Ultra-coarse grain WC-Co hard alloy and preparation method thereof

Abstract

The invention relates to the technical field of powder metallurgy, and particularly discloses an ultra-coarse grain WC-Co hard alloy and a preparation method thereof.The preparation method comprises the following steps that S1, the following raw materials including, by weight, 4.6-9.2 parts of cobalt powder, 96-102 parts of coarse grain tungsten carbide powder, 3.6-5.2 parts of functional gel, 3.4-4.6 parts of modified penetration enhancer, 2.2-2.8 parts of binder and 36-62 parts of organic solvent are prepared; step S2, preparation of a mixture; step S3, carrying out granulation treatment; step S4, compacting; step S5, pressurizing and sintering; the functional gel and the modified penetration enhancer are added, the functional gel contains yttrium oxide, polytannic acid, ultrafine tungsten carbide, tantalum carbide, chromium carbide, silica gel and other components, and the functional gel not only has excellent physical properties, but also can be cross-linked with the modified penetration enhancer to form a more compact silicon dioxide network structure; and the hardness, toughness, impact resistance and wear resistance of the alloy are improved.

Description

Technical Field

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

[0002] WC-Co cemented carbide has advantages such as 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, and is widely used in fields such as geological and mining tools, rolling mill rolls, and cemented carbide stamping dies.

[0003] The nano-powder 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-grained cemented carbide. However, due to the high surface energy of nano-powder, it is easy to agglomerate during the preparation and activation process, forming secondary particles. There are many pores inside the agglomerates, 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 art, the present invention provides an ultra-coarse-grained WC-Co cemented carbide and a preparation method thereof.

[0006] A preparation method of an ultra-coarse-grained WC-Co cemented carbide includes the following steps: Step S1: Prepare 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 promoter, 2.2 - 2.8 parts of binder, and 36 - 62 parts of organic solvent; Step S2: Preparation of the mixture: According to the parts by weight, add the coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration promoter, binder, and organic solvent into a rolling ball mill, ball mill for 14 - 20 h, dry, and screen to obtain the mixture. Among them, the ball milling conditions are: the ball-to-material ratio is 4 - 6:1, and the ball rotation speed is 60 - 80 rpm; the drying conditions are: drying at 80 - 88 °C for 5 - 7 h; the screening mesh number is 320 - 360 mesh; Step S3: Pelletizing treatment: Screen the mixture prepared in Step S2, and then place it in a pelletizer and roll for 4 - 6 min for pelletizing treatment; Step S4: Compacting: Compact the mixture subjected to pelletizing treatment in Step S3 into a green compact; Step S5: Pressure-assisted sintering: Pressure-assisted sinter the green compact prepared in Step S4 into an ultra-coarse-grained WC-Co cemented carbide.

[0007] Preferably, in step S4, the pressing pressure is 160 - 180 MPa.

[0008] Preferably, in step S5, the green compact obtained by pressing is sintered under increased pressure. During sintering, under vacuum, first heat at a heating rate of 4 - 8 °C / min and gradually heat up to 370 - 430 °C, hold for 12 - 18 min, then heat at a heating rate of 14 - 18 °C / min and gradually heat up to 1480 - 1560 °C, hold under vacuum for 20 - 26 min, then increase the pressure to 35 - 45 MPa at a rate of 6 - 8 MPa / min. At the same time, heat at a heating rate of 20 - 24 °C / min and gradually heat up to 1770 - 1830 °C, and then increase the pressure to 84 MPa at a pressure increasing rate of 12 - 16 MPa / min, and perform heat preservation treatment for 2.2 - 2.6 h.

[0009] Preferably, the binder is CP60 long-chain chlorinated paraffin.

[0010] Preferably, the organic solvent is absolute ethanol.

[0011] Preferably, the functionalized gel is prepared by the following steps: Step A1: Add yttrium oxide to an aqueous hydrochloric acid solution, stir evenly, add tannic acid, heat up to 35 - 45 °C, and stir and react for 3 - 5 h. After filtration, washing, and drying, obtain pretreated yttrium oxide. Among them, the mass ratio of yttrium oxide, aqueous hydrochloric acid solution, and tannic acid is 2 - 4:40 - 60:3 - 6. During the above process, tannic acid self-polymerizes on the surface of yttrium oxide, realizing the formation of a polytannic acid layer on the surface of yttrium oxide, endowing yttrium oxide with excellent adhesion. Step A2: Add the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide, and chromium carbide to a mixed acid, stir evenly, adjust the pH to 8 - 9, stir for 25 - 35 min, heat up to 90 - 110 °C, and stir and react for 2 - 3 h. Cool to room temperature to obtain modified yttrium oxide. Among them, the mass ratio of pretreated yttrium oxide, ultra-fine 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. Step A3: Mix the modified yttrium oxide and the cross-linking agent evenly, add the silicon precursor and absolute ethanol, stir until gelation occurs, take out the gel, wash, and dry to obtain the functionalized gel. Among them, the mass ratio of modified yttrium oxide, cross-linking agent, silicon precursor, and absolute ethanol is 3 - 5:2.4 - 3.2:0.4 - 0.6:16 - 22.

[0012] Preferably, in step A1, the mass fraction of the aqueous hydrochloric acid solution is 6 - 10%.

[0013] Preferably, in the step A2, the mixed acid is composed of hydrofluoric acid and concentrated nitric acid mixed in a mass ratio of 1-2:3.

[0014] Preferably, in the step A3, the crosslinking agent is propylene oxide butyl ether, and the silicon precursor is tetraethyl orthosilicate.

[0015] Preferably, the modified penetration enhancer is prepared by the following steps: Step B1: Mix nano-hexagonal boron nitride and an alkali solution evenly, heat up to 100-120 °C, stir and react for 40-50 h, centrifuge, wash and dry the precipitate to obtain modified boron nitride, wherein the mass ratio of nano-hexagonal boron nitride to the alkali solution is 2.2-3.2:500-600; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF, and drop it into the aluminum dihydrogen phosphate aqueous solution while stirring, controlling to finish dropping within 15 min. After dropping, add polyvinyl alcohol, heat up to 60-70 °C, stir and react for 4-6 h to obtain the modified penetration enhancer, wherein the mass ratio of the modified boron nitride, anhydrous DMF (N,N-dimethylformamide), aluminum dihydrogen phosphate aqueous solution and polyvinyl alcohol is 3-5:60-70:20-30:0.2-0.6.

[0016] Preferably, in the step B1, the alkali solution is an aqueous sodium hydroxide solution with a mass fraction of 50-60%.

[0017] Preferably, the mass fraction of the aluminum dihydrogen phosphate aqueous solution is 35-45%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: In the technical solution of the present invention, the polytannic acid layer can not only be adsorbed on the surface of yttrium oxide through hydrogen bonding or coordination to form a steric hindrance layer, but also adsorb ultrafine tungsten carbide and tantalum carbide on the surface of pretreated yttrium oxide, serving as the synthesis sites for ultrafine tungsten carbide, tantalum carbide and chromium carbide. Moreover, yttrium oxide has excellent fluidity and can fill the pores of WC-Co cemented carbide during the sintering process of WC-Co cemented carbide, improving 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 oxide, and the formed ultrafine tungsten carbide, tantalum carbide and chromium carbide, among which, ultrafine tungsten carbide can not only increase the grain boundary area, hinder the movement of dislocations, and improve the hardness of the alloy material, but also delay the crack propagation through the crack deflection and bridging mechanisms, improving 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 slip, but also refine the tungsten carbide grains, synergistically enhancing 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, improving the toughness, but also partially dissolve in the cobalt binder phase during the sintering process, precipitate chromium elements and enrich at the cobalt / tungsten carbide interface or grain boundary, forming a high-energy barrier to hinder the diffusion of W atoms from WC particles to the Co phase, further improving the toughness of WC-Co cemented carbide; In the technical solution of the present invention, the modified yttrium oxide is embedded in the silicon gel network structure to fix the modified yttrium oxide, further improving the dispersion of the modified yttrium oxide 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 silicon gel not only has a high compressive strength itself, but also the silicon dioxide in the silicon gel reacts with tungsten and cobalt to form silicides, which can reduce the solubility of tungsten in cobalt and inhibit the dissolution-precipitation process of tungsten carbide grains, improving the hardness and toughness of WC-Co cemented carbide. At the same time, the Si-O-Si bonds between the gels are further strengthened and crosslinked, and a more dense silicon dioxide network structure can be formed in the ultra-coarse-grained WC-Co cemented carbide system, making the ultra-coarse-grained WC-Co cemented carbide firmly bonded together through the silicon dioxide network structure, further improving the hardness, toughness, impact resistance and wear resistance of WC-Co cemented carbide; In the technical solution of the present invention, nano boron nitride is first hydroxylated and modified to obtain modified boron nitride, and then it is mixed evenly 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 grain WC-Co cemented carbide; In addition, hydroxy boron nitride can also form hydrogen bond interactions with the hydroxyl groups on the surface of the functionalized gel, improving the compatibility while further improving the hardness, toughness, impact resistance and wear resistance of ultra-coarse grain WC-Co cemented carbide; Aluminum dihydrogen phosphate can form a network structure in an aqueous solution, which helps to wrap the modified boron nitride particles and prevent their agglomeration, thereby improving the dispersion performance. At the same time, the hydroxyl groups on the polyvinyl alcohol molecular chain can undergo a condensation reaction with the hydroxyl groups on the surface of nano-silica in the functionalized gel to form stable Si-O-C covalent bonds, so that the polyvinyl alcohol molecules are cross-linked with each other to form a three-dimensional network structure. Introducing it into ultra-coarse grain WC-Co cemented carbide can cooperate with the functionalized gel to jointly improve the hardness, toughness, impact resistance and wear resistance of ultra-coarse grain WC-Co cemented carbide. Detailed implementation mode

[0019] To make the implementation mode of the present invention easier to understand, the present invention will be described in detail below with reference to specific embodiments. These embodiments are only illustrative and are not limited to the application scope of the present invention.

[0020] For those technical or conditions not specified in the embodiments, they shall be in accordance with the technologies or conditions described in the literature in this field, or in accordance with the product specifications. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through regular channels.

[0021] The coarse-grained tungsten carbide powder is produced by Hebei Huazuan Alloy Welding Materials Co., Ltd., with a CAS number of 12070-13-2, a grade of HZ-WC-2, and a mesh number of 60; The cobalt powder is commercially available from Hebei Yirui Alloy Welding Materials Co., Ltd., with a CAS number of Hebei Science and Technology, a brand of Yirui Alloy, and a process of atomization method; The ultra-fine tungsten carbide is produced by Ningbo Luofei Nano Technology Co., Ltd., with a CAS number of 12070-12-1, and the Fisher average particle size of the product is 100 nm; Yttrium oxide is produced by Hebei Huazuan Alloy Welding Materials Co., Ltd., with a CAS number of 1314-36-9 and a grade of HZ-Y 2 O 3-1; Tantalum carbide is produced by Hebei Yinbai Alloy Welding Materials Co., Ltd., with the CAS number YB-1; chromium carbide is produced by Qinghe County Tebo Metal Materials Co., Ltd., with the CAS number TB-1; nano boron nitride is produced by Hebei Tenshuang Metal Materials Co., Ltd., with the CAS number 10043-11-5 and a particle size of 30-50 nm; polyvinyl alcohol is commercially available from Wuhan Runxingyuan Technology Co., Ltd., with the model PVA1788; CP60 long-chain chlorinated paraffin is the CP60 long-chain chlorinated paraffin produced by Xipeng Environmental Protection Technology (Luoyang) Co., Ltd.

[0022] The present invention will be further described in detail below in conjunction with the examples and comparative examples.

[0023] Preparation Examples 1-3 and Comparative Preparation Examples 1-2 provide a functionalized gel.

[0024] Preparation Example 1 This preparation example provides a functionalized gel, which is prepared by the following steps: Step A1: Add yttrium oxide to an aqueous hydrochloric acid solution with a mass fraction of 6%, stir at a rotation speed of 500 rpm for 12 min until uniform, add tannic acid, raise the temperature to 35 °C, maintain the rotation speed unchanged, and continue to stir and react for 3 h. After filtration, wash with absolute ethanol and deionized water three times in sequence, and dry at 60 °C to constant weight to obtain pretreated yttrium oxide, wherein the mass ratio of yttrium oxide, aqueous hydrochloric acid solution and tannic acid is 2:40:3; Step A2: Add the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide and chromium carbide to the mixed acid, stir at a rotation speed of 600 rpm for 20 min until uniform, adjust the pH to 8 with 0.2 M ammonia water solution, stir for 25 min, raise the temperature to 90 °C, maintain the rotation speed unchanged, and continue to stir and react for 2 h. Cool to room temperature to obtain modified yttrium oxide, wherein the mass ratio of the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide, chromium carbide and the mixed acid is 1:0.04:0.01:0.022:45, and the mixed acid is composed of hydrofluoric acid and concentrated nitric acid mixed according to the mass ratio of 1:3; Step A3: Stir the modified yttrium oxide and propylene oxide butyl ether at a rotation speed of 700 rpm for 16 min until uniform, add tetraethyl orthosilicate and absolute ethanol, stir until gelation occurs, take out the gel, wash it with deionized water three times, and dry at 60 °C to constant weight to obtain the functionalized gel, wherein the mass ratio of the modified yttrium oxide, propylene oxide butyl ether, tetraethyl orthosilicate and absolute ethanol is 3:2.4:0.4:16.

[0025] Preparation Example 2 This preparation example provides a functionalized gel, which is prepared by the following steps: Step A1: Add yttrium oxide into an aqueous hydrochloric acid solution with a mass fraction of 8%, stir at a rotation speed of 540 rpm for 16 min until homogeneous, add tannic acid, raise the temperature to 40 °C, stir and react for 4 h, filter, and then wash successively with absolute ethanol and deionized water 4 times, and dry at 65 °C until constant weight to obtain pretreated yttrium oxide. Among them, the mass ratio of yttrium oxide, aqueous hydrochloric acid solution and tannic acid is 3:50:4.5; Step A2: Add the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide and chromium carbide into the mixed acid, stir at a rotation speed of 630 rpm for 22 min until homogeneous, adjust the pH to 8.5 with 0.4 M ammonia aqueous solution, stir for 30 min, raise the temperature to 100 °C, keep the rotation speed unchanged, continue to stir and react for 2.5 h, and cool to room temperature to obtain modified yttrium oxide. Among them, the mass ratio of the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide, chromium carbide and the mixed acid is 2:0.05:0.02:0.028:50, and the mixed acid is composed of hydrofluoric acid and concentrated nitric acid mixed according to the mass ratio of 1.5:3; Step A3: Stir the modified yttrium oxide and propylene oxide butyl ether at a rotation speed of 720 rpm for 18 min until homogeneous, add tetraethyl orthosilicate and absolute ethanol, stir until gelation occurs, take out the gel, wash with deionized water 4 times, and dry at 65 °C until constant weight to obtain the functionalized gel. Among them, the mass ratio of the modified yttrium oxide, propylene oxide butyl ether, tetraethyl orthosilicate and absolute ethanol is 4:2.8:0.5:19.

[0026] Preparation Example 3 This preparation example provides a functionalized gel, which is prepared by the following steps: Step A1: Add yttrium oxide into an aqueous hydrochloric acid solution with a mass fraction of 10%, stir at a rotation speed of 580 rpm for 20 min until homogeneous, add tannic acid, raise the temperature to 45 °C, stir and react for 5 h, filter, and then wash successively with absolute ethanol and deionized water 5 times, and dry at 70 °C until constant weight to obtain pretreated yttrium oxide. Among them, the mass ratio of yttrium oxide, aqueous hydrochloric acid solution and tannic acid is 4:60:6; Step A2: Add the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide and chromium carbide into the mixed acid, stir at a rotation speed of 660 rpm for 24 min until homogeneous, adjust the pH to 9 with 0.6 M ammonia aqueous solution, stir for 35 min, raise the temperature to 110 °C, keep the rotation speed unchanged, continue to stir and react for 3 h, and cool to room temperature to obtain modified yttrium oxide. Among them, the mass ratio of the pretreated yttrium oxide, ultra-fine tungsten carbide, tantalum carbide, chromium carbide and the mixed acid is 3:0.06:0.03:0.034:55, and the mixed acid is composed of hydrofluoric acid and concentrated nitric acid mixed according to the mass ratio of 2:3; Step A3: Stir the modified yttrium oxide and propylene oxide butyl ether at a rotation speed of 740 rpm for 20 min until homogeneous. Add tetraethyl orthosilicate and absolute ethanol, stir until gelation occurs, take out the gel, wash it 5 times with deionized water, and dry it at 70 °C to constant weight to obtain the functionalized gel. Among them, the mass ratio of modified yttrium oxide, propylene oxide butyl ether, tetraethyl orthosilicate, and absolute ethanol is 5:3.2:0.6:22.

[0027] Comparative Preparation Example 1 This Comparative Preparation Example provides a functionalized gel, which is prepared by the following steps: Step A1: Add yttrium oxide to an aqueous hydrochloric acid solution with a mass fraction of 6%, stir at a rotation speed of 500 rpm for 12 min until homogeneous, add malic acid, raise the temperature to 35 °C, maintain the rotation speed unchanged, and continue stirring and reacting for 3 h. After filtration, wash it 3 times successively with absolute ethanol and deionized water, and dry it at 60 °C to constant weight to obtain pretreated yttrium oxide. Among them, the mass ratio of yttrium oxide, aqueous hydrochloric acid solution, and malic acid is 2:40:3; Step A2: Add the pretreated yttrium oxide, ultrafine tungsten carbide, tantalum carbide, and chromium carbide to the mixed acid, stir at a rotation speed of 600 rpm for 20 min until homogeneous, adjust the pH to 8 with 0.2 M ammonia water solution, stir for 25 min, raise the temperature to 90 °C, maintain the rotation speed unchanged, and continue stirring and reacting for 2 h. Cool to room temperature to obtain the modified yttrium oxide. Among them, the mass ratio of pretreated yttrium oxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide, and mixed acid is 1:0.04:0.01:0.022:45, and the mixed acid is composed of hydrofluoric acid and concentrated nitric acid mixed according to a mass ratio of 1:3; Step A3: Stir the modified yttrium oxide and propylene oxide butyl ether at a rotation speed of 700 rpm for 16 min until homogeneous. Add tetraethyl orthosilicate and absolute ethanol, stir until gelation occurs, take out the gel, wash it 3 times with deionized water, and dry it at 60 °C to constant weight to obtain the functionalized gel. Among them, the mass ratio of modified yttrium oxide, propylene oxide butyl ether, tetraethyl orthosilicate, and absolute ethanol is 3:2.4:0.4:16.

[0028] Comparative Preparation Example 2 This Comparative Preparation Example provides a functionalized gel, which is prepared by the following steps: Step A1: Add yttrium oxide to an aqueous hydrochloric acid solution with a mass fraction of 6%, stir at a rotation speed of 500 rpm for 12 min until homogeneous, add tannic acid, raise the temperature to 35 °C, maintain the rotation speed unchanged, and continue stirring and reacting for 3 h. After filtration, wash it 3 times successively with absolute ethanol and deionized water, and dry it at 60 °C to constant weight to obtain pretreated yttrium oxide. Among them, the mass ratio of yttrium oxide, aqueous hydrochloric acid solution, and tannic acid is 2:40:3; Step A2: Add pretreated yttrium oxide, ultrafine tungsten carbide, tantalum carbide, and chromium carbide into the mixed acid, stir at a rotation speed of 600 rpm for 20 min until homogeneous, adjust the pH to 8 with 0.2 M ammonia aqueous solution, stir for 25 min, heat up to 90 °C, keep the rotation speed unchanged, continue stirring and reacting for 2 h, cool to room temperature to obtain modified yttrium oxide. Among them, the mass ratio of pretreated yttrium oxide, ultrafine tungsten carbide, tantalum carbide, chromium carbide, and the mixed acid is 1:0.04:0.01:0.022:45, and the mixed acid is composed of hydrofluoric acid and concentrated nitric acid mixed according to the mass ratio of 1:3; Step A3: Stir the modified yttrium oxide and propylene oxide butyl ether at a rotation speed of 700 rpm for 16 min until homogeneous, add nano-silica and absolute ethanol, stir until gelation occurs, take out the gel, wash it 3 times with deionized water, and dry it to constant weight at 60 °C to obtain a functionalized gel. Among them, the mass ratio of modified yttrium oxide, propylene oxide butyl ether, nano-silica, and absolute ethanol is 3:2.4:0.4:16.

[0029] Preparation Examples 4 - 6 and Comparative Preparation Examples 3 - 5 provide a modified penetration enhancer.

[0030] Preparation Example 4 This preparation example provides a modified penetration enhancer, which is prepared by the following steps: Step B1: Stir nano-hexagonal boron nitride and a 50% sodium hydroxide aqueous solution at a rotation speed of 600 rpm for 14 min until homogeneous, heat up to 100 °C, keep the rotation speed unchanged, continue stirring and reacting for 40 h, centrifuge, wash the precipitate 3 times with absolute ethanol, and dry it to constant weight at 60 °C to obtain modified boron nitride. Among them, the mass ratio of nano-hexagonal boron nitride and the 50% sodium hydroxide aqueous solution is 2.2:500; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency at 40 kHz, ultrasonic power at 600 w, ultrasonic for 16 min, control the rotation speed at 660 rpm, and while stirring, drop it into a 35% aluminum dihydrogen phosphate aqueous solution, control the dropping to be completed within 15 min. After dropping, add polyvinyl alcohol, heat up to 60 °C, keep the rotation speed unchanged, continue stirring and reacting for 4 h to obtain a modified penetration enhancer. Among them, the mass ratio of modified boron nitride, anhydrous DMF, aluminum dihydrogen phosphate aqueous solution, and polyvinyl alcohol is 3:60:20:0.2.

[0031] Preparation Example 5 This preparation example provides a modified penetration enhancer, which is prepared by the following steps: Step B1: Stir nano - hexagonal boron nitride and an aqueous sodium hydroxide solution with a mass fraction of 55% at a rotation speed of 640 rpm for 18 min until uniform. Heat up to 110 °C, keep the rotation speed unchanged, and continue stirring and reacting for 45 h. Centrifuge, wash the precipitate with absolute ethanol 4 times, and dry it at 65 °C to constant weight to obtain modified boron nitride. Among them, the mass ratio of nano - hexagonal boron nitride to the aqueous sodium hydroxide solution with a mass fraction of 55% is 2.7:550; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency at 35 kHz, ultrasonic power at 550 w, and ultrasonic for 20 min. While controlling the rotation speed at 680 rpm, dropwise add an aqueous solution of aluminum dihydrogen phosphate with a mass fraction of 40% while stirring, and control the dropping to be completed within 15 min. After dropping, add polyvinyl alcohol, heat up to 65 °C, keep the rotation speed unchanged, and continue stirring and reacting for 5 h to obtain a modified penetration enhancer. Among them, the mass ratio of modified boron nitride, anhydrous DMF, aqueous aluminum dihydrogen phosphate solution, and polyvinyl alcohol is 4:65:25:0.4.

[0032] Preparation Example 6 This preparation example provides a modified penetration enhancer, which is prepared by the following steps: Step B1: Stir nano - hexagonal boron nitride and an aqueous sodium hydroxide solution with a mass fraction of 60% at a rotation speed of 680 rpm for 22 min until uniform. Heat up to 120 °C, stir and react for 50 h, centrifuge, wash the precipitate with absolute ethanol 5 times, and dry it at 70 °C to constant weight to obtain modified boron nitride. Among them, the mass ratio of nano - hexagonal boron nitride to the aqueous sodium hydroxide solution with a mass fraction of 60% is 3.2:600; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency at 30 kHz, ultrasonic power at 500 w, and ultrasonic for 24 min. While controlling the rotation speed at 700 rpm, dropwise add an aqueous solution of aluminum dihydrogen phosphate with a mass fraction of 45% while stirring, and control the dropping to be completed within 15 min. After dropping, add polyvinyl alcohol, heat up to 70 °C, keep the rotation speed unchanged, and continue stirring and reacting for 6 h to obtain a modified penetration enhancer. Among them, the mass ratio of modified boron nitride, anhydrous DMF, aqueous aluminum dihydrogen phosphate solution, and polyvinyl alcohol is 5:70:30:0.6.

[0033] Comparative Preparation Example 3 This comparative preparation example provides a modified penetration enhancer, which is prepared by the following steps: Step B1: Stir nano - hexagonal boron nitride and deionized water at a rotation speed of 600 rpm for 14 min until uniform. Heat up to 100 °C, keep the rotation speed unchanged, and continue stirring and reacting for 40 h. Centrifuge, wash the precipitate with absolute ethanol 3 times, and dry it at 60 °C to constant weight to obtain modified boron nitride. Among them, the mass ratio of nano - hexagonal boron nitride to deionized water is 2.2:500; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency at 40 kHz, the ultrasonic power at 600 w, ultrasonic for 16 min, control the rotation speed at 660 rpm, and while stirring, dropwise add an aqueous solution of aluminum dihydrogen phosphate with a mass fraction of 35% into it, control to finish dropping within 15 min. After dropping, add polyvinyl alcohol, raise the temperature to 60 °C, maintain the rotation speed unchanged, and continue to stir and react for 4 h to obtain the modified penetration enhancer. Among them, the mass ratio of the modified boron nitride, anhydrous DMF, the aqueous solution of aluminum dihydrogen phosphate, and polyvinyl alcohol is 3:60:20:0.2.

[0034] Comparative Preparation Example 4 This comparative preparation example provides a modified penetration enhancer, which is prepared by the following steps: Step B1: Stir the nano hexagonal boron nitride and an aqueous solution of sodium hydroxide with a mass fraction of 50% at a rotation speed of 600 rpm for 14 min until uniform, raise the temperature to 100 °C, maintain the rotation speed unchanged, and continue to stir and react for 40 h. Centrifuge, wash the precipitate with anhydrous ethanol 3 times, and dry it at 60 °C to constant weight to obtain the modified boron nitride. Among them, the mass ratio of the nano hexagonal boron nitride and the aqueous solution of sodium hydroxide with a mass fraction of 50% is 2.2:500; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF, control the ultrasonic frequency at 40 kHz, the ultrasonic power at 600 w, ultrasonic for 16 min, control the rotation speed at 660 rpm, and while stirring, dropwise add an aqueous solution of aluminum dihydrogen phosphate with a mass fraction of 35% into it, control to finish dropping within 15 min. After dropping, add anhydrous ethanol, raise the temperature to 60 °C, maintain the rotation speed unchanged, and continue to stir and react for 4 h to obtain the modified penetration enhancer. Among them, the mass ratio of the modified boron nitride, anhydrous DMF, the aqueous solution of aluminum dihydrogen phosphate, and anhydrous ethanol is 3:60:20:0.2.

[0035] Comparative Preparation Example 5 This comparative preparation example provides a modified penetration enhancer, which is prepared by the following steps: Step B1: Stir the nano hexagonal boron nitride and an aqueous solution of sodium hydroxide with a mass fraction of 50% at a rotation speed of 600 rpm for 14 min until uniform, raise the temperature to 100 °C, maintain the rotation speed unchanged, and continue to stir and react for 40 h. Centrifuge, wash the precipitate with anhydrous ethanol 3 times, and dry it at 60 °C to constant weight to obtain the modified boron nitride. Among them, the mass ratio of the nano hexagonal boron nitride and the aqueous solution of sodium hydroxide with a mass fraction of 50% is 2.2:500; Step B2: Ultrasonically disperse the modified boron nitride in anhydrous DMF. Control the ultrasonic frequency at 40 kHz, the ultrasonic power at 600 w, and ultrasonicate for 16 min. While stirring at a rotation speed of 660 rpm, dropwise add an aqueous solution of disodium hydrogen phosphate with a mass fraction of 35% within 15 min. After dropping, add polyvinyl alcohol, raise the temperature to 60 °C, maintain the rotation speed unchanged, and continue stirring and reacting for 4 h to obtain a modified penetration enhancer. Among them, the mass ratio of modified boron nitride, anhydrous DMF, aqueous solution of disodium hydrogen phosphate, and polyvinyl alcohol is 3:60:20:0.2.

[0036] Examples 1-3 and Comparative Examples 1-5 provide a method for preparing ultra-coarse-grained WC-Co cemented carbide.

[0037] Example 1 This example provides a method for preparing ultra-coarse-grained WC-Co cemented carbide, including the following steps: Step S1: Prepare the following raw materials in parts by weight: 4.6 parts of cobalt powder, 96 parts of coarse-grained 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 absolute ethanol; Step S2: Preparation of the mixture: According to the parts by weight, add the coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, CP60 long-chain chlorinated paraffin, and absolute ethanol into a rolling ball mill. Control the ball-to-material ratio at 4:1, the ball rotation speed at 60 rpm, and the ball milling time at 14 h. Then dry at 80 °C for 5 h and pass through a 320-mesh sieve to obtain the mixture. Among them, the ball-to-material ratio of cemented carbide, grinding balls, and solid raw materials is 1:1:1; Step S3: Pelletizing treatment: Pass the mixture prepared in Step S2 through an 80-mesh sieve, and then place it in a pelletizer and roll for 4 min for pelletizing treatment; Step S4: Compacting: Compact the mixture obtained by pelletizing treatment in Step S3 at 160 MPa to form a green compact; Step S5: Pressure-assisted sintering: Sinter the green compact prepared in Step S4 into ultra-coarse-grained WC-Co cemented carbide. During sintering, first increase the temperature at a rate of 4 °C / min under vacuum, gradiently increase the temperature to 370 °C, hold for 12 min, then increase the temperature at a rate of 14 °C / min, gradiently increase the temperature to 1480 °C, hold under vacuum for 20 min, then increase the pressure to 35 MPa at a rate of 6 MPa / min. At the same time, increase the temperature at a rate of 20 °C / min, gradiently increase the temperature to 1770 °C, and then increase the pressure to 84 MPa at a pressure increase rate of 12 MPa / min, and perform heat preservation treatment for 2.2 h.

[0038] Example 2 This example provides a method for preparing ultra-coarse-grained WC-Co cemented carbide, including the following steps: Step S1: Prepare the following raw materials in parts by weight: 6.9 parts of cobalt powder, 99 parts of coarse-grained 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 absolute ethanol; Step S2: Preparation of the mixture: According to the parts by weight, add the coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, CP60 long-chain chlorinated paraffin, and absolute ethanol into a rolling ball mill, control the ball-to-material ratio to be 5:1, the ball rotation speed to be 70 rpm, the ball milling time to be 17 h, then place it at 84 °C and dry for 6 h, and pass through a 340-mesh sieve to obtain the mixture. Among them, the ball-to-material ratio of cemented carbide, grinding balls, and solid raw materials is 1:2:1; Step S3: Pelletizing treatment: Pass the mixture prepared in Step S2 through a 100-mesh sieve, and then place it in a pelletizer and roll for 5 min for pelletizing treatment; Step S4: Compacting: Compact the mixture subjected to pelletizing treatment in Step S3 under 170 MPa to form a green compact; Step S5: Pressure-assisted sintering: Sinter the green compact prepared in Step S4 into an ultra-coarse-grained WC-Co cemented carbide. Among them, during sintering, first increase the temperature at a heating rate of 6 °C / min under vacuum, gradient heat up to 400 °C, hold for 15 min, then increase the temperature at a heating rate of 16 °C / min, gradient heat up to 1520 °C, hold under vacuum for 23 min, then increase the pressure to 40 MPa at a rate of 7 MPa / min, and at the same time, increase the temperature at a heating rate of 22 °C / min, gradient heat up to 1800 °C, and then increase the pressure to 84 MPa at a pressure increase rate of 14 MPa / min, and hold for 2.4 h.

[0039] Example 3 This example provides a method for preparing an ultra-coarse-grained WC-Co cemented carbide, including the following steps: Step S1: Prepare the following raw materials in parts by weight: 9.2 parts of cobalt powder, 102 parts of coarse-grained 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 absolute ethanol; Step S2: Preparation of the mixture: According to the parts by weight, add the coarse-grained tungsten carbide powder, cobalt powder, functionalized gel, modified penetration enhancer, CP60 long-chain chlorinated paraffin, and absolute ethanol into a rolling ball mill, control the ball-to-material ratio to be 6:1, the ball rotation speed to be 80 rpm, the ball milling time to be 20 h, then place it at 88 °C and dry for 7 h, and pass through a 360-mesh sieve to obtain the mixture. Among them, the ball-to-material ratio of cemented carbide, grinding balls, and solid raw materials is 1:3:1; Step S3, granulation treatment: Pass the mixture prepared in Step S2 through a 120-mesh sieve, and then place it in a granulator and roll for 6 min for granulation treatment; Step S4, compacting: Compact the granulated mixture in Step S3 into a green compact under a pressure of 180 MPa; Step S5, pressure-assisted sintering: Pressure-assisted sinter the green compact prepared in Step S4 into an ultra-coarse-grained WC-Co cemented carbide. During sintering, first, under vacuum, increase the temperature at a heating rate of 8 °C / min in a gradient manner to 430 °C, hold for 18 min, then increase the temperature at a heating rate of 18 °C / min in a gradient manner to 1560 °C, hold under vacuum for 26 min, then increase the pressure to 45 MPa at a rate of 8 MPa / min. At the same time, increase the temperature at a heating rate of 24 °C / min in a gradient manner to 1830 °C, and then increase the pressure to 84 MPa at a pressure-increasing rate of 16 MPa / min, and perform heat preservation treatment for 2.6 h.

[0040] Comparative Example 1 Comparative Example 1 is the same as Example 1, except that the functionalized gel in Example 1 is replaced with the functionalized gel prepared in Comparative Preparation Example 1.

[0041] Comparative Example 2 Comparative Example 2 is the same as Example 1, except that the functionalized gel in Example 1 is replaced with the functionalized gel prepared in Comparative Preparation Example 2.

[0042] Comparative Example 3 Comparative Example 3 is the same as Example 1, except that the modified penetration enhancer in Example 1 is replaced with the modified penetration enhancer prepared in Comparative Preparation Example 3.

[0043] Comparative Example 4 Comparative Example 4 is the same as Example 1, except that the modified penetration enhancer in Example 1 is replaced with the modified penetration enhancer prepared in Comparative Preparation Example 4.

[0044] Comparative Example 5 Comparative Example 5 is the same as Example 1, except that the modified penetration enhancer in Example 1 is replaced with the modified penetration enhancer prepared in Comparative Preparation Example 5.

[0045] Performance test Perform the following performance tests on the ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5: Preparation of test specimens: Wire-cut and grind the ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5 respectively into test specimens with dimensions of 5.25 mm × 6.5 mm × 20 mm; Flexural strength: Tested according to GB / T 232-2024, the flexural strength of each test sample was tested by the three-point bending method; Vickers hardness: The room temperature hardness (HV) of each test sample was tested on a Vickers hardness tester with a load of 30 kg; According to the Nihara formula, the fracture toughness (KIC) was calculated from the radial crack length generated by the Vickers hardness indentation, with the unit of MPa•m 1 / 2 ; Wear resistance test: The cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5 were wire cut and ground into sample strips with dimensions of 8 mm×12 mm×20 mm, and the wear rate of each sample strip was measured by a wear testing machine. The test load was 50 N, the friction ring rotation speed was 200 rpm, and the time was 2 h. The calculation formula for the wear rate is:

[0046] Impact resistance: The ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 and Comparative Examples 1-5 were wire cut and ground into sample strips with dimensions of 5 mm×5 mm×50 mm, and the impact strength of each sample strip was measured by a pendulum impact testing machine with reference to GB / T 1817-2017. The specific test results are shown in Table 1: Table 1 Performance test results

[0047] It can be seen from the data in Table 1 that compared with Comparative Examples 1-5, the ultra-coarse-grained WC-Co cemented carbides prepared in Examples 1-3 have more excellent hardness, toughness, impact resistance and wear resistance.

[0048] According to the performance data of Example 1 and Comparative Example 1, the presence of tannic acid can form a polytannic acid layer on the surface of yttrium oxide. It can not only adsorb on the surface of yttrium oxide through hydrogen bonding or coordination to form a steric hindrance layer, but also the active carbon generated by the decomposition of polytannic acid can participate in the Co / WC interface reaction to form a more stable chemical bond, significantly improving the toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0049] According to the test results of Example 1 and Comparative Example 2, the silica gel not only has high compressive strength itself, but also the silicon dioxide in the silica gel reacts with tungsten and cobalt to form silicides, inhibiting the dissolution-precipitation process of tungsten carbide grains, improving 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 crosslinked, and a more dense silicon dioxide network structure can be formed in the ultra-coarse-grained WC-Co cemented carbide system, significantly improving the hardness, toughness, impact resistance and wear resistance of the ultra-coarse-grained WC-Co cemented carbide.

[0050] According to the comparative analysis of Example 1 and Comparative Example 3, it can be seen that compared with nano boron nitride, hydroxy boron nitride can form hydrogen bond interactions with the hydroxyl groups on the surface of the functionalized gel, improving the compatibility while significantly enhancing the hardness, toughness, impact resistance, and wear resistance of the ultra-coarse grained WC-Co cemented carbide.

[0051] According to the test results of Example 1 and Comparative Example 4, it can be known that the hydroxyl groups on the molecular chain of polyvinyl alcohol can undergo a condensation reaction with the hydroxyl groups on the surface of nano-silica in the functionalized gel to form stable Si-O-C covalent bonds, thereby crosslinking the polyvinyl alcohol molecules to form a three-dimensional network structure, significantly enhancing the hardness, toughness, impact resistance, and wear resistance of the ultra-coarse grained WC-Co cemented carbide.

[0052] According to the test results of Example 1 and Comparative Example 5, it can be seen that aluminum dihydrogen phosphate can form a network structure in aqueous solution, which helps to wrap the modified boron nitride particles and prevent their agglomeration, thereby improving the dispersion performance while significantly enhancing the hardness, toughness, impact resistance, and wear resistance of the ultra-coarse grained WC-Co cemented carbide.

[0053] This specific embodiment is only an interpretation of the present invention and is not a limitation thereof. Those skilled in the art can make modifications to this embodiment without creative contributions according to their needs after reading this specification, but as long as it is within the scope of the claims of the present invention, it is protected by the 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, prepare 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, preparation of 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, sieving, and obtaining a mixture; Step S3, granulation treatment: sieve the mixture prepared in step S2, and then place it in a granulator and roll it for 4-6 minutes to perform granulation treatment; Step S4, green compacting: pressing the mixed material granulated in step S3 into green compacts; Step S5, pressure-increasing sintering: the green body prepared in step S4 is pressure-increasingly sintered into an ultra-coarse-grained WC-Co cemented carbide.

2. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: 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 for reaction for 3-5 hours, filtering, washing, and drying to obtain pretreated yttrium trioxide; 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 for reaction for 2-3 hours, and cooling to room temperature to obtain modified yttrium trioxide; Step A3, uniformly mix the modified yttrium trioxide and the cross-linking agent, add the silicon precursor and anhydrous ethanol, stir until gelation, take out the gel, wash, and dry to obtain a functionalized gel.

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

4. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 2, characterized in that: In the step A2, the mass ratio of the 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, and the mixed acid is prepared by mixing hydrofluoric acid and concentrated nitric acid in a mass ratio of 1-2:

3.

5. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 2, characterized in that: In the step A3, the mass ratio of the modified yttrium trioxide, the cross-linking agent, the silicon precursor and the anhydrous ethanol is 3-5:2.4-3.2:0.4-0.6:16-22.

6. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 1, characterized in that: Described modified penetration enhancer is prepared by following steps: Step B1, mix nano hexagonal boron nitride and alkali solution evenly, heat to 100-120°C, stir and react for 40-50h, centrifuge, wash and dry the precipitate to obtain modified boron nitride; 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.

7. The method for preparing an ultra-coarse-grained WC-Co cemented carbide according to claim 6, 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%.

8. The method for preparing ultra-coarse-grained WC-Co cemented carbide according to claim 6, 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%.

9. 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 8.

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