JP6559865B1 - Method for producing copper alloy shaped article and copper alloy shaped article - Google Patents

Abstract

The present invention provides a metal powder and a manufacturing method for manufacturing a copper alloy shaped article that can obtain high electrical conductivity and thermal conductivity without performing a heat treatment step by additive manufacturing. A metal powder for additive manufacturing in which copper powder and molybdenum powder are mixed in a ratio of 99.92: 0.08 to 94.5: 5.5 on a mass basis. A first step of forming a thin layer of the metal powder for additive manufacturing, and a second step of irradiating an electromagnetic wave beam to a predetermined position of the thin layer to dissolve and solidify at least a part of the metal powder sequentially A method for producing a copper alloy shaped article that repeatedly produces a laminated shaped article. [Selection] Figure 1

Description

  The present invention relates to an additive manufacturing technique for a copper alloy by a powder bed fusion bonding method, and more particularly to a powder as a raw material, a method for manufacturing a layered object formed from a copper alloy, and a copper alloy shaped object.

  As a method for manufacturing a metal three-dimensional model, an additional manufacturing technique, a so-called 3D printing technique, has attracted attention. Of these, the additive manufacturing method using the powder bed fusion bonding method repeatedly lays the metal powder as a raw material on the modeling stage, and irradiates the predetermined position with a laser beam or an electron beam to melt and solidify the metal powder for lamination. This is a method of modeling a three-dimensional shape. Typical methods include laser sintering (SLS, Selective Laser Sintering) and laser melting (SLM, Selective Laser Melting). By this method, a product having a complicated shape that could not be made by conventional cutting or the like can be manufactured in a relatively short time.

  One problem in the additive manufacturing of metals is that it is difficult to manufacture products that take advantage of the excellent electrical and thermal conductivity of copper. The main causes are that the energy absorption rate of copper with respect to the wavelength of the laser beam (for example, 1090 nm for Yb fiber laser) is extremely low and the melting point cannot be reached. It is that the diffusion does not proceed sufficiently.

  On the other hand, in Patent Documents 1 to 3, electrical conductivity is obtained by preparing a layered object by additive manufacturing using copper alloy powder containing chromium, and heat-treating the layered object at a temperature of 300 ° C. or higher. It is described to improve.

JP 2018-070914 A Japanese Patent No. 6389557 Japanese Patent No. 6346683

  However, in the methods described in Patent Documents 1 to 3, a heat treatment step is indispensable after layered modeling, which has been a cost factor.

  The present invention has been made in view of the above, and an object of the present invention is to provide a copper alloy shaped article that can obtain high electrical conductivity and thermal conductivity without performing a heat treatment step by additive manufacturing.

  The metal powder for additive manufacturing of the present invention is obtained by mixing copper powder and molybdenum powder in a ratio of 99.92: 0.08 to 94.5: 5.5 on a mass basis.

  Another metal powder for additive manufacturing of the present invention is a copper alloy powder containing 0.08% by mass to 5.5% by mass of molybdenum with the balance being copper and impurities.

  The method for producing a copper alloy shaped article of the present invention includes a first step of forming a thin layer of the metal powder for layered shaping, and at least one of the metal powders by irradiating an electromagnetic wave beam at a predetermined position of the thin layer. A layered product is produced by sequentially repeating the second step of dissolving and solidifying the part.

  The copper alloy shaped article of the present invention has a laminated structure of a copper alloy, and the copper alloy contains 0.08% by mass to 5.5% by mass of molybdenum, and the remainder is made of copper and impurities, and conducts electricity at room temperature. The rate is 65% IACS or higher.

  According to the method for producing a metal powder or a copper alloy shaped article for additive manufacturing according to the present invention, copper alloy shaping having high electrical conductivity and thermal conductivity in the state of a shaped material without performing a heat treatment step by additional production. Can be manufactured. According to the copper alloy shaped article of the present invention, high electrical conductivity and thermal conductivity can be obtained at low cost because heat treatment is unnecessary.

A: Scanning electron microscope (SEM) image of a metal powder in which copper powder and molybdenum powder are mixed, and B: Optical microscope (OM) image of a layered object made of a copper-molybdenum alloy. It is a figure which shows the shape of the tension test piece which is a laminate-molded article. It is a SEM image after chemical etching of the layered object which consists of copper or a copper-molybdenum alloy. It is a SEM image after chemical etching of a layered product made of a copper-molybdenum alloy. It is a tension test result of the layered object which consists of copper or a copper-molybdenum alloy.

  In the additive manufacturing metal powder according to an embodiment of the present invention, copper (Cu) powder and molybdenum (Mo) powder are mixed at a mass ratio of 99.92: 0.08 to 94.5: 5.5. It is a thing. Hereinafter, this metal powder is referred to as “Cu / Mo mixed powder”.

  Various commercially available powders can be used as the copper powder and the molybdenum powder.

  The reason why the molybdenum powder is mixed is to absorb the laser beam during the additive manufacturing. The ratio of molybdenum powder to the total of copper powder and molybdenum powder (Mo / (Cu + Mo)) is 0.08% by mass or more, preferably 0.23% by mass or more, and more preferably 0.47% by mass or more. This is because the greater the proportion of molybdenum powder, the greater the amount of laser light absorbed during additive manufacturing. On the other hand, the ratio (Mo / (Cu + Mo)) is 5.5% by mass or less. This is because when the proportion of the molybdenum powder is too large, the relative density (measured density / theoretical density) of the layered object is lowered and ductility is lowered.

  Copper powder and molybdenum powder may contain an impurity element. The impurity element may be an inevitably mixed element (unavoidable impurity) or an intentionally added element (added element). Examples of inevitable impurities include oxygen (O), phosphorus (P), and other metal elements mixed in the raw materials used in manufacturing each powder. As the additive element, a metal element that forms an oxide preferentially over copper or molybdenum and suppresses the influence of oxygen (O) that lowers the thermal conductivity may be added. Examples of the additive element include zirconium (Zr), titanium (Ti), silicon (Si), and the like, which have a low standard free energy of formation of oxides. Note that these elements may be included as inevitable impurities. The content of the impurity element is preferably less than 0.2% by mass.

  The particle sizes of the copper powder and the molybdenum powder can be determined according to the method of the additive manufacturing method, the required dimensional accuracy of the shaped article, and the like. When used in a general SLS method or SLM method, the volume-based median value (d50) of the particle diameter measured by a laser diffraction / scattering method is preferably 1 to 100 μm.

  The metal powder for additive manufacturing in another embodiment is a copper alloy powder containing 0.08% by mass to 5.50% by mass of molybdenum, with the balance being copper and impurities. Hereinafter, this metal powder is referred to as “Cu—Mo alloy powder”.

  The Cu—Mo alloy powder is preferably produced by mechanical alloying. The binary system of Cu—Mo shows a phase diagram of a monotectic reaction type. The melting point of molybdenum (2623 ° C.) is higher than the boiling point of copper (2571 ° C.), and the solubility of molybdenum in liquid copper is extremely low. Therefore, it is difficult to industrially manufacture an alloy powder having a uniform structure of Cu—Mo. If copper and molybdenum are mechanically alloyed using a high energy ball mill or the like, Cu—Mo alloy powder in which the surface of Cu particles is modified with Mo particles can be easily produced.

  The Cu—Mo alloy powder may contain an impurity element, and the impurity element may be an additive element or an inevitable impurity as in the case of the Cu / Mo mixed powder. As for the particle size of the Cu-Mo alloy powder, the volume-based median value (d50) of the particle size measured by the laser diffraction / scattering method is preferably 1 to 100 μm, similarly to the above Cu / Mo mixed powder. It is.

  Various known additive manufacturing techniques can be used for producing the layered object. For example, a first step of forming a thin layer of the Cu / Mo mixed powder and a second step of irradiating an electromagnetic wave beam at a predetermined position of the thin layer to melt and solidify at least a part of the Cu / Mo mixed powder. Are repeated sequentially. When the molybdenum powder absorbs the laser light, at least the copper powder is melted. Alternatively, for example, a first step of forming a thin layer of the Cu—Mo alloy powder and a step of melting and solidifying at least a part of the Cu—Mo alloy powder by irradiating an electromagnetic wave beam to a predetermined position of the thin layer. The two steps are sequentially repeated. When the Mo phase in the Cu—Mo alloy particles absorbs laser light, at least the Cu phase is melted. Finally, by removing excess powder, a layered product of copper alloy is obtained.

  The copper alloy shaped article of the present embodiment is obtained through the above steps. The structure of the copper alloy shaped article is a shaped article having a laminated structure of copper alloys, and has a structure in which the Mo phase is dispersed in the parent phase (matrix phase) of Cu.

  Next, the embodiment will be described in more detail based on some experimental results. The blank in each table below means that no experiment or analysis was performed.

  Using Cu / Mo mixed powder, test pieces for measuring various properties described later were prepared by the SLS method. Fabrication was performed using a powder additive manufacturing system (EOS GmbH, M290) using a Yb fiber laser under conditions of a laminate thickness of 0.01 to 0.06 mm and a laser output of 200 to 400W. For comparison, pure copper test pieces were prepared by the same SLM method using only copper powder. The scanning pattern and speed of the laser light were obtained in advance under the conditions that the following sample Cu0.5Mo was most dense, and the samples Cu, Cu0.1Mo, Cu0.2Mo, and Cu0.5Mo were irradiated with laser light under the same conditions. For samples with a higher proportion of molybdenum powder, the scanning speed and the like were appropriately adjusted according to the absorption rate of the laser beam.

  Table 1 shows the impurity concentration and the particle size of the copper powder and the molybdenum powder used for producing the layered object. The concentration of oxygen (O) and nitrogen (N) was measured by an oxygen / nitrogen analyzer (LECO Corp., ON736), oxygen was measured by a non-dispersive infrared absorption method, and nitrogen was measured by a thermal conductivity method. Oxygen and nitrogen are not considered in the purity of copper or molybdenum. The particle size was measured using a particle size distribution measuring apparatus (MT3200, Microtrac Bell Co., Ltd.) using a laser diffraction / scattering method. In Table 1, MN represents the number average diameter, and MV represents the volume average diameter. In Table 1, d10, d50, and d90 represent the particle diameters at points where the cumulative curves are 10%, 50%, and 90% when the total volume is 100%. d50 is the median diameter.

  Table 2 shows the chemical analysis results of the layered object produced. The Mo content was determined by ICP emission spectroscopic analysis. The analysis of oxygen (O) and nitrogen (N) was performed by the same method as the raw material powder.

  FIG. 1A shows a Cu / Mo mixed powder, and FIG. 1B shows a scanning electron microscope (SEM) image of a cross section of a sample Cu5Mo (L). The length of the black bar at the bottom of FIG. 1A is 300 μm, and the length of the light bar at the bottom of FIG. 1B is 100 μm.

  In FIG. 1A, dark particles are Cu particles (CU) and light particles are Mo particles (ML).

  In FIG. 1B, island-like phases are dispersed in the matrix phase. By energy dispersive X-ray analysis (EDS), it was confirmed that the matrix phase was made of Cu and Mo was not contained, the island-like phase was made of Mo and Cu was not contained, and the Cu phase and the Mo phase were completely separated. . Further, in the X-ray diffraction (XRD) analysis of this sample, only the crystal plane of Cu and the crystal plane of Mo were observed. The copper powder is completely melted to form a dense matrix phase. From the shape of the island phase, it is considered that a part of the Mo particles is melted.

  From the above observation, it is considered that the additive manufacturing process of the Cu / Mo mixed powder proceeded as follows. When the laser beam is irradiated, the Mo particles absorb the laser beam and transmit heat to the surrounding Cu particles. Molybdenum has a high melting point and the energy of the absorbed laser light is dissipated to the surrounding Cu particles, so that the Mo particles themselves are partially melted and remain in a broken particle shape. The temperature of the Cu particles rises due to the heat transferred from the Mo particles. Solid copper has been reported to increase its laser absorptivity and decrease its thermal conductivity with increasing temperature, and further, when copper melts, its laser absorptivity increases dramatically and its thermal conductivity decreases dramatically (Blom et al., " Process spread reduction of laser micro-spot welding of thin copper parts using real-time control ", October 2003, Proc. SPIE 4977, p.497). Therefore, once a part of the Cu particles is melted, the energy of the laser beam is directly absorbed and heat dissipation is also suppressed, so that melting is accelerated. When the Cu particles melt, the interfacial thermal resistance between the Mo particles and the liquid Cu phase decreases, the amount of heat transfer from the Mo particles to the Cu phase increases, and the “cooling” of the Mo particles is promoted. Furthermore, since the solubility of molybdenum in liquid copper is extremely low, the Mo particles remain dispersed in the Cu phase in a partially molten state.

  Next, various characteristics of the manufactured layered product were evaluated.

  A test piece for measuring thermal conductivity was produced by laminating coins having a diameter of 10 mm and a thickness of 3 mm in the direction of one diameter. The thermal conductivity was measured at room temperature in a vacuum using a laser flash method.

The electrical conductivity was estimated from the thermal conductivity. In addition, in this specification, electrical conductivity is shown by ratio (% IACS) with respect to annealing standard annealed copper. The electrical resistivity of the annealed standard annealed copper is 1.7241 × 10 ⁻² μΩ · m.

There is a relationship of the following equation between the electrical conductivity and thermal conductivity of a metal, which is known as Wiedemann-Franz law.
K / σ = LT
Here, K: thermal conductivity, σ: electrical conductivity, L: Lorentz number, T: absolute temperature. The Lorentz number (L) is theoretically given by the following equation.
^{L = (π 2/3)} · (k B / e) 2
= 2.44 × 10 ⁻⁸ WΩK ⁻²
Here, k _B : Boltzmann constant, e: elementary electric charge.

  Test specimens for measuring mechanical properties were prepared by stacking rectangular parallelepipeds 50 mm long x 6 mm wide x 11 mm high in the height direction, cutting out the three shapes shown in FIG. 2 by wire electric discharge machining, and polishing the surface. Made. The measurement of mechanical properties was performed by a tensile test at a room temperature and a strain rate of 0.001 / s using an autograph. Strain measurement was performed using a video non-contact extensometer (Shimadzu Corporation, TRView X120S).

The relative density was obtained by dividing the measured value by a calculated value obtained from the density of copper (8.89 g / cm ³ ), the density of molybdenum (10.28 g / cm ³ ), and the composition ratio of both.

  Table 3 shows the characteristics of the layered object produced. Moreover, the SEM image after carrying out the chemical etching of the cross section of a laminate-molded article with concentrated nitric acid (60% aqueous solution) in FIG. 3 and FIG. 4 is shown. The length of the black bar under each image is 300 μm.

  From Table 3, the relative density of the layered object was increased by adding Mo to Cu, and the maximum Mo content was about 0.5% by mass to about 1% by mass.

  This can also be confirmed from the SEM images of FIGS. A large pore is conspicuous in the sample Cu. As described above, with the copper powder CU alone, a dense structure cannot be obtained by laser additive manufacturing even though the melting point of Cu is 1084 ° C. In addition, when only molybdenum powder is used, a dense structure can be obtained by laser additive manufacturing even though molybdenum has a high melting point. On the other hand, in the sample containing about 0.1 mass% to about 5 mass% of Mo, the matrix phase of Cu was dense. However, the sample Cu0.1Mo did not have a large pore, but there was a coarse interface. Further, in the sample containing about 2% by mass or more of Mo, aggregation of Mo particles is observed, and in the sample Cu10Mo, a large pore is observed again, which is considered to be a cause of a decrease in relative density.

  From Table 3, the thermal conductivity and electrical conductivity of the shaped object are improved by adding Mo to Cu, the Mo content reaches a maximum at about 0.5% by mass, and the Mo content reaches about 5% by mass. The value was higher than that of the sample Cu. This is considered due to the fact that the Cu phase of the matrix is densified and that Mo does not dissolve in the Cu phase and does not impair the thermal conductivity and electrical conductivity of the Cu phase.

  FIG. 5 shows the tensile test result of the layered object. From Table 3 and FIG. 5, the 0.2% proof stress and tensile strength of the layered product increase gradually by adding Mo to Cu, and are higher than the sample Cu until the Mo content reaches about 5 mass%. showed that. Sample Cu10Mo was brittle with a layered product, and cracks were generated in the polishing process during the preparation of the test piece, so data on a tensile test could not be obtained.

  From FIG. 5, the sample Cu is poor in ductility and is broken immediately after passing through the tensile strength. From Table 3 and FIG. 5, the elongation at break of the layered object is improved by adding Mo to Cu, and in particular, it is remarkably improved as the Mo content increases to about 0.2 mass% and about 0.5 mass%. ing. On the other hand, when the Mo content was further increased, the breaking elongation of the samples Cu5Mo (K) and Cu5Mo (L) was reduced to the same level as Cu0.1Mo and Cu0.2Mo. In addition, it was as above-mentioned that the data of sample Cu10Mo were not obtained. In Table 3, there is a certain correlation between the elongation at break and the relative density, and it is considered that the denseness of the structure of the layered object affects the ductility. From this, when Mo content becomes large, it is thought that aggregation of Mo particle | grains shown in FIG. 3 and FIG. 4 has influenced.

  From the experimental results of the elongation at break, it is found that the Mo particles in the Cu phase are uniformly dispersed without agglomeration in order to improve the mechanical properties of the layered object, particularly the ductility whose index is the elongation at break. The knowledge that it was important was obtained. From this point, it is considered that the mechanical properties of the layered object can be improved by using Cu-Mo alloy powder produced by mechanical alloying as the metal powder for layered object modeling.

  Table 3 also shows the thermal conductivity values of the layered objects that were heat-treated at 700 ° C. for 30 minutes and 500 ° C. for 2 hours and then air-cooled. From Table 3, it can be seen that the thermal conductivity is not significantly changed by the heat treatment, but is slightly increased. Molybdenum does not dissolve in copper, and it is unlikely that molybdenum will diffuse through heat treatment. If the thermal conductivity is improved by the heat treatment, it is considered that the structure relaxation of the Cu matrix phase and impurities such as oxygen (O) are precipitated as oxides.

  The present invention is not limited to the above-described embodiments and examples, and can be modified within the scope of the technical idea.

  For example, in the above-described embodiments and examples, the heat source at the time of additional manufacture is laser light, but an electron beam may be used as the heat source.

Claims (4)

Copper powder and molybdenum powder each having a volume-based median value (d50) of the particle diameter measured by the laser diffraction / scattering method of 1 to 100 μm are 99.92: 0.08 to 94.5: A first step of forming a thin layer of metal powder mixed in a proportion of 5.5 ;
By irradiating meltable laser beam the molybdenum powder absorbs energy at a predetermined position of the thin layer, sequentially and repeatedly layered manufacturing in the second step of melting and solidifying at least part, the one of the metal powder Make things,
A method for producing a copper alloy shaped article. In the metal powder in which the copper powder and the molybdenum powder are mixed, the ratio of the number of molybdenum particles to the total number of particles is 13% or more.
The manufacturing method of the copper alloy modeling thing of Claim 1. Volumetric basis of particle size, measured by laser diffraction / scattering method, prepared by mechanical alloying using copper powder and molybdenum powder at a ratio of 99.92: 0.08 to 94.5: 5.5 by mass A first step of forming a thin layer of copper alloy powder having a median value (d50) of 1 to 100 μm ;
By irradiating meltable laser beam absorbs energy in a predetermined position of the thin layer, producing a multilayer molded article and a second step of melting and solidifying at least a portion of said copper alloy powder, sequentially repeating the To
A method for producing a copper alloy shaped article. It has a laminated structure of copper alloy,
The copper alloy contains 0.08% by mass to 5.5% by mass of molybdenum, with the balance being copper and less than 0.2% by mass of impurities less than molybdenum ,
It has a structure in which island-like phases made of molybdenum are dispersed in a matrix phase made of copper,
The relative density is 93.1% or more,
The electrical conductivity at room temperature is 65% IACS or higher,
Copper alloy molding.