ACTIVE METAL PARTICLE SURFACE MODIFICATION METHOD, AND TITANIUM PARTICLES OR TITANIUM ALLOY PARTICLES

Abstract

Active metal particles in which the surface layer is hardly oxidized and a method for producing the active metal particles is provided. In the method for modifying the surface of active metal particles, heat is generated by moving active metal powder in a fluid, and the surface layer of the active metal particles is reacted with an arbitrary component in the fluid by the heat to modify the surface layer. Preferably, moving the active metal powder draws a substantially circular orbit while vibrating. A vibrating mill is preferably used when making such movement with respect to the active metal powder. Then, the powder obtained by the surface modification has a nitrogen-containing coating as a surface layer with a thickness more than 1 nm and less than or equal to 6 nm. The powder has a fluidity in the range of 25 seconds/50 g or more and 45 seconds/50 g or less.

Claims

1. A method for modifying a surface of active metal particles, comprising: generating heat by moving an active metal powder in a fluid; and reacting a surface layer of active metal particles in the active metal powder with an arbitrary component in the fluid by the heat to modify the surface layer.

2. The method for modifying the surface of the active metal particles according to claim 1, wherein the driving force for moving the active metal powder is vibration.

3. The method for modifying the surface of the active metal particles according to claim 1, wherein moving the active metal powder is moving the active metal powder drawing a substantially circular orbit while vibrating.

4. The method for modifying the surface of the active metal particles according to claim 1, wherein moving the active metal powder is moving the active metal powder for a collision of the active metal particles.

5. The method for modifying the surface of the active metal particles according to claim 1, wherein the heat is frictional heat.

6-11. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 It is a diagram showing an example of EELS lines used in measuring the nitride coating thickness in the titanium alloy particles in the titanium alloy powder according to working examples and comparative examples.

[0016] FIG. 2 It is a diagram showing an example of an element concentration profile used in measuring the nitride coating thickness in the titanium alloy particles in the titanium alloy powder according to working examples and comparative examples.

MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, working examples and comparative examples are shown in order to explain the present invention in more detail, but the present invention is not limited to these working examples.

Working Example 1

1. Preparation of Ti-6Al-4V Powder

[0018] First, a Ti-6Al-4V powder (hereinafter referred to as “titanium alloy powder”) was prepared by a gas atomization method disclosed in Japanese Unexamined Patent Application Publication No. H10-204507, and the titanium alloy powder was collected in a mill-pot (MB-1 manufactured by CHUO KAKOHKI CO.LTD.) having an internal volume of 3.4 L in an argon-atmosphere. Next, the inside of the mill pot was replaced with nitrogen, and then the mill pot was set in a vibrating mill (MB-1 manufactured by CHUO KAKOHKI CO.LTD.). Then, the vibration mill was operated for 90 minutes under the condition of a frequency of 1200 rpm, the vibration-crushing process was performed on the titanium alloy powder. Thereafter, the titanium alloy powder after the vibration-crushing process was classified according to the method described in JIS K 0069 using a sieve net having a mesh size of 20 μm and 45 μm, thereby obtaining a titanium alloy powder having a particle size of 20 μm to 45 μm of the purpose. The titanium alloy powder having a particle size of 20 μm or less was subjected to a small gas flame ignition test.

2. Measurement of Physical Properties of Titanium Alloy Powder

[0019] (1) Measurement of Oxygen and Nitrogen Content

[0020] The oxygen content and nitrogen content of the titanium alloy powder having a particle size of 20 μm to 45 μm obtained as described above was measured according to the methods described in JIS H1620 and JIS H 1612, and the oxygen content was 680 ppm and the nitrogen content was 160 ppm.

[0021] (2) Measurement of Nitride Coating Thickness

[0022] (2-1)

[0023] The titanium alloy powder having a particle size of 20 μm to 45 μm obtained as described above was processed into a plate-shaped section having a thickness of 100 nm using a focused ion beam (FIB) apparatus. Then, the section was set in a transmission electron microscope (TEM) (JEM-2100F manufactured by JEOL Ltd.), and electron beam energy-loss spectroscopy (EELS) analysis was performed while increasing the measured depth by 2 nm for a TEM image of 1 million times the section to obtain a EELS line as shown in FIG. 1. Then, the element concentration profile shown in FIG. 2 was obtained from this EELS line (Note that the element concentration profile in the FIG. 1 was merely exemplary.). As shown in the FIG. 1, in this elemental concentration profile, the titanium concentration, the oxygen concentration and the nitrogen concentration are plotted against the measured depth (the titanium concentration was based on the intensity at 454 eV (Ti-2p), the nitrogen concentration was based on the intensity at 397 eV (N-1s), the oxygen concentration was based on the intensity at 530 eV (O-1s)). Then, the difference in the measured depth of two points corresponding to the half value of the maximum nitrogen concentration value in the nitrogen concentration curve of the element concentration profile was measured, and the difference was defined as the coating thickness of the nitride coating. The thickness of the nitride coating of the titanium alloy particles in the titanium alloy powder was 4 nm. Further, it was clarified from the above-described element concentration profile that an oxide coating of 4 nm was formed on the nitride coating.

[0024] (3) Fluidity Measurement

[0025] The fluidity of the titanium-alloy powder having a particle size of 20 μm to 45 μm obtained as described above was measured based on “JIS Z2502:2012 Metal Powder-Fluidity Measuring Methods”, and the fluidity was 31.9 sec/50 g.

[0026] (4) Small Gas Flame Ignition Test

[0027] When a small gas flame ignition test (Fire service act second class hazardous substance test) was performed on each of a titanium alloy powder having a particle size of 20 μm to 45 μm and a titanium alloy powder having a particle size of 20 μm or less, none of the titanium alloy powders ignited.

Working Example 2

1. Preparation of Ti-6Al-4V Powder

[0028] First, a Ti-6Al-4V powder (hereinafter referred to as “titanium alloy powder”) was prepared by a gas atomization method disclosed in Japanese Unexamined Patent Application Publication No. H10-204507, and the titanium alloy powder was transferred to a mill pot of a vibrating mill (FV-20 manufactured by CHUO KAKOHKI CO.LTD.) in an argon-atmosphere. Next, after replacing the inside of the mill pot with argon, the vibration mill was operated for 118 minutes under the condition of a frequency of 1200 rpm (at this time, in order to prevent the change in the reaction rate due to the temperature change during the surface treatment, the temperature adjustment was carried out so that the temperature of the entire powder was constant). Thereafter, the nitrogen gas was rapidly charged into the inside of the mill pot, and the same vibration mill was operated again under the same conditions for 2 minutes. Then, the titanium alloy powder in the mill pot was classified into three fractions having a particle size of 20 μm to 45 μm, a particle size of 45 to 105 μm, and a particle size of 15 μm to 52 μm according to the methods described in JIS K 0069 using a sieve net to obtain a titanium alloy powder of the purpose.

2. Measurement of Physical Properties of Titanium Alloy Powder

[0029] (1) Measurement of Oxygen and Nitrogen Content

[0030] The oxygen content and nitrogen content of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the oxygen content was 700 ppm and the nitrogen content was 130 ppm.

[0031] (2) Measurement of Nitride Coating Thickness

[0032] Titanium alloy particles in a titanium alloy powder having a particle size of 20 μm to 45 μm, titanium alloy particles in a titanium alloy powder having a particle size of 45 to 105 μm, and titanium alloy particles in a titanium alloy powder having a particle size of 15 urn to 52 μm were measured according to the same method as that shown in the working example 1, and the nitride coating thickness of titanium alloy particles in any titanium alloy powder was 1 nm.

[0033] (3) Fluidity Measurement

[0034] The fluidity of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the fluidity was 37.3 sec/50 g.

Working Example 3

1. Preparation of Ti-6Al-4V Powder

[0035] Except that the first operation period of the vibration mill was replaced with 30 minutes and the second operation period of the same vibration mill was replaced with 5 minutes, a titanium alloy powder of the purpose was obtained in the same manufacturing method as the manufacturing method of the titanium alloy powder shown in the working example 2.

2. Measurement of Physical Properties of Titanium Alloy Powder

[0036] (1) Measurement of Oxygen and Nitrogen Content

[0037] The oxygen content and nitrogen content of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the oxygen content was 660 ppm and the nitrogen content was 170 ppm.

[0038] (2) Measurement of Nitride Coating Thickness

[0039] The thickness of the nitride coating of the titanium alloy particles in the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the thickness was 3 nm.

[0040] (3) Fluidity Measurement

[0041] The fluidity of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the fluidity was 35.3 sec/50 g.

Working Example 4

1. Preparation of Ti-6Al-4V Powder

[0042] Except that the first operation period of the vibration mill was replaced with 105 minutes, the second operation period of the same vibration mill was replaced with 15 minutes, a titanium alloy powder of the purpose was obtained in the same manufacturing method as the manufacturing method of the titanium alloy powder shown in the working example 2.

2. Measurement of Physical Properties of Titanium Alloy Powder

[0043] (1) Measurement of Oxygen and Nitrogen Content

[0044] The oxygen content and nitrogen content of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the oxygen content was 690 ppm and the nitrogen content was 250 ppm.

[0045] (2) Measurement of Nitride Coating Thickness

[0046] The thickness of the nitride coating of the titanium alloy particles in the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the thickness was 6 nm.

[0047] (3) Fluidity Measurement

[0048] The fluidity of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the fluidity was 33.3 sec/50 g.

Comparative Example 1

1. Preparation of Ti-6Al-4V Powder

[0049] A Ti-6Al-4V powder (hereinafter referred to as “titanium alloy powder”) was prepared by the gas atomization method disclosed in Japanese Unexamined Patent Application Publication No. H10-204507, and the obtained titanium alloy powder was classified according to the method described in HS K 0069 using a sieve net having a mesh size of 20 μm and 45 μm, thereby obtaining a titanium alloy powder having a particle size of 20 μm to 45 μm of the purpose. The titanium alloy powder having a particle size of 20 μm or less was subjected to a small gas flame ignition test.

2. Measurement of Physical Properties of Titanium Alloy Powder

[0050] (1) Measurement of Oxygen and Nitrogen Content

[0051] The oxygen content and nitrogen content of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the oxygen content was 790 ppm and the nitrogen content was 30 ppm.

[0052] (2) Measurement of Nitride Coating Thickness

[0053] The thickness of the nitride coating of the titanium alloy particles in the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the thickness of the titanium alloy powder was 0 nm.

[0054] (3) Fluidity Measurement

[0055] The fluidity of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the titanium alloy powder did not flow.

[0056] (4) Small Gas Flame Ignition Test

[0057] A small gas flame ignition test (Fire service act second class dangerous substance test) was performed on a titanium alloy powder having a particle size of 20 μm or less according to the same method as that shown in the working example 1, and the titanium alloy powder was ignited.

Comparative Example 2

1. Preparation of Ti-6Al-4V Powder

[0058] A Ti-6Al-4V powder (hereinafter referred to as “titanium alloy powder”) was prepared by a gas atomization method disclosed in Japanese Unexamined Patent Application Publication No. H10-204507, and the titanium alloy powder was collected in a mill-pot (MB-1 manufactured by CHUO KAKOHKI CO.LTD.) having an internal volume of 3.4 L in an open atmosphere. Next, the mill pot was set in a vibration mill (MB-1 manufactured by CHUO KAKOHKI CO.LTD.), and the vibration mill was operated at a frequency of 1200 rpm for 90 minutes to perform a vibration crushing process on the titanium-alloy powder. Thereafter, the titanium alloy powder after the vibration-crushing process was classified according to the method described in HS K 0069 using a sieve net having a mesh size of 20 μm and 45 μm, thereby obtaining a titanium alloy powder having a particle size of 20 μm to 45 μm of the purpose. The titanium alloy powder having a particle size of 20 μm or less was subjected to a small gas flame ignition test.

2. Measurement of Physical Properties of Titanium Alloy Powder

[0059] (1) Measurement of Oxygen and Nitrogen Content

[0060] The oxygen content and nitrogen content of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the oxygen content was 1080 ppm and the nitrogen content was 50 ppm.

[0061] (2) Measurement of Nitride Coating Thickness

[0062] The thickness of the nitride coating of the titanium particles in the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the thickness of the nitride coating was 0 nm.

[0063] (3) Fluidity Measurement

[0064] The fluidity of the titanium alloy powder having a particle size of 20 μm to 45 μm was measured according to the same method as that shown in the working example 1, and the fluidity was 32.4 sec/50 g.

[0065] (4) Small Gas Flame Ignition Test

[0066] A small gas flame ignition test (Fire service act second class dangerous substance test) was performed on a titanium alloy powder having a particle size of 20 μm or less according to the same method as that shown in the working example 1, and the titanium alloy powder was ignited.

[0067] The results obtained in the working examples 1-4 and the comparative examples 1-3 are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 particle oxygen nitrogen nitride Small gas size content content coating Fluidity flame (μm) (ppm) (ppm) thickness (nm) (second/50 g) ignition test Working 20-45 680 160 4 31.9 Not ignited example 1 −20 — — — — Not ignited 20-45 700 130 1 37.3 — Working  45-105 — — 1 — — example 2 15-52 — — 1 — — Working 20-45 660 170 3 35.3 — example 3 Working 20-45 690 250 6 33.3 — example 4 Comparative 20-45 790  30 0 Not flowed — example 1 −20 — — — — ignited Comparative 20-45 1080   50 0 32.4 — example 2 −20 — — — — ignited

Working Example 5

[0068] The titanium alloy powder prepared in the working example 3 and the titanium alloy powder prepared in the comparative Example 2 were heated at 60° C. for 4 hours respectively, to verify the antioxidant effect of the nitride coating. As a result, in the titanium alloy powder prepared in the comparative example 2, the oxygen content was increased by 160 ppm, whereas in the titanium alloy powder prepared in the working example 3, the oxygen content was increased only by 130 ppm, and the oxygen increase was decreased by 20% compared to the titanium alloy powder prepared in the comparative example 2. From this result, the formation of the nitride coating was effective in inhibiting the oxidation of the titanium alloy powder, it is expected to be able to effectively inhibit the increase in the oxygen content during recycling of the titanium alloy powder used for lamination molding.

SUMMARY

[0069] As is apparent from Table 1, the titanium alloy powders according to the working examples 1-4 have a higher nitrogen content than the titanium alloy powders according to the comparative examples 1 and 2, and the titanium alloy particles are covered with a nitride coating of several nm. Therefore, the titanium alloy powders according to the working examples 1-4 are less likely to be oxidized. Incidentally, the titanium alloy powders according to the working examples 1-4 contained oxygen of 650-700 ppm, this is because 400 ppm of oxygen that the titanium alloy powder originally had, and 300 ppm of oxygen added as an oxide coating is considered to have been combined. In addition, the titanium alloy powders of 20 μm to 45 μm according to the working examples 1 to 4 exhibits high fluidity, and can be applied to the lamination molding method. Furthermore, the titanium alloy powders according to the working examples 1-4 does not ignite in the small gas flame ignition test (Fire service act second class dangerous substance test) even when the particle size becomes 20 μm or less. Therefore, the titanium alloy powders according to the working examples 1-4 can be handled with ordinary attention. The titanium alloy powders according to the working examples 1-4 has the above-described properties, and is not previously present.

[0070] The thickness of the nitride coating of the titanium alloy powders according to the working examples 1-4 substantially matches the theoretical value obtained from the following Formula (I), and is about twice the theoretical value obtained from the following Formula (II). Therefore, it is presumed that the nitride coating of the titanium-alloy powders according to the working examples 1-4 is mainly formed of Ti.sub.2N.

d=1/3ΔC.sub.N(d.sub.50/2)(M.sub.Ti2N/M.sub.N(ρ.sub.Ti/ρ.sub.Ti2N)  (I)

d=1/3ΔC.sub.N(d.sub.50/2)(M.sub.TiN/M.sub.N)(ρ.sub.Ti/ρ.sub.TiN)  (II)

[0071] In the two formulae (I) and (II), “d” is the thickness of the nitride coating, “ΔC.sub.N” is the increased amount of nitrogen content with respect to the untreated powder, “d.sub.50” is the median diameter (50% particle diameter) of the titanium alloy powder, “M.sub.Ti2N” is the molecular weight of Ti.sub.2N, “M.sub.TiN” is the molecular weight of TiN, “M.sub.N” is the atomic weight of N, “ρ.sub.Ti” is the density of Ti, “ρ.sub.Ti2N” is the density of Ti.sub.2N, and “ρ.sub.TiN” is the density of TiN.