FOR ITS PREPARATION

The invention relates to a soft magnetic composite with a layered structure, comprising iron-containing layers and inorganic layers with poor electrical conductivity. The invention further relates to a process for producing a layered soft magnetic composite comprising the steps of: a) iron in powder form and a non-ferrous metallic element are loaded, without mixing them, into 1—1 separate powder containers of a recoater of the 3D printer, where the two powders are remotely dispensed from the two containers of the recoater at a predetermined location; b) after software adjustment of the predetermined layer order, the dispenser dispenses a predetermined amount of powder from one of the iron or non-ferrous metallic element to the printing area, which is spread in a uniform layer by the recorder blade of the 3D printer; c) the laser then melts the powder based on the appropriate section of the 3D model; d) steps b) and c) are repeated as required by the layering scheme to obtain a layered composite; and e) if necessary, the resulting layered composite is subjected to heat treatment to achieve improved electrical insulation. The invention also relates to a recoater for 3D printers, wherein the recoater is configured to dispense at least two different powdered materials.

PRIOR ART

The design of highly efficient and energy-saving electronics, such as motors or transformers, the conversion and transfer of electromagnetic energy is only possible by using suitable soft magnetic materials with advantages such as high saturation magnetization, high magnetic permeability, near-zero magnetostriction or even low magnetic loss. One possible solution to achieve higher power is, for example, to produce and use iron cores operating at higher frequencies. When large eddy currents are induced in the iron core, however, large losses are induced in the higher frequency range (some 10 or 100 MHz), which dissipate as heat. This heat load causes the organic insulators to degrade and the iron core to burn in the process. With proper cooling, the operating frequency range of these organic iron cores can be extended somewhat, but a cooling module must be incorporated into the system, further reducing its power balance. Therefore, the development of metal— insulator inorganic composites should be a major focus. The thinnest possible ferromagnetic layers should be separated by inorganic electrical insulating layers. This should be done in such a way that as much of the total volume as possible is ferromagnetic, so that the filling factor is high, which has a significant effect on saturation induction. If the ferromagnetic volume rate is low, it results low saturation induction, which means that only a low-performance device can be done with the given iron core.

In a scientific publication ["Soft magnetic composites prepared by 3D laser printing", Acta Physica Polonic, 137 (2020) 5:886-888], Kocsis and co-workers describe a core— shell structured iron— iron phosphate soft magnetic composite fabricated by both conventional powder metallurgy and 3D printing. By comparing the two composites, which were produced in different ways, it was concluded that it is not possible to ensure both proper mechanical strength and electrical insulation properties for this pair of materials (iron and iron phosphate) at the same time. The conventionally produced pattern is more compact and more resistant to mechanical stress, but its electrical insulation properties are not perfect and it cannot be used effectively in the higher frequency range. The eddy current losses of the 3D printed sample start to increase only in the 10 MHz range, but its mechanical properties, density and homogeneity are worse than those of the conventionally produced sample.

In another paper ["Metallographic and magnetic analysis of direct laser sintered soft magnetic composites", Journal of Magnetism and Magnetic Materials, 501 (2020) 166425], Kocsis and co-workers describe a 3D-printed iron— silicon composite. Based on the publication, the aim was to design a composite, in which Si diffuses slightly into the Fe layer — further improving its magnetic properties (e.g., reduced magnetostriction) — and the Si layer, if thick enough, has a quasi-pure Si layer, which, as a semiconductor, would increase the electrical resistivity of that layer somewhat, thus reducing the induced eddy currents. The results, however, give an almost completely homogeneous Fe— Si alloy iron core with a gradient transition in the amount of Si or Fe (depending on which one is being investigated) depending on the layer order. Thus, the Si layer also became Fe— Si and drastically reduced the cut-off frequency of the iron core, which was about 10 kHz. Microscopic studies have shown that the diffusion movements had destroyed the sample and that the originally pure Si layer had no insulating function, i.e., the technical objective had not been achieved.

International patent application IDO 2009060895 Al/ discloses a high-strength soft magnetic composite. According to the cited document, the composite — unlike the composite according to the present invention — has a core— shell structure and is produced by pressing/buming, wherein the ferromagnetic iron grains are surrounded by a magnesium oxide shell. International patent application WO 2012115137 A1 also discloses a core— shell composite. The composite has low magnetostriction and high magnetic flux density. The composite contains pure iron-based powder particles and Fe— Si alloy powder particles, where the iron-based powder particles are covered with magnesium- or phosphate-containing film as an insulating layer. According to the cited document, the composite shown is produced by pressing and heat treating in a non-oxidizing atmosphere, with the addition of methyl-, methylphenyl- or phenyl-based silicone resins as auxiliary materials. During heat treatment, the products of these resins will separate the powder particles that constitute the composite. From the preparation, it is seen that, unlike the present invention, organic material is used to separate the ferromagnetic grains from each other to produce the composite.

Patent US 6338900 B1 discloses a soft magnetic composite and its preparation. In the production process, a sintered powder of soft magnetic ferrite (Mg— Zn-ferrite) is dispersed in a polymer. The said polymer is polyolefin, polyamide or poly(arylene sulphide). An essential feature is that the sintered powder particles have a random shape and a particle size at least twice that of the average crystal particle size found in them. The sintered powder is granulated into granules by spray drying with ferrite powder, the resulting granules are sintered and then ground.

Patent US 9767956 B2 discloses a composite particle with a core of a soft magnetic metallic material, the core being covered by coating particles, consisting of a soft magnetic material other than the core material to form a so-called fusion-bonded coating. According to the document, the essence of a fusion-bonded coating is that the core and the coating are chemically bonded together, by the core and its material being temporarily melted under pressure. The core is a Fe— Si based material and the coating is pure iron, Fe— B, Fe— Cr or Fe— Ni-based.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: A 3D model of the 3D-printed toroidal iron core according to Example 1 (a), the printed toroidal sample (b) and a microscopic image of the Fe— TiN layer change (c).

Figure 2: The graphical result of a composition analysis performed by a scanning electron microscope (SEM) along the Fe— Ti layer change of the 3D-printed toroid according to Example 1.

Figure 3: Magnetic permeability spectrum of the 3D printed toroid according to Example 1.

Figure 4: CT scan of the 3D printed toroid according to Example 1 for porosity measurement.

Figure 5: An embodiment of a recoater according to the invention.

THE TECHNICAL PROBLEM TO BE SOLVED BY THE INVENTION

The technical problem to be solved by the invention is the preparation of a soft magnetic composite having the following advantageous properties: a) it contains iron-containing layers and layers with poor electrical conductivity in thicknesses of several tens of micrometers, between which chemical bond is formed to provide adequate mechanical strength; b) it is more resistant to thermal stresses than state-of-the-art soft magnetic composites containing layers of organic insulators; c) it has a high saturation induction and a high frequency limit, thus ensuring high energy density during operation.

High saturation induction is necessary to deliver the right power. Additionally, the high operating frequency is necessary to reduce the size of the iron core and thus ensure a better energy balance.

DISCOVERY ON WHICH THE INVENTION IS BASED

In order to achieve these goals, we have carried out systematic experimental work, resulting in our invention. In our experiments, we were surprised to find that we could achieve the technical goal we had set, a) if soft magnetic composites with a layered structure are produced by 3D printing to ensure the thinnest possible ferromagnetic layers (Fe layer thickness: 20—200 /an, the thickness of the poor conductive layer: 20—100 /im); b) if the ferromagnetic layers in said layered composite are separated by inorganic layers having poor electrical conductivity; and c) if the said layered composite is produced using iron and some other metallic element, where the other metallic element is selected according to the following properties

(i) have a sufficiently low diffusion rate that the iron and the other metallic element are not completely mixed during the printing process; and

(ii) be able to form a strong cohesive bond with the iron layer, thus providing adequate mechanical properties of the final product; and

(iii) the electrical resistance of the other metallic element may be increased by a chemical or thermal treatment (e.g., nitriding or oxidation), i.e., to form a poor conductive layer, simultaneously with or after the production of the composite.

BRIEF DESCRIPTION OF THE INVENTION

1. A layered soft magnetic composite, comprising iron-containing layers and layers comprising a compound of a non-ferrous metallic element, wherein the iron layer thickness is 20—200 /zm, the thickness of the layer comprising a compound of a non-ferrous metallic element is 20—100 /an and wherein the compound of a non-ferrous metallic element is titanium nitride or titanium oxide.

2. The soft magnetic composite according to point 1, wherein the iron-containing layers and layers comprising a compound of a non-ferrous metallic element are arranged alternately, wherein the number of iron-containing layers is 1—10 and the number of layers comprising a compound of a non-ferrous metallic element is 1—10 and the thickness of the layers is about 20—10 /trn.

3. The soft magnetic composite according to any one of points 1 to 2, wherein the iron and the non-ferrous metallic element have a volume ratio of 1:2 to 10:1.

4. The soft magnetic composite according to any one of points 1 to 2, wherein the volume ratio of the iron to the non-ferrous metallic element is 1:1 to 1:2. 5. A process for producing layered soft magnetic composite wherein the process comprises the following steps: a) iron in powder form and a metallic element other than iron are loaded — without mixing them — into 1—1 separate containers of a recoater of a 3D printer, where the two powders can be dispensed from the two containers of the recoater; b) the layering scheme is set, c) according to the layering scheme, a predetermined amount of powder from one of the ferrous or non-ferrous metallic elements is fed into the printing area by the feeder and spread in a uniform layer by the recoater blade of the 3D printer; d) laser melts the powder; and e) steps c) and d) are repeated one or more times, preferably up to 20 times, to obtain a layered composite; and f) optionally, the resulting layered composite is heat-treated to achieve better electrical insulation.

6. The process according to point 5, wherein the 3D printing is performed applying a shielding gas atmosphere, preferably nitrogen or argon.

7. The process according to point 5 wherein titanium is used as a metallic element other than iron.

8. The process according to any one of points 5 to 7 wherein said layering scheme is such that the iron powder and the metallic element other than iron in a powder form are alternately fed to the printing area by the recoater.

9. The process according to any one of points 5 to 8 wherein the parameters used in 3D printing are the following: layer thickness: 20 zm, wavelength of the laser beam: 1016 nm, scanning speed: 500— 1000 mm/s, laser power: 110— 185 W, table temperature: 40— 100 °C, scanning strategy: 60° rotation per layer.

10. The process according to any one of points 5 to 9 wherein the heat treatment is carried out in an oxygen-rich environment with a 0.5 to 20 hour heat treatment at a temperature of 500 to 850 °C. 11. Apparatus comprising a powder dispensing adapter, wherein the powder dispensing adapter is adapted to dispense at least two different raw materials in powder form, the powder dispensing adapter comprising two separate 4 powder containers and a 5 housing for holding them; the two 4 powder containers containing the6 raw materials in powder form being contained in the 5 housing: the fixing, bearing and 7 sealing of the 8 splined shafts and the electric motors responsible for driving them; an adapter according to the invention is mounted on the original 2 recoater mechanism of the laser sintering machine, as well as 10 sensors for distance detection, which are connected to a 1 computer by means of a vacuum tight cable (gas-tight) outlet, the 9 power supply for the electric motors and the 10 ultrasonic sensors is also introduced by means of a vacuum tight cable (gas-tight) outlet; and the 11 component is printed on the 12 work surface.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the invention, "one printing cycle" is understood to mean the entire printing process from laser sintering of the first layer of the 3D model of the part to be produced to the final layer.

In the implementation of our invention, we rejected the possibility of using ceramics or other inorganic materials in the design of the layered composite. The disadvantage of organic insulating layers (degradation of organic insulating materials under thermal stress) has been mentioned above. To print ceramics, a laser source with a wavelength of about 10 /an is needed, while to melt metal, a wavelength of 1 /an is required. This can only be done with two different laser sources (e.g., 1 solid-state laser and 1 CO2 laser) can be used. There is, however, no commercially available equipment for this. Furthermore, it would be quite expensive and timeconsuming to build an installation. There are also questions about how the ceramic layer would behave against the huge internal stresses that would arise during printing. Therefore, in the implementation of our invention, we came to the discovery that we are printing iron and some other metallic element, where the diffusion rate of the other metallic element is low, so that the iron and the other metallic element will not be completely mixed during the printing process, but at the same time a strong cohesive bond is formed between them, which gives good mechanical properties to the final product.

We further recognized that the second metallic element other than iron must be chosen so that its electrical resistance can be increased by a chemical or thermal treatment (such as nitriding or oxidation) at the same time as or after printing. In view of the foregoing, examples of metallic elements other than iron that may be used in the production of the composite according to the invention include, without limitation, titanium, aluminum, nickel, cobalt, chromium.

For example, titanium is highly susceptible to oxidation, more than the iron. If melted in a nitrogen atmosphere, it will nitride. Since the EOSINT M270 equipment we used was using nitrogen shielding gas by default, the Ti layer that was being melted was always nitrided during the printing process. The preparation and properties of the resulting Fe— iN composite are described in Example 1.

In another embodiment, the 3D printer is modified so that instead of a nitrogen generator, an argon cylinder is attached to the machine and printing is done under argon shielding gas. Thus, at the end of the printing process, pure Ti and Fe, or a mixed phase of the two elements at the interface, will be present. Subsequently, Ti is oxidized, by annealing in oxygen-rich environment, to obtain TiO, which has a higher electrical resistivity than titanium nitride (see Example 2).

Based on the foregoing, the invention is a soft magnetic composite with a layered structure, comprising iron-containing layers and inorganic layers with poor electrical conductivity.

In one embodiment of the composite according to the invention, the thickness of the iron layer is 20—200 zm, while the thickness of the layer, which has poor electrical conductivity layer is 20—100 zm.

In a preferred embodiment of the composite according to the invention, the iron- containing layers and the inorganic layers with poor electrical conductivity are alternately arranged, wherein the number of iron-containing layers is 1—10 and the number of poor electrically conductive layers is 1—10 and the thickness of the layers is about 20 zm.

In a preferred embodiment of the composite according to the invention, the inorganic layers with poor electrical conductivity comprise a compound of the metallic element other than iron, wherein preferably, the metallic element is titanium and the compound of the metallic element is titanium nitride or titanium oxide.

In one embodiment of the composite according to the invention, the volume ratio of the iron to the non-ferrous metallic element is 1:2—10:1. In a preferred embodiment of the process according to the invention, the volume ratio of the iron to the non-ferrous metallic element is 1:1— 1:2.

The invention further relates to a process for producing a layered soft magnetic composite, comprising the following steps: a) iron in powder form and a metallic element other than iron are loaded — without mixing them — into 1—1 separate containers of a recoater of a 3D printer, where the two powders can be dispensed from the two containers of the powder remotely, at a specific location; b) after software adjustment of the specified layering scheme, a predetermined amount of powder from one of the ferrous or non-ferrous metallic elements is dispensed to the printing area by the feeder and spread in a uniform layer by the recoater blade of the 3D printer; c) the laser then melts the powder based on the corresponding section of the 3D model; and d) steps b) and c) are repeated as prescribed by the layering scheme to obtain a layered composite; and e) optionally, the resulting layered composite is heat-treated to achieve better electrical insulation.

In one embodiment of the process according to the invention, shielding gas is used during 3D printing. Examples of the above-mentioned shielding gases include nitrogen and argon.

In a preferred embodiment of the process according to the invention, the metallic element other than iron is titanium. In a preferred embodiment, said layering scheme is such that the iron powder and the metallic element other than iron in a powder form are alternately fed to the printing area by the recoater.

In one embodiment of the process according to the invention, the parameters used in 3D printing are: layer thickness: 20 zm, wavelength of the laser beam: 1016 nm, scanning speed: 500—1000 mm/s, laser power: 110—185 W, table temperature: 40—100 °C, scanning strategy: 60° rotation per layer.

In an embodiment of the process according to the invention, the heat treatment is carried out in an oxygen-rich environment within 1 hour, within the temperature was kept at 500-850 °C. The invention further relates to a layered soft magnetic composite comprising iron- containing layers and the inorganic layers with poor electrical conductivity, wherein said composite can be produced by the process according to the invention.

The invention further relates to an apparatus comprising a recoater, wherein the recoater is configured to dispense at least two different raw materials in powder form.

In one embodiment (see Figure 5), the recoater consists of two separate 4 powder container and 5 housings for mounting them. Different 6 raw materials were placed in the two 4 powder containers in powder form. The 5 housings are used to mount the 8 splined shafts, their bearings, 7 seals, and the electric motors that drive them. The adapter according to the invention was mounted on the original 2 recoater unit mechanism of the laser sintering, as well as 10 ultrasonic sensors for distance sensing. These allow us to control the location where our individual recoater equipment should start dispensing the powder. The 10 ultrasonic sensors were connected to a 1 computer via a vacuum tight cable outlet. A gas-tight connection solution is essential to prevent an increase in the oxygen concentration in the 3 printing workspaces. This connector is also used to connect the 9 power supply for the electric motors and the 10 ultrasonic sensors. In each case, the 11 parts are printed on a pre -made 12 worksheet.

In the following, we illustrate our invention with exemplified embodiments, which are not intended to be interpreted as limitations of the invention.

EXAMPLES

Example 1: Production of Fe-TiN composite

In this embodiment, the preparation of Fe— TiN composite and the properties it are described.

The example composite was produced by an EOSINT M270 3D printer, where the 3D printer was equipped with a custom-made recoater that, when mounted on the recoater unit of the 3D printer, could handle two different materials (in this case, high purity elemental iron powder and titanium powder) within one print cycle. Production parameters:

The volume ratio of iron— titanium: 1 :2

Average particle size of the raw material powders: 50 zm.

Number of layers formed: Fe: 5 layers, TiN: 10 layers. The essential parameters of printing:

- shielding gas: nitrogen,

- layer thickness: 20 zm,

- wavelength of the laser beam: 1016 nm,

- scanning speed: 800 mm/ s,

- temperature of the building platform: 100 °C.

Line analyses were performed using scanning electron microscope to display the separate Fe— TiN layers. It has been proven that in the Ti layer, there is an intersection, where almost 0 wt% iron is present. That is, with proper nitridation (or oxidation), it is reasonable to expect the insulating function to work.

Figure 1 shows the 3D model of the 3D-printed toroidal iron core (a), the printed toroidal sample (b) and a microscopic image of the Fe— TiN layer change (c).

Figure 2 illustrates the results of the composition analysis of the 3D-printed toroid using a scanning electron microscope (SEM) along an Fe— Ti layer change.

The permeability spectrum of the 3D -printed sample was investigated. The results of the measurement are shown in Figure 3. Furthermore, the CT scan for the porosity measurement is shown in Figure 4.

After the measurement, the printed sample was placed in an oven at 500 °C for 1 hour in an air atmosphere to test the oxidation behavior of nitrided titanium. This experiment did not result in any significant change in the magnetic properties (see Figure 3). Figure 3 shows the real (u) and imaginary (u") parts of the magnetic permeability spectrum. Where the maximum of the imaginary part (u") is found, there is the frequency limit of the iron core, too. In the present case, it can be seen that TiN isolates the Fe layers much better than Si in the case of the Fe— Si composite known from the state of the art, since the frequency limit in the composite of the present example is in the region of 40 MHz, compared to the 10 MHz region in the state of the art, so that the eddy current losses in the composite of the invention start to increase significantly at much higher frequencies. Example 2: Production of Fe-TiO composite

Everything was done as described in Example 1, except the printing was done under argon shielding gas, so it was ensured that the product obtained at the end of the printing was pure Ti and Fe, and that the interface between the two was a mixed phase of the two elements. After printing, Ti is subsequently oxidized by annealing in an oxygen-rich environment to obtain TiO, which has a higher electrical resistivity than titanium nitride. The heat treatment was carried out at 500 °C in an air atmosphere for different periods (1, 4, 8, and 12 hours), the sample was placed in a 500 °C oven and allowed to cool in air after the end of the heat treatment period. INDUSTRIAL APPLICABILITY

The process according to the invention provides the production of soft magnetic composites with a layered structure that can be used in the design of highly efficient and energysaving electronic devices, such as motors or transformers. These composites are more resistant to thermal stress than the soft magnetic composites (e.g., composites formed from ferromagnetic layers impregnated with polymer resins) known from the prior art.