Copper alloy mixed powder and method for evaluating same

Abstract

In order to provide a copper alloy additively manufactured article having high electrical conductivity while controlling the amount of Ag added, the present invention is a copper alloy mixed powder which is obtained by mixing 5.0-50.0 mass% of a second copper alloy powder, which contains Cu as a main component, contains 0.1-2.0 mass% of Ag, and contains Ag, Cr, and Zr in a total amount of 0.2-5.0 mass% into a first copper alloy powder, which contains Cu as a main component, contains Cr, and contains Cr and Zr in a total amount of 0.2-5.0 mass%.

Description

Copper alloy mixed powder and its evaluation method

[0001] The present invention relates to a copper alloy mixed powder and an evaluation method thereof.

[0002] In metal additive manufacturing using a fiber laser as a heat source, pure copper has a low laser absorption rate, and it is very difficult to perform additive manufacturing using pure copper powder. Therefore, alloy powders of chromium copper, zirconium copper, and chromium zirconium copper, which are copper alloys with high electrical conductivity and thermal conductivity after pure copper, have been widely studied. For example, Cu—Cr-based or Cu—Cr—Zr-based alloys shown in Patent Documents 1 to 6 can be mentioned.

[0003] Since these chromium copper, zirconium copper, and chromium zirconium copper have inferior electrical conductivity compared to pure copper, copper alloys containing Ag have been studied as copper alloys having higher electrical conductivity and obtaining high strength. For example, powders of Cu—Ag-based alloys shown in Non-Patent Document 1 and Cu—Cr—Ag-based alloys shown in Patent Document 7 have been studied.

[0004] Patent No. 6030186, Patent No. 6389557, Patent No. 6346983, Patent No. 6693092, Patent No. 7192161, Patent No. 7194087, Patent No. 7394241

[0005] Kuroyanagi Taku, Light Metals (1987) Vol.37 No.4 313-326, Copper and Copper Alloys as Electronic Materials

[0006] However, since the Ag content of these alloy powders cannot be changed, there is a problem that the material cost increases. [[ID=2&]]

[0007] The present invention aims to solve the above problems.

[0008] To achieve the above object, the copper alloy mixed powder according to the present invention is a copper alloy mixed powder in which 5.0 to 50.0% by mass of a second copper alloy powder containing Cu as a main component, containing 0.1 to 2.0% by mass of Ag, and containing 0.2 to 5.0% by mass in total of Ag, Cr, and Zr is mixed with a first copper alloy powder containing Cu as a main component, containing Cr, and containing 0.2 to 5.0% by mass in total of Cr and Zr.

[0009] Furthermore, in order to achieve the above objective, the present invention provides a method for evaluating copper alloy mixed powder, comprising: an additive manufacturing step of additively manufacturing a copper alloy additively manufactured body using an additive manufacturing apparatus with the above copper alloy mixed powder; a heat treatment step of heat-treating the copper alloy additively manufactured body at 700°C for 1 hour; an conductivity measurement step of measuring the conductivity σ (%IACS) of the copper alloy additively manufactured body after the heat treatment step; and a step of evaluating the copper alloy mixed powder to be evaluated as a copper alloy mixed powder capable of additively manufacturing a copper alloy additively manufactured body with high conductivity if the rate of increase or decrease in conductivity (%) calculated based on (Equation 1) is equal to or greater than the amount (mass%) of the second copper alloy powder mixed in. (Equation 1) Rate of increase or decrease in conductivity: (σ - σ １ ) ÷ (σ ２ -σ １ ) × 100 [%] σ １ : Conductivity (%IACS) of a molded object using only the first copper alloy powder after heat treatment at 700°C for 1 hour σ ２ The electrical conductivity (%IACS) of a molded object using only second-order copper alloy powder after heat treatment at 700°C for 1 hour.

[0010] By controlling the amount of Ag added, it is possible to provide copper alloy additive bodies with high conductivity.

[0011] This figure plots the increase or decrease in conductivity against the amount of the second copper alloy powder mixed in. This table shows the amounts of the first and second mixed powders, the composition of the copper alloy powder, and the increase or decrease in conductivity of the copper alloy powder. This table shows the particle size and segregation degree of the first and second copper alloy powders.

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the components described in the following embodiments are merely illustrative and are not intended to limit the technical scope of the present invention to them alone.

[0013] (Embodiment) The copper alloy mixed powder according to the embodiment of the present invention is obtained by mixing a first copper alloy powder and a second copper alloy powder, and is a copper alloy mixed powder containing 5.0 to 50.0% by mass of the second copper alloy powder based on the total amount of the copper alloy mixed powder.

[0014] Here, the first copper alloy powder is a powder mainly composed of Cu, containing Cr, and containing a total of 0.2 to 5.0 mass% of Cr and Zr. The first copper alloy powder is preferably a copper alloy mainly containing Cr, such as chromium copper, zirconium copper, or chromium zirconium copper as specified in UNS and JIS standards. The inclusion of Cr makes it easier to fabricate by increasing the laser absorption rate compared to pure copper in additive manufacturing using a fiber laser as a heat source. In addition, by performing heat treatment after fabrication, the Cr phase precipitates, contributing to strength, and the Cu purity of the solid solution that forms the matrix increases, improving conductivity and thermal conductivity. For this reason, the first copper alloy powder contains Cr.

[0015] The second copper alloy powder is mainly composed of Cu, contains 0.1 to 2.0% by mass of Ag, and contains a total of 0.2 to 5.0% by mass of Ag, Cr, and Zr. It is preferable that Cr is also added to the second copper alloy powder, and in order to avoid a large difference in laser absorption rate between it and the first copper alloy powder, the amount of Cr (by mass) in the second copper alloy powder is preferably 0.5 to 1.5 times the amount of Cr (by mass) in the first copper alloy powder.

[0016] Furthermore, in the first and second copper alloy powders, Zr contributes as a deoxidizing agent during the production of the raw material powder (atomization method) and during additive manufacturing. In addition, by heat treatment after manufacturing, a Zr phase precipitates, similar to Cr, contributing to improved strength and conductivity.

[0017] The Ag in the second copper alloy powder has the effect of promoting the precipitation of Cr and Zr phases that are produced by heat treatment after molding. The amount of Ag added is small enough to promote precipitation, and it is sufficient to have 0.1% by mass or more in the second copper alloy powder. Adding more Ag would result in the disadvantage of higher material costs, so it is preferable to keep it at 2.0% by mass or less. More preferably, it is 0.1 to 0.5% by mass.

[0018] In the first copper alloy powder, if the total amount of Cr and Zr is less than 0.2 mass%, the laser absorption rate is low, making it difficult to fabricate using additive manufacturing with a fiber laser as the heat source. In addition, the amount of Cr and Zr phase precipitation decreases, resulting in low strength. Furthermore, if the total amount exceeds 5.0 mass%, the conductivity decreases significantly, so a total of 0.2 to 5.0 mass% is preferable. In particular, a total of Cr and Zr in the range of 1.0 to 2.0 mass% is more preferable as it provides a good balance between strength and conductivity.

[0019] In the second copper alloy powder, the addition of Ag promotes the precipitation of the Cr and Zr phases, even when the amounts of Cr and Zr added are reduced compared to the first copper alloy powder, due to the effect of Ag. Therefore, the total amount of Ag, Cr, and Zr is preferably 0.2 to 5.0 mass%. In particular, a total of 1.0 to 2.0 mass% of Ag, Cr, and Zr is more preferable as it provides a good balance between strength and conductivity.

[0020] Furthermore, unavoidable impurities are those that are inevitably introduced during the manufacturing process of each raw material, even though they are not intentionally added. Examples include Al, Bi, Fe, Mg, Ni, O, P, Pb, S, Sn, and Zn. The total amount of these is usually 0.3% by mass or less and does not affect the function of the present invention.

[0021] Furthermore, when a molded body is produced under the same conditions using the two types of copper alloy powders described above, it is preferable that the molded body obtained using only the second copper alloy powder has higher conductivity than the molded body obtained using only the first copper alloy powder, both in the as-formed state (before heat treatment) and after heat treatment at 700°C.

[0022] Furthermore, the present invention aims to improve the conductivity of a molded body when it is heat-treated at 700°C for 1 hour by mixing a second copper alloy powder with a first copper alloy powder. Therefore, the second copper alloy powder is a Cu-Ag alloy powder containing Ag, and it is preferable that a molded body obtained using only the second copper alloy powder has higher conductivity than a molded body obtained using only the first copper alloy powder. For this reason, it is preferable that the total content (mass%) of Cr and Zr in the second copper alloy powder is less than the total content (mass%) of Cr and Zr in the first copper alloy powder. Moreover, since the molding is performed using a mixed powder as a raw material, the laser absorption rates must be equivalent in additive manufacturing using a fiber laser as a heat source, and it is preferable that the two copper alloy powders have similar Cr content (mass%). Specifically, it is preferable that the Cr content (mass%) of the second copper alloy powder is in the range of 0.5 to 1.5 times the Cr content (mass%) of the first copper alloy powder.

[0023] The mixing ratio of the second copper alloy powder is preferably 5.0 to 50.0 mass%. If it is less than 5.0 mass%, the amount of Ag in the copper alloy mixed powder is insufficient, and the effect of promoting the precipitation of the Cr and Zr phases by Ag is not obtained, resulting in low conductivity. If it exceeds 50.0 mass%, the balance between the amount of Zr and Ag is disrupted, and the effect of promoting the precipitation of the Cr and Zr phases is not obtained, resulting in a decrease in conductivity.

[0024] Furthermore, since the material is formed as a mixed powder, if there is a discrepancy in the 50% particle size, segregation is likely to occur during powder supply, resulting in variations in conductivity and strength in the resulting molded body. For this reason, it is preferable that the 50% particle size (D150) of the first copper alloy powder and the 50% particle size (D250) of the second copper alloy powder be close. It is preferable that the following conditions be met: "0.45 × D150 ≤ D250 ≤ 2.22 × D150". It is even more preferable that the following conditions be met: "0.60 × D150 ≤ D250 ≤ 1.66 × D150". In addition, from the viewpoint of powder fluidity and squeegeeability in additive manufacturing, 0.45 × D150 and 0.60 × D150 are preferably 10 μm or larger, and considering squeegeeability and ease of segregation, 2.22 × D150 and 1.66 × D150 are preferably 220 μm or smaller.

[0025] The 50% particle size refers to the particle size at which the cumulative value of the powder reaches 50% in the volume-based cumulative particle size distribution, as measured using the laser diffraction / scattering method specified in JIS Z8825.

[0026] A base metal containing Cu and additive components Cr and Zr, each adjusted and blended to a predetermined mass percentage, is heated and melted in a crucible in a melting furnace to form a liquid alloy. After this liquid alloy is formed, a first copper alloy powder can be obtained by atomization.

[0027] Furthermore, a base metal containing Cu and additive components Ag, Cr, and Zr, each adjusted and blended to a predetermined mass percentage, is heated and melted in a crucible in a melting furnace to form a liquid alloy. This alloy can then be atomized to obtain a second copper alloy powder. The atomization method can include gas atomization, water atomization, disk atomization, or plasma rotating electrode method.

[0028] Furthermore, each alloy powder produced by the atomization method is adjusted to a particle size suitable for the desired additive manufacturing method using a vibrating screen or airflow classifier. After particle size adjustment, the first copper alloy powder and the second copper alloy powder are mixed in a predetermined ratio using a mixer such as a V-type mixer to obtain a copper alloy mixed powder. Methods for manufacturing additively manufactured bodies using copper alloy powder include the powder bed method and deposition method, which use a laser or electron beam as a heat source.

[0029] (Method for evaluating copper alloy mixed powder) A copper alloy mixed powder is obtained by mixing x mass% of the second copper alloy powder, and an additive manufacturing structure is produced using an additive manufacturing apparatus or the like. The obtained additive manufacturing structure is subjected to heat treatment at 700°C for 1 hour. The atmosphere for the heat treatment is arbitrary, but a vacuum atmosphere, a reducing atmosphere such as hydrogen, or an inert atmosphere such as nitrogen or argon is preferred. After that, the conductivity σ (%IACS) of the manufactured additive manufacturing structure, and the conductivity σ1 and σ2 (%IACS) of additive manufacturing structures similarly produced using only the first copper alloy powder or only the second copper alloy powder are measured, and the rate of increase or decrease in conductivity y (%) is calculated based on (Equation 1).

[0030] (Equation 1) Percentage change in conductivity: (σ - σ1) ÷ (σ2 - σ1) × 100 [%]

[0031] In (Equation 1), σ1 is the conductivity (%IACS) of a fabricated body using only the first copper alloy powder after heat treatment at 700°C for 1 hour, and σ2 is the conductivity (%IACS) of a fabricated body using only the second copper alloy powder after heat treatment at 700°C for 1 hour. Then, for the additive fabricated body to be evaluated, it is determined whether the rate of increase or decrease in conductivity y (%) is greater than or equal to the amount of second copper alloy powder mixed in x (mass%). For example, a two-dimensional graph (see Figure 1) is created with the amount of second copper alloy powder mixed in x (mass%) and the rate of increase or decrease in conductivity y (%) as axes, and it is determined whether the plotted point (x, y) on the two-dimensional graph is above the boundary line (y = x) (y ≥ x).

[0032] The boundary line (y=x) can be interpreted simply as the sum of the conductivity values ​​of the first copper alloy powder and the second copper alloy powder. If the plotted point (x,y) is in the region above the boundary line (y=x) (y≧x), it can be said that the additively manufactured object exhibits a conductivity higher than the sum of the conductivity values ​​of the first copper alloy powder and the second copper alloy powder. Therefore, the copper alloy mixed powder used in the additively manufactured object can be judged as suitable. On the other hand, if it is in the region below (y<x), the additively manufactured object exhibits a conductivity lower than the sum of the conductivity values ​​of the first copper alloy powder and the second copper alloy powder, and the copper alloy mixed powder used in the additively manufactured object can be judged as unsuitable.

[0033] According to the copper alloy powder evaluation method of this embodiment, it is possible to evaluate copper alloy mixed powders that can produce copper alloy additively fabricated structures with high conductivity while suppressing the amount of Ag (silver).

[0034] As the first copper alloy powder, a gas atomized powder of Cu-1.11Cr-0.24Zr (mass%) with a 50% particle size of 30.5 μm was used, and as the second copper alloy powder, a gas atomized powder of Cu-1.11Cr-0.21Ag (mass%) with a 50% particle size of 31.8 μm was used. Homogeneous mixing was performed using a V-type mixer so that the mixing amounts of the second copper alloy powder were 0, 10, 20, 40, 50, 60, 80, and 100% by mass. The amount of Ag in the mixed powder was calculated as a ratio and was set to 0.00, 0.02, 0.04, 0.09, 0.11, 0.13, 0.17, and 0.21% by mass, respectively.

[0035] The aforementioned first copper alloy powder, second copper alloy powder, and a mixed powder thereof were subjected to an energy density of 144.2 J / mm² using an SLM280 manufactured by SLM Solutions Inc. 3 Under these printing conditions, a 3D object with a diameter of 14 mm and a height of 12 mm was fabricated. The energy density is calculated by dividing the laser output by the product of the laser beam scanning speed, laser pitch, and powder bed thickness.

[0036] The molded object was then heat-treated for 1 hour in a tubular furnace at a furnace temperature of 700°C in a hydrogen reduction atmosphere. The top surface of the molded object was polished with #400 waterproof sandpaper, and the conductivity of the molded object was measured using an eddy current conductivity meter, SigmaCheck, manufactured by Nippon Matec Co., Ltd. In addition, the top surface of the molded object in its as-formed state (before heat treatment) was polished with #400 waterproof sandpaper, and the conductivity was measured. The conductivity increase / decrease rate y (%) was calculated from the conductivity of the molded object using only the first copper alloy powder (σ1), the conductivity of the molded object using only the second copper alloy powder (σ2), and the conductivity of the molded object using the copper alloy mixed powder (σ). Here, it was determined whether the conductivity increase / decrease rate was above the boundary line (y = x, where y is the conductivity increase / decrease rate and x is the amount of second copper alloy powder mixed) connecting the conductivity of the first copper alloy powder and the second copper alloy powder (y = x).

[0037] Figure 2 is a table showing the mixing ratio, components (calculated ratios except for Comparative Examples 1 and 4), and rate of increase or decrease in conductivity (in the as-form (before heat treatment) and after heat treatment at 700°C) of the second copper alloy powder mixture in the examples and comparative examples. Figure 1 shows the rate of increase or decrease in conductivity of the molded body after heat treatment at 700°C. The dashed line in Figure 1 is a straight line (y=x) connecting the results of molded bodies using the first and second copper alloy powders. In Comparative Examples 2 and 3, the mixing amount of the second copper alloy powder was high at 60% and 80% by mass, respectively, and the rate of increase or decrease in conductivity was below y=x. In contrast, in Examples 1 to 4, the rate of increase or decrease in conductivity was higher than y=x, confirming that the conductivity increases when the mixing amount of the second copper alloy powder is reduced to 50% by mass or less.

[0038] Next, as an evaluation of segregation based on a 50% particle size difference, a powder (mixed powder) was prepared by adding and simply mixing 40g of the second copper alloy powder with 60g of the first copper alloy powder, with the amount of the second copper alloy powder being 40% by mass. 100g of the mixed powder was placed at the start position at the end of a trough (100mm wide, 380mm long) using an electromagnetic feeder (CF-1 manufactured by Symphonia Technology Co., Ltd., adjusted to a supply rate of approximately 100g per minute). The electromagnetic feeder was switched on, and approximately 50g was collected from the trough outlet side. After switching off the feeder, the collected powder was designated as the early powder, and the powder remaining in the trough as the late powder. After collection, each was simply mixed to prepare samples for component analysis. The amount of Ag contained in the start powder, early powder, and late powder was measured by ICP analysis. From the amount of Ag, the degree of segregation, defined by the following formula, was calculated. The degree of segregation was calculated as follows: [|(Amount of powder in the first stage) - (Amount of powder in the second stage)| ÷ (Amount of mixed powder in the second stage)] × 100. Furthermore, a degree of segregation of 50% or less is preferred, and 20% or less is even more preferred.

[0039] Figure 3 is a table showing the average particle size (particle size difference) and segregation degree of the first copper alloy powder and the second copper alloy powder, which are the raw materials for the mixed powder. In Figure 3, D150 represents the 50% particle size of the first copper alloy powder. D250 represents the 50% particle size of the second copper alloy powder. ΔD50 represents the absolute value of the difference between D150 and D250. Note that Example C is the result using the powder from Example 3 used in the previous evaluation. Examples A to E show that D250 is "0.45 × D150 ≤ D250 ≤ 2.22 × D １The segregation was within the range of "50 (μm)" and the degree of segregation was 25% or less. In particular, in Examples A to C, D250 was within the range of "0.60 × D150 ≤ D250 ≤ 1.66 × D150 (μm)", and the degree of segregation was further reduced to 10% or less. On the other hand, in Comparative Examples A to D, D250 exceeded the range of "0.45 × D150 ≤ D250 ≤ 2.22 × D150 (μm)", and the degree of segregation was large.

[0040] As described above, by using the copper alloy mixed powder for additive manufacturing of the present invention, it is possible to increase the conductivity of the fabricated body during 700°C heat treatment while suppressing the cost of the raw material powder with a small amount of Ag content, and it is expected that a conductivity close to that of pure copper can be obtained in the fabricated copper alloy body.

[0041] The copper alloy mixed powder of the present invention can be applied not only to additive manufacturing but also to coating applications such as thermal spraying, cold spraying, plasma powder cladding, and laser cladding by adjusting the powder particle size to suit various construction methods.

Claims

1. A copper alloy mixed powder obtained by mixing 5.0 to 50.0% by mass of a second copper alloy powder, which is mainly composed of Cu, contains 0.1 to 2.0% by mass of Ag, and contains 0.2 to 5.0% by mass of Ag, Cr, and Zr.

2. The 50% particle size (D) of the first copper alloy powder. １ 50) and the 50% particle size (D) of the second copper alloy powder ２ 50) The copper alloy mixed powder according to claim 1, satisfying the following formula: 0.45 × D １ 50 ≤ D ２ 50 ≤ 2.22 × D １ 50 3. The copper alloy mixed powder according to claim 1 or claim 2, wherein the first copper alloy powder contains 1.0 to 2.0% by mass of Cr and Zr in total, and the second copper alloy powder contains 0.1 to 0.5% by mass of Ag, and contains 1.0 to 2.0% by mass of Ag, Cr and Zr in total.

4. The copper alloy mixed powder according to claim 3, wherein the total content (mass%) of Cr and Zr in the second copper alloy powder is less than the total content (mass%) of Cr and Zr in the first copper alloy powder, the second copper alloy powder contains 0.1 to 0.5 mass% of Ag, 0.5 to 1.5 times the amount of Cr contained in the first copper alloy powder (mass%), and contains a total of 1.0 to 2.0 mass% of Ag, Cr, and Zr.

5. The copper alloy mixed powder according to claim 1 or claim 2, wherein the remainder after removing Cr and Zr from the first copper alloy powder consists of Cu and unavoidable impurities, and the remainder after removing Ag, Cr, and Zr from the second copper alloy powder consists of Cu and unavoidable impurities.

6. The copper alloy mixed powder according to claim 1 or claim 2, wherein the first and second copper alloy powders are copper alloy powders such that the conductivity of a molded body obtained using only the second copper alloy powder is higher than the conductivity of a molded body obtained using only the first copper alloy powder.

7. A laminating process of laminating a copper alloy laminated body by a laminating apparatus using the copper alloy mixed powder according to claim 1 or claim 2; a heat treatment process of heat-treating the copper alloy laminated body at 700° C. for 1 hour; a conductivity measurement process of measuring the conductivity σ (% IACS) of the copper alloy laminated body after the heat treatment process; and when the increase / decrease rate (%) of the conductivity calculated based on (Equation 1) is not less than the mixing amount (mass %) of the second copper alloy powder, evaluating the copper alloy mixed powder to be evaluated as a copper alloy mixed powder capable of laminating a copper alloy laminated body with high conductivity. An evaluation method for a copper alloy mixed powder. (Equation 1) Increase / decrease rate of conductivity: (σ - σ １ ) ÷ (σ ２ - σ １ ) × 100 [%] σ １ : Conductivity (% IACS) when a body using only the first copper alloy powder is heat-treated at 700° C. for 1 hour σ ２ : Conductivity (% IACS) when a body using only the second copper alloy powder is heat-treated at 700° C. for 1 hour

Images