Ultrafine grain cemented carbide additive manufacturing method

Abstract

An ultrafine grain cemented carbide additive manufacturing method. WC-Co is used as a raw material, a crystal grain growth inhibitor is added, and a rare earth oxide is added as a reinforcing phase; paraffin and a trace amount of low-valence rare earth oxide powder are added, ball milling is carried out for coating cemented carbide powder, and oxygen control is carried out; the cemented carbide powder obtained by ball milling and an organic adhesive are loaded in a vacuum banbury mixer-granulator to prepare a printing feed, then a green body is printed using fused deposition modeling (FDM), and finally, degreasing and two-step sintering are carried out on the green body to prepare ultrafine cemented carbide. By means of the combined effect of the components and process optimization design, the powder properties are regulated, the process range of vacuum banburying and granulation and additive manufacturing is widened, and the problems of pores, interlayer cracks, and oxygen absorption in a printed green body, and abnormal grain growth, oxidation decarburization, and the formation of brittle η-phase in a sintered sample are solved. The prepared ultrafine grain cemented carbide exhibits high relative density, is free of metallurgical defects, possesses excellent mechanical properties, and is suitable for large-scale and mass production.

Description

A method for additive manufacturing of ultrafine-grained cemented carbide Technical Field

[0001] The invention relates to an ultrafine-grained cemented carbide additive manufacturing method, belonging to the technical field of cemented carbide and additive manufacturing. Background Art

[0002] Cemented carbide is a metal-ceramic composite material made from a refractory metal hard compound and a binder metal through powder metallurgy. It exhibits high hardness, strength, and wear resistance and is widely used in aerospace, mineral exploration, and machinery manufacturing. Ultrafine-grained cemented carbide, a metal-ceramic composite material composed of refractory metal carbides with grain sizes less than 0.5 μm and a binder metal, is currently used to manufacture high-efficiency precision cutting tools, micro-drilling and micro-milling tools, and is primarily produced using powder metallurgy methods such as powder injection molding (PIM), compression molding (CM), and extrusion molding (EM).

[0003] In recent years, there has been an urgent demand for cemented carbide parts with complex geometries, and additive manufacturing (AM) technology has provided a new approach to this end. Among existing AM technologies, powder bed fusion (PBF) places high demands on the raw powder's morphology, sphericity, particle size distribution, bulk density, and tap density. The resulting samples are prone to numerous metallurgical defects such as difficult-to-eliminate pores, cracks, and brittle η phases, resulting in poor mechanical properties. Ultrafine-grained cemented carbide, in particular, is susceptible to powder oxidation, the formation of brittle η phases, and abnormal grain growth during the PBF process. The resulting samples exhibit severe cracking, low relative density, and mechanical properties that fail to meet demanding requirements.

[0004] In response to the above problems, a Chinese patent (CN202310192309.4) discloses a cemented carbide and its additive manufacturing method, which uses light curing-debinding sintering and then hot isostatic pressing (HIP) densification treatment to obtain WC-Ni cemented carbide parts with a relative density of 99.8% and a hardness of 1400HV3. Mariani et al. [Mariani M, et al., Mechanical and microstructural characterization of WC-Co consolidated by binder jetting additive manufacturing[J]. International Journal of Refractory Metals and Hard Materials 100(2021)105639.] The WC-12Co cemented carbide prepared by BJAM (Binder jetting additive manufacturing) has a relative density of 97.4%. After HIP treatment, the relative density reaches 99.3%, and its hardness is 1205HV 10, the bending strength is 2257MPa, and the mechanical properties before HIP are not reported. Lee et al. [Lee SW, et al., Phase control of WC-Co hardmetal using additive manufacturing technologies[J]. Powder Metallurgy 65(2021)13-21.] increased the green density by increasing the packing density of FDM (Fused deposition modeling) wire. After degreasing and sintering, they obtained a cemented carbide part with a relative density of 96.3% and a hardness of 89HRA. Lengauer et al. [Lengauer W, et al., Fabrication and properties of extrusion-based 3D-printed hardmetal and cermet components[J]. International Journal of Refractory Metals&Hard Materials 82(2019)141-149.] prepared WC-10%Co cemented carbide indexable inserts using FDM-degreasing and sintering process, but no relative density and mechanical property data were reported. The cemented carbide produced by additive manufacturing methods such as photocuring and BJAM has a low relative density and requires HIP densification treatment, which greatly increases the post-processing cost and preparation process requirements; cemented carbide parts produced by FDM method have problems such as low relative density, low strength and hardness, and poor toughness.

[0005] At present, there are no reports on the use of AM technology to prepare high-quality ultrafine-grained cemented carbide.

[0006] Summary of the Invention

[0007] In response to the above problems, the present invention designs a method for additive manufacturing of ultrafine-grained cemented carbide with high relative density, high hardness and high strength. First, using WC-Co powder as the main raw material, grain growth inhibitors (GGI) and rare earth oxides as reinforcing phases, paraffin wax and / or trace amounts of low-priced rare earths, and using a ball milling process to prepare a uniformly dispersed mixed powder; second, using vacuum mixing and granulation to prepare printing feed; third, FDM printing to prepare a green body with high relative density; finally, the green body is degreased + two-step sintering to obtain an ultrafine-grained cemented carbide product with no metallurgical defects and excellent mechanical properties. The present invention eliminates microstructural defects and refines the grain size of cemented carbide through the synergistic effect of alloy composition regulation and process parameter optimization, thereby improving the relative density and comprehensive mechanical properties of cemented carbide parts.

[0008] The present invention provides a method for additive manufacturing of ultrafine-grained cemented carbide:

[0009] First, paraffin wax is added to the powder raw material, and a uniformly dispersed mixed powder is prepared by ball milling; the added paraffin wax can completely cover the raw material powder after ball milling;

[0010] Alternatively, paraffin wax and a trace amount of low-valent rare earth are added to a powder raw material, and a uniformly dispersed mixed powder is prepared by ball milling; the raw material powder comprises cemented carbide powder, a grain growth inhibitor, and a rare earth oxide; the added paraffin wax can completely cover the raw material powder after ball milling; the valence of the rare earth in the low-valent rare earth is less than or equal to positive divalent; the valence of the oxidized rare earth element in the rare earth oxide is greater than positive divalent;

[0011] Second, vacuum mixing-granulation to prepare additive manufacturing printing feed;

[0012] Third, fused deposition modeling (FDM) printing to prepare green parts;

[0013] Fourth, the green body is degreased and sintered in two steps to obtain an ultrafine-grained cemented carbide product without metallurgical defects; the temperature of the first sintering step is 1350-1500°C, and the temperature of the second sintering step is 30-100°C lower than the temperature of the first sintering step.

[0014] In the present invention, low-valent rare earths include zero-valent rare earths and rare earth oxides with a valence of 2 or less. The zero-valent rare earths can be intermediate alloys of rare earth and Co or elemental rare earths. However, due to the high reactivity of rare earths, they are easily oxidized during production and transfer. Therefore, it is generally recommended to use low-valent rare earth oxides. These low-valent rare earth oxides may have oxidized outer rare earths, but the resulting oxide layer isolates oxygen from the inside, leaving the rare earths inside at zero valence. This outer oxide layer will fall off during ball milling, and the inner zero-valent rare earth layer will then rapidly react with oxygen in other raw materials, thereby capturing oxygen adsorbed by these other raw materials.

[0015] The present invention provides a method for additive manufacturing of ultrafine-grained cemented carbide, which specifically comprises the following steps:

[0016] (1) Ball milling to prepare mixed powder:

[0017] WC-Co powder, grain growth inhibitor, rare earth oxide, and paraffin are ball-milled according to the designed ratio to prepare a uniformly dispersed mixed powder;

[0018] Or: WC-Co powder, grain growth inhibitor, rare earth oxide, paraffin wax, and low-cost rare earth are ball-milled according to a designed ratio to prepare a uniformly dispersed mixed powder;

[0019] Powder ball milling is carried out in a protective atmosphere to achieve full coating and oxygen control of cemented carbide powder;

[0020] (2) Vacuum mixing-granulation preparation of printing feed:

[0021] The mixed powder and the organic binder are mixed according to the designed ratio, and the mixture is placed in a vacuum mixing chamber of a mixer for mixing to prepare a mixed mixture of the mixed powder and the organic binder, and the mixed mixture is placed in a vacuum granulator to prepare a granular printing feed;

[0022] (3) Fused Deposition Modeling (FDM) to prepare printed green bodies:

[0023] Using the granular printing feed obtained in step (2) as raw material, FDM equipment is used to prepare a cemented carbide printing green body;

[0024] (4) green body degreasing: performing solvent degreasing and thermal degreasing on the cemented carbide green body prepared by printing in step (3) to obtain a degreased green body;

[0025] (5) Two-step sintering: The degreased green body treated in step (4) is subjected to two-step sintering to obtain an ultrafine-grained WC-Co cemented carbide product.

[0026] As a preferred embodiment, the present invention provides a method for manufacturing ultrafine-grained cemented carbide additives, wherein the raw materials WC-Co powder, grain growth inhibitor, and rare earth oxide have a particle size D 50 It can be less than 10 μm, preferably less than or equal to 5 μm. More importantly, the present invention has no special requirements on the shape of the raw material powder.

[0027] In step (1), when drum ball milling is used, the ball-to-material ratio is 10:1 to 3:2, preferably 6:1 to 3:1; the rotation speed is 60 to 300 rpm, preferably 100 to 220 rpm; the ball milling time is 8 to 72 hours, preferably 24 to 60 hours; in the mixture, the mass fraction of WC-Co powder is 92 to 99%; the mass fraction of grain growth inhibitor is 0.5 to 4.5%; the mass fraction of raw material rare earth oxide is 0.1 to 1%; the mass fraction of paraffin is 0.5 to 5%; and the mass fraction of low-priced rare earth is 0 to 0.05%, preferably 0.01 to 0.05%.

[0028] Other ball milling processes are also suitable for use with the present invention.

[0029] Both wet milling and dry milling are suitable for the present invention; wet milling preferably uses anhydrous ethanol as the milling medium.

[0030] Preferably, in the method for additively manufacturing ultrafine-grained cemented carbide of the present invention, the paraffin wax added in step (1) accounts for 0.5 to 5% of the total mass of the mixture.

[0031] The present invention provides an ultrafine-grained cemented carbide additive manufacturing method. When low-valent rare earth is added, the added low-valent rare earth accounts for 0.01-0.05% of the total mass of the mixture; wherein, when the low-valent rare earth is added in the form of low-valent rare earth oxide, the added amount is calculated in the form of low-valent rare earth oxide; and when the low-valent rare earth is added in the form of zero-valent rare earth, the added amount is calculated based on the amount of the added zero-valent rare earth.

[0032] The present invention provides a method for additive manufacturing of ultrafine-grained cemented carbide. In step (1), powder ball milling is carried out in a protective atmosphere, wherein the protective atmosphere is one of nitrogen, argon, and helium, or a mixture of several gases, with a purity of 99.99wt%, wherein the oxygen content is less than 0.0001wt%.

[0033] The present invention provides a method for additive manufacturing of ultrafine-grained cemented carbide. In step (1), paraffin wax or paraffin wax and a trace amount of low-valent rare earth are added, and the powder is fully coated and residual oxygen in the powder is adsorbed by ball milling. This prevents the WC-Co powder, grain growth inhibitor, and mixed powder prepared by ball milling from absorbing oxygen and oxidizing during the ball milling process, as well as the mixed powder from absorbing oxygen and oxidizing during subsequent processing. The prepared mixed powder is fully coated with paraffin wax, and the residual oxygen in the powder reacts in situ with the low-valent rare earth and its oxide to form nano rare earth oxides, thereby minimizing oxygen adsorption and oxidation.

[0034] Preferably, the present invention provides an ultrafine-grained cemented carbide additive manufacturing method, wherein the mixed powder comprises paraffin wax, WC-Co, VC, Cr3C2, rare earth oxide powder and low-valent rare earth oxide in a mass ratio of WC-Co: VC: Cr3C2: paraffin wax: rare earth oxide: low-valent rare earth oxide = 96-98.5: 0.5-1: 0.5-1: 0.45-1: 0.1-2: 0.01-0.05; the rare earth oxide is selected from at least one of CeO2, La2O3, Y2O3, etc., and the low-valent rare earth oxide is selected from Ce2O3, Ce7O 12 , La5O7, YO, etc.

[0035] In the banburying mixture of step (2), the volume proportion of the mixed powder is 40-75%, and the volume proportion of the organic binder is 25-60%. The volume proportion of the mixed powder in the banburying mixture is defined as the powder loading amount.

[0036] The present invention optimizes the composition of an organic binder, which includes a backbone component, a plasticizer component, and a dispersed component. The backbone component is at least one of polyethylene, polypropylene, polyethylene glycol, ethylene-vinyl acetate copolymer, polymethyl methacrylate, polystyrene, polyvinyl butyral, and polyacetal. The plasticizer component includes at least one of paraffin wax (including the amount of paraffin wax added during the ball milling process), microcrystalline wax, tung oil, quartz, beeswax, and palm wax. The dispersed component is at least one of fatty acid, polyacrylamide, 2,6-di-tert-butyl-4-methylphenol (BHT), stearic acid, and stearate. The backbone component accounts for 35-65% by volume, preferably 50-60% by volume; the plasticizer accounts for 30-60% by volume, preferably 35-45% by volume; and the dispersed component accounts for 1-15% by volume, preferably 5%-10%.

[0037] As a preferred embodiment, the organic binder is composed of paraffin wax, palm wax, polypropylene, high-density polyethylene, low-density polyethylene, polymethyl methacrylate, stearic acid, dioctyl phthalate, and BHT (2,6-di-tert-butyl-4-methylphenol); calculated by volume, the paraffin wax (including the amount of paraffin added in the ball milling process): palm wax: polypropylene: high-density polyethylene: low-density polyethylene: polymethyl methacrylate: stearic acid: dioctyl phthalate: BHT = 30-40: 18-25: 10-15: 10-15: 8-15: 3-10: 5-8: 4-6: 0.3-0.6.

[0038] The amount of paraffin wax in step (2) includes the amount of paraffin wax added in the ball milling process in step (1), that is, the amount of paraffin wax in the organic binder in step (2), which is composed of the sum of the amount of paraffin wax in the ball milling process in step (1) and the amount of paraffin wax added subsequently.

[0039] In step (2), the organic binder and the ball-milled mixed powder are sequentially added into the vacuum mixing chamber of the mixer, and the mixing chamber is evacuated to a vacuum degree greater than -0.05 MPa, preferably greater than -0.08 MPa; a protective gas is filled, and the mixture is heated to a working temperature of 100-200°C, preferably 110-180°C, for a mixing time greater than 30 minutes, preferably greater than 40 minutes, to ensure that the organic binder and the mixed powder are evenly mixed and fully coated to obtain a mixed material.

[0040] In step (2), the banburying mixture is added to a vacuum granulator, and the material bin of the granulator is evacuated to a vacuum degree greater than -0.05MPa, preferably a vacuum degree greater than -0.08MPa, and a protective gas is filled; finally, the mixture is heated to an operating temperature of 100-200°C, preferably an operating temperature of 110-180°C, and a screw pressure of 3-10kg, preferably a pressure of 5-8kg, is used; and the printed feed is extruded and sheared to obtain a particle diameter of 1-4mm, preferably 2-4mm.

[0041] The cemented carbide green body in step (3) is prepared by printing the granular printing feed prepared in step (2) using an FDM device; designing and optimizing 3D printing process parameters to reduce defects (such as wedge-shaped or diamond-shaped pores, interlayer cracks, etc.) in the cemented carbide green body. The optional printing process parameters of the present invention are: nozzle aperture of 0.2-0.8 mm, preferably 0.2-0.7 mm; printing temperature of 120-200° C., preferably 130-170° C.; layer thickness of 0.05-0.8 mm, preferably 0.1-0.6 mm; printing speed of 15-75 mm / s, preferably 20-50 mm / s; flow rate of 50-130%, preferably 60-100%.

[0042] Wherein, in step (4), the green body is first immersed in n-heptane for degreasing and drying; then the green body degreased by n-heptane is placed in a hot degreasing-sintering integrated furnace for hot degreasing treatment, the degreasing temperature is 400-750°C, the heating rate is 0.1-8°C, preferably 0.1-6°C, further preferably, the heating rate is 0.3-5°C / min, and the degreasing time is greater than 30min.

[0043] Among them, step (5) is to perform two-step sintering of the degreased green body in a hot debinding-sintering integrated furnace using a vacuum or inert gas environment. The two-step sintering process can reduce the temperature of the liquid phase sintering system, avoid the merging and growth of WC grains, and eliminate abnormal grain growth: in the first stage, the temperature is rapidly increased from the hot debinding temperature to the first stage sintering temperature T1 (1350-1500℃) in a vacuum atmosphere at a heating rate of 3-20℃ / min, and the temperature is kept at this temperature for 0.5-4h; preferably, the heating rate is 5-10℃ / min, the sintering temperature T1 (1350-1450℃) is preferably, and the holding time is preferably 0 .5-2h; the second stage sintering temperature T2 is 30-100℃ lower than the first sintering temperature T1, and the temperature is reduced from T1 to the sintering temperature T2 (1200-1350℃) at a cooling rate of 5-20℃ / min, and the temperature is kept at this temperature for 3-10h; preferably, the cooling rate is 5-10℃ / min, the sintering temperature T2 is preferably 1250-1350℃, and the temperature is kept at this temperature for 5-8h to complete the two-step sintering and obtain an ultrafine-grained WC-Co cemented carbide product. The sintered sample is rapidly densified in the first stage T1, and in the second stage T2 is 30-100℃ lower than T1. The WC grains have almost no driving force for growth, and the residual pores in the sample are eliminated by grain boundary diffusion. The diffusion takes a long time, and finally, an ultrafine-grained WC-Co cemented carbide with fine grains is obtained.

[0044] Advantages and positive effects of the present invention:

[0045] The difficulty in manufacturing ultrafine-grained cemented carbide and its additive manufacturing lies in the difficulty in controlling oxidation and decarburization, which can lead to the development of numerous metallurgical defects such as difficult-to-eliminate porosity, cracks, and brittle η phases, as well as abnormal grain growth, resulting in poor mechanical properties. This invention proposes a method for additive manufacturing of ultrafine-grained cemented carbide for the first time. Through the synergistic effect of composition and process design, it effectively eliminates metallurgical defects such as oxygen absorption, oxidation, decarburization, porosity, cracks, brittle η phases, and abnormal grain growth, thereby improving mechanical properties and broadening the process range. This method can efficiently produce high-performance ultrafine-grained cemented carbide products with complex structures.

[0046] (1) The present invention proposes for the first time a method for additive manufacturing of ultrafine-grained cemented carbide. Through the synergistic effect of composition design, various processes and process parameters, it is possible to produce ultrafine-grained cemented carbide products with complex shapes that have high relative density, fine and uniform grains, and excellent mechanical properties. This method effectively solves the problems that have long plagued cemented carbide additive manufacturing, such as the difficult-to-eliminate metallurgical defects such as pores, cracks, brittle η phases, and abnormal grain growth that have appeared in existing additive manufacturing processes, as well as the problems of low relative density and insufficient mechanical properties. In particular, the difficulties in controlling the oxidation and decarburization of ultrafine-grained cemented carbide, the easy generation of brittle η phases, and abnormal grain growth, are problems that have plagued the production of ultrafine-grained cemented carbide.

[0047] (2) The present invention provides a method for additive manufacturing of ultrafine-grained cemented carbide, which can effectively inhibit abnormal grain growth and improve mechanical properties by optimizing the design of components, adding a grain growth inhibitor and further adding rare earth oxides as a reinforcing phase; further adding a trace amount of low-cost rare earth (elemental rare earth or Co-rare earth intermediate alloy or partially oxidized rare earth) to adsorb oxygen in cemented carbide powder and react in situ to generate nano rare earth oxides, thereby preventing the cemented carbide from oxidation, decarburization, and forming a brittle η phase. At the same time, the in-situ generated rare earth oxides act as a dispersion strengthening phase, exerting a strengthening effect on the cemented carbide and converting harmful oxygen into a beneficial strengthening phase component.

[0048] (3) The present invention adopts a process design to first fully coat the powder with an appropriate amount of paraffin wax, and adopts a vacuum mixing-granulation process, which can prevent the raw material powder from absorbing oxygen and oxidizing during the ball milling, mixing and FDM processes, and effectively eliminate metallurgical defects such as oxidation, decarburization, and brittle η phase. After the process parameters are optimized, the vacuum mixing efficiency is further improved, ensuring that the organic binder is evenly dispersed in the mixed powder, and solving the preparation problem of ultrafine-grained printing feed. At the same time, the vacuum mixing-granulation process provides the necessary conditions for the subsequent preparation of high-quality ultrafine-grained cemented carbide under a wider range of preparation process conditions;

[0049] (4) The present invention broadens the FDM printing process parameters through composition design (including the introduction of low-cost rare earths), powder coating and vacuum mixing granulation, eliminates wedge-shaped or diamond-shaped pores and interlayer cracks in the green body, and can produce high relative density, pore-free, complex-shaped cemented carbide green bodies;

[0050] (5) The present invention adopts a two-step sintering process to reduce the temperature of the liquid phase sintering system, avoid the merging and growth of WC grains, and eliminate abnormal grain growth. The prepared ultrafine-grained cemented carbide has no decarburization and brittle phase, eliminates the abnormal grain growth phenomenon, has a smaller and more uniform grain size, a high relative density (greater than 99%), and excellent mechanical properties, achieving a simultaneous improvement in the hardness, strength, and fracture toughness of the ultrafine-grained cemented carbide;

[0051] (6) The present invention fully utilizes the advantages of additive manufacturing and powder metallurgy degreasing and sintering, effectively eliminating the metallurgical defects such as porosity, interlayer cracks, oxygen absorption and oxidation of the green body, as well as oxidation, decarburization, brittle η phase, abnormal grain growth of the sintered sample. It completely eliminates the metallurgical defects such as oxidation, decarburization, porosity, cracks and brittle η phase, abnormal grain growth of the PBF process. There are no special requirements for the raw material powder, and ordinary commercial cemented carbide powder raw materials can be used, with low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIG1 is a SEM image of the WC-9Co cemented carbide raw material powder used in a specific embodiment of the present invention.

[0053] FIG2 is a metallographic microscope image of an ultrafine-grained cemented carbide green body formed by FDM in Example 3 of the present invention (eliminating green body defects).

[0054] FIG3 is a SEM image of a cemented carbide sample after degreasing and sintering according to Example 3 of the present invention.

[0055] FIG4 is a macroscopic structural photograph of the FDM-debinding sintered ultrafine-grained cemented carbide sample of the present invention.

[0056] Example 1:

[0057] (1) The powder raw material composition is composed of 96.5wt.% WC-9Co, 0.5wt.% VC, 0.5wt.% Cr3C2, 0.45wt.% CeO2, 0.05wt.% Ce2O3 and 2wt.% paraffin, with a particle size of less than 2μm. Ultrafine-grained cemented carbide mixed powder is prepared by ball milling in a drum ball mill with an appropriate amount of alcohol in a nitrogen atmosphere for 30 hours. 1.45kg is measured and set aside;

[0058] (2) At room temperature, measure 10cm 3 Stearic acid, 10cm 3 High-density polyethylene, 10cm 3 Low-density polyethylene, 10cm 3 Polypropylene, 25cm 3 Paraffin wax (including the amount of paraffin wax added by ball milling process), 30cm 3 After the vacuum mixer is preheated at 50℃ for 15 minutes, add 10cm 3 Stearic acid, 10cm 3 High-density polyethylene, 10cm 3 Low-density polyethylene, 10cm 3 Polypropylene, 25cm 3 Paraffin wax, 30cm 3 Microcrystalline wax and 1.45 kg of mixed powder D in step (1) were added to the mixing chamber of a mixer. The hammer was closed and the internal air pressure was evacuated to a vacuum degree of -0.07 MPa using a vacuum device. After argon was introduced, the mixer was heated to 160° C. The specific parameters were designed as follows: mixing temperature of 160° C., mixing time of 90 min, and a mixed material with a powder loading of 55% was prepared. The mixed material was cooled and placed in a vacuum granulator. After the granulator was evacuated to a vacuum degree of -0.07 MPa and argon was introduced, the closed chamber temperature was raised to 120° C., the screw speed was 60 rpm, and the piston was pushed with a pressure of 10 kg to obtain a granular printing feed with a powder loading of 55% and a particle size of about 2-3 mm.

[0059] (3) Using the granular printing feed obtained in step (2) as a raw material, a fused deposition modeling device is used to form a cemented carbide green body through 3D printing technology, and the parameters are set as follows: nozzle diameter is 0.5 mm, nozzle temperature is 150 ° C, layer thickness is 0.2 mm, printing speed is 25 mm / s, filling rate is 100%, and a green body of the formed part is formed.

[0060] (4) The cemented carbide green body printed in step (3) is immersed in n-heptane liquid and sealed, and then the n-heptane solution is heated to 40°C in a water bath and kept warm for 14 hours. After drying at 60°C in a drying furnace for 6 hours, the green body is placed in a sintering furnace for thermal degreasing treatment. The temperature is raised from room temperature to 550°C at a heating rate of 2.5°C / min and kept warm for 60 minutes to complete the thermal degreasing.

[0061] (5) The cemented carbide green body treated in step (4) is heated from 550°C to 1400°C at a heating rate of 8°C / min under vacuum conditions and kept warm for 30 minutes; then cooled to 1350°C at a cooling rate of 10°C / min and kept warm for 6 hours; finally cooled to room temperature to obtain an ultrafine-grained cemented carbide solid part.

[0062] The printing feed prepared using this parameter exhibits the shear-thinning characteristics of a pseudoplastic fluid and has good printability. After optimization of the design of ultrafine-grained cemented carbide composition, vacuum refining-granulation protection of the printing feed, and improvement of the sintering process, the relative density of the sintered sample of the ultrafine-grained cemented carbide green body after degreasing and sintering can reach 99.3%. The results of metallographic microscopy showed that the porosity of the sample was A02B00, the uncombined carbon was C00 (100 times metallographic examination after polishing), and the η phase was E00 (slightly corroded by NaOH and K3Fe(CN)6) solutions). The results of microstructure and mechanical properties tests showed that the coercive force was 31.5kA / m, the average WC grain size was 0.395μm, and the hardness was 2093.8HV 30 , flexural strength is 4920MPa, fracture toughness is 12.5MPa·m 1 / 2 .

[0063] Example 2:

[0064] (1) The powder raw material composition is composed of 97.5wt.% WC-9Co, 0.25wt.% VC, 0.75wt.% Cr3C2, 0.45wt.% CeO2, 0.05wt.% Ce2O3 and 1wt.% paraffin, with a particle size of less than 2μm. Ultrafine-grained cemented carbide mixed powder is prepared by ball milling in a drum ball mill with an appropriate amount of alcohol in a nitrogen atmosphere for 30 hours. 1.45kg is measured and set aside;

[0065] (2) At room temperature, measure 10cm3 Stearic acid, 10cm 3 High-density polyethylene, 5cm 3 Low-density polyethylene, 10cm 3 Polypropylene, 20cm 3 Paraffin wax (including the amount of paraffin wax added by ball milling process), 25cm 3 After the vacuum mixer is preheated at 50℃ for 15 minutes, add 10cm 3 Stearic acid, 10cm 3 High-density polyethylene, 5cm 3 Low-density polyethylene, 10cm 3 Polypropylene, 20cm 3 Paraffin wax, 25cm 3 Microcrystalline wax and 1.45 kg of mixed powder D in step (1) were added to the mixing chamber of a mixer. The hammer was closed and the internal air pressure was evacuated to a vacuum degree of -0.08 MPa using a vacuum device. After argon was introduced, the mixer was heated to 160° C. The specific parameters were designed as follows: mixing temperature of 150° C., mixing time of 80 min, and a mixed material with a powder loading of 55% was prepared. The mixed material was cooled and placed in a vacuum granulator. After the granulator was evacuated to a vacuum degree of -0.08 MPa and argon was introduced, the closed chamber temperature was raised to 120° C., the screw speed was 70 rpm, and the piston was pushed with a pressure of 8 kg to obtain a granular printing feed with a powder loading of 55% and a particle size of about 2-3 mm.

[0066] (3) Using the granular printing feed obtained in step (2) as a raw material, a fused deposition modeling device is used to form a cemented carbide green body through 3D printing technology, and the parameters are set as follows: nozzle diameter is 0.5 mm, nozzle temperature is 150 ° C, layer thickness is 0.25 mm, printing speed is 40 mm / s, filling rate is 85%, and a green body of the formed part is formed.

[0067] (4) The cemented carbide green body printed in step (3) is immersed in n-heptane liquid and sealed, and then the n-heptane solution is heated to 40°C in a water bath and kept warm for 14 hours. After drying at 60°C in a drying furnace for 6 hours, the green body is placed in a sintering furnace and subjected to medium-low temperature thermal degreasing treatment. The temperature is raised from room temperature to 550°C at a heating rate of 2.5°C / min and kept warm for 60 minutes to complete the thermal degreasing.

[0068] (5) The cemented carbide green body treated in step (4) is heated from 550°C to 1400°C at a heating rate of 10°C / min under vacuum conditions and kept warm for 30 minutes; then cooled to 1350°C at a cooling rate of 10°C / min and kept warm for 6 hours; finally cooled to room temperature to obtain an ultrafine-grained cemented carbide solid part.

[0069] The printing feed prepared using this parameter exhibits the shear-thinning characteristics of a pseudoplastic fluid and has good printability. After optimization of the design of ultrafine-grained cemented carbide composition, vacuum refining-granulation protection of the printing feed, and improvement of the sintering process, the relative density of the sintered sample of the ultrafine-grained cemented carbide green body after degreasing and sintering can reach 99.0%. The results of metallographic microscopy showed that the porosity of the sample was A02B00, the uncombined carbon was C00 (100 times metallographic examination after polishing), and the η phase was E00 (slightly corroded by NaOH and K3Fe(CN)6) solutions). The results of microstructure and mechanical properties tests showed that the coercive force was 27.8kA / m, the average WC grain size was 0.460μm, and the hardness was 2019.5HV 30 , flexural strength is 4715MPa, fracture toughness is 13.4MPa·m 1 / 2 .

[0070] Example 3:

[0071] (1) The powder raw material composition is composed of 97wt.% WC-9Co, 0.75wt.% VC, 0.25wt.% Cr3C2, 0.45wt.% CeO2, 0.05wt.% Ce2O3, and 1.5wt.% paraffin wax, with a particle size of less than 2μm. Ultrafine-grained cemented carbide mixed powder is prepared by ball milling in a drum ball mill with an appropriate amount of alcohol in a nitrogen atmosphere for 45 hours. 1.45kg of the powder is measured and set aside.

[0072] (2) At room temperature, measure 10cm 3 Stearic acid, 15cm 3 High-density polyethylene, 15cm 3 Low-density polyethylene, 5cm 3 Polypropylene, 25cm 3 Paraffin wax (including the amount of paraffin wax added by ball milling process), 30cm 3 After the vacuum mixer is preheated at 50℃ for 15 minutes, add 10cm 3 Stearic acid, 15cm 3 High-density polyethylene, 15cm 3 Low-density polyethylene, 5cm 3 Polypropylene, 25cm 3 Paraffin wax, 30cm 3Microcrystalline wax and 1.45 kg of mixed powder D in step (1) were added to the mixing chamber of the internal mixer. The hammer was closed and the internal air pressure was evacuated to a vacuum degree of -0.05 MPa using a vacuum device. After argon was filled, the internal mixer was heated to 150°C. The specific parameters were designed as follows: mixing temperature of 150°C, mixing time of 70 min, and a powder loading of 53% was prepared. The obtained internal mixer was cooled and placed in a vacuum granulator. After the granulator was evacuated to a vacuum degree of -0.05 MPa and argon was filled, the closed chamber temperature was raised to 120°C, the screw speed was 80 rpm, and the piston was pushed at a pressure of 10 kg to obtain a granular printing feed with a powder loading of 53% and a particle size of about 2-3 mm.

[0073] (3) Using the granular printing feed obtained in step (2) as a raw material, a fused deposition modeling device is used to form a cemented carbide green body through 3D printing technology, and the parameters are set as follows: nozzle diameter is 0.4 mm, nozzle temperature is 150 ° C, layer thickness is 0.2 mm, printing speed is 60 mm / s, filling rate is 75%, and a green body of the formed part is formed.

[0074] (4) The cemented carbide green body printed in step (3) is immersed in n-heptane liquid and sealed, and then the n-heptane solution is heated to 40°C in a water bath and kept warm for 14 hours. After drying at 60°C in a drying furnace for 6 hours, the green body is placed in a sintering furnace and subjected to medium-low temperature thermal degreasing treatment. The temperature is raised from room temperature to 550°C at a heating rate of 3°C / min and kept warm for 60 minutes to complete the thermal degreasing.

[0075] (5) The cemented carbide green body treated in step (4) was heated from 550°C to 1400°C at a heating rate of 12°C / min under vacuum conditions and kept at this temperature for 30 minutes; then cooled to 1350°C at a cooling rate of 10°C / min and kept at this temperature for 6 hours; finally cooled to room temperature to obtain an ultrafine-grained cemented carbide solid part. The printing feed prepared using these parameters exhibited the shear thinning characteristics of a pseudoplastic fluid and had good printability. After optimizing the design of the ultrafine-grained cemented carbide composition, improving the vacuum mixing-granulation protection printing feed and the sintering process, the relative density of the sintered body sample of the ultrafine-grained cemented carbide green body after degreasing and sintering could reach 99.5%. The results of metallographic microscope examination showed that the porosity of the sample was A02B00, the uncombined carbon was C00 (100 times metallographic examination after polishing), and the η phase was E00 (slightly corroded by NaOH and K3Fe(CN)6) solution). The results of microstructure and mechanical properties test show that the coercive force is 35.8kA / m, the average WC grain size is 0.355μm, and the hardness is 2252HV. 30 , flexural strength 5137MPa, fracture toughness 14.1MPa·m 1 / 2 .

[0076] Example 4:

[0077] (1) The powder raw material composition consists of 96.5wt.% WC-9Co, 0.5wt.% VC, 0.5wt.% Cr3C2, 0.48wt.% CeO2, 0.02wt.% Ce2O3 and 2wt.% paraffin, with a particle size of less than 2μm. Ultrafine-grained cemented carbide mixed powder is prepared by ball milling in a nitrogen atmosphere with the addition of an appropriate amount of alcohol in a drum ball mill for 30 hours. 1.45kg of the powder is then measured and used for later use.

[0078] (2) A fused deposition modeling device was used to form a cemented carbide green body through 3D printing technology. The parameters were set as follows: nozzle diameter was 0.5 mm, nozzle temperature was 150 °C, layer thickness was 0.25 mm, printing speed was reduced to 15 mm / s, filling rate was increased to 130%, and green parts were formed.

[0079] Other operation steps are consistent with those in Example 3.

[0080] After degreasing and sintering, the relative density of the sintered sample of the ultrafine-grained cemented carbide green body reached 99.1%. Metallographic microscopy revealed porosity of A02B00, uncombined carbon of C00 (metallographic examination at 100x magnification after polishing), and η phase of E00 (minor corrosion with NaOH and K3Fe(CN)6 solutions). Microstructural and mechanical property testing revealed a coercive force of 34.8kA / m, an average WC grain size of 0.362μm, and a hardness of 2138HV. 30 , flexural strength 5088MPa, fracture toughness 14.3MPa·m 1 / 2 .

[0081] Embodiment 5:

[0082] (1) The powder raw material composition is composed of 97.5wt.% WC-9Co, 0.5wt.% VC, 0.5wt.% Cr3C2, 0.46wt.% CeO2, 0.04wt.% Ce2O3 and 1.5wt.% paraffin, with a particle size of less than 2μm. Ultrafine-grained cemented carbide mixed powder is prepared by ball milling in a drum ball mill with an appropriate amount of alcohol in a nitrogen atmosphere for 30 hours. 1.45kg is measured and set aside;

[0083] (2) A fused deposition modeling device was used to form a cemented carbide green body through 3D printing technology. The parameters were set as follows: nozzle diameter was 0.4 mm, nozzle temperature was 150 °C, layer thickness was 0.2 mm, printing speed was increased to 75 mm / s, filling rate was reduced to 60%, and the green body of the formed part was formed.

[0084] Other operation steps are consistent with those in Example 3.

[0085] After degreasing and sintering, the relative density of the sintered sample of the ultrafine-grained cemented carbide green body reached 99.0%. Metallographic microscopy revealed porosity of A02B00, uncombined carbon of C00 (metallographic examination at 100x magnification after polishing), and η phase of E00 (minor corrosion with NaOH and K3Fe(CN)6 solutions). Microstructural and mechanical property testing revealed a coercive force of 32.9kA / m, an average WC grain size of 0.373μm, and a hardness of 2091HV. 30 , flexural strength 4989MPa, fracture toughness 13.8MPa·m 1 / 2 .

[0086] Comparative Example 1:

[0087] The difference from step (1) described in Example 3 is that in Comparative Example 1, 2 wt% paraffin was not added to the drum ball mill as in step (1) described in Example 3 to coat the powders A, B, and C. That is, the powders A, B, and C in step (1) described in Example 3 and a trace amount of low-valent rare earth oxide Ce2O3 were directly contacted with the grinding balls and ball-milled in a nitrogen atmosphere to prepare an ultrafine-grained cemented carbide mixed powder. The ball milling time was 30 hours, and 1.45 kg was measured for standby use.

[0088] Other operation steps are consistent with those in Example 3.

[0089] After debinding and sintering, microscopic observation and mechanical property tests showed that the prepared ultrafine-grained cemented carbide contained a small amount of η phase, with a relative density of 98.1%, a coercive force of 24.7kA / m, and an average WC grain size of 0.561μm; the hardness, flexural strength, and fracture toughness of the parts were 1878.2HV respectively. 30 , 4186MPa and 12.2MPa·m 1 / 2 .

[0090] Compared with Example 3, in Comparative Example 1, 2 wt% paraffin was not added to coat powders A, B, and C, resulting in the formation of a brittle η phase. The hardness, strength, and fracture toughness decreased by 16.6%, 18.5%, and 13.5%, respectively. Adding paraffin to coat the powders during the ball milling process effectively eliminates oxygen adsorption and oxidation in the powders, controlling the formation of the brittle η phase. Comparative Example 2:

[0091] The difference from step (1) described in Example 3 is that in Comparative Example 2, nitrogen is not introduced into the drum ball mill as a protective atmosphere as in step (1) described in Example 3, that is, powders A, B, C, low-valent rare earth oxide Ce2O3 and paraffin are added to step (1) described in Example 3, and ball milling is carried out in an air environment to prepare an ultrafine-grained cemented carbide mixed powder. The ball milling time is 30 hours, and 1.45 kg is measured for standby use.

[0092] Other operation steps are consistent with those in Example 3.

[0093] After debinding and sintering, microscopic observation and mechanical property tests showed that the prepared ultrafine-grained cemented carbide contained a large amount of brittle η phase, with a relative density of up to 96.3%, a coercive force of 18.3kA / m, and an average WC grain size of 0.861μm. The hardness, flexural strength, and fracture toughness of the parts were 1631.5HV, respectively. 30 , 3616MPa and 11.7MPa·m 1 / 2 Compared with Example 3, Comparative Example 2, in which nitrogen was not introduced as a protective atmosphere, resulted in the formation of a large amount of brittle η phase, causing hardness, strength, and fracture toughness to decrease by 27.6%, 29.6%, and 17.0%, respectively. Introducing a protective atmosphere during the ball milling process can eliminate the formation of brittle η phase and improve the mechanical properties of the cemented carbide.

[0094] Comparative Example 3:

[0095] The difference from step (1) described in Example 3 is that in Comparative Example 3, no trace amount of low-valent rare earth oxide Ce2O3 powder is added, and the raw material composition consists of 96.5wt.% WC-9Co, 0.5wt.% VC, 0.5wt.% Cr3C2, 0.5wt.% CeO2 and 2wt.% paraffin, with a particle size of less than 2μm. 2wt% paraffin and an appropriate amount of alcohol are added through a drum ball mill, and ultrafine-grained cemented carbide mixed powder is prepared by ball milling in a nitrogen atmosphere. The ball milling time is 30h, and 1.45kg is measured for standby use.

[0096] Other operation steps are consistent with those in Example 3.

[0097] After debinding and sintering, microscopic observation and mechanical property tests showed that the prepared ultrafine-grained cemented carbide had a small amount of η phase formed, the relative density was 98.8%, the coercivity increased to 23.3kA / m, and the average WC grain size grew to 0.513μm; the hardness, flexural strength, and fracture toughness of the parts were 1904.3HV respectively. 30 , 3962MPa and 11.8MPa·m 1 / 2 .

[0098] Compared with Example 3, Comparative Example 3, which did not include trace amounts of low-valent rare earth oxide Ce2O3 powder, showed decreases in hardness, strength, and fracture toughness by 15.5%, 22.9%, and 16.3%, respectively. The appropriate addition of trace amounts of low-valent rare earth oxide can absorb residual oxygen in the powder and react in situ to form nano-rare earth oxides, which act as a dispersion strengthening phase, strengthening the cemented carbide and converting harmful oxygen into beneficial strengthening phase components.

[0099] Comparative Example 4:

[0100] The difference from step (1) described in Example 3 is that in Comparative Example 4, no rare earth oxide is added, and the parameters are modified as follows: the powder raw material composition consists of 96.5wt.% WC-9Co, 1wt.% Cr3C2, 0.5wt.% Cr3C2 and 2wt.% paraffin, with a particle size of less than 2μm, and ultrafine-grained cemented carbide mixed powder is prepared by ball milling, the ball milling time is 30h, and 1.45kg is measured for standby use.

[0101] Other operation steps are consistent with those in Example 3.

[0102] After degreasing and sintering, microscopic observation and mechanical property tests showed that the prepared ultrafine-grained cemented carbide had no η phase formed, the relative density could reach 99.5%, the coercivity dropped to 23.1kA / m, and the average WC grain size grew to 0.502μm; the hardness, flexural strength, and fracture toughness of the parts were 1748.9HV respectively. 30 , 3758MPa and 10.3MPa·m 1 / 2 .

[0103] Compared with Example 3, in Comparative Example 4, where no rare earth oxide was added, the WC grain size significantly increased, and the mechanical properties of the cemented carbide decreased by 22.3%, 26.8%, and 27.0%, respectively. Rare earth oxides can refine the grain size and exert a pinning effect on grain migration. Adding them as a second phase significantly improves the overall mechanical properties of cemented carbide.

[0104] Comparative Example 5:

[0105] The difference from step (2) described in Example 3 is that in Comparative Example 5, the vacuum environment in step (2) described in Example 3 is cancelled, that is, the mixed powder prepared in step (1) described in Example 3 and the adhesive are mixed and granulated in an air environment to prepare granular printing feed.

[0106] Other operation steps are consistent with those in Example 3.

[0107] Microscopic observations show that after sintering, the ultrafine-grained cemented carbide exhibits a distinct η phase, and the relative density of the sample decreases to only 96.4%. Due to the formation of the brittle phase, the mechanical properties of the sample are significantly reduced, with the hardness, flexural strength, and fracture toughness being 1745HV, respectively. 30 , 3435MPa and 9.3MPa·m 1 / 2 .

[0108] Compared with Example 3, vacuum mixing-granulation was not adopted in Comparative Example 5. Since the powder raw material is fine and has high surface activity, it is very easy to oxidize in an air environment, resulting in a decrease in the relative density of the ultrafine-grained cemented carbide, the appearance of carbon-deficient η phase in the microstructure, and the mechanical properties being reduced by 22.5%, 33.1% and 34.0%, respectively.

[0109] Comparative Example 6

[0110] The difference from step (5) described in Example 3 is that in Comparative Example 6, the two-step sintering process is adjusted to a conventional one-step sintering process, and the sintering is maintained at a maximum temperature of 1400° C. for 1 hour.

[0111] Other operation steps are consistent with those in Example 3.

[0112] Microscopic observation shows that the relative density of the ultrafine-grained cemented carbide sample prepared after sintering is 99.0%, the average WC grain size grows to 0.462μm, the hardness, flexural strength and fracture toughness are 1887HV respectively. 30 , 4499MPa and 13.1MPa·m 1 / 2 .

[0113] Compared with Example 3, in Comparative Example 6, the two-step sintering process was not adopted. The relative density of the ultrafine-grained cemented carbide prepared by conventional one-step sintering did not change significantly, the WC grain size grew significantly, and the hardness, flexural strength, and fracture toughness decreased by 16.2%, 12.4%, and 7.1%, respectively.

[0114] Comparative Example 7:

[0115] The difference from step (5) described in Example 3 is that in Comparative Example 7, the two-step sintering process is adjusted so that the first sintering temperature T1 is 50°C lower than the second sintering temperature T1, that is, the first sintering temperature is kept at 1350°C for 30 minutes, then the temperature is increased to 1400°C at a heating rate of 10°C / min, kept for 1 hour, and finally cooled to room temperature.

[0116] Other operation steps are consistent with those in Example 3.

[0117] Microscopic observation shows that the relative density of the cemented carbide sample prepared by the adjusted two-step sintering is 99.1%, the average WC grain size grows to 0.493μm, and the hardness, flexural strength and fracture toughness are 1783.6HV respectively. 30 , 4413MPa and 13.2MPa·m 1 / 2 .

[0118] Compared with Example 3, in the two-step sintering process of Comparative Example 7, the sintering temperature is first low and then high. The relative density of the prepared ultrafine-grained cemented carbide does not change significantly, the WC grain size grows by 0.098 μm, and the hardness, flexural strength, and fracture toughness decrease by 20.8%, 14.1%, and 5.6%, respectively.

Claims

1. A method for additive manufacturing of ultrafine-grained cemented carbide, characterized in that: First, paraffin wax is added to the powder raw material, and a uniformly dispersed mixed powder is prepared by ball milling; the added paraffin wax can completely cover the raw material powder after ball milling; Or: first, paraffin wax and a trace amount of low-valent rare earth are added to the powder raw material, and a uniformly dispersed mixed powder is prepared by ball milling; the raw material powder includes cemented carbide powder, grain growth inhibitor, and rare earth oxide; the added paraffin wax can completely cover the raw material powder after ball milling; the valence state of the rare earth in the low-valent rare earth oxide is less than or equal to positive divalent; the valence state of the rare earth element in the rare earth oxide is greater than positive divalent; Second, vacuum mixing-granulation to prepare additive manufacturing printing feed; Third, fused deposition modeling printing to prepare green bodies; Fourth, green body degreasing + two-step sintering to obtain ultrafine-grained cemented carbide products without metallurgical defects; the temperature of the first step sintering is 1350-1500°C, and the temperature of the second step sintering is 30-100°C lower than the temperature of the first step sintering.

2. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 1, characterized in that: The steps include: (1) Ball milling to prepare mixed powder: Ball milling WC-Co powder, grain growth inhibitor, rare earth oxide and paraffin wax according to the designed proportion to prepare a uniformly dispersed mixed powder; Or: ball-milling WC-Co powder, grain growth inhibitor, rare earth oxide, paraffin wax and low-cost rare earth according to the designed proportion to prepare a uniformly dispersed mixed powder; Powder ball milling is carried out in a protective atmosphere to achieve full coating and oxygen control of cemented carbide powder. (2) Vacuum mixing-granulation to prepare printing feed: The mixed powder and the organic binder are mixed according to the designed ratio, and are put into the vacuum mixing chamber of the mixer for mixing to prepare a mixed powder and the organic binder mixed uniformly, and the prepared mixed mixture is put into a vacuum granulator to prepare a granular printing feed; (3) Preparation of printed green sheets by fused deposition modeling (FDM): Using the granular printing feed obtained in step (2) as a raw material, using FDM equipment to prepare a cemented carbide printing green body; (4) green body degreasing: performing solvent degreasing and thermal degreasing on the cemented carbide green body prepared by printing in step (3) to obtain a degreased green body; (5) Two-step sintering: The degreased green body treated in step (4) is subjected to two-step sintering to obtain ultrafine-grained WC-Co cemented carbide.

3. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 2, characterized in that: Particle size D of WC-Co powder, grain growth inhibitor, and rare earth oxide 50 Less than 10 μm; The paraffin added in step (1) accounts for 0.5-5% of the total mass of the mixture; When low-priced rare earths are added, the added low-priced rare earths account for 0.01-0.05% of the total mass of the mixture; when the low-priced rare earths are added in the form of low-priced rare earth oxides, the added amount is calculated in the form of low-priced rare earth oxides; when the low-priced rare earths are added in the form of zero-valent rare earths, the added amount is calculated based on the amount of zero-valent rare earths added.

4. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 3, characterized in that: In the mixed powder obtained in step (1), the mass fraction of WC-Co is 92-99%; the mass fraction of grain growth inhibitor is 0.5-4.5%; the mass fraction of raw rare earth oxide is 0.1-1%; the mass fraction of paraffin is 0.5-5%; and the mass fraction of low-priced rare earth is 0-0.05%, preferably 0.01-0.05%.

5. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 4, characterized in that: The mixed powder comprises paraffin wax, WC-Co, VC, Cr3C2, rare earth oxide powder and low-priced rare earth oxide in a mass ratio of WC-Co: VC: Cr3C2: paraffin wax: rare earth oxide: low-priced rare earth oxide = 96-98.5: 0.5-1: 0.5-1: 0.45-1: 0.1-2: 0.01-0.05; the rare earth oxide is selected from at least one of CeO2, La2O3, Y2O3, etc., and the low-priced rare earth oxide is selected from Ce2O3, Ce7O 12 , La5O7, YO, etc.

6. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 2, characterized in that: In the banburying mixture described in step (2), the volume proportion of the mixed powder is 40-75%, and the volume proportion of the organic binder is 25-60%; The organic binder comprises a skeleton component, a plasticizing component and a dispersing component; the skeleton component is at least one of polyethylene, polypropylene, polyethylene glycol, ethylene-vinyl acetate copolymer, polymethyl methacrylate, polystyrene, polyvinyl butyral, polyacetal, etc.; the plasticizing component comprises paraffin, micro At least one of crystalline wax, tung oil, quartz, beeswax, palm wax, etc.; the dispersed components are at least one of fatty acids, polyacrylamide, 2,6-di-tert-butyl-4-methylphenol, stearic acid, and stearate; wherein the volume of the skeleton component is 35-65%; the volume of the plasticizer component is 30-60%; and the volume of the dispersed components is 1-15%.

7. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 2, characterized in that: Step (2) sequentially adding the organic binder and the ball-milled mixed powder into a vacuum mixer, heating them to 100-200° C. in an environment with a vacuum degree greater than -0.05 MPa, and the mixing time is greater than 30 min to ensure that the organic binder and the mixed powder are mixed evenly and fully coated to obtain a mixed mixture; the mixed mixture is loaded into a vacuum granulator, heated to 100-200° C. in an environment with a vacuum degree greater than -0.05 MPa, and extruded and sheared using a screw pressure of 3-10 kg to obtain an FDM printing feed with a particle diameter of 1-4 mm.

8. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 2, characterized in that: The cemented carbide green body described in step (3) is obtained by using the granular printing feed prepared in step (2) as a raw material and printing with an FDM device. The printing parameters are: nozzle diameter of 0.2-0.8 mm, printing temperature of 120-200° C., layer thickness of 0.05-0.8 mm, printing speed of 15-75 mm / s, and flow rate of 50-130%.

9. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 2, characterized in that: In step (4), the green body is first immersed in n-heptane for degreasing and drying; then the green body degreased by n-heptane is placed in a hot degreasing-sintering integrated furnace for hot degreasing treatment, the temperature range is 400-750°C, the heating rate is 0.1-8°C / min, and the degreasing time is greater than 30min.

10. The method for additive manufacturing of ultrafine-grained cemented carbide according to claim 2, characterized in that: In the hot debinding-sintering integrated furnace, the debinded green body is sintered in two steps in a vacuum or inert gas environment: the first step is to quickly heat up from the hot debinding temperature to 1350-1500℃ at a heating rate of 3-20℃ / min in a vacuum atmosphere and keep it warm for 0.5-4h; the second step is to cool down to 1200-1350℃ at a cooling rate of 5-20℃ / min and keep it warm for 3-10h to complete the two-step sintering and obtain ultrafine-grained WC-Co cemented carbide.

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