High-entropy hard alloy and preparation method and application thereof

Abstract

The invention provides a high-entropy hard alloy and a preparation method and application thereof.The preparation method comprises the steps that the particle surface of hard phase powder is coated with a binding phase metal layer, then forming, degreasing and vacuum presintering are conducted, and a presintered body with the relative density not exceeding 90% is obtained; the surface of the pre-sintered body is coated with at least two metal layers, and then the high-entropy hard alloy is obtained through vacuum sintering and hot isostatic pressing infiltration treatment; the at least two metal layers comprise an innermost high-entropy alloy layer and an outermost metal layer. Through the arrangement of the binding phase metal layer, the damage of carbon, nitrogen, boron or silicon in the hard phase powder to the crystal structure of the high-entropy alloy is prevented; and in cooperation with subsequent hot isostatic pressing infiltration treatment, the problem that a binding phase of the high-entropy alloy is prone to agglomeration due to a traditional powder mixing method is solved, and meanwhile the problems that infiltration is not thorough and is limited by the appearance and size of a product are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of cemented carbide and relates to a high-entropy cemented carbide and a preparation method and application thereof. Background Art

[0002] Compared with traditional metal alloys, high entropy alloys have high strength, high toughness, high hardness, high wear resistance, excellent corrosion resistance, and good high temperature stability and high temperature performance. Since the high entropy alloy was proposed, it has been well applied. The high entropy alloy systems that have been developed mainly include the following three categories: light metal high entropy alloy systems based on Al and the fourth and fifth period elements Fe, Co, Ni, Cr, Cu, Mn, Sn, Zn, Li, Mg, Zr and Ti; refractory metal high entropy alloy systems based on refractory metal elements Mo, V, Nb, Hf, Ta, Cr and W; and rare earth metal high entropy alloy systems based on rare earth elements.

[0003] In the field of cemented carbide technology, due to the excellent performance of high entropy alloys, researchers have tried to use high entropy alloys as a binder phase to replace traditional binder phases such as Co, Ni or Fe to further improve the toughness of cemented carbide. However, the preparation of high entropy cemented carbide by traditional powder metallurgy has the following problems: on the one hand, since the particle size of the hard phase powder used to prepare cemented carbide is below 2μm, and the hard phase powder is easily crushed and refined during ball milling, and the ultrafine particle high entropy alloy powder with a particle size of less than 5μm is difficult to mass produce; even if ultrafine high entropy alloy powder can be obtained, cold welding is easy to occur between particles during ball milling and mixing, causing agglomeration. Based on the above reasons, it is difficult to mix the hard phase powder and the high entropy alloy powder evenly; on the other hand, during the liquid phase sintering process, atoms such as carbon, boron, nitrogen or silicon in the hard phase powder and additive powder are easily dissolved into the high entropy alloy liquid phase. During the cooling process, atoms such as carbon, boron, nitrogen or silicon are easily reacted with the metal components in the high entropy alloy and precipitated, resulting in the destruction of the high entropy alloy phase structure, so that the high entropy alloy cannot play its due role.

[0004] The prior art CN110643880A and CN113234982A adopt the melt infiltration method to prepare high entropy cemented carbide, but the above method has the problem of limited melt infiltration depth, and the WC blank needs to contain more pores (such as the pore making method adopted in CN113234982A) to facilitate melt infiltration, which makes it impossible to prepare products with larger size and complex shape, and also leads to the problem of high content of high entropy alloy binder phase; in addition, the prior art cannot solve the problem of destruction of the high entropy alloy phase structure during the melt infiltration process.

[0005] Based on the above problems, how to obtain high-performance high-entropy cemented carbide in which the high-entropy alloy binder phase does not agglomerate, its phase structure is not destroyed, and its content is controllable is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] The object of the present invention is to provide a high entropy cemented carbide and a preparation method and application thereof, so as to obtain a high-entropy cemented carbide with high performance in which the bonding phase of the high entropy alloy is not agglomerated, the phase structure is not destroyed and the content thereof is controllable.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0009] The surface of the hard phase powder particles is coated with a binder phase metal layer, and then molded, degreased and vacuum pre-sintered to obtain a pre-sintered body with a relative density not exceeding 90%;

[0010] Coating at least two metal layers on the surface of the pre-sintered body, and then subjecting the pre-sintered body to vacuum sintering and hot isostatic pressing infiltration treatment to obtain the high entropy cemented carbide;

[0011] The at least two metal layers include an innermost high entropy alloy layer and an outermost metal layer;

[0012] The vacuum sintering temperature T 2 The temperature T of hot isostatic pressing infiltration treatment 3 are lower than the melting point T of the bonding phase metal layer m1 ;

[0013] The vacuum sintering temperature T 2 Higher than the melting point T of the high entropy alloy layer m2 ;

[0014] The melting point of the outermost metal layer is T m3 Higher than the melting point T of the bonding metal layer m1 .

[0015] The preparation method provided by the present invention comprises coating a bonding phase metal layer on the particle surface of a hard phase powder as a protective layer to prevent atoms such as carbon, nitrogen, boron or silicon in the hard phase powder from destroying the phase structure of a high entropy alloy; then forming, degreasing and vacuum pre-sintering are performed to obtain a pre-sintered body with pores; then at least two metal layers including an innermost high entropy alloy layer and an outermost metal layer are uniformly coated on the surface of the pre-sintered body, the surface of the pre-sintered body is sealed by vacuum sintering, and then hot isostatic pressing infiltration treatment is performed to diffuse the molten high entropy alloy into the interior of the pre-sintered body along the pores and / or interfaces of the pre-sintered body, thereby obtaining a dense high entropy hard alloy; wherein, the pressure of the hot isostatic pressing infiltration treatment is controlled to obtain a high entropy hard alloy with a gradient distribution of the high entropy alloy bonding phase or a high entropy hard alloy with uniform composition; and the application of the hot isostatic pressing infiltration treatment also solves the problem of easy agglomeration of the high entropy alloy bonding phase caused by the traditional powder mixing method, and at the same time, avoids the problem of incomplete infiltration and limitation of product external dimensions.

[0016] Preferably, the melting point of the high entropy alloy layer is m2 600℃ to 1200℃.

[0017] Preferably, the metal elements in the high entropy alloy layer include a combination of at least five of Al, Fe, Co, Zn, Sn, Ni, Cr, Cu, Mn, Li, Mg or Ti.

[0018] Preferably, the volume of the high entropy alloy layer is not less than the total volume of the pores in the pre-sintered body.

[0019] Preferably, the metal element in the outermost metal layer includes any one of Ti, Zr, Mo, Nb or Ta, or a combination of at least two of them.

[0020] Preferably, the thickness of the outermost metal layer is 0.1 mm to 0.3 mm.

[0021] Preferably, the metal element in the bonding phase metal layer includes any one of Co, Ni or Fe, or a combination of at least two of them.

[0022] Preferably, the vacuum sintering temperature T 2 T than the melting point T of the high entropy alloy layer m2 High 25℃ to 50℃.

[0023] Preferably, the vacuum sintering temperature T 2 Than the melting point T of the bonding metal layer m1 Lower than 200℃.

[0024] Preferably, the holding time of the vacuum sintering is 0.5h to 1h.

[0025] Preferably, the vacuum sintering pressure is 10 -3 Below Pa.

[0026] Preferably, the hot isostatic pressing infiltration treatment is carried out in an inert atmosphere.

[0027] Preferably, the pressure of the hot isostatic pressing infiltration treatment is 5 MPa to 300 MPa.

[0028] Preferably, the temperature of the hot isostatic pressing infiltration treatment is 3 Equal to the vacuum sintering temperature T 2 .

[0029] Preferably, the heat preservation and pressure holding time of the hot isostatic pressing infiltration treatment is 1 hour to 3 hours.

[0030] Preferably, the preparation method further comprises an annealing treatment after the hot isostatic pressing infiltration treatment.

[0031] Preferably, the annealing temperature T 4 Lower than the melting point T of the high entropy alloy layer m2 .

[0032] Preferably, the annealing temperature T 4 T than the melting point T of the high entropy alloy layer m2 100℃ to 200℃ lower.

[0033] Preferably, the pressure of the annealing treatment is below 30 Pa.

[0034] Preferably, the temperature is raised from room temperature to the annealing temperature T at a heating rate of 0.5°C / min to 1°C / min. 4 .

[0035] Preferably, at the annealing temperature T 4 Keep warm for 1h to 3h.

[0036] Preferably, the temperature T of the annealing treatment is lowered at a rate of 1°C / min to 2°C / min. 4 The temperature is lowered to room temperature, and the annealing treatment is completed.

[0037] In a second aspect, the present invention provides a high entropy cemented carbide, which is prepared by the preparation method described in the first aspect.

[0038] Preferably, when the pressure of the hot isostatic pressing infiltration treatment is greater than 5 MPa and less than 80 MPa, the content of the high entropy alloy binder phase in the high entropy cemented carbide gradually decreases from the surface to the inside;

[0039] When the pressure of the hot isostatic pressing infiltration treatment is higher than 80 MPa and lower than 300 MPa, a high entropy cemented carbide with uniform composition is obtained.

[0040] In a third aspect, the present invention provides an application of a high entropy cemented carbide, wherein the high entropy cemented carbide is used to prepare molds, cutting tools or wear-resistant parts;

[0041] The high entropy cemented carbide is prepared by the preparation method described in the first aspect, or is the high entropy cemented carbide described in the second aspect.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The preparation method provided by the present invention comprises coating a bonding phase metal layer on the particle surface of a hard phase powder as a protective layer to prevent atoms such as carbon, nitrogen, boron or silicon in the hard phase powder from destroying the phase structure of a high entropy alloy; then forming, degreasing and vacuum pre-sintering are performed to obtain a pre-sintered body with pores; then at least two metal layers including an innermost high entropy alloy layer and an outermost metal layer are uniformly coated on the surface of the pre-sintered body, the surface of the pre-sintered body is sealed by vacuum sintering, and then hot isostatic pressing infiltration treatment is performed to diffuse the molten high entropy alloy into the interior of the pre-sintered body along the pores and / or interfaces of the pre-sintered body, thereby obtaining a dense high entropy hard alloy; wherein, the pressure of the hot isostatic pressing infiltration treatment is controlled to obtain a high entropy hard alloy with a gradient distribution of the high entropy alloy bonding phase or a high entropy hard alloy with uniform composition; and the application of the hot isostatic pressing infiltration treatment also solves the problem of easy agglomeration of the high entropy alloy bonding phase caused by the traditional powder mixing method, and at the same time, avoids the problem of incomplete infiltration and limitation of product external dimensions. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] A certain embodiment of the present invention provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0046] The surface of the hard phase powder particles is coated with a binder phase metal layer, and then molded, degreased and vacuum pre-sintered to obtain a pre-sintered body with a relative density not exceeding 90%;

[0047] Coating at least two metal layers on the surface of the pre-sintered body, and then subjecting the pre-sintered body to vacuum sintering and hot isostatic pressing infiltration treatment to obtain the high entropy cemented carbide;

[0048] The at least two metal layers include an innermost high entropy alloy layer and an outermost metal layer;

[0049] The vacuum sintering temperature T 2 The temperature T of hot isostatic pressing infiltration treatment 3 are lower than the melting point T of the bonding phase metal layer m1 ;

[0050] The vacuum sintering temperature T 2 Higher than the melting point T of the high entropy alloy layer m2 ;

[0051] The melting point of the outermost metal layer is T m3 Higher than the melting point T of the bonding metal layer m1 .

[0052] The preparation method provided by the present invention comprises coating a bonding phase metal layer on the particle surface of a hard phase powder as a protective layer to prevent atoms such as carbon, nitrogen, boron or silicon in the hard phase powder from destroying the phase structure of a high entropy alloy; then forming, degreasing and vacuum pre-sintering are performed to obtain a pre-sintered body with pores; then at least two metal layers including an innermost high entropy alloy layer and an outermost metal layer are uniformly coated on the surface of the pre-sintered body, the surface of the pre-sintered body is sealed by vacuum sintering, and then hot isostatic pressing infiltration treatment is performed to diffuse the molten high entropy alloy into the interior of the pre-sintered body along the pores and / or interfaces of the pre-sintered body, thereby obtaining a dense high entropy hard alloy; wherein, the pressure of the hot isostatic pressing infiltration treatment is controlled to obtain a high entropy hard alloy with a gradient distribution of the high entropy alloy bonding phase or a high entropy hard alloy with uniform composition; and the application of the hot isostatic pressing infiltration treatment also solves the problem of easy agglomeration of the high entropy alloy bonding phase caused by the traditional powder mixing method, and at the same time, avoids the problem of incomplete infiltration and limitation of product external dimensions.

[0053] The relative density of the pre-sintered body in the present invention refers to the ratio of the density of the pre-sintered body to the theoretical density of the cemented carbide composed of the hard phase powder and the binder phase metal layer. Usually, the relative density of the molded body after molding is not less than 35%.

[0054] In the present invention, the vacuum pre-sintering conditions will affect the relative density of the obtained pre-sintered body. The present invention does not affect the vacuum pre-sintering conditions (such as the vacuum pre-sintering temperature T 1 ) is not specifically limited, and the relative density of the pre-sintered body only needs to be controlled not to exceed 90%, that is, the total volume of the pores in the pre-sintered body is controlled, and the content of the high entropy alloy bonding phase in the high entropy cemented carbide is further controlled.

[0055] In certain embodiments, the hard phase powder includes WC powder and additive powder that are uniformly mixed by ball milling.

[0056] In some embodiments, the additive powder includes Cr 3 C 2 、VC、ZrC、TiC、Mo2 C, TaC, NbC, SiC, B 4 C, ZrB, ZrB 2 , TiB, TiB 2 , WB, W 2 B.W 2 B 5 , CrB, AlN, ZrN, TiN, TiCN, Si 3 N 4 , BN, any one of rare earth metal oxides or rare earth metal borides, or a combination of at least two of them.

[0057] In some embodiments, the ball milling mixing includes: placing the formulated WC powder and the additive powder in a ball mill, injecting anhydrous ethanol into the ball mill, and ball milling and mixing in a protective atmosphere for more than 24 hours to obtain a uniformly mixed hard phase powder.

[0058] In some embodiments, the grinding balls used in the ball milling mixture are carbide balls, and the mass ratio of the grinding balls to the raw material powder is 3:1 to 5:1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0059] In certain embodiments, the protective atmosphere during the ball milling mixing comprises nitrogen and / or an inert gas; the inert gas comprises any one of argon, helium or neon or a combination of at least two thereof, and typical non-limiting combinations include a combination of argon and helium, a combination of helium and neon, a combination of argon and neon, or a combination of argon, helium and neon.

[0060] In certain embodiments, the method of coating the binder phase metal layer on the surface of the hard phase powder particles includes chemical plating.

[0061] In some embodiments, the chemical plating method comprises the following steps:

[0062] After being activated by an activation solution, the hard phase powder is placed in a chemical plating solution for chemical plating, and then cleaned and vacuum dried to complete the chemical plating.

[0063] In some embodiments, the activation solution includes hydrofluoric acid (mass percentage concentration is 40wt%), ammonium fluoride, nitric acid (mass percentage concentration is 65wt%) and hydrochloric acid (mass percentage concentration is 36wt%); wherein the amounts of hydrofluoric acid, ammonium fluoride, nitric acid and hydrochloric acid in the activation solution are 30mL / L to 50mL / L, 2g / L to 4g / L, 20mL / L to 40mL / L and 10mL / L to 30mL / L respectively; and the solvent of the activation solution is deionized water.

[0064] The present invention removes impurities on the surface of hard phase powder particles by activation and modifies the microstructure of the surface of hard phase powder particles, so that micro defects such as active stacking faults or dislocations are generated on the surface of hard phase powder particles, thereby helping to induce the deposition of bonding phase metal ions on the surface and improve the bonding strength.

[0065] In certain embodiments, the activation comprises ultrasonic stirring for 15 min to 30 min, for example, 15 min, 20 min, 25 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0066] In some embodiments, the solid-liquid ratio during chemical plating is 150g / L to 1500g / L, for example, it can be 150g / L, 300g / L, 500g / L, 800g / L, 1000g / L, 1200g / L or 1500g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] In some embodiments, the chemical plating solution includes 20 g / L to 30 g / L of a metal salt compound, 20 g / L to 30 g / L of a reducing agent, 40 g / L to 60 g / L of a complexing agent, and 20 g / L to 30 g / L of a stabilizer.

[0068] In certain embodiments, the metal salt compound includes a metal sulfate compound and / or a metal chloride compound.

[0069] In certain embodiments, the metal salt compound includes any one of a cobalt salt compound, a nickel salt compound or an iron salt compound, or a combination of at least two of them. Typical but non-limiting combinations include a combination of a cobalt salt compound and a nickel salt compound, a combination of a cobalt salt compound and an iron salt compound, a combination of a nickel salt compound and an iron salt compound, or a combination of a cobalt salt compound, a nickel salt compound and an iron salt compound.

[0070] In certain embodiments, the reducing agent comprises sodium hypophosphite.

[0071] In certain embodiments, the complexing agent comprises trisodium citrate.

[0072] In certain embodiments, the stabilizer comprises boric acid.

[0073] In some embodiments, the chemical coating is carried out under ultrasonic stirring at a temperature of 40°C to 60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] In some embodiments, during the chemical coating process, the vacuum drying temperature is 60°C to 120°C, for example, it can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0075] In the present invention, the metal elements in the bonding phase metal layer need to have good compatibility with the hard phase powder, so as to improve the interface strength between the bonding phase metal layer and the hard phase powder; the bonding phase metal layer also needs to have good compatibility with the high entropy alloy bonding phase, so as to facilitate the infiltration of the high entropy alloy during hot isostatic pressing.

[0076] In some embodiments, the metal element in the bonding phase metal layer includes any one or a combination of at least two of Co, Ni or Fe. Typical but non-limiting combinations include a combination of Co and Ni, a combination of Ni and Fe, a combination of Co and Ni, or a combination of Co, Ni and Fe.

[0077] The method of coating the surface of the pre-sintered body with at least two metal layers in the present invention is a conventional method, as long as the non-airtight coating of the metal layer on the surface of the pre-sintered body can be achieved.

[0078] In some embodiments, the at least two metal layers include an innermost high entropy alloy layer and an outermost metal layer. Exemplarily, the method of coating the innermost high entropy alloy layer on the surface of the pre-sintered body includes spraying or alloy thin-walled part casing.

[0079] In certain embodiments, when coating the innermost high entropy alloy layer, the spraying method includes: uniformly spraying a slurry containing high entropy alloy powder on the surface of the pre-sintered body to form the innermost high entropy alloy layer.

[0080] In some embodiments, when coating the innermost high entropy alloy layer, the method of coating the alloy thin-walled member includes: preparing the high entropy alloy to be coated into a plurality of thin-walled members having the same shape as the pre-sintered body, coating the plurality of thin-walled members in combination and closely attaching the plurality of thin-walled members to the surface of the pre-sintered body, and coating the plurality of thin-walled members at the interface thereof by The sleeves are connected to form the innermost high entropy alloy layer.

[0081] Exemplarily, the method of coating the outermost metal layer includes sleeve coating of a thin-walled metal member.

[0082] In some embodiments, when coating the outermost metal layer, the method of sleeve-arranging the metal thin-walled member comprises: preparing the metal component to be coated into a plurality of thin-walled members having the same shape as the pre-sintered body coated with the high entropy alloy layer, sleeve-arranging the plurality of thin-walled members in combination and closely attaching the outer surface of the pre-sintered body coated with the inner metal layer, and the interfaces of the plurality of thin-walled members are The sleeves are connected to form the outermost metal cladding layer.

[0083] In some embodiments, the melting point of the outermost metal layer is m3 Higher than the melting point T of the bonding metal layer m1 .

[0084] The innermost layer of the present invention refers to the metal layer closest to the pre-sintered body among at least two metal layers; the outermost metal layer refers to the metal layer farthest from the pre-sintered body among at least two metal layers.

[0085] In some embodiments, the melting point of the high entropy alloy layer is m2 It is 600°C to 1200°C, for example, 600°C, 800°C, 900°C, 1000°C or 1200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0086] In some embodiments, the metal elements in the high entropy alloy layer include a combination of at least 5 of Al, Fe, Co, Zn, Sn, Ni, Cr, Cu, Mn, Li, Mg or Ti.

[0087] In some embodiments, the volume of the high entropy alloy layer is not less than the total volume of the pores in the pre-sintered body.

[0088] The present invention sets the volume of the high entropy alloy layer to be not less than the total volume of the pores in the pre-sintered body, so that the high entropy alloy in the high entropy alloy layer can fully fill the pores in the pre-sintered body to obtain a dense high entropy cemented carbide.

[0089] Assuming the density of the high entropy alloy to be ρ, the relative density of the pre-sintered body to be D, and the volume of the pre-sintered body to be V, the mass of the required high entropy alloy is obtained to be M≥ρ×V×(1-D).

[0090] In order to enable the preparation method provided by the present invention to proceed smoothly, the outermost metal layer can always remain in a solid state during vacuum sintering and hot isostatic pressing infiltration treatment, thereby avoiding the loss of the high entropy alloy layer due to gravity during the melting process, thereby ensuring complete wrapping and sealing of the pre-sintered body.

[0091] In some embodiments, the metal element in the outermost metal layer includes any one of Ti, Zr, Mo, Nb or Ta, or a combination of at least two of them. Typical but non-limiting combinations include a combination of Ti and Zr, a combination of Mo and Nb, a combination of Mo, Nb and Ta, a combination of Ti, Zr, Mo and Nb, or a combination of Ti, Zr, Mo, Nb and Ta.

[0092] In some embodiments, the thickness of the outermost metal layer is 0.1 mm to 0.3 mm, for example, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm or 0.3 mm, but is not limited to the listed values, and the remaining values ​​not listed in the numerical range are also applicable. Of course, in order for the outermost metal layer to fully play a protective role, in general, the thickness of the outermost metal layer increases accordingly as the volume of the high entropy alloy layer covering increases.

[0093] The present invention melts the high entropy alloy layer through vacuum sintering, and causes a diffusion reaction on the surface of the pre-sintered body to form a dense high entropy alloy sealing layer on the surface of the pre-sintered body, thereby achieving complete sealing of the pre-sintered body.

[0094] In some embodiments, the vacuum sintering is carried out at a pressure of 10 -3 Pa or less.

[0095] In some embodiments, the vacuum sintering temperature T 2 T than the melting point of the high entropy alloy layer m2 25°C to 50°C higher, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0096] In some embodiments, the vacuum sintering temperature T 2 Than the melting point T of the bonding metal layer m1 Lower than 200℃.

[0097] The present invention controls the temperature T of vacuum sintering. 2 and the melting point T of the high entropy alloy layer m2 The temperature is 25°C to 50°C higher, so that the high entropy alloy layer can be fully melted and diffuse into the surface of the pre-sintered body through the pores and / or interfaces of the pre-sintered body, thereby fully sealing the surface of the pre-sintered body; at the same time, the vacuum sintering temperature T is also controlled. 2 T m1 The temperature is lower than 200℃, which can ensure that the bonding metal layer remains in a solid phase, and prevent the carbon, nitrogen, boron or silicon atoms in the hard phase from diffusing across the bonding metal layer and damaging the high entropy alloy phase structure. Moreover, vacuum sintering is carried out under vacuum conditions, which can ensure that various gas phases fully react and discharge the pre-sintered body before the high entropy alloy melts and seals.

[0098] In some embodiments, the holding time of the vacuum sintering is 0.5h to 1h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0099] After vacuum sintering, hot isostatic pressing infiltration treatment is performed. Under the action of gas pressure, the molten high entropy alloy diffuses into the interior of the pre-sintered body along the pores and / or interfaces to fill the pores in the pre-sintered body, thereby obtaining a completely dense high entropy cemented carbide.

[0100] In certain embodiments, the hot isostatic pressing infiltration process is performed in an inert atmosphere.

[0101] The inert atmosphere includes nitrogen and / or an inert gas, and the inert gas includes any one of helium, neon or argon, or a combination of at least two of them.

[0102] In some embodiments, the pressure of the hot isostatic pressing infiltration treatment is 5 MPa to 300 MPa, for example, it can be 5 MPa, 20 MPa, 40 MPa, 50 MPa, 60 MPa, 80 MPa, 100 MPa, 150 MPa, 200 MPa, 250 MPa or 300 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0103] The pressure of hot isostatic pressing infiltration treatment affects the infiltration of the molten high-entropy alloy in the pre-sintered body. When the hot isostatic pressing pressure is below 80MPa, as the sintering temperature increases, the diffusion process of the high-entropy alloy liquid phase will partially lag behind the densification process of the pre-sintered body, thereby forming a gradient high-entropy cemented carbide, that is, the content of the high-entropy alloy bonding phase gradually decreases from the surface to the inside; when the hot isostatic pressing pressure is higher than 80MPa and below 300MPa, the diffusion infiltration process of the high-entropy alloy liquid phase and the densification process of the pre-sintered body are almost carried out simultaneously, so a high-entropy cemented carbide with uniform composition can be obtained.

[0104] In some embodiments, the temperature of the hot isostatic pressing infiltration treatment is 3 Equal to the vacuum sintering temperature T 2 .

[0105] In some embodiments, the heat preservation and pressure holding time of the hot isostatic pressing infiltration treatment is 1h to 3h, for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0106] In some embodiments, the preparation method further comprises an annealing treatment after the hot isostatic pressing infiltration treatment.

[0107] In some embodiments, the annealing temperature T 4 Lower than the melting point T of the high entropy alloy layer m2 .

[0108] The present invention further optimizes the interface bonding force between the binder phase metal layer and the hard phase powder, and between the binder phase metal layer and the high entropy alloy layer through annealing treatment, thereby improving the strength of the high entropy cemented carbide; moreover, by controlling the temperature of the annealing treatment, the internal stress of the high entropy cemented carbide can be effectively reduced, and the toughness of the obtained high entropy cemented carbide can be improved.

[0109] In some embodiments, the annealing temperature T 4 T than the melting point T of the high entropy alloy layer m2 100°C to 200°C lower, for example, 100°C, 120°C, 150°C, 160°C, 180°C or 200°C, but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0110] In some embodiments, the pressure of the annealing process is below 30 Pa.

[0111] In some embodiments, the temperature is raised from room temperature to the annealing temperature T at a heating rate of 0.5°C / min to 1°C / min. 4 .

[0112] The heating rate of the annealing treatment of the present invention is 0.5°C / min to 1°C / min, for example, it can be 0.5°C / min, 0.6°C / min, 0.8°C / min, 0.9°C / min or 1°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0113] In some embodiments, the annealing temperature T 4 The temperature is kept at room temperature for 1 hour to 3 hours, for example, 1 hour, 2 hours or 3 hours, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0114] In some embodiments, the annealing temperature T is lowered at a rate of 1°C / min to 2°C / min. 4 The temperature is lowered to room temperature, and the annealing treatment is completed.

[0115] The cooling rate of the annealing treatment of the present invention is 1°C / min to 2°C / min, for example, it can be 1°C / min, 1.2°C / min, 1.5°C / min, 1.8°C / min or 2°C / min, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0116] The temperature range of "room temperature" in the present invention is 20°C to 30°C, for example, it can be 20°C, 24°C, 25°C, 28°C or 30°C, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0117] In some embodiments, the molding includes at least one of molding, cold isostatic pressing, extrusion molding, injection molding or 3D printing. The present invention does not specifically limit the molding method, as long as a molded body of a desired shape can be obtained. When the desired shape cannot be obtained by one-step molding, the molding also includes cutting.

[0118] In certain embodiments, the degreasing is inert gas negative pressure degreasing or hydrogen positive pressure degreasing.

[0119] If the shape of the molded body after degreasing is inconsistent with the shape of the target product, cutting treatment is performed after degreasing.

[0120] In the present invention, the vacuum pre-sintering temperature T 1 There is no specific limitation, as long as a pre-sintered body with a relative density not exceeding 90% can be obtained. The purpose is to ensure that most of the pores in the pre-sintered body are connected pores, which is conducive to the infiltration process of the high entropy alloy.

[0121] In some embodiments, the holding time of the vacuum pre-sintering is 1 h to 3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0122] In some embodiments, the vacuum pre-sintering pressure is below 30 Pa.

[0123] A certain embodiment of the present invention provides a high entropy cemented carbide, and the high entropy cemented carbide is prepared by the preparation method described in any embodiment.

[0124] In certain embodiments, when the pressure of the hot isostatic pressing infiltration treatment is greater than 5 MPa and less than 80 MPa, the content of the high entropy alloy binder phase in the high entropy cemented carbide gradually decreases from the surface to the inside.

[0125] When the pressure of the hot isostatic pressing infiltration treatment is higher than 80 MPa and lower than 300 MPa, a high entropy cemented carbide with uniform composition is obtained.

[0126] A certain embodiment of the present invention provides an application of a high entropy cemented carbide, wherein the high entropy cemented carbide is used to prepare molds, cutting tools or wear-resistant parts.

[0127] The high entropy cemented carbide is prepared by the preparation method described in any embodiment, or is the high entropy cemented carbide described in any embodiment.

[0128] Example 1

[0129] This embodiment provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0130] (1) In a nitrogen atmosphere, the raw material powder of the formula amount was placed in a ball mill and mixed by ball milling using cemented carbide grinding balls and anhydrous ethanol. The ball milling time was 48 h, and the mass ratio of cemented carbide grinding balls to raw material powder was 4:1, to obtain a hard phase powder with an average particle size of 0.2 μm.

[0131] Wherein, in terms of mass percentage, the raw material powder includes 99wt% WC, 0.5wt% TaC and 0.5wt% NbC.

[0132] (2) The surface of the hard phase powder particles is coated with a bonding phase metal layer by chemical coating, and the bonding phase metal layer is made of cobalt (melting point T m1 1495℃):

[0133] The hard phase powder was placed in an activation solution and ultrasonically stirred for 25 minutes, and then placed in a chemical plating solution at a solid-liquid ratio of 250g / L, and kept warm at 85°C until bubbles were generated. Then, chemical plating was performed under ultrasonic stirring at 50°C until no bubbles were generated, and then the powder was washed with deionized water and vacuum dried at 100°C to complete the chemical plating. A hard phase powder having a bonding phase metal layer (mass percentage of 0.63wt%) coated on the particle surface was obtained.

[0134] The activation solution includes hydrofluoric acid (with a percentage concentration of 40wt%), ammonium fluoride, nitric acid (with a percentage concentration of 65wt%) and hydrochloric acid (with a percentage concentration of 36wt%); wherein the amounts of hydrofluoric acid, ammonium fluoride, nitric acid and hydrochloric acid in the activation solution are 40mL / L, 3g / L, 30mL / L and 20mL / L respectively.

[0135] The chemical plating solution includes 25 g / L of cobalt sulfate, 25 g / L of sodium hypophosphite, 50 g / L of trisodium citrate and 25 g / L of boric acid.

[0136] (3) The hard phase powder with the binder phase metal layer on the surface is granulated and a molded body is obtained by cold isostatic pressing at 200 MPa.

[0137] (4) The molded body is degreased in an argon atmosphere and then pre-sintered in vacuum at a pressure of 30 Pa or less to obtain a pre-sintered body having a relative density D of 86%.

[0138] Among them, the vacuum pre-sintering temperature T 1 The temperature is 1630℃ and kept warm for 2h.

[0139] (5) Two metal layers are coated on the surface of the pre-sintered body, and the innermost metal layer (spray coating) is a high entropy alloy layer (melting point T m2 The outermost metal layer is a titanium layer with a thickness of 0.2 mm (melting point T m3is 1668℃).

[0140] The composition of the high entropy alloy layer is Cu 22.7 Zn 22.7 Mn 22.7 Ni 22.7 Al 9.2 .

[0141] Among them, the density of the high entropy alloy layer is 7.36g / cm 3 According to the relative density D and volume V of the pre-sintered body, the mass M of the high entropy alloy layer in this embodiment is obtained to be ≥ 7.36×V×(1-D).

[0142] (6) Under pressure 10 -3 Under the condition of less than Pa, vacuum sintering is carried out; the vacuum sintering temperature T 2 =T m2 +35℃=1077℃, keep warm for 0.5h.

[0143] (7) Hot isostatic pressing infiltration treatment was carried out under argon atmosphere at a pressure of 10 MPa and a temperature of T 3 The sintering temperature is 1077℃ and the time is 3h to obtain a high entropy cemented carbide sintered body with a gradient structure.

[0144] (8) The obtained gradient structured high entropy cemented carbide sintered body is annealed to optimize the interfacial bonding force between the hard phase and the bonding phase metal layer and reduce the internal stress.

[0145] The annealing treatment was carried out under a pressure of less than 30 Pa; the temperature was raised from room temperature to T at a heating rate of 0.5 °C / min. 4 =T m2 -200℃=842℃, and keep it at this temperature for 1h; then cool down at a rate of 2℃ / min from T 4 The temperature is lowered to room temperature to obtain the high entropy cemented carbide.

[0146] Example 2

[0147] This embodiment provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0148] The steps of preparing the pre-sintered body in steps (1) to (5) are the same as those in Example 1.

[0149] (6) Under pressure 10 -3 Vacuum sintering is carried out under conditions below Pa; the vacuum sintering temperature T 2 =T m2 +25℃=1067℃, keep warm for 1h.

[0150] (7) Hot isostatic pressing infiltration treatment was carried out under argon atmosphere with a pressure of 5 MPa and a temperature of T 3 The temperature is 1067℃ and the holding time is 3h to obtain a high entropy cemented carbide sintered body with a gradient structure.

[0151] (8) The obtained gradient structured high entropy cemented carbide sintered body is annealed to optimize the interfacial bonding force between the hard phase and the bonding phase metal layer and reduce the internal stress.

[0152] The annealing treatment was carried out under a pressure of less than 30 Pa; the temperature was raised from room temperature to T at a heating rate of 0.5 °C / min. 4 =T m2 -100℃=942℃, and keep it for 1h; then cool down at a rate of 2℃ / min from T 4 The temperature is lowered to room temperature to obtain the high entropy cemented carbide.

[0153] Example 3

[0154] This embodiment provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0155] The steps of preparing the pre-sintered body in steps (1) to (5) are the same as those in Example 1.

[0156] (6) Under pressure 10 -3 Under the condition of less than Pa, vacuum sintering is carried out; the vacuum sintering temperature T 2 =T m2 +50℃=1092℃, keep warm for 1h.

[0157] (7) Hot isostatic pressing infiltration treatment was carried out under argon atmosphere with a pressure of 70 MPa and a temperature of T 3 The temperature is 1092℃ and the time is 3h to obtain a high entropy cemented carbide sintered body with a gradient structure.

[0158] (8) annealing the obtained high entropy cemented carbide sintered body with a gradient structure to optimize the interface bonding force between the hard phase and the binder phase metal layer and reduce the internal stress;

[0159] The annealing treatment was carried out under a pressure of less than 30 Pa; the temperature was raised from room temperature to T at a heating rate of 1 °C / min. 4 =T m2 -150℃=892℃, and keep it for 1h; then cool down at a rate of 1℃ / min from T 4 The temperature is lowered to room temperature to obtain the high entropy cemented carbide.

[0160] Example 4

[0161] This embodiment provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0162] The step parameters in step (1) to step (6) are the same as those in Example 1.

[0163] (7) Hot isostatic pressing infiltration treatment was carried out under argon atmosphere with a pressure of 80 MPa and a temperature of T 3 The sintering temperature is 1077℃ and the time is 3h to obtain a high entropy cemented carbide sintered body with a gradient structure.

[0164] (8) The obtained gradient structured high entropy cemented carbide sintered body is annealed to optimize the interfacial bonding force between the hard phase and the bonding phase metal layer and reduce the internal stress to obtain the high entropy cemented carbide; the annealing parameters are the same as those in Example 1.

[0165] Example 5

[0166] This embodiment provides a method for preparing high entropy cemented carbide, which is the same as that of Embodiment 4 except that the pressure of the hot isostatic pressing infiltration treatment is 150 MPa.

[0167] Example 6

[0168] This embodiment provides a method for preparing high entropy cemented carbide, which is the same as that of Embodiment 4 except that the pressure of the hot isostatic pressing infiltration treatment is 300 MPa.

[0169] Example 7

[0170] This embodiment provides a method for preparing high entropy cemented carbide. In addition to the vacuum sintering temperature T 2 And the temperature of hot isostatic pressing infiltration treatment T 3 Except for the temperature being 1052°C, the rest are the same as in Example 5.

[0171] Example 8

[0172] This embodiment provides a method for preparing high entropy cemented carbide. In addition to the vacuum sintering temperature T 2 And the temperature of hot isostatic pressing infiltration treatment T 3 Except for the temperature being 1102°C, the rest are the same as in Example 5.

[0173] Example 9

[0174] This embodiment provides a method for preparing high entropy cemented carbide. In addition to the annealing temperature T 4 Except for the temperature being 992°C, the rest are the same as in Example 5.

[0175] Example 10

[0176] This embodiment provides a method for preparing high entropy cemented carbide. In addition to the annealing temperature T 4 Except for the temperature being 792°C, the rest are the same as in Example 5.

[0177] Embodiment 11

[0178] This embodiment provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0179] (1) In a nitrogen atmosphere, the raw material powder of the formula amount is placed in a ball mill, and the mixture is ball-milled with cemented carbide grinding balls and anhydrous ethanol. The ball milling time is 48 hours, and the mass ratio of cemented carbide grinding balls to raw material powder is 4:1, to obtain a hard phase powder with an average particle size of about 0.2 μm.

[0180] Wherein, in terms of mass percentage, the raw material powder includes 99wt% WC, 0.5wt% TaC, and 0.5wt% NbC.

[0181] (2) A bonding phase metal layer is coated on the surface of the hard phase mixed powder particles by chemical coating, and the bonding phase metal layer is made of nickel (melting point T m1 is 1455℃).

[0182] The hard phase powder was placed in an activation solution and ultrasonically stirred for 25 minutes, and then placed in a chemical plating solution at a solid-liquid ratio of 250g / L, and kept warm at 85°C until bubbles were generated. Then, chemical plating was performed under ultrasonic stirring at 50°C until no bubbles were generated, and then the powder was washed with deionized water and vacuum dried at 100°C to complete the chemical plating. A hard phase powder having a bonding phase metal layer (mass percentage of 0.63wt%) coated on the particle surface was obtained.

[0183] The activation solution includes hydrofluoric acid (mass percentage concentration is 40wt%), ammonium fluoride, nitric acid (mass percentage concentration is 65wt%) and hydrochloric acid (mass percentage concentration is 36wt%); wherein the amounts of hydrofluoric acid, ammonium fluoride, nitric acid and hydrochloric acid in the activation solution are 40mL / L, 3g / L, 30mL / L and 20mL / L respectively; the solvent of the activation solution is deionized water.

[0184] The chemical plating solution includes 25 g / L of nickel sulfate, 25 g / L of sodium hypophosphite, 50 g / L of trisodium citrate and 25 g / L of boric acid.

[0185] (3) The hard phase powder coated with the binder phase metal layer is granulated and a molded body is obtained by cold isostatic pressing at 200 MPa.

[0186] (4) The molded body is degreased in an argon atmosphere and then pre-sintered in vacuum at a pressure of 30 Pa or less to obtain a pre-sintered body having a relative density D of 90%.

[0187] Among them, the vacuum pre-sintering temperature T 1 1250℃, keep warm for 1h.

[0188] (5) Two metal layers are coated on the surface of the pre-sintered body, and the innermost metal layer (spray coating) is a high entropy alloy layer (melting point T m2 The outermost metal layer is a titanium layer with a thickness of 0.1 mm (melting point T m3 is 1668℃).

[0189] The composition of the high entropy alloy layer is Al 80 Li 5 Mg 5 Zn 5 Cu 5 .

[0190] Among them, the density of the high entropy alloy layer is 3.08g / cm 3 According to the relative density D and volume V of the pre-sintered body, the mass M of the high entropy alloy layer in this embodiment is obtained to be ≥ 3.08×V×(1-D).

[0191] (6) Under pressure 10 -3 The vacuum sintering is carried out under the condition of less than Pa; the vacuum sintering temperature is T 2 =T m2 +50℃=685℃, keep warm for 0.5h.

[0192] (7) Hot isostatic pressing infiltration treatment was carried out under argon atmosphere at a pressure of 100 MPa and a temperature of T 3 The sintering temperature is 685℃ and the time is 2h to obtain a high entropy cemented carbide sintered body with uniform composition.

[0193] (8) The obtained high entropy cemented carbide sintered body with uniform composition is annealed to optimize the interfacial bonding force between the hard phase grains and the bonding phase metal layer and reduce the internal stress.

[0194] The annealing treatment was carried out under a pressure of less than 30 Pa; the temperature was raised from room temperature to T at a heating rate of 0.5 °C / min. 4 =T m2 -150℃=485℃, and keep it for 1h; then cool down at a rate of 2℃ / min from T 4 The temperature is lowered to room temperature to obtain the high entropy cemented carbide.

[0195] Example 12

[0196] This embodiment provides a method for preparing a high entropy cemented carbide, the preparation method comprising the following steps:

[0197] (1) In a nitrogen atmosphere, the raw material powder of the formula amount is placed in a ball mill, and the mixture is ball-milled with cemented carbide grinding balls and anhydrous ethanol. The ball milling time is 48 hours, and the mass ratio of cemented carbide grinding balls to raw material powder is 4:1, to obtain a hard phase powder with an average particle size of about 0.2 μm.

[0198] Wherein, in terms of mass percentage, the raw material powder includes 99wt% WC, 0.5wt% TaC and 0.5wt% NbC.

[0199] (2) A bonding phase metal layer is coated on the surface of the hard phase powder particles by chemical coating, and the bonding phase metal layer is made of iron (melting point T m1 is 1538℃).

[0200] The hard phase powder is placed in an activation solution and ultrasonically stirred for 25 minutes, and then placed in a chemical plating solution at a solid-liquid ratio of 250g / L, and kept warm at 85°C until bubbles are generated. Then, chemical plating is performed under ultrasonic stirring at 50°C until no bubbles are generated, and then the powder is washed with deionized water and vacuum dried at 100°C to complete the chemical plating. The hard phase powder having a bonding phase metal layer (mass percentage of about 0.56wt.%) coated on the particle surface is obtained.

[0201] Based on the original formula of hard phase powder and the content of the coated binder phase metal layer, the theoretical density of the cemented carbide composed of the two is calculated to be 15.456 g / cm 3 ; The density of tungsten carbide, tantalum carbide, niobium carbide and iron is 15.63g / cm 3 、14.3g / cm 3 , 7.6g / cm 3 and 7.86g / cm 3 .

[0202] The activation solution includes hydrofluoric acid (mass percentage concentration is 40wt%), ammonium fluoride, nitric acid (mass percentage concentration is 65wt%) and hydrochloric acid (mass percentage concentration is 36wt%); wherein the amounts of hydrofluoric acid, ammonium fluoride, nitric acid and hydrochloric acid in the activation solution are 40mL / L, 3g / L, 30mL / L and 20mL / L respectively; the solvent of the activation solution is deionized water.

[0203] The chemical plating solution includes 25 g / L of ferric sulfate, 25 g / L of sodium hypophosphite, 50 g / L of trisodium citrate and 25 g / L of boric acid.

[0204] (3) The hard phase powder with a binder phase metal layer coated on the particle surface is granulated and a molded body is obtained by cold isostatic pressing at 200 MPa.

[0205] (4) The molded body is degreased in an argon atmosphere and then pre-sintered in a vacuum at a pressure of 30 Pa or less to obtain a pre-sintered body having a relative density D of 82%.

[0206] Among them, the vacuum pre-sintering temperature T 1 The temperature is 1608℃ and kept warm for 1h.

[0207] (5) Two metal layers are coated on the surface of the pre-sintered body, and the innermost metal layer (spray coating) is a high entropy alloy layer (melting point T m2 The outermost metal layer is a titanium layer with a thickness of 0.1 mm (melting point T m3 is 1668℃).

[0208] The composition of the high entropy alloy layer is AlCoCrFeNiTi 0.5 .

[0209] Among them, the density of the high entropy alloy layer is 6.44g / cm 3 According to the relative density D and volume V of the pre-sintered body, the mass M of the high entropy alloy layer in this embodiment is obtained to be ≥ 6.44×V×(1-D).

[0210] (6) Under pressure 10 -3 The vacuum sintering is carried out under the condition of less than Pa; the vacuum sintering temperature is T 2 =T m2 +35℃=1223℃, keep warm for 0.5h.

[0211] (7) Hot isostatic pressing infiltration treatment was carried out under argon atmosphere at a pressure of 100 MPa and a temperature of T 3 The sintering temperature is 1223℃ and the time is 2h to obtain a high-entropy cemented carbide sintered body with uniform composition.

[0212] (8) The obtained high entropy cemented carbide sintered body with uniform composition is annealed to optimize the interfacial bonding force between the hard phase and the binder phase metal layer and reduce the internal stress.

[0213] The annealing treatment was carried out under a pressure of less than 30 Pa; the temperature was raised from room temperature to T at a heating rate of 0.5 °C / min. 4 =T m2 -150℃=1038℃, and keep warm for 1h; then cool down at a rate of 2℃ / min from T 4 The temperature is lowered to room temperature to obtain the high entropy cemented carbide.

[0214] Example 13

[0215] This embodiment provides a method for preparing high entropy cemented carbide, which is the same as that of Embodiment 5 except that annealing treatment is not performed.

[0216] Comparative Example 1

[0217] This comparative example provides a method for preparing a high entropy cemented carbide, which is the same as Example 5 except that the particle surface of the hard phase powder is not coated with a binder phase metal layer;

[0218] Since the particle surface of the hard phase powder is not covered with a binder phase metal layer, at the same vacuum pre-sintering temperature T 1 =1630°C, the sintering activity is greatly reduced. The relative density D of the pre-sintered body obtained in this comparative example is 63%, and the mass M of the high entropy alloy layer is adjusted accordingly according to the formula 7.36×V×(1-D).

[0219] Comparative Example 2

[0220] This comparative example provides a method for preparing a high entropy cemented carbide, which is the same as Example 5 except that the outermost metal layer is omitted.

[0221] Comparative Example 3

[0222] This comparative example provides a method for preparing a high entropy cemented carbide, except that the vacuum pre-sintering temperature T 1 Except for the temperature being 1658°C, the rest are the same as in Example 5.

[0223] Due to the increase in the vacuum pre-sintering temperature T 1 =1658°C, the relative density D of the pre-sintered body obtained in this comparative example is 92%, and the mass M of the high entropy alloy layer is adjusted accordingly according to the formula 7.36×V×(1-D).

[0224] Comparative Example 4

[0225] This comparative example provides a method for preparing a high entropy cemented carbide. 2 and the temperature of hot isostatic pressing infiltration treatment T 3 Except for the temperature being 1500°C, the rest are the same as those in Example 5.

[0226] Performance Characterization

[0227] The metallographic structure, hardness, transverse fracture strength and fracture toughness of the high entropy cemented carbide finally obtained in the above examples and comparative examples were measured, and the results are shown in Table 1.

[0228] The metallographic structure test method is as follows: Due to the composition gradient structure and whether the infiltration is complete, the obtained high entropy cemented carbide sample is cut along the central area, the cut surface is ground and polished, and the entire cut surface is observed and tested using a metallographic microscope or a scanning electron microscope. The test is carried out in accordance with the national standards GB / T3488.1-2014 "Metallographic Determination of Cemented Carbide Microstructure" and GB / T3489-2015 "Metallographic Determination of Cemented Carbide Porosity and Uncombined Carbon".

[0229] The hardness test is carried out in accordance with the national standard GB / T7997-2014 "Test Method for Vickers Hardness of Cemented Carbide". Due to the composition gradient structure involved, the hardness is measured on the cut surface after grinding and polishing based on the sampling method for detecting the metallographic structure. Assuming that the distance from the edge of the cut surface to the center is L, the edge area is taken as the starting point, and the hardness is tested in four areas from the edge 0L, L / 3, 2L / 3, and L from the edge to the center of the sample. At least 3 values ​​are tested in each area and the average value is taken.

[0230] The transverse rupture strength test was carried out in accordance with the national standard GB / T3851-2015 "Method for Determination of Transverse Fracture Strength of Cemented Carbide". Since the composition gradient structure is involved, the transverse rupture strength of the gradient structure cannot be tested. Therefore, the transverse rupture strength test was not carried out for the composition gradient structure specimen.

[0231] The fracture toughness test was carried out in accordance with the international standard ASTM B771-87 (2006) "Test Method for Fracture Toughness of Cemented Carbide Short Rods". Since the composition gradient structure is involved, the fracture toughness of the gradient structure cannot be tested. Therefore, the fracture toughness test was not carried out for the composition gradient structure specimen.

[0232] Table 1. Test results of embodiments and comparative examples

[0233]

[0234] It can be seen from Examples 1 to 6 and Examples 11 and 12 in Table 1 that as the pressure of the hot isostatic pressing infiltration treatment increases, the composition gradient of the obtained high entropy cemented carbide gradually decreases. When the pressure is higher than 80 MPa, the composition gradient disappears, and a high entropy cemented carbide with uniform composition is obtained. At the same time, due to the increase in pressure, it is beneficial to promote the densification of the pre-sintered body, which will cause the high entropy alloy content infiltrated into the pre-sintered body to decrease, and the hardness of the obtained high entropy cemented carbide increases, and the fracture toughness decreases.

[0235] From the comparison between Example 5 and Example 7 in Table 1, it can be seen that due to the decrease in the temperature of vacuum sintering and hot isostatic pressing infiltration treatment, the energy of sintering shrinkage is reduced, and the content of high-entropy alloy bonding phase in the obtained high-entropy cemented carbide increases slightly, resulting in a slight decrease in hardness and strength, and a slight increase in toughness; on the contrary, from the comparison between Example 5 and Example 8 in Table 1, it can be seen that an increase in the temperature of vacuum sintering will cause the hardness and strength of the obtained high-entropy cemented carbide to increase slightly, while the toughness decreases slightly.

[0236] From the comparison between Example 5 and Example 9 and Example 10 in Table 1, it can be seen that if the annealing temperature is too high, the atomic diffusion ability will be enhanced, which may easily lead to changes in the phase structure of the high entropy cemented carbide, while if the annealing temperature is too low, the interface optimization and stress reduction are insufficient, and the fracture toughness of the obtained high entropy cemented carbide is reduced.

[0237] From the comparison between Example 5 and Example 13 in Table 1, it can be seen that due to the lack of annealing treatment, the strength and fracture toughness of the obtained high entropy cemented carbide are reduced. Therefore, as a preferred embodiment of the present invention, annealing treatment is performed after hot isostatic pressing and infiltration treatment.

[0238] From the comparison between Example 5 and Comparative Example 1 in Table 1, it can be seen that due to the lack of a bonding phase metal layer, the phase structure of the high entropy alloy is severely destroyed during vacuum sintering and hot isostatic pressing infiltration treatment, and the hardness, strength and fracture toughness of the obtained high entropy cemented carbide are sharply reduced.

[0239] From the comparison between Example 5 and Comparative Example 2 in Table 1, it can be seen that since the outermost metal layer is not coated, the molten high entropy alloy layer is not protected during vacuum sintering, causing it to flow to the lower part of the product and the upper part is not well sealed. The subsequent hot isostatic pressing infiltration treatment cannot sinter it to a dense state.

[0240] From the comparison between Example 5 and Comparative Example 3 in Table 1, it can be seen that since the temperature of vacuum pre-sintering is increased to be much higher than the melting point of the bonding phase metal layer, the relative density of the pre-sintered body reaches 92%, that is, the pores in the pre-sintered body are almost all closed pores. During the subsequent vacuum pre-sintering and hot isostatic pressing infiltration treatment, the molten high entropy alloy is prevented from diffusing into the interior of the pre-sintered body, resulting in failure to sinter densely.

[0241] From the comparison between Example 5 and Comparative Example 4 in Table 1, it can be seen that since the temperature of vacuum sintering and the temperature of hot isostatic pressing infiltration treatment are higher than the melting point of the bonding phase metal layer, the high entropy alloy phase structure will also be destroyed, and the strength and fracture toughness of the obtained high entropy cemented carbide will be reduced.

[0242] In summary, the present invention coats a bonding phase metal layer on the particle surface of the hard phase powder as a protective layer to prevent atoms such as carbon, nitrogen, boron or silicon in the hard phase powder from destroying the high entropy alloy phase structure; then a pre-sintered body with pores is obtained through molding, degreasing and vacuum pre-sintering; then at least two metal layers including an innermost high entropy alloy layer and an outermost metal layer are uniformly coated on the surface of the pre-sintered body, the surface of the pre-sintered body is sealed by vacuum sintering, and then hot isostatic pressing infiltration treatment is used to make the molten high entropy alloy diffuse into the interior of the pre-sintered body along the pores and / or interfaces of the pre-sintered body, thereby obtaining a dense high entropy cemented carbide; wherein, the pressure of the hot isostatic pressing infiltration treatment is controlled to obtain a high entropy cemented carbide with a gradient distribution of the high entropy alloy bonding phase or a high entropy cemented carbide with a uniform composition; moreover, the application of hot isostatic pressing infiltration treatment also solves the problem of easy agglomeration of the high entropy alloy bonding phase caused by the traditional powder mixing method, and at the same time, it also avoids the problem of incomplete infiltration and being limited by the product's external dimensions.

[0243] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high entropy cemented carbide, characterized in that: The preparation method comprises the following steps: The surface of the hard phase powder particles is coated with a binder phase metal layer, and then molded, degreased and vacuum pre-sintered to obtain a pre-sintered body with a relative density not exceeding 90%; Coating at least two metal layers on the surface of the pre-sintered body, and then subjecting the pre-sintered body to vacuum sintering and hot isostatic pressing infiltration treatment to obtain the high entropy cemented carbide; The at least two metal layers include an innermost high entropy alloy layer and an outermost metal layer; The temperature T2 of the vacuum sintering and the temperature T3 of the hot isostatic pressing infiltration treatment are both lower than the melting point T m1 ; The vacuum sintering temperature T2 is higher than the melting point T m2 ; The melting point of the outermost metal layer is T m3 Higher than the melting point T of the bonding metal layer m1 .

2. The preparation method according to claim 1, characterized in that: The melting point of the high entropy alloy layer is T m2 600℃ to 1200℃.

3. The preparation method according to claim 2, characterized in that: The metal elements in the high entropy alloy layer include a combination of at least five of Al, Fe, Co, Zn, Sn, Ni, Cr, Cu, Mn, Li, Mg or Ti; Preferably, the volume of the high entropy alloy layer is not less than the total volume of the pores in the pre-sintered body.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The metal element in the outermost metal layer includes any one of Ti, Zr, Mo, Nb or Ta or a combination of at least two thereof; Preferably, the thickness of the outermost metal layer is 0.1 mm to 0.3 mm; Preferably, the metal element in the bonding phase metal layer includes any one of Co, Ni or Fe, or a combination of at least two of them.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The vacuum sintering temperature T2 is higher than the melting point T m2 High 25℃ to 50℃; Preferably, the vacuum sintering temperature T2 is higher than the melting point T m1 Low than 200℃; Preferably, the holding time of the vacuum sintering is 0.5h to 1h; Preferably, the vacuum sintering pressure is 10 -3 Below Pa.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The hot isostatic pressing infiltration treatment is carried out in an inert atmosphere; Preferably, the pressure of the hot isostatic pressing infiltration treatment is 5 MPa to 300 MPa; Preferably, the temperature T3 of the hot isostatic pressing infiltration treatment is equal to the temperature T2 of the vacuum sintering; Preferably, the heat preservation and pressure holding time of the hot isostatic pressing infiltration treatment is 1 hour to 3 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The preparation method further comprises an annealing treatment after the hot isostatic pressing infiltration treatment; Preferably, the annealing temperature T4 is lower than the melting point T m2 ; Preferably, the annealing temperature T4 is higher than the melting point T m2 Low 100℃ to 200℃; Preferably, the pressure of the annealing treatment is below 30 Pa; Preferably, the temperature is raised from room temperature to the annealing temperature T4 at a heating rate of 0.5°C / min to 1°C / min; Preferably, the annealing treatment temperature T4 is maintained for 1 to 3 hours; Preferably, the annealing treatment is terminated by cooling the temperature T4 of the annealing treatment to room temperature at a cooling rate of 1° C. / min to 2° C. / min.

8. A high entropy cemented carbide, characterized in that: The high entropy cemented carbide is prepared by the preparation method according to any one of claims 1 to 7.

9. The high entropy cemented carbide according to claim 8, characterized in that: When the pressure of the hot isostatic pressing infiltration treatment is greater than 5 MPa and less than 80 MPa, the content of the high entropy alloy binder phase in the high entropy cemented carbide gradually decreases from the surface to the inside; When the pressure of the hot isostatic pressing infiltration treatment is higher than 80 MPa and lower than 300 MPa, a high entropy cemented carbide with uniform composition is obtained.

10. An application of high entropy cemented carbide, characterized in that: The high entropy cemented carbide is used to prepare molds, cutting tools or wear-resistant parts; The high entropy cemented carbide is prepared by the preparation method described in any one of claims 1 to 7, or is the high entropy cemented carbide described in claim 8 or 9.

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