A cemented carbide rod, a method of manufacturing and use thereof

Abstract

The present application relates to the technical field of hard alloy, and particularly relates to a hard alloy rod, a preparation method and application thereof.The hard alloy rod is prepared from tungsten carbide powder, porous core-shell composite cobalt powder, tantalum carbide powder and a binder through ball milling, spray granulation, pressing and sintering; the porous core-shell composite cobalt powder with a cobalt and titanium element concentration gradient is constructed through a gradient hydrothermal method. ‑6 The hard alloy rod has high hardness, high toughness and high wear resistance, and the volume wear amount is as low as 2.1*10 3 mm 3 / (N*m) at 800 DEG C high temperature, solves the technical problems of the traditional WC-Co alloy that hardness and toughness cannot be compatible and high-temperature wear resistance is poor, and can be widely applied to tool manufacturing under extreme working conditions such as aviation titanium alloy cutting tools and geothermal drilling bits.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide technology, and in particular to a cemented carbide rod, its preparation method, and its application. Background Technology

[0002] With the ever-increasing demands of modern industry on material performance, the design and optimization of high-performance materials has become one of the core research directions in the field of materials science. In fields such as machinery manufacturing, mining, and aerospace, the comprehensive performance of materials under extreme working conditions directly determines the service life and operating efficiency of equipment.

[0003] Tungsten carbide-cobalt cemented carbide (TCC-Co) is widely used in cutting tools (aerospace titanium alloy machining), drill bits, milling cutters, and mining and drilling fields due to its high hardness, high strength, and high impact toughness. Patent document CN112921227A discloses TCC-Co cemented carbide and its preparation method. This invention can effectively slow down the abnormal grain growth of TCC-Co composite powder during sintering without adding any grain inhibitors, avoiding limitations such as brittleness and porosity issues caused by excessive addition of grain inhibitors. However, improving the wear resistance of traditional WC-Co materials faces a fundamental contradiction: high hardness often comes at the cost of fracture toughness, and the Co binder phase oxidizes and softens at high temperatures, thus affecting its service life at high temperatures. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a cemented carbide rod, its preparation method and its application, in order to solve the problem that traditional WC-Co alloys are difficult to have both high hardness and high toughness, as well as poor wear resistance at high temperatures.

[0005] To achieve the above objectives, the present invention provides a method for preparing cemented carbide rods, comprising the following steps:

[0006] S1: Mix tungsten carbide powder, porous core-shell composite cobalt powder, tantalum carbide powder, binder and anhydrous ethanol, and ball mill for 40-50 hours to obtain a slurry;

[0007] S2: Spray granulation of the slurry to obtain composite powder;

[0008] S3: Load the composite powder into the mold, press it into shape, and obtain the blank;

[0009] S4: The raw blank is sintered, heat-treated, and machined to obtain cemented carbide rods;

[0010] The preparation steps of the porous core-shell composite cobalt powder in step S1 are as follows:

[0011] (1) Wash the cobalt powder in hydrochloric acid to obtain pretreated cobalt powder;

[0012] (2) Dissolve cobalt nitrate hexahydrate and titanium sulfate in a mixed solution of methanol and deionized water (4:1), stir until homogeneous, and obtain homogeneous solution 1 and homogeneous solution 2.

[0013] (3) Disperse 2-methylimidazole in deionized water, add pretreated cobalt powder, then add homogeneous solution 1, and react in a reactor at 140-160℃ for 6-8h. Then add homogeneous solution 2 and continue to react at 160-180℃ for 12-16h. The obtained product is purified, dried, and calcined to obtain porous core-shell composite cobalt powder.

[0014] Preferably, the cobalt powder in step (1) has a purity of ≥99.5% and a Fisher particle size of 1.0 μm.

[0015] Preferably, the concentration of hydrochloric acid in step (1) is 5%.

[0016] Preferably, in step (2), the ratio of cobalt nitrate hexahydrate, titanium sulfate, and mixed solution in the homogenized solution 1 is 5.5-6g: 2.3-2.5g: 150-200mL.

[0017] Preferably, the ratio of cobalt nitrate hexahydrate, titanium sulfate, and mixed solution in the homogenized solution 2 in step (2) is 2.8-3g:4.5-5g:150-200mL.

[0018] Preferably, the volume ratio of methanol to deionized water in the mixed solution in step (2) is 4:1.

[0019] Preferably, the ratio of 2-methylimidazole, deionized water, pretreated cobalt powder, homogenized solution 1 and homogenized solution 2 in step (3) is 2-3g:100-150mL:2-3g:50-70mL:50-70mL.

[0020] Preferably, the calcination in step (3) is carried out in an argon atmosphere at 800-1000℃ for 6-7 hours.

[0021] Preferably, the ratio of tungsten carbide powder, porous core-shell composite cobalt powder, tantalum carbide powder, binder and anhydrous ethanol in step S1 is 100-120g:9-13g:2-3g:0.5-1.5g.

[0022] Preferably, the tungsten carbide powder in step S1 has a purity of ≥99.8% and a Fisher particle size of 1.2 μm.

[0023] Preferably, the tantalum carbide powder in step S1 has a purity of ≥99.9% and a Fisher particle size of 0.8μm.

[0024] Preferably, the adhesive used in step S1 is polyvinyl alcohol.

[0025] Preferably, the inlet air temperature of the spray granulation in step S2 is 200-220℃, the outlet air temperature is 90-110℃, and the atomization pressure is 0.25-0.5MPa.

[0026] Preferably, the pressing pressure in step S3 is 300-350 MPa.

[0027] Preferably, the sintering process in step S4 is as follows: the sintering pressure is 9-10 MPa, the temperature is first increased to 500-600℃ at 2℃ / min and held for 90-120 min, then increased to 1000-1100℃ at 5℃ / min and held for 60-90 min, then increased to 1350-1400℃ at 8℃ / min and held for 45-60 min; finally, the temperature is increased to 1450-1500℃ at 3℃ / min and held for 90-110 min.

[0028] Preferably, the heat treatment process in step S4 is as follows: argon atmosphere, pressure of 150MPa, temperature of 1300-1400℃, and heat treatment for 2-3 hours.

[0029] Furthermore, the present invention also provides a cemented carbide rod.

[0030] Furthermore, the present invention also provides an application of cemented carbide rods in extreme environments such as aerospace titanium alloy cutting and geothermal drilling bits.

[0031] The beneficial effects of this invention are:

[0032] This invention uses 2-methylimidazole as a structure directing agent. Through the coordination of 2-methylimidazole with cobalt ions, a core-shell precursor with hierarchical channels is constructed. This not only enhances the ductility of the binder phase, but also increases the contact area between tungsten carbide and porous core-shell composite cobalt powder during sintering. This synergistic effect enables the material to maintain high hardness while also possessing excellent toughness and wear resistance.

[0033] This invention employs a stepwise reaction process combining gradient hydrothermal synthesis with dual homogeneous solutions to construct a core-shell structure with gradually varying titanium concentration on the surface of a cobalt matrix. This effectively alleviates interfacial stress concentration caused by differences in thermal expansion coefficients and enhances the chemical bonding strength between the hard and binder phases. Compared to a single titanium source system, the synergistic effect of the cobalt-titanium dual precursors also inhibits the local aggregation of brittle phases, enabling the material to form a continuous and dense composite oxide layer during high-temperature friction, thus significantly improving its resistance to high-temperature wear. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0035] The sources or properties of the raw materials used in the embodiments and comparative examples of this invention are as follows: Tungsten carbide powder: purity ≥ 99.8%, Fisher particle size 1.2 μm; Tantalum carbide powder: purity ≥ 99.9%, Fisher particle size 0.8 μm; Tungsten carbide powder: purity ≥ 99.8%, Fisher particle size 1.2 μm.

[0036] Example 1: A cemented carbide rod, the specific preparation steps are as follows:

[0037] (1) Place the cobalt powder in 5% dilute hydrochloric acid and ultrasonically clean it for 10 min, then wash it with deionized water and vacuum dry it at 60℃ for 2 h to obtain pretreated cobalt powder.

[0038] (2) Dissolve 5.5g of cobalt nitrate hexahydrate and 2.3g of titanium sulfate in 150mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 1.

[0039] (3) Dissolve 2.8g of cobalt nitrate hexahydrate and 4.5g of titanium sulfate in 150mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 2.

[0040] (4) Disperse 2g of 2-methylimidazole in 100mL of deionized water, and after ultrasonic dispersion, add 2g of pretreated cobalt powder. Then, while stirring, slowly add 50mL of homogeneous solution 1 and transfer it to a reaction vessel. React at 140℃ for 6h. Then, inject 50mL of homogeneous solution 2 through a feed pump, raise the temperature to 160℃, and continue the reaction for 12h. After the reaction is completed, the obtained product is centrifuged and filtered, and washed with methanol and deionized water in sequence. After drying, place the product in an argon atmosphere and heat it to 800℃ at a heating rate of 5℃ / min. Hold for 6h to obtain porous core-shell composite cobalt powder.

[0041] (5) Place 100g of tungsten carbide powder, 9g of porous core-shell composite cobalt powder, 2g of tantalum carbide powder, and 0.5g of polyvinyl alcohol in a planetary ball mill, add 300mL of anhydrous ethanol, and ball mill at 250rpm for 40h to obtain a slurry.

[0042] (6) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 200℃, the outlet air temperature is 90℃, and the atomization pressure is 0.25MPa.

[0043] (7) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 300MPa for 180s to obtain a blank.

[0044] (8) Place the green blank in a sintering furnace, set the sintering pressure to 9 MPa, then raise the temperature to 500℃ at 2℃ / min, hold for 90 min, continue to raise the temperature to 1000℃ at 5℃ / min, hold for 60 min, raise the temperature to 1350℃ at 8℃ / min, hold for 45 min; raise the temperature to 1450℃ at 3℃ / min, hold for 90 min, and obtain the sintered blank;

[0045] (9) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1300 °C. The furnace is held for 2 hours and then cooled before machining to obtain a cemented carbide bar.

[0046] Example 2: A cemented carbide rod, the specific preparation steps are as follows:

[0047] (1) Place the cobalt powder in 5% dilute hydrochloric acid and ultrasonically clean it for 10 min, then wash it with deionized water and vacuum dry it at 60℃ for 2 h to obtain pretreated cobalt powder.

[0048] (2) Dissolve 5.8g of cobalt nitrate hexahydrate and 2.4g of titanium sulfate in 160mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 1.

[0049] (3) Dissolve 2.9g of cobalt nitrate hexahydrate and 4.8g of titanium sulfate in 180mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 2.

[0050] (4) 2.5g of 2-methylimidazole was dispersed in 130mL of deionized water and ultrasonically dispersed evenly. Then, 2.5g of pretreated cobalt powder was added, and 60mL of homogeneous solution 1 was slowly added dropwise while stirring. The mixture was transferred to a reaction vessel and reacted at 150℃ for 7h. Then, 60mL of homogeneous solution 2 was injected through a feed pump, the temperature was raised to 170℃, and the reaction was continued for 14h. After the reaction was completed, the product was centrifuged and filtered, and washed with methanol and deionized water in sequence. The product was dried and placed in an argon atmosphere and heated to 900℃ at a heating rate of 5℃ / min. The temperature was maintained for 7h to obtain porous core-shell composite cobalt powder.

[0051] (5) Place 110g of tungsten carbide powder, 11g of porous core-shell composite cobalt powder, 2.5g of tantalum carbide powder and 1g of polyvinyl alcohol in a planetary ball mill, add 350mL of anhydrous ethanol, and ball mill at 280rpm for 45h to obtain a slurry.

[0052] (6) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 210℃, the outlet air temperature is 100℃, and the atomization pressure is 0.45MPa.

[0053] (7) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 330MPa for 180s to obtain a green blank.

[0054] (8) Place the green blank in a sintering furnace, set the sintering pressure to 10 MPa, then raise the temperature to 550°C at 2°C / min, hold for 100 min, continue to raise the temperature to 1100°C at 5°C / min, hold for 80 min, raise the temperature to 1400°C at 8°C / min, hold for 50 min; raise the temperature to 1500°C at 3°C / min, hold for 110 min, and obtain the sintered blank;

[0055] (9) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1350 °C. The furnace is held for 3 hours and then cooled before machining to obtain a cemented carbide bar.

[0056] Example 3: A cemented carbide rod, the specific preparation steps are as follows:

[0057] (1) Place the cobalt powder in 5% dilute hydrochloric acid and ultrasonically clean it for 10 min, then wash it with deionized water and vacuum dry it at 60℃ for 2 h to obtain pretreated cobalt powder.

[0058] (2) Dissolve 6g of cobalt nitrate hexahydrate and 2.5g of titanium sulfate in 200mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 1.

[0059] (3) Dissolve 3g of cobalt nitrate hexahydrate and 5g of titanium sulfate in 200mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 2.

[0060] (4) Disperse 3g of 2-methylimidazole in 150mL of deionized water, and after ultrasonic dispersion, add 3g of pretreated cobalt powder. Then, while stirring, slowly add 70mL of homogeneous solution 1 and transfer it to a reaction vessel. React at 160℃ for 8h. Then, inject 70mL of homogeneous solution 2 through a feed pump, raise the temperature to 180℃, and continue the reaction for 16h. After the reaction is completed, the obtained product is centrifuged and filtered, and washed with methanol and deionized water in sequence. After drying, place the product in an argon atmosphere and heat it to 1000℃ at a heating rate of 5℃ / min. Hold for 7h to obtain porous core-shell composite cobalt powder.

[0061] (5) Place 120g of tungsten carbide powder, 13g of porous core-shell composite cobalt powder, 3g of tantalum carbide powder, and 1.5g of polyvinyl alcohol in a planetary ball mill, add 400mL of anhydrous ethanol, and ball mill at 300rpm for 50h to obtain a slurry.

[0062] (6) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 220℃, the outlet air temperature is 110℃, and the atomization pressure is 0.5MPa.

[0063] (7) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 350MPa for 180s to obtain a blank.

[0064] (8) Place the green blank in a sintering furnace, set the sintering pressure to 10 MPa, then raise the temperature to 600℃ at 2℃ / min and hold for 120 min, continue to raise the temperature to 1100℃ at 5℃ / min and hold for 90 min, raise the temperature to 1400℃ at 8℃ / min and hold for 60 min; raise the temperature to 1500℃ at 3℃ / min and hold for 110 min to obtain the sintered blank;

[0065] (9) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1400 °C. The furnace is held for 3 hours and then cooled before machining to obtain cemented carbide rods.

[0066] Comparative Example 1: The difference from Example 2 is that cobalt powder was added directly. The specific steps are as follows:

[0067] (1) Place 110g of tungsten carbide powder, 11g of cobalt powder, 2.5g of tantalum carbide powder and 1g of polyvinyl alcohol in a planetary ball mill, add 350mL of anhydrous ethanol, and ball mill at 280rpm for 45h to obtain a slurry.

[0068] (2) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 210℃, the outlet air temperature is 100℃, and the atomization pressure is 0.45MPa.

[0069] (3) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 330MPa for 180s to obtain a blank.

[0070] (4) Place the green blank in a sintering furnace, set the sintering pressure to 10 MPa, then raise the temperature to 550°C at 2°C / min and hold for 100 min, continue to raise the temperature to 1100°C at 5°C / min and hold for 80 min, raise the temperature to 1400°C at 8°C / min and hold for 50 min; raise the temperature to 1500°C at 3°C / min and hold for 110 min to obtain the sintered blank;

[0071] (5) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1350 °C. It is held for 3 hours, cooled, and then machined to obtain a cemented carbide bar.

[0072] Comparative Example 2: The difference from Example 2 is that 2-methylimidazole is not added. The specific steps are as follows:

[0073] (1) Place the cobalt powder in 5% dilute hydrochloric acid and ultrasonically clean it for 10 min, then wash it with deionized water and vacuum dry it at 60℃ for 2 h to obtain pretreated cobalt powder.

[0074] (2) Dissolve 5.8g of cobalt nitrate hexahydrate and 2.4g of titanium sulfate in 160mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 1.

[0075] (3) Dissolve 2.9g of cobalt nitrate hexahydrate and 4.8g of titanium sulfate in 180mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 2.

[0076] (4) Add 2.5g of pretreated cobalt powder to 130mL of deionized water, disperse it evenly by ultrasonication, and slowly add 60mL of homogeneous solution 1 while stirring. Transfer it to a reaction vessel and react at 150℃ for 7h. Then, inject 60mL of homogeneous solution 2 through a feed pump, raise the temperature to 170℃, and continue to react for 14h. After the reaction is completed, the obtained product is centrifuged and filtered, and washed with methanol and deionized water in sequence, dried, and placed in an argon atmosphere. Heat it to 900℃ at a heating rate of 5℃ / min and keep it for 7h to obtain porous core-shell composite cobalt powder.

[0077] (5) Place 110g of tungsten carbide powder, 11g of porous core-shell composite cobalt powder, 2.5g of tantalum carbide powder and 1g of polyvinyl alcohol in a planetary ball mill, add 350mL of anhydrous ethanol, and ball mill at 280rpm for 45h to obtain a slurry.

[0078] (6) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 210℃, the outlet air temperature is 100℃, and the atomization pressure is 0.45MPa.

[0079] (7) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 330MPa for 180s to obtain a green blank.

[0080] (8) Place the green blank in a sintering furnace, set the sintering pressure to 10 MPa, then raise the temperature to 550°C at 2°C / min, hold for 100 min, continue to raise the temperature to 1100°C at 5°C / min, hold for 80 min, raise the temperature to 1400°C at 8°C / min, hold for 50 min; raise the temperature to 1500°C at 3°C / min, hold for 110 min, and obtain the sintered blank;

[0081] (9) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1350 °C. The furnace is held for 3 hours and then cooled before machining to obtain a cemented carbide bar.

[0082] Comparative Example 3: The difference from Example 2 is that homogenized solution 1 and homogenized solution 2 contain only titanium sulfate. The specific steps are as follows:

[0083] (1) Place the cobalt powder in 5% dilute hydrochloric acid and ultrasonically clean it for 10 min, then wash it with deionized water and vacuum dry it at 60℃ for 2 h to obtain pretreated cobalt powder.

[0084] (2) Dissolve 2.4g of titanium sulfate in 160mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 1.

[0085] (3) Dissolve 4.8g of titanium sulfate in 180mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 2.

[0086] (4) 2.5g of 2-methylimidazole was dispersed in 130mL of deionized water and ultrasonically dispersed evenly. Then, 2.5g of pretreated cobalt powder was added, and 60mL of homogeneous solution 1 was slowly added dropwise while stirring. The mixture was transferred to a reaction vessel and reacted at 150℃ for 7h. Then, 60mL of homogeneous solution 2 was injected through a feed pump, the temperature was raised to 170℃, and the reaction was continued for 14h. After the reaction was completed, the product was centrifuged and filtered, and washed with methanol and deionized water in sequence. The product was dried and placed in an argon atmosphere and heated to 900℃ at a heating rate of 5℃ / min. The temperature was maintained for 7h to obtain porous core-shell composite cobalt powder.

[0087] (5) Place 110g of tungsten carbide powder, 11g of porous core-shell composite cobalt powder, 2.5g of tantalum carbide powder and 1g of polyvinyl alcohol in a planetary ball mill, add 350mL of anhydrous ethanol, and ball mill at 280rpm for 45h to obtain a slurry.

[0088] (6) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 210℃, the outlet air temperature is 100℃, and the atomization pressure is 0.45MPa.

[0089] (7) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 330MPa for 180s to obtain a green blank.

[0090] (8) Place the green blank in a sintering furnace, set the sintering pressure to 10 MPa, then raise the temperature to 550°C at 2°C / min, hold for 100 min, continue to raise the temperature to 1100°C at 5°C / min, hold for 80 min, raise the temperature to 1400°C at 8°C / min, hold for 50 min; raise the temperature to 1500°C at 3°C / min, hold for 110 min, and obtain the sintered blank;

[0091] (9) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1350 °C. The furnace is held for 3 hours and then cooled before machining to obtain a cemented carbide bar.

[0092] Comparative Example 4: The difference from Example 2 is that homogenized solution 2 is not added. The specific steps are as follows:

[0093] (1) Place the cobalt powder in 5% dilute hydrochloric acid and ultrasonically clean it for 10 min, then wash it with deionized water and vacuum dry it at 60℃ for 2 h to obtain pretreated cobalt powder.

[0094] (2) Dissolve 5.8g of cobalt nitrate hexahydrate and 2.4g of titanium sulfate in 160mL of a mixed solution of methanol and deionized water (4:1), stir well, and obtain homogeneous solution 1.

[0095] (3) Disperse 2.5g of 2-methylimidazole in 130mL of deionized water, and after ultrasonic dispersion, add 2.5g of pretreated cobalt powder. Then, while stirring, slowly add 60mL of homogeneous solution 1 and transfer it to a reaction vessel. React at 150℃ for 7h. After the reaction is completed, the product is centrifuged and filtered, and washed with methanol and deionized water in sequence. After drying, place the product in an argon atmosphere and heat it to 900℃ at a heating rate of 5℃ / min. Hold for 7h to obtain porous core-shell composite cobalt powder.

[0096] (4) Place 110g of tungsten carbide powder, 11g of porous core-shell composite cobalt powder, 2.5g of tantalum carbide powder and 1g of polyvinyl alcohol in a planetary ball mill, add 350mL of anhydrous ethanol, and ball mill at 280rpm for 45h to obtain a slurry.

[0097] (5) The slurry is transferred to a spray drying tower for spray granulation to obtain composite powder; wherein the inlet air temperature is 210℃, the outlet air temperature is 100℃, and the atomization pressure is 0.45MPa.

[0098] (6) The composite powder is loaded into a cemented carbide mold and formed in an isostatic press at 330MPa for 180s to obtain a green blank.

[0099] (7) Place the green blank in a sintering furnace, set the sintering pressure to 10 MPa, then raise the temperature to 550°C at 2°C / min and hold for 100 min, continue to raise the temperature to 1100°C at 5°C / min and hold for 80 min, raise the temperature to 1400°C at 8°C / min and hold for 50 min; raise the temperature to 1500°C at 3°C / min and hold for 110 min to obtain the sintered blank;

[0100] (8) Under an argon atmosphere, the sintered billet is placed in a hot isostatic pressing furnace, with a pressure of 150 MPa and a temperature of 1350 °C. The furnace is held for 3 hours and then cooled before machining to obtain a cemented carbide bar.

[0101] Performance testing

[0102] Hardness: Tested using a Vickers hardness tester;

[0103] Bending strength: The experiment was conducted according to GB / T 3851-2015 "Test Method for Transverse Fracture Strength of Hard Alloy". A 3mm×4mm×35mm specimen with a span of 30mm was prepared and loaded at a rate of 0.5mm / min on a universal testing machine until fracture.

[0104] Toughness: Tested according to the "GBT1817-2017 Standard for Room Temperature Impact Toughness Test of Hard Alloys";

[0105] Room temperature wear resistance: The wear rate was calculated by weight loss method using a ball-disc high temperature friction tester (load 50N, rotation speed 0.2m / s, temperature room temperature, time 60min);

[0106] High-temperature wear resistance: The wear rate was calculated by using a ball-disc high-temperature friction tester (load 50N, rotation speed 0.2m / s, temperature 800℃, time 60min) and the wear rate was calculated by the weight loss method. The test results are shown in Table 1.

[0107] Table 1 Performance Test Results

[0108]

[0109] Data Analysis: Performance data from Examples 1-3 show that the cemented carbide rods prepared in this invention exhibit excellent comprehensive performance. This is mainly due to the synergistic effect of the porous core-shell composite cobalt powder and the gradient coating structure: the cobalt-titanium gradient coating layer constructed by the hydrothermal method forms a stable interfacial phase during high-temperature sintering, effectively improving the wettability between the cobalt phase and tungsten carbide particles, making the binder phase distribution more uniform and continuous, and significantly improving its bending strength. Simultaneously, the porous nature of the core-shell structure provides a stress buffer mechanism for the material and increases the contact area between tungsten carbide and the porous core-shell composite cobalt powder, thereby achieving simultaneous optimization of hardness and toughness. The outstanding high-temperature performance indicates that the formed (Ti,W)C solid solution and cobalt-titanium oxide composite layer effectively inhibit the softening and oxidative corrosion of the Co binder phase at high temperatures. This multi-scale structural design (nano-coating-micron pores-macro gradient) enables the material to maintain stable mechanical properties and wear resistance under different temperature conditions.

[0110] According to the performance of Example 2 and Comparative Example 1 in Table 1, compared with the comparative scheme that directly uses cobalt powder, this process achieves nanoscale interlocking between the hard phase and the binder phase through the in-situ generated (Co,W,Ti)C composite phase. This microstructure feature is a key factor in the simultaneous improvement of bending strength and impact toughness. The porous core-shell structure constructed by gradient hydrothermal synthesis provides a three-dimensional interpenetrating network for the cobalt binder phase. This special morphology promotes the uniform distribution of liquid cobalt during sintering and optimizes the wettability and interfacial bonding strength of WC grains. Secondly, the gradient doping of titanium effectively alleviates the interfacial stress caused by the difference in thermal expansion coefficients between WC and Co phases. In addition, the gradient distribution of titanium in the core-shell structure also optimizes the oxidation behavior of the material during high-temperature friction, promotes the rapid formation of a composite oxide film with self-lubricating properties, and improves the wear resistance by 73.4%.

[0111] Based on the performance comparison analysis of Example 2 and Comparative Example 2 in Table 1, this invention uses 2-methylimidazole as a structure directing agent. Through the coordination of 2-methylimidazole with cobalt ions, a core-shell precursor with hierarchical channels is constructed. Its unique porous structure optimizes the WC grain distribution during sintering. The nitrogen-doped carbon network formed by the pyrolysis of methylimidazole not only enhances the ductility of the binder phase, but also achieves an upgrade of interfacial bonding from physical adsorption to chemical bonding with the Ti-NC interface phase formed by it and titanium. Furthermore, the hierarchical channels can increase the contact area between tungsten carbide and porous core-shell composite cobalt powder during sintering. This synergistic effect enables the material to maintain high hardness while also possessing excellent toughness and wear resistance.

[0112] Based on the performance data comparison between Example 2 and Comparative Example 3 in Table 1, this invention achieves significantly improved overall performance of cemented carbide rods through a synergistic hydrothermal reaction process using cobalt nitrate and titanium sulfate dual precursors. The introduction of cobalt nitrate forms a Co-Ti-O bonded network during titanium doping, which transforms into a uniformly distributed solid solution phase during subsequent sintering, effectively dispersing interfacial stress. Simultaneously, the cobalt-titanium composite oxide generated under the dual precursor system possesses a unique layered structure, forming an interlocking microstructure during high-temperature sintering, a key factor in simultaneously improving hardness and toughness. Compared to a single titanium source system, the synergistic effect of the cobalt-titanium dual precursors also suppresses local aggregation of brittle phases, enabling the material to form a continuous and dense composite oxide layer during high-temperature friction, significantly improving its resistance to high-temperature wear.

[0113] Based on the performance data comparison between Example 2 and Comparative Example 4 in Table 1, this invention, through a stepwise reaction process combining gradient hydrothermal synthesis and dual homogeneous solutions, enables cemented carbide rods to exhibit significantly improved comprehensive performance. The gradient solution design constructs a core-shell structure with gradually varying titanium concentrations on the cobalt matrix surface. This compositional gradient effectively alleviates interfacial stress concentration caused by differences in thermal expansion coefficients. Secondly, the stepwise introduction of titanium forms a Co-Ti intermetallic compound phase, creating a nanoscale transition layer at the WC / Co interface. This enhances the chemical bonding strength between the hard and binder phases and suppresses grain boundary slip through a pinning effect. Compared to a single solution system, the gradient solution process provides a more continuous diffusion path for titanium in the cobalt matrix, avoiding brittle phase concentration caused by localized component segregation. This is crucial for achieving a synergistic improvement in both hardness and toughness. Furthermore, the three-dimensional mass transfer channels provided by the porous core-shell structure promote uniform liquid phase distribution during sintering, providing a structural basis for a breakthrough improvement in wear resistance.

[0114] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a cemented carbide rod, characterized in that, Includes the following steps: S1: Mix tungsten carbide powder, porous core-shell composite cobalt powder, tantalum carbide powder, binder and anhydrous ethanol, and ball mill to obtain a slurry; S2: Spray granulation of the slurry to obtain composite powder; S3: Load the composite powder into the mold, press it into shape, and obtain the blank; S4: The raw blank is sintered, heat-treated, and machined to obtain cemented carbide rods; The preparation steps of the porous core-shell composite cobalt powder in step S1 are as follows: (1) The cobalt powder was washed in hydrochloric acid to obtain pretreated cobalt powder; (2) Dissolve cobalt nitrate hexahydrate and titanium sulfate in a mixed solution of methanol and deionized water, and stir until homogeneous to obtain homogeneous solution 1 and homogeneous solution 2. (3) Disperse 2-methylimidazole in deionized water, add pretreated cobalt powder, then add homogeneous solution 1, react in a reactor at 140-160℃ for 6-8h, then add homogeneous solution 2, and continue to react at 160-180℃ for 12-16h. The obtained product is purified, dried, and calcined to obtain porous core-shell composite cobalt powder. In step (2), the ratio of cobalt nitrate hexahydrate, titanium sulfate, and mixed solution in homogenized solution 1 is 5.5-6g: 2.3-2.5g: 150-200mL; and the ratio of cobalt nitrate hexahydrate, titanium sulfate, and mixed solution in homogenized solution 2 is 2.8-3g: 4.5-5g: 150-200mL.

2. The method for preparing cemented carbide rods according to claim 1, characterized in that, The concentration of hydrochloric acid in step (1) is 5%.

3. The method for preparing cemented carbide rods according to claim 1, characterized in that, The ratio of the amounts of 2-methylimidazole, deionized water, pretreated cobalt powder, homogenized solution 1 and homogenized solution 2 in step (3) is 2-3g:100-150mL:2-3g:50-70mL:50-70mL.

4. The method for preparing cemented carbide rods according to claim 1, characterized in that, The ratio of tungsten carbide powder, porous core-shell composite cobalt powder, tantalum carbide powder, and binder in step S1 is 100-120g:9-13g:2-3g:0.5-1.5g.

5. The method for preparing cemented carbide rods according to claim 1, characterized in that, The tungsten carbide powder mentioned in step S1 has a purity of ≥99.8% and a Fisher particle size of 1.2 μm; the tantalum carbide powder has a purity of ≥99.9% and a Fisher particle size of 0.8 μm. The adhesive is polyvinyl alcohol.

6. The method for preparing cemented carbide rods according to claim 1, characterized in that, In step S2, the inlet air temperature of the spray granulation is 200-220℃, the outlet air temperature is 90-110℃, and the atomization pressure is 0.25-0.5MPa; in step S3, the pressing pressure is 300-350MPa.

7. The method for preparing cemented carbide rods according to claim 1, characterized in that, The sintering process described in step S4 is as follows: the sintering pressure is 9-10 MPa. First, the temperature is increased to 500-600℃ at 2℃ / min and held for 90-120 min. Then, the temperature is increased to 1000-1100℃ at 5℃ / min and held for 60-90 min. Next, the temperature is increased to 1350-1400℃ at 8℃ / min and held for 45-60 min. Finally, the temperature is increased to 1450-1500℃ at 3℃ / min and held for 90-110 min.

8. The method for preparing cemented carbide rods according to claim 1, characterized in that, The heat treatment process described in step S4 is as follows: argon atmosphere, pressure 150MPa, temperature 1300-1400℃, heat treatment for 2-3 hours.

9. A cemented carbide rod, characterized in that, It is prepared by the method for preparing cemented carbide rods according to any one of claims 1-8.

10. An application of the cemented carbide rod according to claim 9, characterized in that, It is used in aerospace titanium alloy cutting and geothermal drilling bits.

Images