Hard alloy micro-texture tool based on discharge plasma pressureless sintering and preparation method

Abstract

The invention relates to a hard alloy micro-texture tool based on discharge plasma pressureless sintering and a preparation method. Comprising the following steps: preparing a micro-texture male die pressing head; wC-Co mixed powder is obtained; the pressure head in the step (1) is adopted to apply 150-180 MPa pressure to the WC-Co mixed powder, the pressure is maintained for 60 min, and a biscuit is obtained after demolding; putting the biscuit into a graphite mold, assembling the mold, carrying out vacuum pressureless sintering on the biscuit, heating to 1300-1400 DEG C at the heating rate of 90-110 DEG C / min, carrying out heat preservation for 10 + / -2 minutes, and then cooling to room temperature along with a furnace to obtain a hard alloy block with a micro-texture on the surface; and the micro-texture surface of the hard alloy block is only polished to be bright. According to the method, thermal damage and fusion edge collapse are thoroughly avoided, and high-precision, namely high geometric fidelity, high efficiency, namely short sintering period and low-cost preparation of the microstructure is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of micro-textured cutters, and particularly relates to a hard alloy micro-textured cutter based on discharge plasma pressureless sintering and a preparation method. BACKGROUND

[0002] WC-Co hard alloy has become an indispensable key basic material for high-performance metal cutting tools due to its excellent hardness, excellent wear resistance and good toughness. In recent years, by designing and preparing specific micro-texture on the surface of the hard alloy cutter, the cutting friction state can be effectively improved, the adhesion of the chip can be inhibited, and the heat dissipation capacity can be enhanced, thereby significantly improving the service life of the hard alloy cutter. This significant performance advantage makes the surface micro-texture technology of the hard alloy cutter rapidly become a research hotspot in the field. However, the current mainstream surface micro-texture preparation technology of the hard alloy generally faces the bottleneck problems of low processing efficiency, high cost, complex process and difficulty in realizing rapid manufacturing of complex three-dimensional structures, which seriously restricts the industrialization popularization and application of the technology. Therefore, exploring and realizing the rapid and low-cost manufacturing method of the high-performance micro-textured hard alloy cutter has become a key challenge and research focus to be broken through at present.

[0003] Currently, laser machining is the most common technique for micro-textured cemented carbide tools, which is based on the principle of local ablation removal by high-energy laser irradiation to form a predetermined texture on the surface of the blank. Although this technique has the advantages of high machining resolution, flexibility and material universality, it has problems such as high cost and low efficiency. When the laser energy density exceeds the material melting threshold, strong surface melting, vaporization and impact sputtering can easily lead to the deterioration of the machining surface quality. Ion beam etching, as another high-precision micro-nano machining method, realizes structure preparation through high-energy ion beam bombardment, but its machining effect is significantly limited by the quality of the vacuum environment. Residual gas molecules may trigger the competition process of ion-induced sputtering and deposition, which needs to be strictly controlled. Micro-milling technology has the characteristics of low cost, high efficiency and good surface quality, but the increase of cutting force caused by tool wear during machining easily leads to brittle fracture removal of WC grains, which introduces micro-defects on the surface. In contrast, electrochemical machining based on microsecond short pulses shows unique potential. This method can realize non-burr, non-crack and non-heat-affected zone machining by copying micro-texture from the pre-made tool electrode to the workpiece, and has high machining speed and no area limitation. However, the machining precision is easily affected by the inductance effect in the pulse power circuit. When the total current rises with the increase of the machining area, the inductance will prolong the pulse duration required to form an effective double layer. It is worth noting that the method of directly copying micro-texture on the cemented carbide tool powder blank and then sintering can effectively avoid the subsequent process problems such as thermal damage and molten collapse. The geometric characteristics of the texture after sintering are excellent, and the original organization and performance integrity of the substrate can be preserved to the greatest extent. However, so far there are still few reports on this research, and its process mechanism and optimization path need to be further explored.

[0004] The method of directly replicating microtextures on the surface of powder blanks and sintering them requires no surface pressure to be applied during the sintering process. While traditional pressureless sintering meets this condition, it typically relies on high temperatures and long holding times, easily inducing abnormal growth of WC grains, leading to increased brittleness, decreased toughness, and increased porosity and process sensitivity due to difficulties in densification. This makes it difficult to meet the service requirements of cutting tools under complex conditions such as impact and vibration, and it is also less cost-effective. In contrast, spark plasma sintering (SPS) utilizes pulsed current to generate Joule heating inside the sintered body to promote densification, offering advantages such as uniform temperature distribution, rapid heating rate, and short processing cycle. Studies have shown that the spark plasma in the SPS process can clean impurities and oxide layers on the powder surface, accelerate gas release, and significantly suppress residual porosity. Conventional SPS employs a pressure-based sintering mode, where pressure is applied directly to the powder blank through a graphite mold, which can damage the pre-fabricated microtexture. In contrast, in the pressureless SPS graphite mold configuration, a pulsed current generates Joule heating through a conductive graphite mold. This heat is transferred to the blank via conduction and radiation. The nominal system pressure acts only on the graphite mold assembly and is not transferred to the powder surface, thus ensuring the integrity of the microtexture and enabling rapid, damage-free manufacturing. This technology provides an innovative path for the rapid, low-cost manufacturing of high-performance microtextured cemented carbide tools. However, research on pressureless SPS technology remains insufficient, particularly regarding the shrinkage behavior of the material within the graphite mold cavity and its impact on densification and microtexture fidelity, which requires further investigation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for directly imprinting microtextures onto a cemented carbide powder blank and then sintering it to prepare a microtextured cutting tool. This method, based on a spark plasma sintering (SPS) system, achieves efficient and rapid preparation of microtextures on the cemented carbide surface through reasonable process parameter settings, with relatively low process difficulty. The imprinting process achieves a microtexture feature replication accuracy of over 90% from the indenter to the blank, verifying its effectiveness. Compared to the original blank, the prepared cemented carbide block exhibits a longitudinal dimensional shrinkage rate of (20.00±1.00)% and a radial dimensional shrinkage rate of (20.00±1.00)%. This cemented carbide block can be rapidly ground to obtain a microtextured cemented carbide cutting tool.

[0006] The technical solution to achieve the objective of this invention is: a method for preparing cemented carbide microtextured tools based on spark plasma pressureless sintering, comprising the following steps:

[0007] Step (1): Prepare a microtextured punch head;

[0008] Step (2): Obtain WC-Co mixed powder: wherein Co powder accounts for 1%-6% of the total weight;

[0009] Step (3): Preparation of green compact: the WC-Co mixed powder is pressed by the punch of step (1) at a pressure of 150-180 MPa and for 60 min, and the green compact is obtained after demolding;

[0010] Step (4): Sintering: the green compact prepared in step (3) is placed in a graphite mold, the mold is assembled, and then placed in a spark plasma sintering furnace, and the green compact is vacuum sintered at a temperature rising rate of 90-110 ℃ / min to 1300-1400 ℃, and then cooled to room temperature after holding for 10±2 min, to obtain a cemented carbide block with a micro-textured surface;

[0011] Step (5): Polishing: only the micro-textured surface of the cemented carbide block prepared in step (4) is polished to bright, and the rest of the surface is ground to the size of the tool.

[0012] Further, step (1) is specifically: depositing a 500±50 μm thick nickel-phosphorus plating layer on the pressing surface of the SKD11 tool steel, and processing the pressing surface to form a micro-textured convex mold;

[0013] The micro-textured convex mold is formed by concentric circular ring arrays with isosceles trapezoidal cross sections, and the thickness of the micro-textured convex mold is less than the thickness of the nickel-phosphorus plating layer.

[0014] The size of the micro-textured convex mold is 140% to 150% of the size of the micro-textured surface of the desired micro-textured tool.

[0015] Further, step (2) is specifically: weighing the WC powder and Co powder according to the proportion to mix the mixed powder, adding 100%-120% of the weight of the mixed powder to the mixed powder; placing it on an ultrasonic vibration platform for shock mixing, while mechanically stirring at a speed of 100-120 r / min, and processing for 2-3 h to obtain a mixed slurry;

[0016] The mixed slurry is placed in a 120±5 ℃ vacuum drying box for drying; after grinding, it is passed through a 100 mesh sieve to obtain a WC-Co mixed powder.

[0017] Further, the WC powder used in step (2) has a purity of ≥99.9% and an average particle size of 80-120 nm, and the Co powder used has a purity of ≥99.9% and an average particle size of 300-500 nm.

[0018] Further, the graphite mold in step (4) is made of graphite material with a compressive strength of 600-800 MPa.

[0019] Further, the discharge plasma sintering graphite mold comprises a graphite upper end cover, a graphite sleeve, a graphite lower end cover and a graphite gasket; and the mold assembling in step (4) is specifically as follows: the graphite gasket is placed on the graphite lower end cover, and then the green compact is placed on the surface of the graphite gasket; the graphite upper end cover is covered to form a reaction chamber with the three; and the outer layer of the mold is wrapped with multiple layers of graphite grids and is tightly fixed by a graphite rope.

[0020] Further, the sintering in step (4) is specifically as follows: the graphite gasket is placed between the graphite mold and the electrode of the discharge plasma sintering furnace, so that the temperature measuring hole of the graphite mold is opposite to the temperature measuring device of the discharge plasma sintering furnace; the sintering pressure is set to 2.0 MPa, so that the current passes through the graphite mold and the graphite upper end cover does not damage the green compact in the reaction chamber; the sintering atmosphere is vacuum, the temperature is raised to 1300-1400℃ at a temperature rising rate of 90-110℃ / min, the sintering power is turned off after 10 min of heat preservation, and the furnace is naturally cooled to room temperature, so that the hard alloy block body with a micro-textured surface is obtained.

[0021] A hard alloy micro-textured cutter is prepared by the method.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) Breakthrough in micro-texture preparation bottleneck: the micro-texture is directly imprinted in the green compact stage, combined with SPS pressureless sintering (mold pressure 2.0 MPa does not act on the compact), which completely avoids the heat damage, melting collapse and micro-defect problems of laser / ion beam processing, and solves the industrialization problems of low efficiency and high cost of traditional micro-texture technology.

[0024] (2) Accurate and reliable size control: through the pre-compensation design of the size of the pressure head (140%-150% of the final texture size), the longitudinal / radial shrinkage rate of the micro-texture after sintering is stably controlled at (20.00±1.00)%, and the geometric feature fidelity reaches the industrial grade precision requirement.

[0025] (3) Significant improvement in process efficiency: the precision of the imprinting and copying is >90%, combined with SPS rapid sintering (temperature rising rate of 90-110℃ / min, 10 min of heat preservation), which greatly shortens the period of traditional pressureless sintering and avoids the abnormal growth of WC grains. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The preparation method flow chart of the present application.

[0027] Figure 2 The graphite mold structure schematic diagram of the present application.

[0028] Figure 3 The XRD patterns of the hard alloy block before and after grinding in Example 1 of the present application, wherein (a) is the XRD pattern, and (b) is the local enlarged view of (a).

[0029] Figure 4 SEM images and EDS analysis of the surface of the cemented carbide block prepared in Example 1 of the present application before and after grinding and polishing; wherein (a) is before grinding and polishing, and (b) is after grinding and polishing.

[0030] Figure 5 Three-dimensional topography of the indenter, green compact and sintered sample of Example 1 of the present application; wherein (a) is the indenter, (b) is the green compact, (c) is the sintered sample, and (d) is the effective cutting edge region of the tool. DETAILED DESCRIPTION

[0031] The present application will be further described in detail below with reference to the accompanying drawings.

[0032] A method for preparing a cemented carbide micro-textured tool based on discharge plasma pressureless sintering, comprising the following steps:

[0033] 1) Preparation of micro-textured indenter: an indenter is made of SKD11 tool steel, and a 500 μm-thick nickel-phosphorus (Ni-P) plating layer is deposited on the pressing surface thereof to minimize adhesion and facilitate demolding. An accurate micro-textured stamp is formed on the pressing surface by ultra-precision machining; the micro-textured stamp is composed of an array of circular rings with isosceles trapezoidal cross sections; the size of the micro-textured stamp is 140% to 150% of the size of the micro-texture on the surface of the desired micro-textured tool, and this size compensation (equivalent to 40% to 50% of the size of the micro-texture on the tool) is used to offset sintering shrinkage and warping deformation;

[0034] 2) Ultrasonic oscillation mixing: WC powder and Co powder (Co powder accounts for 1% to 6% of the total weight) are weighed according to a specific weight ratio to obtain a raw material mixture; 100% to 120% by weight of anhydrous ethanol is added to the raw material mixture; the mixture is subjected to oscillation mixing on an ultrasonic vibration platform while being mechanically stirred at a speed of 100 to 120 r / min for 2 to 3 h to obtain a mixed slurry;

[0035] 3) Drying and sieving: the mixed slurry obtained in step 2) is dried in a 120℃ vacuum drying box; after manual grinding, coarse particles are removed through a 100-mesh sieve to obtain a mixed powder;

[0036] 4) Powder pre-pressing: a powder tablet press and the indenter obtained in step 1) are used to apply a pressure of 150 to 180 MPa to the mixed powder and maintain the pressure for 60 min; after demolding, a green compact is obtained;

[0037] 5) Mold assembly: A spark plasma sintering graphite mold (3) is set up, which includes a graphite upper end cap (301), a graphite sleeve (302), a graphite lower end cap (304), and a graphite gasket (303); the graphite gasket (303) is placed on the graphite lower end cap (304), and the blank (305) is placed on the surface of the graphite gasket (303); the graphite upper end cap (301) is covered so that the three form a reaction chamber; the outer layer of the mold is wrapped with multiple layers of graphite grids and tied and fixed with graphite rope;

[0038] 6) Sintering: Place the graphite mold (3) containing the blank (305) obtained in step 5) into the spark plasma sintering furnace. Insert a graphite pad (2) between the graphite mold (3) and the electrode (1) of the spark plasma sintering furnace so that the temperature measuring hole of the graphite mold is facing the temperature measuring device of the spark plasma sintering furnace. Set the sintering pressure to 2.0 MPa so that the current passes through the graphite mold (3) and the graphite upper end cap (301) will not damage the blank (305) in the reaction chamber. The sintering atmosphere is vacuum. The temperature is raised to 1300-1400℃ at a heating rate of 90-110℃ / min. After holding for 10 minutes, the sintering power supply is turned off and the furnace is allowed to cool naturally to room temperature to obtain a cemented carbide block with microtexture on the surface.

[0039] 7) Grinding and polishing: The cemented carbide block prepared in step 6) is processed. The micro-textured surface is polished to a bright finish, while the remaining surfaces are ground to the tool size.

[0040] In step 2), the purity of WC powder is ≥99.9% and the particle size is 80-120 nm; the purity of Co powder is ≥99.9% and the particle size is 300-500 nm.

[0041] This method achieves a feature replication accuracy of >90% from the indenter to the blank by directly imprinting microtextures during the blank stage. After sintering, the longitudinal / radial dimensional shrinkage rate of the microtexture is stabilized at (20.00±1.00)%, solving the technical problem of efficient and low-difficulty preparation of microtexture tools.

[0042] Example 1

[0043] like Figure 1 The method shown here for preparing microtextures on the surface of cemented carbide using spark plasma sintering includes the following steps:

[0044] S1 adopts SKD11 tool steel to manufacture the indenter, and a 500 μm-thick nickel-phosphorus (Ni-P) plating layer is deposited on the pressing surface thereof to minimize adhesion and facilitate demolding. On the pressing surface, an accurate micro-textured punch is formed by ultra-precision machining; the micro-textured punch is composed of an array of circular rings with isosceles trapezoidal cross sections; the longitudinal cross section of the micro-textured punch is an isosceles trapezoid with an upper base of 20 μm, a lower base of 120 μm, and a height of 10 μm, and is arranged in the form of a concentric circular ring array with a spacing of 240 μm;

[0045] S2: WC powder and Co powder are weighed in a weight ratio of 96:4 to obtain a raw material mixture; 100% to 120% by weight of anhydrous ethanol is added to the raw material mixture; the mixture is subjected to ultrasonic vibration mixing while being mechanically stirred at a speed of 120 r / min for 2 h to obtain a mixed slurry;

[0046] S3: The mixed slurry is dried in a 120℃ vacuum drying box; after manual grinding, coarse particles are removed through a 100-mesh sieve to obtain a mixed powder;

[0047] S4: The mixed powder is subjected to a pressure of 180 MPa for 60 min using the indenter obtained in S1; after demolding, a green compact is obtained;

[0048] SS5: Mould assembly: a spark plasma sintering graphite mould 3 is provided, which includes a graphite upper end cover 301, a graphite sleeve 302, a graphite lower end cover 304, and a graphite gasket 303; the graphite gasket 303 is placed on the graphite lower end cover 304, and then the green compact 305 is placed on the surface of the graphite gasket 303; the graphite upper end cover 301 is covered to form a reaction chamber; the outer layer of the mould is wrapped with multiple layers of graphite grids and tightly fixed with a graphite rope;

[0049] S6: The spark plasma sintering graphite mould 3 containing the green compact 305 is placed in a spark plasma sintering furnace, and a graphite pad 2 is placed between the spark plasma sintering graphite mould 3 and the electrode 1 of the spark plasma sintering furnace, so that the temperature measuring hole of the graphite mould is opposite the temperature measuring device of the spark plasma sintering furnace; the sintering pressure is set to 2.0 MPa, the current is passed through the graphite mould 3, and the graphite upper end cover 301 will not damage the green compact 305 in the reaction chamber; the sintering atmosphere is vacuum, the temperature is raised to 1300℃ at a rate of 90-110℃ / min, and after 10 min of holding, the sintering power is turned off, and the furnace is naturally cooled to room temperature, to obtain a hard metal block with a micro-textured surface.

[0050] S7: Grinding and polishing: the prepared hard metal block is processed, the micro-textured surface is polished to a bright finish, and the remaining surface is ground to the size of a tool.

[0051] X-ray diffraction analysis showed that Co3W3C phase (η phase) was formed on the surface of the sintered sample, and only WC and Co phases were detected on the polished surface, and the diffraction peaks did not shift significantly, as shown in FIGS. Figure 3 The SEM images and corresponding EDS analysis of the sintered sample before and after grinding and polishing are shown in FIGS. Figure 4 The sintered surface showed elevated carbon (35.2 at.%) and oxygen (6.8 at.%) contents, while the tungsten (55.1 at.%) and cobalt (2.1 at.%) contents were reduced. The polished surface showed a sharp decrease in carbon (14.5 at.%) and oxygen (1.7 at.%) contents, while the tungsten (78.4 at.%) and cobalt (4.0 at.%) concentrations increased to values consistent with the WC-Co matrix composition. This significant change in composition, combined with the significant reduction in the intensity of the η phase diffraction peaks observed in the XRD analysis of the polished surface, indicates that the η phase is mainly enriched in a thin surface layer. The underlying matrix microstructure is still mainly composed of WC and Co phases.

[0052] The micro-texture characteristics of the indenter, green compact and sintered sample surfaces were characterized by three-dimensional morphology, and the results are shown in FIGS. Figure 5 (a)-(c) show that compared with the designed size, the bottom width, height and pitch are reduced by 42%, 10% and 17%, respectively. Figure 5 (d) indicates the effective cutting edge area of the tool, and the warped area outside the sintered sample is precisely ground and removed during tool manufacturing; the warped part in the center area is located in the tool holder clamping area and does not participate in effective cutting.

[0053] The key of the present application is to realize the copying of micro-texture to the surface of the cemented carbide green compact after pre-pressing by machining a micro-texture convex mold on the powder contact end of the indenter, and to prepare a cemented carbide block with a micro-textured surface through a spark plasma sintering device. After grinding, a cemented carbide micro-textured tool is prepared. The present application has the technical effects of low processing cost, fast preparation, effective reduction of sintering temperature and shortening of sintering time, solves the problems caused by high sintering temperature and long holding time in other sintering technologies, and overcomes the difficulties of high cost and poor process effect in other micro-texture processing technologies.

[0054] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing cemented carbide microtextured cutting tools based on discharge plasma pressureless sintering, characterized in that, Includes the following steps: Step (1): Prepare a microtextured punch head; Step (2): Obtain WC-Co mixed powder: wherein Co powder accounts for 1%-6% of the total weight; Step (3): Preparation of green blank: Apply 150-180 MPa pressure to the WC-Co mixed powder using the pressure head of step (1) and hold for 60 min. After demolding, the green blank is obtained. Step (4): Sintering: Place the green blank prepared in step (3) into a graphite mold, assemble the mold, and then place it in a spark plasma sintering furnace to perform vacuum pressureless sintering on the green blank. The temperature is raised to 1300-1400℃ at a heating rate of 90-110℃ / min, held for 10±2min, and then cooled to room temperature with the furnace to obtain a cemented carbide block with microtexture on the surface. Step (5): Polishing: Polish only the microtextured surface of the cemented carbide block prepared in step (4) to a bright finish, and grind the remaining surfaces to the tool size.

2. The method according to claim 1, characterized in that, Step (1) specifically involves depositing a 500±50μm thick nickel-phosphorus plating layer on the pressed surface of SKD11 tool steel, and forming a micro-textured punch on the pressed surface. The microtextured punch is formed by a concentric array of rings with an isosceles trapezoidal cross section, and the thickness of the microtextured punch is less than the thickness of the nickel-phosphorus plating layer. The size of the microtextured punch is 140% to 150% of the microtextured size on the surface of the desired microtextured tool.

3. The method according to claim 1, characterized in that, Step (2) is as follows: Weigh WC powder and Co powder according to the proportion and mix them to obtain a mixed powder. Add 100% to 120% of the weight of anhydrous ethanol to the mixed powder. Place it on an ultrasonic vibration platform for oscillation and mixing, and mechanically stir at a speed of 100 to 120 r / min for 2 to 3 hours to obtain a mixed slurry. The mixed slurry was dried in a vacuum drying oven at 120±5℃; after grinding, it was passed through a 100-mesh sieve to obtain WC-Co mixed powder.

4. The method according to claim 3, characterized in that, The WC powder used in step (2) has a purity of ≥99.9% and an average particle size of 80-120 nm, and the Co powder used has a purity of ≥99.9% and an average particle size of 300-500 nm.

5. The method according to claim 1, characterized in that, The graphite mold in step (4) is made of graphite material with a compressive strength of 600-800 MPa.

6. The method according to claim 5, characterized in that, The graphite mold for spark plasma sintering includes a graphite upper end cap, a graphite sleeve, a graphite lower end cap, and a graphite gasket; step (4) mold assembly is as follows: place the graphite gasket on the graphite lower end cap, and then place the blank on the surface of the graphite gasket; cover the graphite upper end cap so that the three form a reaction chamber; wrap the outer layer of the mold with multiple layers of graphite grids and tie it tightly with graphite rope.

7. The method according to claim 6, characterized in that, The sintering in step (4) is as follows: a graphite pad is placed between the graphite mold and the electrode of the spark plasma sintering furnace, so that the temperature measuring hole of the graphite mold is facing the temperature measuring device of the spark plasma sintering furnace; the sintering pressure is set to 2.0 MPa, so that the current passes through the graphite mold and the graphite upper end cap will not damage the green blank in the reaction chamber; the sintering atmosphere is vacuum, and the temperature is raised to 1300-1400℃ at a heating rate of 90-110℃ / min, held for 10 min, and then the sintering power supply is turned off. The furnace is allowed to cool naturally to room temperature to obtain a cemented carbide block with microtexture on the surface.

8. A cemented carbide microtextured cutting tool, characterized in that, Prepared using the method described in any one of claims 1-7.

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