EP4587604A1

EP4587604A1 - Metal member, implant member, and biocompatible metal member

Info

Publication number: EP4587604A1
Application number: EP23825117.7A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 2023-12-04
Filing date: 2023-12-04
Publication date: 2025-07-23
Also published as: WO2025120700A1; JP2026502756A

Abstract

A metal member includes 98.8 mass% or more of titanium, wherein the metal member includes a first region and a second region, the first region is a region which is located within a distance of 3 μm from a surface of the metal member and in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more, the second region is a region located at an beyond a distance of 40 μm from the surface of the metal member, and a content ratio of omega titanium having an omega phase crystal structure in the second region is 95 volume% or more.

Description

METAL MEMBER, IMPLANT MEMBER, AND BIOCOMPATIBLE METAL MEMBER

The present disclosure relates to a metal member, an implant member, and a biocompatible metal member.

Since a titanium material has a high specific strength, the titanium material has been used in the fields of aerospace industry, automotive industry, and the like. Further, since the titanium material has excellent biocompatibility, a demand arises as a biocompatible metal material such as a dental implant.

Titanium in a titanium material generally used at present is alpha titanium having an alpha phase crystal structure. Alpha pure titanium having a high alpha titanium content ratio has a high breaking elongation (hereinafter, also referred to as "ductility") but has a low tensile strength (hereinafter, also referred to as "strength"). On the other hand, a titanium alloy obtained by adding another metal to titanium has a high tensile strength but has a small breaking elongation. Thus, in the conventional titanium material including the alpha titanium as a main component, the strength and the ductility are in a trade-off relation, and a titanium material having both a high strength and a high ductility could not be obtained.

PTL 1 discloses that a titanium material containing omega titanium having an omega phase crystal structure can have both a high strength and a high ductility.

PTL 1: WO 2023/100603

A metal member of the present disclosure includes 98.8 mass% or more of titanium, wherein
the metal member includes a first region and a second region,
the first region is a region which is located within a distance of 3 μm from a surface of the metal member and in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more,
the second region is a region located at and beyond a distance of 40 μm from the surface of the metal member, and
a content ratio of omega titanium having an omega phase crystal structure in the second region is 95 volume% or more.

Fig. 1 is a schematic cross sectional view of a metal member according to a first embodiment. Fig. 2 is a schematic cross sectional view of a high-pressure cell of an ultrahigh-pressure high-temperature generation apparatus used for manufacturing of the metal member of the first embodiment. Fig. 3 is a schematic diagram showing a basic structure of an implant in which an implant member of a second embodiment is used.

Problem to be Solved by the Present Disclosure

According to PTL 1, as the content ratio of the omega titanium having the omega phase crystal structure in the titanium material is higher, the strength and the ductility are more improved. Therefore, from the viewpoint of improvement of the strength and the ductility, it is presumed effective to increase the content ratio of the omega titanium in the titanium material.

On the other hand, the alpha titanium has been used in a longer history than the omega titanium, and there is plenty of information with regard to a surface treatment method and biocompatibility. From the viewpoint of ease of surface treatment and safety when used as a biocompatible material, the alpha titanium has been required to exist in a surface of the titanium material.

Thus, it is an object of the present disclosure to provide a metal member, an implant member, and a biocompatible metal member, each of which has a higher content ratio of omega titanium than that in the conventional titanium material including the alpha titanium as a main component and has a surface in which the alpha titanium is included.

Advantageous Effect of the Present Disclosure

According to the present disclosure, it is possible to provide a metal member, an implant member, and a biocompatible metal member, each of which has a higher content ratio of omega titanium than that in the conventional titanium material including the alpha titanium as a main component and has a surface in which the alpha titanium is included.

Summary of Embodiments of the Present Disclosure

First, embodiments of the present disclosure will be listed and described.
(1) A metal member of the present disclosure includes 98.8 mass% or more of titanium, wherein
the metal member includes a first region and a second region,
the first region is a region which is located within a distance of 3 μm from a surface of the metal member and in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more,
the second region is a region located at and beyond a distance of 40 μm from the surface of the metal member, and
a content ratio of omega titanium having an omega phase crystal structure in the second region is 95 volume% or more.

(2) In (1), in at least a portion of the first region, the content ratio of the alpha titanium may be 10 volume% or more and less than 50 volume%. With this, at least a portion of the surface of the metal member can have particularly excellent strength, and the metal member can be suitably used in an application in which the strength is particularly required.

(3) In (1), in at least a portion of the first region, the content ratio of the alpha titanium may be 50 volume% or more and 100 volume% or less. With this, since the content ratio of the alpha titanium is high in at least the portion of the surface of the metal member, an existing surface treatment method can be readily applied to the metal member and reliability is high with regard to biocompatibility of the metal member.

(4) In any one of (1) to (3), in at least a portion of the first region, a standard deviation of the content ratio of the alpha titanium may be 1.5% or more. With this, a region having a high content ratio of the alpha titanium and a region having a low content ratio of the alpha titanium can coexist in the surface of the same metal member depending on an application.

(5) An implant member of the present disclosure consists of the metal member according to any one of (1) to (4).

With this, the content ratio of the omega titanium in the implant member is higher than that in a conventional implant member composed of the titanium material including the alpha titanium as a main component, and the implant member can have excellent strength and ductility. Further, since the implant member includes the alpha titanium in the surface thereof, the implant member is excellent in terms of ease of surface treatment and safety on living body.

(6) A biocompatible metal member according to the present disclosure consists of the metal member according to any one of (1) to (4).

With this, the content ratio of the omega titanium in the biocompatible metal member is higher than that in a conventional biocompatible metal member composed of the titanium material including the alpha titanium as a main component, and the biocompatible metal member can have excellent strength and ductility. Further, since the biocompatible metal member includes the alpha titanium in the surface thereof, the biocompatible metal member is excellent in terms of ease of surface treatment and safety on living body.

(7) In (6), the biocompatible metal member may be an artificial skull fixation member, a vertebral device fixation member, a constituent member of a body-implantable device, or a constituent member of a housing of a sensor.

(8) In (7), the artificial skull fixation member or the vertebral device fixation member may be a rod, a plate, or a screw.

Details of Embodiments of the Present Disclosure

Specific examples of the metal member, implant member, and biocompatible metal member of the present disclosure will be described below with reference to figures. In the figures of the present disclosure, the same reference characters represent the same or equivalent portions. Further, dimensional relations such as length, width, thickness, and depth are appropriately changed for clarity and simplification of the figures, and do not necessarily represent actual dimensional relations.

In the present disclosure, the expression "A to B" represents a range of lower to upper limits (i.e., A or more and B or less), and when no unit is indicated for A and a unit is indicated only for B, the unit of A is the same as the unit of B.

<First Embodiment: Metal Member>
A metal member according to one embodiment (hereinafter, also referred to as "first embodiment") of the present disclosure includes 98.8 mass% or more of titanium, wherein
the metal member includes a first region and a second region,
the first region is a region which is located within a distance of 3 μm from a surface of the metal member and in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more,
the second region is a region located at and beyond a distance of 40 μm from the surface of the metal member, and
a content ratio of omega titanium having an omega phase crystal structure in the second region is 95 volume% or more.

<Titanium Content Ratio>
The metal member of the first embodiment includes 98.8 mass% or more of titanium. Thus, the metal member has high specific strength and excellent biocompatibility. The content ratio of the titanium in the metal member may be 98.8 mass% or more and 100 mass% or less, 98.9 mass% or more and 100 mass% or less, 99.0 mass% or more and 99.99 mass% or less, 99.2 mass% or more and 99.99 mass% or less, 99.3 mass% or more and 99.99 mass% or less, or 99.4 mass% or more and 99.99 mass% or less.

The metal member of the first embodiment can consist of titanium and a component other than titanium. The other component can consist of at least one selected from a group consisting of: a general transition metal element (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), gold (Au), or the like); and hydrogen (H), carbon (C), nitrogen (N), and oxygen (O) each serving as an inevitable impurity.

When the other component is a transition metal element, the content ratio of the other component in the metal member of the first embodiment is measured by inductively coupled plasma (ICP) emission spectrometry. When the other component is an element other than the transition metal element such as hydrogen, carbon, nitrogen, or oxygen, the content ratio of the other component in the metal member is measured by secondary ion mass spectrometry (SIMS).

The content ratio of the titanium in the metal member is found by measuring the content ratio of the other component than the titanium in accordance with the above method and subtracting the content ratio of the other component than the titanium from 100 mass% of the metal member.

<Configuration of Metal Member>
Fig. 1 is a schematic cross sectional view of the metal member according to the first embodiment. As shown in Fig. 1, the metal member of the first embodiment includes a first region and a second region.

<<First Region>>
In the metal member of the first embodiment, the first region is a region which is located within a distance of 3 μm from a surface of the metal member and in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more. Here, the region located within a distance of 3 μm from the surface of the metal member can also be expressed as a region sandwiched between the surface of the metal member and an imaginary plane located at a distance of 3 μm from the surface of the metal member toward the inner side of the metal member. In Fig. 1, the whole of the surface of the metal member is constituted of the first region, but a portion of the surface of the metal member may be constituted of the first region.

In the metal member of the first embodiment, the content ratio of the alpha titanium in the first region is 10 volume% or more, may be 10 volume% or more and 100 volume% or less, may be 20 volume% or more and 100 volume% or less, may be 40 volume% or more and 100 volume% or less, may be 60 volume% or more and 100 volume% or less, may be 80 volume% or more and 100 volume% or less, or may be 100 volume%.

In the present disclosure, a method of confirming that the metal member includes the first region is as follows.

Procedure A1. The surface of the metal member is observed using a micro-area X-ray diffractometer ("SmartLab" (trademark) provided by Rigaku) to specify a region in which the alpha titanium exists. Measurement conditions are as follows: an X-ray used is Cu-Ka; an excitation condition is 45 kV and 200 mA; an incident slit size is 0.8 mm × 0.1 mm vertically; a detector is HyPix-3000 (two-dimension); a scanning method is 2θ-θ scan; a measurement range is 2θ = 25° to 90°; a step width is 0.03°; and a scan speed is 0.5°/min. A region in which a diffraction peak is observed in a range of 2θ = 39.7° to 40.4° is determined as a region in which the alpha titanium exists.

The metal member is cut along a line normal to the surface region in which the alpha titanium exists, so as to expose a cross section. When the above-described surface region does not have a planar region, the metal member is cut from any point on the surface region along a direction toward the center of gravity of the metal member so as to expose a cross section. The cross section is mirror-finished by a cross section polisher (provided by JEOL).

Procedure B1. The mirror-finished cross section of the metal member is observed using an electron beam backscattering diffractometer (SEM-EBSD, SEM device: "Gemini450" (trademark) provided by Carl Zeiss; EBSD device: "Symmetry" (trademark) provided by Oxford Instruments) accompanied with a scanning electron microscope. An observation magnification is 1000x to 10,000x. Measurement conditions are as follows: an acceleration voltage of 15 kV; a current value of 15 nA; and 0.1 to 0.02 μm/step. An obtained observation image is subjected to an EBSD analysis.

Procedure C1. An EBSD analysis result is subjected to a phase analysis using commercially available software ("AZtecCrystal" (trademark) provided by Oxford Instruments) so as to obtain a phase mapping image showing a titanium crystal structure. The titanium crystal structure specified here is a crystal structure observed when titanium appearing in the cross section of the metal member is viewed in a plan view in a normal direction of the cross section.

Procedure D1. In the phase mapping image, a quadrangular measurement region of 3 μm × 8 μm is set in the region sandwiched between a surface 23 of the metal member and an imaginary line L1 located at a distance of 3 μm from surface 23 toward the inner side of metal member 20. The measurement region has a length of 3 μm in a depth direction and has a length of 8 μm in a direction orthogonal to the depth direction. When the surface of the metal member has unevenness, in the phase mapping image, the surface of the metal member is regarded as a line that passes through a position of the surface of the metal member protruding the most toward the inner side of the metal member and that is orthogonal to the depth direction. In the present disclosure, the depth direction is a direction perpendicular to the mean line, which is defined in JIS B 0601-1994, of the surface of the metal member in the phase mapping image. The region sandwiched between the surface of the metal member and imaginary line L1 in the phase mapping image corresponds to the region of the metal member located within a distance of 3 μm from the surface of the metal member.

Procedure E1. A percentage of the area of the alpha titanium (hereinafter, also referred to as "alpha titanium area percentage") with respect to the total area of the measurement region is measured using the above-described software.

Procedure F1. The above-described measurement of the alpha titanium area percentage is performed in each of a plurality of measurement regions that do not overlap with each other. The plurality of measurement regions may be provided on the same cross section of the metal member, or may be provided on different cross sections. In the present disclosure, when there are five or more measurement regions each having an alpha titanium area percentage of 10 volume% or more, it is confirmed that the metal member includes the first region which is located within a distance of 3 μm from the surface of the metal member and in which the content ratio of the alpha titanium having the alpha phase crystal structure is 10 volume% or more.

In the present disclosure, as described in procedure F1 above, it is determined that the metal member includes the first region even when five or more measurement regions each having an alpha titanium area percentage of 10 volume% or more exist in the same cross section (hereinafter, also referred to as "first cross section") of the metal member. In this case, it can be confirmed in the following procedure that the first region exists also in a direction orthogonal to the first cross section. The metal member including the first cross section is cut along a line normal to the first cross section so as to pass through the first region in the first cross section, thereby exposing a second cross section. In the second section, the content ratio of the alpha titanium in the measurement region is measured in the same manner as in procedures A1 to F1 described above. When the second cross section includes five or more measurement regions in each of which the content ratio of the alpha titanium is 10 volume% or more, it is confirmed that the first region exists also in the direction orthogonal to the first cross section.

Further, it has been confirmed that the content ratio of the alpha titanium in the first region is substantially the same in a plurality of different cross sections obtained by cutting along respective normal lines of regions of the same metal member in which the alpha titanium exists and for which results of observation by the micro-area X-ray diffractometer in procedure A1 are substantially the same. This indicates that the first region exists to extend in an in-plane direction of the surface of the metal member.

In the present disclosure, when it is confirmed by the above-described confirmation method that the metal member includes the first region, it is determined that the surface of the metal member includes a region in which the content ratio of the alpha titanium is 10 volume% or more.

In the metal member of the first embodiment, the first region can include omega titanium as well as the alpha titanium. The total content ratio of the alpha titanium and the omega titanium in the first region may be 95 volume% or more, 98 volume% or more, 99 volume% or more, or 100 volume%. The first region may include beta titanium as long as the effect of the present disclosure is not impaired.

In the present disclosure, a method of measuring the total content ratio of the alpha titanium and the omega titanium in the first region is as follows. By the method of confirming that the metal member includes the first region, ten measurement regions each having an alpha titanium area percentage of 10 volume% or more are specified. In each measurement region, the total of the percentage of the area of the alpha titanium and the percentage of the area of the omega titanium with respect to the total area of the measurement region is measured using the above-described software. An average of the totals of the percentages of the areas of the alpha titanium and the percentages of the areas of the omega titanium in the ten measurement regions is calculated. In the present disclosure, the average corresponds to the total content ratio of the alpha titanium and the omega titanium in the first region.

In the metal member of the first embodiment, the content ratio of the alpha titanium in at least a portion of the first region may be 10 volume% or more and less than 50 volume%, or 20 volume% or more and 40 volume% or less. With this, since the content ratio of the alpha titanium is less than 50 volume% in at least the portion of the surface of the metal member, excellent strength can be likely to be secured and the metal member can be suitably used in an application particularly requiring strength. Examples of the application include an implant member having a diameter of 2 mm or more and 4 mm or less. The implant member is suitably used for a front tooth, for example.

In the present disclosure, a method of confirming that the content ratio of the alpha titanium in at least the portion of the first region is 10 volume% or more and less than 50 volume% is as follows. The alpha titanium area percentage is measured in each of the plurality of measurement regions in the same manner as in the method of confirming that the metal member includes the first region. In the present disclosure, when there are five or more measurement regions in each of which the alpha titanium area percentage is 10 volume% or more and less than 50 volume%, it is confirmed that the content ratio of the alpha titanium in at least the portion of the first region is 10 volume% or more and less than 50 volume%.

In the present disclosure, when it is confirmed by the above-described confirmation method that the content ratio of the alpha titanium in at least the portion of the first region of the metal member is 10 volume% or more and less than 50 volume%, it is determined that the surface of the metal member includes a region in which the content ratio of the alpha titanium is 10 volume% or more and less than 50 volume%.

In the metal member of the first embodiment, the content ratio of the alpha titanium in at least the portion of the first region may be 50 volume% or more and 100 volume% or less, or 60 volume% or more and 80 volume% or less. With this, since the content ratio of the alpha titanium is high in at least the portion of the surface of the metal member, an existing surface treatment method can be readily applied to the metal member and reliability is high with regard to biocompatibility of the metal member. Examples of an application thereof include an implant member having a diameter of 3 mm or more. The implant member is suitably used for each of an intermediate tooth and a back tooth, for example.

In the present disclosure, a method of confirming that the content ratio of the alpha titanium in at least the portion of the first region is 50 volume% or more and 100 volume% or less is as follows. The alpha titanium area percentage is measured in each of the plurality of measurement regions in the same manner as in the method of confirming that the metal member includes the first region. In the present disclosure, when there are five or more measurement regions each having an alpha titanium area percentage of 50 volume% or more and 100 volume% or less, it is confirmed that the content ratio of the alpha titanium in at least the portion of the first region is 50 volume% or more and 100 volume% or less.

In the present disclosure, when it is determined by the above-described confirmation method that the content ratio of the alpha titanium in at least the portion of the first region of the metal member is 50 volume% or more and 100 volume% or less, it is determined that the surface of the metal member includes a region in which the content ratio of the alpha titanium is 50 volume% or more and 100 volume% or less.

In at least the portion of the first region of the metal member of the first embodiment, a standard deviation of the content ratio of the alpha titanium may be 1.5% or more, 1.5% or more and 4% or less, 1.6% or more and 3% or less, or 1.7% or more and 2% or less. This indicates that there is variation in the content ratio of the alpha titanium in the first region. With this, a region having a high content ratio of the alpha titanium and a region having a low content ratio of the alpha titanium can coexist in the surface of the same metal member depending on an application.

In the present disclosure, a method of measuring the standard deviation of the content ratio of the alpha titanium in at least the portion of the first region is as follows. The alpha titanium area percentage is measured in each of the plurality of measurement regions in the same manner as in the method of confirming that the metal member includes the first region. The plurality of measurement regions are provided such that sides of adjacent measurement regions in the depth direction are in contact with each other. Among the plurality of measurement regions, ten measurement regions are specified in which the alpha titanium area percentage is 10 volume% or more and the sides of the adjacent measurement regions in the depth direction are in contact with each other. A whole of the ten measurement regions is in the form of one quadrangle of 3 μm (length in the depth direction) × 80 μm (length in the direction orthogonal to the depth direction). The standard deviation of the content ratio of the alpha titanium is calculated based on the content ratio of the alpha titanium in each of the ten measurement regions. In the present disclosure, this standard deviation corresponds to the standard deviation of the content ratio of the alpha titanium in at least the portion of the first region.

In the surface of the metal member of the first embodiment, the first region may constitute a whole of the surface or may constitute a portion of the surface. The area of the first region in the surface of the metal member can be appropriately set in accordance with an application of the metal member. The percentage of the area of the first region with respect to the area of the whole of the surface of the metal member may be, for example, 10% or more and 100% or less, 50% or more and 100% or less, or 60% or more and 80% or less.

<<Second Region>>
In the metal member of the first embodiment, the second region is a region located at and beyond a distance of 40 μm from the surface of the metal member. Here, the region located at and beyond a distance of 40 μm from the surface of the metal member can also be expressed as an inner region of the metal member distant away by 40 μm and more from the surface of the metal member. The content ratio of the omega titanium having the omega phase crystal structure in the second region is 95 volume% or more, may be 95 volume% or more and 100 volume% or less, may be 98 volume% or more and 100 volume% or less, may be 99 volume% or more and 100 volume% or less, or may be 100 volume%.

In the present disclosure, a method of measuring the content ratio of the omega titanium in the second region is as follows.

Procedure A2. A phase mapping image of the cross section of the metal member is obtained in the same manner as in procedures A1 to C1 described above.

Procedure B2. In the phase mapping image, a quadrangular measurement region of 3 μm × 8 μm is set in a region on the inner side with respect to an imaginary line L2 located at a distance of 40 μm from surface 23 of metal member 20 (region below imaginary line L2 in Fig. 1). When the surface of the metal member has unevenness, in the phase mapping image, the surface of the metal member is regarded as a line that passes through a position of the surface of the metal member protruding the most toward the inner side of the metal member and that is orthogonal to the depth direction. The region located on the inner side with respect to imaginary line L2 located at a distance of 40 μm from the surface of the metal member in the phase mapping image corresponds to the region located at and beyond a distance of 40 μm from the surface of the metal member.

Procedure C2. The percentage of the area of the omega titanium (hereinafter, also referred to as "omega titanium area percentage") with respect to the total area of the measurement region is measured using the above-described software.

Procedure D2. The above-described measurement of the omega titanium area percentage is performed in each of five measurement regions that do not overlap with each other. An average of the area percentages of the omega titanium in the five measurement regions is calculated. In the present disclosure, the average corresponds to the content ratio of the omega titanium in the second region.

It was confirmed that as long as the measurement is performed on the same sample, even when the position of cutting of the metal member and the measurement region are arbitrarily set and the content ratio of the omega titanium in the second region is measured a plurality of times in accordance with the above-described procedure, there is substantially no variation in the measurement results.

In the metal member of the first embodiment, the second region can include the omega titanium and the alpha titanium. The total content ratio of the alpha titanium and the omega titanium in the first region may be more than 95 volume%, 98 volume% or more, 99 volume% or more, or 100 volume%. The second region may include beta titanium as long as the effect of the present disclosure is not impaired.

In the present disclosure, a method of measuring the total content ratio of the alpha titanium and the omega titanium in the second region is as follows. In each of the five measurement regions set in the method of measuring the content ratio of the omega titanium in the second region, the total of the percentage of the area of the alpha titanium and the percentage of the area of the omega titanium with respect to the total area of the measurement region is measured using the above-described software. An average of the totals of the percentages of the areas of the alpha titanium and the percentages of the areas of the omega titanium in the five measurement regions is calculated. In the present disclosure, the average corresponds to the total content ratio of the alpha titanium and the omega titanium in the second region.

It was confirmed that as long as the measurement is performed on the same sample, even when the position of cutting of the metal member and the measurement region are arbitrarily set and the total content ratio of the alpha titanium and the omega titanium in the second region is measured a plurality of times in accordance with the above-described procedure, there is substantially no variation in the measurement results.

In the metal member of the first embodiment, an average grain size (hereinafter, also referred to as "average grain size of the second region") of the crystal grains of the second region may be 1 μm or more and 1000 μm or less. When the average grain size of the second region is 1 μm or more, the strength of the metal member is improved. When the average grain size of the second region is 1000 μm or less, the ductility of the metal member is improved.

The average grain size of the second region may be 3 μm or more and 500 μm or less, 5 μm or more and 200 μm or less, 10 μm or more and 100 μm or less, 10 μm or more and 50 μm or less, or 20 μm or more and 50 μm or less.

In the present disclosure, a method of measuring the average grain size of the second region is as follows. A cross section of the metal member is polished and the polished surface is imaged using an optical microscope at a magnification of 100x, thereby obtaining an optical microscope image.

A measurement visual field of 50 mm × 50 mm is set in the second region in the optical microscope image. The optical microscope image is subjected to image processing using commercially available image analysis software, the equivalent circle diameter of each crystal grain in the measurement visual field is measured, and an arithmetic average of the equivalent circle diameters is calculated.

The above-described measurement is performed on one measurement sample in three measurement fields that do not overlap with each other, and an average of the arithmetic averages of the equivalent circle diameters in the three measurement fields is calculated. In the present disclosure, the average corresponds to the average grain size of the second region.

It should be noted that it was confirmed that as long as the measurement is performed on the same sample, even when the average grain size of the second region is measured a plurality of times with the measurement visual field being changed, there is substantially no variation in the measurement results.

In the metal member of the first embodiment, the grain sizes of the crystal grains of the second region are preferably small in variation from the viewpoint of uniformity in each of the strength and the ductility. A ratio D90/D10 of a cumulative 90% grain size D90 from the small size side to a cumulative 10% grain size D10 from the small size side in a cumulative grain size distribution that is based on the volume of the crystal grains of the second region may be 5 or more and 1000 or less, or 10 or more and 1000 or less. A smaller value of D90/D10 indicates a smaller variation in the grain sizes of the crystal grains.

A method of measuring D90/D10 is as follows. The equivalent circle diameters of all the crystal grains observed in the measurement visual field are measured in the same manner as in the method of measuring the average grain size of the second region, and the volume-based cumulative grain size distribution is prepared based on them. D90/D10 is calculated based on the cumulative grain size distribution.

It should be noted that it was confirmed that as long as the measurement is performed on the same sample, even when the measurement of D90/D10 was performed a plurality of times with the measurement position being changed, there was substantially no variation in the measurement results.

<Other Region>
The metal member of the first embodiment includes a region other than the first region and the second region. Examples of the other region include: a region sandwiched between the first region and the second region; and a region which is located within a distance of 3 μm from the surface of the metal member toward the inner side of the metal member and in which the content ratio of the alpha titanium is less than 10 volume%. The content ratio of the omega titanium in the other region may be more than or equal to the content ratio of the omega titanium in the first region and less than or equal to the content ratio of the omega titanium in the second region from the viewpoint of manufacturing. With this, it is confirmed that excellent strength and ductility of the metal member are secured. The content ratio of the omega titanium in the other region may be, for example, 90 volume% or more, 93 volume% or more, 95 volume% or more, 98 volume% or more, 99 volume% or more, or 100 volume%.

In the present disclosure, a method of measuring the content ratio of the omega titanium in the other region is as follows.

Procedure A3. A phase mapping image of the cross section of the metal member is obtained by the same method as in procedures A1 to C1 described above.

Procedure B3. In the phase mapping image, a quadrangular measurement region of 3 μm × 8 μm is set in the other region than the first region and the second region.

Procedure C3. A percentage of the area of the omega titanium (hereinafter, also referred to as "omega titanium area percentage") with respect to the total area of the measurement region is measured using the above-described software.

Procedure D3. The above-described measurement of the omega titanium area percentage is performed in each of five measurement regions that do not overlap with each other. An average of the omega titanium area percentages in the five measurement regions is calculated. In the present disclosure, the average corresponds to the content ratio of the omega titanium in the other region.

It was confirmed that as long as the measurement is performed on the same sample, even when the position of cutting of the metal member and the measurement region are arbitrarily set and the content ratio of the omega titanium in the other region was measured a plurality of times in accordance with the above-described procedure, there is substantially no variation in the measurement results.

In the metal member of the first embodiment, the other region can include omega titanium and alpha titanium. The total content ratio of the alpha titanium and the omega titanium in the other region may be more than 95 volume%, 98 volume% or more, 99 volume% or more, or 100 volume%. The other region may include beta titanium as long as the effect of the present disclosure is not impaired.

In the present disclosure, a method of measuring the total content ratio of the alpha titanium and the omega titanium in the other region is as follows. In each of the five measurement regions set in the method of measuring the content ratio of the omega titanium in the other region, the total of the percentage of the area of the alpha titanium and the percentage of the area of the omega titanium with respect to the total area of the measurement region is measured using the above-described software. The average of the totals of the percentages of the areas of the alpha titanium and the percentages of the areas of the omega titanium in the five measurement regions is calculated. In the present disclosure, the average corresponds to the total content ratio of the alpha titanium and the omega titanium in the other region.

It was confirmed that as long as the measurement is performed on the same sample, even when the position of cutting of the metal member and the measurement region are arbitrarily set and the total content ratio of the alpha titanium and the omega titanium in the other region is measured a plurality of times in accordance with the above-described procedure, there was substantially no variation in the measurement results.

<Volume of Metal Member>
The volume of the metal member of the first embodiment may be 0.001 cubic millimeters or more. With this, since the metal member has a sufficient size, the metal member can be readily used for various applications such as an implant member, an artificial skull fixation member, a vertebral device fixation member, a constituent member of a body-implantable device, and a constituent member of a housing of a sensor. Further, since a sufficient amount of the second region can be secured, the metal member can have more excellent strength and ductility.

The volume of the metal member may be 0.001 cubic millimeters or more and 100,000 cubic millimeters or less, 10 cubic millimeters or more and 100,000 cubic millimeters or less, or 100 cubic millimeters or more and 100,000 cubic millimeters or less. The volume of the metal member is measured in accordance with the Archimedes method.

<Shape of Metal Member>
The shape of the metal member of the first embodiment is not particularly limited, and can be appropriately set in accordance with an application. The shape of the metal member may be, for example, a prismatic columnar shape, a circular columnar shape, a circular tubular shape, a prismatic tubular shape, or a flat-plate shape, or may be a screw shape, a nut shape, a bolt shape, or a washer shape. Further, the shape of the metal member may be a shape suitable for an implant member or may be a shape suitable for a biocompatible metal member. A groove or the like suitable for the application may be formed in the surface of the metal member. The thinnest portion of the metal member may have a thickness of 0.2 mm or more.

<Tensile Strength σB and Breaking Elongation δ of Metal Member>
A tensile strength σB of the metal member of the first embodiment may be 400 MPa or more and less than 1550 MPa, 500 MPa or more and 1100 MPa or less, 900 MPa or more and 1100 MPa or less, or 950 MPa or more and 1000 MPa or less.

A breaking elongation δ of the metal member of the first embodiment may be 20% or more and 50% or less, 25% or more and 45% or less, or 30% or more and 45% or less.

In the present disclosure, tensile strength σB and breaking elongation δ of the metal member are measured in accordance with JIS Z 2241:2011, "Metallic materials - Tensile testing - Method of test at room temperature". A test temperature is 23°C±5°C.

<Vickers Hardness>
A Vickers hardness of the metal member of the second region of the first embodiment may be 130 Hv or more and 400 Hv or less, 200 Hv or more and 350 Hv or less, or 230 Hv or more and 280 Hv or less.

In the present disclosure, the Vickers hardness of the metal member is measured in the following procedure. The metal material is cut to expose a cross section. The second region is specified in the cross section. In the second region, the Vickers hardness is measured in accordance with JIS Z 2244:2009, "Vickers hardness test - Test method". A test temperature is 23°C±5°C.

<0.2% Proof Stress in Tensile Test>
A 0.2% proof stress in the tensile test of the metal member of the first embodiment may be 250 MPa or more and 2000 MPa or less, 300 MPa or more and 1000 MPa or less, 600 MPa or more and 900 MPa or less, or 730 MPa or more and 870 MPa or less.

The 0.2% proof stress in the tensile test of the metal member is measured in accordance with JIS Z 2241:2011, "Metallic materials - Tensile testing - Method of test at room temperature". A test temperature is 23°C±5°C.

<0.2% Proof Stress in Compression Test>
A 0.2% proof stress of the metal member of the first embodiment in a compression test may be 580 MPa or more and 5000 MPa or less, 900 MPa or more and 3000 MPa or less, 900 MPa or more and 2000 MPa or less, and 1100 MPa or more and 1500 MPa or less.

The 0.2% proof stress of the metal member in the compression test is measured in accordance with JIS R 1608:2003, "Testing methods for compressive strength of fine ceramics". A test temperature is 23°C±5°C.

<Method of Manufacturing Metal Member>
A method of manufacturing the metal member of the first embodiment can include a source material preparation step, a high-pressure high-temperature treatment step, and a discharging treatment step.

<<Source Material Preparation Step>>
In the source material preparation step, a conventional titanium alloy including 98.8 mass% or more of titanium, or pure titanium is prepared as a source material. Titanium in each of the titanium alloy and the pure titanium is alpha titanium having an alpha phase crystal structure.

<<High-Pressure High-Temperature Treatment Step>>
In the high-pressure high-temperature treatment step, the source material is placed in a sample container composed of a hexagonal boron nitride polycrystalline body, is fed with a pressure to 6 to 11 GPa and then heated to 200 to 600°C using an ultrahigh-pressure high-temperature generation apparatus, and is held for 15 to 120 minutes, thereby obtaining a titanium material in which a content ratio of omega titanium is 95 volume% or more. The titanium material obtained has a uniform structure, and the content ratio of the omega titanium is substantially the same from the inside to the surface thereof.

The ultrahigh-pressure high-temperature generation apparatus will be described with reference to Fig. 2. Fig. 2 is a schematic cross sectional view of a high-pressure cell of the ultrahigh-pressure high-temperature generation apparatus. As shown in Fig. 2, a high-pressure cell 10 includes: a pressure medium 1 having a regular octahedral shape; a sample container 2 disposed inside pressure medium 1; and a heat generator 3 disposed around sample container 2. Sample container 2 is composed of hexagonal boron nitride. Heat generator 3 is composed of graphite. A source material 4 is sealed inside sample container 2. The maximum load of the ultrahigh-pressure high-temperature generation apparatus is, for example, 2800 tons.

<<Discharging Treatment Step>>
In the discharging treatment step, the titanium material is subjected to discharging treatment, thereby obtaining the metal member. Specifically, the discharging treatment is performed onto the surface of the titanium material in such a manner that discharging is caused by allowing a current to flow therethrough with a wire electrode line or a planar electrode being close to the surface of the titanium material in an argon gas or pure water. In the region of the titanium material having been through the discharging treatment, reverse phase transition from the omega titanium to the alpha titanium is caused, thereby increasing the content ratio of the alpha titanium. Thus, the first region in which the content ratio of the alpha titanium is 10 volume% or more is formed in the region located within a distance of 3 μm from the surface of the titanium material, thereby obtaining the metal member of the first embodiment.

Conditions for the discharging treatment can be as follows: a discharge voltage of 0.05 to 5 kV; a discharge current of 0.01 to 500 A; and a pulse width of 1 to 1000 μs.

By adjusting the size of the region to be subjected to the discharging treatment in the surface of the titanium material, the percentage of the area of the first region with respect to the area of the whole of the surface of the metal member can be adjusted.

<Second Embodiment: Implant Member>
An implant member of one embodiment (hereinafter, also referred to as "second embodiment") of the present disclosure is an implant member consisting of the metal member of the first embodiment. The content ratio of the omega titanium in the implant member of the second embodiment is higher than that in a conventional implant member consisting of the titanium material including the alpha titanium as a main component, and the implant member of the second embodiment can have excellent strength and ductility. Further, since the implant member of the second embodiment includes the alpha titanium in a surface thereof, the implant member of the second embodiment is excellent in terms of ease of surface treatment and safety on living body.

Fig. 3 is a schematic diagram showing a basic structure of an implant 30 in which the implant member of the second embodiment is used. Implant 30 can include: an implant body 31 to be implanted in a root of a tooth; an artificial tooth 34 fixed to a tip portion of the implant body; and an abutment 32 and an artificial tooth fixation screw 33 that each couple implant body 31 and artificial tooth 34. The implant member of the second embodiment may be the implant body, the abutment, or the artificial tooth fixation screw.

The implant of Fig. 3 is of a two-piece type in which the implant body and the abutment are separate members. The implant member of the second embodiment may be a one-piece type implant member in which the implant body and the abutment are integrated.

In the implant member of the second embodiment, the first region of the metal member can constitute a surface of the implant member that is to be brought into contact with a living body or can constitute a surface thereof that may be brought into contact with a living body. With this, safety on living body is further improved.

<Third Embodiment: Biocompatible Metal Member>
A biocompatible metal member of one embodiment (hereinafter, also referred to as "third embodiment") of the present disclosure is a biocompatible metal member consisting of the metal member of the first embodiment. The content ratio of the omega titanium in the biocompatible metal member of the third embodiment is higher than that in a conventional biocompatible metal member composed of the titanium material including the alpha titanium as a main component, and the biocompatible metal member of the third embodiment can have excellent strength and ductility. Further, since the biocompatible metal member of the third embodiment includes the alpha titanium in a surface thereof, the biocompatible metal member of the third embodiment is excellent in terms of ease of surface treatment and safety on living body.

The biocompatible metal member of the third embodiment may be, for example, an artificial skull fixation member, a vertebral device fixation member, a constituent member of a body-implantable device, or a constituent member of a housing of a sensor. The artificial skull fixation member or the vertebral device fixation member may be a rod, a plate, or a screw.

In the biocompatible metal member of the third embodiment, the first region of the metal member can constitute a surface of the biocompatible metal member that is to be brought into contact with a living body or can constitute a surface thereof that may be brought into contact with a living body.

<Supplementary Note 1>
A metal member comprising 98.8 mass% or more of titanium, wherein
a surface of the metal member includes a first surface region,
the first surface region is a region in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more,
the metal member includes a second region located at and beyond a distance of 40 μm from the surface of the metal member, and
a content ratio of omega titanium having an omega phase crystal structure in the second region is 95 volume% or more.

<Supplementary Note 2>
In supplementary note 1, in at least a portion of the first surface region, the content ratio of the alpha titanium may be 10 volume% or more and less than 50 volume%.

<Supplementary Note 3>
In supplementary note 1, in at least a portion of the first surface region, the content ratio of the alpha titanium may be 50 volume% or more and 100 volume% or less.

The present embodiment will be described more specifically with reference to examples. However, the present embodiment is not limited by these examples.

<Preparation of Titanium Material>
As a source material of each sample, alpha pure titanium having a composition shown in Table 1 was prepared. Titanium in the alpha pure titanium is alpha titanium (described as "αTi" in Table 1).

The alpha pure titanium was placed in a sample container composed of a hexagonal boron nitride polycrystalline body, was fed with a pressure to 8 GPa and then heated to 500°C using a multi-anvil ultrahigh-pressure high-temperature generation apparatus ("mavo press LPR 1000-400/50" provided by Voggenreiter; a heat generator is composed of graphite and the maximum load is 2800 tons), and is held for 15 minutes, thereby obtaining a titanium material of each of samples 1 to 5. The obtained titanium material had a circular columnar shape with a height of 10 mm and a volume of 500 cubic millimeters.

<Measurement of Titanium Material>
For the titanium material of each sample, the composition of the titanium material, the crystal structure of the titanium, tensile strength σB, breaking elongation δ, the Vickers hardness, the 0.2% proof stress in the tensile test, the 0.2% proof stress in the compression test, the average grain size of the crystal grains of the titanium material, and D90/D10 of the crystal grains of the titanium material were measured. A measurement method for each item is as follows. Results are shown in Tables 2 and 3.

<Composition of Titanium Material>
The content ratio of the titanium in the titanium material, the content ratio of the components other than titanium, and the types of the other components were measured by ICP emission spectrometry.

<Crystal Structure of Titanium>
The titanium material obtained in each sample was cut along a normal line so as to expose a cross section. The cross section was mirror-finished by a cross section polisher (provided by JEOL). The mirror-finished surface was analyzed by a SEM-EBSD to specify the crystal structure of the titanium. Conditions for the measurement by the SEM-EBSD were as follows: an acceleration voltage of 15 kV; a current value of 15 nA; a magnification of 1000x to 10,000x; and 0.1 to 0.02 μm/step. In each of all the samples, the crystal structure of the titanium was confirmed to be 100 volume% of omega titanium from the surface to the inside of the titanium material.

<Tensile Strength σB and Breaking Elongation δ>
Tensile strength σB and breaking elongation δ of the titanium material were measured in accordance with JIS Z 2241:2011, " Metallic materials - Tensile testing - Method of test at room temperature". A test temperature was 23°C.

<Vickers Hardness>
The Vickers hardness of the titanium material was measured in accordance with JIS Z 2244:2009, "Vickers hardness test - Test method". A test temperature was 23°C.

<0.2% Proof Stress in Tensile Test>
The 0.2% proof stress of the titanium material in the tensile test was measured in accordance with JIS Z 2241:2011, "Metallic materials - Tensile testing - Method of test at room temperature". A test temperature was 23°C.

<0.2% Proof Stress in Compression Test>
The 0.2% proof stress of the titanium material in the compression test was measured in accordance with JIS R 1608:2003, "Method for testing compression strength of fine ceramics". A test temperature was 23°C.

<Average Grain Size of Crystal Grains of Titanium Material and D90/D10>
The average grain size and D90/D10 of the crystal grains of the titanium material were measured by the methods described in the first embodiment.

<Preparation of Metal Member>
A plurality of the titanium materials of each of samples 1 to 5 were prepared. A whole of the surface of each titanium material was subjected to discharging treatment to obtain a metal member of each sample. In the discharging treatment, the whole of the surface of the titanium material is subjected to the discharging treatment in such a manner that discharging is caused by allowing a current to flow therethrough with a wire electrode line being close to the surface of the titanium material in an argon gas. Conditions for the discharging treatment in each sample are as shown in Table 4.

<Measurement of Metal Member>
For each metal member of each sample, the content ratio of the titanium, the content ratio of the other components than the titanium, the types of the other components than the titanium, the crystal structure of the titanium, presence or absence of the first region, the content ratio of the alpha titanium in the first region, the standard deviation of the content ratio of the alpha titanium in the first region, and the content ratio of the omega titanium in the second region were measured. Specific measurement methods are described in the first embodiment. Results are shown in Table 5. It should be noted that it was confirmed that the first region existed in each of all the samples.

The metal members of samples 101 to 105, samples 201 to 205, and samples 301 to 305 correspond to examples of the present disclosure.

Tensile strength σB, breaking elongation δ, the 0.2% proof stress in the tensile test, the 0.2% proof stress in the compression test, and the Vickers hardness of the second region were measured in each sample, and were confirmed to be substantially the same as the values of those of the titanium material before the discharging treatment in each of all the samples.

The average grain size and D90/D10 of the crystal grains of the second region were measured in each sample, and were confirmed to be substantially the same as the values of those of the titanium material before the discharging treatment in each of all the samples.

Although the embodiments and examples of the present disclosure have been described above, it is initially expected to appropriately combine or variously modify the configurations of the embodiments and examples described above.
The embodiments and examples disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, rather than the embodiments and examples described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1: pressure medium; 2: sample container; 3: heat generator; 4: source material; 10: high-pressure cell; 20: metal member; 21: first region; 22: second region; 23: surface; 24: other region.

Claims

A metal member comprising 98.8 mass% or more of titanium, wherein
the metal member includes a first region and a second region,
the first region is a region which is located within a distance of 3 μm from a surface of the metal member and in which a content ratio of alpha titanium having an alpha phase crystal structure is 10 volume% or more,
the second region is a region located at and beyond a distance of 40 μm from the surface of the metal member, and
a content ratio of omega titanium having an omega phase crystal structure in the second region is 95 volume% or more.
The metal member according to claim 1, wherein in at least a portion of the first region, the content ratio of the alpha titanium is 10 volume% or more and less than 50 volume%.
The metal member according to claim 1, wherein in at least a portion of the first region, the content ratio of the alpha titanium is 50 volume% or more and 100 volume% or less.
The metal member according to any one of claims 1 to 3, wherein in at least a portion of the first region, a standard deviation of the content ratio of the alpha titanium is 1.5% or more.
An implant member consisting of the metal member according to any one of claims 1 to 4.
A biocompatible metal member consisting of the metal member according to any one of claims 1 to 4.
The biocompatible metal member according to claim 6, wherein the biocompatible metal member is an artificial skull fixation member, a vertebral device fixation member, a constituent member of a body-implantable device, or a constituent member of a housing of a sensor.
The biocompatible metal member according to claim 7, wherein the artificial skull fixation member or the vertebral device fixation member is a rod, a plate, or a screw.