High-performance hard alloy optical mold material and preparation method thereof

Abstract

The preparation method comprises the following steps that WC, Co-Ni, VC, TaC, Mo2C, Si3N4 and MgF2 are mixed according to the proportion, Si3N4 / MgF2 is compounded through wet grinding, aluminum oxide coating is carried out, after the mixture and matrix powder are mixed and subjected to wet grinding, graphene oxide aqueous dispersion is added, then vacuum plasma surface modification treatment is carried out, and the high-performance hard alloy optical mold material is obtained. Carrying out segmented sintering after molding; si3N4 nanocrystalline powder and MgF2 composite modified components are added into a hard phase WC and binding phase Co-Ni system, aluminum oxide sol coating is carried out, graphene oxide coating and vacuum plasma pulse activating treatment are combined, and the powder surface activity can be improved; and the high-performance optical mold material which is compact and fine in grain, excellent in thermal stability and high in surface smoothness is obtained in a graded degreasing, atmosphere alternate sintering and argon-assisted cooling mode.

Description

Technical Field

[0001] This invention relates to the field of optical mold materials, and in particular to a high-performance cemented carbide optical mold material and its preparation method. Background Technology

[0002] Optical mold materials are materials used in the forming and processing of optical glass, crystals or other optical components. Their properties affect the dimensional accuracy, surface quality and service life of the molded products. Among optical mold materials, cemented carbide is widely used due to its high hardness, high wear resistance and good compressive strength.

[0003] In the existing technology, cemented carbide optical mold materials have weak thermal shock resistance. During long-term high-temperature use, they are prone to thermal fatigue cracks, which affects the service life of the optical mold. Secondly, the surface finish of cemented carbide optical mold materials is low, making it difficult to form a smooth surface that meets the requirements of high-precision optics when polishing. In addition, during the high-temperature molding process, the optical mold is also prone to adhesion reaction with the optical product, resulting in difficulty in demolding and thus affecting the optical performance of the molded product.

[0004] Therefore, existing technologies have shortcomings and need to be improved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-performance cemented carbide optical mold material and its preparation method that avoids thermal fatigue cracking and improves the service life of optical molds.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A method for preparing a high-performance cemented carbide optical mold material includes the following steps:

[0008] S1. Mix the raw materials according to the following weight percentages:

[0009] Hard phase WC: 82%-85%, Co-Ni powder: 8-12%, grain refiner VC: 0.6-1.2wt%, high temperature stabilizer TaC: 4-6wt%, reinforcing agent Mo2C: 0.4-0.8wt%, Si3N4 nanocrystalline powder: 0.4-0.8wt%, and MgF2 powder: 0.1-0.3wt%.

[0010] S2. Si3N4 and MgF2 powders are wet-milled and mixed in a certain proportion to obtain Si3N4 / MgF2 composite powder. Then, 0.3-0.5wt% of alumina sol is added and magnetically stirred at 50-60℃ for 1-2 hours to coat the surface of Si3N4 / MgF2 composite powder with alumina. After spray drying, the surface-coated modified component is obtained.

[0011] S3. Add WC, TaC, VC, Mo2C, and Co-Ni powders to a ball mill jar, add anhydrous ethanol, with a liquid-to-solid ratio of 2:1 and a ball-to-material ratio of 5:1, and rotate at 180-240 rpm. After wet milling for 10-12 hours, add the coated modified components and continue wet milling for 4-6 hours. Within 20-30 minutes after the ball milling is completed, add 0.1 wt% graphene oxide aqueous dispersion and mix at a low speed of 60-80 rpm to obtain a mixed slurry.

[0012] S4. Place the mixed slurry in a vacuum drying oven and dry it for 10-12 hours at 55-65℃ and vacuum degree ≤-0.08MPa. Then, sieve it through a 200-mesh sieve to obtain the mixed powder.

[0013] S5. Place the mixed powder in a vacuum plasma treatment chamber, evacuate to 0.01 Pa, introduce Ar / H2 mixed gas with a volume ratio of 95:5 and a total pressure of 200-220 Pa, perform glow discharge at 400 W power for 20-30 min, then use pulse mode to alternately apply power for 2 s and stop for 2 s for plasma activation, and the treatment time is 10-15 min to obtain the mixed powder with plasma surface modification.

[0014] S6. Press the mixed powder into a mold blank to obtain an optical mold material blank;

[0015] S7. Optical mold material is obtained by sintering the optical mold material blank in sections.

[0016] Using the above technical solution, in step S2, Si3N4 and MgF2 powders are mixed, and then 0.5-1wt% polyvinylpyrrolidone (PVP) and anhydrous ethanol are added, with a liquid-to-solid ratio of 2:1. The mixture is then placed in a planetary ball mill for wet milling for 4-6 hours, with a ball-to-material ratio of 4:1 and a rotation speed of 200-300 rpm. After wet milling, the anhydrous ethanol is removed by low-temperature evaporation to obtain Si3N4 / MgF2 composite powder.

[0017] Using the above technical solutions, before step S6, the mixed powder is further subjected to spray drying treatment. Specifically, the plasma-modified mixed powder is added to a 2.0 wt% polyvinyl alcohol aqueous solution, and deionized water is added to adjust the slurry solid content to 60-65 wt%. The slurry is then fed into a spray granulator, with the inlet air temperature controlled at 150℃ and the outlet air temperature at 80℃. The droplet size is controlled at 20-80 μm. Under the action of hot air, the droplets are dried to form spherical granulated powder, and the output moisture content is controlled below 0.5 wt%.

[0018] Using the above technical solutions, in step S1, the particle size of WC is 0.2-0.5μm, the particle size of Co-Ni powder is 1-2μm, the particle size of VC is 0.2-0.3μm, the particle size of TaC is 0.5-0.7μm, the particle size of Mo2C is 0.5-0.8μm, the particle size of Si3N4 is 40-80nm, and the particle size of MgF2 is 0.3-0.5μm.

[0019] Using the above technical solutions, in step S6, the mixed powder is loaded into a mold coated with zinc stearate release agent, and pressed into shape under a pressure of 150-200MPa by unidirectional pressing. After holding the pressure for 10-15s, the pressure is slowly released to obtain the optical mold material blank.

[0020] Using the above technical solutions, the preparation process of the graphene oxide aqueous dispersion in step S3 is as follows:

[0021] Weigh out graphene oxide powder with a particle size of 0.5-5μm according to the target concentration and add it to deionized water. After stirring magnetically for 10-15 minutes at room temperature, transfer the slurry to a polypropylene or polytetrafluoroethylene container and disperse it using a probe-type ultrasonic device at a power of 200-400W for 30-60 minutes. Prevent agglomeration caused by temperature rise under an outer ice-water circulation condition. Then add 0.05-0.1wt% PVP for stabilization treatment. After filtering through a 200-mesh sieve, obtain a graphene oxide aqueous dispersion.

[0022] Using the above technical solutions, in the plasma surface modification process of step S5, the ratio of pulse mode power-on time to power-off time is 1:1, and high-purity hydrogen is switched before the end of the process.

[0023] Using the above technical solutions, in step S7, the pressed optical mold material blank is placed in a vacuum sintering furnace and subjected to graded debinding under a vacuum degree not exceeding 0.001 MPa, specifically as follows:

[0024] First stage: Slowly raise the temperature to 250℃ at a rate of 1-2℃ / min and hold for 1-2 hours; Second stage: Continue raising the temperature to 400℃ and hold in a high-purity nitrogen atmosphere for 2-3 hours; Third stage: Switch to a high-purity hydrogen atmosphere, raise the temperature to 600℃ and hold for 2-3 hours. After degreasing, maintain vacuum conditions, continue raising the temperature to 900℃ and hold for 10-25 minutes for vacuum pre-sintering, with a pre-sintering time of 20-40 minutes.

[0025] The main sintering stage then begins, employing a zoned temperature rise control method. Specifically, in the low-temperature activation zone, the temperature is slowly raised to 1000-1200℃, with the heating rate controlled at 3-4℃ / min. After entering the medium-temperature densification zone, the temperature is raised to 1200-1350℃, with the heating rate reduced to 1-2℃ / min. Finally, in the high-temperature densification zone, the temperature is raised to 1350-1420℃ and held for 40-60 minutes. During the medium- to high-temperature sintering stages, high-purity argon and high-purity hydrogen are alternately introduced, with the atmosphere switched every 20 minutes.

[0026] Using the above technical solutions, in step S7, after sintering is completed, the heating system is turned off, and the temperature is reduced to 600°C at a cooling rate of 2-10°C / min. Then, high-purity argon gas is introduced to assist heat exchange below 600°C, and the temperature is naturally cooled to room temperature below 200°C.

[0027] This technical solution also provides a high-performance cemented carbide optical mold material, which is prepared by any of the above-mentioned methods for preparing high-performance cemented carbide optical mold materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention improves the thermal shock stability and high-temperature demolding performance of optical mold materials by adding a composite modification component of Si3N4 nanocrystal powder and MgF2 powder to the hard phase WC and the bonding phase Co-Ni system, and then using alumina sol coating to stabilize and disperse it. While maintaining high hardness, wear resistance, and compressive strength, the invention also improves the thermal shock stability and high-temperature demolding performance of the optical mold material. Combined with a low-speed rolling coating process of graphene oxide aqueous dispersion, a uniform and dense nano-functional film layer can be formed on the powder surface. Combined with vacuum plasma pulse activation treatment, surface oxides are effectively removed and the wettability of the bonding phase is enhanced, thereby promoting sintering densification and inhibiting grain coarsening to obtain a fine, uniform, and stable structure. During the sintering process, the abnormal grain growth, structural defects, and oxidation problems can be effectively avoided by using staged debinding, alternating atmosphere control for sintering, and argon-assisted cooling. Compared with traditional hard alloy optical mold materials, the optical mold material prepared by this method has superior mechanical properties, thermal stability, surface finish, and service life. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., described below refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the invention can be combined with each other as long as they do not conflict with each other.

[0031] This invention provides a method for preparing a high-performance cemented carbide optical mold material, comprising the following steps:

[0032] S1. Mix the raw materials according to the following weight percentages: hard phase WC: 82%-85%, Co-Ni powder: 8-12%, grain refiner VC: 0.6-1.2wt%, high-temperature stabilizer TaC: 4-6wt%, reinforcing agent Mo2C: 0.4-0.8wt%, Si3N4 nanocrystalline powder: 0.4-0.8wt%, and MgF2 powder: 0.1-0.3wt%. VC, as a grain refiner, can effectively inhibit excessive growth during sintering, making the microstructure fine and uniform, and improving the comprehensive mechanical properties. TaC can improve the structural stability and hardening effect of optical molds to maintain the dimensional accuracy of optical molds during high-temperature forming. Mo2C can enhance grain boundary toughness, improve crack resistance, and improve the wear resistance of optical molds. Si3N4 nanocrystalline powder has a low coefficient of thermal expansion and high strength characteristics, which can effectively improve the thermal shock stability of optical mold materials. MgF2 powder can form a low surface energy phase on the mold surface, thereby reducing adhesion between the mold and the optical product, thus improving the demolding performance.

[0033] S2. Si3N4 and MgF2 powders are wet-milled and mixed in a certain proportion to obtain Si3N4 / MgF2 composite powder. Then, 0.3-0.5 wt% alumina sol is added, and the mixture is magnetically stirred at 50-60℃ for 1-2 hours to coat the surface of the Si3N4 / MgF2 composite powder with alumina. After spray drying, the surface-coated modified component is obtained. Wet milling of Si3N4 and MgF2 powders in a certain proportion can achieve homogenization of the two components through the synergistic effect of liquid media and ball milling media. The composite powder is uniformly distributed, allowing for the formation of a uniform and continuous functional phase network at the grain boundaries during subsequent sintering. This leverages the low thermal expansion of Si3N4 to improve thermal shock resistance, while utilizing the low surface energy and chemical inertness of MgF2 to reduce adhesion between optical products and molds. After wet milling, 0.3-0.5 wt% alumina sol is added to the composite powder and magnetically stirred at 50-60°C. This allows the alumina sol to spread uniformly on the surface of the composite particles and undergo partial hydrolysis and condensation, forming a continuous alumina coating layer. This alumina layer not only serves as a thermally stable ceramic barrier during subsequent sintering but also improves the interfacial wettability and bonding strength between the composite particles and the cemented carbide matrix metal phase.

[0034] S3. Add WC, TaC, VC, Mo2C, and Co-Ni powders to a ball mill jar, add anhydrous ethanol, with a liquid-to-solid ratio of 2:1 and a ball-to-particle ratio of 5:1, and rotate at 180-240 rpm for 10-12 hours. Then add the coated modified components and continue wet milling for 4-6 hours. Within 20-30 minutes after the ball milling is completed, add 0.1 wt% graphene oxide aqueous dispersion and mix at a low speed of 60-80 rpm to obtain a mixed slurry. The addition of graphene oxide aqueous dispersion can utilize the layered structure and high specific surface area of ​​graphene oxide in the liquid phase to allow it to adhere to the surface of powder particles through physical adsorption and electrostatic interaction, thereby forming a dense nanoscale surface functional film. This promotes the densification of the optical mold during sintering and inhibits abnormal grain growth under high temperature conditions, thereby improving the overall performance of the optical mold.

[0035] S4. Place the mixed slurry in a vacuum drying oven and dry it for 10-12 hours at 55-65℃ and a vacuum degree ≤-0.08MPa. After drying, sieve it through a 200-mesh sieve to obtain the mixed powder. This setting can promote the volatilization of liquid media such as ethanol under low temperature and low pressure environment, while avoiding the oxidation or decomposition of powder surface caused by high temperature drying. In addition, the vacuum environment can accelerate the escape of solvent molecules and reduce the oxygen content during the drying process, thereby maintaining the surface activity of the powder and the dispersion state of the particles.

[0036] S5. Place the mixed powder in a vacuum plasma treatment chamber, evacuate to 0.01 Pa, and introduce an Ar / H2 mixed gas with a volume ratio of 95:5 and a total pressure of 200-220 Pa. Perform glow discharge at 400 W for 20-30 min, followed by alternating pulsed energizing (2 s on, 2 s off) for 10-15 min to obtain plasma-modified mixed powder. Placing the mixed powder in a vacuum plasma treatment chamber and evacuating to 0.01 Pa effectively removes oxygen and water vapor from the treatment environment, preventing oxidation during plasma treatment. Then, introducing an Ar / H2 mixed gas with a volume ratio of 95:5 and controlling the total pressure at 200-220 Pa allows the high-energy ions generated by argon under glow discharge conditions to target the powder. The surface is physically bombarded to peel off the adsorbed layer and oxide film, exposing a fresh surface. Simultaneously, residual oxides are removed through chemical reduction using a small amount of hydrogen. Maintaining glow discharge at 400W for 20-30 minutes cleans and activates the powder surface, providing a clean interface for subsequent wetting and diffusion reactions during sintering. A pulsed activation mode of 2s on / 2s off for 10-15 minutes allows control of the surface etching depth during repeated ion bombardment and intermittent cooling, preventing excessive damage to the powder particle surface. This combination of vacuum plasma and pulsed excitation creates a highly clean and chemically active state on the powder surface, significantly improving the wettability and bonding strength between the bonding phase and the hard phase, thereby enhancing the densification process during subsequent sintering and the overall performance of the product.

[0037] S6. Press the mixed powder into a mold blank to obtain an optical mold material blank;

[0038] S7. Optical mold material is obtained by sintering the optical mold material blank in sections.

[0039] Further, in step S2, after mixing Si3N4 and MgF2 powders, 0.5-1 wt% polyvinylpyrrolidone (PVP) and anhydrous ethanol are added, with a liquid-to-solid ratio of 2:1. The mixture is then wet-milled in a planetary ball mill for 4-6 hours at a ball-to-particle ratio of 4:1 and a rotation speed of 200-300 rpm. After wet milling, the anhydrous ethanol is removed by low-temperature evaporation to obtain Si3N4 / MgF2 composite powder. The addition of PVP allows it to adsorb onto the particle surface during grinding, forming a flexible organic film layer, thereby preventing the agglomeration of ultrafine particles under electrostatic action during wet milling.

[0040] Furthermore, prior to step S6, the mixed powder undergoes spray drying. Specifically, the plasma-modified mixed powder is added to a 2.0 wt% aqueous solution of polyvinyl alcohol, while deionized water is added to adjust the slurry solid content to 60-65 wt%. The slurry is then fed into a spray granulator, with the inlet air temperature controlled at 150°C and the outlet air temperature at 80°C. The droplet size is controlled at 20-80 μm. Under the action of hot air, the droplets are dried to form spherical granulated powder, and the output moisture content is controlled below 0.5 wt%. Spray drying of the mixed powder can prepare spherical granulated powder with good flowability and pressing properties from the highly active plasma-modified powder.

[0041] Furthermore, in step S1, the particle size of WC is 0.2-0.5 μm, the particle size of Co-Ni powder is 1-2 μm, the particle size of VC is 0.2-0.3 μm, the particle size of TaC is 0.5-0.7 μm, the particle size of Mo2C is 0.5-0.8 μm, the particle size of Si3N4 is 40-80 nm, and the particle size of MgF2 is 0.3-0.5 μm.

[0042] Furthermore, in step S6, the mixed powder is loaded into a mold coated with zinc stearate release agent, and pressed into shape using a unidirectional pressing method under a pressure of 150-200 MPa. After holding the pressure for 10-15 seconds, the pressure is slowly released to obtain an optical mold material blank. Loading the mixed powder into a mold coated with zinc stearate release agent can reduce the coefficient of friction between the powder and the mold wall during the pressing process, thereby reducing the resistance during demolding and preventing edge chipping, cracking, or uneven density of the blank during forming or demolding.

[0043] Further, in step S3, the preparation process of the graphene oxide aqueous dispersion is as follows: Graphene oxide powder with a particle size of 0.5-5 μm is weighed according to the target concentration and added to deionized water. After magnetic stirring at room temperature for 10-15 min, the slurry is transferred to a polypropylene or polytetrafluoroethylene container and ultrasonically dispersed for 30-60 min using a probe-type ultrasonic filter at a power of 200-400W, with an outer ice-water circulation system to prevent agglomeration caused by temperature rise. Subsequently, 0.05-0.1 wt% PVP is added for stabilization treatment. After filtration through a 200-mesh sieve, the graphene oxide aqueous dispersion is obtained. Dispersion under an outer ice-water circulation system can prevent the local high temperature generated by ultrasound from increasing the sheet structure of the graphene oxide. The subsequent addition of 0.05-0.1 wt% PVP as a dispersion stabilizer can adsorb onto the surface of the graphene oxide to form a steric hindrance layer, thereby significantly extending the stabilization time of the dispersion system.

[0044] Furthermore, during the plasma surface modification process in step S5, the ratio of pulsed mode power-on to power-off time is 1:1, and the process is switched to high-purity hydrogen before the end of treatment. Switching to high-purity hydrogen before the end of treatment is to utilize the strong reducing power of hydrogen in a vacuum glow discharge environment to remove residual oxides and unstable hydrogenated surface-active species, forming a chemically stable clean state on the powder surface. This improves the wettability and diffusion capacity of the bonded relatively hard phase, promotes microstructure densification, and enhances interfacial bonding strength.

[0045] Furthermore, in step S7, the pressed optical mold material blank is placed in a vacuum sintering furnace and degreased in stages under a vacuum degree not exceeding 0.001 MPa. Specifically: First stage: slowly raise the temperature to 250℃ at a rate of 1-2℃ / min and hold for 1-2 hours; Second stage: continue raising the temperature to 400℃ and hold for 2-3 hours in a high-purity nitrogen atmosphere; Third stage: switch to a high-purity hydrogen atmosphere, raise the temperature to 600℃ and hold for 2-3 hours. After degreasing, maintain the vacuum conditions and continue raising the temperature to 900℃ and holding for 10-25 minutes for vacuum pre-treatment. Sintering: The pre-sintering time is 20-40 min; then, the main sintering stage begins, with zoned temperature rise control of the sintering process. Specifically: in the low-temperature activation zone, the temperature is slowly raised to 1000-1200℃, with the heating rate controlled at 3-4℃ / min; after entering the medium-temperature densification zone, the temperature is raised to 1200-1350℃, with the heating rate reduced to 1-2℃ / min; finally, in the high-temperature densification zone, the temperature is raised to 1350-1420℃ and held for 40-60 min. During the medium-temperature to high-temperature sintering stage, high-purity argon and high-purity hydrogen are alternately introduced, with the atmosphere switched every 20 min. The pressed optical mold material blank is placed in a vacuum sintering furnace and subjected to staged degreasing under a vacuum level not exceeding 0.001 MPa. This controlled atmosphere and temperature allows for the gradual removal of organic binders and residual volatiles from the blank, preventing rapid vaporization that could cause porosity, cracking, or structural loosening. The first stage involves slowly heating to 250°C and holding at that temperature to remove low-molecular-weight binders through low-temperature decomposition, while avoiding surface hardening due to excessively rapid heating that could hinder the release of internal volatiles. The second stage involves heating to 400°C and holding in high-purity nitrogen to further decompose medium-molecular-weight binders; the nitrogen environment effectively inhibits powder oxidation. The third stage switches to high-purity hydrogen and heats to 600°C, using the strong reducing properties of hydrogen to remove high-molecular-weight binders and decomposition products, while simultaneously reducing surface oxides and restoring the high chemical activity of the powder surface. After degreasing, the blank is kept warm. Vacuuming and short-term pre-sintering at 900℃ allows for preliminary sintering between particles, improving the strength of the green body for subsequent high-temperature sintering, while avoiding excessive densification that could affect gas exhaust channels. During the main sintering stage, zoned temperature rise control is employed. The low-temperature activation zone uses a heating rate of 3-4℃ / min to promote diffusion reactions and interface wetting. The medium-temperature densification zone reduces the heating rate to 1-2℃ / min to control grain growth and achieve pore closure. The high-temperature densification zone is held at a high temperature for an extended period to drive grain boundary migration and eliminate porosity, resulting in a high-density microstructure. Alternating introduction of high-purity argon and high-purity hydrogen in the medium- to high-temperature zones achieves a balance between the inert protection of argon and the reducing activation effect of hydrogen. This prevents abnormal grain growth while maintaining a clean and activated interface between the bonding phase and the hard phase, effectively improving microstructure uniformity, density, and overall performance.

[0046] Furthermore, in step S7, after sintering is completed, the heating system is turned off, and the temperature is reduced to 600°C at a cooling rate of 2-10°C / min. Then, high-purity argon gas is introduced to assist heat exchange below 600°C, and the temperature is naturally cooled to room temperature below 200°C. Introducing high-purity argon gas when the temperature drops below 600°C serves two purposes: firstly, it accelerates the uniform release of heat through convection and conduction of the inert gas, shortening the cooling time; secondly, it continuously isolates the powder from air during the low-temperature stage, preventing the powder surface from being re-exposed to oxygen and undergoing oxidation.

[0047] Example 1

[0048] Embodiment 1 of the present invention provides a method for preparing a high-performance cemented carbide optical mold material, comprising the following steps:

[0049] S1. Mix the raw materials according to the following weight percentages:

[0050] Hard phase WC: 85%, Co-Ni powder: 8.7%, grain refiner VC: 1.2wt%, high temperature stabilizer TaC: 4wt%, reinforcing agent Mo2C: 0.4wt%, Si3N4 nanocrystalline powder: 0.4wt%, and MgF2 powder: 0.3wt%.

[0051] Among them, the particle size of WC is 0.2μm, the particle size of Co-Ni powder is 1μm, the particle size of VC is 0.2μm, the particle size of TaC is 0.5μm, the particle size of Mo2C is 0.5μm, the particle size of Si3N4 is 40nm, and the particle size of MgF2 is 0.3μm.

[0052] S2. After mixing Si3N4 and MgF2 powders, add 1 wt% polyvinylpyrrolidone (PVP) and anhydrous ethanol at a liquid-to-solid ratio of 2:1. Then, place the mixture in a planetary ball mill for wet milling for 6 hours at a ball-to-material ratio of 4:1 and a rotation speed of 200 rpm. After wet milling, remove the anhydrous ethanol by low-temperature evaporation to obtain Si3N4 / MgF2 composite powder. Then, add 0.5 wt% alumina sol and stir magnetically at 60°C for 2 hours to coat the surface of the Si3N4 / MgF2 composite powder with alumina. After spray drying, obtain the surface-coated modified component.

[0053] S3. Add WC, TaC, VC, Mo2C, and Co-Ni powders to a ball mill jar, add anhydrous ethanol, with a liquid-to-solid ratio of 2:1 and a ball-to-material ratio of 5:1, and a rotation speed of 240 rpm. After wet milling for 10 hours, add the coated modified components and continue wet milling for 4 hours. Within 20 minutes after the ball milling is completed, add 0.1 wt% graphene oxide aqueous dispersion and mix at a low speed of 60 rpm to obtain a mixed slurry.

[0054] The preparation process of the graphene oxide aqueous dispersion is as follows: Graphene oxide powder with a particle size of 5 μm is weighed according to the target concentration and added to deionized water. After magnetic stirring for 15 min at room temperature, the slurry is transferred to a polypropylene or polytetrafluoroethylene container and ultrasonically dispersed for 60 min at a power of 400W using a probe-type ultrasonic method. Ice water circulation is used to prevent agglomeration caused by temperature rise. Then, 0.1 wt% PVP is added for stabilization treatment. After filtration through a 200-mesh sieve, the graphene oxide aqueous dispersion is obtained.

[0055] S4. Place the mixed slurry in a vacuum drying oven and dry it for 12 hours at 65℃ and a vacuum degree ≤-0.08MPa. Then, sieve it through a 200-mesh sieve to obtain the mixed powder.

[0056] S5. Place the mixed powder in a vacuum plasma treatment chamber, evacuate to 0.01 Pa, introduce Ar / H2 mixed gas with a volume ratio of 95:5 and a total pressure of 220 Pa, and perform glow discharge at 400 W power for 30 min. Then, use pulse mode to alternately activate plasma for 2 s on and 2 s off for 15 min. The ratio of pulse mode activation to shutdown time is 1:1. Before the end of the treatment, switch to high-purity hydrogen gas to obtain the mixed powder with plasma surface modification.

[0057] The plasma-modified mixed powder was added to a 2.0 wt% polyvinyl alcohol aqueous solution, and deionized water was added to adjust the slurry solid content to 65 wt%. The slurry was then fed into a spray granulator, with the inlet air temperature controlled at 150℃ and the outlet air temperature at 80℃. The droplet size was controlled at 20 μm. The droplets were dried under the action of hot air to form spherical granulated powder, and the output moisture content was controlled below 0.5 wt%.

[0058] S6. The mixed powder is loaded into a mold coated with zinc stearate release agent and pressed into shape under 150MPa pressure by unidirectional pressing. After holding the pressure for 15s, the pressure is slowly released to obtain the optical mold material blank.

[0059] S7. The pressed optical mold material blank is placed in a vacuum sintering furnace and degreased in stages under a vacuum degree not exceeding 0.001 MPa, specifically as follows:

[0060] First stage: Slowly raise the temperature to 250℃ at a rate of 2℃ / min and hold for 2 hours; Second stage: Continue raising the temperature to 400℃ and hold for 3 hours in a high-purity nitrogen atmosphere; Third stage: Switch to a high-purity hydrogen atmosphere, raise the temperature to 600℃ and hold for 3 hours. After degreasing, maintain vacuum conditions, continue raising the temperature to 900℃ and hold for 25 minutes for vacuum pre-sintering. The pre-sintering time is 20 minutes.

[0061] The main sintering stage then begins, employing a zoned temperature rise control method. Specifically, in the low-temperature activation zone, the temperature is slowly raised to 1200℃ at a rate of 4℃ / min. In the medium-temperature densification zone, the temperature is raised to 1350℃ at a rate of 2℃ / min. Finally, in the high-temperature densification zone, the temperature is increased to 1420℃ and held for 60 minutes. During the medium- to high-temperature sintering stages, high-purity argon and high-purity hydrogen are alternately introduced, with the atmosphere switched every 20 minutes.

[0062] After sintering is completed, the heating system is turned off, and the temperature is reduced to 600°C at a cooling rate of 10°C / min. Then, high-purity argon gas is introduced to assist heat exchange below 600°C, and the temperature is naturally cooled to room temperature below 200°C.

[0063] Example 2

[0064] Embodiment 2 of the present invention provides a method for preparing a high-performance cemented carbide optical mold material, comprising the following steps:

[0065] S1. Mix the raw materials according to the following weight percentages:

[0066] Hard phase WC: 82%, Co-Ni powder: 12%, grain refiner VC: 0.6wt%, high temperature stabilizer TaC: 4wt%, reinforcing agent Mo2C: 0.4wt%, Si3N4 nanocrystalline powder: 0.8wt%, and MgF2 powder: 0.2wt%.

[0067] Among them, the particle size of WC is 0.5μm, the particle size of Co-Ni powder is 2μm, the particle size of VC is 0.3μm, the particle size of TaC is 0.7μm, the particle size of Mo2C is 0.8μm, the particle size of Si3N4 is 80nm, and the particle size of MgF2 is 0.5μm.

[0068] S2. After mixing Si3N4 and MgF2 powders, add 0.5wt% polyvinylpyrrolidone (PVP) and anhydrous ethanol at a liquid-to-solid ratio of 2:1. Then, place the mixture in a planetary ball mill for wet milling for 6 hours at a ball-to-material ratio of 4:1 and a rotation speed of 300 rpm. After wet milling, remove the anhydrous ethanol by low-temperature evaporation to obtain Si3N4 / MgF2 composite powder. Then, add 0.5wt% alumina sol and stir magnetically at 50°C for 2 hours to coat the surface of the Si3N4 / MgF2 composite powder with alumina. After spray drying, obtain the surface-coated modified component.

[0069] S3. Add WC, TaC, VC, Mo2C, and Co-Ni powders to a ball mill jar, add anhydrous ethanol, with a liquid-to-solid ratio of 2:1 and a ball-to-material ratio of 5:1, and rotate at 180 rpm. After wet milling for 10 hours, add the coated modified components and continue wet milling for 4 hours. Within 20 minutes after the ball milling is completed, add 0.1 wt% graphene oxide aqueous dispersion and mix at a low speed of 60 rpm to obtain a mixed slurry.

[0070] The preparation process of the graphene oxide aqueous dispersion is as follows: Graphene oxide powder with a particle size of 0.5 μm is weighed according to the target concentration and added to deionized water. After stirring magnetically for 10 min at room temperature, the slurry is transferred to a polypropylene or polytetrafluoroethylene container and ultrasonically dispersed for 60 min at a power of 200W using a probe-type ultrasonic method. Ice water circulation is used to prevent agglomeration caused by temperature rise. Subsequently, 0.1 wt% PVP is added for stabilization treatment. After filtration through a 200-mesh sieve, the graphene oxide aqueous dispersion is obtained.

[0071] S4. Place the mixed slurry in a vacuum drying oven and dry it for 10 hours at 55℃ and a vacuum degree ≤-0.08MPa. Then, sieve it through a 200-mesh sieve to obtain the mixed powder.

[0072] S5. Place the mixed powder in a vacuum plasma treatment chamber, evacuate to 0.01 Pa, introduce Ar / H2 mixed gas with a volume ratio of 95:5 and a total pressure of 200 Pa, and perform glow discharge at 400 W power for 30 min. Then, use pulse mode to alternately apply power for 2 s and stop for 2 s for plasma activation, with a treatment time of 10 min. The ratio of pulse mode power-on to power-off time is 1:1, and switch to high-purity hydrogen gas before the end of the treatment. Finally, obtain the mixed powder with plasma surface modification.

[0073] The plasma-modified mixed powder was added to a 2.0 wt% polyvinyl alcohol aqueous solution, and deionized water was added to adjust the slurry solid content to 60 wt%. The slurry was then fed into a spray granulator, with the inlet air temperature controlled at 150℃ and the outlet air temperature at 80℃. The droplet size was controlled at 20 μm. The droplets were dried under the action of hot air to form spherical granulated powder, and the output moisture content was controlled below 0.5 wt%.

[0074] S6. The mixed powder is loaded into a mold coated with zinc stearate release agent and pressed into shape under 200MPa pressure by unidirectional pressing. After holding the pressure for 15s, the pressure is slowly released to obtain the optical mold material blank.

[0075] S7. The pressed optical mold material blank is placed in a vacuum sintering furnace and degreased in stages under a vacuum degree not exceeding 0.001 MPa, specifically as follows:

[0076] First stage: Slowly raise the temperature to 250℃ at a rate of 2℃ / min and hold for 1 hour; Second stage: Continue raising the temperature to 400℃ and hold for 2 hours in a high-purity nitrogen atmosphere; Third stage: Switch to a high-purity hydrogen atmosphere, raise the temperature to 600℃ and hold for 2 hours. After degreasing, maintain vacuum conditions, continue raising the temperature to 900℃ and hold for 10 minutes for vacuum pre-sintering. The pre-sintering time is 20 minutes.

[0077] The main sintering stage then begins, employing a zoned temperature rise control method. Specifically, in the low-temperature activation zone, the temperature is slowly raised to 1000℃ at a rate of 3℃ / min. In the medium-temperature densification zone, the temperature is raised to 1200℃ at a rate of 1℃ / min. Finally, in the high-temperature densification zone, the temperature is increased to 1350℃ and held for 40 minutes. During the medium- to high-temperature sintering stages, high-purity argon and high-purity hydrogen are alternately introduced, with the atmosphere switched every 20 minutes.

[0078] After sintering is completed, the heating system is turned off, and the temperature is reduced to 600°C at a cooling rate of 6°C / min. Then, high-purity argon gas is introduced to assist heat exchange below 600°C, and the temperature is naturally cooled to room temperature below 200°C.

[0079] Comparative Example 1

[0080] The difference between the high-performance cemented carbide optical mold material and its preparation method in Comparative Example 1 and Example 1 is that Si3N4 and MgF2 are not added in step S1.

[0081] Comparative Example 2

[0082] The difference between the high-performance cemented carbide optical mold material and its preparation method in Comparative Example 2 and Example 1 is that in step S2, Si3N4 and MgF are directly dry mixed without alumina sol coating.

[0083] Comparative Example 3

[0084] The difference between the high-performance hard alloy optical mold material and its preparation method in Comparative Example 3 and Example 1 is that graphene oxide aqueous dispersion is not added in step S3.

[0085] Comparative Example 4

[0086] The difference between the high-performance cemented carbide optical mold material and its preparation method in Comparative Example 4 and Example 1 is that in step S5, the plasma modification adopts a continuous DC mode instead of a pulse mode.

[0087] Comparative Example 5

[0088] The difference between the high-performance cemented carbide optical mold material and its preparation method in Comparative Example 5 and Example 1 is that, in step S6, zinc stearate release agent is not coated inside the mold.

[0089] Comparative Example 6

[0090] The difference between the high-performance cemented carbide optical mold material and its preparation method in Comparative Example 6 and Example 1 is that: in step S7, high-purity argon is used throughout the sintering process, and argon / hydrogen alternation is not performed.

[0091] Comparative Example 7

[0092] The difference between the high-performance cemented carbide optical mold material and its preparation method in Comparative Example 7 and Example 1 is that in step S7, when the temperature is cooled to below 600°C after sintering, high-purity argon gas is not introduced to assist heat exchange, and the material is directly cooled naturally.

[0093] The following experiments were conducted on the above Examples 1-2 and Comparative Examples 1-7 to verify or understand their performance in the high-performance cemented carbide optical mold materials prepared in the above Examples 1-2 and Comparative Examples 1-7.

[0094]

[0095] Table 1. Comparison of Performance Tests of High-Performance Hard Alloy Optical Mold Materials in Each Example and Comparative Example

[0096] As shown in Table 1 above, the high-performance cemented carbide optical mold materials prepared in Examples 1 and 2, by adding Si3N4 nanocrystal powder and MgF2 powder as composite modification components to the hard phase WC and the bonding phase Co-Ni system, and using alumina sol coating to stabilize and disperse them, effectively improve the thermal shock stability and high-temperature demolding performance of the optical mold materials while maintaining high hardness, wear resistance, and compressive strength. Combined with a low-speed rolling coating process using graphene oxide aqueous dispersion, a uniform and dense nano-functional film layer can be formed on the powder surface. Combined with vacuum plasma pulse activation treatment, surface oxides are effectively removed, and the wettability of the bonding phase is enhanced, thereby promoting sintering densification and inhibiting grain coarsening to obtain a fine, uniform, and stable structure. During the sintering process, by graded degreasing, alternating atmosphere control of sintering, and argon-assisted cooling, abnormal grain growth, structural defects, and oxidation problems can be effectively avoided. Compared with traditional cemented carbide optical mold materials, the optical mold materials prepared by this method have superior mechanical properties, thermal stability, surface smoothness, and service life.

[0097] In Comparative Example 1, the absence of Si3N4 and MgF2 modification components resulted in the optical mold material lacking the low thermal expansion and high strength enhancement provided by Si3N4 under high temperature conditions. It also failed to form a low surface energy phase through MgF2 to reduce adhesion to optical products. The lack of the synergistic effect of these two components significantly reduced the thermal shock life of the material, making it prone to thermal fatigue cracks. At the same time, it increased the demolding force and reduced the surface finish, thus affecting the quality of the molded product and the life of the mold.

[0098] In Comparative Example 2, Si3N4 and MgF2 were directly dry-mixed without alumina sol coating, which caused the two modified components to easily agglomerate during mixing and sintering, and their dispersibility was poor. They could not form a uniform functional phase network in the microstructure. Due to the lack of ceramic isolation protection from the alumina coating layer, Si3N4 and MgF2 were prone to adverse reactions at high temperatures, resulting in decreased grain boundary bonding, uneven microstructure, and reduced sintering density, thereby affecting the fracture toughness, thermal shock life, and demolding performance of the material.

[0099] In Comparative Example 3, no graphene oxide aqueous dispersion was added in step S3. The powder particles lacked a uniform nano-functional film layer formed by graphene oxide. During the sintering process, the wettability of the relatively hard phase was insufficient, and the diffusion bonding efficiency between particles was reduced. This resulted in a significant increase in the average grain size after sintering, poorer microstructure uniformity, and a decrease in both toughness and density.

[0100] In Comparative Example 4, the plasma modification process adopted a continuous DC mode instead of a pulsed mode, which caused the powder surface to be easily over-etched during the plasma bombardment process. The accumulation of local high temperature caused the particle morphology to collapse, thereby reducing the chemical activity of the powder surface and resulting in a significant reduction in the toughness and thermal stability of the material.

[0101] In Comparative Example 5, the absence of zinc stearate release agent inside the mold resulted in a significant increase in the coefficient of friction between the powder and the mold wall during the pressing process. This increased the demolding resistance and made it easier for the edges and corners of the blank to crack during demolding, thereby reducing the mechanical strength of the material. At the same time, the increased demolding force also affected the mold life.

[0102] In Comparative Example 6, high-purity argon was used throughout the sintering process without alternating between argon and hydrogen. The lack of surface reduction and activation by hydrogen in the medium and high temperature stages made it easy for oxides to remain on the surface of the bonding phase, reducing the interfacial wettability and diffusion capacity. Under the protection of a single argon atmosphere, the grain suppression effect was poor, and abnormal growth was prone to occur, resulting in coarsening of the microstructure, decrease in density, weakening of toughness, and a decrease in thermal shock performance.

[0103] In Comparative Example 7, after sintering, the temperature was lowered to below 600℃ without the introduction of high-purity argon gas to assist heat exchange. Instead, the material was directly cooled naturally, resulting in the material surface being exposed to air for a long time during the cooling process. This caused oxidation and discoloration, and a decrease in surface smoothness. At the same time, the lack of rapid and uniform heat exchange from argon gas led to uneven cooling rates, resulting in large internal and external temperature differences. This caused residual thermal stress and even microcracks, reducing the molding precision of the product.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-performance cemented carbide optical mold material, characterized in that, Includes the following steps: S1. Mix the raw materials according to the following weight percentages: Hard phase WC: 82%-85%, Co-Ni powder: 8-12%, grain refiner VC: 0.6-1.2wt%, high temperature stabilizer TaC: 4-6wt%, reinforcing agent Mo2C: 0.4-0.8wt%, Si3N4 nanocrystalline powder: 0.4-0.8wt%, and MgF2 powder: 0.1-0.3wt%. S2. Si3N4 and MgF2 powders are wet-milled and mixed in a certain proportion to obtain Si3N4 / MgF2 composite powder. Then, 0.3-0.5wt% of alumina sol is added and magnetically stirred at 50-60℃ for 1-2 hours to coat the surface of Si3N4 / MgF2 composite powder with alumina. After spray drying, the surface-coated modified component is obtained. S3. Add WC, TaC, VC, Mo2C, and Co-Ni powders to a ball mill jar, add anhydrous ethanol, with a liquid-to-solid ratio of 2:1 and a ball-to-material ratio of 5:1, and rotate at 180-240 rpm. After wet milling for 10-12 hours, add the coated modified components and continue wet milling for 4-6 hours. Within 20-30 minutes after the ball milling is completed, add 0.1 wt% graphene oxide aqueous dispersion and mix at a low speed of 60-80 rpm to obtain a mixed slurry. S4. Place the mixed slurry in a vacuum drying oven and dry it for 10-12 hours at 55-65℃ and vacuum degree ≤-0.08MPa. Then, sieve it through a 200-mesh sieve to obtain the mixed powder. S5. Place the mixed powder in a vacuum plasma treatment chamber, evacuate to 0.01 Pa, introduce Ar / H2 mixed gas with a volume ratio of 95:5 and a total pressure of 200-220 Pa, perform glow discharge at 400 W power for 20-30 min, then use pulse mode to alternately apply power for 2 s and stop for 2 s for plasma activation, and the treatment time is 10-15 min to obtain the mixed powder with plasma surface modification. S6. Press the mixed powder into a mold blank to obtain an optical mold material blank; S7. Optical mold material is obtained by sintering the optical mold material blank in sections.

2. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, In step S2, Si3N4 and MgF2 powders are mixed, and 0.5-1 wt% polyvinylpyrrolidone (PVP) and anhydrous ethanol are added. The liquid-to-solid ratio is 2:

1. Then, the mixture is placed in a planetary ball mill for wet milling for 4-6 hours with a ball-to-material ratio of 4:1 and a rotation speed of 200-300 rpm. After wet milling, the anhydrous ethanol is removed by low-temperature evaporation to obtain Si3N4 / MgF2 composite powder.

3. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, Before step S6, the mixed powder is spray-dried. Specifically, the plasma-modified mixed powder is added to a 2.0 wt% polyvinyl alcohol aqueous solution, and deionized water is added to adjust the slurry solid content to 60-65 wt%. The slurry is then fed into a spray granulator, with the inlet air temperature controlled at 150℃ and the outlet air temperature at 80℃. The droplet size is controlled at 20-80 μm. Under the action of hot air, the droplets are dried to form spherical granulated powder, and the output moisture content is controlled below 0.5 wt%.

4. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, In step S1, the particle size of WC is 0.2-0.5 μm, the particle size of Co-Ni powder is 1-2 μm, the particle size of VC is 0.2-0.3 μm, the particle size of TaC is 0.5-0.7 μm, the particle size of Mo2C is 0.5-0.8 μm, the particle size of Si3N4 is 40-80 nm, and the particle size of MgF2 is 0.3-0.5 μm.

5. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, In step S6, the mixed powder is loaded into a mold coated with zinc stearate release agent, and pressed into shape under a pressure of 150-200MPa using a unidirectional pressing method. After holding the pressure for 10-15s, the pressure is slowly released to obtain an optical mold material blank.

6. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, In step S3, the preparation process of the graphene oxide aqueous dispersion is as follows: Weigh out graphene oxide powder with a particle size of 0.5-5μm according to the target concentration and add it to deionized water. After stirring magnetically for 10-15 minutes at room temperature, transfer the slurry to a polypropylene or polytetrafluoroethylene container and disperse it using a probe-type ultrasonic device at a power of 200-400W for 30-60 minutes. Prevent agglomeration caused by temperature rise under an outer ice-water circulation condition. Then add 0.05-0.1wt% PVP for stabilization treatment. After filtering through a 200-mesh sieve, obtain a graphene oxide aqueous dispersion.

7. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, In the plasma surface modification process of step S5, the ratio of pulse mode power-on time to power-off time is 1:1, and high-purity hydrogen is switched before the end of the process.

8. The method for preparing high-performance cemented carbide optical mold material according to claim 1, characterized in that, In step S7, the pressed optical mold material blank is placed in a vacuum sintering furnace and subjected to graded debinding under a vacuum degree not exceeding 0.001 MPa. Specifically: First stage: Slowly raise the temperature to 250℃ at a rate of 1-2℃ / min and hold for 1-2 hours; Second stage: Continue raising the temperature to 400℃ and hold in a high-purity nitrogen atmosphere for 2-3 hours; Third stage: Switch to a high-purity hydrogen atmosphere, raise the temperature to 600℃ and hold for 2-3 hours. After degreasing, maintain vacuum conditions, continue raising the temperature to 900℃ and hold for 10-25 minutes for vacuum pre-sintering, with a pre-sintering time of 20-40 minutes. The main sintering stage then begins, employing a zoned temperature rise control method. Specifically, in the low-temperature activation zone, the temperature is slowly raised to 1000-1200℃, with the heating rate controlled at 3-4℃ / min. After entering the medium-temperature densification zone, the temperature is raised to 1200-1350℃, with the heating rate reduced to 1-2℃ / min. Finally, in the high-temperature densification zone, the temperature is raised to 1350-1420℃ and held for 40-60 minutes. During the medium- to high-temperature sintering stages, high-purity argon and high-purity hydrogen are alternately introduced, with the atmosphere switched every 20 minutes.

9. The method for preparing high-performance cemented carbide optical mold material according to claim 8, characterized in that, In step S7, after sintering is completed, the heating system is turned off, and the temperature is reduced to 600°C at a cooling rate of 2-10°C / min. Then, high-purity argon gas is introduced to assist heat exchange below 600°C, and the temperature is naturally cooled to room temperature below 200°C.

10. A high-performance cemented carbide optical mold material, characterized in that, It is prepared by the method for preparing high-performance cemented carbide optical mold material according to any one of claims 1-9.

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