TITANIUM MATERIAL

There is provide a titanium material containing 91% by mass or more of titanium, wherein a tensile strength σB MPa and a fracture elongation δ% of the titanium material have a relation of the following formula I: σ ⁢ B ≥ 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 ⁢ δ ; Formula ⁢ I in the above formula I, σB≥400 and δ≥20.

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Description
TECHNICAL FIELD

The present disclosure relates to a titanium material. The present application claims priority from Japanese application, Japanese Patent Application No. 2021-194773, filed on Nov. 30, 2021. The entire description contents of the Japanese application are hereby incorporated by reference into the present description.

BACKGROUND ART

Titanium materials, since having a high specific strength, have been used in the fields of aerospace industries, automotive industries and the like. Further, titanium materials, since being excellent in biocompatibility, have been in high demand as metal materials for living bodies, such as dental implants.

Patent Literature 1 discloses, as a titanium material having a high strength, a titanium material having α-phases and ω-phases mixedly present at normal temperature and normal pressure.

CITATION LIST Patent Literature

    • PTL 1: Japanese Patent Laying-Open No. 2009-228053

SUMMARY OF INVENTION

The titanium material of the present disclosure is a titanium material containing 91% by mass or more of titanium,

    • wherein a tensile strength σB MPa and a fracture elongation δ% of the titanium material have a relation of the following formula I:

σ B 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 δ , Formula I

    • in the above formula I, σB≥400 and δ≥20.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a coordinate system showing the relation between the strength and the ductility of conventional titanium materials and titanium materials of Embodiment 1.

FIG. 2 is an example of optical microscopic images of titanium materials of the present Embodiment.

FIG. 3 is a temperature-pressure phase diagram of titanium.

FIG. 4 is an example of X-ray diffraction patterns obtained by irradiation of a titanium material with X rays.

FIG. 5 is a coordinate system showing the relation between the 0.2% yield strength in a tensile test of conventional titanium materials and titanium materials of Embodiment 2 and the content of components other than titanium in these titanium materials.

FIG. 6 is a coordinate system showing the relation between the tensile strength of conventional titanium materials and titanium materials of Embodiment 3 and the content of components other than titanium in these titanium materials.

FIG. 7 is a schematic cross-sectional view of a high-pressure cell of an ultrahigh-pressure high-temperature generator to be used in manufacture of the titanium material of the present disclosure.

DETAILED DESCRIPTION Problem to be Solved by the Present Disclosure

In recent years, along with spread of applications of titanium materials, a titanium material having a higher strength has been demanded.

The present disclosure has an object to provide a titanium material having a high strength.

Advantageous Effect of the Present Disclosure

The titanium material of the present disclosure can have a high strength.

Description of Embodiments

First, Embodiments of the present disclosure will be listed and described.

(1) The titanium material of the present disclosure is a titanium material containing 91% by mass or more of titanium,

    • wherein a tensile strength σB MPa and a fracture elongation δ% of the titanium material have a relation of the following formula I:

σ B 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 δ ; Formula I

    • in the above formula I, σB≥400 and δ≥20.

The titanium material of the present disclosure can have a high strength. Further, the titanium material of the present disclosure can have a high ductility.

(2) In the above (1), the titanium material may contain 98.8% by mass or more of titanium. Thereby, the biocompatibility of the titanium material can be enhanced.

(3) The titanium material of the present disclosure is a titanium material containing 91% by mass or more of titanium,

    • wherein a 0.2% yield strength σ0.2 MPa in a tensile test of the titanium material and a content c % by mass of components other than titanium in the titanium material have a relation of the following formula II:

σ 0.2 > 600 c + 180 ; Formula II

    • in the above formula II, c is 0 or more and 9 or less.

The titanium material of the present disclosure can have a high strength.

(4) In the above (3), the titanium material may contain 98.8% by mass or more of titanium. Thereby, the biocompatibility of the titanium material can be enhanced.

(5) The titanium material of the present disclosure is a titanium material containing 91% by mass or more of titanium,

    • wherein a tensile strength σB MPa of the titanium material and a content c % by mass of components other than titanium in the titanium material have a relation of the following formula III:

σ B > 600 c + 280 ; Formula III

    • in the above formula III, c is 0 or more and 9 or less.

The titanium material of the present disclosure can have a high strength.

(6) In the above (5), the titanium material may contain 98.8% by mass or more of titanium. Thereby, the biocompatibility of the titanium material can be enhanced.

(7) In the above (5) or (6), the tensile strength σB MPa and a fracture elongation δ% of the titanium material may have a relation of the following formula I:

σ B 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 δ ; Formula I

    • in the above formula I, σB≥400 and δ≥20.

Thereby, the titanium material can have a high strength.

(8) In any of the above (5) to (7), the 0.2% yield strength σ0.2 MPa in a tensile test of the titanium material and the content c % by mass of components other than titanium in the titanium material may have a relation of the following formula II.

σ 0.2 > 600 c + 180 ; Formula II

    • in the above formula II, c is 0 or more and 9 or less.

Thereby, the titanium material can have a high strength.

(9) In any of the above (1) to (8), the average grain diameter of crystal grains constituting the titanium material is 1 μm or more and 1,000 μm or less; and the titanium material may contain 50% by mass or more of titanium having a crystal structure of an omega phase. Thereby, the titanium material can have a high strength and a high ductility.

(10) In any of the above (1) to (9), the 0.2% yield strength in a compression test of the titanium material may be 570 MPa or more. Thereby the titanium material can have a high strength.

(11) In any of the above (1) to (10), the Vickers hardness of the titanium material may be 200 Hv or more. Thereby, the titanium material can have a high hardness.

(12) In any of the above (1) to (11), the heat-resistant temperature of the titanium material may be 100° C. or more. Thereby, the titanium material can hold a high strength even at a high temperature of 100° C. or more.

(13) In any of the above (1) to (12), the volume of the titanium material may be 0.001 m3 or more. The titanium material, since having a size sufficient as a metal material for living bodies, can be used in various applications such as dental implants and artificial joints.

(14) In any of the above (1) to (13), the titanium material contains 98.8% by mass or more of titanium,

    • wherein the titanium material contains at least one impurity element selected from the group consisting of hydrogen, carbon, nitrogen, oxygen and iron; and
    • the total content of the titanium and the impurity element of the titanium material may be 99.99% by mass or more.

Thereby, the titanium material can have excellent biocompatibility.

(15) In any of the above (1) to (14), a proportion D90/D10 of a cumulative 90% grain diameter D90 from a small diameter side to a cumulative 10% grain diameter D10 from the small diameter side in a cumulative grain size distribution based on volume of crystal grains constituting the titanium material may be 5 or more and 1,000 or less.

Thereby, the strength and the ductility of the titanium material are homogenized and the titanium material can have a higher strength and a higher ductility.

Detailed Description of Embodiments

Referring to drawings, the titanium material of the present disclosure will be described hereinafter. In the drawings of the present disclosure, the same reference sign represents the same part or a corresponding part. Then, the dimensional relation among length, width, thickness, depth and the like is suitably varied for clarification and simplification of the drawings, and does not always represent an actual dimensional relation.

In the present description, the notation in the form of “A to B” means the upper limit and the lower limit in a range (that is, A or more and B or less), and in the case where A has no description of a unit and only B has a description of a unit, the unit of A and the unit of B are the same.

In the present description, the “strength” has a meaning including at least one of the tensile strength, the 0.2% yield strength in a tensile test and the 0.2% yield strength in a compression test.

Embodiment 1: Titanium Materials

Titanium materials according to one embodiment (hereinafter, referred to also as “Embodiment 1”) of the present disclosure will be described.

First, in order to promote a better understanding of the present disclosure, the strength and the ductility of conventional titanium materials will be described using FIG. 1. FIG. 1 is a coordinate system showing the relation between the strength and the ductility of conventional titanium materials and titanium materials of Embodiment 1. In the coordinate system of FIG. 1, the X axis indicates the tensile strength σB (MPa), and the Y axis indicates the fracture elongation δ (%). The tensile strength is one index indicating the strength of materials, and the index indicates that the higher the numerical value, the higher the strength. The fracture elongation is one index indicating the ductility of materials, and the index indicates that the higher the numerical value, the higher the ductility. In FIG. 1, the conventional titanium materials are shown as JIS-1 to JIS-4, Ti—Fe, Ti-3Al-2.5V and β-alloy, and the data of the tensile strength and the fracture elongation thereof were prepared by reference to FIG. 1 in Hideki Fujii, Takashi Maeda, “Titanium Alloys Developed by Nippon Steel & Sumitomo Metal Corporation”, Shinnittetsu Sumikin giho, No. 396, 2013, pp. 16-22.

The JIS-1 to JIS-4 and β-alloy mean industrial pure titanium described in JIS H4600:2012 “Titanium and titanium alloys—Sheets, plates and strips”. Specifically, the JIS-1 means JIS H4600 Class 1; the JIS-2 means JIS H4600 Class 2; the JIS-3 means JIS H4600 Class 3; and the JIS-4 means JIS H4600 Class 4. The JIS-1 to JIS-4 have a content of titanium of about 99% by mass or more, and have a crystal structure of an alpha phase. Hereinafter, pure titanium having a crystal structure of an alpha phase is referred to also as alpha pure titanium.

The Ti—Fe, Ti-3Al-2.5V and J-alloy (JIS H4600 Class 80, Ti-22V-4Al) mean titanium alloys.

As shown in FIG. 1, alpha pure titanium having a high titanium content, though having a high fracture elongation (hereinafter, referred to also as ductility), is low in tensile strength (referred to also as strength). By contrast, titanium alloys having other metals added to titanium, though having a high tensile strength, are low in fracture elongation. The conventional titanium materials thus have a tradeoff relationship between the strength and the ductility, and there can be provided no titanium materials which can simultaneously satisfy both a high strength and a high ductility.

As a result of exhaustive studies, the present inventors could produce titanium materials having a high strength and a high ductility. Hereinafter, the details of titanium materials of Embodiment 1 will be described.

<Titanium Materials>

The titanium materials of Embodiment 1 are titanium materials containing 91% by mass or more of titanium,

    • wherein a tensile strength σB MPa and a fracture elongation δ% of the titanium materials have a relation of the following formula I.

σ B 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 δ ; Formula I

and

    • in the above formula I, σB≥400 and δ≥20.

The titanium materials having the relation of the above formula I will be described using FIG. 1. In FIG. 1, the region having the relation of the above formula I is a region indicated by oblique lines. The region indicated by oblique lines is the region where the fracture elongation is 20% or more, high in ductility, and the tensile strength is 400 MPa or more, high in strength. The titanium materials of Embodiment 1, since satisfying the relation of the above formula I, have a high strength and a high ductility. The conventional titanium materials all have a strength and a ductility in a region indicated by σB<1,600−30δ, not satisfying the relation of the above formula I.

Further, in the region having the relation of the above formula I, as compared with the conventional titanium materials having the same strengths, the magnitude of the fracture elongation is high. That is, the titanium materials of Embodiment 1 are, as compared with the conventional titanium materials having the same strengths, excellent in ductility.

It is preferable that the tensile strength σB MPa and the fracture elongation δ% of the titanium materials have a relation of the following formula I-A.

σ B > 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 875 - 30 δ Formula I - A

In the above formula I-A, σB≥400 and δ≥20.

The titanium materials satisfying the relation of the above formula I-A can have a higher strength and a higher ductility.

It is preferable that the tensile strength σB MPa and the fracture elongation δ% of the titanium materials have a relation of the following formula I-B.

σ B > 1 , TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 900 - 30 δ Formula I - B

In the above formula I-B, σB≥400 and δ≥20.

The titanium materials satisfying the relation of the above formula I-B can have a higher strength and a higher ductility.

<Tensile Strength σB>

The lower limit of the tensile strength σB of the titanium materials of Embodiment 1 is 400 MPa or more. The lower limit of the tensile strength σB of the titanium materials is, from the viewpoint of securing excellent strength, preferably 500 MPa or more, more preferably 600 MPa or more and still more preferably 800 MPa or more. The upper limit of the tensile strength σB of the titanium materials is not especially limited, and can be, for example, less than 1,550 MPa. The tensile strength σB of the titanium materials is preferably 400 MPa or more and less than 1,550 MPa, preferably 500 MPa or more and less than 1,550 MPa, more preferably 600 MPa or more and less than 1,550 MPa and still more preferably 800 MPa or more and less than 1,550 MPa.

The measurement of the tensile strength σB of the titanium materials is carried out according to JIS Z2241:2011 “Metallic materials—Tensile testing—Method of test at room temperature”. The test temperature is set at 23° C.±5° C.

<Fracture Elongation δ>

The fracture elongation δ of the titanium materials of Embodiment 1 is 20% or more. The lower limit of the fracture elongation δ of the titanium materials is, from the viewpoint of securing excellent ductility, preferably 25% or more, more preferably 30% or more and still more preferably 35% or more. The upper limit of the fracture elongation δ of the titanium materials can be, for example, 50% or less, or 45% or less. The fracture elongation δ of the titanium materials is preferably 20% or more and 50% or less, preferably 25% or more and 50% or less, preferably 30% or more and 50% or less, preferably 35% or more and 50% or less, preferably 20% or more and 45% or less, preferably 25% or more and 45% or less, or preferably 30% or more and 45% or less.

The measurement of the fracture elongation δ of the titanium materials is carried out according to JIS Z2241:2011 “Metallic materials—Tensile testing—Method of test at room temperature”. The test temperature is set at 23° C.±5° C.

<Composition>

The titanium materials of Embodiment 1 contain 91% by mass or more of titanium. The lower limit of the titanium content of the titanium materials is, from the viewpoint of enhancing biocompatibility, more preferably 95% by mass or more, preferably 98% by mass or more, still more preferably 98.955% by mass or more, still more preferably 99.2% by mass or more, still more preferably 99.495% by mass or more and still more preferably 99.999% by mass or more. The upper limit of the titanium content of the titanium materials is preferably 100% by mass or less. That is, the titanium materials can also be made of 100% by mass of titanium. The titanium content of the titanium materials is preferably 91% by mass or more and 100% by mass or less, preferably 95% by mass or more and 100% by mass or less, preferably 98% by mass or more and 100% by mass or less, preferably 98.955% by mass or more and 100% by mass or less, preferably 99.2% by mass or more and 100% by mass or less, preferably 99.495% by mass or more and 100% by mass or less, or preferably 99.999% by mass or more and 100% by mass or less.

The upper limit of the titanium content of the titanium materials of Embodiment 1, in the case of taking inevitable impurities into consideration, can be, for example, 99.9999% by mass or less. The titanium content of the titanium materials is preferably 91% by mass or more and 99.9999% by mass or less, preferably 95% by mass or more and 99.9999% by mass or less, preferably 98% by mass or more and 99.99990% by mass or less, preferably 98.955% by mass or more and 99.9999% by mass or less, preferably 99.2% by mass or more and 99.9999% by mass or less, preferably 99.495% by mass or more and 99.9999% by mass or less, or preferably 99.9990% by mass or more and 99.9999% by mass or less.

The titanium materials of Embodiment 1 can be made of 100% by mass of titanium. Then, the titanium materials of Embodiment 1 can contain more than 0% by mass and 9% by mass or less of components other than titanium. Examples of the components other than titanium include common transition metal elements such as scandium (Sc), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), hafnium (Hf), tantalum (Ta), tungsten (W), platinum (Pt) and gold (Au), and as inevitable impurities, hydrogen (H), carbon (C), nitrogen (N) and oxygen (O).

The upper limit of the content of the components in the titanium materials, including also the inevitable impurities, other than titanium of the titanium materials is 9% by mass or less. The content of the components other than titanium in the titanium materials can be a value obtained by subtracting the content of titanium from 100% by mass of the whole titanium material.

The content of the components other than titanium in the titanium materials is measured, in the case where the components are transition metal elements, by ICP spectrometry (radio-frequency inductively coupled plasma atomic emission spectrometry). The content thereof is measured, in the case where the components are elements other than transition metal elements, such as C, N, O and H, by SIMS analysis (secondary-ion mass spectrometry).

With regard to a method of measuring the titanium content of the titanium material, the titanium content is determined by measuring the content of the components other than titanium by the above method, and, with the titanium material being taken as 100% by mass, subtracting the content of the components other than titanium from the 100% by mass.

In Embodiment 1, it is preferable that the titanium materials contain 98.8% by mass or more of titanium; the titanium materials contain at least one impurity element selected from the group consisting of hydrogen, carbon, nitrogen, oxygen and iron; and the total content of titanium and the impurity element in the titanium material is 99.99% by mass or more. Thereby, since the titanium materials contain no components harmful to living bodies, such as vanadium (V) and aluminum (Al), which are contained in the conventional titanium alloys, or even if containing the components, contain the components in a trace amount, the titanium materials can have excellent biocompatibility.

The total content of titanium and the impurity element in the titanium material is preferably 99.99% by mass or more and 100% by mass or less, more preferably 99.999% by mass or more and 100% by mass or less and most preferably 100% by mass.

<Average Grain Diameter>

The average grain diameter of crystal grains constituting the titanium materials of Embodiment 1 (hereinafter, referred to also as “average grain diameter of the titanium materials”) is preferably 1 μm or more and 1,000 μm or less. Thereby, the titanium materials can have excellent strength and ductility.

The lower limit of the average grain diameter of the titanium materials is, from the viewpoint of securing excellent strength, preferably 1 μm or more, preferably 3 μm or more, preferably 5 μm or more, preferably 10 μm or more, or preferably 20 μm or more. The upper limit of the average grain diameter of the titanium materials is, from the viewpoint of securing excellent strength, preferably 1,000 μm or less, preferably 500 μm or less, preferably 200 μm or less, preferably 100 μm or less, or preferably 50 μm or less. The average grain diameter of the titanium materials is preferably 1 μm or more and 1,000 μm or less, preferably 3 μm or more and 500 μm or less, preferably 5 μm or more and 200 μm or less, preferably 10 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less, or preferably 20 μm or more and 50 μm or less.

In the present description, the average grain diameter of the titanium materials is measured by an intercept procedure. A specific measuring procedure is as follows. A polished faces of the titanium materials are imaged by using an optical microscope at a magnification of 100 times to obtain optical microscopic images. One example of optical microscopic images of the titanium materials of Embodiment 1 is shown in FIG. 2.

A circle of 50 mm in diameter is drawn on the optical microscopic image; 8 straight lines are radially drawn from the center of the circle to the periphery thereof; and the number of the straight lines crossing grain boundaries in the circle is counted; and an average intercept length is determined by dividing the length of the straight lines by the crossing number of the straight lines; then, a value as an average grain diameter is obtained by multiplying the average intercept length by a conversion factor, 1.128, to a two-dimensional grain diameter.

The above measurement is carried out on three positions for one measuring sample, and an average value of average grain diameters at the three positions is taken as the average grain diameter of the titanium materials in the present description.

Here, as far as the measurement by the applicant went, and as far as the measurement was carried out on the same sample, even when the measurement of the average grain diameter of the titanium materials was carried out several times by changing the measuring positions, almost no dispersion in the measurement result was observed, confirming that even when any measuring positions was set, the measurement results did not become arbitrary.

It is preferable, from the viewpoint of homogenizing strength and ductility, that the grain diameter of crystal grains constituting the titanium materials is low in dispersion. The proportion D90/D10 of a cumulative 90% grain diameter D90 from a small diameter side to a cumulative 10% grain diameter D10 from the small diameter side in a cumulative grain size distribution based on volume of crystal grains constituting the titanium is preferably 5 or more and 1,000 or less, or preferably 10 or more and 1,000 or less. It is indicated that the less the value of D90/D10, the less the dispersion in grain diameter of crystal grains.

The grain diameter of each crystal grain for calculating the D90/D10 is determined by carrying out image processing using a commercially available image analysis software on an optical microscopic image taken under the same condition as in the above intercept procedure, to measure an equivalent circle diameter of each crystal grain. A measuring visual field of 50 mm×50 mm is set in the optical microscopic image, and a volume-base cumulative grain size distribution is formed based on all crystal grains observed in the measuring visual field. The D90/D10 is calculated based on the cumulative grain size distribution.

<Titanium Having a Crystal Structure of an Omega Phase>

It is preferable that the titanium materials of Embodiment 1 contain 50% by mass or more of titanium having a crystal structure of an omega phase. Thereby, the titanium materials can have excellent strength and ductility.

In order to promote a better understanding of the titanium material of the present disclosure, the crystal structure of titanium will be described. As shown in the temperature-pressure phase diagram of titanium of FIG. 3, in titanium, there are three phases of alpha titanium having a crystal structure of an alpha phase (phase indicated as α in FIG. 3), beta titanium having a crystal structure of a beta phase (phase indicated as β in FIG. 3), and omega titanium having a crystal structure of an omega phase (phase indicated as ω in FIG. 3). The alpha titanium is in a stable phase at normal temperature and normal pressure, and has a crystal structure of a hexagonal close-packed (hcp). The beta titanium is a stable phase on the higher temperature side, and has a crystal structure of a body-centered cubic (bcc). The omega titanium is a metastable transition phase formed when the alpha titanium is crystallized from the beta titanium, and has a simple hexagonal crystal structure.

So far, the presence of the omega titanium at normal temperature and normal pressure has been confirmed as crystalizing as nano grains in a trace amount in alpha titanium phases in the manufacture process of alpha pure titanium containing about 99% by mass or more of alpha titanium. The omega titanium causes alpha pure titanium to become brittle. Accordingly, it has conventionally been considered that it is preferable to reduce the content of omega titanium in the alpha pure titanium.

As a result of try-and-error under the idea completely opposite to the conventional technical idea of reducing the content of omega titanium in the alpha pure titanium, the present inventors have produced titanium materials containing 50% by volume or more of omega titanium. The titanium materials have been confirmed to have excellent strength and ductility.

The lower limit of the content of titanium having a crystal structure of an omega phase of the titanium materials (hereinafter, referred to also as content of omega titanium) is, from the viewpoint of improving strength and ductility, preferably 50% by mass or more, or, preferably, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 98.8% by mass or more, 99% by mass or more, 99.2% by mass or more, 99.5% by mass or more, or 99.999% by mass or more. The upper limit of omega titanium of the titanium materials is preferably 100% by mass or less. That is, the titanium materials can be made of 100% by mass of omega titanium. The omega titanium content of the titanium materials is preferably, 50% by mass or more and 100% by mass or less, 55% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 65% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 75% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 85% by mass or more and 100% by mass or less, 90% by mass or less and 100% by mass or less, 95% by mass or less and 100% by mass or less, 98.8% by mass or more and 100% by mass or less, 99% by mass or more and 100% by mass or less, 99.2% by mass or more and 100% by mass or less, or 99.999% by mass or more and 100% by mass or less.

The upper limit of the omega titanium content of the titanium materials of Embodiment 1, in the case of taking inevitable impurities into consideration, can be, for example, 99.9999% by mass or less. The omega titanium content of the titanium materials is preferably, 50% by mass or more and 99.9999% by mass or less, 55% by mass or more and 99.9999% by mass or less, 60% by mass or more and 99.9999% by mass or less, 65% by mass or more and 99.9999% by mass or less, 70% by mass or more and 99.9999% by mass or less, 75% by mass or more and 99.9999% by mass or less, 80% by mass or more and 99.9999% by mass or less, 85% by mass or more and 99.99990% by mass or less, 90% by mass or more and 99.9999% by mass or less, 95% by mass or more and 99.9999% by mass or less, 98.8% by mass or more and 99.9999% by mass or less, 99% by mass or more and 99.9999% by mass or less, 99.2% by mass or more and 99.9999% by mass or less, or 99.9990% by mass or more and 99.9999% by mass or less.

The titanium materials of Embodiment 1 are allowed to contain, in addition to omega titanium, either or both of alpha titanium and beta titanium in the range of exhibiting the advantageous effect of the present disclosure. The upper limit of the total content of alpha titanium and beta titanium in the titanium materials is preferably 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, 1.2% by mass or less, or 1% by mass or less. The lower limit of the total content of alpha titanium and beta titanium in the titanium materials is not especially limited, and is preferably, for example, 0% by mass or more, but may be 0.01% by mass or more. The total content of alpha titanium and beta titanium in the titanium materials is preferably, 0% by mass or more and 50% by mass or less, 0% by mass or more and 45% by mass or less, 0% by mass or more and 40% by mass or less, 0% by mass or more and 35% by mass or less, 0% by mass or more and 30% by mass or less, 0% by mass or more and 25% by mass or less, 0% by mass or more and 20% by mass or less, 0% by mass or more and 15% by mass or less, 0% by mass or more and 10% by mass or less, 0% by mass or more and 5% by mass or less, 0% by mass or more and 1.2% by mass or less, 0% by mass or more and 1% by mass or less, 0.01% by mass or more and 50% by mass or less, 0.01% by mass or more and 45% by mass or less, 0.01% by mass or more and 40% by mass or less, 0.01% by mass or more and 35% by mass or less, 0.01% by mass or more and 30% by mass or less, 0.01% by mass or more and 25% by mass or less, 20% by mass or less, 0.01% by mass or more and 15% by mass or less, 0.01% by mass or more and 10% by mass or less, 0.01% by mass or more and 5% by mass or less, 0.01% by mass or more and 1.2% by mass or less, or 0.01% by mass or more and 1% by mass or less.

The contents of omega titanium, alpha titanium and beta titanium in the titanium materials are calculated from intensity ratios of X-ray diffraction peaks characteristic to omega titanium, alpha titanium and beta titanium.

<0.2% Yield Strength in a Compression Test>

The 0.2% yield strength in a compression test of the titanium materials of Embodiment 1 is preferably 570 MPa or more. Thereby, the titanium materials can have a high strength.

The lower limit of the 0.2% yield strength in a compression test of the titanium materials is, from the viewpoint of securing excellent strength, preferably 600 MPa or more, more preferably 700 MPa or more and still more preferably 800 MPa or more. The upper limit of the 0.2% yield strength in a compression test of the titanium materials is, since a higher one is better, not especially limited, and can be, for example, 5,000 MPa or less. The 0.2% yield strength in a compression test of the titanium materials is preferably 570 MPa or more and 5,000 MPa or less, preferably 600 MPa or more and 5,000 MPa or less, more preferably 700 MPa or more and 5,000 MPa or less and still more preferably 800 MPa or more and 5,000 MPa or less.

The measurement of the 0.2% yield strength in a compression test of the titanium materials is carried out according to JIS R1608:2003 “Testing methods for compressive strength of fine ceramics”. The test temperature is set at 23° C.±5° C.

<Vickers Hardness>

The Vickers hardness of the titanium materials of Embodiment 1 is preferably 200 Hv or more. Thereby, the titanium materials can have excellent hardness. The titanium materials hardly generate wear.

The lower limit of the Vickers hardness of the titanium materials is, from the viewpoint of securing excellent hardness, preferably 200 Hv or more and more preferably 220 Hv or more. The upper limit of the Vickers hardness of the titanium materials is, since a higher one is better, not especially limited, and can be, for example, 400 Hv or less. The Vickers hardness of the titanium materials is preferably 200 Hv or more and 400 Hv or less and more preferably 220 Hv or more and 400 Hv or less.

The measurement of the Vickers hardness of the titanium materials is carried out according to JIS Z2244:2009 “Vickers hardness test—Test method”. The test temperature is set at 23° C.±5° C.

Here, as far as the measurement by the applicant went, and as far as the measurement was carried out on the same sample, even when the measurement of the Vickers hardness of the titanium materials was carried out several times by changing the measuring positions, almost no dispersion in the measurement result was observed, confirming that even when any measuring positions was set, the measurement results did not become arbitrary.

<Heat-Resistant Temperature>

The heat-resistant temperature of the titanium materials of Embodiment 1 is preferably 100° C. or more. Thereby, the titanium materials can hold excellent strength even at a high temperature of 100° C. or more.

The lower limit of the heat-resistant temperature of the titanium materials of Embodiment 1 is, from the viewpoint of securing excellent strength, preferably 100° C. or more, more preferably 120° C. or more and still more preferably 140° C. or more. The upper limit of the heat-resistant temperature of the titanium materials is, since a higher one is better, not especially limited, and can be, for example, 190° C. or less. The heat-resistant temperature of the titanium materials is preferably 100° C. or more and 190° C. or less, more preferably 120° C. or more and 190° C. or less and still more preferably 140° C. or more and 190° C. or less.

The heat-resistant temperature of the titanium materials is measured by X-ray diffractometry and comparing an X-ray diffraction pattern at 25° C. with X-ray diffraction patterns at predetermined temperatures. A specific measuring method for the measurement is as follows.

A measuring sample is prepared by polishing the surface of the titanium materials. The measuring sample is irradiated with X rays under the following condition by using an X-ray diffraction device to obtain X-ray diffraction patterns. A plurality of temperatures of 25° C. and exceeding 25° C. in the measurement are suitably selected and X-ray diffraction patterns are obtained at respective temperatures.

(Condition of the X-Ray Diffraction Device)

    • Characteristic X-ray: Cu-Kα (wavelength: 1.54 Å)
    • Filter: multilayer mirror
    • Optical system: focusing beam
    • X-ray diffractometry: θ-2θ method

An X-ray diffraction pattern at 25° C. and X-ray diffraction patterns at predetermined temperatures exceeding 25° C. (hereinafter, referred to also as “predetermined temperatures”) are compared; and in the case where shapes of both of the X-ray diffraction patterns coincide, it is determined that the crystal structure of the measuring sample is held at the predetermined temperatures, and the measuring sample has heat resistance. Here, “both of the X-ray diffraction patterns coincide” is confirmed by coincidences of all diffraction peak positions, and also coincidences of the order of intensities of respective diffraction peaks.

The above X-ray diffraction measurement is carried out by raising the temperature condition until X-ray diffraction patterns at the predetermined temperatures exceeding 25° C. assume a shape different from the ray diffraction pattern at 25° C. Among a plurality of X-ray diffraction patterns obtained, an X-ray diffraction pattern at a highest temperature coinciding with the X-ray diffraction pattern at 25° C. is specified. The highest temperature is taken as the heat-resistant temperature of the measuring sample.

One example of X-ray diffraction patterns obtained by irradiating the titanium materials of Embodiment 1 with X rays is shown in FIG. 4. In FIG. 4, the X axis indicates 2θ (deg); and the Y axis indicates the intensity (cps). The X-ray diffraction measurement is carried out at 25° C. and at a temperature condition of from 40° C. to 210° C. at 10° C. intervals on the same titanium material, and in FIG. 4, X-ray diffraction patterns at respective temperatures thereby obtained are shown.

Comparing the shapes of the X-ray diffraction patterns at respective temperatures shown in FIG. 4, it is confirmed that the X-ray diffraction pattern at 25° C. coincides with the X-ray diffraction patterns at 40° C. to 180° C. Therefore, the heat-resistant temperature of the titanium material shown in FIG. 4 is judged to be 180° C.

<Volume>

The volume of the titanium materials of Embodiment 1 is preferably 0.001 mm3 or more. The titanium materials, since having a sufficiently large volume as a metal material for living bodies, can be used in various applications such as dental implants and artificial joints.

The lower limit of the volume of the titanium materials is preferably 0.001 mm3 or more, more preferably 10 mm3 or more and still more preferably 100 mm3 or more. The upper limit of the volume of the titanium materials is, since a larger volume is better, not especially limited, and is preferably, for example, 100,000 mm3 or less. The volume of the titanium materials is preferably 0.001 mm3 or more and 100,000 mm3 or less, more preferably 10 mm2 or more and 100,000 mm3 or less and still more preferably 100 mm3 or more and 100,000 mm3 or less. The volume of the titanium materials is measured by the Archimedes method.

Embodiment 2: Titanium Materials

Titanium materials according to another embodiment (hereinafter, referred to also as “Embodiment 2”) of the present disclosure will be described.

First, in order to promote a better understanding of the present disclosure, the relation between the 0.2% yield strength in a tensile test of conventional titanium materials and the content of components other than titanium in the titanium materials will be described using FIG. 5. FIG. 5 is a coordinate system showing the relation between the 0.2% yield strength in a tensile test of conventional titanium materials and titanium materials of Embodiment 2 and the content of components other than titanium in these titanium materials. In the coordinate system of FIG. 5, the X axis indicates the content c (% by mass) of components other than titanium in the titanium materials, and the Y axis indicates the 0.2% yield strength σ0.2 (MPa) in a tensile test. The 0.2% yield strength in a tensile test is one index indicating the strength of materials, and the index indicates that the higher the numerical value, the higher the strength. In FIG. 5, the conventional titanium materials are shown as ASTM Gr. 1 to ASTM Gr. 4, and for each titanium material, the upper limit and the lower limit of the 0.2% yield strength in a tensile test are indicated. These data are prepared based on data described in ASTM (American Society for Testing and Materials) and a homepage prepared by NIPPON STEEL STRUCTURAL SHAPES CORPORATION (https://www.nipponsteel.com/product/titan/pdf/index01.pdf).

The above ASTM Gr.1 to ASTM Gr.4 mean pure titanium described in ASTM. The pure titanium has a content of titanium of about 99% by mass or more, and are alpha pure titanium having a crystal structure of an alpha phase.

As shown in FIG. 5, in the conventional titanium materials, a higher content of components other than titanium gives a higher 0.2% yield strength in a tensile test, giving a higher strength. By contrast, particularly in applications of metal materials for living bodies, from the viewpoint of biocompatibility, it is not preferable to make the content of components other than titanium high. As shown in FIG. 5, however, in the conventional titanium materials, in order to make the 0.2% yield strength in a tensile test high, the content of components other than titanium is needed to be high.

As a result of exhaustive studies, the present inventors could produce titanium materials having, with the content of components other than titanium being held, a high 0.2% yield strength, that is, a high strength. Hereinafter, the details of the titanium materials of Embodiment 2 will be described.

<Titanium Materials>

The titanium materials of Embodiment 2 are titanium materials containing 91% by mass or more of titanium,

    • wherein a 0.2% yield strength σ0.2 MPa in a tensile test of the titanium materials and a content c % by mass of components other than titanium in the titanium materials have a relation of the following formula II:

σ 0.2 > 600 c + 180 ; Formula II

and

    • in the above formula II, c is 0 or more and 9 or less.

The titanium materials having the relation of the above formula II will be described using FIG. 5. In FIG. 5, the region having the relation of the above formula II is a region indicated by oblique lines. In the region having the relation of the above formula II, as compared with the conventional titanium materials having the same contents of components other than titanium, the 0.2% yield strength in a tensile test is high. That is, the titanium materials of Embodiment 2 satisfying the relation of the above formula II are, as compared with the conventional titanium materials having the same contents of components other than titanium, high in strength. Then, the conventional titanium materials have all a 0.2% yield strength in a tensile test and a content of components other than titanium in the region indicated by σ0.2<600c+180, not satisfying the relation of the above formula II.

It is preferable that the 0.2% yield strength σ0.2 MPa in a tensile test of the titanium materials and the content c % by mass of components other than titanium in the titanium materials have a relation of the following formula II-A:

σ 0.2 > 600 c + 180 ; Formula II - A

and

    • in the above formula II-A, c is 0 or more and 9 or less, or c is 0 or more and 1.2 or less.

The titanium materials satisfying the relation of the above formula II-A, as compared with the conventional titanium materials having the same contents of components other than titanium, can have a higher strength.

It is preferable that the 0.2% yield strength σ0.2 MPa in a tensile test of the titanium materials and the content c % by mass of components other than titanium in the titanium materials have a relation of the following formula II-B:

σ 0.2 > 600 c + 250 ; Formula II - B

and

    • in the above formula II-B, c is 0 or more and 9 or less, or c is 0 or more and 1.2 or less.

The titanium materials satisfying the relation of the above formula II-B, as compared with the conventional titanium materials having the same contents of components other than titanium, can have a higher strength.

<0.2% Yield Strength σ0.2 in a Tensile Test>

The 0.2% yield strength σ0.2 in a tensile test of the titanium materials of Embodiment 2 is more than 180 MPa. The lower limit of the 0.2% yield strength σ0.2 in a tensile test of the titanium materials is, from the viewpoint of securing excellent strength, preferably 250 MPa or more, more preferably 400 MPa or more and still more preferably 550 MPa or more. The upper limit of the 0.2% yield strength σ0.2 in a tensile test of the titanium materials is, since a higher one is better, not especially limited.

The measurement of the 0.2% yield strength in a tensile test of the titanium materials is carried out according to JIS Z2241:2011 “Metallic materials—Tensile testing—Method of test at room temperature”. The test temperature is set at 23° C.±5° C.

In Embodiment 2, the ranges, of the composition of the titanium materials, the average grain diameter of crystal grains constituting the titanium materials, the content of titanium having a crystal structure of an omega phase of the titanium materials, the 0.2% yield strength in a compression test of the titanium materials, the Vickers hardness of the titanium materials, the heat-resistant temperature of the titanium materials and the volume of the titanium materials, can be the same as the ranges described in Embodiment 1.

In Embodiment 2, the titanium materials may contain 98.8% by mass or more of titanium. In Embodiment 2, it is preferable that the titanium materials contain 98.8% by mass or more of titanium, wherein the titanium materials contain at least one impurity element selected from the group consisting of hydrogen, carbon, nitrogen, oxygen and iron, and have a total content of the titanium and the impurity element of 99.99% by mass or more. Thereby, the strength and the ductility of the titanium materials are more improved.

In Embodiment 2, the relation between the tensile strength σB MPa and the fracture elongation δ% of the titanium materials can be the same as in Embodiment 1. That is, it is preferable that the tensile strength σB MPa and the fracture elongation δ% of the titanium materials have the relation of the formula I, the formula I-A or the formula I-B described in Embodiment 1. Thereby, the strength and the ductility of the titanium materials are more improved.

Embodiment 3: Titanium Materials

Titanium materials according to another embodiment (hereinafter, referred to also as “Embodiment 3”) of the present disclosure will be described.

First, in order to promote a better understanding of the present disclosure, the relation between the tensile strength of conventional titanium materials and the content of components other than titanium in the titanium materials will be described using FIG. 6. FIG. 6 is a coordinate system showing the relation between the tensile strength of conventional titanium materials and titanium materials of Embodiment 3 and the content of components other than titanium in these titanium materials. In the coordinate system of FIG. 6, the X axis indicates the amount c (% by mass) of components other than titanium in the titanium materials, and the Y axis indicates the tensile strength σB (MPa) of the titanium materials. The tensile strength is one index indicating the strength of materials, and the index indicates that the higher the numerical value, the higher the strength. In FIG. 6, the conventional titanium materials are shown as JIS-1 to JIS-4, and for the each titanium material, the upper limit and the lower limit of the tensile strength are indicated. These data are prepared based on data described in JIS H4600:2012 “Titanium and titanium alloys—Sheets, plates and strips” and a homepage prepared by NIPPON STEEL STRUCTURAL SHAPES CORPORATION (https://www.nipponsteel.com/product/titan/pdf/index01.pdf).

As shown in FIG. 6, in the conventional titanium materials, a higher content of components other than titanium gives a higher tensile strength, giving a higher strength. By contrast, particularly in applications of metal materials for living bodies, from the viewpoint of biocompatibility, it is not preferable to make the content of components other than titanium high. As shown in FIG. 6, however, in the conventional titanium materials, in order to make the tensile strength high, the content of components other than titanium is needed to be high.

As a result of exhaustive studies, the present inventors could produce titanium materials having, with the content of components other than titanium being held, a high tensile strength, that is, a high strength. Hereinafter, the details of the titanium materials of Embodiment 3 will be described.

<Titanium Materials>

The titanium materials of Embodiment 3 are titanium materials containing 91% by mass or more of titanium,

    • wherein a tensile strength σB MPa of the titanium materials and a content c % by mass of components other than titanium in the titanium materials have a relation of the following formula III:

σ B > 600 c + 280 ; Formula III

    • in the above formula III, c is 0 or more and 9 or less.

The titanium materials having the relation of the above formula III will be described using FIG. 6. In FIG. 6, the region having the relation of the above formula III is a region indicated by oblique lines. In the region having the relation of the above formula III, as compared with the conventional titanium materials having the same contents of components other than titanium, the tensile strength is higher. That is, the titanium materials of Embodiment 3 satisfying the relation of the above formula III are, as compared with the conventional titanium materials having the same contents of components other than titanium, higher in tensile strength. Then, the conventional titanium materials have all a tensile strength and a content of components other than titanium in the region indicated by σB<600c+280, not satisfying the relation of the above formula III.

It is preferable that the tensile strength σB MPa of the titanium materials and the content c % by mass of components other than titanium in the titanium materials have a relation of the following formula III-A:

σ B > 600 c + 280 ; Formula III - A

    • in the above formula III-A, c is 0 or more and 9 or less, or 0.15 or more and 9 or less.

The titanium materials satisfying the relation of the above formula III-A, as compared with the conventional titanium materials having the same contents of components other than titanium, can have a higher strength.

It is preferable that the tensile strength σB MPa of the titanium materials and the content c % by mass of components other than titanium in the titanium materials have a relation of the following formula III-B:

σ B > 600 c + 320 ; Formula III - B

    • in the above formula III-B, c is 0 or more and 9 or less, or 0.15 or more and 9 or less.

The titanium materials satisfying the relation of the above formula III-B, as compared with the conventional titanium materials having the same contents of components other than titanium, can have a higher strength.

In Embodiment 3, the composition of the titanium materials, the average grain diameter of crystal grains constituting the titanium materials, the content of titanium having a crystal structure of an omega phase of the titanium materials, the 0.2% yield strength in a compression test of the titanium materials, the Vickers hardness of the titanium materials, the heat-resistant temperature of the titanium materials and the volume of the titanium materials can be the same as in Embodiment 1.

In Embodiment 3, the titanium materials may contain 98.8% by mass or more of titanium. In Embodiment 3, it is preferable that the titanium materials contain 98.8% by mass or more of titanium, wherein the titanium materials contain at least one impurity element selected from the group consisting of hydrogen, carbon, nitrogen, oxygen and iron, and have a total content of the titanium and the impurity element of 99.99% by mass or more. Thereby, the strength and the ductility of the titanium materials are more improved.

In Embodiment 3, the relation between the tensile strength σB MPa and the fracture elongation δ% of the titanium materials can be the same as in Embodiment 1. That is, it is preferable that the tensile strength σB MPa and the fracture elongation δ% of the titanium materials have the relation of the formula I, the formula I-A or the formula I-B described in Embodiment 1. Thereby, the strength and the ductility of the titanium materials are more improved.

In Embodiment 3, the relation between the 0.2% yield strength σ0.2 MPa in a tensile test of the titanium materials and the content c % by mass of components other than titanium in the titanium materials can be the same as in Embodiment 2. That is, it is preferable that the 0.2% yield strength σ0.2 MPa in a tensile test of the titanium materials and the content c % by mass of components other than titanium in the titanium materials have the relation of the formula II, the formula II-A or the formula II-B described in Embodiment 2. Thereby, the strength and the ductility of the titanium materials are more improved.

Embodiment 4: A Method for Manufacturing the Titanium Materials

A method for manufacturing the titanium materials of Embodiment 1 to Embodiment 3 (hereinafter, referred to also as “Embodiment 4”) will be described hereinafter. Then, the titanium material of the present disclosure is not limited to those produced by the following manufacturing method, and includes those produced by other methods.

In order to promote a better understanding of the method for manufacturing the titanium materials of Embodiment 4, a conventional method for manufacturing a titanium material will be described.

In Patent Literature 1, a titanium material is manufactured by subjecting pure titanium, an α-titanium alloy and an α+β-titanium alloy to plastic working of a working strain of 0.5 or more under a pressure of 1.5 GPa or more. It is presumed that since the grain size of the crystal grains constituting the titanium material of Patent Literature 1 is as small as several hundreds of nanometers, the ductility is low. Then, since the titanium material is produced with a working strain being imparted to a raw material, strain gradients are present between the center part and edge parts of the titanium materials and the titanium material is heterogeneous, so the titanium material is inappropriate as an object for measuring mechanical properties such as tensile strength.

As a result of exhaustive studies, the present inventors have newly found a method for manufacturing the titanium material of the present disclosure having a high strength and a high ductility. Hereinafter, the details of the method for manufacturing the titanium materials of Embodiment 4 will be described.

<Ultrahigh-Temperature High-Pressure Generator>

First, an ultrahigh-pressure high-temperature generator to be used for manufacture of the titanium materials of Embodiment 4 will be described using FIG. 7. FIG. 7 is a schematic cross-sectional view of a high-pressure cell of an ultrahigh-pressure high-temperature generator to be used in Embodiment 4. As shown in FIG. 7, a high-pressure cell 10 is equipped with a pressure medium 1 having a regular octahedral shape, a sample container 2 disposed inside pressure medium 1, and a heating element 3 disposed in the circumference of the sample container. Sample container 2 is composed of hexagonal boron nitride. Heating element 3 is composed of graphite. A raw material 4 is enclosed inside sample container 2. The maximum load of the ultrahigh-pressure high-temperature generator to be used in Embodiment 4 is, for example, 2,800 tons.

(Preparation of a Raw Material)

As a raw material, a conventional titanium alloy or pure titanium containing 98.8% by mass or more of titanium is prepared. The titanium in the titanium alloy or pure titanium is an alpha titanium having a crystal structure of an alpha phase.

(High-Pressure High-Temperature Treatment)

The above raw material is put in a sample container made of a polycrystalline hexagonal boron nitride, and by using an ultrahigh-pressure high-temperature generator, pressurized up to 6 to 11 GPa, thereafter heated up to 200 to 600° C. and held for 1 to 5 hours. Thereby, the titanium material of the present disclosure is obtained. The titanium material of the present disclosure obtained by the above method has a high strength and a high ductility. The reason therefor is presumably as follows.

By the high-pressure high-temperature treatment under the above condition, at least part of the alpha titanium in the raw material is transformed to an omega titanium. In the phase transformation from the alpha titanium to the omega titanium, rearrangement of atoms is carried out. The rearrangement of atoms needs an energy. Accordingly, the phase transformation from the alpha titanium to the omega titanium is initiated at a pressure and a temperature beyond the dotted line indicated by the α->ω hysteresis of FIG. 3, due to the effect of hysteresis.

In Embodiment 4, the high-pressure high temperature treatment is carried out under the pressure and temperature condition in the vicinity of the dotted line indicated by the α->ω hysteresis of FIG. 3. Under this condition, the overpressure is low, and crystal nuclei of the omega titanium are generated only at limited places such as grain boundary junction points and excess generation of crystal nuclei hardly occurs. Accordingly, it is presumed that the grain diameter of the crystal grains constituting obtained titanium materials easily becomes large and the titanium materials have a high ductility.

In Embodiment 4, for the heating element of the ultrahigh-pressure high-temperature generator, a graphite having a high thermal conductivity (thermal conductivity: 2,000 W/(m·K)) is used; and for the sample container, a hexagonal boron nitride having a high thermal conductivity (thermal conductivity: 600 W/(m·K)) is used. These materials, since being very high in thermal conductivity, hardly cause any temperature gradient in the raw material surrounding in the high-pressure high-temperature treatment. Further, since the graphite and the hexagonal boron nitride are soft, it becomes easy for the pressure applied on the sample to be uniformized. Accordingly, it is presumed that the crystal nuclei grow homogeneously and the obtained titanium materials are uniform in grain diameter of the crystal grains and have a high strength and a high ductility.

In the manufacturing method of Embodiment 4, since the synthesis pressure is 6 to 11 GPa and the maximum load of the manufacturing apparatus is 2,800 tons, there can be produced, for example, cylindrical large-sized titanium materials of 10 mm or more in diameter, 6 mm or more in height and 471 mm3 or more in volume. Since the titanium materials have a sufficient diameter, test pieces for carrying out a tensile test can be produced therefrom.

Then, in Sawahata, et al., (2018) “Synthesis and Mechanical Characteristic Evaluation of Polycrystalline Single-Phase ω-Ti and ω-Zr under High Pressure” (in Japanese), High Pressure Science & Technology, 28, Special Issue, and in Sawahata, et al., (2019) “Synthesis and Bending Characteristic Evaluation of Polycrystalline Single-Phase ω-Ti under High Pressure” (in Japanese), High Pressure Science & Technology, 29, Special Issue, 93, it is disclosed that by using a multianvil high-pressure generator (maximum load: 1,000 tons), ω-Ti was produced by treating a commercially available α-Ti at 12 GPa and 400° C. for 3 hours. In these literatures, in order to make easy the phase transformation from the alpha titanium to the omega titanium, the α-Ti is treated at 12 GPa and 400° C., which sufficiently exceed the dotted line indicated by the α->ω hysteresis of FIG. 3. Since this pressure and temperature condition is away from the dotted line indicated by the α->ω hysteresis of FIG. 3, and the overpressure is high, many crystal nuclei of the omega titanium are generated. Accordingly, it is presumed that the grain diameter of crystal grains constituting the obtained titanium materials is small and is about several tens to several hundreds of nanometers.

Further, in these literatures, as a heating element of the ultrahigh-pressure high-temperature generator, a lanthanum chromite oxide (LaCr2O3, thermal conductivity: 5 W/(m·K) or less) is used; and as a sample container, a magnesia (MgO: 60 W/(m·K)) is used. These materials, since being low in thermal conductivity, easily cause some temperature gradient in the raw material surrounding in the high-pressure high-temperature treatment. Further, these materials, since being high in hardness, easily cause some pressure gradient. Accordingly, it is presumed that it is easy for the grain diameter of crystal grains of the obtained titanium materials to become diverse. From the above, it is presumed that the ω-Ti produced in these literatures is low in strength and ductility as compared with the titanium material of the present disclosure.

Further, the titanium materials obtained in the above literatures are small (cylindrical with 4 mm in diameter, 3 mm in height, and 37.7 mm3 in volume), and cannot be processed to a test piece for measuring mechanical properties such as tensile strength. Since the manufacturing condition of the above literatures uses a pressure of as high as 12 GPa, the upsizing of the titanium materials is difficult.

EXAMPLES

The present embodiments will be described more specifically by way of Examples. However, the present embodiments are not any more limited to these Examples.

Example 1 <Manufacture of a Titanium Material>

As a raw material, alpha pure titanium having the following composition was prepared. N: 0.03% by mass, C: 0.08% by mass, H: 0.015% by mass, O: 0.18% by mass, Fe: 0.20% by mass, Ti (having a crystal structure of an alpha phase): balance.

The alpha pure titanium was put in a sample container made of a polycrystalline hexagonal boron nitride, and pressurized up to 8 GPa and thereafter heated up to 400° C., and held for 3 hours, by using a multianvil ultrahigh-pressure high-temperature generator (“mavo press LPR 1000-400/50”, manufactured by Voggenreiter Verlag GmbH, heating element: made of graphite, maximum load: 2,800 tons), to thereby obtain a titanium material. The obtained titanium material was cylindrical and had a size of 10 mm in diameter, 6 mm in height and 471 mm3 in volume.

<Evaluation>

The titanium material was produced by the above manufacturing method; and there were measured the composition, the tensile strength σB, the fracture elongation δ%, the 0.2% yield strength σ0.2 in a tensile test, the content of omega titanium, the content c of components other than titanium in the titanium material, the average grain diameter of crystal grains constituting the titanium material, the 0.2% yield strength in a compression test, the Vickers hardness and the heat-resistant temperature. Since the measuring methods of respective measurement items were as described in Embodiment 1 and Embodiment 2, the description thereof is not repeated. The results are as follows.

    • Composition: N: 0.03% by mass, C: 0.08% by mass, H: 0.015% by mass, O: 0.18% by mass, Fe: 0.20% by mass, Ti: balance (99.495% by mass)
    • Tensile strength σB: 833 MPa
    • Fracture elongation δ%: 34%
    • 0.2% yield strength σ0.2 in a tensile test: 634 MPa
    • Content of omega titanium: 99% by mass
    • Content c of components other than titanium in the titanium material: 0.505% by mass
    • Average grain diameter of crystal grains constituting the titanium material: 20 μm
    • 0.2% yield strength in a compression test: 900 MPa
    • Vickers hardness: 230 Hv
    • Heat-resistant temperature: 180° C.

<Discussions>

It was confirmed that the titanium material of Example 1 contained 91% by mass or more of titanium, and as shown in FIG. 1, FIG. 5 and FIG. 6, the titanium material satisfied the relations of the above formula I, formula II and formula III, and had a high strength and a high ductility.

Example 2 <Manufacture of a Titanium Material>

As a raw material, alpha pure titanium having the following composition was prepared. N: 0.05% by mass, C: 0.08% by mass, H: 0.015% by mass, O: 0.40% by mass, Fe: 0.50% by mass, Ti (having a crystal structure of an alpha phase): balance.

The alpha pure titanium was put in a sample container made of a polycrystalline hexagonal boron nitride, and pressurized up to 8 GPa and thereafter heated up to 400° C., and held for 3 hours, by using a multianvil ultrahigh-pressure high-temperature generator (“mavo press LPR 1000-400/50”, manufactured by Voggenreiter Verlag GmbH, heating element: made of graphite, maximum load: 2,800 tons), to thereby obtain a titanium material. The obtained titanium material was cylindrical and had a size of 10 mm in diameter, 6 mm in height and 471 mm3 in volume.

<Evaluation>

The titanium material was produced by the above manufacturing method; and there were measured the composition, the tensile strength σB, the fracture elongation δ%, the 0.2% yield strength σ0.2 in a tensile test, the content of omega titanium, the content c of components other than titanium in the titanium material, the average grain diameter of crystal grains constituting the titanium material, the 0.2% yield strength in a compression test, the Vickers hardness and the heat-resistant temperature. Since the measuring methods of respective measurement items were as described in Embodiment 1 and Embodiment 2, the description thereof is not repeated. The results are as follows.

    • Composition: N: 0.05% by mass, C: 0.08% by mass, H: 0.015% by mass, O: 0.40% by mass, Fe: 0.50% by mass, Ti: balance (98.955% by mass)
    • Tensile strength σB: 1,090 MPa
    • Fracture elongation δ%: 30%
    • 0.2% yield strength σ0.2 in a tensile test: 985 MPa
    • Content of omega titanium: 99% by mass
    • Content c of components other than titanium in the titanium material: 1.045% by mass
    • Average grain diameter of crystal grains constituting the titanium material: 10 μm
    • 0.2% yield strength in a compression test: 1,180 MPa
    • Vickers hardness: 300 Hv
    • Heat-resistant temperature: 180° C.

<Discussions>

It was confirmed that the titanium material of Example 2 contained 91% by mass or more of titanium, and as shown in FIG. 1, FIG. 5 and FIG. 6, the titanium material satisfied the relations of the above formula I, formula II and formula III, and had a high strength and a high ductility.

Example 3 <Manufacture of a Titanium Material> <Manufacture of a Titanium Material>

As a raw material, alpha pure titanium having the following composition was prepared. The total of Fe and O: 0.001% by mass, Ti (having a crystal structure of an alpha phase): balance.

The alpha pure titanium was put in a sample container made of a polycrystalline hexagonal boron nitride, and pressurized up to 8 GPa and thereafter heated up to 400° C., and held for 3 hours, by using a multianvil ultrahigh-pressure high-temperature generator (“mavo press LPR 1000-400/50”, manufactured by Voggenreiter Verlag GmbH, heating element: made of graphite, maximum load: 2,800 tons), to thereby obtain a titanium material. The obtained titanium material was cylindrical and had a size of 10 mm in diameter, 6 mm in height and 471 mm3 in volume.

<Evaluation>

The titanium material was produced by the above manufacturing method; and there were measured the composition, the tensile strength σB, the fracture elongation δ%, the 0.2% yield strength σ0.2 in a tensile test, the content of omega titanium, the content c of components other than titanium in the titanium material, the average grain diameter of crystal grains constituting the titanium material, the 0.2% yield strength in a compression test, the Vickers hardness and the heat-resistant temperature. Since the measuring methods of respective measurement items were as described in Embodiment 1 and Embodiment 2, the description thereof is not repeated. The results were as follows.

    • Composition: total of Fe and O: 0.001% by mass, Ti: balance (99.999% by mass)
    • Tensile strength σB: 527 MPa
    • Fracture elongation δ%: 38%
    • 0.2% yield strength σ0.2 in a tensile test: 264 MPa
    • Content of omega titanium: 99% by mass
    • Content c of components other than titanium in the titanium material: 0.001% by mass
    • Average grain diameter of crystal grains constituting the titanium material: 50 μm
    • 0.2% yield strength in a compression test: 570 MPa
    • Vickers hardness: 145 Hv
    • Heat-resistant temperature: 180° C.

<Discussions>

It was confirmed that the titanium material of Example 3 contained 91% by mass or more of titanium, and as shown in FIG. 1, FIG. 5 and FIG. 6, the titanium material satisfied the relations of the above formula I, formula II and formula III, and had a high strength and a high ductility.

Hitherto, Embodiments and Examples of the present disclosure have been described, but it is contemplated from the beginning to suitably combine and variously modify the above-mentioned constitutions of the Embodiments and Examples.

It should be understood that the Embodiments and Examples disclosed herein are illustrative in every respect and not restrictive. The scope of the present invention is defined not by the above-mentioned Embodiments and Examples but by the terms of the claims and is intended to include any modifications within the meaning and the range equivalent to the terms of the claims.

REFERENCE SIGNS LIST

    • 1 Pressure medium; 2 Sample container; 3 Heating element; 4 Raw material; and 10 High-pressure cell.

Claims

1. A titanium material comprising 91% by mass or more of titanium, σ ⁢ B ≥ 1, TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 ⁢ δ; Formula ⁢ I

wherein a tensile strength σB MPa and a fracture elongation δ% of the titanium material have a relation of the following formula I:
in the above formula I, σB 400 and δ≥20,
an average grain diameter of crystal grains constituting the titanium material is 1 μm or more and 1,000 μm or less; and
the titanium material comprises 50% by mass or more of titanium having a crystal structure of an omega phase.

2. The titanium material according to claim 1, wherein the titanium material comprises 98.8% by mass or more of titanium.

3. A titanium material comprising 91% by mass or more of titanium, σ 0.2 > 600 ⁢ c + 180; Formula ⁢ II

wherein a 0.2% yield strength σ0.2 MPa in a tensile test of the titanium material and a content c % by mass of components other than titanium in the titanium material have a relation of the following formula II:
in the above formula II, c is 0 or more and 9 or less,
an average grain diameter of crystal grains constituting the titanium material is 1 μm or more and 1,000 μm or less; and
the titanium material comprises 50% by mass or more of titanium having a crystal structure of an omega phase.

4. The titanium material according to claim 3, wherein the titanium material comprises 98.8% by mass or more of titanium.

5. A titanium material comprising 91% by mass or more of titanium, σ ⁢ B > 600 ⁢ c + 280; Formula ⁢ III

wherein a tensile strength σB MPa of the titanium material and a content c % by mass of components other than titanium in the titanium material have a relation of the following formula III:
in the above formula III, c is 0 or more and 9 or less,
an average grain diameter of crystal grains constituting the titanium material is 1 μm or more and 1,000 μm or less; and
the titanium material comprises 50% by mass or more of titanium having a crystal structure of an omega phase.

6. The titanium material according to claim 5, wherein the titanium material comprises 98.8% by mass or more of titanium.

7. The titanium material according to claim 5, σ ⁢ B ≥ 1, TagBox[",", "NumberComma", Rule[SyntaxForm, "0"]] 600 - 30 ⁢ δ; Formula ⁢ I

wherein the tensile strength σB MPa and a fracture elongation δ% of the titanium material have a relation of the following formula I:
in the above formula I, σB≥400 and δ≥20.

8. The titanium material according to claim 5, σ 0.2 > 600 ⁢ c + 180; Formula ⁢ II

wherein a 0.2% yield strength σ0.2 MPa in a tensile test of the titanium material and the content c % by mass of components other than titanium in the titanium material have a relation of the following formula II:
in the above formula II, c is 0 or more and 9 or less.

9. (canceled)

10. The titanium material according to claim 1, wherein a 0.2% yield strength in a compression test of the titanium material is 570 MPa or more.

11. (canceled)

12. The titanium material according to claim 1, wherein a heat-resistant temperature of the titanium material is 100° C. or more.

13.-14. (canceled)

15. The titanium material according to claim 1,

wherein a proportion D90/D10 of a cumulative 90% grain diameter D90 from a small diameter side to a cumulative 10% grain diameter D10 from the small diameter side in a cumulative grain size distribution based on volume of crystal grains constituting the titanium material is 5 or more and 1,000 or less.

16. The titanium material according to claim 3, wherein a 0.2% yield strength in a compression test of the titanium material is 570 MPa or more.

17. The titanium material according to claim 3, wherein a heat-resistant temperature of the titanium material is 100° C. or more.

18. The titanium material according to claim 3,

wherein a proportion D90/D10 of a cumulative 90% grain diameter D90 from a small diameter side to a cumulative 10% grain diameter D10 from the small diameter side in a cumulative grain size distribution based on volume of crystal grains constituting the titanium material is 5 or more and 1,000 or less.

19. The titanium material according to claim 5, wherein a 0.2% yield strength in a compression test of the titanium material is 570 MPa or more.

20. The titanium material according to claim 5, wherein a heat-resistant temperature of the titanium material is 100° C. or more.

21. The titanium material according to claim 5,

wherein a proportion D90/D10 of a cumulative 90% grain diameter D90 from a small diameter side to a cumulative 10% grain diameter D10 from the small diameter side in a cumulative grain size distribution based on volume of crystal grains constituting the titanium material is 5 or more and 1,000 or less.
Patent History
Publication number: 20250027185
Type: Application
Filed: Nov 8, 2022
Publication Date: Jan 23, 2025
Applicant: Sumitomo Electric Industries, Ltd. (Osaka-shi, Osaka)
Inventors: Norimasa NISHIYAMA (Osaka-shi, Osaka), Minori TERAMOTO (Osaka-shi, Osaka)
Application Number: 18/714,196
Classifications
International Classification: C22C 14/00 (20060101); C22C 1/04 (20060101);