JP7330459B2 - machine parts - Google Patents

Description

The present invention relates to mechanical parts.

Conventionally, titanium alloys are known as one of the materials constituting machine parts. As for the titanium alloy, it is known that elements such as oxygen (0) and nitrogen (N) are introduced into the crystal structure to strengthen the solid solution (see, for example, Japanese Patent Application Laid-Open No. 2012-132057).

JP 2012-132057 A

As described above, solid-solution strengthening with oxygen or nitrogen is known as a method for strengthening titanium alloys that constitute machine parts. It is not known heretofore to improve

SUMMARY OF THE INVENTION An object of the present invention is to provide a mechanical component made of a titanium alloy with improved surface hardness.

A mechanical component according to the present disclosure is a mechanical component made of a titanium alloy and having a surface layer, the surface layer including a boron-infiltrated boride region. The concentration of boron on the surface of the boride region is 4% by mass or more and 10% by mass or less.

According to the above, it is possible to obtain a machine part made of a titanium alloy having improved surface hardness by forming a boride region.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which shows the structure of the deep groove ball bearing which concerns on embodiment of this invention. FIG. 2 is an enlarged view showing the configuration of region II in FIG. 1; 4 is a graph showing the relationship between Vickers hardness and depth from the surface of a test piece after immersion treatment. 4 is a graph showing the relationship between the boron concentration of a test piece after boron immersion treatment and the depth from the surface. It is a crystal layer map in the cross section of the test piece after the immersion treatment. It is a graph which shows the relationship between the boron concentration and Vickers hardness in a test piece.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the drawings below, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

(Embodiment)
<Configuration of rolling device (rolling bearing)>
First, the configuration of a rolling bearing using a bearing component, which is an example of a mechanical component according to an embodiment of the present invention, will be described. A rolling bearing is an example of a rolling device. In this embodiment, a deep groove ball bearing will be described as an example of a rolling bearing.

FIG. 1 is a schematic cross-sectional view showing the configuration of a deep groove ball bearing according to an embodiment of the invention. FIG. 2 is an enlarged view showing the configuration of region II in FIG. Referring to FIG. 1, a deep groove ball bearing 1 of the present embodiment includes an annular outer ring 11, an annular inner ring 12 arranged inside the outer ring 11, and arranged between the outer ring 11 and the inner ring 12, A plurality of balls 13 as rolling elements held in an annular retainer 14 are provided. The outer ring 11 has an outer ring raceway surface 11A on its inner peripheral surface. The inner ring 12 has an inner ring raceway surface 12A on its outer peripheral surface. That is, the inner peripheral surface of the outer ring 11 is formed with an outer ring raceway surface 11A, and the outer peripheral surface of the inner ring 12 is formed with an inner ring raceway surface 12A. The outer ring 11 and the inner ring 12 are arranged such that the outer ring raceway surface 11A and the inner ring raceway surface 12A face each other.

The outer ring 11 and the inner ring 12 are examples of mechanical parts of the present embodiment, and are made of a titanium alloy. The titanium alloy forming the outer ring 11 and the inner ring 12 is an α+β type titanium alloy such as Ti-6%Al-4%V.

The plurality of balls 13 are configured to roll between the outer ring raceway surface 11A and the inner ring raceway surface 12A. The plurality of balls 13 contact the outer ring raceway surface 11A and the inner ring raceway surface 12A at the ball rolling surface 13A. The plurality of balls 13 are arranged by the retainer 14 at a predetermined pitch in the circumferential direction, so that they are rotatably retained on an annular orbit. Moreover, in the ball 13, the entire surface is the ball rolling surface 13A. With the above configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 are rotatable relative to each other.

Any material such as steel, titanium alloy, or resin can be used as the material for forming the retainer 14 . Any material such as steel, titanium alloy, ceramics, or the like can be used as the material for forming the ball 13 . For example, the material forming ball 13 may be high carbon chromium bearing steel specified in JIS standard JIS G 4805:2008.

A space sandwiched between the outer ring 11 and the inner ring 12, more specifically, a space sandwiched between the outer ring raceway surface 11A and the inner ring raceway surface 12A may be filled with, for example, a grease composition (not shown). This grease composition may form an oil film between each of outer ring 11 and inner ring 12 and ball 13 .

The outer ring 11, the inner ring 12 and the balls 13 as rolling parts constituting the deep groove ball bearing 1 will be described with reference to FIG. A ball 13 as a second rolling member is in contact with each of the outer ring 11 and the inner ring 12 as the first rolling member.

The surfaces of outer ring 11 and inner ring 12 include boride regions 11B and 12B. Boroned regions 11B and 12B, which are regions in which boron has penetrated into the titanium alloy, are formed on at least part of the surface of outer ring 11 and inner ring 12 . Bored regions 11B and 12B may be formed on all surfaces of the outer ring 11 and the inner ring 12 as shown in FIG. Moreover, the boron regions 11B and 12B may be formed at least on the outer ring raceway surface 11A and the inner ring raceway surface 12A of the outer ring 11 and the inner ring 12, respectively. A general boriding treatment results in a machine part in which a compound is formed on the surface of a titanium alloy. On the other hand, since the compound layer is removed in the boron immersion treatment in the present embodiment, the machine part has no compound layer on the surface of the titanium alloy.

The concentration of boron on the surface of boride regions 11B and 12B is 4% by mass or more and 10% by mass or less. The surface hardness of the boride regions 11B and 12B is 650HV or more and 1200HV or less. The thickness of the boride region 11B, that is, the depth T1 of the boride region 11B from the surface of the outer ring 11 is 0.02 mm or more and 0.03 mm or less. The thickness of the boride region 12B, that is, the depth T2 of the boride region 12B from the surface of the inner ring 12 is 0.02 mm or more and 0.03 mm or less.

<Manufacturing method of machine parts>
A method for manufacturing a mechanical component according to this embodiment will be described.

In the method of manufacturing a mechanical component according to the present embodiment, first, a preparatory step is performed. In this preparatory step, a titanium alloy workpiece to be machined is prepared. For example, a ring-shaped member having substantially the same shape as the outer ring 11 and the inner ring 12 shown in FIGS. 1 and 2 is prepared as a workpiece.

Next, an immersion treatment step is performed. In this boron immersion step, boron is introduced from the surface of the material to be processed into the inside to form a boride region. Any method can be used to form the boride region. For example, a method of placing the material to be processed in a gas atmosphere containing boron and heat-treating it, or a method of applying powder containing boron on the surface of the material to be processed. A method of heat-treating by bringing a solid into contact with such as can be used. In this boron immersion step, a boride region is formed on the surface of the material to be processed, and a compound of boron and titanium is formed on the surface.

Next, a grinding process is implemented. In this grinding step, the surface of the material to be processed is removed by grinding to a depth of about 0.01 mm, for example. This step removes the compound of boron and titanium formed on the surface of the material to be processed in the above-described boron immersion step.

Next, a post-treatment process is performed. In this post-treatment process, a polishing process, a cleaning process, and the like are performed for adjusting the shape, surface roughness, and the like. Thus, the mechanical component according to this embodiment can be obtained.

<Effect>
The outer ring 11 and the inner ring 12 as mechanical parts according to the present disclosure are machine parts made of a titanium alloy and having a surface layer, and the surface layer includes boride regions 11B and 12B in which boron is infiltrated. The concentration of boron on the surfaces of the boride regions 11B and 12B is 4% by mass or more and 10% by mass or less.

By doing so, the surface hardness of the machine part can be improved by forming the boride regions 11B and 12B in which boron penetrates into the surface layers of the outer ring 11 and the inner ring 12 as the machine part made of titanium alloy. can. As a result, it is possible to obtain a mechanical component having excellent wear resistance.

Here, the boride regions 11B and 12B mean regions in which boron penetrates into the crystal of the titanium alloy. Boron in the titanium alloy can be measured, for example, by EPMA (Electron Probe Micro Analyzer). In the boride regions 11B and 12B in this embodiment, most of boron does not exist in a precipitated state as a compound with titanium. In other words, boron exists in the crystal structure of the titanium alloy as an interstitial atom or in a state in which some of the atoms forming the crystal lattice of the titanium alloy are substituted. The boron regions 11B and 12B have relatively high hardness due to the presence of boron.

The reason why the lower limit of the boron concentration is set to 4% by mass is that the hardness of the titanium alloy can be increased to 650 HV or more by increasing the concentration to 4% by mass or more. The lower limit of the boron concentration may be 5% by mass or 7% by mass. Moreover , the upper limit of the boron concentration may be 9% by mass or 8% by mass.

The surface hardness of the outer ring 11 and the inner ring 12 as the mechanical parts may be 650 HV or more and 1200 HV or less. In this case, the surface hardness of the outer ring 11 and the inner ring 12 as bearing parts can be set to the values necessary for the bearing parts. As a method for measuring hardness, the Vickers hardness test method specified in JIS (JIS Z 2244:2009) can be used.

In the outer ring 11 and the inner ring 12 as the mechanical parts, the depths T1 and T2 of the boride regions 11B and 12B from the surface may be 0.02 mm or more and 0.03 mm or less. In this case, the hardness can be improved up to a depth of about 0.03 mm from the surfaces of the outer ring 11 and the inner ring 12 as mechanical parts. The depth of the boride region is, for example, the hardness measured from the surface in the cross section of the material to be processed, and the hardness value is the hardness value (reference value) at the central portion in the depth direction of the material to be processed. can be determined as a position higher by 50 HV or more. As a method for measuring hardness, the Vickers hardness test method specified in JIS (JIS Z 2244:2009) can be used.

In the outer ring 11 and the inner ring 12 as the machine parts, the titanium alloy may be an α+β type titanium alloy. The α+β type titanium alloy may be, for example, a Ti-6Al-4V alloy (hereinafter referred to as "64 titanium") defined in ASTM standard (B348-13 GR.5). Examples of α + β type titanium alloys include Ti-3Al-2.5V alloy, Ti-6Al-2Sn-4Zr-6Mo alloy, Ti-6Al-6V-2Sn (Cu+Fe) alloy, etc., which are defined in ASTM standards. be done. In this case, the bearing including the outer ring 11 and the inner ring 12 as mechanical parts can be used in various fields such as medical, chemical, aerospace, and nuclear power industries.

Note that the α+β type titanium alloy is a titanium alloy exhibiting a two-phase structure composed of an α phase and a β phase at room temperature. The α-phase is a low-temperature phase of titanium with an hcp (hexagonal closed pack) structure, and the β-phase is a high-temperature phase of titanium with an fcc (face centered cubic) structure.

(Example)
<Preparation of test piece>
As a test piece, a test piece made of 64 titanium was prepared. The composition of 64 titanium constituting the test piece is Al: 5.50% by mass or more and 6.75% by mass or less, V: 3.50% by mass or more and 4.50% by mass or less, Fe: 0.40% by mass. Below, O: 0.20% by mass or less, C: 0.08% by mass or less, N: 0.05% by mass or less, and H: 0.015% by mass or less. The size of the test piece is disc-shaped with an outer diameter of 19 mm and a thickness of 5 mm.

An immersion treatment was performed on the test piece. Specifically, the heat treatment was performed while the B ₄ C powder was in contact with the test piece. The heating temperature of the test piece was 1000° C., and the soaking holding time was 100 hours. After the soaking holding time had elapsed, the test piece was cooled to room temperature by furnace cooling.

<Measurement>
The following measurements were performed on the test pieces that had been subjected to the immersion treatment as described above.

Hardness measurement:
A test piece was cut and the hardness distribution on the cut surface was measured. As a method for measuring hardness, the Vickers hardness test method specified in JIS (JIS Z 2244:2009) was used.

Boron concentration measurement:
The elemental concentration distribution of boron was measured by EPMA on the cut surface of the test piece.

Crystal layer map:
EBSD (Electron Backscatter Diffraction) was used to obtain crystal layer map data on the cross section of the test piece.

<Results>
Hardness measurement results:
FIG. 3 is a graph showing the relationship between Vickers hardness and depth from the surface of the test piece after immersion treatment. The horizontal axis in FIG. 3 indicates the depth (unit: mm) from the surface of the test piece, and the vertical axis indicates the Vickers hardness. The hardness of the 64 titanium base material constituting the test piece (hardness in a region deeper than 0.08 mm from the surface) is about 300 to 350 HV. As can be seen from FIG. 3, in the test piece, the hardness of the region from the surface to a depth of about 0.04 mm is higher than that of the base material described above. The position indicated by line segment A in FIG. 3 is a position at a depth of 0.01 mm from the surface. The area on the surface side of the line segment A is a compound layer, which is an area in which a compound of titanium and boron is formed, as can be seen from the map described later. A hardness level of 650 HV indicated by line segment B is a hardness level required for mechanical parts such as bearing parts.

Boron concentration measurement results:
FIG. 4 is a graph showing the relationship between the boron concentration of the test piece after the boron immersion treatment and the depth from the surface. The horizontal axis in FIG. 4 indicates the depth from the surface of the test piece (unit: mm), and the vertical axis indicates the boron concentration (unit:
mass %). The 64 titanium base material (the part of the base material located deeper than 0.08 mm from the surface) that constitutes the test piece does not substantially contain boron, but the hardness is 0.04 mm from the surface. Boron intrusion was observed in regions up to a depth of about 100 mm. It is believed that boron in excess of the solid solubility limit of boron in titanium forms compounds such as TiB ₂ and TiB on the outermost surface (region shallower than 0.01 mm in depth). In addition, FIG. 3 shows a diffusion layer in which boron is diffused in a region from 0.01 mm to 0.04 mm in depth. The diffusion layers correspond to the boride regions 11B and 12B shown in FIG.

Image of the crystal layer map:
FIG. 5 is a crystal layer map in the cross section of the test piece after the immersion treatment. As shown in FIG. 5, _TiB2 precipitates 21 and TiB precipitates 22 are formed on the outermost surface of the test piece. Also shown in FIG. 5 is the measurement position 23 at which the hardness measurement was performed. The compound layer in which the precipitates 21 and 22 are formed is a region from the surface to a depth of about 0.01 mm. A region with a depth of 0.01 mm to 0.04 mm is a diffusion layer in which boron is diffused.

When the mechanical parts are subjected to the above-described boron immersion treatment, the compound layer must be removed by grinding or the like. When the hardness required for the product surface of the mechanical part is 650 HV, it can be seen from FIG. 1 that sufficient hardness can be obtained on the surface of the mechanical part after the compound layer is removed as described above.

Investigation of boron concentration on the surface of boride region:
FIG. 6 is a graph showing the relationship between boron concentration and Vickers hardness in test pieces. The horizontal axis of FIG. 6 indicates the boron concentration, and the vertical axis indicates the Vickers hardness. FIG. 6 is created based on the data in FIGS. 3 and 4. FIG.

As can be seen from FIG. 6, the hardness is improved in proportion to the increase in boron concentration. To obtain a hardness of 650 HV, a boron concentration of about 4% by mass is required. By the boron immersion treatment used in the method of manufacturing the mechanical component according to the present embodiment described above, it was possible to infiltrate the above 4% by mass or more of boron into the titanium alloy. As a result, it was possible to harden the surface and the inside of the machine part made of titanium alloy.

It should be considered that the embodiments and examples disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the meaning and range of equivalents of the scope of the claims.

Reference Signs List 1 deep groove ball bearing, 11 outer ring, 11A outer ring raceway surface, 11B, 12B boride region, 12 inner ring, 12A inner ring raceway surface, 13 ball, 13A ball rolling surface, 14 retainer, 21, 22 precipitates, 23 measurement position .

Claims (4)

A mechanical part made of a titanium alloy and having a surface layer,
the surface layer comprises a boron-infiltrated boride region;
the boron concentration in the surface of the boride region is 4% by mass or more and 10% by mass or less;
The boride region is a region in which boron has penetrated into the crystal of the titanium alloy,
A mechanical component, wherein the boride region is exposed on the outermost surface of the surface layer . 2. The mechanical component according to claim 1, wherein said surface has a hardness of 650 HV or more and 1200 HV or less. 3. The mechanical component according to claim 1, wherein the boride region has a depth of 0.02 mm or more and 0.03 mm or less from the surface. The mechanical component according to any one of claims 1 to 3, wherein the titanium alloy is an α+β type titanium alloy.

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