Ultra-coarse-grained WC-Co cemented carbide and preparation method thereof

Abstract

The invention relates to the technical field of powder metallurgy, and specifically discloses an ultra-coarse-grained WC-Co cemented carbide and a preparation method thereof. The method comprises the following steps: step S1, preparing the following raw materials in parts by weight: 4.6-9.2 parts of cobalt powder, 96-102 parts of coarse-grained tungsten carbide powder, 3.6-5.2 parts of functionalized gel, 3.4-4.6 parts of modified penetration enhancer, 2.2-2.8 parts of binder and 36-62 parts of organic solvent; step S2, preparing a mixture; step S3, granulation treatment; step S4, compacting; and step S5, pressurizing sintering. The functionalized gel and the modified penetration enhancer are added to the functionalized gel, wherein the functionalized gel contains components such as yttrium trioxide, polytannic acid, ultra-fine tungsten carbide, tantalum carbide, chromium carbide and silica gel. The functionalized gel not only has excellent physical properties itself, but can also be cross-linked with the modified penetration enhancer to form a denser silicon dioxide network structure, thereby improving the hardness, toughness, impact resistance and wear resistance of the alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of powder metallurgy, and in particular to an ultra-coarse-grained WC-Co cemented carbide and a preparation method thereof. Background Art

[0002] WC-Co cemented carbide has the advantages of high hardness, excellent wear resistance and good impact fracture toughness. Among them, ultra-coarse-grained cemented carbide exhibits excellent wear resistance, thermal fatigue resistance and thermal shock resistance under extreme working conditions and continuous operation. It is widely used in mining tools, steel rolling rollers and cemented carbide stamping dies.

[0003] The nanopowder activation method is to add fine-grained WC powder to coarse-grained WC powder, and perform conventional ball milling and sintering to prepare ultra-coarse cemented carbide. However, due to the high surface energy of nanopowder, it is easy to agglomerate during the preparation and activation process to form secondary particles. The agglomerates have many pores inside, and internal defects are easily generated during sintering, resulting in poor performance of the prepared alloy.

[0004] Therefore, how to prepare an ultra-coarse-grained WC-Co cemented carbide with excellent performance is a technical problem that needs to be solved at present. Summary of the Invention

[0005] In order to solve the problems mentioned in the above background technology, the present invention provides an ultra-coarse-grained WC-Co cemented carbide and a preparation method thereof.

[0006] A method for preparing ultra-coarse-grained WC-Co cemented carbide comprises the following steps:

[0007] Step S1, preparing the following raw materials by weight: 4.6-9.2 parts of cobalt powder, 96-102 parts of coarse-crystalline tungsten carbide powder, 3.6-5.2 parts of functionalized gel, 3.4-4.6 parts of modified penetration enhancer, 2.2-2.8 parts of binder, and 36-62 parts of organic solvent;

[0008] Step S2, preparation of a mixture: adding coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, binder, and organic solvent to a rolling ball mill according to parts by weight, ball milling for 14-20 hours, drying, and sieving to obtain a mixture, wherein the ball milling conditions are: a ball-to-material ratio of 4-6:1, a ball speed of 60-80 rpm; drying conditions are: drying at 80-88° C. for 5-7 hours; and the sieve mesh size is 320-360 mesh.

[0009] Step S3, granulation treatment: the mixture prepared in step S2 is sieved, and then placed in a granulator and rolled for 4-6 minutes for granulation treatment;

[0010] Step S4, green compacting: pressing the granulated mixture in step S3 into green compacts;

[0011] Step S5, pressure sintering: the green body prepared in step S4 is pressure sintered into ultra-coarse grained WC-Co cemented carbide.

[0012] Preferably, in step S4, the pressing pressure is 160-180 MPa.

[0013] Preferably, in step S5, the pressed green body is sintered under pressurized conditions. During sintering, the temperature is first increased to 370-430°C at a heating rate of 4-8°C / min under vacuum, and kept warm for 12-18min. Then, the temperature is increased to 1480-1560°C at a heating rate of 14-18°C / min, and kept warm in vacuum for 20-26min. Then, the pressure is increased to 35-45MPa at a rate of 6-8MPa / min. At the same time, the temperature is increased to 1770-1830°C at a heating rate of 20-24°C / min, and then the pressure is increased to 84Mpa at a pressurizing rate of 12-16MPa / min, and kept warm for 2.2-2.6h.

[0014] Preferably, the binder is CP60 long-chain chlorinated paraffin.

[0015] Preferably, the organic solvent is anhydrous ethanol.

[0016] Preferably, the functionalized gel is prepared by the following steps:

[0017] Step A1, adding yttrium trioxide to a hydrochloric acid aqueous solution, stirring evenly, adding tannic acid, raising the temperature to 35-45° C., stirring and reacting for 3-5 hours, filtering, washing, and drying to obtain pretreated yttrium trioxide, wherein the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution, and tannic acid is 2-4:40-60:3-6. During the above process, tannic acid self-polymerizes on the surface of yttrium trioxide to form a polytannic acid layer on the surface of yttrium trioxide, thereby imparting excellent adhesion to yttrium trioxide;

[0018] Step A2, adding pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide and chromium carbide to the mixed acid, stirring evenly, adjusting the pH to 8-9, stirring for 25-35 minutes, heating to 90-110° C., stirring and reacting for 2-3 hours, and cooling to room temperature to obtain modified yttrium trioxide, wherein the mass ratio of pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide and mixed acid is 1-3:0.04-0.06:0.01-0.03:0.022-0.034:45-55;

[0019] Step A3: uniformly mix the modified yttrium trioxide and the crosslinking agent, add the silicon precursor and anhydrous ethanol, stir until gelation occurs, remove the gel, wash, and dry to obtain a functionalized gel, wherein the mass ratio of the modified yttrium trioxide, the crosslinking agent, the silicon precursor, and the anhydrous ethanol is 3-5:2.4-3.2:0.4-0.6:16-22.

[0020] Preferably, in step A1, the mass fraction of the hydrochloric acid aqueous solution is 6-10%.

[0021] Preferably, in step A2, the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1-2:3.

[0022] Preferably, in step A3, the crosslinking agent is propylene oxide butyl ether, and the silicon precursor is tetraethyl orthosilicate.

[0023] Preferably, the modified penetration enhancer is prepared by the following steps:

[0024] Step B1, mixing nano hexagonal boron nitride and alkali solution uniformly, heating to 100-120° C., stirring and reacting for 40-50 hours, centrifuging, washing and drying the precipitate to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to alkali solution is 2.2-3.2:500-600;

[0025] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, and add it dropwise to the aqueous solution of aluminum dihydrogen phosphate while stirring. The dripping is controlled to be completed within 15 minutes. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 60-70°C, and the reaction is stirred for 4-6 hours to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF (N,N-dimethylformamide), aqueous solution of aluminum dihydrogen phosphate and polyvinyl alcohol is 3-5:60-70:20-30:0.2-0.6.

[0026] Preferably, in step B1, the alkali solution is a sodium hydroxide aqueous solution with a mass fraction of 50-60%.

[0027] Preferably, the mass fraction of the aluminum dihydrogen phosphate aqueous solution is 35-45%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] In the technical solution of the present invention, the polytannic acid layer can not only be adsorbed on the surface of yttrium trioxide through hydrogen bonding or coordination to form a spatial steric hindrance layer, but also can adsorb ultrafine tungsten carbide and tantalum carbide to the surface of pretreated yttrium trioxide as a synthesis site for ultrafine tungsten carbide, tantalum carbide and chromium carbide, and yttrium trioxide has excellent fluidity. During the sintering process of WC-Co cemented carbide, it can be filled into the pores of WC-Co cemented carbide to improve the density and the wear resistance of WC-Co cemented carbide; ultrafine tungsten carbide and tantalum carbide are formed on the surface of pretreated yttrium trioxide, and the ultrafine tungsten carbide, tantalum carbide and chromium carbide formed, wherein the ultrafine tungsten carbide can not only increase the grain boundary area, but also hinder dislocation. Movement, improve the hardness of the alloy material, and it can also delay crack propagation through crack deflection and bridging mechanism, improve the toughness of the alloy material, the presence of tantalum carbide can not only further improve the toughness of the alloy material by promoting crack bifurcation and grain boundary sliding, but also refine the tungsten carbide grains, synergistically improve the hardness, toughness, impact resistance and wear resistance, the presence of chromium carbide can not only refine the tungsten carbide grains to make the crack propagation path more tortuous and improve toughness, but also it partially dissolves in the cobalt binder phase during sintering, precipitates chromium elements and enriches them at the cobalt / tungsten carbide interface or grain boundary, forming a high-energy barrier, hindering the diffusion of W atoms from WC particles to the Co phase, further improving the toughness of WC-Co cemented carbide;

[0030] In the technical solution of the present invention, modified yttrium trioxide is embedded in the silica gel network structure to achieve fixation of the modified yttrium trioxide, further improving the dispersibility of the modified yttrium trioxide in the ultra-coarse-grained WC-Co cemented carbide: the gel is filled into the ultra-coarse-grained WC-Co cemented carbide system, granulated and pressed to form a green body, the silica gel not only has high compressive strength itself, but also the silica in the silica gel reacts with tungsten and cobalt to form silicide, which can reduce the solubility of tungsten in cobalt, inhibit the dissolution-precipitation process of tungsten carbide grains, and improve the hardness and toughness of the WC-Co cemented carbide. At the same time, the Si-O-Si bonds between the gels are further strengthened and cross-linked, and a denser silica network structure can be formed in the ultra-coarse-grained WC-Co cemented carbide system, so that the ultra-coarse-grained WC-Co cemented carbide is firmly bonded together through the silica network structure, further improving the hardness, toughness, impact resistance and wear resistance of the WC-Co cemented carbide;

[0031] In the technical solution of the present invention, nano boron nitride is first modified by hydroxylation to obtain modified boron nitride, which is then uniformly mixed with an aqueous solution of aluminum dihydrogen phosphate and polyvinyl alcohol to obtain a modified penetration enhancer. The presence of hydroxy boron nitride can not only reduce stress concentration, but also make the grain size distribution of tungsten carbide more uniform, increase the grain boundary area, hinder dislocation movement, and improve the hardness, toughness, impact resistance and wear resistance of ultra-coarse-grained WC-Co cemented carbide; in addition, hydroxy boron nitride can also produce hydrogen bonds with the hydroxyl groups on the surface of the functionalized gel, thereby improving the compatibility and further improving the hardness of the ultra-coarse-grained WC-Co cemented carbide. , toughness, impact resistance and wear resistance; aluminum dihydrogen phosphate can form a network structure in aqueous solution, which helps to wrap the modified boron nitride particles and prevent them from agglomerating, thereby improving the dispersion performance. At the same time, the hydroxyl groups on the polyvinyl alcohol molecular chain can undergo condensation reaction with the hydroxyl groups on the surface of nano-silica in the functionalized gel to form stable Si-OC covalent bonds, thereby cross-linking the polyvinyl alcohol molecules to form a three-dimensional network structure. Introducing it into ultra-coarse-grained WC-Co cemented carbide can synergize with the functionalized gel to jointly improve the hardness, toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide. DETAILED DESCRIPTION

[0032] In order to make the embodiments of the present invention easier to understand, the present invention will be described in detail below with reference to specific examples. These examples are only for illustration and do not limit the scope of application of the present invention.

[0033] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in this field or the product instructions were used. Reagents or instruments used without manufacturer specified were all conventional products that can be purchased through regular channels.

[0034] Coarse-grained tungsten carbide powder was produced by Hebei Huazuan Alloy Welding Materials Co., Ltd., with a CAS number of 12070-13-2, a brand of HZ-WC-2, and a mesh size of 60 mesh. Cobalt powder was commercially available from Hebei Yirui Alloy Welding Materials Co., Ltd., with a CAS number of Hebei Technology and a brand of Yirui Alloy, using an atomization process. Ultrafine tungsten carbide was produced by Ningbo Luofei Nanotechnology Co., Ltd., with a CAS number of 12070-12-1, and a Fisher average particle size of 100 nm. Yttrium trioxide was produced by Hebei Huazuan Alloy Welding Materials Co., Ltd., with a CAS number of 1314-3. 6-9, brand HZ-Y2O3-1; tantalum carbide is produced by Hebei Yinbai Alloy Welding Materials Co., Ltd., CAS number YB-1; chromium carbide is produced by Qinghe County Tebo Metal Materials Co., Ltd., CAS number TB-1; nano boron nitride is produced by Hebei Teng Bimetallic Materials Co., Ltd., CAS number 10043-11-5, particle size 30-50nm; polyvinyl alcohol is commercially available from Wuhan Runxingyuan Technology Co., Ltd., model PVA1788; CP60 long-chain chlorinated paraffin is CP60 long-chain chlorinated paraffin produced by Xipeng Environmental Protection Technology (Luoyang) Co., Ltd.

[0035] The present invention is further described in detail below with reference to Examples and Comparative Examples.

[0036] Preparation Examples 1-3 and Comparative Preparation Examples 1-2 provide a functionalized gel.

[0037] Preparation Example 1

[0038] This preparation example provides a functionalized gel, which is prepared by the following steps:

[0039] Step A1, adding yttrium trioxide to a 6% mass fraction hydrochloric acid aqueous solution, stirring at a speed of 500 rpm for 12 minutes until uniform, adding tannic acid, heating to 35°C, maintaining the speed unchanged, and continuing to stir and react for 3 hours, filtering, and then washing with anhydrous ethanol and deionized water three times in sequence, and drying at 60°C to constant weight to obtain pretreated yttrium trioxide, wherein the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution and tannic acid is 2:40:3;

[0040] Step A2, adding pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide and chromium carbide to the mixed acid, stirring at a speed of 600 rpm for 20 minutes until uniform, adjusting the pH to 8 with 0.2M ammonia solution, stirring for 25 minutes, heating to 90°C, maintaining the speed unchanged, continuing to stir and react for 2 hours, and cooling to room temperature to obtain modified yttrium trioxide, wherein the mass ratio of pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide and mixed acid is 1:0.04:0.01:0.022:45, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1:3;

[0041] Step A3, the modified yttrium trioxide and propylene oxide butyl ether were stirred at a speed of 700 rpm for 16 minutes until uniform, tetraethyl orthosilicate and anhydrous ethanol were added, and stirred until gelation occurred. The gel was removed, washed three times with deionized water, and dried at 60°C to constant weight to obtain a functionalized gel, wherein the mass ratio of modified yttrium trioxide, propylene oxide butyl ether, tetraethyl orthosilicate and anhydrous ethanol was 3:2.4:0.4:16.

[0042] Preparation Example 2

[0043] This preparation example provides a functionalized gel, which is prepared by the following steps:

[0044] Step A1, adding yttrium trioxide to an 8% by mass aqueous solution of hydrochloric acid, stirring at a speed of 540 rpm for 16 minutes until uniform, adding tannic acid, heating to 40°C, stirring and reacting for 4 hours, filtering, then washing with anhydrous ethanol and deionized water four times, and drying at 65°C to constant weight to obtain pretreated yttrium trioxide, wherein the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution and tannic acid is 3:50:4.5;

[0045] Step A2, adding pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide and chromium carbide to the mixed acid, stirring at a speed of 630 rpm for 22 minutes until uniform, adjusting the pH to 8.5 with 0.4M ammonia solution, stirring for 30 minutes, heating to 100°C, maintaining the speed unchanged, continuing to stir and react for 2.5 hours, and cooling to room temperature to obtain modified yttrium trioxide, wherein the mass ratio of pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide and mixed acid is 2:0.05:0.02:0.028:50, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1.5:3;

[0046] Step A3, the modified yttrium trioxide and propylene oxide butyl ether were stirred at a speed of 720 rpm for 18 minutes until uniform, tetraethyl orthosilicate and anhydrous ethanol were added, and stirred until gelation occurred. The gel was removed, washed with deionized water 4 times, and dried at 65°C to constant weight to obtain a functionalized gel, wherein the mass ratio of modified yttrium trioxide, propylene oxide butyl ether, tetraethyl orthosilicate and anhydrous ethanol was 4:2.8:0.5:19.

[0047] Preparation Example 3

[0048] This preparation example provides a functionalized gel, which is prepared by the following steps:

[0049] Step A1, adding yttrium trioxide to a 10% mass fraction hydrochloric acid aqueous solution, stirring at a speed of 580 rpm for 20 minutes until uniform, adding tannic acid, heating to 45°C, stirring and reacting for 5 hours, filtering, then washing with anhydrous ethanol and deionized water 5 times in sequence, and drying at 70°C to constant weight to obtain pretreated yttrium trioxide, wherein the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution and tannic acid is 4:60:6;

[0050] Step A2, adding pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide and chromium carbide to a mixed acid, stirring at a speed of 660 rpm for 24 minutes until uniform, adjusting the pH to 9 with a 0.6M ammonia solution, stirring for 35 minutes, heating to 110°C, maintaining the speed unchanged, continuing to stir and react for 3 hours, and cooling to room temperature to obtain modified yttrium trioxide, wherein the mass ratio of the pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, and chromium carbide mixed acid is 3:0.06:0.03:0.034:55, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 2:3;

[0051] Step A3, the modified yttrium trioxide and propylene oxide butyl ether were stirred at a speed of 740 rpm for 20 minutes until uniform, tetraethyl orthosilicate and anhydrous ethanol were added, and stirred until gelation occurred. The gel was removed, washed with deionized water 5 times, and dried at 70°C to constant weight to obtain a functionalized gel, wherein the mass ratio of modified yttrium trioxide, propylene oxide butyl ether, tetraethyl orthosilicate and anhydrous ethanol was 5:3.2:0.6:22.

[0052] Comparative Preparation Example 1

[0053] This comparative preparation example provides a functionalized gel, which is prepared by the following steps:

[0054] Step A1, adding yttrium trioxide to a 6% mass fraction hydrochloric acid aqueous solution, stirring at a speed of 500 rpm for 12 minutes until uniform, adding malic acid, heating to 35°C, maintaining the speed unchanged, and continuing to stir and react for 3 hours, filtering, and then washing with anhydrous ethanol and deionized water three times in sequence, and drying at 60°C to constant weight to obtain pretreated yttrium trioxide, wherein the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution and malic acid is 2:40:3;

[0055] Step A2, adding pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide and chromium carbide to the mixed acid, stirring at a speed of 600 rpm for 20 minutes until uniform, adjusting the pH to 8 with 0.2M ammonia solution, stirring for 25 minutes, heating to 90°C, maintaining the speed unchanged, continuing to stir and react for 2 hours, and cooling to room temperature to obtain modified yttrium trioxide, wherein the mass ratio of pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide and mixed acid is 1:0.04:0.01:0.022:45, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1:3;

[0056] Step A3, the modified yttrium trioxide and propylene oxide butyl ether were stirred at a speed of 700 rpm for 16 minutes until uniform, tetraethyl orthosilicate and anhydrous ethanol were added, and stirred until gelation occurred. The gel was removed, washed three times with deionized water, and dried at 60°C to constant weight to obtain a functionalized gel, wherein the mass ratio of modified yttrium trioxide, propylene oxide butyl ether, tetraethyl orthosilicate and anhydrous ethanol was 3:2.4:0.4:16.

[0057] Comparative Preparation Example 2

[0058] This comparative preparation example provides a functionalized gel, which is prepared by the following steps:

[0059] Step A1, adding yttrium trioxide to a 6% mass fraction hydrochloric acid aqueous solution, stirring at a speed of 500 rpm for 12 minutes until uniform, adding tannic acid, heating to 35°C, maintaining the speed unchanged, and continuing to stir and react for 3 hours, filtering, and then washing with anhydrous ethanol and deionized water three times in sequence, and drying at 60°C to constant weight to obtain pretreated yttrium trioxide, wherein the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution and tannic acid is 2:40:3;

[0060] Step A2, adding pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide and chromium carbide to the mixed acid, stirring at a speed of 600 rpm for 20 minutes until uniform, adjusting the pH to 8 with 0.2M ammonia solution, stirring for 25 minutes, heating to 90°C, maintaining the speed unchanged, continuing to stir and react for 2 hours, and cooling to room temperature to obtain modified yttrium trioxide, wherein the mass ratio of pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide and mixed acid is 1:0.04:0.01:0.022:45, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1:3;

[0061] Step A3, the modified yttrium trioxide and propylene oxide butyl ether were stirred at a speed of 700 rpm for 16 minutes until uniform, nano-silica and anhydrous ethanol were added, and stirred until gelation occurred. The gel was removed, washed with deionized water three times, and dried at 60°C to constant weight to obtain a functionalized gel, wherein the mass ratio of modified yttrium trioxide, propylene oxide butyl ether, nano-silica and anhydrous ethanol was 3:2.4:0.4:16.

[0062] Preparation Examples 4-6 and Comparative Preparation Examples 3-5 provide a modified penetration enhancer.

[0063] Preparation Example 4

[0064] This preparation example provides a modified penetration enhancer, which is prepared by the following steps:

[0065] Step B1, stirring nano hexagonal boron nitride and a 50% sodium hydroxide aqueous solution at a speed of 600 rpm for 14 minutes until uniform, heating to 100°C, maintaining the speed unchanged, continuing to stir and react for 40 hours, centrifuging, washing the precipitate with anhydrous ethanol three times, and drying at 60°C to constant weight to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to the 50% sodium hydroxide aqueous solution is 2.2:500;

[0066] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency to 40kHz, the ultrasonic power to 600w, the ultrasonication for 16min, control the speed to 660rpm, and add it dropwise to a 35% by mass fraction of aluminum dihydrogen phosphate aqueous solution while stirring. The dripping is controlled within 15min. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 60°C, the speed is maintained unchanged, and the stirring reaction is continued for 4h to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution and polyvinyl alcohol is 3:60:20:0.2.

[0067] Preparation Example 5

[0068] This preparation example provides a modified penetration enhancer, which is prepared by the following steps:

[0069] Step B1, stirring nano hexagonal boron nitride and a 55% sodium hydroxide aqueous solution at a speed of 640 rpm for 18 minutes until uniform, heating to 110°C, maintaining the speed unchanged, continuing stirring and reacting for 45 hours, centrifuging, washing the precipitate with anhydrous ethanol four times, and drying at 65°C to constant weight to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to the 55% sodium hydroxide aqueous solution is 2.7:550;

[0070] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency to 35kHz, the ultrasonic power to 550w, the ultrasonication for 20min, control the speed to 680rpm, and add a 40% mass fraction of aluminum dihydrogen phosphate aqueous solution while stirring. The dripping is controlled within 15min. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 65°C, the speed is maintained unchanged, and the stirring reaction is continued for 5h to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution and polyvinyl alcohol is 4:65:25:0.4.

[0071] Preparation Example 6

[0072] This preparation example provides a modified penetration enhancer, which is prepared by the following steps:

[0073] Step B1, stirring nano hexagonal boron nitride and a 60% sodium hydroxide aqueous solution at a speed of 680 rpm for 22 minutes until uniform, heating to 120°C, stirring and reacting for 50 hours, centrifuging, washing the precipitate with anhydrous ethanol 5 times, and drying at 70°C to constant weight to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to the 60% sodium hydroxide aqueous solution is 3.2:600;

[0074] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency to 30kHz, the ultrasonic power to 500w, the ultrasonication for 24min, control the speed to 700rpm, and add a 45% mass fraction of aluminum dihydrogen phosphate aqueous solution while stirring. The dripping is controlled within 15min. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 70°C, the speed is maintained unchanged, and the stirring reaction is continued for 6h to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution and polyvinyl alcohol is 5:70:30:0.6.

[0075] Comparative Preparation Example 3

[0076] This comparative preparation example provides a modified penetration enhancer, which is prepared by the following steps:

[0077] Step B1, stirring nano hexagonal boron nitride and deionized water at a speed of 600 rpm for 14 minutes until uniform, heating to 100°C, maintaining the speed unchanged, continuing stirring and reacting for 40 hours, centrifuging, washing the precipitate with anhydrous ethanol three times, and drying at 60°C to constant weight to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to deionized water is 2.2:500;

[0078] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency to 40kHz, the ultrasonic power to 600w, the ultrasonic for 16min, control the speed to 660rpm, and add a 35% mass fraction of aluminum dihydrogen phosphate aqueous solution while stirring. The dripping is controlled within 15min. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 60°C, the speed is maintained unchanged, and the stirring reaction is continued for 4h to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution and polyvinyl alcohol is 3:60:20:0.2.

[0079] Comparative Preparation Example 4

[0080] This comparative preparation example provides a modified penetration enhancer, which is prepared by the following steps:

[0081] Step B1, stirring nano hexagonal boron nitride and a 50% sodium hydroxide aqueous solution at a speed of 600 rpm for 14 minutes until uniform, heating to 100°C, maintaining the speed unchanged, continuing to stir and react for 40 hours, centrifuging, washing the precipitate with anhydrous ethanol three times, and drying at 60°C to constant weight to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to the 50% sodium hydroxide aqueous solution is 2.2:500;

[0082] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency to 40kHz, the ultrasonic power to 600w, the ultrasonication for 16min, control the speed to 660rpm, and add a 35% mass fraction of aluminum dihydrogen phosphate aqueous solution dropwise while stirring. The dripping is controlled within 15min. After the dripping is completed, anhydrous ethanol is added, the temperature is raised to 60°C, the speed is maintained unchanged, and the stirring reaction is continued for 4h to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution and anhydrous ethanol is 3:60:20:0.2.

[0083] Comparative Preparation Example 5

[0084] This comparative preparation example provides a modified penetration enhancer, which is prepared by the following steps:

[0085] Step B1, stirring nano hexagonal boron nitride and a 50% sodium hydroxide aqueous solution at a speed of 600 rpm for 14 minutes until uniform, heating to 100°C, maintaining the speed unchanged, continuing to stir and react for 40 hours, centrifuging, washing the precipitate with anhydrous ethanol three times, and drying at 60°C to constant weight to obtain modified boron nitride, wherein the mass ratio of nano hexagonal boron nitride to the 50% sodium hydroxide aqueous solution is 2.2:500;

[0086] Step B2, ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency to 40kHz, the ultrasonic power to 600w, the ultrasonic for 16min, control the speed to 660rpm, and add a 35% mass fraction of disodium hydrogen phosphate aqueous solution while stirring. The dripping is controlled within 15min. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 60°C, the speed is maintained unchanged, and the stirring reaction is continued for 4h to obtain a modified penetration enhancer, wherein the mass ratio of modified boron nitride, anhydrous DMF, disodium hydrogen phosphate aqueous solution and polyvinyl alcohol is 3:60:20:0.2.

[0087] Examples 1-3 and Comparative Examples 1-5 provide a method for preparing an ultra-coarse-grained WC-Co cemented carbide.

[0088] Example 1

[0089] This embodiment provides a method for preparing ultra-coarse-grained WC-Co cemented carbide, comprising the following steps:

[0090] Step S1, preparing the following raw materials in parts by weight: 4.6 parts of cobalt powder, 96 parts of coarse-crystalline tungsten carbide powder, 3.6 parts of the functionalized gel prepared in Preparation Example 1, 3.4 parts of the modified penetration enhancer prepared in Preparation Example 4, 2.2 parts of CP60 long-chain chlorinated paraffin, and 36 parts of anhydrous ethanol;

[0091] Step S2, preparation of a mixture: coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, CP60 long-chain chlorinated paraffin, and anhydrous ethanol were added to a rolling ball mill according to weight, with the ball-to-material ratio controlled at 4:1, the ball speed at 60 rpm, and the ball milling time at 14 h. The mixture was then dried at 80° C. for 5 h and passed through a 320-mesh sieve to obtain a mixture, wherein the ball-to-material ratio of cemented carbide, grinding balls, and solid raw materials was 1:1:1;

[0092] Step S3, granulation treatment: the mixture prepared in step S2 is passed through an 80-mesh sieve, and then placed in a granulator and rolled for 4 minutes for granulation treatment;

[0093] Step S4, green compacting: pressing the granulated mixture in step S3 into a green compact at 160 MPa;

[0094] Step S5, pressure sintering: The green body prepared in step S4 is pressure-sintered into an ultra-coarse-grained WC-Co cemented carbide. During sintering, the temperature is first increased to 370°C at a heating rate of 4°C / min under vacuum, and kept warm for 12 minutes. Then, the temperature is increased to 1480°C at a heating rate of 14°C / min, and kept warm in vacuum for 20 minutes. Then, the pressure is increased to 35MPa at a rate of 6MPa / min. At the same time, the temperature is increased to 1770°C at a heating rate of 20°C / min, and then the pressure is increased to 84Mpa at a pressure increase rate of 12MPa / min, and kept warm for 2.2 hours.

[0095] Example 2

[0096] This embodiment provides a method for preparing ultra-coarse-grained WC-Co cemented carbide, comprising the following steps:

[0097] Step S1, prepare the following raw materials in parts by weight: 6.9 parts of cobalt powder, 99 parts of coarse-crystalline tungsten carbide powder, 4.4 parts of the functionalized gel prepared in Preparation Example 2, 4.0 parts of the modified penetration enhancer prepared in Preparation Example 5, 2.5 parts of CP60 long-chain chlorinated paraffin, and 49 parts of anhydrous ethanol;

[0098] Step S2, preparation of a mixture: coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, CP60 long-chain chlorinated paraffin, and anhydrous ethanol were added to a rolling ball mill according to weight, with the ball-to-material ratio controlled at 5:1, the ball speed at 70 rpm, and the ball milling time at 17 h. The mixture was then placed at 84° C., dried for 6 h, and passed through a 340-mesh sieve to obtain a mixture, wherein the ball-to-material ratio of cemented carbide, grinding balls, and solid raw materials was 1:2:1;

[0099] Step S3, granulation treatment: the mixture prepared in step S2 is passed through a 100-mesh sieve, and then placed in a granulator and rolled for 5 minutes for granulation treatment;

[0100] Step S4, green compacting: pressing the granulated mixture in step S3 into a green compact at 170 MPa;

[0101] Step S5, pressure sintering: The green body prepared in step S4 is pressure-sintered into an ultra-coarse-grained WC-Co cemented carbide. During sintering, the temperature is first increased to 400°C at a heating rate of 6°C / min under vacuum, and kept warm for 15 minutes. Then, the temperature is increased to 1520°C at a heating rate of 16°C / min, and kept warm in vacuum for 23 minutes. Then, the pressure is increased to 40MPa at a rate of 7MPa / min. At the same time, the temperature is increased to 1800°C at a heating rate of 22°C / min, and then the pressure is increased to 84Mpa at a pressure increase rate of 14MPa / min, and kept warm for 2.4 hours.

[0102] Example 3

[0103] This embodiment provides a method for preparing ultra-coarse-grained WC-Co cemented carbide, comprising the following steps:

[0104] Step S1, prepare the following raw materials in parts by weight: 9.2 parts of cobalt powder, 102 parts of coarse-crystalline tungsten carbide powder, 5.2 parts of the functionalized gel prepared in Preparation Example 3, 4.6 parts of the modified penetration enhancer prepared in Preparation Example 6, 2.8 parts of CP60 long-chain chlorinated paraffin, and 62 parts of anhydrous ethanol;

[0105] Step S2, preparation of a mixture: coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, CP60 long-chain chlorinated paraffin, and anhydrous ethanol were added to a rolling ball mill according to weight, with the ball-to-material ratio controlled at 6:1, the ball speed at 80 rpm, and the ball milling time at 20 h. The mixture was then placed at 88° C., dried for 7 h, and passed through a 360-mesh sieve to obtain a mixture, wherein the ball-to-material ratio of cemented carbide, grinding balls, and solid raw materials was 1:3:1;

[0106] Step S3, granulation treatment: the mixture prepared in step S2 is passed through a 120-mesh sieve, and then placed in a granulator and rolled for 6 minutes for granulation treatment;

[0107] Step S4, green compacting: pressing the granulated mixture in step S3 into a green compact at 180 MPa;

[0108] Step S5, pressurized sintering: The green body prepared in step S4 is pressurized and sintered into an ultra-coarse-grained WC-Co cemented carbide. During sintering, the temperature is first increased to 430°C at a heating rate of 8°C / min under vacuum, and kept warm for 18 minutes. Then, the temperature is increased to 1560°C at a heating rate of 18°C / min, and kept warm in vacuum for 26 minutes. Then, the pressure is increased to 45MPa at a rate of 8MPa / min. At the same time, the temperature is increased to 1830°C at a heating rate of 24°C / min, and then the pressure is increased to 84Mpa at a pressurizing rate of 16MPa / min, and kept warm for 2.6 hours.

[0109] Comparative Example 1

[0110] Comparative Example 1 is the same as Example 1, except that the functionalized gel in Example 1 is replaced by the functionalized gel prepared in Comparative Preparation Example 1.

[0111] Comparative Example 2

[0112] Comparative Example 2 is the same as Example 1, except that the functionalized gel in Example 1 is replaced by the functionalized gel prepared in Comparative Preparation Example 2.

[0113] Comparative Example 3

[0114] Comparative Example 3 is the same as Example 1, except that the modified penetration enhancer in Example 1 is replaced by the modified penetration enhancer prepared in Comparative Preparation Example 3.

[0115] Comparative Example 4

[0116] Comparative Example 4 is the same as Example 1, except that the modified penetration enhancer in Example 1 is replaced by the modified penetration enhancer prepared in Comparative Preparation Example 4.

[0117] Comparative Example 5

[0118] Comparative Example 5 is the same as Example 1, except that the modified penetration enhancer in Example 1 is replaced by the modified penetration enhancer prepared in Comparative Preparation Example 5.

[0119] Performance Testing

[0120] The following performance tests were performed on the ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5:

[0121] Preparation of test samples: The ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5 were respectively cut and ground into test samples with a size of 5.25 mm × 6.5 mm × 20 mm;

[0122] Bending strength: Tested according to GB / T 232-2024, using the three-point bending method to test the bending strength of each test sample;

[0123] Vickers hardness: The room temperature hardness (HV) of each test sample was measured on a Vickers hardness tester with a load of 30 kg. The fracture toughness (KIC) was calculated from the radial crack length generated by the Vickers hardness indentation according to the Nihara formula. The unit is MPa•m. 1 / 2 ;

[0124] Wear resistance test: The cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5 were wire-cut and ground into test strips measuring 8 mm × 12 mm × 20 mm. The wear rate of each test strip was measured using a wear tester. The test load was 50 N, the friction ring speed was 200 rpm, and the test time was 2 h. The wear rate was calculated as follows:

[0125]

[0126] Impact resistance: The ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5 were respectively cut and ground into test strips with a size of 5 mm × 5 mm × 50 mm. The impact strength of each test strip was measured using a pendulum impact tester in accordance with GB / T 1817-2017. The specific test results are shown in Table 1:

[0127] Table 1 Performance test results

[0128]

[0129] It can be seen from the data in Table 1 that, compared with Comparative Examples 1-5, the ultra-coarse-grained WC-Co cemented carbide prepared in Examples 1-3 has more excellent hardness, toughness, impact resistance and wear resistance.

[0130] The performance data of Example 1 and Comparative Example 1 show that the presence of tannic acid can form a polytannic acid layer on the surface of yttrium trioxide. Not only can tannic acid be adsorbed on the surface of yttrium trioxide through hydrogen bonding or coordination to form a steric hindrance layer, but the activated carbon generated by the decomposition of polytannic acid can participate in the Co / WC interface reaction to form a more stable chemical bond, thereby significantly improving the toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0131] According to the test results of Example 1 and Comparative Example 2, the silicone gel not only has high compressive strength itself, but also the silica in the silicone gel reacts with tungsten and cobalt to form silicide, which inhibits the dissolution-precipitation process of tungsten carbide grains and improves the hardness and toughness of the WC-Co cemented carbide. At the same time, the Si-O-Si bonds between the gels are further strengthened and cross-linked, and a denser silica network structure can be formed in the ultra-coarse-grained WC-Co cemented carbide system, which significantly improves the hardness, toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0132] According to the comparative analysis of Example 1 and Comparative Example 3, compared with nano-boron nitride, hydroxyl boron nitride can produce hydrogen bonds with the hydroxyl groups on the surface of the functionalized gel, thereby improving the compatibility and significantly improving the hardness, toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0133] According to the test results of Example 1 and Comparative Example 4, the hydroxyl groups on the polyvinyl alcohol molecular chain can undergo a condensation reaction with the hydroxyl groups on the surface of the nano-silica in the functionalized gel to form a stable Si-OC covalent bond, thereby cross-linking the polyvinyl alcohol molecules to form a three-dimensional network structure, which significantly improves the hardness, toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0134] According to the test results of Example 1 and Comparative Example 5, aluminum dihydrogen phosphate can form a network structure in an aqueous solution, which helps to encapsulate the modified boron nitride particles and prevent them from agglomerating, thereby improving the dispersion performance while significantly improving the hardness, toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0135] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed. However, as long as such modifications are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing ultra-coarse-grained WC-Co cemented carbide, characterized in that: The following steps are involved: Step S1, preparing the following raw materials by weight: 4.6-9.2 parts of cobalt powder, 96-102 parts of coarse-crystalline tungsten carbide powder, 3.6-5.2 parts of functionalized gel, 3.4-4.6 parts of modified penetration enhancer, 2.2-2.8 parts of binder, and 36-62 parts of organic solvent; Step S2, preparing a mixture: adding coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, binder and organic solvent into a rolling ball mill according to weight, ball milling for 14-20 hours, drying and sieving to obtain a mixture; Step S3, granulation treatment: the mixture prepared in step S2 is sieved, and then placed in a granulator and rolled for 4-6 minutes for granulation treatment; Step S4, green compacting: pressing the granulated mixture in step S3 into green compacts; Step S5, pressure sintering: pressure sintering the green body prepared in step S4 into ultra-coarse grained WC-Co cemented carbide; The functionalized gel is prepared by the following steps: Step A1, adding yttrium trioxide to a hydrochloric acid aqueous solution, stirring evenly, adding tannic acid, heating to 35-45°C, stirring and reacting for 3-5 hours, filtering, washing, and drying to obtain pretreated yttrium trioxide; Step A2: adding the pretreated yttrium trioxide, ultrafine tungsten carbide, tantalum carbide, and chromium carbide to the mixed acid, stirring evenly, adjusting the pH to 8-9, stirring for 25-35 minutes, heating to 90-110° C., stirring for 2-3 hours, and cooling to room temperature to obtain modified yttrium trioxide; Step A3, uniformly mixing the modified yttrium trioxide and the cross-linking agent, adding the silicon precursor and anhydrous ethanol, stirring until gelation, taking out the gel, washing, and drying to obtain a functionalized gel; Described modified penetration enhancer is prepared by following steps: Step B1, mixing nano hexagonal boron nitride and alkali solution evenly, heating to 100-120°C, stirring and reacting for 40-50 hours, centrifuging, washing the precipitate, and drying to obtain modified boron nitride; Step B2: ultrasonically disperse the modified boron nitride in anhydrous DMF, and add the aqueous solution of aluminum dihydrogen phosphate dropwise while stirring. The dripping is controlled to be completed within 15 minutes. After the dripping is completed, polyvinyl alcohol is added, the temperature is raised to 60-70°C, and the reaction is stirred for 4-6 hours to obtain a modified penetration enhancer.

2. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: In the step A1, the mass ratio of yttrium trioxide, hydrochloric acid aqueous solution and tannic acid is 2-4:40-60:3-6.

3. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: In step A2, the mass ratio of pretreated yttrium oxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide and mixed acid is 1-3:0.04-0.06:0.01-0.03:0.022-0.034:45-55, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1-2:

3.

4. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: In step A3, the mass ratio of modified yttrium trioxide, crosslinking agent, silicon precursor and anhydrous ethanol is 3-5:2.4-3.2:0.4-0.6:16-22.

5. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: In the step B1, the mass ratio of nano hexagonal boron nitride to alkali solution is 2.2-3.2:500-600, and the alkali solution is a sodium hydroxide aqueous solution with a mass fraction of 50-60%.

6. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: In the step B2, the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution and polyvinyl alcohol is 3-5:60-70:20-30:0.2-0.6, and the mass fraction of the aluminum dihydrogen phosphate aqueous solution is 35-45%.

7. An ultra-coarse-grained WC-Co cemented carbide prepared by the method for preparing an ultra-coarse-grained WC-Co cemented carbide according to any one of claims 1 to 6.

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