In-situ carbide reinforced refractory high-entropy alloy, preparation method and application

Abstract

The invention discloses an in-situ carbide reinforced refractory high-entropy alloy, a preparation method and application, and belongs to the technical field of powder preparation. According to the preparation method, ingot melting, hydrogenation crushing, plasma spheroidizing and dehydrogenation processes are combined, and a carbon source added in the process is regulated and controlled, so that a carbide reinforced phase is generated in situ in the preparation process of the in-situ carbide reinforced refractory high-entropy alloy; and the preparation of the high-entropy alloy composite powder material with high-uniformity dispersion of the reinforced phase, controllable content and morphology and low impurity content can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of powder preparation, and in particular, to an in-situ carbide reinforced refractory high-entropy alloy, a preparation method and an application thereof. Background Art

[0002] Refractory high-entropy alloy composites mostly use FCC or BCC single-phase refractory high-entropy alloys as the matrix, and add metal carbides or nitrides as the second reinforcing phase. Among them, refractory high-entropy alloys generally consist of 3-7 elements among Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W and additional elements such as Al, C, Co, Ni to form a complex and diverse alloy system. Refractory high-entropy alloy composites have superior high-temperature mechanical properties, high-temperature oxidation resistance and radiation resistance compared with traditional nickel-based superalloys, and have great application prospects in the fields of aerospace, nuclear energy and processing manufacturing.

[0003] At present, the preparation technologies of refractory high-entropy alloy composites include vacuum arc melting method and powder metallurgy method. Among them, the composites prepared by the vacuum melting method have non-uniform microstructures, especially the problems of non-uniform size and distribution of the second phase, which lead to the rapid deterioration of the properties of the composites in high-temperature environments. Moreover, this method is difficult to prepare in batches and is generally used for laboratory research. The powder metallurgy method prepares composites with better tissue uniformity than the melting method by mechanically alloying and ball milling + sintering refractory powders and second reinforcing phase powders. However, the high-energy ball milling and mixing of powders takes as long as 8-24 hours or even more, and the powder is easily contaminated by the tank body and balls during the mixing process, introducing impurity elements and causing the deterioration of the properties of the composites.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide an in-situ carbide reinforced refractory high-entropy alloy, a preparation method and an application thereof, so as to obtain a high-entropy alloy with a low impurity content.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, the present invention provides a preparation method of an in-situ carbide reinforced refractory high-entropy alloy, including:

[0008] Melting, mixing raw material powders including Nb, Mo, Ta and W with a carbon source and performing melting to form an ingot;

[0009] Hydrogenation and crushing, heating and hydrogenating the ingot in a mixed atmosphere of an inert gas and hydrogen, and then crushing and sieving the hydrogenated ingot to obtain hydrogenated powder;

[0010] Plasma spheroidization: Under the protection of carrier gas, the hydrogenated powder is transported to the high-temperature plasma region of the plasma spheroidization equipment for melting, and then condensed into spheres to obtain spherical refractory high-entropy alloy powder;

[0011] Dehydrogenation and deoxidation: The spherical refractory high-entropy alloy powder is subjected to a reduction reaction in hydrogen and then calcined to obtain the in-situ carbide-reinforced refractory high-entropy alloy powder.

[0012] In an optional embodiment, the particle size of the raw material powder is 0.1 - 10 μm;

[0013] And / or, the particle size of the carbon source is less than 1 μm;

[0014] And / or, the mass ratio of the raw material powder to the carbon source powder is 1:(0.0005 - 0.3);

[0015] And / or, the raw material powder is selected from at least one of metal elemental powder and alloy powder;

[0016] And / or, the molar fraction of Nb in the raw material powder is 15% - 35%, the molar fraction of Mo is 15% - 35%, the molar fraction of Ta is 15% - 35%, and the molar fraction of W is 15% - 35%;

[0017] And / or, the carbon source is amorphous carbon.

[0018] In an optional embodiment, the melting temperature is 2000 - 3200 °C, the melting time is 3 - 5 h, and the number of melting times is 5 - 8 times;

[0019] And / or, the volume fraction of hydrogen in the mixed gas is 20 - 80%;

[0020] And / or, the hydrogenation temperature is 400 - 700 °C, and the holding time of hydrogenation is 1 - 6 h;

[0021] And / or, the crushing is carried out by mechanical crushing, and the crushing time is 5 - 60 s.

[0022] In an optional embodiment, the temperature of plasma spheroidization is 8000 - 12000 °C, and the pressure is 0.01 - 0.15 Mpa;

[0023] And / or, the power of the plasma spheroidization equipment is 15 - 100 kw;

[0024] And / or, the side gas of the plasma spheroidization equipment includes carbon-rich gases;

[0025] And / or, the feeding rate of the hydrogenated powder of the plasma spheroidization equipment is 0.1 - 100 g / min;

[0026] And / or, after condensing into spheres, the material is washed and dried to obtain the in-situ carbide reinforced refractory high-entropy alloy, wherein the drying is carried out under the protection of inert gas;

[0027] And / or, the reduction reaction temperature is 500-600 °C and the time is 1-5 h;

[0028] And / or, the calcination temperature is 600-750 °C and the time is 2-5 h.

[0029] In an alternative embodiment, the carbon-rich gas is selected from alkanes or alkenes;

[0030] And / or, the side gas of the plasma spheroidization equipment consists of a carbon-rich gas, H2 and an inert gas, and the central gas is an inert gas;

[0031] And / or, in the side gas of the plasma spheroidization equipment, the molar ratio of the carbon-rich gas, H2 and the inert gas is (0.005-0.1):(0.005-0.05):1;

[0032] And / or, the flow rate of the side gas is 45-75 L / min;

[0033] And / or, the flow rate of the central gas is 15-25 L / min;

[0034] And / or, the carrier gas is argon and / or helium, and the flow rate is 1-5 L / min.

[0035] In a second aspect, the present invention provides an in-situ carbide reinforced refractory high-entropy alloy powder prepared by the method according to any one of the foregoing embodiments, satisfying at least one of the following conditions:

[0036] A. The particle size is 10-300 um;

[0037] B. The Hall flow rate is 10-15 s / 50 g;

[0038] C. The carbon content is 0.05-5 wt.%; preferably, when the carbon content < 0.1 wt.%, nano-sized carbides are distributed in the in-situ carbide reinforced refractory high-entropy alloy; preferably, when the carbon content is 0.1 wt.% - 1 wt.%, micron-sized carbides are distributed in the in-situ carbide reinforced refractory high-entropy alloy;

[0039] D. The oxygen content is less than 300 ppm.

[0040] In a third aspect, the present invention provides a method for preparing a 3D printed article, comprising:

[0041] Forming, laying the in-situ carbide reinforced refractory high-entropy alloy powder according to the foregoing embodiment at a specified position, and then performing selective laser melting forming to obtain a printed part;

[0042] Heat treatment is carried out on the printed part to obtain the 3D printed product.

[0043] In an optional embodiment, the equipment model used for selective laser melting forming is AMC-M1508B;

[0044] And / or, the power of selective laser melting forming is 180 - 400 W, the scanning speed is 500 - 1000 mm / s, the laser stripe spacing is 0.03 - 0.1 mm, and the powder spreading thickness is 20 - 40 μm;

[0045] And / or, the heat treatment temperature is 600 - 1200 °C, and the holding time is 1 - 10 h.

[0046] In a fourth aspect, the present invention provides a 3D printed product prepared by the method described in the foregoing embodiment. The density of the 3D printed product is greater than 99%, and the Vickers hardness is 1029 - 1265 HV.

[0047] In a fifth aspect, the present invention provides an application of the in-situ carbide reinforced refractory high-entropy alloy described in the foregoing embodiment in the field of additive manufacturing or thermal spraying.

[0048] The present invention has the following beneficial effects:

[0049] In the present invention, the processes of ingot melting, hydrogenation and crushing, plasma spheroidization and dehydrogenation are combined. By regulating the carbon source added during the process, the carbide reinforcing phase is in-situ generated during the preparation of the in-situ carbide reinforced refractory high-entropy alloy, and a high-entropy alloy composite powder material with high uniform dispersion of the reinforcing phase, controllable content and morphology, and low impurity content can be prepared. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0051] Figure 1 Powder morphology obtained by hydrogenation and crushing in Example 1;

[0052] Figure 2 Powder morphology of the in-situ carbide reinforced refractory high-entropy alloy prepared in Example 1;

[0053] Figure 3 XRD of the in-situ carbide reinforced refractory high-entropy alloy powder prepared in Example 1;

[0054] Figure 4 The particle size distribution of the in-situ carbide reinforced refractory high-entropy alloy powder prepared in Example 1. Detailed implementation manners

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0056] The embodiments of the present invention provide a method for preparing an in-situ carbide reinforced refractory high-entropy alloy, including:

[0057] Melting: Mixing raw material powders including Nb, Mo, Ta, and W and a carbon source and performing melting to form an ingot;

[0058] Hydrogenation and crushing: Heating and hydrogenating the ingot in a mixed atmosphere of an inert gas and hydrogen, then crushing and sieving the hydrogenated ingot to obtain hydrogenated powder;

[0059] Plasma spheroidization: Under the protection of a carrier gas, transporting the hydrogenated powder to the high-temperature plasma region of a plasma spheroidization device for melting, and then condensing into spheres to obtain spherical refractory high-entropy alloy powder;

[0060] Dehydrogenation and oxygen reduction: Performing a reduction reaction on the spherical refractory high-entropy alloy powder in hydrogen and then calcining to obtain the in-situ carbide reinforced refractory high-entropy alloy powder.

[0061] In the process of preparing the powder of the present invention, an appropriate amount of carbon source is added to enable the in-situ generation of carbide reinforcement phases during the preparation of the high-entropy alloy powder. The carbon source will form carbides such as NbC, Mo2C and MoC, TaC, WC with the Nb, Mo, Ta, and W elements in the powder. The formation of these carbides can well improve the strength, hardness, and wear resistance of the material. These carbides are in-situ generated during the powder preparation process, which is conducive to achieving high-uniform dispersion of the reinforcement phase, and the content and morphology are controllable. Specifically:

[0062] Adding the carbon source during the melting of the alloy ingot can enable it to fully form carbides inside the alloy and be evenly distributed.

[0063] Since long-term mixing and grinding of raw materials is avoided, other metals or inorganic impurities will not be introduced, and the ultra-high temperature of plasma (8000-12000°C) can gasify the oxide on the surface of the powder into steam and separate from the powder. In addition, the stronger binding force of H element with oxygen at ultra-high temperature can further separate the dissolved oxygen in the powder, and the oxygen content of the powder can be reduced to 100-300ppm. Therefore, the combination of plasma spheroidization and dehydrogenation steps can fully reduce the oxygen content.

[0064] In the plasma spheroidization process, the hydrogenated powder is transported through the high-temperature plasma area under the protection of the carrier gas, melts in a very short time (0.005-0.1s), and forms spherical droplets under the action of surface tension. After the droplets leave the high-temperature heating zone with the air flow, they condense into spherical, dense, spherical refractory high-entropy alloy powders during the descent process in the cooling chamber and are collected in the collection device.

[0065] In an optional embodiment, the particle size of the raw material powder is 0.1 to 10 um, and the purity is greater than 99.9%;

[0066] And / or, the particle size of the carbon source is less than 1 um and the purity is greater than 99.9%; the reasonable selection of the particle sizes of the raw material powder and the carbon source powder is conducive to uniform mixing of the two. If the particle size of the carbon source is too large or the particle size of the raw material powder is too large, the uniformity of distribution will be reduced, but if the particle size of the raw material powder is too small, the uniformity of distribution may also be reduced due to agglomeration.

[0067] And / or, the mass ratio of the raw material powder to the carbon source powder is 1:(0.0005-0.3); the carbon source is added during the smelting process, so that the carbide reinforcement phase is generated in situ during the preparation of the high entropy alloy powder, thereby achieving a relatively uniform dispersion of the reinforcement phase in the high entropy alloy, which is beneficial to improving the performance of the high entropy alloy;

[0068] And / or, the raw material powder is selected from at least one of a metal element powder and an alloy powder, for example, an alloyed NbMoTaW high entropy alloy powder can be selected;

[0069] And / or, the molar fraction of Nb in the raw material powder is 15% to 35%, the molar fraction of Mo is 15% to 35%, the molar fraction of Ta is 15% to 35%, and the molar fraction of W is 15% to 35%;

[0070] And / or, the carbon source is amorphous carbon.

[0071] In an optional embodiment, the smelting temperature is 2000-3200°C, the smelting time is 3-5h, and the smelting times are 5-8 times;

[0072] And / or, the volume fraction of hydrogen in the mixed gas is 20 to 80%;

[0073] And / or, the hydrogenation temperature is 400 - 700 °C, and the holding time for hydrogenation is 1 - 6 h;

[0074] And / or, the crushing is carried out by mechanical crushing, and the crushing time is 5 - 60 s.

[0075] In an alternative embodiment, the temperature of plasma spheroidization is 8000 - 12000 °C, and the pressure is 0.01 - 0.15 Mpa;

[0076] And / or, the power of the plasma spheroidization equipment is 15 - 100 kw;

[0077] And / or, the side gas of the plasma spheroidization equipment includes carbon-rich gases;

[0078] And / or, the feeding rate of the hydrogenated powder of the plasma spheroidization equipment is 0.1 - 100 g / min;

[0079] And / or, after condensation into spheres, the material is washed and dried to obtain the in-situ carbide-reinforced refractory high-entropy alloy, wherein the drying is carried out under the protection of inert gas; specifically, the washing can be carried out 2 - 3 times, and the drying conditions can be drying at 80 - 120 °C in an N2 atmosphere for 0.5 - 2 h.

[0080] And / or, the reduction reaction temperature is 500 - 600 °C, and the time is 1 - 5 h;

[0081] And / or, the calcination temperature is 600 - 750 °C, and the time is 2 - 5 h.

[0082] In an alternative embodiment, the carbon-rich gas is selected from alkanes or alkenes; preferably, the carbon-rich gas is selected from at least one of methane, ethylene, and propylene; adding carbon-rich gas to the side gas is mainly to increase the carbon partial pressure in the gas phase in the high-temperature reaction region of the plasma, thereby inhibiting the combination of C element in the particles and H in the gas phase in the plasma reaction region, so that the carbon element in the powder is lost into the gas phase.

[0083] And / or, the side gas of the plasma spheroidization equipment consists of carbon-rich gas, H2, and inert gas, and the central gas is inert gas;

[0084] And / or, in the side gas of the plasma spheroidizing equipment, the molar ratio of carbon-rich gas, H2 and inert gas is (0.005 - 0.1):(0.005 - 0.05):1; there is strong flow inside the powder after liquefaction, which enables carbon elements to dissolve inside the powder and in-situ react to form carbides. If the carbon partial pressure in the gas is increased, it can even promote the deposition of carbon elements in the gas phase on the particle surface, and then react with the metal to undergo a carbonization reaction, thereby increasing the carbon content of the composite material. Therefore, during the plasma spheroidizing process, the secondary control of the carbon content in the powder can be achieved by regulating the C and H contents and ratios in the side gas.

[0085] And / or, the flow rate of the side gas is 45 - 75 L / min;

[0086] And / or, the flow rate of the central gas is 15 - 25 L / min;

[0087] And / or, the carrier gas is argon and / or helium, and the flow rate is 1 - 5 L / min.

[0088] The embodiment of the present invention also provides an in-situ carbide reinforced refractory high-entropy alloy powder prepared by the method described in any one of the foregoing embodiments, satisfying at least one of the following conditions:

[0089] A. The particle size is 10 - 300 um;

[0090] B. The Hall flow rate is 10 - 15 s / 50 g;

[0091] C. The carbon content is 0.05 - 5 wt.%; preferably, when the carbon content < 0.1 wt.%, nano-scale carbides are distributed in the in-situ carbide reinforced refractory high-entropy alloy; preferably, when the carbon content is 0.1 wt.% - 1 wt.%, micron-scale carbides are distributed in the in-situ carbide reinforced refractory high-entropy alloy;

[0092] D. The oxygen content is less than 300 ppm.

[0093] The embodiment of the present invention also provides a preparation method for a 3D printed product, including:

[0094] Forming, laying the in-situ carbide reinforced refractory high-entropy alloy powder described in the foregoing embodiment to a specified position, and then performing selective laser melting forming to obtain a printed part;

[0095] Heat treatment, performing heat treatment on the printed part to obtain the 3D printed product.

[0096] In an alternative embodiment, the equipment model used for selective laser melting forming is AMC-M1508B;

[0097] And / or, the power of selective laser melting is 180 - 400 W, the scanning speed is 500 - 1000 mm / s, the laser stripe spacing is 0.03 - 0.1 mm, and the powder spreading thickness is 20 - 40 μm;

[0098] And / or, the heat treatment temperature is 600 - 1200 °C, and the holding time is 1 - 10 h.

[0099] An embodiment of the present invention further provides a 3D printed product prepared by the method described in the foregoing embodiment. The density of the 3D printed product is greater than 99%, and the Vickers hardness is 1029 - 1265 HV.

[0100] Using the in-situ carbide reinforced refractory high-entropy alloy powder of the present invention in the field of additive manufacturing results in a relatively high density and material hardness of the 3D printing, showing good application prospects.

[0101] An embodiment of the present invention further provides an application of the in-situ carbide reinforced refractory high-entropy alloy described in the foregoing embodiment in the field of additive manufacturing or thermal spraying.

[0102] The features and properties of the present invention will be further described in detail below in conjunction with examples.

[0103] Example 1

[0104] This example provides an in-situ carbide reinforced refractory high-entropy alloy with a target carbide content of 0.05 wt.% and its preparation method, including the following steps:

[0105] (1) Alloy ingot melting

[0106] Mix Ta powder, Nb powder, W powder, and Mo powder with a particle size of 0.5 - 5 μm in a molar ratio of 1:1:1:1. Then mix the above pre-mixed metal powder with amorphous carbon powder with a particle size less than 0.2 μm in a mass ratio of 1:0.0005. Melt the above uniformly mixed powder through a vacuum levitation melting furnace to form an ingot; the melting temperature is 2100 °C, the melting time for each furnace is 4 h, and the melting is repeated 8 times to obtain an alloy ingot;

[0107] (2) Hydrogenation and crushing

[0108] Heat the alloy ingot to 500 °C in a mixed gas of inert gas and hydrogen, and hold for 3 h; then perform mechanical crushing, with a crushing time of 50 s, and collect the powder after sieving. The morphology is as shown in Figure 1 shown;

[0109] (3) Plasma spheroidization

[0110] The powder is loaded into the feeder of a 40KW plasma spheroidizing device. After the high-temperature plasma zone, a dense spheroidizing physical reaction occurs to obtain spherical and dense NbMoTaW high-entropy alloy composite powder with in-situ dispersion strengthening of carbides. Among them, the feeding rate is 30 g / min, the carrier gas is argon at 1 L / min, the central gas is argon at 20 L / min, and the plasma side gas is a mixed gas of ethylene, hydrogen, and argon with a molar ratio of ethylene:hydrogen:argon = 0.05:0.02:1, and the flow rate of the plasma side gas is 60 L / min. The pressure in the reaction chamber is 0.1 Mpa. The spherical and dense composite powder is placed in water and washed 2 - 3 times, and then dried at 80℃ under a N2 protective atmosphere.

[0111] (4) Dehydrogenation and deoxidation

[0112] The spheroidized powder is reduced in hydrogen at 600℃ for 2 h to reduce the oxygen content in the powder; then it is calcined in an inert gas at 600℃ for 3 h to obtain the in-situ carbide-reinforced refractory high-entropy alloy as described, with the morphology, XRD, and particle size distribution as Figures 2 - 4 shown;

[0113] (5) 3D printing and forming

[0114] The in-situ carbide-reinforced refractory high-entropy alloy powder with a particle size of 15 - 53μm is selected by screening and formed through a selective laser melting 3D printing process to obtain the 3D printed refractory high-entropy alloy product. Among them, the powder spreading thickness is 30μm, the laser power is 400W, the laser scanning speed is 900mm / s, and the laser stripe spacing is 0.1mm for selective laser melting forming.

[0115] (6) Heat treatment

[0116] The printed refractory high-entropy alloy product is heat-treated at a temperature of 1000℃ for 2 hours.

[0117] Powder properties: The powder is dense and spherical, the particle size of the powder is 10 - 150μm, the carbon content is 0.047 wt.%, and the oxygen content is 220 ppm.

[0118] 3D printing experiments are carried out on the prepared powder for verification. The powder with a particle size of 15 - 53μm is selected for selective laser melting forming to prepare a NbMoTaW high-entropy alloy specimen. After printing, heat treatment is carried out to eliminate the internal stress of the formed part. The density of the printed part is 99.2%, and the hardness is 863 HV.

[0119] Example 2

[0120] This embodiment provides an in-situ carbide-reinforced refractory high-entropy alloy with a target carbide content of 0.2 wt.%, and its preparation method. The difference from Example 1 lies in the addition amount of the carbon source. The specific steps are as follows:

[0121] (1) Alloy ingot melting

[0122] Mix Ta powder, Nb powder, W powder, and Mo powder with a particle size of 0.5 - 5 μm in a molar ratio of 1:1:1:1. Then mix the above pre-mixed metal powder with amorphous carbon powder with a particle size of less than 0.2 μm in a mass ratio of 1:0.002. Melting the above uniformly mixed powder through a vacuum levitation melting furnace to melt the raw materials and form an ingot; the melting temperature is 2100 °C, the melting time per furnace is 4 h, and the melting is repeated 8 times to obtain an alloy ingot;

[0123] (2) Hydrogenation and crushing

[0124] Heat the alloy ingot to 500 °C in a mixed gas of inert gas and hydrogen, and keep it warm for 3 h; then perform mechanical crushing, with a crushing time of 50 s, and collect the powder after sieving;

[0125] (3) Plasma spheroidization

[0126] Load the powder into the feeder of a 40KW plasma spheroidization device. After the high-temperature plasma zone, a dense spheroidization physical reaction occurs to obtain spherical and dense in-situ carbide-dispersion-strengthened NbMoTaW high-entropy alloy composite powder. Among them, the feeding rate is 30 g / min, the carrier gas is Ar at 1 L / min, the central gas is argon at 20 L / min, the plasma side gas is a hydrogen / argon mixed gas, and the molar ratio is ethylene: hydrogen: argon = 0.05:0.02:1, and the flow rate of the plasma side gas is 60 L / min. The reaction chamber pressure is 0.1 Mpa. Wash the spherical and dense composite powder in water 2 - 3 times, and then dry it at 80 °C under a N2 protective atmosphere.

[0127] (4) Dehydrogenation and deoxidation

[0128] Reduce the powder in hydrogen at 600 °C for 2 h to reduce the oxygen content in the powder; then calcine it in an inert gas at 600 °C for 3 h to obtain the in-situ carbide-reinforced refractory high-entropy alloy;

[0129] (5) 3D printing and forming

[0130] Sieve and select in-situ carbide-reinforced refractory high-entropy alloy powder with a particle size of 15 - 53 μm, and form it through a selective laser melting 3D printing process to obtain the 3D printed refractory high-entropy alloy product. Among them, the powder spreading thickness is 30 μm, the laser power is 400 W, the laser scanning speed is 900 mm / s, and the laser stripe spacing is 0.1 mm for selective laser melting and forming.

[0131] (6) Heat treatment

[0132] The printed refractory high-entropy alloy products are heat-treated at a temperature of 1000 °C for 2 hours of holding time.

[0133] Powder properties: The powder is dense and spherical, with a powder particle size of 10 - 150 μm, a carbon content of 0.194 wt.%, and an oxygen content of 247 ppm.

[0134] 3D printing experiments are carried out on the prepared powder for verification. Powders with a size of 15 - 53 μm are selected for selective laser melting to form NbMoTaW high-entropy alloy specimens. After printing, heat treatment is carried out to eliminate the internal stress of the formed parts. The density of the printed parts is 99.1%, and the hardness is 912 HV.

[0135] Example 3

[0136] This example provides an in-situ carbide-reinforced refractory high-entropy alloy with a target carbide content of 1 wt.% and its preparation method. The difference from Example 1 lies in the different addition amounts of the carbon source, including the following steps:

[0137] (1) Alloy ingot melting

[0138] Ta powder, Nb powder, W powder, and Mo powder with a size of 0.5 - 5 μm are mixed in a molar ratio of 1:1:1:1. Then the above pre-mixed metal powder and amorphous carbon powder with a size less than 0.2 μm are mixed in a mass ratio of 1:0.01. The above uniformly mixed powder is melted by a vacuum suspension melting furnace to form an ingot; the melting temperature is 2100 °C, the melting time per furnace is 4 h, and the melting is repeated 8 times to obtain an alloy ingot;

[0139] (2) Hydrogenation and crushing

[0140] The alloy ingot is heated to 500 °C in a mixed gas of inert gas and hydrogen and held for 3 h; then mechanical crushing is carried out, the crushing time is 50 s, and the powder is collected after sieving;

[0141] (3) Plasma spheroidization

[0142] The powder is loaded into the feeder of a 40KW plasma spheroidizing device. After passing through the high-temperature plasma zone, a dense spheroidizing physical reaction occurs to obtain spherical and dense NbMoTaW high-entropy alloy composite powder with in-situ dispersed strengthened carbides. Among them, the feeding rate is 30 g / min, the carrier gas is Ar at 1 L / min, the central gas is argon at 20 L / min, the plasma side gas is a hydrogen / argon mixed gas, and the molar ratio of ethylene: hydrogen: argon = 0.05: 0.02: 1. The flow rate of the plasma side gas is 60 L / min. The pressure in the reaction chamber is 0.1 Mpa. The spherical and dense composite powder is placed in water and washed 2 - 3 times, and then dried at 80 °C under a N2 protective atmosphere.

[0143] (4) Dehydrogenation and deoxidation

[0144] The spheroidized powder is reduced in hydrogen at 600 °C for 2 h to reduce the oxygen content in the powder; then it is calcined in an inert gas at 600 °C for 3 h to obtain the in-situ carbide-reinforced refractory high-entropy alloy.

[0145] (5) 3D printing and forming

[0146] The in-situ carbide-reinforced refractory high-entropy alloy powder with a particle size of 15 - 53 μm is selected by sieving and formed by selective laser melting 3D printing process to obtain the 3D printed refractory high-entropy alloy product. Among them, the powder spreading thickness is 30 μm, the laser power is 400 W, the laser scanning speed is 900 mm / s, and the laser stripe spacing is 0.1 mm for selective laser melting forming.

[0147] (6) Heat treatment

[0148] The printed refractory high-entropy alloy product is heat-treated at a temperature of 1000 °C for 2 hours.

[0149] Powder properties: The powder is dense and spherical, the particle size of the powder is 10 - 150 μm, the carbon content is 0.992 wt.%, and the oxygen content is 186 ppm.

[0150] 3D printing experiments are carried out on the prepared powder for verification. The powder with a particle size of 15 - 53 μm is selected for selective laser melting forming to prepare NbMoTaW high-entropy alloy specimens. After printing, heat treatment is carried out to eliminate the internal stress of the formed parts. The density of the printed parts is 99.4%, and the hardness is 956 HV.

[0151] Example 4

[0152] This example provides an in-situ carbide-reinforced refractory high-entropy alloy with a target carbide content of 5 wt.% and its preparation method. The difference from Example 1 is only the addition amount of the carbon source, including the following steps:

[0153] (1) Melting of alloy ingot

[0154] Mix Ta powder, Nb powder, W powder, and Mo powder with a particle size of 0.5 - 5 μm in a molar ratio of 1:1:1:1. Then mix the above pre-mixed metal powder with amorphous carbon powder with a particle size less than 0.2 μm in a mass ratio of 1:0.05. Melting the above uniformly mixed powder through a vacuum suspension melting furnace to melt the raw materials and form an ingot; the melting temperature is 2100 °C, the melting time for each furnace is 4 h, and the melting is repeated 8 times to obtain an alloy ingot;

[0155] (2) Hydrogenation and crushing

[0156] Heat the alloy ingot to 500 °C in a mixed gas of inert gas and hydrogen and hold for 3 h; then perform mechanical crushing, the crushing time is 50 s, and collect the powder after sieving;

[0157] (3) Plasma spheroidization

[0158] Load the powder into the feeder of a 40KW plasma spheroidization device. After the high-temperature plasma zone, a dense spheroidization physical reaction occurs to obtain spherical and dense carbide in-situ dispersion strengthened NbMoTaW high-entropy alloy composite powder. Among them, the feeding rate is 30 g / min, the carrier gas is Ar at 1 L / min, the central gas is argon at 20 L / min, the plasma side gas is a hydrogen / argon mixed gas, and the molar ratio is ethylene: hydrogen: argon = 0.05:0.02:1, and the flow rate of the plasma side gas is 60 L / min. The pressure in the reaction chamber is 0.1 Mpa. Wash the spherical and dense composite powder in water 2 - 3 times, and then dry it at 80 °C under a N2 protective atmosphere.

[0159] (4) Dehydrogenation and deoxidation

[0160] Reduce the powder in hydrogen at 600 °C for 2 h to reduce the oxygen content in the powder; then calcine it in an inert gas at 600 °C for 3 h to obtain the in-situ carbide-reinforced refractory high-entropy alloy;

[0161] (5) 3D printing and forming

[0162] Sieve and select in-situ carbide-reinforced refractory high-entropy alloy powder with a particle size of 15 - 53 μm, and form it through a selective laser melting 3D printing process to obtain the 3D printed refractory high-entropy alloy product. Among them, the powder spreading thickness is 30 μm, the laser power is 400 W, the laser scanning speed is 900 mm / s, and the laser stripe spacing is 0.1 mm for selective laser melting forming.

[0163] (6) Heat treatment

[0164] Heat-treat the printed refractory high-entropy alloy product, the heat treatment temperature is 1000 °C, and the holding time is 2 hours.

[0165] Powder properties: The powder is dense and spherical, the particle size of the powder is 10 - 150 μm, the carbon content is 4.95 wt.%, and the oxygen content is 179 ppm.

[0166] The prepared powder was verified by 3D printing experiments. Powders with a size of 15 - 53 μm were selected for selective laser melting to prepare NbMoTaW high-entropy alloy specimens. After printing, heat treatment was carried out to eliminate the internal stress of the formed parts. The density of the printed parts was 98.2%, and the hardness was 831 HV.

[0167] Comparative Example 1

[0168] This comparative example provides a preparation of NbMoTaW high-entropy alloy powder without adding a carbon source. The other parameters are the same as those in Example 1 except for the carbon content.

[0169] Powder properties: The powder is dense and spherical, the particle size of the powder is 10 - 150 μm, and the oxygen content is 179 ppm.

[0170] The prepared powder was verified by 3D printing experiments. Powders with a size of 15 - 53 μm were selected for selective laser melting to prepare NbMoTaW high-entropy alloy specimens. After printing, heat treatment was carried out to eliminate the internal stress of the formed parts. The density of the printed parts was 97.6%, and the hardness was 756 HV.

[0171] Comparative Example 2

[0172] This comparative example provides an in-situ carbide-reinforced refractory high-entropy alloy and its preparation method. The difference from Example 1 is only that: the side gas of the plasma spheroidization equipment does not include carbon-rich gas.

[0173] Powder properties: The powder is dense and spherical, the particle size of the powder is 10 - 150 μm, and the oxygen content is 210 ppm.

[0174] The prepared powder was verified by 3D printing experiments. Powders with a size of 15 - 53 μm were selected for selective laser melting to prepare NbMoTaW high-entropy alloy specimens. After printing, heat treatment was carried out to eliminate the internal stress of the formed parts. The density of the printed parts was 99.0%, and the hardness was 843 HV.

[0175] The in-situ carbide-reinforced refractory high-entropy alloys and the printed parts were tested, and the results are shown in Table 1.

[0176] Table 1

[0177] Serial number Target carbon content wt% Particle size μm Oxygen content ppm Printing density Hardness HV Example 1 0.05 10～150 220 99.2％ 863 Example 2 0.2 10～150 247 99.1％ 912 Example 3 1 10～150 186 99.4％ 956 Example 4 5 10～150 179 98.2％ 831 Comparative example 1 0 10～150 179 97.6 756 Comparative example 2 0.02 10～150 210 99.0％ 843

[0178] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an in-situ carbide reinforced refractory high entropy alloy, characterized in that: include: Smelting, mixing raw material powders including Nb, Mo, Ta and W and a carbon source and smelting to form an ingot; Hydrogenation and crushing: the ingot is placed in a mixed atmosphere of inert gas and hydrogen for heating and hydrogenation, and then the hydrogenated ingot is crushed and sieved to obtain hydrogenated powder; Plasma spheroidization, transporting the hydrogenated powder to a high-temperature plasma region of a plasma spheroidization device under carrier gas protection to melt, and then condensing into balls to obtain spherical refractory high-entropy alloy powder; Dehydrogenation and oxygen reduction are performed, and the spherical refractory high entropy alloy powder is subjected to a reduction reaction in hydrogen and then calcined to obtain the in-situ carbide reinforced refractory high entropy alloy powder.

2. The method for preparing an in-situ carbide reinforced refractory high entropy alloy according to claim 1, characterized in that: The particle size of the raw material powder is 0.1 to 10 μm; And / or, the particle size of the carbon source is less than 1 um; and / or, the mass ratio of the raw material powder to the carbon source powder is 1:(0.0005-0.3); And / or, the raw material powder is selected from at least one of metal element powder and alloy powder; And / or, the molar fraction of Nb in the raw material powder is 15% to 35%, the molar fraction of Mo is 15% to 35%, the molar fraction of Ta is 15% to 35%, and the molar fraction of W is 15% to 35%; And / or, the carbon source is amorphous carbon.

3. The method for preparing an in-situ carbide reinforced refractory high entropy alloy according to claim 1, characterized in that: The smelting temperature is 2000-3200°C, the smelting time is 3-5h, and the smelting times are 5-8 times; And / or, the volume fraction of hydrogen in the mixed gas is 20 to 80%; and / or, the hydrogenation temperature is 400-700° C., and the hydrogenation holding time is 1-6 hours; And / or, the crushing is carried out by mechanical crushing, and the crushing time is 5 to 60 seconds.

4. The method for preparing an in-situ carbide reinforced refractory high entropy alloy according to claim 1, characterized in that: The temperature of plasma spheroidization is 8000-12000°C and the pressure is 0.01-0.15Mpa; And / or, the power of the plasma spheroidization equipment is 15-100kw; And / or, the side gas of the plasma spheroidization device includes carbon-rich gas; and / or, the hydrogenated powder feed rate of the plasma spheroidization device is 0.1 to 100 g / min; and / or, after condensing into balls, washing and drying the material to obtain the in-situ carbide reinforced refractory high entropy alloy, wherein the drying is performed under the protection of an inert gas; and / or, the reduction reaction temperature is 500-600° C. and the time is 1-5 h; And / or, the calcination temperature is 600-750° C. and the calcination time is 2-5 hours.

5. The method for preparing an in-situ carbide reinforced refractory high entropy alloy according to claim 4, characterized in that: The carbon-rich gas is selected from alkanes or alkenes; And / or, the side gas of the plasma spheroidization device is composed of carbon-rich gas, H2 and inert gas, and the center gas is inert gas; And / or, in the side gas of the plasma spheroidization device, the molar ratio of carbon-rich gas, H2 and inert gas is (0.005-0.1):(0.005-0.05):1; And / or, the flow rate of the side gas is 45 to 75 L / min; And / or, the flow rate of the central gas is 15 to 25 L / min; And / or, the carrier gas is argon and / or helium with a flow rate of 1 to 5 L / min.

6. An in-situ carbide reinforced refractory high entropy alloy powder prepared by the method according to any one of claims 1 to 5, characterized in that: At least one of the following conditions is met: A. Particle size 10~300um; B. Hall flow rate is 10-15s / 50g; C, the carbon content is 0.05-5wt.%; preferably, when the carbon content is less than 0.1wt.%, nano-sized carbides are distributed in the in-situ carbide-enhanced refractory high entropy alloy; preferably, when the carbon content is 0.1wt.%-1wt.%, micron-sized carbides are distributed in the in-situ carbide-enhanced refractory high entropy alloy; D. Oxygen content is less than 300ppm.

7. A method for preparing a 3D printed product, characterized in that: include: Forming, spreading the in-situ carbide reinforced refractory high entropy alloy powder according to claim 6 to a designated position, and then performing laser selective melting forming to obtain a printed part; Heat treatment: heat treatment is performed on the printed part to obtain the 3D printed product.

8. The method for preparing a 3D printed product according to claim 7, characterized in that: The equipment model used for laser selective melting molding is AMC-M1508B; And / or, the power of laser selective melting is 180-400W, the scanning speed is 500-1000mm / s, the laser stripe spacing is 0.03-0.1mm, and the thickness of the powder is 20-40μm; And / or, the heat treatment temperature is 600-1200° C., and the insulation time is 1-10 hours.

9. A 3D printed product, characterized in that: Prepared by the method of claim 7 or 8, the 3D printed product has a density greater than 99% and a Vickers hardness of 1029 to 1265 HV.

10. An application of the in-situ carbide reinforced refractory high entropy alloy according to claim 9, characterized in that: Such applications include applications in the field of additive manufacturing or thermal spraying.

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