Long-life super-fine low cobalt cemented carbide tool, formula and preparation method

Abstract

This invention relates to the field of cemented carbide materials and cutting tools, and discloses a long-life ultrafine low-cobalt cemented carbide tool, its formulation, and preparation method. The tool is composed of the following raw materials in weight percentages: 85.0%–92.5% ultrafine tungsten carbide powder; 3.0%–9.0% cobalt powder; and 1.6%–2.0% composite grain growth inhibitor. The average grain size of the ultrafine tungsten carbide powder is 0.2–0.4 μm. The composite grain growth inhibitor is composed of at least two of chromium carbide, vanadium carbide, and a mixture of tantalum and niobium carbides, and is a core-shell structured composite powder, wherein the core layer is one type of carbide, and the shell layer is another type or more carbides. Through the synergistic innovation of core-shell structured composite grain growth inhibitor design, low-temperature plasma surface activation treatment, high-pressure sintering, and gradient nanocomposite coating, a unified high hardness, high toughness, and excellent red hardness of ultrafine-grained cemented carbide is achieved under low cobalt content conditions, significantly improving tool life during high-speed machining of high-temperature alloys.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide materials and cutting tools, specifically to a long-life ultra-fine low-cobalt cemented carbide cutting tool, its formulation, and its preparation method. Background Technology

[0002] Cemented carbide is a metal-ceramic composite material with tungsten carbide (WC) as the hard phase and cobalt (Co) as the binder phase. Due to its excellent combination of hardness, wear resistance, and toughness, it is widely used in cutting tools, mining tools, and wear-resistant parts. With the increasing demand for machining high-temperature alloys (such as nickel-based high-temperature alloys and titanium alloys) in high-end manufacturing fields such as aerospace and energy equipment, more stringent requirements are being placed on the red hardness, resistance to diffusion wear, and thermal shock resistance of cemented carbide tool materials.

[0003] Currently, commercially available cemented carbide cutting tools typically employ a formulation system of medium-fine grained carbide (WC) with a high cobalt content (generally above 6 wt.%), relying on the toughness of the cobalt phase to ensure the tool's resistance to chipping. However, the cobalt phase is prone to softening under high-temperature cutting conditions and interdiffusion with elements such as Ni and Ti in the workpiece material, leading to rapid crater wear and flank wear on the tool, severely limiting machining efficiency and tool life. To address this challenge, the industry trend is shifting towards using ultrafine / nanocrystalline WC and reducing the cobalt content, aiming to simultaneously improve hardness and wear resistance through the fine-grain strengthening effect while reducing the adverse effects of the cobalt phase at high temperatures.

[0004] However, low cobalt content significantly impairs the fracture toughness of materials, and ultrafine WC powder, due to its enormous surface energy and extremely high activity, is prone to abnormal grain growth during sintering, thus losing its fine-grain strengthening effect. To suppress grain growth, traditional techniques often employ single or simple mixtures of grain growth inhibitors such as VC and Cr3C2. While these inhibitors can hinder the dissolution-precipitation growth of WC grains to some extent, they have the following inherent drawbacks: First, the mechanism of action of a single inhibitor is singular, making it difficult to simultaneously address the dual needs of inhibiting WC dissolution and suppressing precipitation; second, the dispersion uniformity of simply physically mixed inhibitor powders is poor during ball milling, easily leading to localized agglomeration or "depletion," resulting in uneven microstructure, coarse grains, or the precipitation of brittle third phases; third, the non-uniform distribution of inhibitors at grain boundaries weakens interfacial bonding strength, thereby impairing the strength and toughness of the alloy.

[0005] In terms of sintering processes, conventional vacuum sintering or low-pressure hot isostatic pressing (Sinter-HIP) struggles to achieve high densification while simultaneously suppressing grain growth. For low-cobalt-content ultrafine-grained cemented carbides, the small amount of liquid phase and high capillary forces necessitate higher pressures for adequate densification. However, increasing the pressure equates to raising the effective sintering temperature, which intensifies the dissolution of WC in the liquid phase and leads to the precipitation of more coarse WC during cooling, thus promoting grain growth. This technical contradiction between densification and grain growth has become a key bottleneck restricting the preparation of high-performance ultrafine low-cobalt cemented carbides.

[0006] In addition, existing surface coating technologies for cemented carbide cutting tools mostly use a single TiAlN or TiN coating. The bonding strength between the coating and the substrate, high-temperature oxidation resistance, and anti-diffusion performance need to be improved, making it difficult to meet the requirements of extreme thermo-mechanical coupling during high-speed machining of high-temperature alloys. Summary of the Invention

[0007] The present invention aims to provide a long-life ultrafine low-cobalt cemented carbide cutting tool, its formulation and preparation method, in order to solve the technical contradiction that existing ultrafine-grained cemented carbides cannot simultaneously achieve high hardness, high toughness and excellent high-temperature performance at low cobalt content, as well as the technical problems of uneven dispersion of traditional grain growth inhibitors and difficulty in coordinating sintering densification and grain growth control.

[0008] To solve the above problems, the present invention adopts the following technical solution: Option 1: A long-life ultrafine low-cobalt cemented carbide tool formulation, comprising the following raw materials by weight percentage: 85.0%–92.5% ultrafine tungsten carbide powder; 3.0–9.0 wt.% cobalt powder; 1.6–2.0 wt.% composite grain growth inhibitor; wherein the average grain size of the ultrafine tungsten carbide powder is 0.2–0.4 μm; the composite grain growth inhibitor is composed of at least two of chromium carbide, vanadium carbide, and tantalum-niobium mixed carbides, and the inhibitor is a core-shell structured composite powder, wherein the core layer is one type of carbide and the shell layer is another type or more carbides.

[0009] Beneficial Effects: By replacing traditional single or simple mixed inhibitors with core-shell structured composite inhibitors, synergistic effects of different inhibitors are achieved. The core layer Cr3C2 mainly reduces the solubility of WC in the liquid phase, while the shell layer VC mainly deposits on the WC surface, reduces surface energy, and inhibits precipitation and growth. The tantalum-niobium mixed carbide (TaC / NbC) further enhances grain boundary bonding and high-temperature stability. The physical coating relationship of the core-shell structure ensures the synergistic release and uniform distribution of multiple inhibitors during sintering, avoiding the local segregation or "depletion" phenomenon caused by traditional physical mixing. This results in superior grain growth inhibition with a low total inhibitor addition, while reducing the risk of brittle third phase precipitation.

[0010] Furthermore, the composite grain growth inhibitor is characterized by being composed of a core-shell structured composite powder with chromium carbide as the core and vanadium carbide as the shell.

[0011] Beneficial effects: The core-shell structure with Cr3C2 as the core and VC as the shell represents the optimal functional synergy. The Cr3C2 core preferentially dissolves in the cobalt phase during the initial sintering stage, reducing the solid solubility of W and thermodynamically inhibiting WC dissolution. The VC shell gradually releases at high temperatures and deposits at the WC grain boundaries, kinetically hindering precipitation growth. This temporal synergistic mechanism ensures the inhibitory effect persists throughout the entire sintering process, and the core-shell mass ratio can precisely control the contribution weights of the two inhibitory mechanisms, enabling customized inhibitory strategies targeting specific grain sizes.

[0012] Furthermore, in the core-shell composite powder, the weight ratio of the core to the shell is (1:0.3) to (1:1.5).

[0013] Beneficial effects: The defined core-shell weight ratio ensures that the Cr3C2 core layer has sufficient volume to play a solubility-regulating role, while the VC shell layer has an appropriate thickness to effectively cover the WC grain boundaries. This ratio range has been optimized and balanced to maximize the synergistic effect of the two inhibition mechanisms while avoiding grain boundary embrittlement caused by excessive VC or precipitation of Cr-containing third phases caused by excessive Cr3C2, thus achieving the optimal balance between alloy strength and toughness.

[0014] Furthermore, the hardness of the cemented carbide is not less than 92.0 HRA, and the transverse fracture strength is not less than 3000 MPa.

[0015] Beneficial effects: This performance index limits the technical effect of the cemented carbide of the present invention to achieve both high hardness and high toughness under low cobalt content conditions, breaking through the traditional technical prejudice that "low cobalt necessarily means low toughness", and proving the technical value of the synergistic innovation of core-shell structure inhibitors and subsequent preparation processes.

[0016] Furthermore, the average grain size of the ultrafine tungsten carbide powder is 0.2–0.4 μm, and the cobalt powder content is 3.0–9.0 wt.%.

[0017] Beneficial effects: Further limiting the range of WC grain size and cobalt content, clarifying the specific technical solution of the present invention for ultrafine grains (submicron level) and low cobalt, which has the optimal combination of red hardness and anti-diffusion wear performance in high-temperature alloy high-speed processing scenarios.

[0018] Furthermore, the total content of the composite grain growth inhibitor is 1.6–2.0 wt.%.

[0019] Beneficial effects: This content range, combined with the core-shell structure design, ensures sufficient inhibition of grain growth while keeping the total amount of inhibitor at a low level. This avoids the problems of brittle phase precipitation and toughness loss caused by adding more inhibitor to achieve the same inhibition effect in traditional technologies.

[0020] Option 2: A method for preparing a long-life, ultra-fine, low-cobalt cemented carbide cutting tool, using the cemented carbide cutting tool formulation described in any of the preceding options, comprising the following steps: Step 1: Raw material pretreatment, the core-shell structure composite grain growth inhibitor is surface activated with ultrafine tungsten carbide powder and cobalt powder under an inert atmosphere; Step 2: Wet high-energy ball milling, using a planetary ball mill, wet milling is carried out after the raw material powders are mixed. The wet milling medium is anhydrous ethanol, the ball-to-material ratio is 5:1 to 10:1, and the wet milling time is 12 to 50 hours. Step 3: Spray drying granulation, the slurry is spray dried to obtain a well-flowing composite powder; Step 4: Molding and sintering, using high-pressure sintering process, sintering temperature 1350℃~1420℃, pressure 30~60MPa, holding time 30~60 minutes.

[0021] Beneficial effects: This method significantly improves the surface activity and reactivity of powder through surface activation pretreatment, promoting uniform mixing and interfacial bonding of core-shell inhibitors with WC and Co powders during subsequent ball milling; optimization of high-energy ball milling process parameters ensures sufficient crushing and uniform dispersion of ultrafine powders, while controlling ball milling time to avoid lattice distortion and increased oxygen content caused by over-grinding; high-pressure sintering process achieves high densification at relatively low temperatures, inhibiting grain growth and forming a synergistic effect with core-shell structure inhibitors.

[0022] Furthermore, the surface activation treatment in step one is performed using low-temperature plasma treatment for a duration of 10–30 minutes.

[0023] Beneficial effects: Low-temperature plasma treatment is a key innovative step in this invention. By bombarding the powder surface with plasma, active sites are introduced, the surface oxide layer is cleaned, and microscopic roughening is generated, significantly enhancing the wettability and reactivity of the powder surface. This treatment achieves molecular-level surface activation without altering the bulk crystal structure and particle size distribution of the powder, promoting the uniform dispersion and tight bonding of the core-shell inhibitor with the matrix powder during subsequent ball milling. This effect is difficult to achieve using traditional mechanical mixing or chemical dispersion methods.

[0024] Furthermore, during the sintering process described in step four, a carburizing treatment of 0.5 to 2 hours is performed at the end of the sintering period to repair the surface carbon potential.

[0025] Beneficial effects: Carburizing at the end of sintering addresses the surface decarburization problem that easily occurs in low-cobalt ultrafine-grained cemented carbide during high-pressure sintering. By supplementing carbon sources to repair the surface carbon potential, the formation of brittle phases such as η phase (Co3W3C) is avoided, ensuring the integrity and wear resistance of the cutting edge area of ​​the tool. This is a key post-processing technology for achieving long-life tools.

[0026] Option 3: A long-life ultra-fine low-cobalt cemented carbide cutting tool, made using the cemented carbide cutting tool formulation described in any of the preceding options, wherein the surface of the cutting tool is coated with a TiAlN / TiAlCrN multilayer nanocomposite coating with a coating thickness of 5–15 μm.

[0027] Beneficial effects: The coating has a gradient structure, consisting of a TiN transition layer, a TiAlN layer, and a TiAlN / TiAlCrN nanolayer structure from the substrate to the surface. TiAlN / TiAlCrN refers to a mixture of TiAlN and TiAlCrN.

[0028] This tool is suitable for nickel-based superalloys and titanium alloys. Under cutting speeds of 120–300 m / min and feed rates of 0.05–0.3 mm / r, the tool life is increased by more than 50% compared to conventional carbide tools.

[0029] The gradient coating structure enhances the adhesion between the coating and the cemented carbide substrate through a TiN transition layer. The TiAlN layer provides excellent high-temperature hardness and oxidation resistance. The TiAlN / TiAlCrN nanolayer structure further improves the high-temperature stability and resistance to diffusion wear by utilizing the multilayer interface effect and solid solution strengthening of Cr. This coating system works synergistically with the low-cobalt ultrafine-grained cemented carbide substrate of this invention, exhibiting a significantly extended service life during high-speed machining of high-temperature alloys, with tool life increased by more than 50%.

[0030] The advantages of this invention are: This invention achieves a balance of high hardness, high toughness, and high thermal stability in ultrafine-grained cemented carbide by synergistic design of inhibitor structure innovation, powder pretreatment process optimization, and advanced sintering process while ensuring low cobalt content. It is also compatible with high-performance surface coating technology, effectively addressing key technical issues in this field.

[0031] This invention achieves a unified high hardness, high toughness, and excellent red hardness of ultrafine-grained cemented carbide under low cobalt content conditions through the synergistic innovation of core-shell structure composite grain growth inhibitor design, low-temperature plasma surface activation treatment, high-pressure sintering, and gradient nanocomposite coating, significantly improving tool life during high-speed machining of high-temperature alloys.

[0032] The core advantage of this invention lies in overcoming a long-standing technical contradiction in the field of ultrafine-grained cemented carbide: simultaneously achieving a synergistic improvement in high hardness, high toughness, and excellent high-temperature performance under low cobalt content conditions. Traditional understanding holds that reducing cobalt content inevitably leads to a decrease in toughness, while ultrafine WC inevitably exacerbates the risk of sintered grain growth. The combination of these two factors makes "low cobalt + ultrafine grain" a technically challenging objective. This invention, through the innovative design of a core-shell structure inhibitor, combined with the synergistic process of low-temperature plasma activation and high-pressure sintering, successfully overcomes this technical barrier, producing an ultrafine low-cobalt cemented carbide with a hardness of not less than 92.0 HRA and a transverse fracture strength of not less than 3000 MPa, achieving a significant improvement in tool life of over 50% in high-speed machining of high-temperature alloys.

[0033] The unexpected aspect of this invention's solution lies in the fact that traditional techniques for addressing the low-cobalt, low-toughness problem typically involve adding alloying elements such as Ni and Fe to strengthen the binder phase or using Co-based pre-alloyed powders. This invention, however, takes the opposite approach, solving the strength and toughness problem through structural innovation of the inhibitor rather than adjusting the binder phase composition. The core-shell structure of Cr3C2 and VC makes the inhibitor itself a "functional composite material." During sintering, the Cr3C2 in the core layer partially dissolves in the cobalt phase, effectively providing an additional effect of micro-alloying to strengthen the binder phase. Meanwhile, the uniform deposition of VC at the grain boundaries in the shell layer avoids the grain boundary embrittlement caused by the direct addition of VC in traditional methods. This unexpected "dual-effect" effect allows low-cobalt-content cemented carbides to achieve a strength and toughness balance superior to conventional cobalt-content alloys.

[0034] The unexpected aspect of this invention lies in the synergistic effect of low-temperature plasma surface activation treatment and core-shell structure inhibitors. Traditional powder pretreatment techniques often focus on dispersant addition, ultrasonic dispersion, or mechanical alloying, while the low-temperature plasma treatment introduced in this invention, originally used primarily in thin film deposition or surface modification, represents an unexpected cross-disciplinary application in cemented carbide powder pretreatment. Plasma activation generates numerous dangling bonds and active sites on the powder surface. These sites selectively adsorb and chemically bond with specific crystal planes of the core-shell structure inhibitor shell, resulting in the inhibitor not undergoing simple physical mixing during ball milling, but rather forming a uniformly dispersed state with "active anchoring." The unexpected effect of this dispersion is evident during sintering: guided by the active sites, the core-shell inhibitor particles preferentially distribute at the WC-Co interface, rather than randomly dispersing in the cobalt phase, thus achieving precise positioning of the inhibitor at the grain boundaries, significantly improving inhibition efficiency and reducing the required total amount. Attached Figure Description

[0035] Figure 1 The X-ray diffraction patterns are those of the cemented carbide in Examples 1-3 of this invention.

[0036] Figure 2 The image shows a comparison of the flank wear of the tools used in the example and the comparative example after high-speed milling of GH4169 alloy. Detailed Implementation

[0037] The following detailed description illustrates the specific implementation method: The long-life ultrafine low-cobalt cemented carbide formulation for high-speed machining of high-temperature alloys of the present invention is composed of the following raw materials in weight percentages: 85.0%–92.5% ultrafine tungsten carbide (WC) powder; 3.0%–9.0% cobalt (Co) powder; and 1.6%–2.0% composite grain growth inhibitor. The ultrafine tungsten carbide powder has an average grain size of 0.2–0.4 μm. The composite grain growth inhibitor is composed of at least two of chromium carbide (Cr3C2), vanadium carbide (VC), and tantalum carbide / niobium carbide (TaC / NbC), and the inhibitor is a core-shell structured composite powder, wherein the core layer is one type of carbide, and the shell layer is another type or more carbides.

[0038] The composite grain growth inhibitor is composed of a core-shell structured composite powder with chromium carbide (Cr3C2) as the core and vanadium carbide (VC) as the shell.

[0039] In the core-shell composite powder, the weight ratio of the core to the shell is (1:0.3) to (1:1.5).

[0040] The hardness of the cemented carbide is not less than 92.0 HRA, and the transverse fracture strength is not less than 3000 MPa.

[0041] The preparation method for the aforementioned cemented carbide includes the following steps: S1: Raw material pretreatment, the core-shell structure composite grain growth inhibitor is surface activated with ultrafine WC powder and Co powder under an inert atmosphere; S2: Wet high-energy ball milling, using a planetary ball mill, wet milling is carried out after the raw material powders are mixed. The wet milling medium is anhydrous ethanol, the ball-to-material ratio is 5:1 to 10:1, and the wet milling time is 12 to 50 hours. S3: Spray drying granulation, which involves spray drying the slurry to obtain a well-flowing composite powder; S4: Molding and sintering, using high-pressure sintering process, sintering temperature 1350℃~1420℃, pressure 30~60 MPa, holding time 30~60 minutes.

[0042] The surface activation treatment described in S1 uses low-temperature plasma treatment for a time of 10 to 30 minutes.

[0043] During the sintering process described in S4, a carburizing treatment of 0.52 hours is performed at the end of the sintering period to repair the surface carbon potential.

[0044] The cutting tool made of the aforementioned cemented carbide is coated with a TiAlN / TiAlCrN multilayer nanocomposite coating with a thickness of 5–15 μm. The coating has a gradient structure, consisting of a TiN transition layer, a TiAlN layer, and a TiAlN / TiAlCrN nanolayer structure from the substrate to the surface. This tool is suitable for nickel-based superalloys and titanium alloys, and its tool life is increased by more than 50% compared to conventional cemented carbide tools under cutting speeds of 120–300 m / min and feed rates of 0.05–0.3 mm / r.

[0045] The differences and advantages of this invention compared to conventional techniques in the field are as follows: Commonly used techniques in this field typically include: (1) single or simple mixed grain growth inhibitors; (2) conventional wet ball milling mixing; (3) vacuum sintering or low-pressure hot isostatic pressing sintering; and (4) single TiAlN or TiN coating.

[0046] Differences: This invention breaks through the combination of the above-mentioned conventional technologies and innovatively introduces the synergistic integration of four key technologies: core-shell structure inhibitor, low-temperature plasma activation, high-pressure sintering + carburizing treatment, and TiAlN / TiAlCrN nano-multilayer gradient coating.

[0047] Advantages: Compared with conventional technology, this invention achieves excellent performance with a hardness of not less than 92.0 HRA and a transverse fracture strength of not less than 3000 MPa under low cobalt content (3.0-9.0%). Conventional technology usually cannot achieve such high hardness and toughness at the same cobalt content. The tool of this invention has a lifespan of more than 50% under high-speed machining conditions of high-temperature alloys at cutting speeds of 120-180 m / min, which is significantly better than the performance of conventional technology tools under the same conditions.

[0048] The specific implementation process is as follows: Example 1 A long-life ultrafine low-cobalt cemented carbide for high-speed machining of high-temperature alloys, wherein the alloy chemical composition consists of the following components by weight percentage: WC: 90.5%, Co: 6.5%, and composite grain growth inhibitor: 1.6% (wherein Cr3C2@VC core-shell powder, core-shell ratio 1:1).

[0049] The preparation method of the above-mentioned long-life ultrafine low-cobalt cemented carbide includes the following steps: Step 1: Activate the above powder with low-temperature plasma under an Ar atmosphere for 20 minutes; Step 2: After activation, the powder is placed in a ball mill with cemented carbide balls and anhydrous ethanol at a ball-to-powder ratio of 8:1 and milled for 24 hours. Step 3: Spray dry to obtain granulated powder, add 2.0% paraffin, and mix evenly; Step 4: Press and mold at 50 MPa, then sinter at 1380℃ / 40 MPa, followed by carburizing treatment for 1 hour.

[0050] The hardness of the cemented carbide is 92.2 HRA, and the transverse fracture strength is 3250 MPa.

[0051] A gradient coating was prepared on the cemented carbide substrate by PVD: first, a TiN transition layer was deposited, then a TiAlN layer was deposited, and finally a TiAlN / TiAlCrN nanomultilayer structure was deposited.

[0052] The coated insert was used for milling GH4169 high-temperature alloy at a cutting speed of 180 m / min and a feed rate of 0.15 mm / r. Under the same milling time, the flank wear width was 161.548 mm. 50.145μm, a 200.873 μm reduction in flank wear width compared to commercially available general-purpose coated inserts. 63.253.

[0053] Example 2 An ultrafine low-cobalt cemented carbide with adjusted composition, the chemical composition of which consists of the following components by weight percentage: WC: 88.0%, Co: 5.0%, composite grain growth inhibitor: 2.0% (of which Cr3C2@VC core-shell powder, core-shell ratio 1:0.8).

[0054] The preparation process is the same as in Example 1, except that the ball milling time is 30 hours and the high-pressure sintering conditions are 1360℃ / 50MPa.

[0055] The hardness of the cemented carbide is 92.8 HRA, and the transverse fracture strength is 3213 MPa.

[0056] The coating structure is the same as in Example 1. In high-speed milling of GH4169 high-temperature alloy, at a cutting speed of 180 m / min and a feed rate of 0.15 mm / r, under the same milling time, the flank wear width is 205.825 mm. 57.331μm.

[0057] Example 3 An ultrafine-grained cemented carbide using finer WC raw materials has the following chemical composition by weight percentage: WC: 92.0%, Co: 4.5%, and composite grain growth inhibitor: 2.0% (of which Cr3C2@VC core-shell powder has a core-shell ratio of 1:1.2).

[0058] The preparation process is the same as in Example 1, except that the ball-to-material ratio is 10:1, ball milling is performed for 30 hours, and the sintering conditions are 1400℃ / 60MPa. The hardness of the cemented carbide is 93.5 HRA, and the transverse fracture strength is 3021 MPa.

[0059] The coating structure is the same as in Example 1. In high-speed milling of GH4169 high-temperature alloy, at a cutting speed of 180 m / min and a feed rate of 0.15 mm / r, the flank wear width was 386.988 mm under the same milling time. 53.203μm.

[0060] Comparative Examples To objectively evaluate the technological advancements of this invention, a commercially available general-purpose carbide end mill insert from a certain brand was selected as a comparative example. The typical composition of this comparative example insert is: approximately 10% cobalt content and a WC grain size of approximately 1.0 μm.

[0061] The hardness of the alloy in the comparative example is approximately 89.5 HRA.

[0062] In the same high-speed milling test of GH4169 high-temperature alloy, the wear width of the flank face of commercially available general-purpose coated inserts was 362.423 μm, and the wear mode of the flank face was mainly diffusion wear and adhesive wear, indicating that its red hardness and anti-diffusion ability were significantly lower than those of the embodiments of the present invention.

[0063] Figure 1 The X-ray diffraction patterns are those of the cemented carbide in Examples 1-3 of this invention. Figure 2 This is a comparison of the flank wear of the tools used in the example and the comparative example after high-speed milling of GH4169 alloy. From... Figure 1 It can be clearly seen that the cemented carbides prepared in Examples 1-3 of this invention are all composed only of WC and Co phases, and no harmful phases such as η phase (e.g., Co3W3C or Co6W6C) or free graphite were detected. This indicates that the addition of the composite grain growth inhibitor Cr3C2@VC core-shell powder can effectively inhibit the abnormal growth of WC grains while ensuring the pure phase structure of the alloy. Figure 2It can be clearly seen that, under the same high-speed milling conditions of GH4169 high-temperature alloy, the wear width of the flank face of the coated inserts in Examples 1 and 2 of this invention is 161.548±50.145 μm and 205.825±57.331 μm, respectively, both significantly smaller than the 362.423 μm of the comparative example. In particular, Example 1 has the smallest wear width, with its wear amount reduced by approximately 55.4% compared to the comparative example, exhibiting excellent wear resistance and high-temperature red hardness. The wear width of Example 3 is 386.988±53.203 μm, slightly higher than the comparative example, but its hardness reaches 93.5 HRA, indicating that toughness and wear resistance can be further balanced by adjusting the composition and process. In summary, this invention, through the design of a core-shell structure grain growth inhibitor, combined with high-pressure sintering and gradient nano-coating technology, successfully achieves a synergistic improvement in high hardness, high toughness, and excellent high-temperature performance of ultrafine-grained cemented carbide under low cobalt content. This tool exhibits significantly extended service life and stable machining quality in high-speed cutting of difficult-to-machine materials such as high-temperature alloys and titanium alloys, and has important industrial application value.

[0064] Furthermore, under the same conditions as in Example 1, the only changes were made to the weight percentage of ultrafine tungsten carbide (WC) powder (85.0% or 92.5%), the weight percentage of cobalt (Co) powder (3.0% or 9.0%), and the weight percentage of the composite grain growth inhibitor (1.6% or 1.8%); or, the only change was made to the average grain size of the ultrafine tungsten carbide powder (0.2 or 0.4 μm). By replacing Example 1 with the above single variables, the properties of the resulting alloy formulations were all slightly inferior to those of Example 1, and will not be elaborated further here.

[0065] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A long-life, ultra-fine, low-cobalt cemented carbide cutting tool formulation, characterized in that, The raw materials are composed of the following weight percentages: 85.0%–92.5% ultrafine tungsten carbide powder; 3.0%–9.0% cobalt powder; and 1.6%–2.0% composite grain growth inhibitor. The average grain size of the ultrafine tungsten carbide powder is 0.2–0.4 μm. The composite grain growth inhibitor is composed of at least two of chromium carbide, vanadium carbide, and tantalum carbide / niobium carbide, and the inhibitor is a core-shell structured composite powder, wherein the core layer is one type of carbide and the shell layer is another type or more carbides.

2. The long-life ultra-fine low-cobalt cemented carbide tool formulation according to claim 1, characterized in that, The composite grain growth inhibitor is composed of a core-shell structured composite powder with chromium carbide as the core and vanadium carbide as the shell.

3. The long-life ultra-fine low-cobalt cemented carbide tool formulation according to claim 2, characterized in that, In the core-shell composite powder, the weight ratio of the core to the shell is (1:0.3) to (1:1.5).

4. The long-life ultra-fine low-cobalt cemented carbide tool formulation according to claim 1, characterized in that, The hardness of the cemented carbide is not less than 92.0 HRA, and the transverse fracture strength is not less than 3000 MPa.

5. The long-life ultra-fine low-cobalt cemented carbide tool formulation according to any one of claims 1 to 4, characterized in that, The average grain size of the ultrafine tungsten carbide powder is 0.2–0.4 μm, and the cobalt powder content is 3.0–9.0 wt.%.

6. The long-life ultra-fine low-cobalt cemented carbide tool formulation according to any one of claims 1 to 4, characterized in that, The total content of the composite grain growth inhibitor is 1.6–2.0 wt.%.

7. A method for preparing a long-life, ultra-fine, low-cobalt cemented carbide cutting tool, characterized in that, The carbide cutting tool formulation according to any one of claims 1 to 4 includes the following steps: Step 1: Raw material pretreatment, the core-shell structure composite grain growth inhibitor is surface activated with ultrafine tungsten carbide powder and cobalt powder under an inert atmosphere; Step 2: Wet high-energy ball milling, using a planetary ball mill, wet milling is carried out after the raw material powders are mixed. The wet milling medium is anhydrous ethanol, the ball-to-material ratio is 5:1 to 10:1, and the wet milling time is 12 to 50 hours. Step 3: Spray drying granulation, the slurry is spray dried to obtain a well-flowing composite powder; Step 4: Molding and sintering, using high-pressure sintering process, sintering temperature 1350℃~1420℃, pressure 30~60 MPa, holding time 30~60 minutes.

8. The method according to claim 7, characterized in that, The surface activation treatment in step one uses low-temperature plasma treatment, and the treatment time is 10 to 30 minutes.

9. The method according to claim 7 or 8, characterized in that, In the sintering process described in step four, a carburizing treatment of 0.5 to 2 hours is performed at the end of the sintering period to repair the surface carbon potential.

10. A long-life, ultra-fine, low-cobalt cemented carbide cutting tool, characterized in that, The tool is made using the cemented carbide tool formulation as described in any one of claims 1-4, wherein the tool surface is coated with a TiAlN / TiAlCrN multilayer nanocomposite coating with a coating thickness of 5-15 μm.

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