Powder for sintering

Abstract

This powder for sintering contains: a primary powder composed of aluminum or an aluminum alloy; and an oxide of at least one rare earth metal element selected from scandium, yttrium, and lanthanoid elements. This powder (1) for sintering is composed of a mixed powder having: particles (2) of a primary powder composed of aluminum or an aluminum alloy; and additive particles (3) composed of an oxide of at least one rare earth metal element selected from scandium, yttrium, and lanthanoid elements, wherein at least some of the additive particles (3) may adhere to the surface of the particles (2) of the primary powder.

Description

sintering powder

[0001] The present invention relates to a sintering powder having excellent sinterability. This application claims priority to Japanese Patent Application No. 2023-211202, filed on December 14, 2023, the contents of which are incorporated herein by reference.

[0002] Aluminum is used in heat sinks for equipment due to its light weight and good electrical and thermal conductivity, but it is a metallic material that has significant processing limitations due to the formation of a dense, strong oxide film on its surface that protects the interior. Conventionally, for casting materials, a method has been used in which components are joined by using flux (brazing filler metal) to destroy the surface oxide film and give the desired shape.

[0003] However, these methods have had the problem of being difficult to achieve sufficient precision and spatial resolution for heat exchange materials that require complex and precise shape control, such as pin, fin, and lattice shapes. In contrast, powder sintering allows for near-net-shape manufacturing, and the technology is expected to develop as a means of achieving complex shapes inexpensively. Even with powder sintering, aluminum remains a major constraint due to its difficulty in sintering due to the formation of an oxide film. Due to scale limitations, it is difficult to destroy the oxide film with flux, making it difficult to densify the structure.

[0004] In powder sintering, as typified by hot pressing, pressure is applied to the powder compact to improve the powder packing and promote sintering. However, additive manufacturing processes, which are attracting attention as a method for creating complex shapes with high precision, have a problem in that, in principle, it is difficult to apply techniques such as pressure.

[0005] In these methods, increasing the fluidity of the powder and improving its packing properties during spontaneous deposition are also important development factors. To achieve this, nanoparticles such as oxides have been added to the powder to interpose the nanoparticles between the powder particles. For example, a technique is known in which oxide nanoparticles such as silica or alumina are added to powders of titanium alloys or nickel alloys to coat the surfaces of the powder particles with the oxide nanoparticles (see Patent Documents 1, 2, and 3). Another technique is known in which nanostructures are precipitated on the surfaces of powder particles by thermal plasma treatment, thereby reducing the contact area between the powder particles and improving the fluidity of the powder (see Patent Document 2).

[0006] Japanese Patent Application Publication No. 2016-041850 Japanese Patent Application Publication No. 2019-112699 Japanese Patent Application Publication No. 2021-075784 US Patent Application Publication No. 2020 / 0399744 Chinese Patent Application Publication No. 111230098 Japanese Patent Application Publication No. 2021-134428 Japanese Patent Application Publication No. 2023-081771 Japanese Patent Application Publication No. 2022-177440

[0007] However, in the above-mentioned method, the oxide nanoparticles interposed between the metal particles tend to become foreign matter during sintering, and in cases where they cause problems in the process, it is difficult to apply the above-mentioned method.

[0008] On the other hand, for materials that require mechanical properties at high temperatures exceeding 1000°C, such as iron-based alloys, nickel-based alloys, and medium-entropy alloys, the formation of so-called oxide dispersion strengthened (ODS) alloys, which have improved tensile strength at high temperatures, is intentionally attempted. In this type of oxide dispersion strengthened alloy, a technique is known that utilizes the fact that oxide nanoparticles remain as foreign matter, and aims to improve strength at high temperatures by using the remaining foreign matter (see Patent Documents 4, 5, 6, and 7).

[0009] However, since there are few applications requiring heat resistance for aluminum-based materials with low melting points (the melting point of pure aluminum is 660.3°C), there is not much demand for oxide dispersion strengthened alloys as described above. Furthermore, oxide nanoparticles known for such applications do not function as fluxes in the sintering process and do not have the effect of destroying oxide films.

[0010] A prior art technique is also known in which silica nanoparticles are added to titanium alloy powder, and the silica is reduced by metallic titanium during sintering, resulting in a solid solution in the titanium structure, thereby reducing the risk of the silica remaining as foreign matter (see Patent Document 8).

[0011] The technical concept of Patent Document 8 utilizes the fact that the standard free energy of formation of silica is lower than that of titanium oxide. In other words, the technology is based on the fact that the oxide film on the titanium powder breaks during sintering, allowing the silica to come into contact with the titanium metal, i.e., the destruction of the oxide film on the titanium powder occurs relatively easily. However, this technology is also thought to be difficult to apply to aluminum, which has a strong oxide film.

[0012] Given the above background, it has been difficult to find benefits that outweigh the disadvantages of interposing oxide nanoparticles on the surface of powder particles in aluminum-based materials, which are difficult to sinter. Therefore, there is a need for a technology that can impart high sinterability by having aluminum powder particles and oxide nanoparticles coexist.

[0013] The present invention was devised in light of the above-mentioned problems, and its purpose is to provide a technology that can achieve both excellent sintered density and shape retention by incorporating oxide nanoparticles, which have traditionally been considered to have little benefit, into aluminum powder particles, which are known as a difficult-to-sinter material in that their oxide coating is difficult to destroy.

[0014] As a result of extensive investigations, the present inventors have found that it is possible to provide a sintering powder having the following aspects that can solve these problems, and have thus completed the present invention.

[0015] (Aspect 1) The sintering powder of aspect 1 according to the present invention is a sintering powder containing a main powder made of aluminum or an aluminum alloy and an oxide of one or more rare earth metal elements selected from scandium, yttrium, and lanthanoid elements, characterized in that the content of the oxide of the rare earth metal element relative to the total mass of the sintering powder is 0.02 mass% or more and 1.5 mass% or less.

[0016] (Aspect 2) In the sintering powder of Aspect 1, an oxide of the rare earth metal element may be present on the surface of the particles of the main powder. (Aspect 3) The sintering powder of Aspect 3 comprises a mixed powder having particles of a main powder made of aluminum or an aluminum alloy and additive particles made of an oxide of one or more rare earth metal elements selected from scandium, yttrium, and lanthanoid elements, the content of the oxide of the rare earth metal element relative to the total mass of the mixed powder being 0.02 mass% or more and 1.5 mass% or less, and at least a portion of the additive particles may be attached to the surface of the particles of the main powder.

[0017] (Aspect 4) In the sintering powder of any one of Aspects 1 to 3, the rare earth metal element may be one or more selected from the group consisting of praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these rare earth metal elements, one or more selected from the group consisting of praseodymium, samarium, gadolinium, dysprosium, and ytterbium may be used.

[0018] (Aspect 5) In the sintering powder of any one of Aspects 1 to 4, the particle diameter of the additive particles may be smaller than the particle diameter of the main powder. (Aspect 6) In the sintering powder of any one of Aspects 1 to 5, the volume-based 50% cumulative average particle diameter (median diameter D ５０ ) may be 20 μm or more and 65 μm or less.

[0019] The sintering powder of the present invention contains a main powder containing aluminum and an oxide of a rare earth metal element in an amount appropriate for this main powder. Therefore, when this sintering powder is sintered, at least a portion of the oxide of the rare earth metal element is reduced, and the rare earth metal element breaks the oxide film on the surface of the particles of the main powder and forms a eutectic with the aluminum on the surface of the particles of the main powder, thereby generating an appropriate amount of liquid phase on the surface of the particles of the main powder, but not in excess. This promotes bonding between the particles of the main powder, improves the sintered density, and maintains good shape retention after sintering.

[0020] Therefore, even when using a sintering powder whose main component is aluminum or an aluminum alloy, which is known to be a difficult-to-sinter material, it is possible to obtain a sintered body that has a high sintering density and is less likely to deviate from the desired shape.

[0021] 4A and 4B are respectively an EDS map image showing the distribution of oxygen obtained by an EDS detector in correspondence with the SEM image shown in FIG. 4A in Example 2-1; an EDS map image showing the distribution of samarium obtained by an EDS detector in correspondence with the SEM image shown in FIG. 4A in Example 2-1; an SEM image showing an example of a sintering powder obtained by an EDS detector in correspondence with the SEM image shown in FIG. 4A in Example 2-1; an SEM image showing an example of a sintering powder obtained by an EDS detector in correspondence with the SEM image shown in FIG. 5A in Example 3-5; an EDS map image showing the distribution of oxygen obtained by an EDS detector in correspondence with the SEM image shown in FIG. 5A in Example 3-5; an EDS map image showing the distribution of gadolinium obtained by an EDS detector in correspondence with the SEM image shown in FIG. 5A in Example 3-5; an SEM image showing an example of a sintering powder obtained by an EDS detector in correspondence with the SEM image shown in FIG. 4A in Example 3-5; 6A in Example 4-4. FIG. 6B is an EDS map image showing the distribution of oxygen obtained by an EDS detector in correspondence with the SEM image shown in FIG. 6A in Example 4-4. FIG. 6C is an EDS map image showing the distribution of dysprosium obtained by an EDS detector in correspondence with the SEM image shown in FIG. 6A in Example 4-4. FIG. 6D is a graph showing a differential thermal analysis curve of the sintering powder of Comparative Example 1-1. FIG. 6E is a graph showing a differential thermal analysis curve of the sintering powder of Comparative Example 4-1. FIG. 6F is a graph showing a differential thermal analysis curve of the sintering powder of Example 1-1. FIG. 6G is a graph showing a differential thermal analysis curve of the sintering powder of Example 2-1. FIG. 6H is a graph showing a differential thermal analysis curve of the sintering powder of Example 5-1. FIG. 6I is a partial cross-sectional view of a sintered body produced using the sintering powder of Comparative Example 1-1. FIG. 6I is a partial cross-sectional view of a sintered body produced using the sintering powder of Example 1-1. FIG. 6I is a partial cross-sectional view of a sintered body produced using the sintering powder of Example 2-1. FIG. 6I is a partial cross-sectional view of a sintered body produced using the sintering powder of Example 3-5. 18 is a partial cross-sectional view of a sintered body produced using the sintering powder of Example 4-4. 19 is a partial cross-sectional view of a sintered body produced using the sintering powder of Example 5-1. 20 is a photograph showing EDS point analysis positions in a cross-section of a sintered body produced using the sintering powder of Example 2-1. 21 is a graph showing spectra corresponding to the EDS point analysis positions shown in FIG. 18 and the quantitative calculation results of each element.Graph showing the particle size distribution of the sintering powder of Comparative Example 1-1. Graph showing the particle size distribution of the sintering powder of Comparative Example 1-2. Graph showing the particle size distribution of the sintering powder of Comparative Example 1-3. Graph showing the particle size distribution of the sintering powder of Example 2-1. Graph showing the particle size distribution of the sintering powder of Examples 3-5.

[0022] Although embodiments of the present invention will be described in detail below, the present invention is not limited to the following embodiments. FIG. 1 is an enlarged schematic diagram showing particles of a sintering powder 1 according to a first embodiment of the present invention. This sintering powder 1 is mainly composed of a main powder 2 made of aluminum or an aluminum alloy, and contains an oxide of a rare earth metal element in an amount of 0.02 mass % to 1.5 mass % of the total mass of the sintering powder 1. When observed in more detail under magnification, the particles of the sintering powder 1 include particles of the main powder 2 made of aluminum or an aluminum alloy, and additive particles 3 made of an oxide of a rare earth metal element dispersed on the surfaces of the particles of the main powder 2. The sintering powder 1 does not necessarily need to include additive particles 3 that are not attached to the surfaces of the particles of the main powder 2, but may include such particles.

[0023] When the main powder 2 is made of an aluminum alloy, the elements contained in the aluminum alloy to be applied are not particularly limited, and any elements contained in commonly known aluminum alloys may be contained.

[0024] As the main powder 2, for example, any aluminum alloy of a composition system typified by JIS standards, such as the A1000 series, A2000 series, A3000 series, A4000 series, A5000 series, A6000 series, and A7000 series, may be used. Alternatively, aluminum alloy powder made of other common aluminum alloys to which elements not specified in these alloy series have been added may also be used. In this specification, percentages indicating the content of elements all refer to mass % unless otherwise specified.

[0025] A1050 is aluminum with a purity of 99.5% or higher and may contain inevitable impurities such as Fe and Si. The A1100 series is an aluminum alloy with a purity of 99% or higher. For example, A1100 has a composition of Fe and Si totaling 1.0% or less, Cu: approximately 0.05 to 0.20%, Mn: 0.05% or less, Zn: 0.1% or less, and the remainder being impurities.

[0026] The A2000 series is an aluminum alloy with a large amount of Cu added, and one example is A2024, which is an aluminum alloy containing 0.5% or less Si, 0.5% or less Fe, 3.8 to 4.9% Cu, 0.3 to 0.9% Mn, 1.2 to 1.8% Mg, 0.1% or less Cr, and 0.25% or less Zn. The A3000 series is an AlMn-based aluminum alloy, and one example is A3003, which is an aluminum alloy containing 0.6% or less Si, 0.7% or less Fe, 0.05% or less Cu, 1.0 to 1.5% Mn, and 0.1% or less Zn.

[0027] The A4000 series is an aluminum alloy containing Si, such as A4032, which contains 11.0 to 13.5% Si, 1.0% or less Fe, 0.5 to 1.3% Cu, 0.8 to 1.3% Mg, 0.10% or less Cr, and 0.25% or less Zn. The A5000 series is an aluminum alloy containing Mg, such as A5052, which contains 0.25% or less Si, 0.4% or less Fe, 0.10% or less Cu, 0.1% or less Mn, 2.2 to 2.8% Mg, 0.15 to 0.35% Cr, and 0.1% or less Zn.

[0028] The A6000 series is an aluminum alloy containing Mg and Si, such as A6061, which contains 0.4-0.8% Si, 0.7% or less Fe, 0.15-0.4% Cu, 0.15% or less Mn, 0.8-1.2% Mg, 0.15-0.35% Cr, 0.25% or less Zn, and 0.15% or less Ti. The A7000 series is an aluminum alloy containing mainly Zn and Mg, such as A7075, which contains 0.4% or less Si, 0.5% or less Fe, 1.2-2.0% Cu, 0.3% or less Mn, 2.1-2.9% Mg, 0.18-0.35% Cr, 5.1-6.1% Zn, and 0.2% or less Ti.

[0029] The rare earth elements constituting the additive particles 3 are preferably one or more selected from the group consisting of praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and more preferably one or more selected from the group consisting of praseodymium (Pr), samarium (Sm), gadolinium (Gd), dysprosium (Dy), and ytterbium (Yb).

[0030] These rare earth elements can be described as consisting of scandium, yttrium, and other lanthanoid elements. Among the rare earth elements, lanthanoid elements include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. In this embodiment, it is preferable to use an element with an atomic number larger than that of praseodymium, and it is particularly preferable to use one or more of praseodymium, samarium, gadolinium, dysprosium, and ytterbium, as described above.

[0031] The additive particles 3 are preferably fine particles with a smaller particle size than the particles of the main powder 2, and are dispersed and attached to any position on the surface of the particles of the main powder 2. The particles of the main powder 2 may be nearly spherical as shown in the figure, or may be flat, or may be irregular. A nearly spherical shape improves the fluidity of the main powder 2. The additive particles 3 may also be nearly spherical, or may be flat so that they can easily adhere to the particles of the main powder 2, or may be irregular.

[0032] The volume-based 50% cumulative average particle diameter (median diameter D ５０ The average particle diameter (D ５０ ) is within the above-mentioned range, when the sintering powder 1 of this embodiment is used in powder metallurgy, it becomes easy to ensure the required molding precision while maintaining suitable fluidity.

[0033] If the average particle size of the sintering powder 1 is larger than 65 μm, the flowability of the sintering powder 1 is improved, but voids are more likely to occur between the particles, making it difficult to obtain a high-density sintered body when sintered in a powder sintering apparatus. From the viewpoint of obtaining a high-density sintered body, it is more preferable that the average particle size of the sintering powder 1 is 45 μm or less.

[0034] If the average particle size of the sintering powder 1 is smaller than 20 μm, the fluidity of the sintering powder 1 will decrease, and there will be a risk of fire and dust scattering, which are specific to aluminum powder. Taking these into consideration, it is more preferable that the average particle size of the sintering powder 1 be 20 μm or more and 45 μm or less.

[0035] The particle size of the additive particles 3 is preferably smaller than that of the main powder 2. In this case, a mixed powder consisting of a plurality of main powders 2 containing the aforementioned amount of additive particles 3 is less likely to lose packing density during sintering. Furthermore, since the relatively small additive particles 3 can exist between the particles of a plurality of main powders 2, they can play a role in connecting the particles of the main powder 2 even if rare earth metal elements remain between the particles of the main powder 2 after sintering. Note that, because the particle size of the rare earth metal element oxide particles is smaller than that of the main powder 2, the average particle size of the sintering powder 1 and the average particle size of the main powder 2 are equivalent when the additive amount is about 1.5 mass % or less.

[0036] The ratio of the average particle size of the additive particles 3 to the average particle size of the main powder 2 is not limited in the present invention, but may be 1% or more and 50% or less, or 8% or more and 30% or less. These average particle sizes are defined as the 50% cumulative average particle size (median diameter D ５０ ) may also be used.

[0037] The additive particles 3 have the effect of generating a liquid phase on the surface of the main powder 2 when heated during sintering. The mechanism by which the liquid phase is generated is thought to be that a portion of the additive particles 3, which are oxides, is reduced during sintering, and the resulting rare earth metal breaks through the oxide film on the surface of the main powder 2 to form a eutectic with the internal aluminum. The resulting rare earth metal-aluminum eutectic generates a liquid phase, promoting bonding between particles of the main powder 2. In the mixed powder, the appropriate content of the additive particles 3 is 0.02% by mass to 1.5% by mass, or alternatively, 0.05% by mass to 1.2% by mass, or even 0.1% by mass to 1.1% by mass, relative to the total mass of the sintering powder 1. By adjusting the content of the additive particles 3 within this range, an appropriate amount of liquid phase can be generated on the surface of the main powder 2. If the content of the additive particles 3 exceeds the aforementioned range, an excessive liquid phase is generated, causing the shape of the sintered compact to collapse. Since the particle size of the additive particles 3 is smaller than that of the main powder 2, a good amount of liquid phase is generated without reducing the packing density of the main powder 2, and a high-density sintered body can be obtained after sintering.

[0038] To obtain a structure in which the additive particles 3 are dispersed on the surface of the main powder 2, a method can be used in which the main powder 2 and the additive particles 3 are prepared separately and then mixed together. Alternatively, a method can be used in which the additive particles 3 are attached to the surface of the main powder 2 using a particle deposition method such as sputtering. In either case, when producing a powder for sintering, it is preferable to obtain a state in which the additive particles 3 are dispersed as uniformly as possible around the main powder 2.

[0039] Alternatively, a structure can be adopted in which the entire particle of the main powder 2 contains the appropriate amount of rare earth element oxide to be contained as the additive particle 3, or a structure in which only the surface or surface layer of the particle of the main powder 2 contains the appropriate amount of rare earth element oxide to be contained as the additive particle 3.

[0040] To produce the sintering powder 1, for example, gas atomization can be used. Gas atomization is a method in which molten metal is ejected as fine droplets into air or an inert gas at high speed from the tip of an injection device such as a nozzle, together with an inert gas, to rapidly cool the molten metal and produce a powder composed of rapidly cooled particles of the molten metal. When ejecting the molten metal from the nozzle, an inert gas such as argon gas or nitrogen gas can be used. Gas atomization can produce a powder with a uniform particle size and a target composition. A sintering powder can also be obtained by forming a main powder 2 by gas atomization, adding and mixing additive particles 3 made of a rare earth metal separately produced by gas atomization or another method to the main powder 2, and then adhering a required amount of at least some of the additive particles 3 to the surfaces of the main powder 2 particles.

[0041] Next, the effects of the present invention will be demonstrated by examples of the present invention. Using molten aluminum, main powders shown in Comparative Examples 1-1, 1-2, and 1-3 in Table 1 below were prepared by nitrogen gas atomization, and the 50% cumulative average particle diameter (median diameter D ５０Any of gadolinium oxide particles, dysprosium oxide particles, praseodymium oxide particles, and ytterbium oxide particles was blended with these main powders so as to obtain the content (mass %) shown in Table 1, thereby preparing a mixed powder for sintering.

[0042] Similarly, the main powders shown in Examples 2-1 and 3-5 in Table 1 were prepared by nitrogen gas atomization using molten aluminum, and the 50% cumulative average particle diameter (median diameter D ５０ ) was measured. Samarium oxide particles and gadolinium oxide particles were blended with these main powders so as to obtain the contents (mass %) shown in Table 1, and powders for sintering were prepared with each oxide particle attached to the surface. In addition, mixed powders for sintering of example samples and comparative samples were prepared with rare earth metal element oxide particles shown in Table 1 attached to the surface, and with the rare earth metal element contents and 50% cumulative average particle diameters on a volume basis shown in Table 1.

[0043] Each of the obtained sintering powders was filled into a cylindrical cell made of boron nitride with an inner diameter of approximately 5.6 mm and a depth of approximately 3.5 mm, and after 300 tap fillings, it was filled at 100 mL min. -1 The sintered body was heated to 650°C for 1 hour in argon gas supplied at 100°C. The sintered density of the obtained sintered body was measured, assuming that the density of pure aluminum is 1. If the sintered density was below 85% at this point, it was determined that the amount of liquid phase was insufficient. If a sintered density of 85% or more was recorded, the dimensions (outer diameter and height) of the sintered body were measured, and it was determined whether the amount of liquid phase generated was appropriate or excessive.

[0044] The criteria for determining whether the amount of liquid phase generated was appropriate or excessive were whether the maximum outer diameter was 5.12 mm or less and the height was 3.5 mm or less. When both the maximum outer diameter and the height satisfied these criteria, it was determined that the shape had not collapsed and that there was no excessive generation of liquid phase, i.e., that an appropriate amount of liquid phase had been generated. When either or both of the maximum outer diameter and the height did not satisfy the conditions, it was determined that there had been shape collapse, i.e., that the amount of liquid phase was excessive.

[0045] The sample of Comparative Example 1-1 was confirmed by glow discharge mass spectrometry (GDMS) to have a Sc and Ce content of 0.1 ppm each, a La content of 0.2 ppm, and other rare earth elements below the detection limit (0.1 ppm).

[0046] The sample of Comparative Example 1-2 was confirmed by glow discharge mass spectrometry (GDMS) to have a Sc content of 0.1 ppm, a La content of 0.2 ppm, a Ce content of 0.3 ppm, a Sm content of 2 ppm, and other rare earth elements below the detection limit (0.1 ppm).

[0047] It was confirmed by glow discharge mass spectrometry (GDMS) that the samples of Comparative Examples 1-3 had Sc, Y, and Nd contents of 0.1 ppm each, La content of 2 ppm, Ce content of 3 ppm, and other rare earth elements below the detection limit (0.1 ppm).

[0048] The sample of Example 1-1 was prepared by adding D to the aluminum powder (main powder) of Comparative Example 1-1. ５０ A commercially available Pr ６ O １１ The samples of Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-3 were prepared by adding D powder (additive particles) to the aluminum powder (main powder) of Comparative Example 1-1. ５０ A commercially available Gd ２ O ３ It was prepared by adding powder (additive particles).

[0049] The samples of Examples 4-1 to 4-4 and 4-6 and the samples of Comparative Examples 4-1, 4-2, 4-4, 4-6 and 4-7 were prepared by adding D to the aluminum powder (main powder) of Comparative Example 1-1. ５０ A commercially available Dy ２ O ３ The sample of Example 4-5 was prepared by adding D powder (additive particles) to the aluminum powder (main powder) of Comparative Example 1-2. ５０ A commercially available Dy ２ O ３ It was prepared by adding powder (additive particles).

[0050] The samples of Comparative Examples 4-3 and 4-5 were prepared by adding the aluminum powder (main powder) of Comparative Example 1-3 to D ５０ A commercially available Dy ２ O ３ The sample of Example 5-1 was prepared by adding D powder (additive particles) to the aluminum powder (main powder) of Comparative Example 1-1. ５０ A commercially available Yb ２ O ３ It was prepared by adding powder (additive particles).

[0051] "Measurement of particle size distribution" The particle size distribution of the sintering powder is measured by the laser diffraction method, and the volume-based frequency cumulative diameter (D ５０ ) was calculated as the average particle size.

[0052] "Measurement of Differential Scanning Calorimetry (DSC) Spectrum of Sintering Powder" Approximately 10 to 20 mg of a sintering powder sample was placed in an alumina DSC pan, and Ar gas (G2 grade) was introduced at a rate of 100 mL min. －１ While flowing, the temperature was raised from room temperature to 15°C min. －１ The temperature was raised to 650° C. using a 1000 V AC power, and then the temperature was maintained at 650° C. for 1 hour, and a differential scanning calorimetry (DSC) spectrum was measured.

[0053] "ICP Measurement of Rare Earth Elements in Sintering Powder Samples" The sintering powder samples were dissolved in acid, and the content of rare earth elements in the sintering powder samples was measured by ICP.

[0054] "Glow discharge mass spectrometry of rare earth elements in sample powder" The powder sample to be sintered was press-molded and measured in a flat cell using a Nu Instruments Astrum under Ar (>99.9999) discharge gas at 2.5 mA, 1.0 kV, and a constant current mode with an integration time of 160 msec / ch. A Ta sample mask (10 mm) was used, and the mass resolution was 4000 (Δ / Δm: 10% peak height).

[0055] "Measurement of sintered density" The true density was calculated by the Archimedes substitution method. The sintered density in Table 1 is shown as a percentage, with the density of bulk pure aluminum being 1.

[0056] "Measurement of maximum outer diameter and height of sintered body" The maximum outer diameter and height of the sintered body were measured using a digital caliper. The test results for each item described above are summarized in Table 1 below. In Table 1, the rare earth element content was measured by ICP (inductively coupled plasma) unless otherwise noted.

[0057]

[0058] As shown in Table 1, all of the samples in the examples were sintering powders containing 0.02% to 1.40% by mass of any of gadolinium oxide particles, dysprosium oxide particles, praseodymium oxide particles, samarium oxide particles, and ytterbium oxide particles. The sintering powders of these examples produced sintered bodies that exhibited high sintered densities in the range of 89.6 to 98.4% and were free from shape collapse due to excessive liquid phase generation. On the other hand, in the sample in Comparative Example 4-1, in which the content of rare earth metal elements was 0.012% by mass, the amount of rare earth metal element added was so small that the sintered density was not sufficiently high.

[0059] Furthermore, as shown in Comparative Examples 3-1 to 3-3 or Comparative Examples 4-2, 4-4, 4-6, and 4-7, in the samples in which the amount of rare earth metal element added was 1.9 to 9.7 mass%, the amount of rare earth metal added was too large, causing excessive development of a liquid phase, resulting in the shape of the sintered body being distorted.

[0060] In Comparative Examples 3-1 and 3-2, as shown in the image in Figure 2, an excessive liquid phase appeared on the side surface of the sintered body. Due to the appearance of such a liquid phase, the maximum outer diameter exceeded 5.12 mm. In Comparative Example 4-2, as shown in the image in Figure 3, an excessive liquid phase appeared on the bottom surface of the sintered body. Due to this liquid phase, the height exceeded 3.5 mm.

[0061] From the above comparison, it was found that a sintering powder made of aluminum or an aluminum alloy containing 0.02% by mass or more and 1.5% by mass or less of a rare earth metal element around the main powder exhibits a high sintered density of 89% or more and can produce a sintered body that does not lose its shape. In this example, a sintered density of 85% or more, a maximum outer diameter of 5.12 mm or less, and a height of 3.5 mm or less is considered to be "a high sintered density after sintering, and the liquid phase is generated in an appropriate amount, so there is no shape collapse," and powder samples that satisfied this were used as examples.

[0062] Fig. 4A shows the field of view of the sintering powder in the sample of Example 2-1 where an EDS map was acquired, Fig. 4B shows the oxygen distribution in the same field of view of the same sample, and Fig. 4C shows the samarium (Sm) distribution in the same field of view of the same sample. From the analysis results shown in Fig. 4A to Fig. 4C, it was found that samarium and oxygen were present at the same position on the surface of the aluminum powder, and therefore samarium oxide was distributed on the surface of the aluminum powder.

[0063] Fig. 5A shows the field of view of the sintering powder in the sample of Example 3-5 where the EDS map was acquired, Fig. 5B shows the oxygen distribution in the same field of view of the same sample, and Fig. 5C shows the gadolinium (Gd) distribution in the same field of view of the same sample. From the analysis results shown in Fig. 5A to Fig. 5C, it was found that gadolinium and oxygen were present at the same position on the surface of the aluminum powder, and therefore gadolinium oxide was distributed on the surface of the aluminum powder.

[0064] Fig. 6A shows the field of view of the sintering powder in the sample of Example 4-4 where an EDS map was acquired, Fig. 6B shows the oxygen distribution in the same field of view of the same sample, and Fig. 6C shows the dysprosium (Dy) distribution in the same field of view of the same sample. From the analysis results shown in Fig. 6A to Fig. 6C, it was found that dysprosium and oxygen were present at the same position on the surface of the aluminum powder, and therefore dysprosium oxide was distributed on the surface of the aluminum powder.

[0065] Fig. 7 is a graph showing a differential thermal analysis curve for the sintering powder of Comparative Example 1-1, Fig. 8 is a graph showing a differential thermal analysis curve for the sintering powder of Comparative Example 4-1, Fig. 9 is a graph showing a differential thermal analysis curve for the sintering powder of Example 1-1, Fig. 10 is a graph showing a differential thermal analysis curve for the sintering powder of Example 2-1, and Fig. 11 is a graph showing a differential thermal analysis curve for the sintering powder of Example 5-1.

[0066] The sinterability of all samples using the sintering powders of the Examples was good. From this, it was estimated from the results of differential thermal analysis that, when using sintering powders containing rare earth metal elements as in the Examples, a liquid phase that promotes sintering is generated by the chemical reaction between aluminum and the rare earth metal element, but not to an extent that it is excessive.

[0067] 7 to 11 show the results of differential thermal analysis under conditions almost equivalent to those during sintering. In the results of differential thermal analysis of the examples, the occurrence of another endothermic peak or shoulder immediately before the main endothermic peak attributed to partial melting of aluminum was confirmed.

[0068] FIG. 12 shows an SEM image of a cross section of a sintered body made using the powder of Comparative Example 1-1, FIG. 13 shows an SEM image of a cross section of a sintered body made using the powder of Example 1-1, and FIG. 14 shows an SEM image of a cross section of a sintered body made using the powder of Example 2-1. FIG. 15 shows an SEM image of a cross section of a sintered body made using the powder of Example 3-5, FIG. 16 shows an SEM image of a cross section of a sintered body made using the powder of Example 4-4, and FIG. 17 shows an SEM image of a cross section of a sintered body made using the powder of Example 5-1. The observation magnification for all SEM images was 850x, and the scale bar shown in each figure (the horizontal white bar below the SEM image) indicates 20 μm. From a comparison of FIGS. 12 to 17, it was found that the density after sintering of Examples 1-1, 2-1, 3-5, 4-4, and 5-1 was higher than that of Comparative Example 1-1.

[0069] Since all of the example samples exhibited high sintered densities, it was estimated that the liquid phase generation that contributes to improved sintered density was due to the reduction of rare earth metal element oxides. As an example, Figure 18 shows a cross section of a sintered body produced using the sintering powder of Example 2-1, and Figure 19 shows a point analysis spectrum obtained by EDS (energy dispersive X-ray spectroscopy) at the position indicated by the + sign in Figure 18. The position indicated by the + sign in Figure 18 is a part of an amorphous samarium precipitate formed inside the aluminum matrix by the reaction of aluminum and samarium.

[0070] In the sintering powder according to the present invention, the rare earth metals exist as oxides in the powder state as explained above. However, considering the atomic ratio of Al:Sm:O of 88.2:9.4:2.4 shown in Fig. 19 after the sintering, the quantitative ratio of samarium to oxygen in the sintered structure is not considered to be the ratio of oxides.

[0071] From this, it can be inferred that a portion of the rare earth metal element oxide is reduced by contact with aluminum during sintering, forming an alloy between aluminum and the rare earth metal element, which causes a eutectic melting point depression and causes the rare earth metal element to function as a sintering aid that creates a liquid phase. Therefore, it can be assumed that the same effect can be achieved if the rare earth metal additive particles are not completely oxidized, but are only partially oxidized, such as on the surface, and that the same effect can be achieved not only with rare earth metal element oxides but also with rare earth metal element fluorides, rare earth metal element chlorides, or composite oxides of rare earth metal elements and aluminum.

[0072] FIG. 20 shows the aluminum powder (D ５０ 21 shows the particle size distribution of the aluminum powder (D ５０ 21.3 μm), and FIG. 22 shows the particle size distribution of the aluminum powder (D ５０ The particle size distribution is 10.3 μm.

[0073] Under the same sintering conditions as Comparative Example 1-1, sintered bodies were produced using the aluminum powder of Comparative Example 1-3, but with the addition of dysprosium oxide in an amount such that the dysprosium content was 2.3% by mass relative to the aluminum powder of Comparative Example 1-3, or the sintering powder of Comparative Example 4-5, with the addition of dysprosium oxide in an amount such that the dysprosium content was 3.2% by mass. As a result, the sintered density of the sintered body obtained using the sintering powder of Comparative Example 1-3 was 61.4%, the sintered density of the sintered body obtained using the sintering powder of Comparative Example 4-3 was 70.3%, and the sintered density of the sintered body produced using the sintering powder of Comparative Example 4-5 was 69.7%.

[0074] This indicates that if aluminum powder with a small average particle size is used as the main powder, a good sintered density cannot be obtained, even if rare earth metal elements are contained. ５０ It has been found that if the particle size is less than 20 μm, the flowability decreases and a good sintered density cannot be obtained.

[0075] As shown in Table 1, all of the samples in which praseodymium oxide particles, samarium oxide particles, gadolinium oxide particles, dysprosium oxide particles, or ytterbium oxide particles were added to pure aluminum powder had high sintered densities and appropriate liquid phase amounts.

[0076] 1...Sintering powder (particles) 2...Main powder (particles) 3...Additive particles

Claims

1. A sintering powder containing a main powder made of aluminum or an aluminum alloy and an oxide of one or more rare earth metal elements selected from scandium, yttrium and lanthanoid elements, wherein the content of the oxide of the rare earth metal element in the total mass of the sintering powder is 0.02 mass% or more and 1.5 mass% or less.

2. The powder for sintering according to claim 1, characterized in that an oxide of the rare earth metal element is present on the surface of the particles of the main powder.

3. A powder for sintering comprising a mixed powder having main powder particles made of aluminum or an aluminum alloy and additive particles made of an oxide of one or more rare earth metal elements selected from scandium, yttrium and lanthanoid elements, wherein the content of the oxide of the rare earth metal element in the total mass of the mixed powder is 0.02 mass% or more and 1.5 mass% or less, and at least a portion of the additive particle is adhered to the surface of the main powder particle.

4. The sintering powder according to any one of claims 1 to 3, characterized in that the rare earth metal element is one or more selected from the group consisting of praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

5. The sintering powder according to claim 3, characterized in that the particle size of the additive particles is smaller than the particle size of the main powder.

6. The volume-based 50% cumulative average particle diameter (median diameter D ５０ 3. The powder for sintering according to claim 1, wherein the average particle size is 20 μm or more and 65 μm or less.

7. The volume-based 50% cumulative average particle diameter (median diameter D) of the particles of the sintering powder measured by a laser diffraction / scattering method ５０ 4. The powder for sintering according to claim 3, characterized in that the average particle size is 20 μm or more and 65 μm or less.

8. The volume-based 50% cumulative average particle diameter (median diameter D) of the particles of the sintering powder measured by a laser diffraction / scattering method ５０ 5. The powder for sintering according to claim 4, characterized in that the average particle size is 20 μm or more and 65 μm or less.

9. The volume-based 50% cumulative average particle diameter (median diameter D) of the particles of the sintering powder measured by a laser diffraction / scattering method ５０ 6. The powder for sintering according to claim 5, characterized in that the average particle size is 20 μm or more and 65 μm or less.

Images