WO2022071823A1

WO2022071823A1 - A spherical carbide-coated metal powder and method for production thereof

Info

Publication number: WO2022071823A1
Application number: PCT/RU2020/000507
Authority: WO
Inventors: Mikhail Vladimirovich RYAZANOV; Denis Yurievich SARAEV; Albert Harisovich GILMUTDINOV; Konstantin Yurievich NAGULIN
Original assignee: Siemens Energy Global Gmbh & Go. Kg
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2022-04-07

Abstract

The present invention provides a method for production of a spherical carbide-coated metal powder. An initial metal alloy powder is introduced into an inductive plasma reactor. Wherein the initial metal alloy powder comprises initial metal alloy powder particles, each of which is composed of a metal matrix with the one or more alloying elements. Further, the initial metal alloy powder particles pass through an inductive plasma jet formed in the inductive plasma reactor by a plasma forming gas, are being heated by the inductive plasma jet and further melted into molten particle droplets. Wherein such melting is carried out in a carbon-containing gas atmosphere. Finally, the molten particle droplets are being cooled and solidified into the spherical metal alloy powder particles covered with a metal-carbide based coating enriched with the one or more alloying elements. According to the present invention, the method is characterized in that, the initial metal alloy powder is fed into the inductive plasma reactor with such a feed rate and in such a way to avoid evaporation of the initial metal alloy powder particles inside the inductive plasma reactor. Furthermore, the hydrocarbon gas is introduced into the inductive plasma reactor with such a flow rate and in such a way to avoid the deposition of pure carbon on the surface of the molten particle droplets and while they are solidifying into the spherical metal alloy powder particles. Additionally, the present invention provides a spherical carbide-coated metal powder is presented wherein the spherical carbide-coated metal powder is a metal alloy powder that comprises spherical metal alloy powder particles, each of which is (i) composed of a metal matrix with one or more alloying elements, (ii) covered with a metal carbide coating enriched with the one or more alloying elements, and (iii) of highly spherical shape.

Description

A SPHERICAL CARBIDE-COATED METAL POWDER AND METHOD FOR

PRODUCTION THEREOF

The present invention relates to a carbide-coated metal powder for additive manufacturing, which is particularly advantageous for industrial applications that require materials to be working under high temperatures . Furthermore, the present invention refers to a method of production such carbide-coated metal powder .

Additive manufacturing is a very flexible method of manufacturing, wherein a product is manufactured by adding material on an existing part or right from the scratch . In recent years the possibilities significantly improved, and this new method of manufacturing products has been introduced into industrial applications . Especially, the possibility to build up structures utilizing geometries not possible using conventional methods of manufacturing significantly increases the benefit provided herewith .

With additive manufacturing, a laser beam is directed at fine layers of metal powder, which are heated and melted . The laser is removed, the metal cools . The process is repeated layer by layer until the blade model from the 3D printer is finished . The metal powder that was not heated and melted by the laser beam, is removed and, in case it is of still good quality, such metal powder can be used for further layers . However, the particles of the metal powder that were close to the laser beam suffer from the laser beam heat : some of them are sintered with each other, others lose their spherical shape . So, some part of the removed metal powder cannot be further used in additive manufacturing processes . To make additive manufacturing more economically effective , there is a tendency to introduce a waste-free production, i . e . minimize the quantity of powder that cannot be used after several production cycles .

As said above issue in this additive manufacturing process is properties of metal powder and final properties of a product resulted from the additive manufacturing process . The final properties of the product strongly depend on the properties of the metal powder used in additive manufacturing process , Therefore, despite the high flexibility provided with such additive manufacturing method, certain requirements to metal powder are still to be considered especially for industrial applications in which the products must work under sever conditions including exploitation under very high temperatures . Examples of such industrial applications are turbine blades , that are subj ected to significant rotational and gas bending stresses at extremely high temperatures . In addition to normal start and shutdown operation unexpected interruptions and shutdowns introduce severe thermo-mechanical loading cycles . The turbine entry temperature is typically in excess of 1375C with basemetal temperature ranging from 700 to > 1050C . To meet these requirements , an increase in the efficiency by running higher turbine temperatures , more advanced materials must be used .

High performance alloys can be used in relatively severe environments to provide enhanced mechanical properties such as high strength, creep resistance, and oxidation resistance . Due to their superior properties , high temperature nickel-based superalloys are commonly used for a wide range of components that operate under high mechanical stress while withstanding harsh operating conditions . For this reason, nickel-based superalloys are a preferred material for hhoott ggaass path components of gas turbines such aass discs , casings, vane segments, turbine blades and etc .

There are known different types of metal powders and methods for their productions . For example, the patent US 9796019 describes a method for producing a metal powder material with attached oxide nanoparticles on surface . The patent US 9796019 describes a method for producing a metal powder material with attached ceramic nanoparticles to the surface of metal particles . The disclosed method includes cleaning surfaces of a powder material, coating the cleaned surfaces with an organic bonding agent, mixing the coated particles with a dispersion that contains ceramic nanoparticles, drying the mixture to remove a carrier of the dispersion, and thermally removing the organic bonding agent to attach the ceramic nanoparticles to the surfaces of spherical metal particles . Such composite powders can be used in additive manufacturing processes for producing dispersion-strengthened alloys , where oxide nanoparticles act as a reinforcement second phase embedded in the metal matrix . However, for such industrial applications like gas turbines, powders with oxide/oxidic coating have little practical interest due to detrimental impact of oxide phases on properties of printed parts .

Another patent - US 9943909 describes a method for creation of carbon coatings on pure metal powder, in particular on nickel . Such powder is claimed to be advantageous for increasing electrical conductivity in, for example, internal conductors ( internal electrodes ) , terminal electrodes , etc used in multi-layer electronic components . This method of producing such spherical carbon coated metal powder includes melting and vaporizing an initial pure metal powder in an inductive plasma reactor, and further rapidly cooling the metal vapor by endothermic decomposition of a supplied carbon source . Therefore, during the cooling the metal vapor in the carbon atmosphere a carbon coating film is generated on the surface of metal particles . Additionally, during such cooling of the metal vapor new metal particles that appears have highly spherical shape . Therefore, this method can be used only for producing metal powder out of pure metal particles , but nor for multi-alloy metal powder .

In most cases products made of pure nickel and such nickel powder do not fit mechanical requirements to be used in gas turbines . For the product to be used in gas turbines , industrial alloys that have complex chemical composition, consisting many alloying elements are used .

Moreover, in additive manufacturing processes , the quality of products is strongly dependent on characteristics of metal powders, such as particle size distribution, shape factor, presence of contaminants and pores . Highly spherical metal powders have better flowability inside an additive manufacturing machine, resulting in smoother layers , improved packing density and increased heat conduction in the powder bed . In general , the process of spheroidization by using an inductive plasma reactor is well known . Spheroidization reduces internal porosity and provides higher packing density while removing contamination and increasing purity .

Therefore, there is a demand for a highly spherical multi- element alloy metal powder that provide high mechanical characteristics to a product to be able to work under sever conditions , including high temperatures, on the one hand, and on the other hand, the a highly-spherical multi-element alloy metal powder that can be re-used in several additive manufacturing cycles . Furthermore, there is a demand for a method by which the mentioned above highly spherical multi- alloy metal powder can be produced .

Accordingly, the object of the present invention is to provide a method for production of a spherical carbide-coated metal powder and a spherical carbide-coated metal powder wherein the spherical carbide-coated metal powder can be used for manufacturing products to be used in industrial applications with severe conditions .

The object of the present invention is achieved by a method for production of a spherical carbide-coated metal powder as defined in claim 1 and by a spherical carbide-coated metal powder as defined in claim 12 . Advantageous embodiments of the present invention are provided in dependent claims . Features of claims 1 and 12 can be combined with features of dependent claims, and features of dependent claims can be combined together .

In an aspect of the present invention, a method for production of a spherical carbide-coated metal powder is presented wherein the spherical carbide-coated metal powder comprises spherical metal alloy powder particles, each of which is ( i ) composed of a metal matrix with one or more alloying elements, (ii ) covered with a metal-carbide based coating enriched with the one or more alloying elements , and (iii ) of highly spherical shape .

The method comprises the following steps .

At an initial powder feeding step, an initial metal alloy powder is introduced into an inductive plasma reactor . Wherein the initial metal alloy powder comprises initial metal alloy powder particles , each of which is composed of a metal matrix with the one or more alloying elements . In most cases , the initial metal alloy powder particles can be of dif ferent shape and there is no coating on these initial metal alloy powder particles .

Further, at an initial powder melting step, the initial metal alloy powder particles pass through an inductive plasma jet formed in the inductive plasma reactor by a plasma forming gas , are being heated by the inductive plasma jet and further melted into molten particle droplets . Wherein such melting is carried out in a carbon-containing gas atmosphere formed by hydrocarbon gas supplied into the inductive plasma reactor . The hydrocarbon gas is used as a reactive gas in the inductive plasma reactor .

At a spherical powder solidifying step, the molten particle droplets are being cooled and solidified into the spherical metal alloy powder particles covered with a metal-carbide based coating enriched with the one or more alloying elements .

The method is characterized in that , at the initial powder feeding step, the initial metal alloy powder is fed into the inductive plasma reactor with such a feed rate and in such a way to avoid evaporation of the initial metal alloy powder particles inside the inductive plasma reactor . Furthermore , the hydrocarbon gas - a reactive gas - is introduced into the inductive plasma reactor with such a flow rate and in such a way to avoid the deposition of pure carbon on the surface of the molten particle droplets and while they are solidifying into the spherical metal alloy powder particles .

In another aspect of the present invention, a spherical carbide-coated metal powder is presented wherein the spherical carbide-coated metal powder is a metal alloy powder that comprises spherical metal alloy powder particles , each of which is ( i ) composed of a metal matrix with one or more alloying elements , ( ii ) covered with a metal carbide coating enriched with the one or more alloying elements , and ( iii ) of highly spherical shape . The present invention is based on the insight that the initial metal powder, that composed of initial metal alloy powder particles, is introduced into the inductive plasma reactor in such way to avoid evaporation of initial metal alloy powder particles : the initial metal powder is j ust being melted in the inductive plasma reactor . It is known that while solidifying the molten particles droplets form highly spherical particles . Furthermore, during melting the initial metal alloy powder and, further, during solidifying the molten particle droplets, the hydrocarbon gas is supplied into the inductive plasma reactor . So, these processes - melting and solidifying - are carried out in a carbon-containing gas atmosphere . Carbon and alloying elements that are part of the initial metal powder particles react to each other and therefore, the metal-carbide based coating enriched with the one or more alloying elements is formed on the surface of the spherical metal alloy powder particles .

Further, due to ( i ) the highly spherical shape, (ii ) a metal- carbide based coating on the surface of metal alloy powder particles, ( ii) the fact that this metal-carbide coating is enriched with the one or more alloying elements that are part of the metal alloy powder particles , the spherical carbide- coated metal powder possesses specific features . The metal- carbide coating has a higher melting point . Therefore, when using such carbide-coated metal powder in the additive manufacturing process , the particles of ssuucchh spherical carbide-coated metal powder - that was close to the laser beam, but was not melted by the laser beam do not sinter each other and do not lose their spherical shape , Therefore, such remaining after an additive manufacturing cycle powder can be used further in the following cycles . Additionally, carbide coating is beneficial for are beneficial for metal powders as such carbides can be inherently embedded in the metal matrix and act as an additional reinforcing phase, thus increasing the mechanical strength of the product manufactured out of such powder .

The present invention refers to a powder material for additive manufacturing providing an improved microstructure and shape of a product .

Thus , the present invention is proposed to provide a method for production of a spherical carbide-coated metal powder and a spherical carbide-coated metal powder, that has specific features, that allows to use such powder to manufacture products to be used in industrial applications with sever conditions .

Additionally, usage of such spherical carbide-coated metal powder for manufacturing products decrease the cost of such products because of re-usability of the spherical carbide- coated metal powder .

Further embodiments of the present invention are subj ect of the further sub-claims and of the following description, referring to the drawings .

In a possible embodiment of the method for manufacturing of a spherical carbide-coated metal powder, after the spherical powder solidifying step, the method further comprises a post- heat treatment step, during which the spherical metal alloy powder particles obtained after solidification of the molten particle droplets are subj ected to high temperatures .

Such post-heat treatment allows to obtain more dense metal carbide coatings on the surface of the spherical metal alloy powder particles . In case of presence of any quantity of carbon on the surface of the spherical metal alloy powder particles , such pure carbon under the influence of high temperatures react with the alloying elements that are part of the spherical metal alloy powder particles and forms metal carbide on the surface of the spherical metal alloy powder particles . Therefore, as a result of this post-heat treatment step, any flaws in the coating are corrected and the metal powder is covered with the metal-carbide coating, but with no pure carbon on the surface of the spherical metal alloy powder particles . Pure carbon on the surface of the spherical metal alloy powder particles provide negative influence on the mechanical properties of the product .

Additionally, in case of insufficient coating after the spherical powder solidifying step, the process of a carbide coating formation is completed during the post-heat treatment step under the influence of high temperatures, and the coating of a good quality appears at the surface of the spherical metal alloy powder particles .

In an advanced embodiment of the method for manufacturing of a spherical carbide-coated metal powder, the holding time of the post-heat treatment of the spherical metal alloy powder particles is at least 30 minute and the temperature of such post-heat treatment of the spherical metal alloy powder particles is at least 1000 °C .

Such conditions temperature and time - in which post-heat treatment of the spherical metal alloy powder particles obtained after solidification of the molten particle droplets is carried out, allows completion of carbide coating formation process .

There are different gases that can be used to form an induced plasma jet in inductive plasma reactors . For this particular method, it is preferably to use chemically inactive gas ( i . e . inert gas ) . For example, helium can be used . In a possible embodiment of the method, Argon is used as the plasma forming gas . Argon as the plasma forming gas allows to reach such temperature regime for the induced plasma jet inside the inductive plasma reactor and, therefore, allows to have initial metal powder melted but not vaporized .

In an enhanced embodiment of the method the initial metal alloy powder particles are fed into an induced plasma jet vortex zone (that is a top part of the induction coil area) of the inductive plasma reactor with the feed rate of no more than 5 g per minute . Such conditions of introducing the initial metal alloy powder - as close to the plasma jet as possible, and with such feed rate - no more than 5 gram per minute, allows for the initial metal alloy powder particles to spend minimum time in the induced plasma jet, and, therefore, allows avoiding vaporization of the initial metal alloy powder particles . The initial metal alloy powder particles are only being melted .

In another enhanced embodiment of the method, the hydrocarbon gas is fed into the inductive plasma reactor with the flow rate not exceeding 11/min . Such slow hydrocarbon gas supply into the inductive plasma reactor allows to avoid forming layer of pure carbon on the surface of the spherical metal alloy powder particles . There should be such amount of carbon and no more that it - to make all pure carbon get reacted with the alloying elements that are part of the initial metal alloying powder particles and to form metal-carbide coating enriched with the one or more alloying elements .

Different gases, for example methane, can be used as a as a carbon-containing gas . In embodiment of the method, propane is used as a carbon-containing gas . Propane is easily available carbon-containing gas .

The discharge power to maintain plasma jet in the inductive plasma reactor is in the range of 15-30 kW .

In case of higher discharge power, the temperature of induced plasma jet in the inductive plasma reactor is too high, therefore, it will be difficult to avoid vaporization of the initial metal alloy powder particles .

In case of discharge power below 15kW, the induced plasma jet temperature in the inductive plasma reactor is not sufficient to get the initial metal alloy powder particles melted while they are passing through the plasma jet.

In possible embodiment of the method, the chemical composition of the spherical metal alloy powder particles that are resulted out of the spherical powder solidifying step is equivalent to (i ) the chemical composition of the initial metal powder material plus ( ii) carbon, which is comprised in the metal- carbide based coating enriched with the one or more alloying elements , that covers the spherical metal alloy powder .

Such chemical composition of the resulted spherical metal alloy powder particles is obtained including due to the specific conditions and requirements for the rate of initial metal alloy powder particles feeding and for the flow rate of the hydrocarbon gas supply.

This feature allows to obtain metal powder of required chemical composition . It is very important when such metal powder comprises one or more alloying elements .

Additionally, the metal powder that already was used in the additive manufacturing process - that was close to the laser beam, but was not melted by the laser beam, but suffered from the heat of the laser beam - can be used as an initial metal alloy powder . Therefore, such metal powder after using the method according to the preset invention will be brought to a condition suitable for further use in the additive manufacturing process .

In an enhanced embodiment of the method, the initial metal alloy powder is a nickel-based powder containing nickel as a main component , wherein each initial metal alloy powder particle is composed of a nickel matrix with at least five alloying elements .

Ni-based superalloys are known for their mechanical properties that fits industrial applications with high temperatures, e . g . gas turbines . Pure nickel possesses not enough mechanical properties for such industrial application .

Due to its good mechanical properties at high temperatures, Nickel superalloys are widely used in the design of turbine components . Material features - high strength, good ductility, excellent corrosion resistance

Titanium (Ti ) , Niobium (Nb) and Molybdenum (Mo) are the usual alloying elements that add more quality to mechanical properties of the product .

Furthermore, these alloying elements form the metal-carbide based coating on the spherical metal alloy powder particles . Such coating is of MC-type and enriched with at least one of Ti , Nb and / or Mo .

The metal-carbide based (MC-type) coating has higher temperature of melting then initial metal powder without such coating . Therefore, during additive manufacturing process , the spherical metal-carbide coated powder particles that are close to the area molten by laser beam, do not suffer from this high temperature and their spherical form does not suffer also . Therefore, such powder can be used in other cycles of additive manufacturing processes .

In possible embodiment of the spherical carbide-coated metal powder, the spherical carbide-coated metal powder is a nickel- based powder containing nickel as a main component, wherein each spherical metal alloy powder particles is a nickel matrix with at least five alloying elements .

As it was mentioned above, Ni-based superalloys are known for their mechanical properties that fits industrial applications with high temperatures , e . g . gas turbines . Pure nickel possesses not enough mechanical properties for such industrial application .

Due to its good mechanical properties at high temperatures , Nickel superalloys are widely used in the design of turbine components . Material features - high strength, good ductility, excellent corrosion resistance

In enhanced embodiment of the spherical carbide-coated metal powder, the spherical metal alloy powder particles comprise at least one of Ti, Nb and Mo as the one or more alloying elements, and the metal-carbide based coating of the spherical metal alloy powder particles is of MC-type and enriched with at least one of Ti, Nb and / or Mo .

In general , it is known that coating of nickel carbide (Ni3C) has a negative effect on the properties of the product . Carbides based on Ti, Nb, Mo (higher melting elements ) belong to a different family and have a different composition and have a positive effect on the properties of the product manufactured out of such metal powder with such MC-type coating .

In another enhanced embodiment of the spherical carbide-coated metal powder, such spherical carbide-coated metal powder is produced according to the method for production of a spherical carbide-coated metal powder of any of claims 1 - 11 .

As it was described above, methods to manufacture powders with coatings by using an inductive plasma reactor are well known . However, manufacturing of the spherical carbide-coated metal powder requires special conditions and features as they were described above . Additionally, such method allows producing the spherical carbide-coated metal powder out of the initial metal alloy powder that has almost the same chemical composition as the spherical carbide-coated metal powder . In some cases , it is very important to receive the same chemical composition during powder manufacturing method, i . e . do not 'loose' any alloying element out of the chemical composition .

For a more complete understanding of the present invention and advantages thereof , reference is now made to the following description taken in accompanying drawings . The invention is explained in more details below using exemplary embodiments which are specified in the schematic figures of the drawings, in which :

FIG 1 . shows aa schematic diagram illustrating an example configuration of an inductive plasma reactor

FIG 2 . shows schematically the method for manufacturing a spherical carbide-coated metal powder according to the present invention;

FIG 3 . shows schematically one of the embodiments of the method for manufacturing a spherical carbide-coated metal powder according to the present invention;

FIG 4 shows a table with the results of the local chemical analysis of the surface of the initial metal alloy powder and the spherical metal alloy powder received as a result of the method for manufacturing aa spherical carbide-coated metal powder according to the present invention;

FIG 5 shows a high magnification micrograph of the spherical metal alloy powder particles according to the present invention;

For manufacturing coated metal powders for further use in additive manufacturing (3D printing) processes, an inductive plasma reactor is used . Inductive plasma reactors and principals of their work are well known .

FIG 1 is a schematic diagram illustrating an example of the configuration of an inductive plasma reactor 1 that can be used in a method for manufacturing a spherical carbide-coated metal powder in accordance with the present invention .

The inductive plasma reactor 1 consist of a reaction vessel 2 ; a feed port 3 that serves ttoo ssuuppppllyy aann initial metal alloy powder 31 into the reaction vessel 2 ; a plasma forming gas supply port 4 ttoo supply a plasma forming gas 41 into the reaction vessel 2 ; a reacting gas supply port 5 to supply a reacting gas 51 into the reaction vessel 2 ; an induction coil 6 to create a magnetic field inside the reaction vessel 2 that initiate a plasma jet (not shown on FIG 1 ) appeared in an the top part of the induction coil area 61 ( i . e . induced plasma jet vortex zone) under the influence of the magnetic field created by the induction coil 6; and necessary support structures , e . g . cooling chamber, collector, vacuum system, and so forth (not shown on FIG 1 ) .

FIG 2 is a schematic diagram illustrating the method 200 for manufacturing a spherical carbide-coated metal powder 33 .

At a initial powder feeding step 201 an initial metal alloy powder 31 is introduced into an inductive plasma reactor 1 . The initial metal alloy powder 31 comprises initial metal alloy powder particles 310, each of which is composed of a metal matrix with the one or more alloying elements .

The initial metal alloy powder particles 310 can bbee of different sizes and of different shape . Usually industrial superalloys are used .

Additionally, the metal powder that already was used in the additive manufacturing process that was close to the laser beam, but was not melted by the laser beam, but suffered from the heat of the laser beam - can be used as an initial metal alloy powder 31 .

Additionally, the initial metal alloy powder 31 can be a nickel-based powder containing nickel (Ni) as a main component, wherein each initial metal alloy powder particle 310 is composed of a nickel matrix with at least five alloying elements . Industrial Ni-based superalloy powders with an average particle size of 20 to 50 pm can be used as the initial metal alloy powder 31 . The initial metal alloy powder particles 310 can comprise at least one of Ti , Nb and Mo as the one or more alloying elements . Also, Si and/or Cr, and / or Fe can be among alloying elements . These alloying elements improve qualities of the metal they are added to .

Ideally, the initial metal alloy powder 31 should have the chemical composition required for the product to be made from the powder obtained after applying this method .

At an initial powder melting step 202 , the initial metal alloy powder particles 310 is being melted into molten particle droplets 320 in the inductive plasma reactor 1 . Such melting occurs in the induction coil area 61 .

Such melting within the initial powder melting step 202 , is carried out in a carbon-containing gas atmosphere formed by a hydrocarbon gas 51 that is used as a reactive gas and supplied into the inductive plasma reactor 1 through the reacting gas supply port 5 .

Further at a spherical powder solidifying step 203 the molten particle droplets 320 are cooled and solidified into the spherical metal alloy powder particles 330 covered with a metal-carbide based [MC-type] coating 331 enriched with the one or more alloying elements .

Finally, as an option, a post-heat treatment step 204 can be performed to obtain more dense carbide coatings on the surface of the spherical metal alloy powder particles 330. Such post treatment usually occurs in a special furnace out of the inductive plasma reactor 1 .

The method for production of a spherical carbide-coated metal powder 200 works as the following .

The initial metal alloy powder 31 that comprises of the initial metal alloy powder particles 310 is fed through the feed port 3 of the inductive plasma reactor 1 into the reaction vessel 2.

The initial metal alloy powder 31 iiss supplied in powered, already working inductive plasma reactor 1 , when the inductive plasma jet (not shown on FIG) in the induction coil area 61 is already induced . Preferably, the discharge power to the inductive plasma jet in the inductive plasma reactor 1 is in the range of 15-30 kW . The plasma forming gas 41 is also supplied to the inductive plasma reactor 1 to get the inductive plasma jet induced . Preferably, Argon is used as the plasma forming gas 41 . However, it can be other chemically inactive gas , for example helium.

Also, the plasma forming gas 41 can be used as transport gas to supply the initial metal alloy powder 31 into the inductive plasma reactor 1 .

The initial metal alloy powder particles 310 should be fed into the inductive plasma reactor 1 with such a feed rate and in such a way to avoid evaporation of the initial metal alloy powder particles 310 inside the inductive plasma reactor 1 .

According to the embodiment of the present inventions, the initial metal alloy powder particles 310 should be fed into a induced plasma jet vortex zone (top part of the induction coil area 61 ) of the inductive plasma reactor 1 with the feed rate of no more than 5 g per minute . The delivery of the initial metal alloy powder 31 into the can be done by the induced plasma jet vortex zone of the inductive plasma reactor 1 can be carried out by the feed port 3 that is adopted to move up and down relatively the induction coil area 61 .

The induced plasma jet vortex zone is a top part of the upper part of the induction coil area 61 .

Taken into account the fact that metal and each of one or more alloying elements can have different melting temperature, the initial metal alloy powder 31 should be fed into the inductive plasma reactor 1 as close to the induced plasma jet as possible to have minimum time in the induced plasma jet to avoid vaporization . The initial metal alloy powder particles 310 should be melted while passing the inductive plasma jet formed in the inductive plasma reactor 1 by the plasma forming gas 41 , but they - the initial metal alloy powder particles 310 - should not vaporize .

In fact avoiding vaporization the initial metal alloy powder particles 310 in whole or partly allows to avoid changes in chemical composition of the initial metal alloy powder particles 310 while their going through the spheroidization process in accordance with the present invention . Therefore, as a result of the method 200, the chemical composition of the spherical metal alloy powder particles 330 is almost equivalent to the chemical composition of the initial metal powder particles 310. The only difference is a carbon, which is comprised in the metal-carbide based coating 331 enriched with the one or more alloying elements, that covers the spherical metal alloy powder particles 330.

Furthermore, since the melting of the initial metal alloy powder 310 into the into molten particle droplets 320 in the inductive plasma reactor 1 within the initial powder melting step 202 is carried out in a carbon-containing gas atmosphere formed by a hydrocarbon gas 41 supplied into the inductive plasma reactor 1 through the reactive gas supply port 4 , carbon released by the hydrocarbon gas decomposition reacts with the one or more alloying elements of the molten particle droplets 320. Such reaction of the carbon with one or more alloying elements occurs at the initial powder melting step 202 , as well as at a spherical powder solidifying step 203 (described below) .

As a result, a metal-carbide based coating enriched with the one or more alloying elements is being formed on the surface of the spherical metal alloy powder particles 330.

It is very important that the hydrocarbon gas 41 - a reactive gas is introduced into the inductive plasma reactor 1 with such a flow rate and in such a way to avoid the deposition of pure carbon on the surface of the molten particle droplets 320 and the spherical metal alloy powder particles 330. All carbon should fully bond with one or more alloying elements of the initial metal alloy powder 31 .

Metal-carbide coating improves the properties of the spherical carbide-coated metal powder 33 and have positive effect on the mechanical properties of the product manufactured out of such spherical carbide-coated metal powder 33. While the pure carbon on the surface of the spherical metal alloy powder particles worse the properties of the spherical carbide-coated metal powder and have negative effect on the mechanical properties of the product manufactured out of such powder, especially when such product is used severe conditions in industrial applications with high temperatures .

According to one of the embodiments of the present invention, the hydrocarbon gas 41 should be fed into the inductive plasma reactor 1 with the flow rate not exceeding 11/min . It will allow to avoid appearing a pure carbon coating on the surface of the spherical carbide-coated metal powder 33 .

Different gases, for example methane, can be used as a as a carbon-containing gas . In embodiment of the method 200 in accordance with the present invention, propane is used as a carbon-containing gas 41 .

Further, at the spherical powder solidifying step 203 while the molten particle droplets 320 go down out of the inductive plasma jet vortex zone (the top part of the induction coil area 61 ) , they are cooled and solidify into the spherical metal alloy powder particles 330 covered with a metal-carbide based coating 331 enriched with the one or more alloying elements .

This coating 331 can be all over the surface of the spherical metal alloy powder particles 330 and be as a coating film, or to cover the surface of the spherical metal alloy powder particles 330 partly .

As an addition to the three steps 201 , 202 , 203 of the method 200, a post-heat treatment 204 of the spherical metal alloy powder particles 330 can be performed . Such post-heat treatment is occurred in a furnace (not shown on FIG) out of the inductive plasma reactor 1 .

Such post-heat treatment step 204 allows to obtain more dense metal-carbide coating 331 on the surface of the spherical metal alloy powder particles 330. In case of presence of any quantity of carbon on the surface of the spherical metal alloy powder particles 331 , such pure carbon under the influence of high temperatures react with the one or more alloying elements that are part of the spherical metal alloy powder particles 330 and forms metal carbide on the surface of the spherical metal alloy powder particles 330. Therefore, as a result of this post-heat treatment step, any flaws in the coating are corrected and the metal powder is covered with the metal-carbide coating 331 , but with no pure carbon on the surface of the spherical metal alloy powder particles 330. Pure carbon on the surface of the spherical metal alloy powder particles provide negative influence on the mechanical properties of the product .

Additionally, in case of a loose coating after the spherical powder solidifying step 203, then at high temperatures the process of formation of a carbide coating 331 is completed, and the coating of a food quality appears at the surface of the spherical metal alloy powder particles 330.

In an advanced embodiment of the method for manufacturing of a spherical carbide-coated metal powder 33 , the holding time of the post-heat treatment of the spherical metal alloy powder particles 330 is at least 30 minute and the temperature of such post-heat treatment of the spherical metal alloy powder particles 330 is at least 1000°C .

Such conditions - temperature and time in which post-heat treatment of the spherical metal alloy powder particles 330 obtained after solidification 203 of the molten particle droplets 320 is carried out, allows all process of formation of a carbide coating 331 is being completed .

As it was mentioned before, according to the one of the embodiments of the present invention, the initial metal alloy powder particles 31 can comprise at least one of Titanium (Ti ) and/or Niobium (Nb) and / or Molybdenum (Mo) as the one or more alloying elements . According to the one of the embodiments of the present invention, the metal-carbide based coating formed on the spherical metal alloy powder particles is of MC- type and enriched with at least one of Titanium (Ti ) , and / or Niobium (Nb) and / or Molybdenum (Mo) .

A table on FIG 4 shows the results of the local chemical analysis of the surface of the initial metal alloy powder 31 and the spherical metal alloy powder 33 . A column 410 of the table lists the alloying elements , a column 420 shows the quantity ( in weight % ) of these alloying elements oonn the surface of the initial metal alloy powder 31 , while a column 430 shows the quantity ( in weight % ) of these alloying elements on .the surface of the spherical metal alloy powder 33 that is resulted from processing in accordance with the method 200.

As it is seen out of the table, the local chemical analysis reveals a considerably increased content of carbide forming elements , in particular Ti and / or Nb and / or Mo along with carbon, which implies formation of metal carbides within the coatings on the surface of spherical metal alloy powder particles 330 after the spherical powder solidifying step 203.

In case the initial metal alloy powder particle 310 comprise Ti and / or Nb and / or Mo as alloying elements , metal-carbide with these elements will be formed on the surface of the spherical metal alloy powder particle 330 as a result of the method 200 according to the present invention : it can be (i ) only one of them - TiC or NbC or MoC, or ( ii ) all of them TiC or NbC or MoC in different proportion, or ( iii ) any combination of them. However, in any case the stoichiometry of metal and carbon is always kept as 1 : 1 . So, it will be MC-type coating 331 , but not M3C .

Additionally, should be mentioned, that during the melting and further the solidification tthhee initial metal alloy powder particles 310 become shape ooff sphere . I . e . during these processes in parallel the process of spheroidization goes on .

FIG 5 shows a high magnification micrograph of a spherical carbide-coated metal powder 33, in particular spherical metal alloy powder particles 330 from which the spherical carbide- coated metal powder 33 is comprised of .

Each spherical metal alloy powder particle 330 composed of a metal matrix with one or more alloying elements (not shown on FIG) and is covered with thin metal-carbide coating 331 enriched with the one or more alloying elements .

This coating 331 can be all over the surface of the spherical metal alloy powder particles 330 and be as a coating film, or to cover the surface of the spherical metal alloy powder particles 330 partly . Furthermore, each spherical metal alloy powder particle 330 is of highly spherical shape .

In possible embodiment of the spherical carbide-coated metal powder, the spherical metal alloy powder 33 is a nickel-based powder containing nickel as a main component , wherein each spherical metal alloy powder particles 330 is a nickel matrix with at least five alloying elements .

As it was mentioned above, Ni-based superalloys are known for their mechanical properties that fits industrial applications with high temperatures, e . g . gas turbines .

An average size of spherical metal alloy powder particles 330 can be 20 to 50 μm. That is the size of particles ooff the industrial Ni-based superalloy that are usually used to manufacture products (e . g . vanes , blades, etc. )) for further use industrial applications under sever conditions (e . g . in gas turbines ) .

In enhanced embodiment of the spherical carbide-coated metal powder 33, the spherical metal alloy powder particles 330 comprise at least one of Titanium (Ti) and / or Niobium (Nb) and / or Molybdenum (Mo) as the one or more alloying elements , and the metal-carbide based coating 331 of the spherical metal alloy powder particles 330 is of MC-type and enriched with at least one of Titanium (Ti ) , Niobium (Nb) and / or Molybdenum (Mo) .

In case the spherical metal alloy powder particle 330 comprise Ti and / or Nb and / or Mo as alloying elements , metal-carbide with these elements will be formed on the surface of the spherical metal alloy powder particle 330 : it can be ( i) only one of them TiC or NbC or MoC, or (ii) all of them TiC or

NbC or MoC in different proportion, or (iii) any combination of them. However, in any case the stoichiometry of metal and carbon is always kept as 1 : 1 . So, it will be MC-type coating 331, but not M3C .

In another enhanced embodiment of the spherical carbide-coated metal powder 33, such spherical carbide-coated metal powder 33 is produced according to the method 200 for production of a spherical carbide-coated metal powder 33 as it is described above .

While the present invention has been described in detail with the reference to certain embodiments, it should be appreciated that the present invention is not limited to those precise embodiments . Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention . The scope of the invention is , therefore, indicated by the following claims rather than by the foregoing description . All changes , modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope .

Reference numerals

1 - inductive plasma reactor

2 reaction vessel

3 - feed port

31 - initial metal alloy powder

310 - initial metal alloy powder particles

320 - molten particle droplets

330 - spherical metal alloy powder particles

4 - plasma forming gas supply port

41 - plasma forming gas

5 - reacting gas supply port

51 - reacting gas

6 induction coil

61 induction coil area

200 method

201 204 - steps of the method

Claims

PATENT CLAIMS

1. A method for production of a spherical carbide-coated metal powder (200) , wherein the spherical carbide-coated metal powder (33) comprises spherical metal alloy powder particles (330) , each of which is (i) composed of a metal matrix with one or more alloying elements, (ii) covered with a metal-carbide based coating (331) enriched with the one or more alloying elements, and (iii) of highly spherical shape, the method (200) comprises the following steps: a initial powder feeding step (201) of feeding an initial metal alloy powder (31) into an inductive plasma reactor (1), wherein the initial metal alloy powder (31) comprises initial metal alloy powder particles (310) , each of which is composed of a metal matrix with the one or more alloying elements; an initial powder melting step (202) of melting the initial metal alloy powder particles (310) into molten particle droplets (320) in the inductive plasma reactor (1) by passing the initial metal alloy powder particles (310) through an inductive plasma jet formed in the inductive plasma reactor by a plasma forming gas (41), wherein such melting is carried out in a carbon-containing gas atmosphere formed by a hydrocarbon gas (51) supplied into the inductive plasma reactor (1) ; a spherical powder solidifying step (203) of solidifying the molten particle droplets (320) into the spherical metal alloy powder particles (330) covered with a metal-carbide based coating (331) enriched with the one or more alloying elements; the method (200) is characterized in that the initial metal alloy powder (31) is fed into the inductive plasma reactor (1) with such a feed rate and in such a way to avoid evaporation of the initial metal alloy powder particles (310) inside the inductive plasma reactor (1); the hydrocarbon gas (51) is introduced into the inductive plasma reactor (1) with such a flow rate and in such a way to avoid the deposition of pure carbon on the surface of the spherical metal alloy powder particles (330) .

2. The method (200) of claim 1, wherein after the spherical powder solidifying sstteepp (21), the method (200) further comprises a post-heat treatment step (204) of post-heat treatment of the spherical metal alloy powder particles (330) obtained after solidification (204) of the molten particle droplets (320) at high temperatures.

3. The method (200) of claim 2, wherein the holding time of the post-heat treatment (204) of the spherical metal alloy powder particles (330) is at least 30 minute and the temperature of such post-heat treatment (204) of the spherical metal alloy powder particles (330) is at least 1000 °C.

4. The method (200) of any of claims 1 - 3, wherein Argon is used as the plasma forming gas (41) .

5. The method (200) of any of claims 1 - 4, wherein the initial metal alloy powder particles (310) are fed into a induced plasma jet vortex zone of the inductive plasma reactor (1) with the feed rate of no more than 5 g per minute.

6. The method (200) of any of claims 1 5, wherein the hydrocarbon gas (51) is fed into the inductive plasma reactor (1) with the flow rate not exceeding 11/min.

7. The method (200) of any of claims 1 6, wherein the hydrocarbon gas (51) is propane.

8. The method (200) of any of claims 1 - 7, wherein the discharge power to maintain an inductive plasma jet in the inductive plasma reactor (1) is in the range of 15-30 kW.

9. The method (200) of any of claims 1 - 8, wherein the chemical composition of the spherical metal alloy powder particles (330) is equivalent to (i) the chemical composition of the initial metal powder particles (310) plus (ii) carbon, which is comprised in the metal-carbide based coating (331) enriched with the one or more alloying elements, that covers the spherical metal alloy powder.

10. The method (200) of any ccllaaiimmss ooff 1 - 9, wherein the initial metal alloy powder (31) iiss aa nickel-based powder containing nickel as a main component, wherein each initial metal alloy powder particle (310) is composed of a nickel matrix with at least five alloying elements.

11. The method (200) of any claim of 1 - 10, wherein the initial metal alloy powder particles (310) comprise at least one of Titanium (Ti) , Niobium (Nb) and / or Molybdenum (Mo) as the one or more alloying elements, and, therefore, the metal- carbide based coating (331) formed on the spherical metal alloy powder particles (330) is of MC-type and enriched with at least one of Titanium (Ti) , Niobium (Nb) and / or Molybdenum (Mo) .

12. A spherical carbide-coated metal powder (33) comprising spherical metal alloy powder particles (330) , each of which is (i) composed of a metal matrix with one or more alloying elements, (ii) covered with a metal-carbide based coating (331) enriched with the one or more alloying elements, and (iii) of highly spherical shape,

13. The spherical carbide-coated metal powder (33) of claim 12, wherein the spherical carbide-coated metal powder (33) is a nickel-based powder containing nickel as a main component, wherein each spherical metal alloy powder particle (330) is a nickel matrix with at least five alloying elements.

14. The spherical carbide-coated metal powder (33) of claim 13, wherein the spherical metal alloy powder particles (330) comprise at least one of Titanium (Ti) , Niobium (Nb) and / or Molybdenum (Mo) as the one or more alloying elements, and the metal-carbide based coating (331) of the spherical metal alloy powder particles (330) is of MC-type and enriched with at least one of Titanium (Ti), Niobium (Nb) and / or Molybdenum (Mo) .

15. The spherical carbide-coated metal powder (33) of any of claims 12 - 14, wherein such spherical carbide-coated metal powder (33) is produced according to the method (200) for production of a spherical carbide-coated metal powder of any of claims 1 - 11.