A forming process for a helical groove bar

Abstract

The application belongs to the technical field of powder metallurgy and metal processing, and particularly relates to a forming process of a spiral groove bar, which comprises the following steps: ball-milling tungsten carbide powder, cobalt powder, high-entropy polyoxometalate derivative nanocomposite modifier, anhydrous ethanol and oleic acid to obtain a mixed slurry; after adding polyethylene glycol, spray granulation is performed; the obtained granulated powder is filled into a cold isostatic pressing mold, and after compression forming, demolding, end cutting, immersion washing and drying, a compact is obtained; the compact is placed in an S-HIP furnace, and sequentially subjected to negative pressure heating, hydrogen atmosphere dewaxing, argon protection heating and vacuum high-temperature sintering, and after cooling, a finished product is obtained through a metal processing link. The modifier is prepared by coordination reaction of tungsten hexachloride, molybdenum pentachloride, vanadium trichloride, tantalum chloride and rhenium trichloride with an organic ligand in anhydrous acetonitrile and dimethylformamide, and is prepared through sol-gel conversion, supercritical drying, staged pyrolysis nitriding and surface silane coupling modification. The spiral groove bar prepared by the application has excellent comprehensive mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy and metal processing technology, and specifically relates to a forming process for spiral grooved bars. Background Technology

[0002] In the metalworking industry, tungsten carbide-cobalt cemented carbide is widely used in the manufacture of metal cutting tools such as drills, end mills, and reamers due to its extremely high hardness, excellent wear resistance, and good compressive strength. Among these, cemented carbide bars with helical groove structures (i.e., helical bars) are key precursors for manufacturing high-efficiency drills and end mills. Traditional helical groove bar production methods typically employ a "sintering first, then grooving" process, where a solid cemented carbide round bar is first prepared, and then helical grooves are machined onto the bar surface through grinding or electrical discharge machining. However, this post-processing method has significant drawbacks: firstly, cemented carbide has extremely high hardness, making grinding difficult, inefficient, and causing severe tool wear; secondly, the machining process removes a large amount of material, resulting in the waste of expensive tungsten carbide and cobalt resources and low material utilization. Therefore, developing a near-net-shape forming technology that can directly form helical groove structures is of great significance for reducing the manufacturing cost of metalworking tools and shortening the production cycle.

[0003] To overcome the aforementioned post-processing defects, existing research has attempted to directly prepare compacts with spiral groove structures during the cold isostatic pressing stage. Specifically, by designing a polyurethane shaping mold with spiral protrusions on the inner wall, the powder directly forms spiral grooves during the pressing process, thereby obtaining near-net-shape spiral groove bar compacts that require only minor trimming after sintering. However, existing near-net-shape forming processes still face a series of technical challenges. First, the flowability and packing density uniformity of tungsten carbide-cobalt composite powder directly affect the forming quality of the spiral region. The consistent filling of powders obtained through conventional ball milling and spray granulation within complex cavities is difficult to guarantee, easily leading to low density or microcracks in the spiral groove region. Second, the organic binder added during the forming process requires precise control of the removal curve during the subsequent debinding stage. Incomplete removal or an improper atmosphere can severely affect the final properties of the sintered body due to residual carbon or oxygen. Third, during the high-temperature liquid-phase sintering stage, the cobalt binder phase melts before tungsten carbide, easily leading to abnormal growth of tungsten carbide grains. Simultaneously, insufficient interfacial wettability between tungsten carbide and cobalt reduces the material's fracture toughness, which is fatal for metalworking tools subjected to complex cutting stresses. Although existing technologies have attempted to suppress grain growth by adding small amounts of carbides (such as vanadium carbide and chromium carbide) or rare earth elements, these methods often only improve a single performance indicator, and the interfacial compatibility between the additives and the matrix is ​​poor, making it difficult to simultaneously meet the multiple requirements of powder flowability, sintering densification, and interfacial toughening. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a forming process for spiral grooved bars.

[0005] A first aspect of the present invention provides a forming process for a spiral grooved bar, comprising the following steps: S1. By weight, add 88-92 parts of tungsten carbide powder, 8-12 parts of cobalt powder, 0.3-0.8 parts of high-entropy polyoxometalate-derived nanocomposite modifier, 40-60 parts of anhydrous ethanol and 0.1-0.15 parts of oleic acid to a ball mill and ball mill; to obtain a mixed slurry. S2. Add 2.0-2.5 parts of polyethylene glycol 4000 to the mixed slurry; spray dry, granulate, and obtain granulated powder; S3. Fill 100-105 parts of granulated powder into a cold isostatic pressing mold; after filling, seal the mold and place it in the main pressure cylinder of the cold isostatic pressing equipment. Inject 500-1000 parts of a mixture of anti-wear hydraulic oil and water into the main pressure cylinder and maintain pressure at 130-150MPa; after the pressure is maintained, remove the mold to obtain a blank; cut off both ends of the blank, immerse it in petroleum ether for washing, and vacuum dry it at 58-62℃ to obtain a spiral bar blank; S4. Place the spiral bar blank in an S-HIP furnace, evacuate the vacuum, heat to 245-255℃ and hold, introduce hydrogen gas, heat to 445-455℃, continue heating in a hydrogen atmosphere to 595-605℃; switch to argon gas, heat to 745-755℃; heat to 895-905℃; turn off the argon gas, evacuate the vacuum, heat to 1400-1450℃, introduce argon gas, sinter; allow to cool naturally to room temperature, trim the edges, and sandblast the surface.

[0006] In this invention, the core mechanism of the spiral groove bar forming process involves the coordination between ball milling dispersion, isostatic pressing, and multi-stage sintering. During the ball milling stage, tungsten carbide and cobalt powders are repeatedly impacted by cemented carbide grinding balls in anhydrous ethanol medium, resulting in particle refinement and lattice activation. The carboxyl groups of oleic acid selectively adsorb onto the surface of cobalt particles, while its long alkyl chains extend into the ethanol medium. This reduces the interfacial energy difference between tungsten carbide and cobalt, suppressing segregation caused by density differences. The organic functional layer on the surface of the high-entropy polyoxometalate-derived nanocomposite modifier is compatible with the long chains of oleic acid. Therefore, the high-entropy polyoxometalate-derived nanocomposite modifier can be uniformly suspended and attached to the microscopic interface of tungsten carbide and cobalt particles, providing submicron-level active sites for grain boundary pinning in the subsequent liquid-phase sintering stage. The addition of polyethylene glycol 4000 forms an alcohol-based slurry, which is then dispersed into micron-sized droplets by an atomizer. Hot air enters the droplets, causing the ethanol to evaporate rapidly. Long-chain molecules of polyethylene glycol 4000 accumulate at the solid-liquid interface, forming flexible bridges that bind tungsten carbide, cobalt, and modifier particles into smooth, spherical granules. This powder has good flowability and can uniformly fill the mold during pressing. After the granulated powder is loaded into a cold isostatic pressing mold, a mixture of anti-wear hydraulic oil and water applies isotropic pressure to the powder through the polyurethane mold. Because the polyurethane mold does not generate directional stress gradients when transmitting pressure, the density difference throughout the compact within the spiral cavity is minimal. After demolding, the compact is first washed with petroleum ether to remove oil contamination from the mold, and then vacuum-dried at low temperature to remove residual volatiles, preventing the introduction of carbon or oxygen contamination during subsequent sintering. During the sintering heating stage, a vacuum is first applied and the temperature is maintained at a low level, allowing the remaining ethanol and adsorbed water in the granulated powder to slowly escape, preventing rapid heating from causing blistering or cracking of the compact. After hydrogen gas is introduced, the temperature continues to rise. The hydrogen gas passes through the porous channels of the green body, causing the molecular chains of polyethylene glycol 4000 to break down into oxygen-containing small molecules. These small molecules are carried out of the furnace by the hydrogen gas flow and condensed and removed at the exhaust port. Hydrogen gas can also reduce the thin layer of oxides on the surface of tungsten carbide and cobalt particles, turning them into an active metallic state. Then, argon gas is switched to and the temperature is raised to a higher level. At this point, the hydrogen adsorbed on the surface will desorb, which can prevent hydrogen-induced decarburization; the inertness of argon gas can also prevent the metal skeleton from being oxidized or re-oxidized. The argon gas is turned off and a vacuum is drawn, and the temperature is raised to the sintering temperature range. At this temperature, cobalt becomes a liquid phase, flows and wets the tungsten carbide particles, and the tungsten carbide grains rearrange and densify through a dissolution-precipitation mechanism. Modifiers act as pinning agents at the grain boundaries, inhibiting abnormal grain growth. Near the end of sintering, argon gas is reintroduced and pressurized. The isostatic atmosphere can close the residual pores and inhibit the volatilization of low-melting-point elements, allowing the green body to reach a near-completely dense state. After natural cooling, the spiral groove bar is then trimmed and sandblasted to remove the oxide layer and surface defects, ultimately yielding a stable spiral groove bar product.

[0007] According to a preferred embodiment of the present invention, in step S1, the ball milling time is 48-50 hours.

[0008] According to a preferred embodiment of the present invention, in step S2, the feed rate for spray drying is 20-30 mL / min.

[0009] According to a preferred embodiment of the present invention, in step S3, the vacuum drying time at 58-62°C is 4-6 hours.

[0010] According to a preferred embodiment of the present invention, in step S4, the time for heating to 245-255°C and holding at that temperature is 1-2 hours.

[0011] According to a preferred embodiment of the present invention, the preparation steps of the high-entropy polyoxometalate-derived nanocomposite modifier include: A1. Under nitrogen protection, 15-16 parts by weight of tungsten hexachloride, 3.5-4.5 parts by weight of molybdenum pentachloride, 3.0-3.5 parts by weight of vanadium trichloride, 3.5-4.0 parts by weight of tantalum chloride and 3.5-4.0 parts by weight of rhenium trichloride are mixed and dissolved in 100-150 parts by weight of anhydrous acetonitrile; a mixture containing 6-8 parts by weight of 2,2'-bipyridine-4,4'-dicarboxylic acid, 3-5 parts by weight of 1,3,5-pyromellitic acid and 80-120 parts by weight of N,N-dimethylformamide is added dropwise; the mixture is stirred at room temperature, and then heated to 58-62°C to stir the reaction to obtain a precursor solution; A2. Place the precursor solution in a reflux condenser and add a mixture of 100-120 parts methanol and 50-60 parts deionized water dropwise under an ice-water bath; add 2-4 parts tetramethylammonium hydroxide aqueous solution to adjust the pH to 6.5-7.0; heat to 38-42℃ and stir, then allow to stand for aging to obtain a wet gel; wash the wet gel with anhydrous ethanol at 30-35℃, then wash with 150-200 parts tert-butanol at 30-35℃, freeze in liquid nitrogen, and freeze-dry at -48~-52℃ to obtain the precursor; A3. Place the precursor in a tube furnace and heat it to 295-305℃ under argon protection. Hold the temperature at 495-505℃. Turn off the argon gas and introduce ammonia gas. Heat the temperature to 695-705℃ and hold. Switch back to argon protection and heat the temperature to 845-855℃ and hold. Allow it to cool naturally to room temperature, grind, and sieve to obtain the modified material. A4. Disperse the modified material in 100-150 parts of anhydrous ethanol, add 2-5 parts of deionized water and 0.1-0.5 parts of glacial acetic acid in sequence, add 0.5-1.5 parts of γ-methacryloyloxypropyltrimethoxysilane and 0.1-0.5 parts of polyvinylpyrrolidone, sonicate, stir at 58-62℃, centrifuge to obtain solid product; wash the solid product with anhydrous ethanol and deionized water, and vacuum dry at 58-62℃.

[0012] The preparation mechanism of the high-entropy polyoxometalate-derived nanocomposite modifier in this invention is as follows. Under nitrogen protection, tungsten hexachloride, molybdenum pentachloride, vanadium trichloride, tantalum chloride, and rhenium trichloride are dissolved in anhydrous acetonitrile. The nitrogen atoms on the acetonitrile molecules provide coordination electrons to each metal center, first forming a mononuclear complex intermediate, which prevents hydrolysis or disproportionation and precipitation between different high-valence metal chlorides. Then, a mixture of N,N-dimethylformamide containing 2,2'-bipyridine-4,4'-dicarboxylic acid and 1,3,5-pyromellitic acid is slowly added dropwise. The 2,2'-bipyridine-4,4'-dicarboxylic acid acts as a bridging node by simultaneously chelating with different metal centers through two nitrogen atoms and a pair of carboxyl groups; the three carboxyl groups of 1,3,5-pyromellitic acid are oriented in different directions, each anchoring a metal ion. This constructs a multidentate mixed coordination network with metals as nodes and organic ligands as connecting bridges. Heating and stirring the reaction shift the coordination equilibrium towards highly symmetric octahedral clusters, allowing various metals to randomly occupy equivalent sites at the atomic scale, thus yielding a high-entropy metal-organic framework precursor solution with configurational entropy gain. Adding a co-solvent of methanol and deionized water under ice-water bath conditions slowly increases the dielectric constant of the solution, promoting controlled hydrolytic condensation between metal nodes via oxygen bridges. Simultaneously adding tetramethylammonium hydroxide aqueous solution maintains the pH in a near-neutral range, preventing carboxyl protonation under acidic conditions and the formation of metal hydroxide precipitates under alkaline conditions. The framework grows by crosslinking molybdenum-oxygen polynuclear clusters and tungsten-oxygen polynuclear clusters as basic units, forming a wet gel. The wet gel is then subjected to fractional solvent replacement with anhydrous ethanol and tert-butanol in a constant-temperature water bath, gradually reducing the surface tension of the liquid phase within the pores. Tert-butanol, with its high supercooling and high freezing point, forms tiny crystals rather than large ice crystals upon rapid freezing in liquid nitrogen. These crystals then sublimate directly from the framework in a low-temperature vacuum, preventing capillary collapse of the pores and resulting in a solid precursor with a high specific surface area. The solid precursor is placed in a tubular resistance furnace and heated to the intermediate temperature range under argon protection. The organic ligands undergo decarboxylation and dehydrogenation reactions and carbonize, while the metal nodes are gradually reduced. Heating continues to the intermediate-high temperature range, at which point the argon gas is shut off and ammonia is introduced. The ammonia decomposes on the surface of the metal clusters, releasing active nitrogen and hydrogen atoms. The hydrogen atoms further reduce residual chlorine and oxygen species, while the active nitrogen atoms insert into the newly formed metal-carbon framework, forming stable metal-carbon-nitrogen bonds and entering the carbon matrix lattice. Finally, the argon protection is switched back, and heating to the high temperature range allows the nanocrystals to fully crystallize, resulting in a denser interface and ultimately a modified material with metal nanocrystals embedded in a nitrogen-doped carbon matrix. The nitrogen-doped carbon layer and residual hydroxyl groups on the surface of the modified material provide anchoring sites for the hydrolysis products of the silane coupling agent. In anhydrous ethanol dispersion, glacial acetic acid catalyzes the slow hydrolysis of the methoxy group of γ-methacryloyloxypropyltrimethoxysilane to silanol groups, which then undergo dehydration condensation grafting with the material surface. The amide groups of polyvinylpyrrolidone are adsorbed on the outer edge of the particles, forming a steric hindrance layer.The combined effect of these two factors inhibits the aggregation of nanoparticles, ultimately resulting in a modifier with an organic functional layer on its surface. This organic functional layer can participate in subsequent polymerization or improve wettability.

[0013] According to a preferred embodiment of the present invention, in step A1, the time for stirring the reaction at 58-62°C is 6-8 hours.

[0014] According to a preferred embodiment of the present invention, in step A2, the stirring time at 38-42°C is 48-50 hours.

[0015] According to a preferred embodiment of the present invention, in step A3, the time for holding the temperature at 845-855°C is 2-4 hours.

[0016] According to a preferred embodiment of the present invention, in step A4, the vacuum drying time at 58-62°C is 12-14 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention simplifies the production process of spiral grooved bars and reduces the manufacturing cost of metalworking tools. Traditional processes require sintering solid bars before grinding and grooving, resulting in significant material waste and a long cycle. This invention utilizes the spiral protrusions on the inner wall of a cold isostatic pressing mold to directly form spiral grooves during the pressing stage. After sintering, only trimming and sandblasting are required before use. Due to the addition of high-entropy polyoxometalate-derived nanocomposite modifiers, the granulated powder formed by tungsten carbide powder, cobalt powder, and polyethylene glycol 4000 has good fluidity and can uniformly fill the spiral cavity of the mold, resulting in minimal density differences throughout the pressed blank. The pressed blank will not crack or deform after being immersed in petroleum ether and dried under low-temperature vacuum. During the sintering stage, hydrogen gas is introduced at a lower temperature to address the thermal decomposition characteristics of polyethylene glycol 4000, allowing the oxygen-containing small molecules generated by the decomposition of the binder to be promptly carried out of the furnace, avoiding residual contamination. This invention is suitable for large-scale industrial production in the metalworking industry.

[0018] (2) The high-entropy polyoxometalate-derived nanocomposite modifier of the present invention can simultaneously improve powder dispersibility, inhibit tungsten carbide grain growth, and enhance the interfacial bonding between tungsten carbide and cobalt. This high-entropy polyoxometalate-derived nanocomposite modifier is prepared via a multi-step chemical method. Its surface organic functional layer is compatible with the long chains of oleic acid and can uniformly adhere to the microscopic interface of tungsten carbide and cobalt particles during ball milling. When the sintering temperature rises above the melting point of cobalt, cobalt becomes a liquid phase. The metal nitride and carbide nanocrystals in the high-entropy polyoxometalate-derived nanocomposite modifier create a pinning effect at the grain boundaries, preventing excessive growth of tungsten carbide grains. Ultimately, the grain size of the sintered body is controlled within a very small range. Simultaneously, the microporous channels formed by the nitrogen-doped carbon matrix facilitate capillary flow of the cobalt liquid phase, resulting in more complete densification. These microscopic changes enable the finished spiral bar material to possess both high hardness and good fracture toughness, meeting the requirements of metalworking tools for wear resistance and impact resistance.

[0019] (3) The segmented sintering process and modifier of the present invention work synergistically to ensure the dimensional accuracy and performance stability of the spiral grooved bar. The sintering steps sequentially include vacuum debinding, hydrogen reduction degreasing, argon-protected heating, and vacuum high-pressure liquid-phase sintering, which completely decomposes polyethylene glycol 4000, reduces oxides, and cleans grain boundaries. Due to the pinning effect of the modifier at the grain boundaries, grain growth is suppressed during sintering, and the shrinkage behavior of the compact in the spiral groove region and the matrix region tends to be consistent, preventing spiral groove deformation or dimensional deviations due to anisotropic shrinkage. After natural cooling, the spiral grooved bar is trimmed and sandblasted, resulting in high geometric accuracy, which can be directly used to manufacture metal processing tools without subsequent finishing. The drill bit manufactured using the spiral grooved bar produced by the process of the present invention has a significantly improved lifespan, and vibration and noise during cutting are significantly reduced. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0021] Figure 1 This is a schematic diagram of the spiral grooved bar blank product of the present invention.

[0022] Figure 2 This is a schematic diagram of the finished product after the spiral groove bar blank of the present invention has been cut. Detailed Implementation

[0023] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0024] Example 1 This embodiment provides a forming process for spiral grooved bars, including the following steps: Step S1: Load 490g of tungsten carbide-cobalt cemented carbide grinding balls (6mm in diameter) into a planetary ball mill. Then add 90g of tungsten carbide powder, 10g of cobalt powder, 0.55g of high-entropy polyoxometalate-derived nanocomposite modifier, 50g of anhydrous ethanol, and 0.125g of oleic acid sequentially. Tightly close the mill jar, set the mill speed to 280rpm, and mill for 49 hours. Mill continuously in one direction, stopping for 10 minutes every 6 hours, and take samples to analyze the powder particle size distribution using a laser particle size analyzer. After milling, open the mill jar, pour the slurry through a 40-mesh sieve to separate the grinding balls, and collect the undersized mixture.

[0025] Step S2: Add 2.25g of polyethylene glycol 4000 (with an average molecular weight of 4000) to the mixed slurry. Add anhydrous ethanol to adjust the solid content of the slurry to 70%. Stir at 500rpm for 30min using a high-speed disperser to completely dissolve the polyethylene glycol. Transfer the slurry to the feed hopper of a closed-loop centrifugal spray granulation equipment. Set the atomizer speed to 13500rpm, the feed rate to 25mL / min, the hot air inlet temperature to 120℃, and the outlet temperature to 65℃. Start spray granulation. The slurry is ejected through the atomizing disc to form micron-sized droplets. The droplets rapidly evaporate the solvent upon contact with hot air in the drying tower. Collect the powder from the bottom of the tower and the cyclone separator. Pass the resulting granulated powder through an 80-mesh sieve to remove a small amount of large particles, and then sieve through a 200-mesh sieve to remove fine powder, obtaining spherical granulated powder.

[0026] Step S3: Weigh 102.5g of the above granulated powder. The cold isostatic pressing mold is a polyurethane shaping mold with four spiral protrusions on the inner wall. The spiral lead is 50mm and the spiral groove depth is 1.5mm. Seal the lower end of the mold and slowly fill the mold with powder using a suspended vibrating funnel. During the filling process, continuous vibration is used on a vibrating table to compact the powder. The amplitude of the vibrating table is 0.3mm and the frequency is 50Hz. Fill the mold to 5mm below the upper edge of the mold, cover it with the upper end, and seal it with a sealing ring and clamps. Place the sealed mold into the main pressure cylinder of the cold isostatic pressing equipment. Inject 750g of a mixture of anti-wear hydraulic oil and deionized water into the main pressure cylinder. The volume ratio of the mixture is 1:1. Set the pressure to 140MPa and the holding time to 50 seconds, and start the pressurization program. After the holding time is completed, the pressure will be automatically released. Open the main cylinder and remove the mold. Remove the mold body and carefully remove the pressed blank. The non-spiral end areas of 5 mm at each end of the billet were removed using a semi-automatic double-end cutting machine. The billet after end removal was immersed in petroleum ether for 8 minutes, gently agitated during immersion to remove surface oil. The billet was then removed and dried in a vacuum oven at 60℃ for 5 hours (vacuum degree of 10 kPa) to obtain a green spiral bar billet.

[0027] Step S4: Place the green compact in an S-HIP furnace. The effective working area of ​​this pressure sintering furnace is 200mm in diameter and 300mm in height. Close the furnace door and turn on the vacuum pump to evacuate the furnace to an absolute pressure below 10Pa. Increase the temperature from room temperature to 250℃ at a rate of 3℃ / min, and hold at 250℃ for 1.5 hours, maintaining a vacuum during this stage. After holding, introduce high-purity hydrogen into the furnace at a flow rate of 5L / min. Continue increasing the temperature to 450℃ at a rate of 2℃ / min, then to 600℃ at a rate of 2℃ / min, maintaining a hydrogen atmosphere throughout the heating process. At 600℃, close the hydrogen valve and switch to high-purity argon at a flow rate of 10L / min, increasing the temperature to 750℃ at a rate of 2℃ / min, then to 900℃ at a rate of 2℃ / min. At 900℃, close the argon valve and evacuate again to an absolute pressure below 10Pa. The temperature was raised to 1425℃ at a heating rate of 5℃ / min. Upon reaching 1425℃, high-purity argon was immediately reintroduced into the furnace to a pressure of 8MPa, and sintering was carried out at this pressure for 2.5 hours. After sintering, the temperature was lowered to 600℃ under argon protection at a cooling rate of 8℃ / min, and then allowed to cool naturally to room temperature. The furnace door was opened, and the sintered parts were removed. The surface of the bars was first roughened using a belt sander to remove minor surface protrusions, and then dry-blasted using white corundum abrasive with a particle size of 100 mesh at a blasting pressure of 0.5MPa to remove the oxide layer and surface defects. The final product was a WC-Co cemented carbide spiral groove bar with a smooth surface, complete spiral grooves, and no cracks.

[0028] Preparation steps of high-entropy polyoxometalate-derived nanocomposite modifiers: Step A1: Under nitrogen protection, with a nitrogen flow rate of 200 mL / min, 15.5 g tungsten hexachloride, 4.0 g molybdenum pentachloride, 3.25 g vanadium trichloride, 3.75 g tantalum chloride, and 3.75 g rhenium trichloride were sequentially added to a three-necked flask. 125 g anhydrous acetonitrile was added, and a magnetic stirrer was started at 400 rpm. The mixture was stirred at room temperature for 30 min until completely dissolved, yielding a clear yellow solution. While continuing to stir, a mixture containing 7.0 g 2,2'-bipyridine-4,4'-dicarboxylic acid, 4.0 g 1,3,5-pyromellitic acid, and 100 g N,N-dimethylformamide was added dropwise at a rate of 0.5 mL / min using a constant-pressure dropping funnel. During the addition, the solution gradually turned dark brown. After the addition was complete, the mixture was stirred at room temperature for 12 hours, then heated to 60°C and stirred at this temperature for 7 hours at a stirring speed of 300 rpm, with nitrogen protection maintained throughout the reaction. After the reaction was completed, the mixture was allowed to cool naturally to room temperature to obtain a homogeneous and transparent precursor solution.

[0029] Step A2: Transfer the above precursor solution to a three-necked flask equipped with a reflux condenser and place it in an ice-water bath at 0°C. Add a pre-mixed co-solvent of 110 g methanol and 55 g deionized water dropwise at a rate of 0.2 mL / min using a constant-pressure dropping funnel. Simultaneously, add 3 g of tetramethylammonium hydroxide aqueous solution (25% by mass) dropwise at a rate of 0.1 mL / min using another dropping funnel. Monitor the pH online using a pH meter during the addition, maintaining the pH at 6.8. After the addition is complete, remove the ice-water bath and allow the system to naturally warm to 40°C. Then, continue stirring in a constant-temperature water bath at 40°C for 48 hours at a stirring speed of 200 rpm to obtain a wet gel with a certain degree of fluidity. Allow the wet gel to age at 40°C for 24 hours. After aging, the supernatant was discarded, and the wet gel was transferred to a Buchner funnel. It was washed three times with 250g of anhydrous ethanol (83g each time) in a 32°C water bath, with filtration for 5 minutes after each wash. The washed wet gel was then transferred to a beaker and washed three times with 175g of tert-butanol (58g each time) in a 32°C water bath, with immersion for 30 minutes after each wash, after which the liquid was discarded. The replaced wet gel was spread evenly in a petri dish and rapidly frozen in liquid nitrogen for 45 minutes. After complete solidification, it was transferred to a freeze dryer and freeze-dried at -50°C and a vacuum of 10 Pa for 72 hours to obtain the solid precursor.

[0030] Step A3: Place the solid precursor in a quartz boat and then place it in a tubular resistance furnace with a furnace tube diameter of 60 mm. Introduce high-purity argon gas at a flow rate of 200 mL / min. Increase the temperature from room temperature to 300 °C at a rate of 10 °C / min and hold at 300 °C for 2 hours. Then increase the temperature to 500 °C at a rate of 5 °C / min. Upon reaching 500 °C, close the argon gas valve and simultaneously introduce high-purity ammonia gas at a flow rate of 100 mL / min, increasing the temperature to 700 °C at a rate of 3 °C / min, and hold at 700 °C for 2 hours. After holding at 700 °C, close the ammonia gas valve and reintroduce high-purity argon gas at a rate of 200 mL / min, increasing the temperature to 850 °C at a rate of 5 °C / min, and hold at 850 °C for 3 hours. After holding at 850 °C, allow the mixture to cool naturally to room temperature under argon protection. The product was removed and manually ground in an agate mortar for 15 minutes. It was then passed through a 400-mesh standard sieve with a mesh size of 38 μm. The black powder that passed through the sieve was collected to obtain the modified material.

[0031] Step A4: In a conical flask, disperse the modified material obtained in Step A3 in 125g of anhydrous ethanol according to the specified ratio. Add 3.5g of deionized water, 0.3g of glacial acetic acid, 1.0g of γ-methacryloyloxypropyltrimethoxysilane, and 0.3g of polyvinylpyrrolidone sequentially. Place the conical flask in an ultrasonic cell disruptor (probe diameter 6mm, power 300W) and sonicate in an ice-water bath for 30min in pulse mode (3 seconds on, 2 seconds off). After sonication, transfer the conical flask to a constant-temperature water bath shaker and stir at 60℃ and 150rpm for 6h. After the reaction is complete, transfer the mixture to a centrifuge tube and centrifuge at 8000rpm for 15min, discarding the supernatant. Wash the solid product three times with 150g of anhydrous ethanol (50g ethanol each time), centrifuging at 8000rpm for 15min after each wash and discarding the liquid. The product was washed three times with 150g of deionized water each time, and centrifuged again. The washed solid product was spread in a petri dish and placed in a vacuum drying oven. It was dried at 60℃ and 0.1kPa for 12h to obtain the high-entropy polyoxometalate-derived nanocomposite modifier.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that this embodiment provides a forming process for a spiral grooved bar, including the following steps: Step S1: Add 88g of tungsten carbide powder, 8g of cobalt powder, 0.3g of high-entropy polyoxometalate-derived nanocomposite modifier, 40g of anhydrous ethanol and 0.10g of oleic acid to a ball mill and ball mill for 48h to obtain a mixed slurry.

[0033] Step S2: Add 2.0g of polyethylene glycol 4000 to the mixed slurry; spray dry at a feed rate of 20mL / min, granulate, and obtain granulated powder.

[0034] Step S3: Fill 100g of granulated powder into a cold isostatic pressing mold; after filling, seal the mold and place it in the main pressure cylinder of the cold isostatic pressing equipment. Inject 500g of a mixture of anti-wear hydraulic oil and water (volume ratio 1:1) into the main pressure cylinder and maintain the pressure at 130MPa for 40s; remove the mold, cut off the ends of the blank, immerse it in petroleum ether for 5min, and vacuum dry it at 58℃ for 4h to obtain a spiral groove bar blank.

[0035] Step S4: Place the spiral bar blank in an S-HIP furnace, evacuate the vacuum, heat to 245°C and hold for 1 hour, introduce hydrogen gas, heat to 445°C, and continue heating to 595°C in a hydrogen atmosphere; switch to argon gas, heat to 745°C; heat to 895°C; turn off the argon gas, evacuate the vacuum, heat to 1400°C, introduce argon gas, and sinter for 2 hours; allow to cool naturally to room temperature, trim the edges, and sandblast the surface to obtain the finished spiral groove bar.

[0036] Preparation steps of high-entropy polyoxometalate-derived nanocomposite modifiers: Step A1: Under nitrogen protection, 15.0 g of tungsten hexachloride, 3.5 g of molybdenum pentachloride, 3.0 g of vanadium trichloride, 3.5 g of tantalum chloride and 3.5 g of rhenium trichloride were mixed and dissolved in 100 g of anhydrous acetonitrile; a mixture containing 6.0 g of 2,2'-bipyridine-4,4'-dicarboxylic acid, 3.0 g of 1,3,5-pyromellitic acid and 80 g of N,N-dimethylformamide was added dropwise; the mixture was stirred at room temperature, and then heated to 58 °C and stirred for 6 h to obtain the precursor solution.

[0037] Step A2: Place the precursor solution in a reflux condenser and add a mixture of 100g methanol and 50g deionized water dropwise under an ice-water bath; add 2g tetramethylammonium hydroxide aqueous solution (25% by mass) to adjust the pH to 6.5; heat to 38℃ and stir for 48h, then allow to stand for aging to obtain a wet gel; wash the wet gel with 200g anhydrous ethanol at 30℃, then wash with 150g tert-butanol at 30℃, freeze in liquid nitrogen for 30min, and freeze-dry at -48℃ for 72h to obtain the precursor.

[0038] Step A3: Place the precursor in a tube furnace and heat it to 295°C under argon protection and hold for 2 hours; turn off the argon gas when the temperature reaches 495°C, introduce 20g of ammonia gas, and heat it to 695°C and hold for 2 hours; switch to argon protection and heat it to 845°C and hold for 2 hours; allow it to cool naturally to room temperature, grind it through a 400-mesh sieve to obtain the modified material.

[0039] Step A4: Disperse the modified material in 100g anhydrous ethanol, add 2.0g deionized water and 0.1g glacial acetic acid sequentially, add 0.5g γ-methacryloyloxypropyltrimethoxysilane and 0.1g polyvinylpyrrolidone, sonicate for 30min, stir at 58℃ for 6h, centrifuge, wash the solid product three times each with 100g anhydrous ethanol and 100g deionized water, and vacuum dry at 58℃ for 12h to obtain the high-entropy polyoxometalate-derived nanocomposite modifier.

[0040] Example 3 The difference between this embodiment and Embodiment 1 is that this embodiment provides a forming process for a spiral grooved bar, including the following steps: Step S1: Add 92g of tungsten carbide powder, 12g of cobalt powder, 0.8g of high-entropy polyoxometalate-derived nanocomposite modifier, 60g of anhydrous ethanol and 0.15g of oleic acid to a ball mill and ball mill for 50h to obtain a mixed slurry.

[0041] Step S2: Add 2.5g of polyethylene glycol 4000 to the mixed slurry; spray dry at a feed rate of 30mL / min, granulate, and obtain granulated powder.

[0042] Step S3: Fill 105g of granulated powder into the cold isostatic pressing mold; after filling, seal the mold and place it in the main pressure cylinder of the cold isostatic pressing equipment. Inject 1000g of a mixture of anti-wear hydraulic oil and water (volume ratio 1:1) into the main pressure cylinder and maintain the pressure at 150MPa for 60s; remove the mold, cut off the ends of the blank, immerse it in petroleum ether for 10min, and vacuum dry it at 62℃ for 6h to obtain the spiral bar blank.

[0043] Step S4: Place the spiral grooved bar blank in an S-HIP furnace, evacuate the vacuum, heat to 255°C and hold for 2 hours, introduce hydrogen gas, heat to 455°C, and continue heating to 605°C in a hydrogen atmosphere; switch to argon gas, heat to 755°C; heat to 905°C; turn off the argon gas, evacuate the vacuum, heat to 1450°C, introduce argon gas, and sinter for 4 hours; allow to cool naturally to room temperature, trim the edges, and sandblast the surface to obtain the finished spiral bar.

[0044] Preparation steps of high-entropy polyoxometalate-derived nanocomposite modifiers: Step A1: Under nitrogen protection, 16.0 g of tungsten hexachloride, 4.5 g of molybdenum pentachloride, 3.5 g of vanadium trichloride, 4.0 g of tantalum chloride and 4.0 g of rhenium trichloride were mixed and dissolved in 150 g of anhydrous acetonitrile; a mixture containing 8.0 g of 2,2'-bipyridine-4,4'-dicarboxylic acid, 5.0 g of 1,3,5-pyromellitic acid and 120 g of N,N-dimethylformamide was added dropwise; the mixture was stirred at room temperature, and then heated to 62 °C and stirred for 8 h to obtain the precursor solution.

[0045] Step A2: Place the precursor solution in a reflux condenser and add a mixture of 120g methanol and 60g deionized water dropwise under an ice-water bath; add 4g tetramethylammonium hydroxide aqueous solution (25% by mass) to adjust the pH to 7.0; heat to 42℃ and stir for 50h, then allow to stand for aging to obtain a wet gel; wash the wet gel with 300g anhydrous ethanol at 35℃, then wash with 200g tert-butanol at 35℃, freeze in liquid nitrogen for 60min, and freeze-dry at -52℃ for 72h to obtain the precursor.

[0046] Step A3: Place the precursor in a tube furnace and heat it to 305°C under argon protection and hold for 2 hours; turn off the argon gas when the temperature reaches 505°C, introduce 40g of ammonia gas, and heat it to 705°C and hold for 2 hours; switch to argon protection and heat it to 855°C and hold for 4 hours; allow it to cool naturally to room temperature, grind it through a 400-mesh sieve to obtain the modified material.

[0047] Step A4: Disperse the modified material in 150g of anhydrous ethanol, add 5.0g of deionized water and 0.5g of glacial acetic acid, then add 1.5g of γ-methacryloyloxypropyltrimethoxysilane and 0.5g of polyvinylpyrrolidone, sonicate for 30min, stir at 62℃ for 6h, centrifuge, wash the solid product three times each with 200g of anhydrous ethanol and 200g of deionized water, and vacuum dry at 62℃ for 14h to obtain the high-entropy polyoxometalate-derived nanocomposite modifier.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that no high-entropy polyoxometalate-derived nanocomposite modifier is added; the remaining steps and parameters are exactly the same as in Example 1.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that vanadium carbide powder of equal mass is used instead of the high-entropy polyoxometalate-derived nanocomposite modifier, while the other raw materials and processes are the same as in Example 1.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that an equal mass of nano-tungsten carbide powder is used instead of the high-entropy polyoxometalate-derived nanocomposite modifier, while the other raw materials and processes are the same as in Example 1.

[0051] The properties of the spiral bars provided in the above embodiments and comparative examples were tested using the following methods: Hardness Testing: After cutting off both ends of the spiral grooved bar, the middle section was used. The test surface was ground flat along the axial direction with a diamond wheel and polished until the surface roughness Ra was no greater than 0.4 μm. A Rockwell hardness tester was used, with a diamond conical indenter (cone angle 120 degrees, spherical radius of the tip 0.2 mm) and a scale of HRA. At room temperature (25℃±2℃), an initial test force of 98.07 N was applied, and the indenter was held in contact with the sample surface for 2 seconds. Then, a main test force of 490.3 N was applied (bringing the total test force to 588.4 N), and held for 10 seconds after loading. The main test force was then removed back to the initial test force, and the hardness value was read. For each sample, six test points were evenly selected along the circumference of the bar, avoiding the bottom and edge of the spiral groove, with a spacing of no less than 3 mm between each test point. The arithmetic mean of the six test points was calculated as the final hardness value of the sample, and the result was rounded to one decimal place.

[0052] Fracture toughness test: A regular, dense cuboid specimen with a length of 30 mm, a width of 5 mm, and a height of 2.5 mm was machined by cutting and completely grinding away the helical grooves from the helical bar. The long side of the specimen was parallel to the axis of the bar. A straight-through notch was machined along the width direction in the middle of the specimen using a diamond grinding wheel. The notch depth was 1.25 mm, the notch width was no greater than 0.2 mm, and the radius of the arc at the notch root was no greater than 0.1 mm. A three-point bending loading method was used, with a lower span of 20 mm, two lower support rollers with a diameter of 6 mm each, and an upper pressure roller with a diameter of 6 mm. The specimen was placed on the two lower support rollers with the notch facing down and located in the middle of the two support rollers. Pressure was applied at a constant loading rate of 0.05 mm / min on a universal testing machine, and the maximum load at which the specimen fractured was recorded. The fracture toughness value was calculated using the formula of the single-sided straight-through notch beam method, which involves the specimen width, height, notch depth, and span. Five specimens were tested for each sample, and the arithmetic mean of the fracture toughness values ​​was taken, with the result rounded to one decimal place.

[0053] Relative density test: A cubic specimen measuring 10mm × 10mm × 10mm was cut from the spiral grooved bar. The six faces of the specimen were lightly sanded with 400-grit sandpaper to remove the surface oxide layer. The specimen was ultrasonically cleaned in anhydrous ethanol for 10 minutes, then dried in a 105℃ forced-air drying oven for 2 hours, and then cooled to room temperature in a desiccator. The mass of the specimen in air was measured using an analytical balance with an accuracy of 0.1 mg. The specimen was placed in a basket made of 0.2mm diameter filament in a beaker containing distilled water (with 1 drop of wetting agent added to eliminate surface air bubbles), and its buoyant weight in the water was measured at a temperature of 25℃ ± 1℃. The measured density of the specimen was calculated using Archimedes' principle and then divided by the theoretical density of 15.0 g / cm³. 3 (The theoretical density is calculated based on the mass fraction of WC-10Co), thus obtaining the relative density. Three test blocks were tested for each sample, and the arithmetic mean was taken, with the result rounded to one decimal place.

[0054] Lead shrinkage rate range test: During the compaction stage, a three-dimensional optical profilometer is used to select a cross-section every 20 mm along the axial direction of the helical bar, for a total of 5 cross-sections. The lead (axial distance between corresponding points of two adjacent helical teeth) of the same helical groove is measured at each cross-section. The lead values ​​of the 5 cross-sections are recorded, and their arithmetic mean is calculated as the compaction lead reference. On the sintered finished bar, the same method is used to measure the lead values ​​of 5 cross-sections at the corresponding axial positions of the same helical groove (coordinate conversion based on the overall axial sintering shrinkage rate of the bar, or proportional positions divided into 5 equal parts according to the total length of the bar), and their arithmetic mean is calculated as the finished product lead. According to the formula Lead shrinkage rate = (Compaction lead - Finished product lead) / Compaction lead × 100%, the lead shrinkage rate of each of the 5 cross-sections is calculated. Then, the difference between the maximum and minimum values ​​of the 5 lead shrinkage rates is calculated, which is the lead shrinkage rate range. The smaller the range value, the better the consistency of shrinkage rate at different axial positions of the bar.

[0055] Groove depth shrinkage rate range test: During the pressing stage, a three-dimensional optical profilometer is used to select a section every 20 mm along the axial direction of the spiral groove bar, for a total of 5 sections (the same 5 sections as the lead measurement). The groove depth (radial distance from the cylindrical surface of the bar matrix to the bottom of the groove) is measured at each section. The groove depth values ​​of the 5 sections are recorded, and their arithmetic mean is calculated as the benchmark for the pressed groove depth. On the sintered finished bar, the same method is used to measure the groove depth of the 5 sections at the corresponding axial position of the same spiral groove (coordinate conversion based on the overall axial sintering shrinkage rate of the bar, or using a proportional position divided into 5 equal parts according to the total length of the bar), and their arithmetic mean is calculated as the finished groove depth. According to the formula Groove depth shrinkage rate = (Pressed groove depth - Finished groove depth) / Pressed groove depth × 100%, the groove depth shrinkage rate of each of the 5 sections is calculated. Then, the difference between the maximum and minimum values ​​of the 5 groove depth shrinkage rates is the groove depth shrinkage rate range. The smaller the range value, the better the uniformity of axial shrinkage of the spiral groove.

[0056] The performance test data above are shown in Table 1.

[0057] Table 1 Performance Test Results

[0058] As can be seen from the above, Examples 1-3 have achieved significant improvements over Comparative Examples 1-3 in five core indicators: hardness, fracture toughness, relative density, and shrinkage uniformity of lead and groove depth.

[0059] Comparative Example 1, without the addition of high-entropy polyoxometalate-derived nanocomposite modifiers, exhibits a hardness of only 87.5 HRA and a fracture toughness of 8.6 MPa·m. 1 / 2The relative density is 96.2%, and the lead shrinkage rate range is as high as 1.12% and the groove depth shrinkage rate range is as high as 1.35%. This indicates that under the traditional unmodified process, the spiral groove bar has coarse grains, insufficient densification, and severe anisotropic shrinkage in the spiral groove region after sintering, which cannot meet the requirements of metal processing tools for high hardness and high precision.

[0060] Comparative Example 2 added an equal mass of ordinary vanadium carbide powder, which increased the hardness to 91.2 HRA and the fracture toughness to 10.3 MPa·m. 1 / 2 The relative density increased to 97.8%, and the shrinkage range was also slightly improved. However, vanadium carbide can only inhibit grain growth and cannot improve the wettability of cobalt liquid phase and powder flowability. Therefore, the performance is still significantly lower than that of the example, and peeling occurs at the edge of the spiral groove.

[0061] Comparative Example 3 added an equal mass of ordinary nano-tungsten carbide powder. Due to the severe agglomeration of nano-tungsten carbide during ball milling and its tendency to grow abnormally during sintering, its hardness was only 89.4 HRA and its fracture toughness was 9.1 MPa·m. 1 / 2 The relative density was 96.9%, and the shrinkage range was not effectively controlled.

[0062] In contrast, Examples 1-3 fully utilize the high-entropy polyoxometalate-derived nanocomposite modifier of the present invention. This high-entropy polyoxometalate-derived nanocomposite modifier constructs a high-entropy metal-organic framework by combining five metal chlorides (tungsten hexachloride, molybdenum pentachloride, vanadium trichloride, tantalum chloride, and rhenium trichloride) with organic ligands. After carbothermic reduction and nitriding, a composite structure is formed in which multiple metal carbides and nitride nanocrystals are uniformly embedded in a nitrogen-doped carbon matrix. Then, surface silane coupling grafting makes the modifier compatible with oleic acid, and it is uniformly attached to the interface of tungsten carbide and cobalt particles during ball milling.

[0063] During the liquid-phase sintering stage, the high-entropy nanocrystals in the high-entropy polyoxometalate-derived nanocomposite modifier pinned grain boundaries and inhibited abnormal tungsten carbide growth. Simultaneously, the metal nitrides partially dissolved in the cobalt liquid phase to form a high-entropy solid solution, improving interfacial wettability. The microporous channels formed after the nitrogen-doped carbon matrix was etched by hydrogen promoted uniform flow of the cobalt liquid phase, resulting in a hardness of 93.8-94.5 HRA and a fracture toughness of 14.2-15.1 MPa·m in Examples 1-3. 1 / 2 The relative density reaches 99.1-99.7%, which is much higher than that of the control group.

[0064] More importantly, the high-entropy polyoxometalate-derived nanocomposite modifier ensures uniform powder dispersion after ball milling, good flowability of granulated powder, and small density differences in various parts of the compact. Furthermore, during sintering, the grains grow uniformly and shrink isotropically. The lead shrinkage rate range of Examples 1-3 is reduced to 0.22-0.35%, and the groove depth shrinkage rate range is reduced to 0.25-0.40%, while Comparative Example 1 has a range as high as 1.12% and 1.35%, respectively. This means that the present invention solves the dimensional deviation problem caused by uneven density and coarse grains in the spiral groove region in the traditional process. The sintered spiral bar can be directly used for the manufacture of metal processing tools without subsequent finishing, thereby significantly reducing material waste and processing costs, and improving tool life and cutting stability.

[0065] Therefore, by introducing a high-entropy polyoxometalate-derived nanocomposite modifier, this invention successfully solves the technical problems of poor powder flowability, uneven density in the spiral groove region, abnormal growth of WC grains, insufficient interfacial wettability, and severe anisotropic shrinkage in the existing spiral groove bar forming process.

Claims

1. A forming process for a spiral grooved bar, characterized in that, Includes the following steps: S1. By weight, add 88-92 parts of tungsten carbide powder, 8-12 parts of cobalt powder, 0.3-0.8 parts of high-entropy polyoxometalate-derived nanocomposite modifier, 40-60 parts of anhydrous ethanol and 0.1-0.15 parts of oleic acid to a ball mill and ball mill; to obtain a mixed slurry. S2. Add 2.0-2.5 parts of polyethylene glycol 4000 to the mixed slurry; spray dry, granulate, and obtain granulated powder; S3. Fill 100-105 parts of granulated powder into a cold isostatic pressing mold; after filling, seal the mold and place it in the main pressure cylinder of the cold isostatic pressing equipment. Inject 500-1000 parts of a mixture of anti-wear hydraulic oil and water into the main pressure cylinder and maintain pressure at 130-150MPa; after maintaining pressure, remove the mold to obtain a blank; cut off both ends of the blank, immerse it in petroleum ether for washing, and vacuum dry it at 58-62℃ to obtain a spiral groove bar blank; S4. Place the spiral grooved bar blank in an S-HIP furnace, evacuate the vacuum, heat to 245-255℃ and hold, introduce hydrogen gas, heat to 445-455℃, continue heating in a hydrogen atmosphere to 595-605℃; switch to argon gas, heat to 745-755℃; heat to 895-905℃; turn off the argon gas, evacuate the vacuum, heat to 1400-1450℃, introduce argon gas, sinter; allow to cool naturally to room temperature, trim the edges, and sandblast the surface.

2. The forming process of the spiral grooved bar according to claim 1, characterized in that, In step S1, the ball milling time is 48-50 hours.

3. The forming process of the spiral grooved bar according to claim 1, characterized in that, In step S2, the feed rate for spray drying is 20-30 mL / min.

4. The forming process of the spiral grooved bar according to claim 1, characterized in that, In step S3, the vacuum drying time at 58-62℃ is 4-6 hours.

5. The forming process of the spiral grooved bar according to claim 1, characterized in that, In step S4, the temperature is raised to 245-255℃ and held for 1-2 hours.

6. The forming process of the spiral grooved bar according to any one of claims 1-5, characterized in that, The preparation steps of the high-entropy polyoxometalate-derived nanocomposite modifier include: A1. Under nitrogen protection, 15-16 parts by weight of tungsten hexachloride, 3.5-4.5 parts by weight of molybdenum pentachloride, 3.0-3.5 parts by weight of vanadium trichloride, 3.5-4.0 parts by weight of tantalum chloride and 3.5-4.0 parts by weight of rhenium trichloride are mixed and dissolved in 100-150 parts by weight of anhydrous acetonitrile; a mixture containing 6-8 parts by weight of 2,2'-bipyridine-4,4'-dicarboxylic acid, 3-5 parts by weight of 1,3,5-pyromellitic acid and 80-120 parts by weight of N,N-dimethylformamide is added dropwise; the mixture is stirred at room temperature, and then heated to 58-62°C to stir the reaction to obtain a precursor solution; A2. Place the precursor solution in a reflux condenser and add a mixture of 100-120 parts methanol and 50-60 parts deionized water dropwise under an ice-water bath; add 2-4 parts tetramethylammonium hydroxide aqueous solution to adjust the pH to 6.5-7.0; heat to 38-42℃ and stir, then allow to stand for aging to obtain a wet gel; wash the wet gel with anhydrous ethanol at 30-35℃, then wash with 150-200 parts tert-butanol at 30-35℃, freeze in liquid nitrogen, and freeze-dry at -48~-52℃ to obtain the precursor; A3. Place the precursor in a tube furnace and heat it to 295-305℃ under argon protection. Hold the temperature at 495-505℃. Turn off the argon gas and introduce ammonia gas. Heat the temperature to 695-705℃ and hold. Switch back to argon protection and heat the temperature to 845-855℃ and hold. Allow it to cool naturally to room temperature, grind, and sieve to obtain the modified material. A4. Disperse the modified material in 100-150 parts of anhydrous ethanol, add 2-5 parts of deionized water and 0.1-0.5 parts of glacial acetic acid in sequence, add 0.5-1.5 parts of γ-methacryloyloxypropyltrimethoxysilane and 0.1-0.5 parts of polyvinylpyrrolidone, sonicate, stir at 58-62℃, centrifuge to obtain solid product; wash the solid product with anhydrous ethanol and deionized water, and vacuum dry at 58-62℃.

7. The forming process of the spiral grooved bar according to claim 6, characterized in that, In step A1, the temperature is raised to 58-62℃ and the stirring reaction is carried out for 6-8 hours.

8. The forming process of the spiral grooved bar according to claim 6, characterized in that, In step A2, the stirring time is 48-50 hours after heating to 38-42℃.

9. The forming process of the spiral grooved bar according to claim 6, characterized in that, In step A3, the temperature is raised to 845-855℃ and held for 2-4 hours.

10. The forming process of the spiral grooved bar according to claim 6, characterized in that, In step A4, the vacuum drying time at 58-62℃ is 12-14 hours.

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