EP3823779A1

EP3823779A1 - Use of powders of highly reflective metals for additive manufacture

Info

Publication number: EP3823779A1
Application number: EP19761729.3A
Authority: EP
Inventors: Moritz Stolpe; Jakob Fischer; Tim PROTZMANN; Michael Klosch-Trageser
Original assignee: Heraeus Additive Manufacturing GmbH
Current assignee: Heraeus Additive Manufacturing GmbH
Priority date: 2018-07-19
Filing date: 2019-07-17
Publication date: 2021-05-26
Also published as: CN112423919A; WO2020016301A1; US20210291275A1; TW202012645A; JP2021529885A

Abstract

The invention relates to the use of a metal in powder form for additive manufacture of a metal moulded body by laser beam melting, the metal being a metal of group 11 of the Periodic Table of Elements or aluminium or an alloy or intermetallic phase of one of these metals and having an oxygen content of at least 2500 ppm by weight.

Description

Use of powders of highly reflective metals for additive manufacturing

The present invention relates to the use of powders of highly reflective metals (such as copper, gold, silver or aluminum) for additive manufacturing by laser beam melting.

Additive manufacturing processes work without tools and without a mold. The volume of an object is built up layer by layer according to a digital computer model.

Metallic moldings can also be produced using additive manufacturing. For example, additive manufacturing is carried out by beam melting a metal powder (powder bed-based process). Laser or electron beams are used as beam sources (selective laser beam melting, selective

Electron beam melting).

In selective laser beam melting, the material to be processed is applied in powder form in a thin layer on the building board or in a previously deposited material layer. The powdery material is partially or completely melted locally by means of laser radiation and forms a solid material layer after solidification. The base plate is then lowered by the amount of a layer thickness and powder is applied again. This cycle is repeated until the finished shaped body is obtained. With selective Electron beam melting is the local melting of the powder by an electron beam.

The current state of additive manufacturing of metallic molded bodies, e.g. by laser beam and electron beam melting of layered metal powder, for example, describe D. Herzog et al., Acta Materialia, 117 (2016), pp. 371-392.

Metals with high electrical conductivity, especially copper, gold, silver and aluminum, are interesting materials. Because of their strong reflection in the infrared wavelength range, the processing of these materials by a laser beam represents a great challenge, since most currently available continuously radiating high-power lasers (cw Laser) exactly in this

Wavelength range work. This problem is discussed by M.

Naeem, Laser Technik Journal, Volume 10, January 2013, pp. 18-20, and in US

2015/0102016 Al described. To improve the absorption of laser radiation by highly reflective metals, lasers with a lower wavelength can be used (e.g. "green" lasers). However, these lasers currently do not have sufficient power and stability.

If a material shows a low absorption behavior in the wavelength range of the exciting radiation (e.g. due to high reflectivity), only a small amount of energy can be injected into the material, making it difficult or even impossible for the material to melt. This can lead to the fact that a stable weld pool is not formed. For the realization of relevant component properties (such as

Density, electrical and thermal conductivity, strength, surface quality), the formation of a stable weld pool is of particular importance.

In addition to the optical properties (absorption, reflection), the thermal properties of the material also influence the formation of the weld pool. For example, the thermal conductivity decides how quickly the local

coupled heat is distributed to the environment. Materials with high thermal conductivities therefore make additive manufacturing difficult. EP 3 093 086 A1 describes the use of a copper powder, which as

Contains alloying elements silicon and / or chromium for additive manufacturing by laser beam melting. The oxygen content of the copper powder is less than 1000 ppm by weight. DE 10 2017 102 355 A1 describes the production of a shaped object from a metal powder using an additive method, the powder being modified by suitable measures so that the absorption of the laser beam is increased. The metal powder is introduced into the construction space in the form of a powder layer, for example, and this powder layer is oxidized on the surface. To ensure adequate oxidation of the powder layer, the contains

Sufficient atmospheric oxygen in the installation space. The oxygen content of the surface oxidized metal powder is not specified.

US 2018/0051376 A1 describes the production of a shaped object from a metal powder by means of an additive method, the powder particles introduced into the installation space being provided with a coating of a “sacrificial material”. The sacrificial material is, for example, an oxide. The metal particles and the sacrificial material are provided separately and then the sacrificial material is applied to the powder particles using suitable coating methods, such as CVD or PVD.

P. Frigola et al., “Fabricating Copper Components with Electron Beam Melting”, Advanced Materials & Processes, July 2014, pp. 20-24 describe the production of Cu moldings by electron beam melting. However, the problem of high reflectivity does not arise. R. Guschlbauer et ab, "Challenge in the Additive Manufacturing of Pure Copper with Selective Electron Beam Melting", Metall, 11/2017, pp. 459-462 describe the production of Cu moldings

Electron beam melting.

An object of the present invention is to provide an additive manufacturing process by means of fiber beam melting, which is suitable for metals with low fiber beam absorption and also enables the production of high density metallic moldings when using fibers which work in the infrared wavelength range.

The metallic molded body obtained via additive manufacturing should preferably have other properties such as electrical or thermal conductivity, the molded body, which can be obtained using conventional processes such as Casting are made as close as possible.

The object is achieved by a process for the additive manufacturing of a metallic molded body by fiber beam melting, comprising

(i) applying a powdered metal in the form of a layer on a

Substrate in an installation space, the metal

is a metal from group 11 of the Periodic Table of the Elements or aluminum or a compound or intermetallic phase of one of these metals and

- has an oxygen content of at least 2500 ppm by weight;

(ii) selective melting of the powdery metal in the layer by means of a fiber beam and solidification of the molten metal,

(iii) applying a further layer of the powdered metal on the previously applied layer, (iv) selective melting of the powdery metal in the further layer by the laser beam and solidification of the melted metal;

(v) repeating steps (iii) - (iv) until the metallic shaped body

is finished.

The metals of group 11 of the periodic table of elements such as copper, silver or gold as well as the metal aluminum have in common that they are in the NIR range, in particular in the wavelength range of 800-1250 nm (and thus in the wavelength range of most currently available continuously radiating) High power laser) have an absorption of less than 20%.

By using a powder of these metals, the oxygen content of which is at least 2500 ppm by weight, a stable weld pool can be achieved during laser treatment. This in turn leads to the formation of a high density metal after solidification.

The metal of group 11 of the periodic table of the elements is preferably copper, silver or gold or an alloy or intermetallic phase of one of these metals.

The term “alloy of a metal” is understood to mean an alloy which contains this metal as the main component (for example in a proportion of more than 50 at%, more preferably more than 65 at% or even more than 75 at%) and also one or more alloying elements , Furthermore, the alloy can, for example, two or more of the above-mentioned metals (for example at least two metals of group 11 of the periodic table or at least one metal of group 11 of the periodic table and aluminum) in a total amount of at least 65 at%, more preferably at least 75 at% or even contain at least 85 at%. The oxygen content of the metal is determined in a reduction-extraction process in accordance with DIN EN ISO 4491-4: 2013-08.

The powdered metal preferably has an oxygen content of at least 3500 ppm by weight, more preferably at least 5000 ppm by weight

In a preferred embodiment, the powdered metal has an oxygen content in the range of 2500-15000 ppm by weight, more preferably 3500-10000 ppm by weight, more preferably 5000-10000 ppm by weight, most preferably 5500-10000 ppm by weight.

As described in more detail below, it can be preferred that the metal solidified after one of the laser melting steps or the metallic molded body undergoes a thermal treatment in a vacuum or in a reducing treatment

To undergo gas atmosphere. This thermal treatment can at least partially remove the oxygen from the metal again, which can have an advantageous effect on certain properties such as thermal or electrical conductivity. With an oxygen content of at most 15,000 ppm by weight, more preferably at most 10,000 ppm by weight, the time required for the thermal treatment can be shortened.

In an exemplary embodiment, the metal consists of copper, oxygen in one of the amounts specified above and optionally one or more further constituents which, if present, in a total amount of at most 1% by weight, more preferably at most 0.5% by weight, even more preferably at most 0.04% by weight are present.

A powdered metal containing oxygen in the amounts indicated above can be made by methods known to those skilled in the art. The powdered metal is preferably produced by spraying in an oxygen-containing atmosphere. Suitable process conditions through which the Oxygen content of the powder can be adjusted are known to the person skilled in the art or can optionally be determined by routine tests. When atomized, molten metal is broken up into small droplets and these rapidly solidify before they come into contact with one another or with a solid surface. The principle of the process is based on the division of a thin, liquid metal jet by a gas stream hitting at high speed. As is known to those skilled in the art, by varying

Process parameters such as shape and arrangement of the nozzles, pressure and flow rate of the atomizing medium or thickness of the liquid metal jet, the particle size can be set in a wide range.

Suitable particle sizes of a metal powder as part of an additive

Manufacturing processes are known to the person skilled in the art or can optionally be determined by routine tests. For example, the powdered metal has a volume distribution sum curve with particle sizes in the range of 1-100 mhi. In an exemplary embodiment, the powdered metal has a volume distribution sum curve with a di ₀ value of at least 2 mhi and a dyo value of at most 90 mhi.

The particle size distribution based on a volume distribution sum curve is determined by laser diffraction. The powder is used as a dry dispersion

Laser diffraction particle size analysis according to ISO 13320: 2009 measured and the volume distribution sum curve is determined from the measurement data. The values d _l0 and d _{90 can be} calculated from the volume distribution sum curve in accordance with ISO 9276-2: 2014. Here, for example, “d ₁₀ ” means that 10% by volume of the particles have a diameter below this value.

The application of the powdered metal in the form of a layer on one

Substrate in an installation space of a device for laser beam melting takes place under conditions which are known to the person skilled in the art in the context of an additive manufacturing process. The substrate can be the as yet uncoated building board in the installation space of the device or, alternatively, material layers of the shaped body to be produced that have already been deposited on the building board. Alternatively, you could also use a prefabricated insert on this or another material. The powdered metal is applied in layers, for example, by means of a doctor blade, a roller, a press or by screen printing or a combination of at least two of these methods. After the powder has been applied, step (ii) can be carried out, for example, without further intermediate steps.

An inert or reductive gas atmosphere is preferably present in the installation space.

In step (ii), the powdery metal is selectively melted by at least one laser beam. As is known, the term “selective” expresses the fact that, in the additive manufacturing of a shaped body, the melting of the metal powder on the basis of digital 3D data of the shaped body takes place only in defined, predetermined areas of the layer.

Lasers which can be used for additive manufacturing by laser beam melting are known to the person skilled in the art. By using the above

described metal powder can also be realized with a laser beam with a wavelength in the IR range, an advantageous melting behavior. In a preferred embodiment, an IR laser, that is to say a laser beam with a wavelength in the infrared range (for example 750 nm to 30 pm), is therefore used for the additive manufacturing of the metallic shaped body. Alternatively, however, laser beams with a lower wavelength, for example in the range of visible light (for example 400-700 nm), can also be used within the scope of the present invention. After the molten metal has solidified, step (iii) can take place, for example, without further intermediate steps. Alternatively, for example after step (ii) and before step (iii), the solidified metal can be subjected to a thermal treatment. This thermal treatment is preferably carried out in a vacuum (for example at 10 ³ to 10 ⁶ mbar, more preferably 10 ⁴ to 10 ⁵ mbar) or in a reducing gas atmosphere (for example a gas atmosphere which contains hydrogen or a forming gas). The thermal treatment is carried out, for example, at a temperature in the range from 0.1 × T _m to 0.99 × T _m , where T _{m is} the melting temperature of the metal. For example, the thermal treatment can be carried out at a relatively moderate temperature in the range from 0.1 x T _m to 0.6 x T _m . However, it is also possible to carry out the temperature treatment at a higher temperature in the range from 0.6 x T _m to 0.99 x T _m . If the metal is copper, the thermal treatment of the solidified metal is carried out, for example, at a temperature in the range from 10 ° C to 980 ° C. For example, the thermal treatment of the solidified copper can be carried out at a temperature in the range from 10 ° C to 650 ° C, more preferably 150 ° C to 400 ° C. However, it is also possible to carry out the heat treatment of the solidified copper at a higher temperature in the range from 650 ° C. to 980 ° C., more preferably 700 ° C. to 900 ° C. The thermal treatment of the solidified metal in a vacuum or in a reducing atmosphere can have an advantageous effect on certain properties, such as thermal or electrical conductivity.

Between step (ii) and step (iii), the building board is preferably lowered by an amount which essentially corresponds to the layer thickness of the powder layer applied. This procedure as part of additive manufacturing

Shaped body is generally known to the person skilled in the art.

A further layer of the powdered metal in step (iii) can be applied in the same way as in step (i). Step (iv) can also be carried out on the can be carried out in the same way as step (ii). After step (iv), thermal treatment can optionally be carried out again under those already described above

Conditions. The process steps described above are repeated until the metallic molded body is finished.

After its completion, the metallic molded body is preferably subjected to a thermal treatment. As already described above, this thermal treatment is preferably carried out in a vacuum (for example at 10 ³ to 10 ⁶ mbar, more preferably 10 ⁴ to 10 ⁵ mbar) or in a reducing gas atmosphere (for example a gas atmosphere which contains hydrogen or a forming gas). The thermal treatment is carried out, for example, at a temperature in the range from 0.1 × T _m to 0.99 × T _m , where T _{m is} the melting temperature of the metal. For example, the thermal treatment at a relatively moderate

Temperature in the range of 0.1 x T _m to 0.6 x T _{m are} carried out. However, it is also possible to carry out the temperature treatment at a higher temperature in the range from 0.6 x T _m to 0.99 x T _m . If the metal is copper, the thermal treatment of the shaped body is carried out, for example, at a temperature in the range from 10 ° C to 980 ° C. For example, the thermal treatment of the shaped body can be carried out at a temperature in the range from 10 ° C. to 650 ° C., more preferably 150 ° C. to 400 ° C. However, it is also possible to carry out the heat treatment of the shaped body at a higher temperature in the range from 650 ° C. to 980 ° C., more preferably 700 ° C. to 900 ° C. The duration of the thermal treatment is, for example, 1-180 hours, more preferably 5-40 hours. The thermal treatment of the shaped body in a vacuum or in a reducing atmosphere can affect certain

Properties such as thermal or electrical conductivity have an advantageous effect. Furthermore, the present invention relates to the use of the above

described powdery metal for additive manufacturing

Laser melting. Regarding the preferred properties of the

powdered metal can be referred to the above statements.

The invention is explained in more detail by the following examples.

Examples In the following examples and comparative examples, the following lasers were used for the selective laser melting: Yb fiber laser, 1060-1100 nm.

Example 1 In example 1, a copper powder with an oxygen content of 7300 ppm by weight was used. The powder had a volume-based particle size distribution with a di ₀ value of 20 mhi and ad ₉₀ value of 52 mhi.

The copper powder was applied in the installation space of the device in the form of a thin layer (layer thickness of approximately 20 mhi) to the building board. The metal powder was melted in defined areas of the applied layer at room temperature. Argon was used as the gas atmosphere in the installation space.

The laser melting step was then started. The laser beam moved at a speed of 500 mm / s with a beam power of 370 W and a distance of adjacent lines of 70 pm over a predefined area of 10 x 10 mm ^{2 of} the applied layer.

A stable powder was formed with the copper powder used in Example 1

Melt pool. Micrographs were made of the area captured by the laser beam. The micrographs show a structure of high density. The porosity was only 0.3%.

The electrical conductivity (% IACS) of the shaped body was determined before and after annealing (10 h at 800 ° C. in a vacuum):

Before: 64%

After: 84%

The electrical conductivity was determined using the four-point method. Example 2

In Example 2, a copper powder with an oxygen content of 5740 ppm by weight was used. The powder had a volume-based particle size distribution with a dio value of 16 mhi and a dyo value of 53 mhi.

The test parameters were identical to those in Example 1.

A stable powder was formed with the copper powder used in Example 2

Melt pool.

Micrographs were made of the area captured by the laser beam. The micrographs show a structure of high density. The porosity was only 0.2%.

The electrical conductivity (% IACS) of the shaped body was determined before and after annealing (15 h at 600 ° C. in a vacuum):

Before: 66%

After: 82%

The electrical conductivity was determined using the four-point method. Comparative Example 1

In comparative example 1, a copper powder with an oxygen content of 318 ppm by weight was used. The powder had a volume-based

Particle size distribution with a dio value of 20 mhi and a dco value of 56 mhi.

The copper powder was applied to a building board under the same conditions as in Example 1 and subjected to a laser beam treatment.

A stable molten bath could not be formed with the copper powder used in Comparative Example 1, and accordingly a mechanically stable high-density component could not be obtained.

Micrographs were made of the area captured by the laser beam. The micrographs show a defect-rich structure. The porosity was> 5%.

Comparative Example 2

In comparative example 2, a copper powder with an oxygen content of 2219 ppm by weight was used. The powder had a volume-based

Particle size distribution with a dio value of 15 mhi and a dco value of 41 mhi.

The copper powder was applied to a building board under the same conditions as in Example 1 and subjected to a laser beam treatment. A stable molten bath could not be formed with the copper powder used in Comparative Example 2, and accordingly a mechanically stable high-density component could not be obtained. Micrographs were made of the area captured by the laser beam. The micrographs show a defect-rich structure. The porosity was 4.4%.

The results of the examples described above are summarized in Table 1 below.

Table 1: Stability of the weld pool and porosity of the solidified metal

Claims

Expectations

1. A method for the additive manufacturing of a metallic molded body by

Fiber beam melting, comprising

(i) applying a powdered metal in the form of a layer on a substrate in an installation space, the metal being a metal from Group 11 of the Periodic Table of the Elements or aluminum or a cleaning or intermetallic phase of this metal and

has an oxygen content of at least 2500 ppm by weight;

(ii) selective melting of the powdered metal in the layer by at least one fiber beam and allowing the molten metal to solidify,

(iii) applying a further layer of the powdered metal on the previously applied layer,

(iv) selective melting of the powdered metal in the further layer by the fiber jet and solidification of the

molten metal;

(v) repeating steps (iii) - (iv) until the metallic molded body is finished.

2. The method of claim 1, wherein the metal is copper, silver or gold, or an embossing or intermetallic phase of one of these metals.

3. The method of claim 1 or 2, wherein the oxygen content of the powdered metal is 2500-15000 ppm by weight, more preferably 3500-10000 ppm by weight, more preferably 5000-10000 ppm by weight, most preferably 5500-10000 ppm by weight. ppm is.

4. The method according to any one of the preceding claims, wherein the powdered metal is produced by spraying in an oxygen-containing atmosphere.

5. The method according to any one of the preceding claims, wherein the

powdery metal has particle sizes in the range of 1 to 100 pm.

6. The method according to any one of the preceding claims, wherein the installation space contains an inert or reducing gas atmosphere.

7. The method according to any one of the preceding claims, wherein after the solidification of the molten metal and before the application of a further layer, the solidified metal is subjected to a thermal treatment in a vacuum or in a reducing gas atmosphere;

and / or the metallic molded body after its completion a thermal treatment in a vacuum or in a reducing

Is subjected to gas atmosphere.

8. Use of the powdered metal according to any one of claims 1-5 for additive manufacturing by fiber beam melting.