron, from 0.20 to 0.30 oxygen, incidental impurities, and titanium. The alpha/beta titanium alloys disclosed in the '655 patent are referred to herein as “the '655 alloys”. A commercially available alloy composition within the '655 alloys nominally includes, in weight percentages based on total alloy weight, 4.00 aluminum, 2.50 vanadium, 1.50 iron, 0.25 oxygen, incidental impurities, and titanium, and may be referred to herein as Ti-4Al-2.5V-1.5Fe-0.250 alloy.
Because of the difficulty in cold working Ti-6Al-4V alloy, the alloy is generally worked (e.g., forged, rolled, drawn, and the like) at elevated temperatures, generally above the α₂solvus temperature. Ti-6Al-4V alloy cannot be effectively cold worked to increase strength because of, for example, a high incidence of cracking (i.e., workpiece failure) during cold deformation. However, as described in U.S. Patent Application Publication No. 2004/0221929, which is hereby incorporated herein by reference in its entirety, it was surprisingly and unexpectedly discovered that the '655 alloys have a substantial degree of cold deformability/workability.
The '655 alloys surprisingly may be cold worked to achieve high strength while retaining a workable level of ductility. A workable level of ductility is defined herein a condition wherein an alloy exhibits greater than 6% elongation. Also, the strength of the '655 alloys is comparable to that which can be achieved with Ti-6Al-4V alloy. For example, as is shown in Table 6 of the '655 patent, the tensile stress measured for a Ti-6Al-4V alloy is 145.3 ksi (1,002 MPa), whereas tested samples of '655 alloys exhibited tensile strengths in a range from 138.7 ksi to 142.7 ksi (956.3 MPa to 983.9 MPa).
Aerospace Material Specification 6946B (AMS 6946B) specifies a more limited chemistry range than is recited in the claims of the '655 patent. The alloys specified in AMS 6946B retain the formability of the broader elemental range limits of the '655 patent, but the mechanical strength property minimums allowed by AMS 6946B are lower than those specified for commercially available Ti-6Al-4V alloy. For example, according to AMS-4911L, the minimum tensile strength for 0.125 inch (3.175 mm) thick Ti-6Al-4V plate is 134 ksi (923.9 MPa) and the minimum yield strength is 126 ksi (868.7 MPa). In comparison, according to AMS 6946B, the minimum tensile strength for 0.125 inch (3.175 mm) thick Ti-4Al-2.5V-1.5Fe-0.250 plate is 130 ksi (896.3 MPa) and the minimum yield strength is 115 ksi (792.9 MPa).
Given the continuing need for reduced fuel consumption through weight reduction of aircraft and other vehicles, a need exists for an improved ductile alpha/beta titanium alloy which preferably exhibits mechanical properties comparable or superior to those exhibited by Ti-6Al-4V alpha/beta titanium alloy.

SUMMARY

According to an aspect of the present disclosure, an alpha/beta titanium alloy comprises, in percent by weight based on total alloy weight: 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; up to 0.015 hydrogen; titanium; and up to a total of 0.30 of other elements.
According to another aspect of the present disclosure, an alpha/beta titanium alloy consists essentially of, in percent by weight: 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; up to 0.015 hydrogen; titanium; and up to a total of 0.30 of other elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of alloys and related methods described herein may be better understood by reference to the accompanying drawings in which:

FIG. 1 is a plot of ultimate tensile strength and yield strength as a function of aluminum equivalent for bar and wire comprised of non-limiting embodiments of alloys according to the present disclosure;

FIG. 2 is a plot of ultimate tensile strength and yield strength as a function of aluminum equivalent for 0.5 inch (1.27 cm) diameter wire comprised of non-limiting embodiments of alloys according to the present disclosure; and

FIG. 3 is a plot of tensile strength, yield strength, and percent elongation as a function of aluminum equivalent for 1 inch (2.54 cm) thick plate comprised of non-limiting embodiments of alloys according to the present disclosure.

The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of certain non-limiting embodiments of alloys and related methods according to the present disclosure.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

In the present description of non-limiting embodiments, other than in the operating examples or where otherwise indicated, all numbers expressing quantities or characteristics are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description are approximations that may vary depending on the desired properties one seeks to obtain in the materials and by the methods according to the present disclosure. 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 be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Any patent, publication, or other disclosure material that is said to be incorporated, in whole or in part, by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in the present disclosure. As such, and to the extent necessary, the disclosure as set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, 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.
Non-limiting embodiments of alpha/beta titanium alloys according to the present disclosure comprise, consist of, or consist essentially of, in percent by weight: 3.9 to 4.5 aluminum; 2.2 to 3.0 vanadium; 1.2 to 1.8 iron; 0.24 to 0.30 oxygen; up to 0.08 carbon; up to 0.05 nitrogen; up to 0.015 hydrogen; titanium; and up to a total of 0.30 of other elements. In certain non-limiting embodiments according to the present disclosure, other elements that may be present in the alpha/beta titanium alloy (as part of the up to 0.30 weight percent of other elements) include one or more of boron, tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, yttrium, and cobalt, and in certain non-limiting embodiments the weight level of each such other element present is 0.10 or less, but with two exceptions. The exceptions are boron and yttrium, which if present at all as part of the other elements are present in individual concentrations less than 0.005 weight percent.

I. Alloy Composition

Non-limiting embodiments of alloys according to the present disclosure comprise titanium, aluminum, vanadium, iron, and oxygen. If only the alloying elements are stated in compositions discussed below, it is to be understood that the balance includes titanium and incidental impurities.

A. Aluminum

Aluminum is an alpha phase strengthener in titanium alloys. The compositional range of aluminum in non-limiting embodiments of alpha/beta titanium alloys according to the present disclosure is narrower than the aluminum range disclosed in the '655 patent. Also, the minimum level of aluminum according to certain non-limiting embodiments of alloys according to the present disclosure is greater than the minimum level set out in AMS 6946B. It has been observed that these compositional features allow the alloy to more consistently exhibit mechanical properties comparable to Ti-6Al-4V alloy. The minimum concentration of aluminum in alpha/beta titanium alloys according to the present disclosure is 3.9 percent by weight. The maximum concentration of aluminum in alpha/beta titanium alloys according to the present disclosure is 4.5 percent by weight.

B. Vanadium

Vanadium is a beta phase stabilizer in titanium alloys. The minimum concentration of vanadium in alpha/beta titanium alloys according to the present disclosure is greater than minimum concentration disclosed in the '655 patent and set out in AMS 6946B. It has been observed that this compositional feature provides for an optimal, controlled balance of the volume fractions of the alpha and beta phases. The balance of alpha and beta phases provides alloys according to the present disclosure with excellent ductility and formability. Vanadium is present in alpha/beta titanium alloys according to the present disclosure in a minimum concentration of 2.2 percent by weight. The maximum concentration of vanadium in alpha/beta titanium alloys according to the present disclosure is 3.0 percent by weight.

C. Iron

Iron is a eutectoid beta stabilizer in titanium alloys. The alpha/beta titanium alloys according to the present disclosure include a greater minimum concentration and a narrower range of iron as compared with the alloy described in the '655 patent. These features have been observed to provide an optimal, controlled balance of the volume fractions of the alpha and beta phases. The balance provides alloys according to the present disclosure with excellent ductility and formability. Iron is present in the alpha/beta alloys according to the present disclosure in a minimum concentration of 1.2 percent by weight. The maximum concentration of iron in alpha/beta titanium alloys according to the present disclosure is 1.8 percent by weight.

D. Oxygen

Oxygen is an alpha phase strengthener in titanium alloys. The compositional range of oxygen in alpha/beta titanium alloys according to the present disclosure is narrower than the ranges disclosed in the '655 patent and in the AMS 6946B specification. Also, the minimum concentration of oxygen in non-limiting embodiments of alloys according to the present disclosure is greater than in the '655 patent and the AMS 6946B specification. It has been observed that these compositional features allow alloys according to the present disclosure to consistently exhibit mechanical properties comparable to certain Ti-6Al-4V mechanical properties. The minimum concentration of oxygen in alpha/beta titanium alloys according to the present disclosure is 0.24 percent by weight. The maximum concentration of oxygen in alpha/beta titanium alloys according to the present disclosure is 0.30 percent by weight.
In addition to including titanium, aluminum, vanadium, iron, and oxygen as discussed above, certain non-limiting embodiments of alpha/beta titanium alloys according to the present disclosure include other elements in a total concentration not exceeding 0.30 percent by weight. In certain non-limiting embodiments, these other elements include one or more of boron, tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, yttrium, and cobalt, wherein, with two exceptions, the weight percent of each such element is 0.10 or less. The exceptions are boron and yttrium. If present in alloys according to the present disclosure, the weight percentage each of boron and yttrium is less than 0.005.
Incidental impurities may also be present in alpha/beta titanium alloys according to the present disclosure. For example, carbon may be present up to about 0.008 percent by weight. Nitrogen may be present up to about 0.05 percent by weight. Hydrogen may be present up to about 0.015 percent by weight. Other possible incidental impurities will be apparent to those having ordinary skill in the metallurgical arts.
Table 1 provides a summary of the compositions of (i) certain non-limiting embodiments of alpha/beta titanium alloys according to the present disclosure and (ii) certain alloys disclosed in the '655 patent and specified in AMS 6946B.

TABLE 1

Alloy Compositions

Percent by Weight

	Non-Limiting
	Embodiments
Alloying	according to the	U.S. Pat. No.
Element	Present Disclosure	5,980,655	AMS 6946B

Aluminum	3.9 to 4.5	2.5 to 5.4	3.5 to 4.5
Vanadium	2.2 to 3.0	2.0 to 3.4	2.0 to 3.0
Iron	1.2 to 1.8	0.2 to 2.0	1.2 to 1.8
Oxygen	0.24 to 0.30	0.2 to 0.3	0.20 to 0.30
Carbon	0.08 max	0.1 max	0.08 max
Nitrogen	0.05 max	0.1 max	0.03 max
Hydrogen	0.015 max	not specified	0.015 max
other elements	0.10 max each,	0.10 max each,	0.10 max each,
	0.30 max total	no total specified	0.30 max total

The present inventors unexpectedly discovered that providing the present alloy with minimum levels of aluminum, oxygen, and iron greater than minimum levels taught in the '655 patent provides an alpha/beta titanium alloy that consistently exhibits mechanical properties, such as strength, for example, at least comparable to certain mechanical properties of mill annealed Ti-6Al-4V alloy. The inventors also unexpectedly discovered that increasing the minimum levels and narrowing the ranges of iron and vanadium relative to those minimums and ranges disclosed in the '655 patent provides alloys that exhibit an optimal and controlled balance of the volume fractions of the alpha and beta phases in a mill annealed form. This optimal balance of phases in the alpha/beta titanium alloys according to the present disclosure provides embodiments of the alloys with improved ductility compared to Ti-6Al-4V alloys, while retaining the ductility of alloys disclosed in the '655 patent and specified in AMS 6946B.
A person skilled in the art understands that strength and ductility of metallic materials generally exhibit an inverse relationship. In other words, in general, as the strength of a metallic material increases, the ductility of the material decreases. The combination of increased mechanical strength and retained ductility of the alpha/beta titanium alloys according to the present disclosure was not expected because an inverse relationship between strength and ductility generally is observed for mill annealed titanium alloys. The unexpected and surprising combination of increased mechanical strength and retained ductility is a particularly advantageous feature of alloy embodiments according to the present disclosure. It was surprising to observe that embodiments of mill annealed alloys according to the present disclosure exhibit strengths comparable to Ti-6Al-4V alloys without exhibiting decreasing ductility.
Certain non-limiting embodiments of alpha/beta alloys according to the present disclosure having an aluminum equivalent value (Al_eq) of at least 6.3, or more preferably at least 6.4, have been observed to exhibit strength at least comparable to the strength of Ti-6Al-4V alloys. Such alloys also have been observed to exhibit ductility superior to Ti-6Al-4V alloys, which typically has an aluminum equivalent value of about 7.5. As used herein, “aluminum equivalent value” or “aluminum equivalent” (Al_eq) means a value equal to the aluminum concentration in weight percent in an alloy plus ten times the oxygen concentration in weight percent of the alloy. In other words, an alloy's aluminum equivalent may be determined as follows: Al_eq=Al_{(wt. %)}+10 (O_{(wt. %)}).
While it is recognized that the mechanical properties of titanium alloys are generally influenced by the size of the specimen being tested, in non-limiting embodiments according to the present disclosure, an alpha/beta titanium alloy comprises an aluminum equivalent value of at least 6.4, or is in certain embodiments within the range of 6.4 to 7.2, and a yield strength of at least 120 ksi (827.4 MPa), or in certain embodiment is at least 130 ksi (896.3 MPa).
In other non-limiting embodiments according to the present disclosure, an alpha/beta titanium alloy comprises an aluminum equivalent value of at least 6.4, or in certain embodiments is in a range of 6.4 to 7.2, and a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa).
In yet other non-limiting embodiments, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value of at least 6.4, or in certain embodiments is in a range of 6.4 to 7.2, and an ultimate tensile strength of at least 130 ksi (896.3 MPa), or in certain embodiments is at least 140 ksi (965.3 MPa).
In additional non-limiting embodiments according to the present disclosure, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value of at least 6.4, or in certain embodiments is in a range of 6.4 to 7.2, and an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa).
In yet further non-limiting embodiments, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value of at least 6.4, or in certain embodiments is in a range of 6.4 to 7.2, and a ductility of at least 12%, or at least 16% (percent elongation).
In still further non-limiting embodiments, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value of at least 6.4, or in certain embodiments is in a range of 6.4 to 7.2, and a ductility in the range of 12% to 30% (percent elongation or “% el”).
While according to certain non-limiting embodiments of the present disclosure, 6.3 is the absolute minimum value for Al_eq, the inventors have determined that an Al_eqvalue of at least 6.4 is required to achieve the same strength as exhibited by Ti-6Al-4V alloy. It also recognized that in other non-limiting embodiments of an alpha/beta titanium alloy according to this disclosure, the maximum value for Al_eqis 7.5 and that the relationship of strength to ductility according to other non-limiting embodiments disclosed herein applies.
According to a non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value of at least 6.4, a yield strength of at least 120 ksi (827.4 MPa), an ultimate tensile strength of at least 130 ksi (896.3 MPa), and a ductility of at least 12% (percent elongation).
According to another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value of at least 6.4, a yield strength of at least 130 ksi (896.3 MPa), an ultimate tensile strength of at least 140 ksi (965.3 MPa), and a ductility of at least 12%.
In still another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure comprises an aluminum equivalent value in the range of 6.4 to 7.2, a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa), an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa), and a ductility in the range of 12% to 30% (percent elongation).
In one non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ultimate tensile strength (UTS) that satisfies the equation:
UTS≧14.767 (Al_eq)+48.001.
In another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average yield strength (YS) that satisfies the equation:
YS≧13.338 (Al_eq)+46.864.
In still another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ductility of:
% el≧3.3669 (Al_eq)−1.9417.
In yet another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ultimate tensile strength (UTS) that satisfies the equation:
UTS≧14.767 (Al_eq)+48.001;
an average yield strength (YS) that satisfies the equation:
YS≧13.338 (Al_eq)+46.864;
and an average ductility that satisfies the equation:
% el≧3.3669 (Al_eq)−1.9417.
In one non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ultimate tensile strength (UTS) that satisfies the equation:
UTS≧12.414 (Al_eq)+64.429.
In another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average yield strength (YS) that satisfies the equation:
YS≧13.585 (Al_eq)+44.904.
In still another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ductility of:
% el≧4.1993 (Al_eq)+7.4409.
In yet another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ultimate tensile strength (UTS) that satisfies the equation:
UTS≧12.414 (Al_eq)+64.429;
an average yield strength (YS) that satisfies the equation:
YS≧13.585 (Al_eq)+44.904;
and an average ductility that satisfies the equation:
% el≧4.1993 (Al_eq)+7.4409.
In one non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ultimate tensile strength (UTS) that satisfies the equation:
UTS≧10.087 (Al_eq)+76.785.
In another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average yield strength (YS) that satisfies the equation:
YS≧13.911 (Al_eq)+39.435.
In still another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ductility of:
% el≧1.1979 (Al_eq)+8.5604.
In still another non-limiting embodiment, an alpha/beta titanium alloy according to the present disclosure exhibits an average ultimate tensile strength (UTS) that satisfies the equation:
UTS≧10.087 (Al_eq)+76.785;
an average yield strength (YS) that satisfies the equation:
YS≧13.911 (Al_eq)+39.435;
and an average ductility in percent elongation (%el) that satisfies the equation:
% el≧1.1979 (Al_eq)+8.5604.
It has been determined that non-limiting embodiments of alpha/beta titanium alloys according to the present disclosure exhibit comparable or higher mechanical strength, higher ductility, and improved formability compared with Ti-6Al-4V alloy. Therefore, it is possible to use articles formed of alloys according to the present disclosure as substitutes for Ti-6Al-4V alloy articles in aerospace, aeronautic, marine, automotive, and other applications. The high strength and ductility of embodiments of alloys according to the present disclosure permits manufacturing of certain mill and finished article shapes with high tolerances and which cannot presently be manufactured from Ti-6Al-4V alloy.
An aspect of the present disclosure is directed to articles of manufacture comprising and/or made from an alloy according to the present disclosure. Certain non-limiting embodiments of the articles of manufacture may be selected from an aircraft engine component, an aircraft structural component, an automotive component, a medical device component, a sports equipment component, a marine applications component, and a chemical processing equipment component. Other articles of manufacture that may be comprise and/or be made from embodiments of alpha/beta titanium alloys according to the present disclosure that are known now or hereafter to a person of ordinary skill in the art are within the scope of embodiments disclosed herein. Articles of manufacture comprising and/or made from alloys according to the present disclosure by forming and other fabrication techniques known now or at a future time buy those having ordinary skill in the art.
The examples that follow are intended to further describe certain non-limiting embodiments, without restricting the scope of the present invention. Persons having ordinary skill in the art will appreciate that variations of the following examples, as well as other embodiments not specifically described herein, are possible within the scope of the invention, which is defined solely by the claims.

EXAMPLE 1

Alpha/beta titanium alloy ingots having a composition according to the present disclosure were cast using conventional vacuum arc remelting (VAR), plasma arc melting (PAM), or electron beam cold hearth melting (EB) for primary melting, and were remelted using VAR. The compositions of the ingots were within the ranges listed in the “Non-Limiting Embodiments according to the Present Disclosure” column includes in Table 1 above.
The ingot compositions produced in this Example 1 had aluminum equivalent values ranging from about 6.0 to about 7.1. The ingots were processed using various hot rolling practices into hot rolled bars and wire having diameters between 0.25 inch (0.635 cm) and 3.25 inch (8.255 cm). Hot rolling was conducted at starting temperatures between 1550° F. (843.3° C.) and 1650° F. (898.9° C.). This temperature range is below the alpha/beta transus temperature of the alloys of this example, which is about 1750° F. to about 1850° F. (about 954.4° C. to about 1010° C.), depending upon the actual chemistry. After hot rolling, the hot rolled bars and wire were annealed at 1275° F. (690.6° C.) for one hour, followed by air cooling. The diameter, aluminum concentration, iron concentration, oxygen concentration, and calculated Al_eqof each of the bar and wire samples produced in Example 1 are provided in Table 2.

TABLE 2

Sample	Diameter	Al	Fe	O	Al_eq
No.	(in.)	(wt. %)	(wt. %)	(wt. %)	(Al % + 10 · O %)

1	3.25	4.07	1.56	0.25	6.53
2	3.25	4.10	1.77	0.19	5.96
3	3.25	4.27	1.90	0.19	6.13
4	2	4.05	1.54	0.25	6.57
5	2	4.05	1.55	0.25	6.58
6	2	4.26	1.88	0.21	6.38
7	1	4.35	1.44	0.24	6.74
8	1	4.36	1.28	0.27	7.08
9	0.5	4.38	1.24	0.28	7.15
10	0.5	4.33	1.42	0.25	6.81
11	0.5	4.14	1.47	0.24	6.51
12	0.344	4.37	1.50	0.26	6.95
13	0.25	3.93	1.58	0.23	6.27
14	0.25	4.12	1.56	0.25	6.65
15	0.25	4.40	1.35	0.27	7.10
16	0.25	3.95	1.53	0.24	6.30
17	0.25	4.33	1.35	0.27	7.06

FIG. 1 graphically displays room temperature ultimate tensile strengths (UTS), yield strengths (YS), and percent elongation (%el) for the bar and wire samples listed in Table 2 as a function of the aluminum equivalent value of the alloy in the sample. FIG. 1 also includes trend lines through the UTS, YS, and %el data points determined by linear regression. It is seen that both average strength and the average percent elongation increase with increasing Al_eq. This relationship is surprising and unexpected as it is counter to the generally observed relationship that increasing strength is accompanied by decreasing ductility.
Typical Ti-6Al-4V minimums for UTS and YS are 135 ksi (930.8 MPa) and 125 ksi (861.8 MPa), respectively. The YS for the inventive samples listed in Table 2 ranged from about 125 ksi for a sample with Al_eqof about 6.0, up to about 141 ksi for a sample with Al_eqof about 7.1. A sample having Al_eqof about 6.4 exhibited YS of about 130 ksi (896.3 MPa). The UTS for the inventive samples listed in Table 2 ranged from about 135 ksi for a sample with Al_eqof about 6.0, up to about 153 ksi for a sample with Al_eqof about 7.1. A sample having Al_eqof about 6.4 exhibited YS of about 141 ksi (972 MPa).

EXAMPLE 2

Wire sample nos. 9-11 from Example 1, having a diameter of 0.5 inch (1.27 cm) and aluminum equivalent values of about 6.5, about 6.8 and about 7.15, were tensile tested at room temperature. The results of the tensile tests are displayed graphically in FIG. 2. All of these samples exhibited tensile and yield strengths that are comparable to or higher than strengths exhibited by commercial Ti-6Al-4V alloy. As with FIG. 1, it is seen from FIG. 2 that increasing Al_eqresults in increased strength, along with an increase in average percent elongation. As discussed above, this trend is surprising and unexpected because it is counter to the generally observed relationship that increasing strength is accompanied by decreasing ductility. There is less scatter in the data of FIG. 2, which is representative of testing done on samples of the same size, as compared with FIG. 1, which is representative of testing done on samples of various sizes, because mechanical properties are influenced to some degree by the size of the test sample.

EXAMPLE 3

Hot rolled 1 inch (2.54 cm) thick plate samples were fabricated from ingots manufactured according to steps described in Example 1. The alloys ingots had compositions within the ranges listed in the “Non-Limiting Embodiments according to the Present Disclosure” column in Table 1 above, with aluminum and oxygen concentrations and aluminum equivalent values as listed in Table 3.

TABLE 3

Sample	Diameter	Al	Fe	O	Al_eq
No.	(in.)	(wt. %)	(wt. %)	(wt. %)	(Al % + 10 · O %)

18	1	4.08	1.53	0.24	6.43
19	1	4.13	1.44	0.24	6.48
20	1	4.22	1.49	0.29	7.12
21	1	4.25	1.40	0.28	7.05
22	1	4.21	1.38	0.29	7.08

All hot rolling temperatures were below the alpha/beta transus temperatures of the alloys. The alloys had Al_eqvalues from about 6.5 to about 7.1. Room temperature tensile testing was used to determine tensile strength, yield strength, and percent elongation (ductility). The results of tensile testing are displayed graphically in FIG. 3. It is seen From FIG. 3 that alloys including increased levels of Al and O, as indicated by calculated aluminum equivalents, exhibited room temperature strength at least comparable strength levels exhibited by Ti-6Al-4V alloy. Further, strength was observed to increase with increasing Al_eq. In addition, the average ductility of the inventive alloys either increased slightly or remained generally unchanged with increasing Al_eqand increasing strength. This trend is surprising and unexpected as it is counter to the generally observed relationship that increasing strength is accompanied by decreasing ductility.
The present disclosure has been written with reference to various exemplary, illustrative, and non-limiting embodiments. However, it will be recognized by persons having ordinary skill in the art that various substitutions, modifications, or combinations of any of the disclosed embodiments (or portions thereof) may be made without departing from the scope of the invention as defined solely by the claims. Thus, it is contemplated and understood that the present disclosure embraces additional embodiments not expressly set forth herein. Such embodiments may be obtained, for example, by combining and/or modifying any of the disclosed steps, ingredients, constituents, components, elements, features, aspects, and the like, of the embodiments described herein. Thus, this disclosure is not limited by the description of the various exemplary, illustrative, and non-limiting embodiments, but rather solely by the claims. In this manner, it will be understood that the claims may be amended during prosecution of the present patent application to add features to the claimed invention as variously described herein.

Claims

1. An alpha/beta titanium alloy comprising, in percent by weight based on total alloy weight:

3.9 to 4.5 aluminum;

2.2 to 3.0 vanadium;

1.2 to 1.8 iron;

0.24 to 0.30 oxygen;

up to 0.08 carbon;

up to 0.05 nitrogen;

up to 0.015 hydrogen

titanium; and

up to a total of 0.30 of other elements.

2. The alpha/beta titanium alloy of claim 1, wherein:

the up to a total of 0.30 of other elements includes at least one of boron, tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, yttrium and cobalt;

the level of each of boron and yttrium, if present, is less than 0.005; and

the level each of tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, if present, is no greater than 0.10.

3. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value of at least 6.4 and exhibits a yield strength of at least 120 ksi (827.4 MPa).

4. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value of at least 6.4 and exhibits an ultimate tensile strength of at least 130 ksi (896.3 MPa).

5. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value of at least 6.4 and exhibits a ductility of at least 12 percent elongation.

6. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value of at least 6.4, exhibits a yield strength of at least 120 ksi (827.4 MPa), exhibits an ultimate tensile strength of at least 130 ksi (896.3 MPa), and exhibits a ductility of at least 12 percent elongation.

7. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, and exhibits a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa).

8. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, and exhibits an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa).

9. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, and exhibits a ductility in the range of 12 to 30 percent elongation.

10. The alpha/beta titanium alloy of claim 1, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, exhibits a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa), exhibits an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa), and exhibits a ductility in the range of 12 to 30 percent elongation.

11. An alpha/beta titanium alloy consisting essentially of, in percent by weight based on total alloy weight:

3.9 to 4.5 aluminum;

2.2 to 3.0 vanadium;

1.2 to 1.8 iron;

0.24 to 0.30 oxygen;

up to 0.08 carbon;

up to 0.05 nitrogen;

up to 0.015 hydrogen titanium; and

up to a total of 0.30 of other elements.

12. The alpha/beta titanium alloy of claim 11, wherein:

the level of each of boron and yttrium, if present, is less than 0.005; and

the level of each of tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, if present, is no greater than 0.10.

13. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value of at least 6.4 and exhibits a yield strength of at least 120 ksi (827.4 MPa).

14. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value of at least 6.4 and exhibits an ultimate tensile strength of at least 130 ksi (896.3 MPa).

15. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value of at least 6.4 and exhibits a ductility of at least 12 percent elongation.

16. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value of at least 6.4, exhibits a yield strength of at least 120 ksi (827.4 MPa), exhibits an ultimate tensile strength of at least 130 ksi (896.3 MPa), and exhibits a ductility of at least 12 percent elongation.

17. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, and exhibits a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa).

18. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, and exhibits an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa).

19. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, and exhibits a ductility in the range of 12 to 30 percent elongation.

20. The alpha/beta titanium alloy of claim 11, wherein the alloy comprises an aluminum equivalent value in the range of 6.4 to 7.2, exhibits a yield strength in the range of 120 ksi (827.4 MPa) to 155 ksi (1,069 MPa), exhibits an ultimate tensile strength in the range of 130 ksi (896.3 MPa) to 165 ksi (1,138 MPa), and exhibits a ductility in the range of 12 to 30 percent elongation.

21. An article of manufacture comprising the alloy of claim 1.

22. The article of manufacture of claim 21, wherein the article of manufacture consists of the alloy of claim 1.

23. The article of manufacture of claim 21, wherein the article of manufacture is selected from an aircraft engine component, an aircraft structural component, an automotive component, a medical device component, a sports equipment component, a marine applications component, and a chemical processing equipment component.

24. The article of manufacture of claim 22, wherein the article of manufacture is selected from an aircraft engine component, an aircraft structural component, an automotive component, a medical device component, a sports equipment component, a marine applications component, and a chemical processing equipment component.

25. An article of manufacture comprising the alloy of claim 11.

26. The article of manufacture of claim 25, wherein the article of manufacture consists of the alloy of claim 11.

27. The article of manufacture of claim 25, wherein the article of manufacture is selected from an aircraft engine component, an aircraft structural component, an automotive component, a medical device component, a sports equipment component, a marine applications component, and a chemical processing equipment component.

28. The article of manufacture of claim 26, wherein the article of manufacture is selected from an aircraft engine component, an aircraft structural component, an automotive component, a medical device component, a sports equipment component, a marine applications component, and a chemical processing equipment component.