Additive manufacturing high-performance ultra-fine grain hard alloy

Abstract

The invention discloses an additive manufacturing high-performance ultra-fine grain hard alloy. The high-performance ultra-fine grain hard alloy is prepared through hard alloy component control and a material extrusion-degreasing sintering process. By utilizing the synergistic effect of the rare earth oxide and the GGI, the dosage of the rare earth oxide and the GGI is reduced, the quality of a green body and a hard alloy sintered part is improved, and meanwhile, abnormal growth of WC grains is inhibited; and a nano second phase is generated in situ, so that the hardness, the transverse breaking strength and the breaking toughness of the hard alloy are synchronously improved, and the problem that the hardness and the breaking toughness of the hard alloy are mutually restricted is solved. According to the WC-Co ultra-fine grain hard alloy and the preparation method thereof, the grain size of the prepared WC-Co ultra-fine grain hard alloy is smaller than 330 nm, the hardness is larger than 2250 HV30, the transverse breaking strength is larger than 3900 MPa, the fracture toughness is larger than 14.2 MPa.m < 1 / 2 >, and the hardness, the transverse breaking strength and the fracture toughness are synergistically improved. The common hard alloy powder raw material is used, the cost is low, and the method is simple and suitable for batch production.

Description

Technical Field

[0001] The present invention relates to an additive manufacturing high-performance ultrafine-grained cemented carbide, and particularly to a method for additive manufacturing of an ultrafine-grained cemented carbide with fine WC grain size, high hardness, high strength and high fracture toughness, belonging to the technical fields of cemented carbide and additive manufacturing. Background Art

[0002] Cemented carbide is composed of refractory metal hard compounds and binder metals and is widely used in fields such as aerospace, mineral exploration, and mechanical manufacturing. Among them, ultrafine-grained cemented carbide has advantages such as high hardness and high strength and is a key material for producing products such as precision tools, micro drills, and micro milling cutters. The rapid development of the manufacturing industry has put forward an urgent demand for complex-structured parts of ultrafine-grained cemented carbide. Additive manufacturing (AM) technology provides a new technical approach for the preparation of complex-structured parts of cemented carbide.

[0003] Zhao et al. [Z. Zhao, et al., Material extrusion printing of WC-8%Co cemented carbide based on partly water-soluble binder and post-processing, Journal of Materials Research and Technology 29 (2024) 4394-4405] prepared WC-8Co cemented carbide by combining material extrusion (MEX) additive manufacturing with pressure sintering at 1340 °C. The relative density was 99.0%, the average WC grain size was 1.5 μm, and the microhardness was 1392 HV 30 , the transverse rupture strength was 1678±125 MPa, and the fracture toughness was not reported. In terms of the powder metallurgy (PM) preparation process, Liu et al. [X. Liu, et al., Complexions in WC-Co cemented carbides, Acta Materialia 149 (2018) 164-178] added vanadium carbide (VC), and the average WC grain size was 0.33 μm. The microhardness, transverse rupture strength, and fracture toughness were 1740 HV 30 , 2189 MPa and 10.3 MPa·m 1 / 2 ; by adding chromium carbide (Cr3C2), the average WC grain size was 0.42 μm, and the microhardness, transverse rupture strength, and fracture toughness were 1645 HV 30, 3745 MPa and 13.3 MPa·m 1 / 2 ; By adding tantalum carbide (TaC), the average grain size of WC is 0.46 μm, and the microhardness, transverse rupture strength and fracture toughness are 1600 HV 30 , 2750 MPa and 14.2 MPa·m 1 / 2 ; By adding titanium carbide (TiC), the average grain size of WC is 0.51 μm, and the microhardness, transverse rupture strength and fracture toughness are 1580 HV 30 , 2620 MPa and 13.2 MPa·m 1 / 2 . For the WC-8Co-0.5VC-0.5Cr3C2 cemented carbide prepared by Wang et al. [H. Wang, et al., Grain size effect on wear resistance of WC-Co cemented carbides under different tribological conditions, Journal of Materials Science & Technology 35(11) (2019) 2435-2446], the average grain size of WC is 0.4 μm, the microstructure is unevenly distributed and there are a large number of pores, the relative density is only 98.5%, and the hardness is 2154±27 HV 30 , and the fracture toughness is 11.3±0.3 MPa·m 1 / 2 . The transverse rupture strength was not reported. For the WC-8Co-0.5Y2O3 cemented carbide prepared by Yang et al. [Y. Yang, et al., Microstructure and wear performance of a WC-8Co hard alloy modified using W powders doped with Y2O3, International Journal of Refractory Metals and Hard Materials 116 (2023) 106350], the average grain size of WC decreased from 2.62 μm to 1.87 μm, the relative density is 99.4%, and the hardness, transverse rupture strength and fracture toughness are 15.88 GPa, 2490 MPa and 13.1 MPa·m 1 / 2。The relative density of the WC-10Co cemented carbide prepared by Cai et al. [H. Cai, et al., Effects of micro / nano CeO2 on the microstructure and properties of WC-10Co cemented carbides, International Journal of Refractory Metals and Hard Materials 95 (2021) 105432] is 99.0%, and the hardness, transverse rupture strength and fracture toughness are 1742 HV 30 , 2650 MPa and 10.7 MPa·m 1 / 2 , respectively. Coarse WC grains appear in the microstructure. In summary, the common problems of WC-Co cemented carbides prepared by additive manufacturing and powder metallurgy processes reported currently are low relative density, difficult-to-eliminate defects, abnormal growth of WC grains, etc., resulting in poor mechanical properties.

[0004] To address the above problems, the inventors previously prepared a WC-9Co cemented carbide by MEX-DS (debinding and sintering), with a relative density of 99.7%, an average WC grain size of 1.2 μm, and the microhardness, transverse rupture strength and fracture toughness being 1525±3HV 30 , 3492±45 MPa and 20.4±0.5 MPa·m 1 / 2 , respectively, significantly improving the transverse rupture strength and fracture toughness of MEX WC-Co cemented carbides [Liu Zuming et al., A method for additive manufacturing of cemented carbides, CN202311420909.8; C. Chen, et al., Material extrusion additive manufacturing of WC-9Co cemented carbide, Additive Manufacturing 86 (2024) 104203]. While maintaining high transverse rupture strength and high fracture toughness, to further improve the hardness of the cemented carbide, the present invention provides an additive manufacturing high-performance ultrafine-grained cemented carbide. By synergistically controlling the cemented carbide composition and the MEX-DS process, an ultrafine-grained cemented carbide solid part with an average WC grain size of less than 330 nm, a hardness greater than 2250 HV 30 , a transverse rupture strength greater than 3900 MPa, and a fracture toughness greater than 14.2 MPa·m 1 / 2 , and excellent comprehensive mechanical properties is prepared. Summary of the Invention

[0005] The present invention provides an additive manufacturing high-performance ultrafine-grained cemented carbide. First, control the composition of the cemented carbide, and compound and add GGI and rare earth oxides with a total mass fraction of less than 1.0% in the cemented carbide, and control the ratio of the two within the range of 5:2 to 5:8; second, prepare a high powder loading MEX printing feedstock in a vacuum environment; third, optimize the MEX-DS process to prepare a high-density and high-quality green body of the cemented carbide; fourth, perform solvent debinding-thermal debinding combined with pressure sintering, control the pressure to be greater than or equal to 5 MPa, and prepare a high-performance ultrafine-grained cemented carbide. Through the coordination of the control of the cemented carbide composition and the MEX-DS process, a WC average grain size of less than 330 nm, a hardness greater than 2250 HV 30 , a transverse rupture strength greater than 3900 MPa, and a fracture toughness greater than 14.2 MPa·m 1 / 2 , an ultrafine-grained cemented carbide solid part with uniform microstructure.

[0006] The present invention relates to an additive manufacturing high-performance ultrafine-grained cemented carbide; the high-performance ultrafine-grained cemented carbide includes a hard phase, a metal binder phase, a transition metal carbide phase (grain growth inhibitor), and a rare earth oxide phase. Among them, the mass fraction of the binder metal is 6.0 to 20.0%, the mass fraction of the grain growth inhibitor is 0.1 to 3.0%, the mass fraction of the rare earth oxide is 0.1 to 2.0%, and the balance is the hard phase. The specific steps are as follows:

[0007] (1) Ball milling to prepare cemented carbide powder:

[0008] Mix and ball mill the hard raw material powder, grain growth inhibitor, rare earth oxide, and binder metal raw material powder according to the designed content to prepare a uniformly dispersed cemented carbide powder;

[0009] The hard raw material powder is selected from at least one of WC, TiC, Ti(C, N), (W, Ti)C, and (W, Ti, Ta)C;

[0010] The grain growth inhibitor is selected from at least one of transition metal carbides VC, Cr3C2, TaC, TiC, NbC, ZrC, and SiC;

[0011] The rare earth oxide is selected from at least one of La2O3, Y2O3, CeO2, Sc2O3, Nd2O3, and Pr6O 11 in;

[0012] The binder metal raw material powder is selected from at least one of Co and Ni;

[0013] (2) Kneading and granulating to prepare a printing feedstock:

[0014] Mix the cemented carbide powder and the organic binder in the designed proportion, and load them into the kneading chamber of a kneader for vacuum kneading to prepare a uniformly kneaded mixture of cemented carbide powder and organic binder;

[0015] Load the prepared mixture into a granulator to prepare granular printing feedstock with a particle size of 1 - 4 mm;

[0016] (3)Prepare a green body by material extrusion (MEX) printing:

[0017] Use the granular printing feedstock obtained in step (2) as the raw material, and adopt MEX forming equipment to print and prepare a cemented carbide green body;

[0018] (4)Solvent debinding of the cemented carbide green body: First, soak and debind with n - heptane, and then perform vacuum drying to obtain a solvent - debound green body; among them, the soaking and debinding time is determined according to the size of the green body; the debinding temperature, drying temperature and time are determined according to the characteristic temperatures of the organic binder and the solvent;

[0019] Among them, the characteristic temperatures of the organic binder and the solvent refer to the melting / melting temperature and the volatilization temperature.

[0020] (5)Thermal debinding - pressure sintering: Perform thermal debinding - pressure sintering on the solvent - debound green body obtained in step (4) to obtain a cemented carbide solid part; during pressure sintering, control the pressure to be greater than or equal to 5 MPa to obtain an ultrafine - grained cemented carbide solid part.

[0021] The cemented carbide powder, GGI, rare - earth oxide and binder metal Co, Ni raw material powders described in step (1) are powders that meet the requirements of commercial powder - metallurgy cemented carbide. The ball - milling can adopt the ball - milling process used in the existing powder - metallurgy preparation technology of cemented carbide; in addition to the raw material powders, paraffin is further added, and the amount of paraffin added accounts for 0.5 - 5% of the total mass of the raw material powders.

[0022] The composition of the cemented carbide powder described in step (1) is strictly controlled; among them, the particle size D of the hard raw material powder 50 is less than 2.0 μm; the particle size D of the binder metal raw material powder 50 is less than 2.0 μm, preferably less than 1.0 μm, and accounts for 6.0 - 20.0% of the total mass of the cemented carbide powder; the particle size D of the grain growth inhibitor powder 50 is less than 1.0 μm, preferably less than 0.5 μm, and accounts for 0.1 - 3.0% of the total mass of the cemented carbide powder, preferably 0.1 - 1.0%, and further preferably 0.1 - 0.5%; the particle size D of the rare - earth oxide powder 50Less than 1.0 μm, preferably less than 0.5 μm. As a further preference, the particle size distribution of the rare earth oxide powder is 0.05 - 0.5 μm, accounting for 0.1 - 2.0% of the total mass of the cemented carbide powder, preferably 0.1 - 1.0%; the balance is the hard raw material powder.

[0023] In the present invention, the requirements for each raw material are much lower than those of the existing additive manufacturing technology. The present invention uses a trace amount of rare earth of 0.05 - 0.5 μm in combination with a trace amount of grain growth inhibitor powder to obtain a product with a microhardness greater than 2250 HV 30 , a transverse rupture strength greater than 3900 MPa, and a fracture toughness greater than 14.2 MPa·m 1 / 2 of high quality.

[0024] Preferably, the hard raw material powder is selected from at least one of WC, TiC, Ti(C, N), (W, Ti)C, (W, Ti, Ta)C.

[0025] As a further preference, the hard raw material powder is WC.

[0026] Preferably, the binder metal raw material powder is selected from at least one of Co and Ni.

[0027] As a further preference, the binder metal raw material powder is Co.

[0028] Preferably, the grain growth inhibitor is selected from at least one of transition metal carbides VC, Cr3C2, and TaC; the mass fraction of the grain growth inhibitor is 0.1 - 3.0%.

[0029] As a further preference, the grain growth inhibitor is Cr3C2, and the preferred mass fraction is 0.1 - 0.5%.

[0030] Preferably, the rare earth oxide is selected from at least one of La2O3, Y2O3, and CeO2.

[0031] As a further preference, the rare earth oxide is CeO2, and the preferred mass fraction is 0.1 - 1.0%, which includes 0.3 - 0.4%.

[0032] Preferably, the mass fraction ratio of Cr3C2 and CeO2 is 5:2 - 5:8.

[0033] As a further preference, the mass fraction ratio of Cr3C2 and CeO2 is 5:3 - 5:6.

[0034] All powders of the present invention include powders that meet the requirements of commercial powder metallurgy cemented carbides. Among them, when using a ball mill for ball milling, 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, and the ball milling time is 8 - 72 h, preferably 24 - 60 h. The ball mill includes at least one of planetary balls and drum ball mills.

[0035] In the printing feedstock described in step (2), the volume fraction of the cemented carbide powder is 40 - 75%, and the volume fraction of the organic binder is 25 - 60%. The volume fraction of the cemented carbide powder in the organic binder is defined as the powder loading.

[0036] Among them, the difficulty in designing the organic binder in step (2) lies in that while the printing feedstock has a high loading, the surface quality of the extruded microfilaments is good and it has good temperature stability and thermoplasticity, ensuring that MEX has a wide printing process window, and the printed green body has high quality, high relative density and high strength. The present invention optimizes the composition of the organic binder. The organic binder includes a skeleton component, a plasticizer component and a dispersant component; the skeleton component is at least one of polyethylene, polyethylene glycol, polypropylene, polymethyl methacrylate, polyvinyl butyral, ethylene-vinyl acetate copolymer, polystyrene, polyacetal, etc.; the plasticizer component includes at least one of paraffin wax, microcrystalline wax, tung oil, quartz, beeswax, palm wax, etc.; the dispersant component is at least one of fatty acids, polyacrylamide, 2,6-di-tert-butyl-4-methylphenol (BHT), stearic acid, stearate. Among them, the volume fraction of the skeleton component in the organic binder is 35 - 65%, preferably 50 - 60%; the volume fraction of the plasticizer component is 30 - 60%, preferably 35 - 45%; the volume fraction of the dispersant component is 1 - 15%, preferably 5% - 10%.

[0037] Preferably, the organic binder is composed of paraffin wax, microcrystalline wax, high-density polyethylene, low-density polyethylene, polypropylene, polymethyl methacrylate, stearic acid, dioctyl phthalate, BHT (2,6-di-tert-butyl-4-methylphenol); by volume ratio, paraffin wax: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] Among them, the preparation parameters of the mixture of the cemented carbide powder and the organic binder in step (2) are: the internal mixer temperature is 100 - 200 °C, the rotation speed is 30 - 100 rpm, the internal mixing time is 30 - 300 min, and the internal mixing is completed in a vacuum environment with a vacuum value less than 1000 Pa.

[0039] Among them, the granulation parameters in step (2) are: the screw speed is 30 - 100 rpm, the screw pressure is 3 - 10 kg, and the diameter of the prepared particles is 1 - 4 mm.

[0040] The cemented carbide green body in step (3) uses the granular printing feedstock prepared in step (2) as the raw material, and adopts MEX forming equipment to print and prepare the cemented carbide green body. The printing process is as follows: a three-dimensional CAD model is established on a computer according to the part shape, the part model is sliced and layered using software, and imported into the additive manufacturing system; through the numerical control system, after heating the granular printing feedstock, according to the sliced and layered data of the imported three-dimensional CAD model of the part, the granular material is extruded using a screw and printed layer by layer according to the sliced data to obtain a printed green body.

[0041] Among them, the technical difficulty of the MEX green body printing in step (3) lies in optimizing the printing process parameters to reduce defects (such as wedge-shaped or diamond-shaped pores, interlayer cracks, etc.) in the cemented carbide green body and improve the quality of the green body. The printing process parameters selected in the present invention are: the nozzle diameter is 0.1 - 0.8 mm, the printing temperature is 120 - 200 °C, the printing layer thickness is 0.05 - 0.8 mm, the printing speed is 15 - 75 mm / s, the filling flow rate is 50 - 130%, the filling method is one of [0°, 90°], [45°, -45°], or a combination of the two filling methods, and the substrate preheating temperature is 50 - 150 °C.

[0042] Preferably, the nozzle diameter is 0.2 - 0.6 mm, the printing temperature is 130 - 180 °C, the printing layer thickness is 0.1 - 0.4 mm, the printing speed is 20 - 50 mm / s, and the filling flow rate is 60 - 100%.

[0043] The difficulty of the solvent debinding in step (4) lies in that it is necessary to design the debinding temperature and time of n-heptane according to the composition of the organic binder to improve the debinding efficiency while avoiding swelling of the high molecular components of the organic binder in the printed green body and causing the green body to crack.

[0044] Among them, the solvent debinding parameters in step (4) are: soaking in n-heptane for 5 - 30 h, the debinding temperature is 10 - 50 °C; the soaking time is 5 - 30 h; the drying temperature is 40 - 80 °C; the drying time is 3 - 14 h.

[0045] Preferably, the debinding temperature is 20 - 40 °C; the soaking time is 10 - 20 h; the drying temperature is 40 - 60 °C; the drying time is 6 - 8 h.

[0046] The thermal debinding-pressure sintering in step (5) is an integrated process: the green compact thermal debinding adopts a gradient thermal debinding process. In the first step, first evacuate the sintering chamber to a pressure less than 1000 Pa, preferably less than 100 Pa, without introducing reducing gas, then heat at a heating rate of 1.0 - 5.0 °C / min to 120 - 350 °C, and finally hold for 30 - 80 min. In the second step, first, under the condition that the thermal debinding in the first step is completed, introduce reducing gas at a flow rate less than or equal to 0.4 m 3 / h and control the furnace pressure to 20 - 90 KPa, preferably 20 - 60 KPa, and the preferred flow rate is less than or equal to 0.3 m 3 / h, and the preferred reducing gas is H2, then heat at a heating rate of 1.0 - 8.0 °C / min to 400 - 800 °C, and finally hold for 30 - 120 min to obtain a thermally debound blank with complete removal of the organic binder. For pressure sintering, first use an inert gas to completely remove the reducing gas introduced during thermal debinding. The preferred inert gas is Ar, evacuate to a pressure in the sintering chamber less than 1000 Pa, preferably less than 100 Pa. Secondly, heat the thermally debound blank to a sintering temperature of 1150 - 1500 °C at a heating rate of 0.5 - 10 °C / min, then introduce Ar to pressurize to 5 - 10 MPa, preferably 6 - 8 MPa, during sintering holding, and the pressurizing time is 30 - 180 min. Finally, cool to room temperature at a cooling rate of 10 - 20 °C / min to obtain an ultrafine-grained cemented carbide solid part.

[0047] In the present invention, vacuum debinding is first carried out at 120 - 350 °C and then thermal debinding is carried out at 400 - 800 °C with appropriate reduction pressure, which can improve the quality of the debound blank as much as possible and provide necessary conditions for obtaining high-density, high-hardness, and high-strength products subsequently.

[0048] Further preferably, for the gradient thermal debinding process, the heating rate in the first step is 1.0 - 3.0 °C / min, heat to 180 - 320 °C, and the holding time is 40 - 60 min. In the second step, heat at a heating rate of 1.0 - 6.0 °C / min to 450 - 750 °C, and the holding time is 40 - 90 min.

[0049] Further preferably, the heating rate for pressure sintering is 1.0 - 8.0 °C / min, the sintering temperature is 1250 - 1400 °C, and the sintering pressurizing time is 60 - 120 min.

[0050] The present invention provides an additive manufacturing high-performance ultrafine-grained cemented carbide. By compounding and adding a small amount of Cr3C2 and CeO2, the mass fraction ratio of Cr3C2 and CeO2 is strictly controlled to be 5:3 to 5:6. At the same time, the organic binder system and MEX printing parameters are regulated to improve the surface quality of the MEX microfilament, reduce the MEX defects of the cemented carbide green body, improve the green body quality and relative density. By synergistically controlling the cemented carbide composition and the MEX-DS process, the abnormal growth of the WC grains of the hard phase is inhibited. At the same time, nano-second-phase particles in-situ generated by Cr3C2 and CeO2 realize the synergistic improvement of hardness, transverse rupture strength and fracture toughness. The prepared WC-9Co ultrafine-grained cemented carbide has an average WC grain size of less than 330 nm, a hardness greater than 2250 HV 30 , a transverse rupture strength greater than 3900 MPa, and a fracture toughness greater than 14.2 MPa·m 1 / 2 .

[0051] In the present invention, by controlling the total amount of the grain growth inhibitor powder + rare earth oxide powder to be 0.50 to 0.95% including 0.70 to 0.90%, and the ratio between the two, a high-performance ultrafine-grained cemented carbide with a hardness greater than 2250 HV is obtained for the first time 30 , a transverse rupture strength greater than 3900 MPa, and a fracture toughness greater than 14.2 MPa·m 1 / 2 .

[0052] Advantages and positive effects of the present invention:

[0053] (1) The present invention provides an additive manufacturing high-performance ultrafine-grained cemented carbide. By controlling the cemented carbide composition and the organic binder system and their synergy with the MEX-DS process, the surface quality of the MEX microfilament is improved, the MEX defects of the cemented carbide green body are reduced, the green body quality and relative density are improved, the cemented carbide defects are reduced, the relative density and quality are improved, the abnormal growth of WC grains is inhibited, and an ultrafine-grained cemented carbide with fine WC grains and uniform microstructure is prepared, effectively solving the problem of mutual restriction between the hardness and fracture toughness of the additive manufacturing ultrafine WC-Co cemented carbide, and realizing the synergistic improvement of hardness, transverse rupture strength and fracture toughness. The present invention has no special requirements for the raw material powder, uses common cemented carbide powder raw materials, has low cost, simple method, and is suitable for batch production.

[0054] (2) The cemented carbide composition designed in the present invention strictly optimizes the types of GGI and rare earth oxides, and at the same time controls the mass fraction and ratio of the composite addition, effectively regulating the content of in-situ generated nano second-phase particles. At the same time, paraffin is added to the cemented carbide powder composition to fully coat the powder, avoiding the oxygen absorption and oxidation of the cemented carbide powder and the organic binder, effectively eliminating problems such as powder oxidation and decarburization caused by oxygen absorption during the preparation process, and preparing an MEX printing feedstock with low oxygen content and uniform dispersion, which can effectively eliminate the oxidation and decarburization of cemented carbide during the subsequent process.

[0055] (3) The organic binder system designed in the present invention has a high powder loading, good surface quality of the extruded microfilaments, good temperature stability and thermoplasticity, a wide MEX printing process window, and high quality, high relative density and high strength of the printed green body, providing the necessary conditions for obtaining products with high hardness, high density and high strength.

[0056] (4) The MEX-DS process designed in the present invention is integrated. By synergistically regulating the organic binder system, MEX process, solvent debinding-thermal debinding rate, sintering temperature and sintering time, etc., the quality of MEX green body, debound body and sintered sample is improved, the defects of MEX green body are successfully eliminated, debinding cracking, sintering porosity and WC grain coarsening and other defects are avoided, and the prepared cemented carbide product is nearly fully dense, without sintering defects, cracks, low porosity, and without harmful phases such as decarburized phase, free carbon and brittle phase.

[0057] (5) The present invention eliminates the macroscopic defects and sintering defects of cemented carbide by controlling the cemented carbide composition and organic binder system and their synergy with the MEX-DS process, inhibits the growth of hard phase grains, improves the mechanical properties of cemented carbide by using in-situ generated second-phase particles, and the prepared ultrafine-grained cemented carbide product has high relative density, high quality, fine hard phase grains, high hardness and excellent comprehensive mechanical properties.

[0058] (6) The present invention eliminates the macroscopic defects and sintering defects of cemented carbide by the synergy of cemented carbide composition control and MEX-DS process, inhibits the growth of hard phase grains, improves the mechanical properties of cemented carbide by using in-situ generated second-phase particles, and prepares an ultrafine-grained cemented carbide with fine WC grain size, high quality, uniform microstructure and excellent comprehensive mechanical properties. Controlling the total mass fraction of rare earth oxide and GGI to be 0.70 - 0.90%, and the ratio of the two to be 5:3 - 5:6, the average WC grain size of the prepared ultrafine-grained cemented carbide is less than 330 nm, and the microhardness, transverse rupture strength and fracture toughness are respectively greater than 2250 HV 30 、3900 MPa and 14.2 MPa·m 1 / 2, the synergistic improvement of hardness, transverse rupture strength and fracture toughness is achieved, and the comprehensive mechanical properties are significantly better than those of recently reported cemented carbides, as shown in Table 1.

[0059]

[0060] [1] X. Deng, H. Zhang, G. Zhang, Effect of CeO2 and VC co-doping onthe microstructure and properties of WC-10Co cemented carbide, InternationalJournal of Refractory Metals and Hard Materials 108 (2022) 105938.

[0061] [2] B. Wang, J. Jia, Z. Wang, Z. Yin, L. Huang, J. Yuan, Fabricationand performance of graded ultrafine WC–Co cemented carbide tool by one / two-step spark plasma sintering, Ceramics International 47(6) (2021) 8322-8329.

[0062] [3] T. Wolfe, R. Shah, K. Prough, J.L. Trasorras, Coarse cementedcarbide produced via binder jetting 3D printing, International Journal ofRefractory Metals and Hard Materials 110 (2023) 106016.

[0063] [4] Z. Zhao, R. Liu, J. Chen, X. Xiong, Additive manufacturing of cemented carbide using analogous powder injection molding feedstock, International Journal of Refractory Metals and Hard Materials 111 (2023) 106095. Brief Description of the Drawings

[0064] Figure 1 For Example 1 of the present invention, the SEM microstructure of the cemented carbide solid part shows no Co pool, small WC grain size, and uniform microstructure distribution.

[0065] Figure 2 For Example 1 of the present invention, the XRD phase analysis results of the sintered cemented carbide sample show that it is composed of four phases: WC, Co, Cr3C2, and CeO2, without harmful phases such as free carbon, decarburized phase, ternary or multi-component brittle phases.

[0066] Figure 3 For Example 1 of the present invention, the EBSD microstructure of the sintered cemented carbide sample shows that the WC grain size is 323.1 nm, there is no abnormal growth of WC grains, and the microstructure distribution is uniform.

[0067] Figure 4 For Comparative Example 4 of the present invention, the SEM microstructure of the cemented carbide solid part shows that some WC grains have abnormal growth.

[0068] The present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that these embodiments are only for illustration and not for limiting the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims of this application.

[0069] Example 1:

[0070] (1)The composition of the cemented carbide powder consists of 99.1 wt. % WC - 9 wt. % Co, 0.5 wt. % Cr3C2, 0.4 wt. % CeO2, and paraffin. The particle sizes of WC and Co powders are less than 2.0 μm, the particle size of the Cr3C2 powder is less than 1.0 μm, and the particle size of the CeO2 powder is less than 0.5 μm (the particle size distribution is 0.05 - 0.5 μm). Absolute ethanol is used as the ball - milling medium, and it is loaded into a drum ball - mill and ball - milled in a nitrogen atmosphere for 30 h, then vacuum - dried for 12 h and sieved. 1.5 kg is measured and reserved to obtain ultrafine WC - 9 wt. % Co cemented carbide powder;

[0071] (2)Using a vacuum internal mixer, after preheating at 50 °C for 15 min, 15 cm 3 stearic acid, 20 cm 3 low - density polyethylene, 20 cm 3 high - density polyethylene, 10 cm 3 polypropylene, 20 cm 3 paraffin wax (including the amount of paraffin wax added in the ball - milling process), 30 cm 3 palm wax, and 1.5 kg of WC - 9 wt. % Co cemented carbide powder from step (1) are put into the internal mixer chamber of the internal mixer. The vacuum value of the internal mixer is less than 1000 Pa, the rotation speed is 35 r / min, the internal mixing temperature is 160 °C, and the internal mixing time is 2 h to obtain an internal - mixed mixture with a powder loading of 54 vol. %. Then, it is granulated using a granulator. The temperatures of the heating chamber and the discharge port of the granulator are 130 °C and 120 °C respectively, the rotation speed is 50 r / min, and the screw pressure is 10 kg to obtain a printing feedstock with a particle size of 1.5 - 3.5 mm;

[0072] (3)Using material extrusion MEX printing to prepare a cemented carbide green body: Using the granular printing feedstock prepared in step (2) as the raw material, the parameter settings are as follows: the nozzle diameter is 0.4 mm, the nozzle temperature is 150 °C, the printing layer thickness is 0.1 mm, the printing speed is 30 mm / s, the filling flow rate is 60%, the printing trace pattern is [45°, - 45°], the preheating temperature of the substrate is 100 °C, and the obtained cemented carbide green body has high quality and a relative density of about 92.3%.

[0073] (4)Solvent debinding: The cemented carbide green body formed by printing in step (3) is immersed and sealed in n - heptane liquid, and then the n - heptane solution is heated to 40 °C in a water - bath and debound for 14 h, and dried in a drying oven at 50 °C for 6 h.

[0074] (5) Thermal debinding + pressure sintering: Using a thermal debinding - pressure sintering integrated furnace, the cemented carbide green compact obtained from solvent debinding in step (4) is processed using a gradient thermal debinding process. In the first step, the heating rate for thermal debinding is 2.5 °C / min, the debinding temperature is 300 °C, and the holding time is 60 min (the inside of the furnace is in a vacuum state with a pressure less than 1000 Pa); in the second step, first, H2 is introduced at a flow rate of 0.2 m 3 / h, and then it is heated to 720 °C at a heating rate of 2.0 °C / min, and the holding time for debinding is 60 min (the pressure inside the furnace is 60 KPa). Pressure sintering is carried out on the debound blank after thermal debinding: First, Ar is used to remove all H2 in the thermal debinding process, then it is evacuated to a vacuum value less than 100 Pa, secondly, it is heated to the sintering temperature of 1360 °C at a heating rate of 3 °C / min, then Ar is introduced to pressurize to 6 MPa, and the pressurizing time is 60 min; finally, it is cooled to room temperature at a cooling rate of 10 °C / min to obtain a high-performance ultrafine-grained cemented carbide solid part.

[0075] For the sintered sample of ultrafine-grained WC-9Co cemented carbide prepared by the above process, the relative density is 99.77%, the porosity is 0.21%, the porosity detection result is A02B00, the maximum volume of pores detected by Micro–CT scanning is 23.743 μm 3 , and the minimum volume is 0.362 μm 3 ; the average grain size of WC grains is 323.1 nm, no Co pool is formed, and the microstructure is uniform; among the series of samples prepared, the best detected indexes are: the microhardness is 2291 HV 30 , the transverse rupture strength is 3982 MPa, and the fracture toughness is 14.58 MPa·m 1 / 2 .

[0076] Example 2:

[0077] Other conditions are the same as those in Example 1, the differences are: the grain growth inhibitor added is VC, the powder particle size is less than 1.0 μm, the rare earth oxide is Y2O3, the powder particle size is less than 0.5 μm, and the mass ratio remains unchanged. The relative density of the prepared ultrafine-grained WC-9Co cemented carbide solid part is 99.61%, the porosity is 0.38%, the average WC grain size is 346.3 nm, the microhardness is 2211 HV 30 , the transverse rupture strength is 3845 MPa, and the fracture toughness is 14.35 MPa·m 1 / 2 .

[0078] Example 3:

[0079] Other conditions are the same as those in Example 1, except that: the added grain growth inhibitor is TaC powder with a particle size less than 1.0 μm, the rare earth oxide is La2O3, the powder particle size is less than 0.5 μm, and the mass ratio remains unchanged. The relative density of the prepared ultrafine-grained WC-9Co cemented carbide solid part is 99.65%, the porosity is 0.33%, the average grain size of WC is 339.5 nm, and the microhardness is 2238 HV 30 , the transverse rupture strength is 3916 MPa, and the fracture toughness is 14.04 MPa·m 1 / 2 .

[0080] Example 4:

[0081] Other conditions are the same as those in Example 1, except that: the mass ratio of the rare earth oxide CeO2 is increased to 0.6 wt.%, the powder particle size is less than 0.5 μm. The relative density of the prepared ultrafine-grained WC-9Co cemented carbide solid part is 99.40%, the porosity is 0.54%, the average grain size of WC is 399.7 nm, and the microhardness is 2215 HV 30 , the transverse rupture strength is 3717 MPa, and the fracture toughness is 14.97 MPa·m 1 / 2 .

[0082] Example 5

[0083] Other conditions are the same as those in Example 1, except that: in the second step, first introduce H2 at a flow rate of 0.4 m 3 / h, then heat to 720 °C at a heating rate of 2.0 °C / min, and the holding degreasing time is 60 min (the furnace pressure is 80 KPa). The relative density of the prepared ultrafine-grained WC-9Co cemented carbide solid part is 99.2%, the porosity is 0.76%, and the microhardness of the product is 2051 HV 30 , the transverse rupture strength is 3474 MPa, and the fracture toughness is 12.84 MPa·m 1 / 2 .

[0084] As a comparative example, the following are the WC-Co cemented carbides prepared by the MEX additive manufacturing-degreasing sintering process reported in the literature and the comparative experiments of the present invention.

[0085] Comparative Example 1:

[0086] [4] Z. Zhao, R. Liu, J. Chen, X. Xiong, Additive manufacturing of cemented carbide using analogous powder injection molding feedstock, International Journal of Refractory Metals and Hard Materials 111 (2023) 106095.

[0087] WC-8Co cemented carbide prepared by MEX-degreasing sintering by Zhao et al. [4] has a relative density of 99.1%, an average WC grain size of 2.1 μm, and some WC grains grow abnormally. The microhardness, transverse rupture strength, and fracture toughness are 1350 HV 30 , 1624 MPa, and 7.1 MPa·m 1 / 2 , as shown in Table 1.

[0088] Comparative Example 2:

[0089] [5] H. Kim, J.-I. Kim, Y. Do Kim, H. Jeong, S.-S. Ryu, Material extrusion-based three-dimensional printing of WC–Co alloy with a paste prepared by powder coating, Additive Manufacturing 52 (2022) 102679.

[0090] WC-10Co cemented carbide prepared by MEX-degreasing sintering by Kim et al. [5] has a relative density of 99.0%, and some WC grains grow abnormally. The microhardness and fracture toughness are 1690 HV 30 and 10.1 MPa·m 1 / 2 , and the average WC grain size and transverse rupture strength are not reported, as shown in Table 2.

[0091] Comparative Example 3:

[0092] [6] C. Chen, B. Huang, Z. Liu, L. Chen, Y. Li, D. Zou, Y. Chang, X.Cheng, R. Zhou, Y. Liu, Material extrusion additive manufacturing of WC-9Co cemented carbide, Additive Manufacturing 86 (2024) 104203.

[0093] For WC-9Co cemented carbide prepared by Chen et al. [6] using MEX-degreasing sintering, the relative density is 99.7%, the average WC grain size is 1.3 μm, and abnormal growth of some WC grains is observed at the fracture surface. The microhardness, transverse rupture strength and fracture toughness are 1525 HV 30 , 3492 MPa and 20.42 MPa·m 1 / 2 , as shown in Table 2.

[0094] Comparative Example 4:

[0095] The difference from step (1) of Example 1 is that in Comparative Example 4, the grain growth inhibitors Cr3C2 and rare earth oxide CeO2 were not added to the cemented carbide powder as described in step (1) of Example 1, and the WC-9Co cemented carbide raw materials were directly ball-milled. The particle sizes of WC and Co powders are both less than 2.0 μm.

[0096] Other operation steps are the same as those of Example 1.

[0097] After degreasing sintering, microscopic observation and mechanical property tests show that the relative density of the prepared cemented carbide is 98.93%, the porosity is 1.05%, the maximum pore volume by Micro–CT scanning is 152.7 μm 3 , and the minimum volume is 0.599 μm 3 , the average WC grain size is 753.2 nm, a large number of WC grains grow abnormally, and the microhardness, transverse rupture strength and fracture toughness are 1773 HV 30 , 2497 MPa and 9.85 MPa·m 1 / 2 , as shown in Table 2.

[0098] Compared with Example 1, in Comparative Example 4, the grain growth inhibitors Cr3C2 and rare earth oxide CeO2 were not added, resulting in an increase in pore defects, a decrease in relative density, abnormal growth of WC grains, and a decrease in microhardness, transverse rupture strength and fracture toughness by 22.6%, 37.3% and 32.4% respectively.

[0099] Comparative Example 5:

[0100] The difference from step (1) in Example 1 is that in Comparative Example 5, rare earth oxides were not added to the cemented carbide powder according to step (1) in Example 1, and only the grain growth inhibitor Cr3C2 was added. The powder particle size was less than 1.0 μm, and it was ball-milled with WC-9Co cemented carbide.

[0101] Other operating steps were the same as those in Example 1.

[0102] After debinding and sintering, microscopic observation and mechanical property tests showed that the relative density of the prepared cemented carbide was 99.23%, the porosity was 0.76%, and the maximum pore volume by Micro–CT scan was 123.185 μm 3 and the minimum volume was 0.730 μm 3 The average grain size of WC was 542.9 nm, and the microhardness, transverse rupture strength, and fracture toughness were 1879 HV 30 、3140 MPa and 9.39 MPa·m 1 / 2 , as shown in Table 2.

[0103] Comparative Example 6:

[0104] Other conditions were the same as those in Example 1. The difference was that in Comparative Example 6, the mass fraction of rare earth oxide CeO2 was increased to 0.8 wt. %, and the powder particle size was less than 0.5 μm.

[0105] Other operating steps were the same as those in Example 1.

[0106] After debinding and sintering, microscopic observation and mechanical property tests showed that the relative density of the prepared cemented carbide

[0107] was 99.37%, the porosity was 0.62%, partial WC grain abnormal growth occurred, the average grain size was 460.6 nm, and the microhardness was 1923 HV 30 , the transverse rupture strength was 2924 MPa, and the fracture toughness was 11.25 MPa·m 1 / 2 , as shown in Table 2.

[0108] Compared with Example 1, in Comparative Example 4, there was no grain growth inhibitor Cr3C2 and CeO2, resulting in an increase in pore defects, a decrease in relative density, and abnormal growth of some WC grains. The microhardness, transverse rupture strength, and fracture toughness decreased by 22.6%, 37.3%, and 32.4% respectively. Compared with Comparative Example 4, in Comparative Example 5, after adding the grain growth inhibitor Cr3C2, the relative density increased, the WC grain size decreased, and the microhardness and transverse rupture strength increased, but the fracture toughness decreased.

[0109] Compared with the prior art reports and the comparative examples obtained from the comparative experiments of the present invention, the WC-Co cemented carbide prepared by MEX degreasing sintering has a significantly increased relative density, a reduced number of pores, fine WC grain size and uniform microstructure, and the comprehensive mechanical properties are significantly improved.

[0110]

[0111] [4] Z. Zhao, R. Liu, J. Chen, X. Xiong, Additive manufacturing of cemented carbide using analogous powder injection molding feedstock, International Journal of Refractory Metals and Hard Materials 111 (2023) 106095.

[0112] [5] H. Kim, J.-I. Kim, Y. Do Kim, H. Jeong, S.-S. Ryu, Material extrusion-based three-dimensional printing of WC–Co alloy with a paste prepared by powder coating, Additive Manufacturing 52 (2022) 102679.

[0113] [6] C. Chen, B. Huang, Z. Liu, L. Chen, Y. Li, D. Zou, Y. Chang, X. Cheng, R. Zhou, Y. Liu, Material extrusion additive manufacturing of WC-9Co cemented carbide, Additive Manufacturing 86 (2024) 104203.

[0114] Obviously, the above-mentioned Example 1 and Comparative Examples 1, 2, 3, 4, 5 and 6 are only examples for clear illustration, and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. An additive manufacturing high-performance ultrafine-grained cemented carbide, characterized in that: The high-performance ultrafine-grained cemented carbide comprises a hard phase, a metallic binder phase, a transition metal carbide phase, and a rare earth oxide phase; wherein, the mass fraction of the binder metal is 6.0-20.0%, the mass fraction of the grain growth inhibitor is 0.1-3.0%, the mass fraction of the rare earth oxide is 0.1-2.0%, and the balance is the hard phase; its preparation includes the following steps: (1) Ball milling to prepare cemented carbide powder: Mix and ball mill the hard raw material powder, grain growth inhibitor, rare earth oxide, and binder metal raw material powder according to the designed content to obtain a uniformly dispersed cemented carbide powder; The hard raw material powder is selected from at least one of WC, TiC, Ti(C, N), (W, Ti)C, and (W, Ti, Ta)C; The grain growth inhibitor is selected from at least one of transition metal carbides VC, Cr3C2, TaC, TiC, NbC, ZrC, and SiC; The rare earth oxide is selected from at least one of La2O3, Y2O3, CeO2, Sc2O3, Nd2O3, and Pr6O 11 ; The binder metal raw material powder is selected from at least one of Co and Ni; (2) Kneading-granulating to prepare a printing feedstock: Mix the cemented carbide powder and the organic binder in a designed ratio, load them into the kneading chamber of a kneader for vacuum kneading to obtain a kneaded and uniform mixture of the cemented carbide powder and the organic binder; Load the prepared mixture into a granulator to prepare granular printing feedstock with a particle size of 1-4 mm; (3) Material extrusion (MEX) printing to prepare a green body: Using the granular printing feedstock obtained in step (2) as the raw material, adopt MEX forming equipment to print and prepare a cemented carbide green body; (4) Solvent debinding of the cemented carbide green body: First, soak and debind with n-heptane, and then vacuum dry to obtain a solvent-debound blank; wherein, the soaking and debinding time is determined according to the size of the green body; the debinding temperature, drying temperature, and time are determined according to the characteristic temperatures of the organic binder and the solvent; (5) Thermal debinding-pressure sintering: Perform thermal debinding-pressure sintering on the solvent-debound blank obtained in step (4) to obtain a cemented carbide solid part; during pressure sintering, control the pressure to be greater than or equal to 5 MPa to obtain an ultrafine-grained cemented carbide solid part.

2. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, characterized in that: The hard raw material powder in step (1) is selected from at least one of WC, TiC, Ti(C, N), (W, Ti)C, and (W, Ti, Ta)C; The particle size D of the cemented carbide powder described in step (1) 50 is less than 2.0 μm; the particle size D of the bonded metal raw material powder 50 is less than 2.0 μm, and the mass fraction is 6.0 - 20.0%; the particle size D of the grain growth inhibitor powder 50 is less than 1.0 μm, the powder mass fraction is 0.1 - 3.0%, preferably 0.1 - 1.0%; the particle size D of the rare earth oxide powder 50 is less than 1.0 μm, the powder mass fraction is 0.1 - 2.0%, preferably 0.1 - 1.0%; the balance is the hard raw material powder.

3. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, characterized in that: The grain growth inhibitor is preferably at least one of transition metal carbides VC, Cr3C2, and TaC, more preferably Cr3C2; the rare earth oxide is preferably at least one of La2O3, Y2O3, and CeO2, with a preferred mass fraction of 0.1-2.0%, preferably 0.1-1.0%; the mass fraction ratio of Cr3C2 and CeO2 is 5:2-5:8, preferably 5:3-5:

6.

4. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, wherein: In the printing feedstock in step (2), the volume proportion of the cemented carbide powder is 40-75%, and the volume proportion of the organic binder is 25-60%. Here, the volume proportion of the cemented carbide powder is defined as the powder loading.

5. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, characterized in that: The kneading parameters in step (2) are: the kneading temperature is 100 - 200 °C, the rotation speed is 30 - 100 rpm, the kneading time is 30 - 300 min, and it is completed in a vacuum environment.

6. An additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, characterized in that: The printing feed granulation parameters described in step (2) are: the screw rotation speed is 30 - 100 rpm, the screw pressure is 3 - 10 kg, and the diameter of the obtained granules is 1 - 4 mm.

7. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, wherein: The hard alloy green body MEX printing process parameters described in step (3) are: the nozzle diameter is 0.1 - 0.8 mm, the printing temperature is 120 - 200 °C, the printing layer thickness is 0.05 - 0.8 mm, the printing speed is 15 - 75 mm / s, the filling flow rate is 50 - 130%, the filling method is one of [0°, 90°], [45°, -45°], or a combination of the two filling methods, and the substrate preheating temperature is 50 - 150 °C.

8. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, characterized in that: In the solvent debinding process described in step (4), the green body prepared by MEX in step (3) is soaked in n - heptane for 5 - 30 h for debinding and then dried; among them: the debinding temperature of n - heptane is 10 - 50 °C; the soaking time is 5 - 30 h; the drying temperature is 40 - 80 °C; the drying time is 3 - 14 h.

9. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, wherein: The step (5) of green body thermal debinding-pressure sintering is an integrated process of thermal debinding-pressure sintering: The green body thermal debinding adopts a gradient thermal debinding process. In the first step, the sintering chamber is first evacuated to a pressure less than 1000 Pa without introducing reducing gas, and then heated at a heating rate of 1.0 - 5.0 °C / min to 120 - 350 °C and held for 30 - 80 min. In the second step, first, reducing gas is introduced at a flow rate less than or equal to 0.4 m 3 / h and the furnace pressure is controlled to be 20 - 90 KPa under the condition that the thermal debinding in the first step is completed, then heated at a heating rate of 1.0 - 8.0 °C / min to 400 - 800 °C, and finally held for 30 - 120 min to obtain a thermally debound blank with the organic binder completely removed. For pressure sintering, first, the reducing gas introduced in the thermal debinding process is removed completely using inert gas, and the sintering chamber is evacuated to a pressure less than 1000 Pa. Secondly, the thermally debound blank is heated to a sintering temperature of 1150 - 1500 °C at a heating rate of 0.5 - 10 °C / min, then inert gas is introduced during sintering holding to pressurize to 5 - 10 MPa, and the pressurizing time is 30 - 180 min. Finally, it is cooled to room temperature at a cooling rate of 10 - 20 °C / min to obtain an ultrafine-grained cemented carbide solid part.

10. The additive manufacturing high-performance ultrafine-grained cemented carbide according to claim 1, characterized in that: The prepared WC-Co ultrafine-grained cemented carbide has an average WC grain size of less than 330 nm, a hardness of greater than 2250 HV 30 , a transverse rupture strength of greater than 3900 MPa, and a fracture toughness of greater than 14.2 MPa·m 1 / 2 .

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