Titanium material, titanium container, and method for producing titanium material

Abstract

Provided are a titanium material, a titanium container, and a method for producing the titanium material, which have not existed hitherto. This titanium material comprises a titanium carbide layer on a surface thereof. The thickness of the titanium carbide layer is at least 5 μm and the arithmetic average roughness (Ra) of the surface of the titanium carbide layer is at least 0.90 μm. When the surface of the titanium carbide layer is observed by an optical microscope, the average of the equivalent circle diameters of regions in which the orientations of twin crystals are aligned in crystal grains including the twin crystals is at least 563.7 μm.

Description

Titanium material, titanium container, and method for manufacturing titanium material

[0001] The present invention relates to a titanium material, a titanium container, and a method for manufacturing a titanium material.

[0002] The present applicant has filed a patent application relating to a titanium vacuum insulated double container as disclosed in, for example, Patent Document 1.

[0003] Patent No. 5297436

[0004] The present invention was completed as a result of further research and development by the inventors, who discovered conditions under which the surface of a titanium material has reduced gloss, is resistant to fingerprint smudges, and has a refined texture with a gray base. The object of the present invention is to provide a novel titanium material, a titanium container, and a method for manufacturing a titanium material.

[0005] The gist of the present invention will be explained with reference to the accompanying drawings.

[0006] A first aspect of the present invention relates to a titanium material having a titanium carbide layer on its surface, characterized in that the titanium carbide layer has a thickness of 5 μm or more and an arithmetic mean roughness (Ra) of the surface of the titanium carbide layer of 0.90 μm or more, and the average equivalent circular diameter of regions in which the twins in crystal grains containing twins are aligned when the surface of the titanium carbide layer is observed with an optical microscope is 563.7 μm or more.

[0007] A second aspect of the present invention relates to the titanium material of the first aspect, characterized in that the titanium carbide layer has a thickness of 10 μm or more.

[0008] A third aspect of the present invention relates to the titanium material of the first aspect, wherein the titanium carbide layer has an arithmetic mean roughness (Ra) of the surface of 1.70 μm or more.

[0009] A fourth aspect of the present invention relates to the titanium material of the second aspect, characterized in that the titanium carbide layer has an arithmetic mean roughness (Ra) of the surface of 1.70 μm or more.

[0010] A fifth aspect of the present invention relates to the titanium material of any one of the first to fourth aspects, wherein the titanium carbide layer has an average equivalent circular diameter of 575.4 μm or more in the region where the twin crystals are aligned.

[0011] A sixth aspect of the present invention relates to a titanium container according to any one of the first to fourth aspects, characterized in that the container has the titanium carbide layer on its outer surface.

[0012] A seventh aspect of the present invention relates to a titanium container according to the fifth aspect, characterized in that the container has the titanium carbide layer on its outer surface.

[0013] An eighth aspect of the present invention relates to a method for producing a titanium material having a titanium carbide layer on its surface, comprising: a first heat treatment step of vacuum-heating the titanium material in a carbon-containing atmosphere to a first temperature at which titanium transitions from the α phase to the β phase, and then cooling the titanium material to a temperature below the first temperature; and a polishing step of polishing the surface of the titanium material after the first heat treatment step.

[0014] A ninth aspect of the present invention relates to the method for producing a titanium material according to the eighth aspect, characterized in that after the polishing step, the titanium material is vacuum-heated in a state where it is stored in a lidded container or in a carbon-free atmosphere to a second temperature at which titanium undergoes a transition from the α phase to the β phase, and then cooled to a temperature below the second temperature.

[0015] A tenth aspect of the present invention relates to the method for producing a titanium material according to the ninth aspect, characterized in that the vacuum heating in the first heat treatment step and the second heat treatment step is carried out for 15 to 40 minutes.

[0016] An eleventh aspect of the present invention relates to a method for producing a titanium material according to any one of the eighth to tenth aspects, characterized in that the first heat treatment step is repeated once or multiple times after the first heat treatment step and before the polishing step.

[0017] A twelfth aspect of the present invention relates to the method for producing a titanium material according to any one of the eighth to tenth aspects, characterized in that the titanium material is a container, and the heat treatment step is carried out by placing the container on a flat surface with its opening facing downwards so as to close the opening.

[0018] A thirteenth aspect of the present invention relates to the method for producing a titanium material according to the eleventh aspect, characterized in that the titanium material is a container, and the heat treatment step is carried out by placing the container on a flat surface with its opening facing downwards so as to close the opening.

[0019] The present invention is configured as described above, and thus provides a titanium material, a titanium container, and a method for manufacturing a titanium material that have never been seen before.

[0020] 4 is a schematic explanatory cross-sectional view of the present embodiment, a table for comparing the steps of a comparative example and an experimental example, comparative photographs of the appearance of a comparative example and an experimental example, results of X-ray diffraction measurements of a comparative example and an experimental example, an enlarged view of the dashed line portion in FIG. 4, and photographs showing examples of colonies of a comparative example and an experimental example.

[0021] A preferred embodiment of the present invention will be briefly described below, illustrating the operation of the present invention with reference to the drawings.

[0022] The titanium material according to the present invention can be used, for example, in titanium containers. In this case, the outer surface of the container can have a subdued gloss, be resistant to fingerprint smudges, and have an elegant texture with a gray base.

[0023] That is, although details will be described later, it was confirmed that when the titanium carbide layer has a thickness of 5 μm or more, an arithmetic mean roughness (Ra) of 0.90 μm or more, and an average equivalent circular diameter of the region where the twin crystals are aligned is 563.7 μm or more, the gloss is suppressed (a matte finish is imparted), fingerprint smudges are less likely to adhere, and a surface structure with a gray base is obtained.

[0024] Furthermore, the manufacturing method disclosed in Patent Document 1 has problems such as low reproducibility, unstable quality, and low yield, but the inventors have discovered a manufacturing method that can produce the above titanium material with good reproducibility.

[0025] Specific embodiments of the present invention will be described with reference to the drawings.

[0026] In this example, the container is made of titanium and has a titanium carbide layer on the outer surface.

[0027] Specifically, as shown in Fig. 1, this embodiment is a vacuum insulated double container (tumbler) used to store beverages, and is composed of a cylindrical outer cylinder 1 with a bottom and a cylindrical inner cylinder 2 with a bottom disposed within the outer cylinder 1. The space between the outer cylinder 1 and the inner cylinder 2 is a vacuum insulated space. In the figure, reference numeral 3 denotes a brazing material (titanium brazing) for sealing, and 4 denotes a sealing plate.

[0028] A titanium carbide layer is provided on at least the outer surface of the double container (outer cylinder 1).

[0029] The titanium carbide layer has a thickness of 5 μm or more and an arithmetic mean roughness (Ra) of the surface of 0.90 μm or more. When the surface of the titanium carbide layer is observed with an optical microscope, the average equivalent circular diameter of regions (colonies) in which the twins in the crystal grains containing twins are aligned is 563.7 μm or more.

[0030] The double container according to this embodiment can be manufactured by subjecting an outer tube 1 and an inner tube 2 made of commercially pure titanium (e.g., titanium having a chemical composition that falls under JIS Class 1) to a predetermined processing. Specifically, the outer tube 1 and the inner tube 2 are integrated by welding their opening-side ends together, and then the double container can be manufactured by sequentially carrying out the following steps A to E.

[0031] Step A: The double container is placed in a vacuum furnace with a heating function and subjected to vacuum sealing treatment.

[0032] Specifically, a double-walled container with its neck welded together is placed on a flat surface with its opening facing downwards (so as to close the opening), and brazing filler metal 3 is placed around a degassing port 5 at the bottom of the outer tube 1, with a sealing plate 4 placed on the brazing filler metal 3. The container is then placed in a lidded container (made of stainless steel) and placed in a vacuum furnace. As with the known method disclosed in Patent Document 1 and other publications, the vacuum furnace is heated and depressurized to evacuate the space between the outer tube 1 and the inner tube 2 and melt the brazing filler metal 3, thereby sealing the space while maintaining a vacuum state with the brazing filler metal 3 and the sealing plate 4, forming a vacuum insulation space. A cooling process is then performed.

[0033] The degree of vacuum in the vacuum furnace during processing was 10 －３ Torr ~ 10 －４ The pressure is about Torr, the heating temperature is higher than the temperature at which titanium transitions from the α phase to the β phase (about 880°C) (about 1050°C in this example), and the heating time is about 15 to 40 minutes. Cooling is performed by stopping the heating and allowing natural cooling to occur until the temperature drops below 700°C, then introducing nitrogen gas into the furnace to return the pressure to normal and cool it to room temperature.

[0034] The container is heated above the temperature at which titanium transitions from the α phase to the β phase, and then cooled below that temperature, resulting in the formation of unevenness on the surface of the container, resembling that of ceramic, giving it a unique appearance. The entire double-walled container is nitrided using nitrogen gas. The reason for storing the container in a lidded container during the vacuum sealing process is to prevent deterioration of the brazing material due to nitrogen gas. Therefore, if a gas that does not deteriorate the brazing material is used, the process can be performed without storing the container in a lidded container.

[0035] Step B: A vacuum heat treatment is carried out to form a titanium carbide layer.

[0036] This vacuum heat treatment is carried out without placing the double container in a container with a lid, but rather in a state where it is exposed to the furnace atmosphere where carbon is present (as in step A, it is carried out by placing it on a flat surface with the opening facing downwards so that the opening is closed).

[0037] For example, by using an appropriate means such as disposing carbon powder in a vacuum furnace or introducing a small amount of carbon gas into the furnace, the atmosphere in the furnace is made carbon-containing during heating, and the vacuum furnace is heated and depressurized, and then cooled. The degree of vacuum, heating temperature, and heating time are the same as in step A, and cooling is also carried out in the same manner as in step A.

[0038] By this vacuum heating treatment, titanium undergoes the following transition: α phase (hcp structure) → β phase (bcc structure) → α phase (hcp structure); at this time, when dense hcp structure changes to sparse bcc structure, carbon atoms in the atmosphere enter the gaps in the bcc structure, and when returning to hcp structure again, the carbon atoms that entered are pushed out, and the pushed out carbon atoms accumulate on the surface (the outer surface of outer cylinder 1 that is exposed to the carbon-existing atmosphere), forming a titanium carbide layer.

[0039] Step C: The same vacuum heating treatment as in step B is carried out once or multiple times as necessary (in this example, once).

[0040] Step D: The outer surface of the double container is polished.

[0041] Specifically, the outer surface is polished using an abrasive material with a lathe.

[0042] By performing the polishing process, titanium containers with a unique texture formed on the surface with unevenness can be produced with good reproducibility (good yield) (the manufacturing method in Patent Document 1 does not include a polishing step, which is different from the present embodiment).

[0043] Step E: Vacuum heat treatment is performed with the double container housed in a container with a lid (similar to step A, the container is placed on a flat surface with the opening facing downwards so that the opening is closed.) The container is housed in a container with a lid so that the vacuum heat treatment is performed in an atmosphere with as little carbon present as possible; if the inside of the furnace can be made into a carbon-free atmosphere, the treatment may be performed without housed in the double container with a lid.

[0044] This vacuum heating treatment further promotes the growth of twins inside (twin crystals also grow in steps B and C), and when the grown twin crystals reach the surface, the surface is further roughened, making it possible to achieve a configuration with an arithmetic mean roughness (Ra) of 0.90 μm or more and an average equivalent circular diameter of the colonies of 563.7 μm or more. The degree of vacuum, heating temperature, heating time, and cooling are the same as in step A, etc. In this example, the heating temperature in steps B and C is the same as that in step E, but different temperatures may also be used. Similarly, the heating time in steps B and C may be different from that in step E.

[0045] A titanium vacuum insulated double-layer container having the above-described configuration can be manufactured by the above steps A to E. Note that although this example describes a titanium container, the present invention can be similarly applied to other titanium products, such as when a titanium carbide layer is provided on the main surface (widest surface) of a plate material, and is not limited to containers.

[0046] Furthermore, it is possible to produce titanium containers with a unique texture with good reproducibility by performing at least steps A, B, and D. However, it was confirmed that by performing the step for forming the titanium carbide layer multiple times (performing step C) in addition to steps A, B, and D, and also performing step E for promoting the growth of twin crystals, it is possible to achieve a more pleasant feel, a matte finish, and a gray-based appearance.

[0047] Specifically, as shown in FIG. 2, a comparative example produced by sequentially performing the above steps A, B, and D (excluding steps C and E) was compared with an experimental example produced by sequentially performing the above steps A to E.

[0048] Figure 3 shows photographs of the appearance of the comparative example and the experimental example. It can be seen that the experimental example has a lower gloss than the comparative example and is primarily gray rather than black. It has also been confirmed that fingerprints are less likely to stick to the experimental example (are less noticeable) than the comparative example.

[0049] Figures 4 and 5 show the results of X-ray diffraction measurements of the comparative example and the experimental example. From these results, it can be confirmed that a titanium carbide layer is formed on the surface (the outer surface of the outer cylinder 1) and that twinning occurs in the [10-12] plane, as the peak corresponding to the [10-12] plane is shifted to the left (see Figure 5). The thickness of the titanium carbide layer in the comparative example is approximately 5 μm, while the thickness of the titanium carbide layer in the experimental example is approximately 10 μm. The hue varies depending on the thickness of the titanium carbide layer on the surface, and the surface roughness varies depending on the degree of twin growth. In the experimental example, the titanium carbide layer became thicker through step C, and the twins grew further through step E, which is thought to have resulted in a more favorable hue, matte finish, and feel.

[0050] Table 1 shows the colony size measurements for the Comparative Example and Experimental Example, and Table 2 shows the surface roughness (arithmetic mean roughness (Ra)) measurements. Using a 3 mm × 7 mm sample, the areas of colonies visible under an optical microscope were calculated using image processing software and converted into equivalent circular diameters (the diameter when a certain region is replaced with a perfect circle of the same area), and average values ​​were calculated. An example of a colony observed under an optical microscope is shown in Figure 6 (the magnification is the same for the Comparative Example and Experimental Example in Figure 6). Surface roughness was measured in accordance with JIS B0633 (2001) using a surface roughness measuring instrument (SURFCOM 1500DX 3DF) manufactured by ACCRETECH (Tokyo Seimitsu). The measurement conditions were: measurement length: 4.0 mm, reference length (cutoff value): 0.8 mm, measurement magnification: 2000x, probe radius: 2 μm, measurement speed: 0.3 mm / s, cutoff type: Gaussian, tilt correction: least squares linear correction. Note that "rolled material" in the table indicates the equivalent circular diameter and surface roughness of the rolled material (plate material) of commercially pure titanium before being processed into a cylindrical shape.

[0051]

[0052]

[0053] From the above comparison, it can be confirmed that the equivalent circular diameter and Ra of both the Comparative Example and the Experimental Example are larger than those of the rolled material, and that the equivalent circular diameter (average diameter) and Ra of the Experimental Example are both larger than those of the Comparative Example. Although the average colony diameter (563.7 μm) and Ra (0.90 μm) of the Comparative Example still result in a favorable appearance, when the values ​​of the Comparative Example are exceeded (for example, when the average colony diameter of 575.4 μm and Ra of 1.70 μm of the Experimental Example), an even better appearance is considered to be presented, and steps C and E are considered to be necessary to obtain the values ​​of the Experimental Example.

[0054] Since this embodiment is configured as described above, it is an unprecedented titanium container that has a subdued gloss, is resistant to fingerprint stains, and has an elegant texture with a gray base.

Claims

1. A titanium material having a titanium carbide layer on its surface, the titanium carbide layer having a thickness of 5 μm or more and a surface arithmetic mean roughness (Ra) of 0.90 μm or more, and the average equivalent circular diameter of areas in which the twins in crystal grains containing twins are aligned as confirmed when the surface of the titanium carbide layer is observed with an optical microscope is 563.7 μm or more.

2. The titanium material according to claim 1, wherein said titanium carbide layer has a thickness of 10 μm or more.

3. The titanium material according to claim 1, wherein the titanium carbide layer has a surface arithmetic mean roughness (Ra) of 1.70 μm or more.

4. The titanium material according to claim 2, wherein the titanium carbide layer has a surface arithmetic mean roughness (Ra) of 1.70 μm or more.

5. A titanium material as claimed in any one of claims 1 to 4, characterized in that the average equivalent circular diameter of the region in which the twin crystals are aligned in the titanium carbide layer is 575.4 µm or more.

6. A titanium container made using the titanium material according to any one of claims 1 to 4, characterized in that the titanium container has the titanium carbide layer on its outer surface.

7. A titanium container made using the titanium material according to claim 5, characterized in that the titanium container has the titanium carbide layer on its outer surface.

8. A method for producing a titanium material having a titanium carbide layer on its surface, comprising: a first heat treatment step of vacuum heating the titanium material in a carbon-present atmosphere to a first temperature at which titanium transitions from the α phase to the β phase, and then cooling the titanium material to a temperature lower than the first temperature; and a polishing step of polishing the surface of the titanium material after the first heat treatment step.

9. A method for producing titanium material as described in claim 8, further comprising a second heat treatment step of vacuum heating the titanium material after the polishing step, in a state in which the titanium material is stored in a covered container or in a carbon-free atmosphere, to a second temperature at which titanium transitions from the alpha phase to the beta phase, and then cooling the titanium material to a temperature lower than the second temperature.

10. A method for producing titanium material according to claim 9, characterized in that the vacuum heating in the first heat treatment step and the second heat treatment step is carried out for 15 to 40 minutes.

11. A method for producing a titanium material as set forth in any one of claims 8 to 10, characterized in that the first heat treatment step is repeated once or a plurality of times after the first heat treatment step and before the polishing step.

12. A method for manufacturing a titanium material according to any one of claims 8 to 10, characterized in that the titanium material is a container, and the heat treatment step is carried out by placing the titanium material on a flat surface with an opening facing down so as to close the opening.

13. A method for producing titanium material as claimed in claim 11, characterized in that the titanium material is a container, and the heat treatment process is carried out by placing the titanium material on a flat surface with an opening facing down so as to close the opening.

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