Low density titanium alloy, golf club head, and process for prouducing low density titanium alloy part

Abstract

The present invention relates to a low density titanium alloy, containing: 7.1 to 10.0 mass % of Al; 0.1 to 3.0 mass % of Fe; 0.01 to 0.3 mass % of O; 0.5 mass % or less of N; 0.5 mass % or less of C; and a remainder being Ti and inevitable impurities; a golf club head using the alloy; and a production method for a low density titanium alloy part using the alloy. The alloy of the invention may further contain 0.01 to 2.0 mass % of V. The alloy of the invention has higher specific strength as compared to the Ti-6Al-4V alloy, is excellent in hot workability, and is reduced in cost.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a low density titanium alloy, a golf club head, and a process for producing a low density titanium alloy part, more specifically, to a low density titanium alloy having high specific strength and excellent in hot workability, a golf club head using the low density titanium alloy, and a process for producing a low density titanium alloy part using the low density titanium alloy.

BACKGROUND OF THE INVENTION

[0002] Practical titanium alloys are broadly classified into:

[0003] (1) an .alpha. type alloy formed of an .alpha.-phase (low temperature phase) of a hexagonal closed packed lattice;

[0004] (2) a .beta. type alloy formed of a .beta.-phase (high temperature phase) of a body-centered cubic crystal; and

[0005] (3) an .alpha.+.beta. type alloy having a mixed structure of the .alpha.-phase and the .beta.-phase.

[0006] Among the above, the .alpha.+.beta. type alloy is a well-balanced material as being excellent in strength, specific strength, heat processability, workability, corrosion resistance, and the like, and therefore it has heretofore been used mainly as an aerospace material. Furthermore, the .alpha.+.beta. type alloy has heretofore been used as an automobile material, a mechanical structure part material, a general civilian goods material, and the like. Particularly, a Ti-6Al-4V alloy among the .alpha.+.beta. type alloys has widely been used as a general purpose high tensile titanium alloy, and about 80% of whole the Ti alloy consumption is occupied with the Ti-6Al-4V alloy consumption.

[0007] However, the Ti-6Al-4V alloy entails a high cost since it contains V which is expensive. Further, although the Ti alloys are generally high in specific strength, further reduction in cost and further improvement in specific strength has been in demand for certain applications such as application in golf club head.

[0008] In order to solve the above problems, various proposals have heretofore been made.

[0009] For instance, Patent Reference 1 discloses an .alpha.+.beta. type Ti alloy containing, in terms of mass %, 5.5% to 7.0% of Al, 0.5% to 4.0% of Fe, 0.5% or less of O, and a remainder being Ti and inevitable impurities.

[0010] The Patent Reference 1 discloses that:

[0011] (1) it is possible to impart mechanical property equal to or better than the conventional Ti-6Al-4V alloy by using Fe in place of V and mixing Fe at a predetermined ratio, and

[0012] (2) it is possible to produce the Ti alloy at an industrially low cost since Fe is less expensive than V.

[0013] Patent Reference 2 discloses a high strength Ti alloy containing, in terms of mass %, 5.00% to 7.00% of Al, 1.00 to 3.50% of V, more than 0.40% but 1.00% or less of Fe, 0.20% to 0.50% of O, 0.05% or less of C, 0.05% or less of N, and a remainder being substantially Ti, in which a V equivalent (=V %+4.2Fe %) is 3.00% to 5.50%.

[0014] The Patent Reference 2 discloses that:

[0015] (1) it is possible to achieve strength that is higher than or equal to the Ti-6Al-4V alloy by substituting a portion of V of Ti-6Al-4V by Fe and maintaining the V equivalent within the predetermined range; and

[0016] (2) it is possible to produce a high strength Ti alloy at a low cost since it is possible to use, as a raw material, an inexpensive sponge titanium containing Fe as impurity.

[0017] Further, Patent Reference 3 discloses a high strength Ti alloy contaihing, in terms of mass %, 5.50% to 7.00% of Al, 0.50% to 4.00% of Fe, 0.02% to 0.10% of N, 0.05% to 0.40% of O, and a remainder being Ti and inevitable impurities.

[0018] The Patent Reference 3 discloses that:

[0019] (1) it is possible to achieve strength that is higher than or equal to the Ti-6Al-4V alloy by substituting V of Ti-6Al-4V by Fe and adding the appropriate amount of N; and

[0020] (2) it is possible to produce a high strength Ti alloy at a low cost since it is possible to use, as a raw material, an inexpensive sponge titanium containing Fe as impurity.

[0021] Patent Reference 1: Japanese Patent No. 3306878

[0022] Patent Reference 2: JP-A-2001-115221

[0023] Patent Reference 3: JP-A-2004-10963

SUMMARY OF THE INVENTION

[0024] In recent years, there has been an increasing demand for achievement of a lower density of a golf club head among golf equipment manufacturers. Therefore, Ti-6Al-1Fe alloy is being used as a low density titanium alloy for golf club heads.

[0025] However, the effect of the Ti-6Al-1Fe alloy for the achievement of low density is weaker than that of a Ti-6Al-4V alloy that is the representative titanium alloy.

[0026] An increase in content of Al which is a light element is effective for the achievement of low density. However, a simple increase in Al content entails a reduction in hot workability.

[0027] An object of the invention is to provide a low density titanium alloy having higher specific strength as compared to the Ti-6Al-4V alloy, excellent in hot workability, and reduced in cost; a golf club head using the low density titanium alloy; and a low density titanium alloy part using the low density titanium alloy.

[0028] In order to attain the above-described object, the present invention relates to the following items 1 to 32.

[0029] 1. A low density titanium alloy, comprising:

[0030] 7.1 to 10.0 mass % of Al;

[0031] 0.1 to 3.0 mass % of Fe;

[0032] 0.01 to 0.3 mass % of O;

[0033] 0.5 mass % or less of N;

[0034] 0.5 mass % or less of C; and

[0035] a remainder being Ti and inevitable impurities.

[0036] 2. The low density titanium alloy according to item 1, further comprising:

[0037] 0.01 to 2.0 mass % of V.

[0038] 3. The low density titanium alloy according to item 1, further comprising:

[0039] 2.0 mass % or less of at least one element selected from the group consisting of Cr, Ni, and Mo.

[0040] 4. The low density titanium alloy according to item 2, further comprising:

[0041] 2.0 mass % or less of at least one element selected from the group consisting of Cr, Ni, and Mo.

[0042] 5. The low density titanium alloy according to item 1, further comprising:

[0043] at least one of

[0044] 0.01 to 0.3 mass % of B, and

[0045] 0.01 to 0.3 mass % of Si.

[0046] 6. The low density titanium alloy according to item 2, further comprising:

[0047] at least one of

[0048] 0.01 to 0.3 mass % of B, and

[0049] 0.01 to 0.3 mass % of Si.

[0050] 7. The low density titanium alloy according to item 3, further comprising:

[0051] at least one of

[0052] 0.01 to 0.3 mass % of B, and

[0053] 0.01 to 0.3 mass % of Si.

[0054] 8. The low density titanium alloy according to item 4, further comprising:

[0055] at least one of

[0056] 0.01 to 0.3 mass % of B, and

[0057] 0.01 to 0.3 mass % of Si.

[0058] 9. The low density titanium alloy according to item 1, which has a specific strength of 205 or more.

[0059] 10. The low density titanium alloy according to item 2, which has a specific strength of 205 or more.

[0060] 11. The low density titanium alloy according to item 3, which has a specific strength of 205 or more.

[0061] 12. The low density titanium alloy according to item 4, which has a specific strength of 205 or more.

[0062] 13. The low density titanium alloy according to item 5, which has a specific strength of 205 or more,

[0063] 14. The low density titanium alloy according to item 6, which has a specific strength of 205 or more.

[0064] 15. The low density titanium alloy according to item 7, which has a specific strength of 205 or more.

[0065] 16. The low density titanium alloy according to item 8, which has a specific strength of 205 or more.

[0066] 17. The low density titanium alloy according to item 1, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0067] 18. The low density titanium alloy according to item 2, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0068] 19. The low density titanium alloy according to item 3, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0069] 20. The low density titanium alloy according to item 4, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0070] 21. The low density titanium alloy according to item 5, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0071] 22. The low density titanium alloy according to item 6, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0072] 23. The low density titanium alloy according to item 7, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0073] 24. The low density titanium alloy according to item 8, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0074] 25. The low density titanium alloy according to item 9, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0075] 26. The low density titanium alloy according to item 10, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0076] 27. The low density titanium alloy according to item 11, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0077] 28. The low density titanium alloy according to item 12, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0078] 29. The low density titanium alloy according to item 13, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0079] 30. The low density titanium alloy according to item 14, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0080] 31. The low density titanium alloy according to item 15, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0081] 32. The low density titanium alloy according to item 16, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

[0082] Furthermore, the present invention also relates to a golf club head containing the above-mentioned low density titanium alloy.

[0083] In addition, the present invention also relates to a process for producing a low density titanium alloy part, the process including: blending raw materials so as to obtain the above-mentioned low density titanium alloy, followed by melting and casting the raw materials to thereby obtain an ingot; and heating the ingot to a temperature which is .beta. transus temperature or higher and is 1200.degree. C. or lower, followed by forging or rolling the ingot to thereby complete a rough processing step.

[0084] In the .alpha.+.beta. type low density titanium alloy, it is possible to reduce density of the alloy by increasing an Al content.

[0085] On the other hand, the increase in Al content generally entails deterioration of hot workability. However, it is possible to improve the hot workability while ensuring the low density by optimizing a Fe content and an O content and optionally further adding a very small amount of V, as well as increasing the Al content.

[0086] Further, since Fe is contained in the alloy as a principal addition element, it is possible to reduce a cost by using the inexpensive raw materials and reducing the amount of expensive V.

[0087] The low density titanium alloy according to the invention is usable for various structure parts, parts for anti-corrosion, and the like that are used for golf club heads, chemical industrial apparatuses, electric appliances, aerospace appliances, airplanes, boats and ships, wheeled vehicles, medical equipments, condensers, heat exchangers, desalination apparatuses, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

[0088] Hereinafter, one embodiment of the invention will be described in detail.

[0089] Herein, in the present specification, all the percentages defined by mass are the same as those defined by weight.

1. Low Density Titanium Alloy

[0090] A low density titanium alloy according to the invention contains following elements with a remainder being Ti and inevitable impurities. Types of addition elements, component ratios thereof, and reasons for limitation are as follows.

(1) 7.1.ltoreq.Al.ltoreq.10.0 Mass %

[0091] Al is the element that achieves solution hardening of an .alpha.-phase of the alloy. Further, since Al is lighter than Ti, Al acts for reducing density of the alloy (i.e. for achieving high specific strength). In order to attain such effects, an Al content may preferably be 7.1 mass % or more.

[0092] On the other hand, when the Al content is excessive, an intermetallic compound Ti.sub.3Al is precipitated to cause embrittlement of the alloy. Therefore, the Al content may preferable by 10.0 mass % or less.

(2) 0.1.ltoreq.Fe.ltoreq.3.0 Mass %

[0093] Fe has an effect of stabilizing a .beta.-phase. In order to attain such effect, a Fe content may preferably be 0.1 mass % or more.

[0094] On the other hand, although strength is increased along with an increase in Fe content, rigidity is increased when the Fe content is excessive. Therefore, the Fe content may preferably be 3.0 mass % or less.

(3) 0.01.ltoreq.O.ltoreq.0.3 Mass %

[0095] O has an effect of strengthening the .alpha.-phase as being dissolved into the .alpha.-phase. In order to attain such effect, an O content may preferably be 0.01 mass % or more.

[0096] On the other hand, when the O content is excessive, rigidity is increased to deteriorate ductibility. Therefore, the O content may preferably be 0.3 mass % or less.

(4) N.ltoreq.0.5 Mass %

[0097] Similar to O, N has an effect of strengthening the .alpha.-phase as being dissolved into the .alpha.-phase. On the other hand, when a N content is excessive, an inclusion such as TiN is formed, and the low density inclusion becomes the cause of fatigue breaking to reduce fatigue strength. Therefore, the N content may preferably be 0.5 mass % or less.

(5) C.ltoreq.0.5 Mass %

[0098] Similar to O and N, C has an effect of strengthening the .alpha.-phase as being dissolved into the .alpha.-phase. On the other hand, when a C content is excessive, carbonate is formed to deteriorate hot workability. Therefore, the C content may preferably be 0.5 mass % or less.

[0099] The low density titanium alloy according to the invention may further contain one or more of elements described below.

(6) 0.01.ltoreq.V.ltoreq.2.0 Mass %

[0100] Similar to Fe, V has an effect of stabilizing a .beta.-phase. In order to attain such effect, a V content may preferably be 0.01 mass % or more.

[0101] On the other hand, when the V content is excessive, a specific gravity is increased. Therefore, the V content may preferably be 2.0 mass % or less.

[0102] In this regard, a pure metal or a Ti-6Al-4V alloy scrap may be used as a V source in the production of the alloy.

(7) At Least One of Cr, Ni and Mo.ltoreq.2.0 Mass %

[0103] Each of Cr, Ni and Mo has an effect of stabilizing the .beta.-phase. On the other hand, when a content of these elements is excessive, a specific gravity is increased. Therefore, a sole or total amount of at least one element selected from the group consisting of Cr, Ni and Mo may preferably be 2.0 mass % or less.

(8) 0.01.ltoreq.B.ltoreq.0.3 Mass %

(9) 0.01.ltoreq.Si.ltoreq.0.3 Mass %

[0104] Each of B and Si has an effect of fining grains. In order to attain such effect, each of a B content and a Si content may preferably be 0.01 mass % or more.

[0105] On the other hand, when the contents of these elements are increased, crude boride and silicide are deposited to deteriorate fatigue strength. Therefore, each of the B content and the Si content may preferably be 0.3 mass % or less. In this regard, B and Si may be added solely or both of them may be added simultaneously.

2. Actions of Low Density Titanium Alloy

[0106] In the .alpha.+.beta. type low density titanium alloy, it is possible to reduce density of the alloy by increasing the Al content.

[0107] On the other hand, the increase in Al content generally entails deterioration of hot workability. However, it is possible to improve the hot workability while ensuring the low density by optimizing a Fe content and an O content and optionally further adding a very small amount of V, as well as increasing the Al content.

[0108] Therefore, by optimizing contents of the addition elements, it is possible to obtain:

[0109] (1) a low density titanium alloy having a specific strength of 205 or more;

[0110] (2) a low density titanium alloy having a reduction of area at 1000.degree. C. of 40% or more, and/or

[0111] (3) a low density titanium alloy having a flow stress at 1000.degree. C. of 200 MPa or less.

[0112] Since the low density titanium alloy according to the invention contains Fe as the principal addition element, it is possible to use, as a raw material, an inexpensive sponge titanium containing Fe as impurity. Further, by adding Fe, it is possible to reduce the amount of expensive V to be used. Therefore, it is possible to reduce a cost of the low density titanium alloy.

[0113] Furthermore, since the low density titanium alloy according to the invention has high specific strength and is excellent in hot workability, it is possible to obtain, for example, a golf club head, that is inexpensive, light-weight, and high in repulsion by using the low density titanium alloy.

3. Process for Producing Low Density Titanium Alloy Part

[0114] A process for producing a low density titanium alloy part according to the invention includes a melting/casting step, a rough processing step, a finish processing step, and an annealing step.

3.1. Melting/Casting Step

[0115] The melting/casting step is a step of blending raw materials so as to obtain the low density titanium alloy of the invention, followed by melting and casting the raw materials.

[0116] Since the low density titanium alloy according to the invention contains Fe as the essential element, it is possible to use, as a Ti source, not only a high purity sponge titanium but also a low purity sponge titanium containing 0.1 to 2.0 mass % of Fe or a Ti-6Al-4V alloy scrap. Therefore, it is possible to reduce a cost for the titanium alloy part.

[0117] The melting/casting of the blended materials is not particularly limited, and it is possible to employ a conventional method.

3.2. Rough Processing Step

[0118] The rough processing step is a step of heating an ingot, which is obtained by blending the raw materials so as to obtain the low density titanium alloy according to the invention followed by melting and casting the raw materials, to a temperature which is .beta. transus temperature (.beta. transforming point) or higher and is 1200.degree. C. or lower, followed by forging or rolling the ingot.

[0119] When the processing temperature is too low, the .alpha.-phase remains to cause cracking and creasing. Therefore, the processing temperature in the rough processing may preferably be the .beta. transus temperature or higher at which only the .beta.-phase remains.

[0120] On the other hand, when the processing temperature is too high, crystal grains tend to be coarsened. Therefore, the processing temperature in the rough processing may preferably be 1200.degree. C. or less.

3.3. Finish Processing Step

[0121] The finish processing step is a step of performing a finish-forging or finish-rolling of the low density titanium alloy forged or rolled in the rough processing step after heating the alloy to a temperature which is 600.degree. C. or higher and is less than the .beta. transus temperature. The finish processing step is performed according to the necessity.

[0122] When the finish processing step is performed at a relatively low temperature, grains are fined to achieve high strength. However, when the processing temperature is too low, flow stress is increased to make the processing difficult. Therefore, the processing temperature in the finish processing step may preferably be 600.degree. C. or more.

[0123] On the other hand, when the processing temperature is too high, grains tend to be coarsened due to recrystallization. Therefore, the processing temperature in the finish processing step may preferably be less than .beta. transus temperature.

3.4. Annealing Step

[0124] The annealing step is a step of annealing the low density titanium alloy forged or rolled in the finish processing step. The annealing step is performed according to the necessity.

[0125] The annealing is performed for the purpose of eliminating a strain after the finish processing step. Annealing conditions are not particularly limited, and optimum conditions may be selected depending on the alloy composition.

EXAMPLES

Examples 1 to 40 and Comparative Examples 1 to 5

1. Preparation of Samples

[0126] Raw materials were weighed so as to achieve predetermined compositions, and titanium alloy ingots each having a mass of 6 kg and a diameter of 100 mm were produced through melting using a plasma skull furnace. Shown in Table 1 are chemical compositions of the thus-obtained ingots.

[0127] From each of the ingots, a test piece for high-temperature high-speed tensile test was cut out.

[0128] Additionally, each of the ingots was heated to 1000.degree. C., and a round bar having a diameter of 20 mm was obtained by hot forging. Further, a heat treatment at 750.degree. C. for 2 h under an air cooling (AC) was performed. From the round bar after the heat treatment, a No. 3 tensile test piece (diameter: 6.35 mm, evaluation distance: 25 mm) defined in ASTM E8 was prepared.

TABLE-US-00001 TABLE 1 Composition (mass %) Al Fe V O N C Others Ex. 1 7.2 0.1 -- 0.07 0.01 0.01 Ex. 2 9.9 0.2 -- 0.09 0.02 0.01 Ex. 3 8.1 0.8 -- 0.14 0.01 0.01 Ex. 4 7.9 2.8 -- 0.16 0.02 0.02 Ex. 5 7.1 0.5 -- 0.27 0.01 0.01 Ex. 6 7.1 0.1 0.01 0.08 0.01 0.02 Ex. 7 7.5 0.2 0.02 0.05 0.02 0.01 Ex. 8 8.2 0.2 0.02 0.07 0.01 0.01 Ex. 9 8.5 0.2 0.02 0.09 0.02 0.01 Ex. 10 8.7 0.2 0.01 0.10 0.01 0.02 Ex. 11 9.0 0.1 0.01 0.08 0.02 0.01 Ex. 12 9.2 0.2 0.02 0.07 0.01 0.02 Ex. 13 9.5 0.2 0.02 0.06 0.01 0.01 Ex. 14 9.7 0.2 0.01 0.10 0.01 0.01 Ex. 15 9.9 0.2 0.01 0.10 0.02 0.01 Ex. 16 10.0 0.2 0.01 0.09 0.01 0.02 Ex. 17 8.2 0.8 0.02 0.15 0.01 0.01 Ex. 18 8.3 1.2 0.01 0.16 0.01 0.01 Ex. 19 8.0 1.5 0.02 0.14 0.01 0.02 Ex. 20 9.0 2.0 0.01 0.13 0.01 0.01 Ex. 21 8.8 2.2 0.01 0.15 0.02 0.01 Ex. 22 8.0 2.8 0.02 0.16 0.02 0.02 Ex. 23 7.8 3.0 0.01 0.17 0.01 0.02 Ex. 24 8.2 0.8 1.00 0.14 0.02 0.01 Ex. 25 8.0 1.0 1.20 0.15 0.01 0.02 Ex. 26 8.2 1.2 1.50 0.16 0.01 0.01 Ex. 27 8.5 0.9 1.80 0.15 0.01 0.01 Ex. 28 8.2 1.1 2.00 0.14 0.01 0.02 Ex. 29 7.1 0.5 0.02 0.21 0.01 0.01 Ex. 30 7.2 0.5 0.01 0.28 0.01 0.02 Ex. 31 7.1 0.5 0.02 0.13 0.30 0.01 Ex. 32 7.5 0.4 0.03 0.15 0.50 0.01 Ex. 33 7.2 0.4 0.02 0.13 0.01 0.10 Ex. 34 7.1 0.5 0.02 0.11 0.01 0.40 Ex. 35 7.5 0.4 0.03 0.02 0.01 0.01 Cr: 0.4, Ni: 0.1, Mo: 0.2 Ex. 36 7.4 0.3 0.02 0.02 0.01 0.02 Cr: 0.2, Ni: 0.1, Mo: 0.5 Ex. 37 7.1 0.5 0.02 0.01 0.01 0.01 B: 0.08 Ex. 38 7.5 0.4 0.03 0.02 0.01 0.02 B: 0.15 Ex. 39 7.2 0.3 0.03 0.02 0.01 0.03 Si: 0.02 Ex. 40 7.6 0.5 0.02 0.03 0.02 0.01 Si: 0.10 Comp. Ex. 1 10.5 1.0 0.03 0.15 0.01 0.02 Comp. Ex. 2 11.9 1.2 0.02 0.11 0.01 0.01 Comp. Ex. 3 13.0 1.3 0.03 0.15 0.01 0.01 Comp. Ex. 4 8.5 5.0 0.01 0.25 0.01 0.02 Comp. Ex. 5 6.0 4.00 0.12 0.03 0.01

2. Test Method

[0129] 2.1. High-Temperature High-Speed Tensile Test

[0130] A high-temperature high-speed tensile test was performed at 1000.degree. C. to measure flow stress and reduction of area at 1000.degree. C.

[0131] 2.2. Tensile Test

[0132] A tensile test was performed using an insutoron type tensile test at a crosshead speed of 5.times.10.sup.-5 m/s machine to measure tensile strength.

[0133] 2.3. Specific Strength

[0134] A specific gravity of each of the tensile test pieces was measured by employing a water-impregnation method. Specific strength was calculated from the detected specific gravity and tensile strength.

[0135] 2.4. Manufacturability

[0136] Manufacturability was evaluated in terms of reduction of area at 1000.degree. C. Those having reduction of area at 1000.degree. C. of 40% or more is evaluated as "good", and those having reduction of area at 1000.degree. C. of less than 40% is evaluated as "poor".

3. Results

[0137] Shown in Table 2 are test results. Comparative Examples 1 to 3 are remarkably poor in manufacturability due to the high content of Al. Particularly, it was impossible to measure the flow stress and reduction of area of Comparative Examples 2 and 3 having the Al content exceeding 11 mass %. Comparative Example 4 having the Fe content exceeding 3.0 mass % has poor manufacturability though it has high tensile strength and specific strength. Comparative Example 5 (Ti-4Al-6V alloy) has good manufacturability, but it has low tensile strength and specific strength.

[0138] In contrast, each of Examples 1 to 40 has high tensile strength and specific strength due to the appropriate content of Al. Furthermore, each of Examples 1 to 40 also has good hot workability due to the adjustment of the Fe content and the O content and the optional addition of the small amount of V, as well as the relatively increased Al content.

TABLE-US-00002 TABLE 2 High-Temperature High-Speed Tensile Test (1000.degree. C.) Flow Reduction Tensile stress of Strength Specific (MPa) area (%) (MPa) Strength Manufacturability Ex. 1 127 91 1040 238 good Ex. 2 148 73 1215 281 good Ex. 3 141 80 1155 264 good Ex. 4 152 69 1245 280 good Ex. 5 150 71 1230 281 good Ex. 6 127 91 1040 238 good Ex. 7 130 89 1065 244 good Ex. 8 133 87 1090 250 good Ex. 9 135 85 1100 253 good Ex. 10 137 83 1125 259 good Ex. 11 140 81 1150 265 good Ex. 12 142 79 1165 269 good Ex. 13 144 77 1180 272 good Ex. 14 146 75 1200 277 good Ex. 15 148 73 1215 281 good Ex. 16 150 70 1230 285 good Ex. 17 141 80 1155 264 good Ex. 18 143 78 1175 268 good Ex. 19 145 75 1190 270 good Ex. 20 147 73 1205 274 good Ex. 21 150 71 1230 279 good Ex. 22 152 69 1245 280 good Ex. 23 155 66 1270 285 good Ex. 24 142 79 1170 267 good Ex. 25 144 77 1175 267 good Ex. 26 145 75 1180 268 good Ex. 27 147 73 1190 271 good Ex. 28 148 74 1200 272 good Ex. 29 145 75 1190 272 good Ex. 30 150 71 1230 281 good Ex. 31 152 69 1245 284 good Ex. 32 155 66 1270 290 good Ex. 33 135 85 1110 254 good Ex. 34 138 82 1130 258 good Ex. 35 139 82 1140 259 good Ex. 36 137 83 1125 255 good Ex. 37 139 83 1140 260 good Ex. 38 141 80 1155 264 good Ex. 39 138 82 1130 258 good Ex. 40 140 80 1150 263 good Comp. 295 15 1350 311 poor Ex. 1 Comp. impossible impossible -- -- poor Ex. 2 to measure to measure Comp. impossible impossible -- -- poor Ex. 3 to measure to measure Comp. 205 38 1300 289 poor Ex. 4 Comp. 110 98 900 202 good Ex. 5

[0139] While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

[0140] The present application is based on Japanese Patent Application No. 2007-239713 filed on Sep. 14, 2007 and Japanese Patent Application No. 2008-231619 filed on Sep. 10, 2008, the contents thereof being incorporated herein by reference.

Claims

1. A low density titanium alloy, comprising: 7.1 to 10.0 mass % of Al; 0.1 to 3.0 mass % of Fe; 0.01 to 0.3 mass % of O; 0.5 mass % or less of N; 0.5 mass % or less of C; and a remainder being Ti and inevitable impurities.

2. The low density titanium alloy according to claim 1, further comprising: 0.01 to 2.0 mass % of V.

3. The low density titanium alloy according to claim 1, further comprising; 2.0 mass % or less of at least one element selected from the group consisting of Cr, Ni, and Mo.

4. The low density titanium alloy according to claim 2, further comprising: 2.0 mass % or less of at least one element selected from the group consisting of Cr, Ni, and Mo.

5. The low density titanium alloy according to claim 1, further comprising: at least one of 0.01 to 0.3 mass % of B, and 0.01 to 0.3 mass % of Si.

6. The low density titanium alloy according to claim 2, further comprising: at least one of 0.01 to 0.3 mass % of B, and 0.01 to 0.3 mass % of Si.

7. The low density titanium alloy according to claim 3, further comprising: at least one of 0.01 to 0.3 mass % of B, and 0.01 to 0.3 mass % of Si.

8. The low density titanium alloy according to claim 4, further comprising: at least one of 0.01 to 0.3 mass % of B, and 0.01 to 0.3 mass % of Si.

9. The low density titanium alloy according to claim 1, which has a specific strength of 205 or more.

10. The low density titanium alloy according to claim 2, which has a specific strength of 205 or more.

11. The low density titanium alloy according to claim 3, which has a specific strength of 205 or more.

12. The low density titanium alloy according to claim 4, which has a specific strength of 205 or more.

13. The low density titanium alloy according to claim 5, which has a specific strength of 205 or more.

14. The low density titanium alloy according to claim 6, which has a specific strength of 205 or more.

15. The low density titanium alloy according to claim 7, which has a specific strength of 205 or more.

16. The low density titanium alloy according to claim 8, which has a specific strength of 205 or more.

17. The low density titanium alloy according to claim 1, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

18. The low density titanium alloy according to claim 2, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

19. The low density titanium alloy according to claim 3, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

20. The low density titanium alloy according to claim 4, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

21. The low density titanium alloy according to claim 5, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

22. The low density titanium alloy according to claim 6, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

23. The low density titanium alloy according to claim 7, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

24. The low density titanium alloy according to claim 8, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

25. The low density titanium alloy according to claim 9, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

26. The low density titanium alloy according to claim 10, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

27. The low density titanium alloy according to claim 11, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

28. The low density titanium alloy according to claim 12, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

29. The low density titanium alloy according to claim 13, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

30. The low density titanium alloy according to claim 14, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

31. The low density titanium alloy according to claim 15, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.

32. The low density titanium alloy according to claim 16, which has a reduction of area at 1000.degree. C. of 40% or more and a flow stress at 1000.degree. C. of 200 MPa or less.