RU2718946C1 - Method of producing granular metal-particle composition (feedstock) and composition obtained using said method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to processing of metal powders, namely to production of granulated materials (feedstocks) used for production of metal products by injection moulding/pressure casting and additive production. Deagglomeration and microcapsulation of particles of bimodal metal powder containing nanoparticles with size of less than 100 nm and microparticles with size of not more than 5 mcm is carried out with content of nanoparticles in the mixture of not more than 20 wt. %. Method then includes mechanical mixing of microencapsulated powder particles with binder, which is a mixture of thermoplastic polymer and plasticiser. Mixture is heated and extruded to produce granules containing bimodal metal powder, microencapsulating organic substance, plasticiser and thermoplastic polymer at the following ratio of components, wt. %: bimodal metal powder 85–95; microencapsulating organic substance 0.5–1.5; plasticiser 0.1–1.5; thermoplastic polymer 2–14.

EFFECT: ensuring uniform distribution of nano- and microparticles in volume of granules, fluidity in the temperature range of 115–160 °C, reduction of sintering temperature and density of sintered parts of not less than 0_95 of theoretical density.

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Description

FIELD OF TECHNOLOGY

The invention relates to the field of processing of metal powders, in particular to the production of granular materials (feedstock) used to obtain metal products by injection molding / injection molding and additive manufacturing.

BACKGROUND

Known metal-polymer composition for the manufacture of steel billets, disclosed in [RU 2310542, publ. November 20, 2007], obtained by mechanical mixing of two mixtures, the components of one of which are highly dispersed powders of at least one alloying element, iron and iron oxide, wt.%, And the components of the second are thermosetting phenol-formaldehyde resin 8-15 wt.% And plasticizer - salt of stearic acid.

The disadvantages include the fact that to create a metal-polymer composition, a mixture of powders of different metals and iron oxide is used, and there may be a problem of uniform distribution of alloying additives in the metal-polymer composition of iron / iron oxide.

A known method of producing metal feedstock for PIM technologies, disclosed in [RU 2630142, publ. 09/05/2017], including mechanical mixing of a metal powder and a binder, while powders based on a metal selected from Fe, Ti, Al are used as a metal powder, and paraffin and wax are used as a binder.

The use of paraffin and wax as a binder due to the low melting temperature of the binder does not allow molding products using injection molding machines. High fragility of products using paraffin and wax does not allow molding parts in automatic mode.

A known feedstock for 3D manufacturing processes, in particular Fused Filament Fabrication, disclosed in [WO2018091517 (A1) - 2018-05-24] containing (P) sintered particles made of metal, metal alloy, glass, ceramic material or mixtures thereof; and (B) a binder composition containing a plasticizer (b1) 5-15 wt.% from the total weight of the polymer composition and a polymer binder component (b2) 85-95 wt.% of the total weight of the binder composition, the amount of sintered particles (P) is 40 vol.% or more of the composition.

The disadvantages of the above include the possible uneven distribution of components - metal particles - over the volume of granules used in the future to obtain a metal-polymer thread (billet, core), which is used for layer-by-layer 3D printing of the product (additive technology). The uneven distribution is due to the fact that in the manufacture of feedstock, mainly particles with a size of 50-100 microns and very few nanoparticles with a size of 0.1 microns are used, and particles larger than 1 micron are more preferred, and this can lead to high porosity in the final product.

Known feedstock in the form of a thread, disclosed in [WO2016004985 (A1) - 2016-01-14] (filament), suitable for use in a device for 3D printing (Fused Deposition Modeling Device), where the thread contains a metal and / or ceramic powder, thermoplastic binder and additives. The invention also relates to the use of a binder for the manufacture of filaments for 3D printing devices. The following components are used to obtain feedstock: a binder and stainless steel powder with an average diameter of 15 microns obtained by atomization are mixed at 130 ° C in a mixer and homogenized for 1 hour to obtain a plastic composition.

The disadvantages of this technical solution can be attributed, as in the above size of the used particles. Metal particles are obtained by atomization, which allows to obtain particles of only micron size, i.e. in the initial powder there are no nanoparticles providing a decrease in the sintering temperature of particles and a dense packing of particles.

SUMMARY OF THE INVENTION

The basis of the invention is the task of developing a method for producing granular material (feedstock) based on bimodal microencapsulated metal powders made of / on the basis of nano- and microparticles of heat-resistant, heat-resistant, corrosion-resistant alloys for molding complex parts using additive technologies and injection molding.

EFFECT: obtaining a feedstock having fluidity in the temperature range 115 - 160 ° C, with a uniform distribution of nano- and microparticles in the volume of feedstock granules, which ensures a decrease in sintering temperature and density of sintered parts of at least 0.95 of the theoretical alloy density.

The problem is achieved in that, like the known proposed method for producing a granular metal powder composition (feedstock), involves mechanical mixing of the metal powder and a binder.

New is the fact that the aforementioned feedstock for forming complex parts is obtained in two stages:

- deagglomeration and microencapsulation of bimodal metal powder particles based on nano- and microparticles;

- mechanical mixing of the microencapsulated particles with a polymer and a plasticizer, heating the resulting mixture and extruding the melt to obtain granules.

In this case, bimodal powders are used as a metal powder, consisting of nano- and microparticles of alloys selected from the group including heat-resistant, heat-resistant, and corrosion-resistant alloys based on iron, as well as chromium-nickel alloys.

And as a binder, a melt of a thermoplastic polymer selected from the group consisting of polylactide, polymethyl methacrylate, polystyrene, a copolymer of ethyl vinyl acetate, low density polyethylene, polyethylene wax or a mixture thereof, and a plasticizer selected from the group consisting of dibutyl phthalate, dibutyl sebacinate is used.

In addition, deagglomeration and microencapsulation is carried out by mixing a bimodal powder based on nano- and microparticles with a solution of microencapsulating organic matter and simultaneously dispersing the mixture in the form of a suspension of the above powder in a solution with a concentration of from 1% to 10%, in the following ratio, wt.%:

Bimodal powder based on nano- and microparticles of metal alloys 98.5-99.5;

Microencapsulating organic matter 0.5-1.5.

In this case, deagglomeration and microencapsulation of particles of the above-mentioned bimodal powder is carried out by mixing it with a solution of microencapsulating organic matter in isopropyl alcohol or an oil solvent and simultaneously dispersing the resulting suspension.

Also as microencapsulating organic substances use organic compounds containing polar functional groups, including oxygen or nitrogen and oxygen, providing a strong interaction of organic molecules with metal cations on the surface of nano- and microparticles.

Preferably, acetylacetone solutions are used as microencapsulating organic matter; PEG400 polyethylene glycol and PEG 6000; polyethylene glycol ether syntanol DS-10; 1,5-diaminoanthraquinone, oleic and / or stearic acid, and alcohols, for example, isopropyl alcohol, ethanol, or low boiling hydrocarbons, for example petroleum ether, nefras 80-120, are used as a solvent.

In addition, to obtain granules of the metal powder composition of the required size, the resulting mixture of microencapsulated metal powder and a binder is heated and extruded.

The granular metal powder composition (feedstock) obtained by the above method is intended for additive manufacturing or injection molding (injection molding) of complex metal parts.

The ratio of components in the resulting granular metal material, mass. %:

Bimodal Metal Powder 85-95 Microencapsulating substance 0.5-1.5 Plasticizer 0.1-1.5 Polymer 2-14

To achieve the technical result of the present invention, it is proposed to use bimodal powders consisting of nano- and microparticles of alloys obtained by the method of electric wire explosion (EEC), in which nanoparticles fill the space between the microparticles, help reduce the sintering temperature of the “green” parts and provide low porosity of the product after sintering. The EVP method allows one to obtain bimodal powders in which nanoparticles and microparticles are uniformly mixed with each other, in contrast to bimodal powders obtained by mixing two powders — nanopowders and micropowders obtained by other methods. In addition, when using powders obtained by EEC, it is possible to exclude the long and costly stage of mixing the two powders.

Bimodal powders obtained by the EVP method include nanoparticles up to 100 nm in size and microparticles up to 5 microns in size. The limitation in the size of microparticles to 5 μm is associated with a lower sintering temperature of such particles compared to larger microparticles. Nanoparticles fill the space between the microparticles and also provide a reduction in sintering temperature. In addition, nanoparticles provide a decrease in the viscosity of the metal powder composition. However, with an increase in the content of nanoparticles over 20%, an increase in the viscosity of the metal-powder composition occurs. Thus, the selected dimensional characteristics of nano- and microparticles and the indicated content of nanoparticles in bimodal powders make it possible to reduce the sintering temperature of particles, lower the viscosity of the metal powder composition and, thereby, increase the content of bimodal powder in the metal powder composition.

Deagglomeration is carried out simultaneously with microencapsulation to destroy large agglomerates, prevent oxidation, uniform distribution of nano- and microparticles in the polymer. Particle microencapsulation improves the combination of nano- and microparticles with polymers.

To obtain a metal-powder composition, microencapsulated metal powder is combined with a mixture of polymers and plasticizer, using thermoplastic polymers, for example, low density polyethylene, high density polyethylene, polypropylene, ethyl vinyl acetate copolymer, polystyrene, polymethyl methacrylate, polylactide, polyethylene wax or mixtures thereof, and dibutyl phthalate or dibutyl sebacinate is used as a plasticizer.

Microencapsulating organic substances (acetylacetone; polyethylene glycol PEG400 and PEG 6000; polyethylene glycol ether syntanol DS-10; 1,5-diaminoantraquinone) are used in an amount of 0.5-1.5% by weight. Such an amount is necessary for the formation of a thin protective layer on the surface of the particles. Less than 0.5% of the mass. not enough for uniform and complete microencapsulation of nano- and microparticles of alloys. The use of more than 1.5% of the mass. microencapsulating substances leads to the adhesion of particles together with the formation of large agglomerates. The specified concentration range provides complete dissolution of the organic matter and uniform thin coating of the alloy particles with a microencapsulating substance.

Plasticizers (dibutyl phthalate or dibutyl sebacinate) are used in an amount of 0.1 - 1.5% of the mass. to increase the plasticity of polymers during processing. The additive is more than 1.5% of the mass. plasticizer leads to sweating and the formation of large drops.

The content of the alloy powder should be 85 to 95% of the mass . The powder content is less than 85% of the mass. leads to significant shrinkage of sintered products, and with more than 95% of the mass. Melt flow decreases.

Granular material (feedstock) can be used for molding products in the following ways:

- injection molding, or injection molding in an automatic molding machine: granules of the metal-powder composition are loaded into the hopper, heated, the resulting plastic mass is supplied under pressure to the mold for molding products;

- additive molding using a 3D printer with a microextruder, nozzle diameter 0.7 mm: the granules of the metal powder composition are loaded into the hopper, heated to a softening temperature, a thread 0.7 mm thick is extruded from the resulting plastic mass with an extruder screw and the product is printed in layers.

THE INVENTION IS EXPLAINED BY GRAPHIC MATERIALS

Figure 1 presents micrographs of bimodal powder alloys: a) XN70YU, b) XH60BT and c) 316L.

Figure 2 presents TEM micrographs of microencapsulated bimodal powders of alloys: a) ХН70Ю, b) ХН60ВТ and c) 316L.

Figure 3 presents microphotographs of fractures of granules of a metal powder composition based on microencapsulated bimodal powders of alloys: a) ХН70Ю, b) ХН60ВТ and c) 316L.

Figure 4 presents a fracture of a part printed using a 3D printer, feedstock from a 316L grade corrosion-resistant alloy.

In FIG. 5 shows a fracture of a part obtained by injection molding, a feedstock of a 316L grade corrosion-resistant alloy.

DETAILED DESCRIPTION OF THE INVENTION

The invention is also illustrated by the following examples of specific performance.

Example 1. Obtaining feedstock from a heat-resistant alloy brand ХН70Ю. On figa presents an SEM image of a bimodal powder alloy ХН70Ю.

Deagglomeration and microencapsulation of bimodal powder of ХН70Ю alloy.

0.46 g of stearic acid is dissolved in 600 ml of hydrocarbon solvent Nefras 80-120. 60 g of bimodal alloy powder is added to the solution and mixed with a homogenizer at a speed of 5000 rpm for 30 minutes. The bimodal powder was obtained by the EEC method and contains nanoparticles and microparticles with a size of not more than 5 microns. The average nanoparticle size is 80 nm, the content of nanoparticles is 16% of the mass. Then, the solvent was distilled off using a rotary evaporator and microencapsulated powder was recovered. Accumulate about 470 g of microencapsulated powder alloy ХН70Ю. On figa presents a TEM image of a microencapsulated bimodal powder alloy ХН70Ю.

Combination of microencapsulated particles of a bimodal powder of KhN70Y alloy with a melt of a polymer mixture.

A mixture of polymers consisting of 15 g of polymethylmethacrylate, 15 g of polyethylene wax and 1.5 g of dibutyl phthalate plasticizer is loaded into a sigma-Z-shaped mixer and stirred at a speed of 200 rpm for 30 minutes. Then, gradually stopping the stirring, add 470 g of microencapsulated powder of ХН70Ю alloy, heat and mix at a temperature of 140 ° С at a speed of 200 rpm for 1 hour.

The heated mixture is loaded into the hopper of the extruder, heated to 160 ° C and extruded to obtain granules of a metal powder composition based on ХН70Ю alloy.

Feedstock composition, mass. %

ХН70Ю alloy powder 93 Stearic acid 0.7 Dibutyl phthalate 0.3 Polyethylene wax 3 Polymethylmethacrylate 3

On figa presents a fracture of a granule based on alloy XH70U, showing a uniform distribution of nanoparticles, microparticles and a polymer binder.

Example 2. Obtaining feedstock from a heat-resistant alloy brand ХН60ВТ. In FIG. 1b shows an SEM image of a bimodal powder of an XH60BT alloy.

Deagglomeration and microencapsulation of bimodal powder alloy ХН60ВТ.

0.4 g of PEG400 is dissolved in 600 ml of isopropyl alcohol. 60 g of bimodal alloy powder is added to the solution and mixed with a homogenizer at a speed of 5000 rpm for 30 minutes. The bimodal powder of the XH60BT alloy obtained by the EEC method contains nanoparticles with an average size of 75 nm, and microparticles with a size of not more than 5 μm. The content of nanoparticles is 14% of the mass. Then, the solvent was distilled off using a rotary evaporator and microencapsulated powder was recovered. Accumulate about 470 g of microencapsulated powder alloy XH60BT. Figure 2b shows a TEM image of a microencapsulated bimodal powder of an XH60BT alloy.

Combination of microencapsulated particles of a bimodal powder of an XH60BT alloy with a melt of a polymer mixture.

A mixture of polymers consisting of 12.5 g of a copolymer of ethyl vinyl acetate, 17.5 g of polyethylene wax and 2 g of a plasticizer of dibutyl phthalate is loaded into a sigma-Z-shaped mixer and stirred at a speed of 200 rpm for 30 minutes. Then, gradually stopping the stirring, add 470 g of microencapsulated powder of KhN60BT alloy, heat and mix at 140 ° C at a speed of 200 rpm for 1 h. The heated mixture is loaded into the extruder hopper and processed into granules at 160 ° C. Get granules of metal powder compositions based on alloy KhN60BT size 1-5 mm

Feedstock composition, mass. %

XN60WT Alloy Powder 93 PEG400 0.6 Dibutyl phthalate 0.4 Polyethylene wax 3,5 Ethyl Vinyl Acetate Copolymer 2,5

Figure 3b shows a fracture of a granule based on the KhN60BT alloy, showing a uniform distribution of nanoparticles, microparticles and a polymer binder.

Example 3. Obtaining feedstock from a corrosion-resistant alloy grade 316L. In FIG. 1c shows an SEM image of a bimodal powder of alloy 316L.

Deagglomeration and microencapsulation of bimodal powder alloy 316L.

0.33 g of syntanol DS-10 is dissolved in 600 ml of isopropyl alcohol. 60 g of bimodal alloy powder 316L are added to the solution and mixed with a homogenizer at a speed of 5000 rpm for 30 minutes. The bimodal powder of alloy 316L obtained by the EEC method contains nanoparticles and microparticles. The average nanoparticle size is 75 nm, the content of nanoparticles is 14% of the mass. The size of the microparticles is not more than 5 microns. Then, the solvent was distilled off using a rotary evaporator and microencapsulated powder was recovered. Approximately 470 g of microencapsulated alloy 316L powder is accumulated. In FIG. 2c shows a TEM image of a microencapsulated bimodal powder of alloy 316L.

Combination of microencapsulated particles of bimodal powder of alloy 316L with polymer melt.

A mixture of polymers consisting of 17.5 g of polylactide, 14 g of polyethylene wax and 1 g of dibutyl sebacinate plasticizer is loaded into a sigma-Z-shaped mixer and stirred at a speed of 200 rpm for 30 minutes. Then, gradually, without stopping stirring, 470 g of microencapsulated 316L alloy powder was introduced, heated and stirred at 140 ° C at a speed of 200 rpm for 1 h. The heated mixture was loaded into the extruder hopper and processed into granules at 160 ° C. Get granules of metal powder composition based on alloy 316L with a size of 1-5 mm

Feedstock composition, mass. %

Alloy Powder 316L 93 Sintanol DS-10 0.5 Dibutylsebacinate 0.2 Polyethylene wax 2,8 Polylactide 3,5

On figv presents a fracture of the granule based on alloy 316L, showing a uniform distribution of nanoparticles, microparticles and a polymer binder.

Example 4. Additive molding of parts.

The feedstock from a 316L corrosion-resistant alloy obtained according to Example 3 is loaded into the hopper of a 3D printer equipped with a microextruder with a nozzle diameter of 0.7 mm, heated to a feedstock melting point of 140 ° C and the product is printed using the resulting filament. In FIG. 4 is a fracture of a part printed using a 3D printer, showing a uniform distribution of nanoparticles, microparticles and a polymeric binder, and low porosity of the green part.

Example 5 - Injection Molding

Feedstock from a 316L corrosion-resistant alloy obtained in Example 3 is loaded into an injection molding machine, heated to a feedstock melting point of 120 ° C, and the melt is fed under pressure of 75 MPa into the mold. Figure 5 shows a fracture of a die cast part. The molded parts are sintered in a vacuum oven at a temperature of 1300 ° C for 30 minutes. The density of sintered products obtained from a metal-powder composition based on 316L alloy is 0.95 ± 0.02 of the theoretical density of the alloy.

Claims (10)

1. A method of obtaining a granular metal-powder composition, comprising mechanically mixing particles of a metal powder with a binder, characterized in that before mechanical mixing, deagglomeration and microencapsulation of particles of a bimodal metal powder containing nanoparticles less than 100 nm in size and microparticles no more than 5 microns in size, with nanoparticles in a mixture of not more than 20 wt.%, then the microencapsulated powder particles are mechanically mixed with a binder, which is mixture of thermoplastic polymer and plasticizer, after which the resulting mixture is heated and extruded to obtain pellets. 2. The method according to p. 1, characterized in that deagglomeration and microencapsulation is carried out by mixing a bimodal powder with a solution of microencapsulating organic matter and simultaneously dispersing the mixture in the form of a suspension of said powder in a solution with a concentration of from 1 to 10%, in the following ratio, wt .%: Bimodal powder 98.5-99.5 Microencapsulating organic matter 0.5-1.5 3. The method according to p. 2, characterized in that as the microencapsulating organic substance using substances selected from the group including acetylacetone, polyethylene glycol PEG400 and PEG 6000, polyethylene glycol ether syntanol DS-10 or 1,5-diaminoantraquinone. 4. The method according to p. 2, characterized in that the solvent used is alcohols, preferably isopropyl alcohol, or low boiling hydrocarbons, preferably an oil solvent. 5. The method according to p. 1, characterized in that as a thermoplastic polymer using substances selected from the group comprising polylactide, polymethyl methacrylate, polystyrene, a copolymer of ethyl vinyl acetate, low density polyethylene or a mixture thereof, and as a plasticizer use dibutyl phthalate or dibutyl sebacinate, when this mechanical mixing is carried out in the following ratio of components, wt.%: Microencapsulated particles bimodal powder 86.5-95.5 Thermoplastic polymer 2-14 Plasticizer 0.1-1.5 6. The method according to p. 1, characterized in that they use a bimodal powder obtained by the method of electric wire explosion (EEC) from heat-resistant, heat-resistant, corrosion-resistant alloys based on iron and chromium-nickel alloys. 7. Granular metal powder composition, characterized in that it is obtained by the method according to any one of paragraphs. 1-6 in the form of granules containing bimodal metal powder, microencapsulating organic matter, plasticizer and thermoplastic polymer in the following ratio, wt.%: Bimodal Metal Powder 85-95 Microencapsulating organic matter 0.5-1.5 Plasticizer 0.1-1.5 Thermoplastic polymer 2-14

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