A chalcogenide glass aspherical lens mold core material and a preparation method thereof

Abstract

The application discloses a kind of chalcogenide glass aspherical lens mould pressing mould core material and preparation method thereof, belong to infrared optical device manufacturing technical field.The mould core material is made of composite powder including niobium carbide powder, chromium carbide powder and metal nickel powder by discharge plasma sintering, wherein the mass content of nickel powder is 0wt% to 2wt%, the mass ratio of niobium carbide and chromium carbide is 30~35:65~70.The material is up to 8.5×10 ‑6 / K~9.5×10 ‑6 / K at 600 DEG C, and is well matched with chalcogenide glass, while having high hardness (1700~1900 HV30) and high fracture toughness (6.0~7.0 MPa·m¹ / ²).The preparation method key includes powder mixing under inert atmosphere, mould pre-pressing, and using gradient temperature and gradient pressure SPS sintering process.The application effectively solves the lens breakage and demoulding difficulty problem caused by insufficient thermal expansion coefficient of traditional mould material, and significantly improves the qualified rate of chalcogenide glass mould pressing.

Description

Technical Field

[0001] This application relates to the field of infrared optical device manufacturing technology, and more specifically, to a mold core material for molding chalcogenide glass aspherical lenses and its preparation method. Background Technology

[0002] Currently, the demand for miniaturized, lightweight infrared optical systems with high imaging quality is growing rapidly, driving the widespread application of various small-aperture aspherical infrared optical lenses. Chalcogenide glass, with its superior optical properties and processing characteristics, is gradually replacing traditional infrared materials and becoming the core lens material in next-generation infrared optical systems.

[0003] However, the unique physical properties of chalcogenide glasses pose a significant challenge to the molding process: their high coefficient of thermal expansion and low glass transition temperature make them prone to quality problems during molding, such as lens breakage, reduced molding accuracy, and difficulty in demolding. The root cause of these problems lies in the mismatch between the coefficient of thermal expansion of existing mold materials and chalcogenide glasses. Particularly under high-temperature molding conditions, the difference in thermal expansion between the mold and the glass material can lead to stress concentration. Currently, the industry commonly uses pure tungsten carbide mold materials, which, while possessing high hardness and strength, have a coefficient of thermal expansion of only 4.2-4.9 × 10⁻⁶ within the range of 200-800℃. -6 The coefficient of thermal expansion ( / K) is far from meeting the specific requirements of chalcogenide glass molding processes for mold materials' thermal expansion properties. This limitation severely restricts the improvement of production efficiency and yield of chalcogenide glass aspherical lenses. Therefore, developing a mold material that combines high hardness, high strength, and a suitable coefficient of thermal expansion has become the key to breaking through the bottleneck of chalcogenide glass precision molding technology.

[0004] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0005] The purpose of this application is to provide a mold core material for molding chalcogenide glass aspherical lenses, its preparation method, and an optical mold, which has the advantages of a thermal expansion coefficient that is highly matched with that of chalcogenide glass, effectively reducing thermal stress concentration during the molding process.

[0006] This application provides mold core materials for molding aspherical lenses made of chalcogenide glass, and the technical solution is as follows:

[0007] It is made by spark plasma sintering of a composite powder containing niobium carbide powder, chromium carbide powder, and metallic nickel powder.

[0008] The mass content of metallic nickel powder is 0wt% to 2wt%, with the balance being niobium carbide powder and chromium carbide powder;

[0009] The mass ratio of niobium carbide powder to chromium carbide powder is 30~35:65~70;

[0010] The core material has a coefficient of thermal expansion of 8.5×10-6 / K~9.5×10-6 / K at 600℃, a fracture toughness of 6.0~7.0MPa·m1 / 2, a hardness of 1700~1900HV30, and a density of 6.8~7.0g / cm³.

[0011] The diameter of the optical mold material is 30~100mm, and the height is 10~65mm;

[0012] Furthermore, this application also proposes that the preferred mass content of the nickel powder is 0 wt% to 1.5 wt%.

[0013] Furthermore, this application also proposes that the purity of the nickel powder is ≥99.5% and the particle size is ≤1μm.

[0014] Furthermore, this application also proposes that the coefficient of thermal expansion of the mold core material at 600℃ is 8.9×10-6 / K~9.4×10-6 / K.

[0015] Furthermore, this application also proposes that the preparation method includes the following steps:

[0016] (1) Mixing and drying of raw material powders: Niobium carbide powder, chromium carbide powder and nickel powder are mixed in an inert atmosphere to obtain composite powder, which is then dried, sieved and stored in an inert atmosphere;

[0017] (2) Molding and pre-pressing: The composite powder is loaded into the graphite mold and pre-pressed. The pre-pressing pressure is 10~20MPa. After pre-pressing, the height of the upper and lower pressure heads is adjusted so that the height of the exposed part of the female mold is consistent.

[0018] (3) Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation;

[0019] (4) Spark plasma sintering: The graphite mold treated in step (3) is placed in the spark plasma sintering system. After vacuuming, the power is turned on for gradient heating sintering. The maximum sintering temperature is 1450℃~1650℃, and the temperature is held for 0~10 minutes. The maximum sintering pressure is 40~100MPa. After sintering, the current is cut off for cooling until the mold temperature is below 100℃ before taking it out of the furnace.

[0020] (5) Post-processing: Take out the sintered sample and remove the surface deposits.

[0021] Furthermore, this application also proposes that, in step (1), the particle size of niobium carbide powder and chromium carbide powder are both 1 to 2 micrometers, and the purity is both 99.5 wt.% to 99.9 wt.%.

[0022] Furthermore, this application also proposes that in step (1), the mixing process adopts planetary ball milling, drum wet milling or tilting wet milling; the grinding balls are cemented carbide balls, preferably, the ball-to-material ratio during ball milling is 3~5:1, the ball milling speed is 30~200r / min, and the ball milling time is 12~48h.

[0023] Furthermore, this application also proposes that in step (1), the inert atmosphere is a nitrogen atmosphere, and the nitrogen purity is greater than 99.999%.

[0024] Furthermore, this application also proposes that, in step (4), the gradient heating is specifically as follows: the heating rate from room temperature to 1000℃ is 30~50℃ / min, and after the temperature is greater than 1000℃, the heating rate is adjusted to 10~15℃ / min.

[0025] Furthermore, this application also proposes that in step (4), sintering is carried out by gradient pressure, specifically including: the initial pressure is 0~10MPa; when the temperature reaches above 700℃, the sintering pressure is increased to 20MPa; when the temperature reaches 1300℃, the sintering pressure is increased to 40~100MPa; after the heat preservation is completed, the sintering pressure is adjusted to 0MPa.

[0026] Furthermore, this application also proposes that the optical mold for molding aspherical chalcogenide glass lenses is prepared from the above-mentioned mold core material.

[0027] As can be seen from the above, the mold core material for molding chalcogenide glass aspherical lenses, its preparation method, and the optical mold provided in this application achieve a thermal expansion coefficient of 8.5 × 10⁻⁶ at 600℃ through a specific ratio of niobium carbide and chromium carbide combined with a spark plasma sintering process. -6 / K~9.5×10 -6 / K forms a good match with chalcogenide glasses, and has the advantage of having a high coefficient of thermal expansion that matches that of chalcogenide glasses, effectively reducing the concentration of thermal stress during the molding process.

[0028] Compared with existing technologies, this invention, through the organic combination of material system innovation and process route optimization, successfully prepared a mold core material that is highly compatible with chalcogenide glasses. Its main advantages can be summarized as follows:

[0029] 1. This invention, by precisely controlling the specific ratio of niobium carbide to chromium carbide (30~35:65~70), forms a composite matrix with complementary thermal expansion properties, resulting in a thermal expansion coefficient of up to 8.9×10⁻⁶ at 600℃. -6 / K ~ 9.4×10 -6 / K. This coefficient is similar to that of chalcogenide glasses (~8.3×10). -6The gradient matching ( / K) not only ensures the synchronous expansion of the mold and glass during the molding process, but also makes the mold shrink slightly larger during cooling, forming a micro gap that facilitates demolding.

[0030] 2. This invention introduces submicron-sized high-purity nickel powder as a toughening phase, which is distributed at the carbide grain boundaries during sintering and effectively absorbs crack propagation energy through plastic deformation. Precise control of the nickel powder content promotes densification through liquid-phase sintering while avoiding a decrease in matrix hardness due to excessive metallic phase. While maintaining high hardness (1700~1900 HV30), it possesses excellent fracture toughness (6.0~7.0 MPa·m¹ / ²), overcoming the contradiction of "high hardness leading to brittleness" in traditional mold materials.

[0031] 3. This invention employs a unique process combining spark plasma sintering (SPS) with gradient heating and gradient pressurization. Utilizing instantaneous high temperature and the activation effect of the electric field, it achieves rapid densification of powder particles. By optimizing process parameters—including rapid heating at low temperatures to improve sintering efficiency, slow heating at high temperatures to precisely control the maximum temperature, and step-pressurization to promote complete gas expulsion—it ensures the formation of a uniform and fine microstructure, free of pores and defects, and exhibits excellent radial property consistency. This provides the mold with excellent high-temperature stability and a long service life, and the finished surface has a high degree of smoothness, free of defects such as white spots and chipping.

[0032] The mold core material and preparation method provided by this invention systematically solve the core bottleneck problem in the molding of chalcogenide glass. By achieving perfect thermal matching, excellent mechanical properties and stable microstructure, it ultimately achieves a comprehensive effect of significantly improving the molding pass rate, production efficiency and mold life. Attached Figure Description

[0033] Figure 1 The results show the thermal expansion coefficient of the mold core material for molding aspherical chalcogenide glass prepared according to Example 1 of this application. Detailed Implementation

[0034] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0035] In existing technologies, the demand for miniaturized aspherical lenses in infrared optical systems has driven chalcogenide glass to become the mainstream material. Chalcogenide glass has a high coefficient of thermal expansion and a low conversion temperature, which means that the mold material during molding must have a higher coefficient of thermal expansion to match its thermal behavior. The coefficient of thermal expansion of traditional pure tungsten carbide molds is insufficient, and they cannot meet the comprehensive requirements of mold deformation resistance and thermal matching during chalcogenide glass molding, resulting in problems such as cracking and difficulty in demolding during lens forming.

[0036] To address these issues, researchers discovered that while simply increasing the carbide content could increase hardness, it would decrease the coefficient of thermal expansion. By studying the thermal expansion characteristics of different carbides, they found that the difference in the coefficients of thermal expansion between niobium carbide and chromium carbide could be utilized. Further analysis revealed that adjusting the ratio of the two carbides could control the overall coefficient of thermal expansion of the composite material while maintaining high hardness. Considering the material's insufficient toughness, they attempted to introduce a metallic phase as a toughening agent, but excessive metallic phase weakened the hardness. After repeated experimental verification, they finally determined that adding a limited proportion of nickel powder to the carbide matrix could balance hardness and toughness.

[0037] Therefore, this application proposes a mold core material prepared by spark plasma sintering of a composite powder composed of niobium carbide powder, chromium carbide powder, and nickel powder. The mass ratio of niobium carbide to chromium carbide is 30~35:65~70, and the nickel powder content is 0wt% to 2wt%. The coefficient of thermal expansion of this material at 600℃ is 8.5×10⁻⁶. -6 / K~9.5×10 -6 / K, fracture toughness is 6.0~7.0 MPa·m 1 / 2 The hardness is 1700~1900HV30, and the density is 6.8~7.0g / cm³; the diameter of the optical mold material is 30~100mm, and the height is 10~65mm.

[0038] This application further proposes that the mass content of nickel powder is from 0.5 wt% to 1.2 wt%.

[0039] This application further proposes that the purity of the nickel powder be ≥99.5% and the particle size be ≤1μm.

[0040] Among them, a purity of ≥99.5% means that the content of non-nickel elements in the nickel powder does not exceed 0.5%.

[0041] This application further proposes that the coefficient of thermal expansion of the mold core material at 600℃ is 8.9 × 10⁻⁶. -6 / K~9.2×10 -6 / K.

[0042] This application further proposes a method for preparing mold core material for molding chalcogenide glass aspherical lenses, including the following steps:

[0043] (1) Mixing and drying of raw material powder: Niobium carbide powder, chromium carbide powder and nickel powder are mixed in an inert atmosphere to obtain composite powder, which is then dried, sieved and stored in an inert atmosphere; (2) Molding and pre-pressing: The composite powder is loaded into a graphite mold and pre-pressed at a pressure of 10-20 MPa. After pre-pressing, the height of the upper and lower pressure heads is adjusted so that the height of the exposed part of the mold is consistent; (3) Insulation wrapping: Two to three layers of 5 mm thick carbon felt are wrapped around the graphite mold for insulation; (4) Spark plasma sintering: The graphite mold treated in step (3) is placed in a spark plasma sintering system. After vacuuming, the power is turned on for gradient heating sintering. The maximum sintering temperature is 1450℃-1650℃, and the temperature is held for 0-10 minutes. The maximum sintering pressure is 40-100 MPa. After sintering, the current is cut off for cooling until the mold temperature is below 100℃ before taking it out of the furnace; (5) Post-treatment: The sintered sample is taken out and the surface deposits are removed.

[0044] This application further proposes that, in the raw material powder mixing and drying steps, the particle size of niobium carbide powder and chromium carbide powder are both 1 to 2 micrometers, and the purity is both 99.5 wt.% to 99.9 wt.%.

[0045] This application further proposes that the mixing process adopts planetary ball milling, drum wet milling or tilting wet milling, the grinding balls are cemented carbide balls, the ball-to-material ratio is 3~5:1, the ball milling speed is 30~200 r / min, and the ball milling time is 12~48 h.

[0046] This application further proposes using nitrogen gas with a purity greater than 99.999% as an inert atmosphere during the mixing process of raw material powders.

[0047] This application further proposes a gradient heating method: the heating rate from room temperature to 1000℃ is 30~50℃ / min, and after the temperature exceeds 1000℃, the heating rate is adjusted to 10~15℃ / min.

[0048] This application further proposes a gradient pressurization method during the sintering process, specifically including an initial pressure of 0 to 10 MPa, increasing the pressure to 20 MPa when the temperature reaches above 700℃, further increasing the pressure to 40 to 100 MPa when the temperature reaches 1300℃, and adjusting the sintering pressure to 0 MPa after the heat preservation is completed.

[0049] First, cut graphite paper to size according to the graphite mold and place it on the inner wall of the mold, ensuring it fits snugly. Next, place the lower indenter into the graphite mold and add two layers of graphite paper with the same diameter as the indenter, ensuring they fit snugly. Then, mix and dry the composite powder according to the specified ratio and load it into the graphite mold. Finally, add two layers of graphite paper and the upper indenter in sequence, and apply pre-pressure and maintain pressure using a hydraulic press. After completing these steps, wrap the mold with high-temperature graphite felt. The dimensions of the graphite mold and indenter are determined by the size of the sample to be prepared.

[0050] The spark plasma sintering systems used in the following embodiments are from SINTER LAND Corporation of Japan, specifically models LABOX-350, LABOX-6020, and continuous production lines. It should be noted that the preparation of cemented carbide blocks using equipment from other manufacturers and models, employing the methods described in this invention, is also within the scope of this invention. Spark plasma sintering includes pulsed current-pressure sintering, electric field-assisted sintering, and pulsed current rapid sintering.

[0051] The density results in the following examples were obtained using Archimedes' method of displacement.

[0052] Hardness tests were performed using a Vickers hardness tester under a load of 30 kg and a holding time of 15 s.

[0053] The fracture toughness test was conducted in accordance with the international standard ISO 28079-2009 "Hardmetals - Palmqvist toughness test". The total length of the four cracks at the tip of the indentation was measured and calculated, and the fracture toughness KIC was calculated in combination with the Vickers hardness value of the sample under the indentation.

[0054] Test method for coefficient of thermal expansion: According to the national standard GB / T 4339-2008 "Determination of characteristic parameters of thermal expansion of metallic materials", the coefficient of thermal expansion of the sample is tested within the specified range.

[0055] Example 1

[0056] An optical mold material with a diameter of φ40mm×18mm was prepared, wherein the mass ratio of niobium carbide:chromium carbide:nickel powder in the composite powder was 30:69:1.

[0057] 1. Raw material powder mixing and drying: 2 kg of powder weighed according to the above mass ratio is placed in a wet drum mill and wet-milled under a nitrogen atmosphere. The abrasive is cemented carbide balls, the ball-to-powder ratio is 3.5:1, the milling speed is 30 r / min, and the milling time is 24 h. The milled powder is then dried and sieved at 100℃ and stored under a nitrogen atmosphere.

[0058] 2. Molding and pre-pressing: Take 130g of the dried composite powder and put it into the graphite negative mold. Use a hydraulic press to pre-press it. The pre-pressing pressure is 15MPa. After pre-pressing, adjust the height of the upper and lower pressure heads so that they are exposed at the same height in the negative mold.

[0059] 3. Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation;

[0060] 4. Spark plasma sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 10 MPa, evacuate to below 10 Pa, and start sintering by powering on; during the sintering process, use a gradient heating method for sintering, from room temperature to 1000℃, the heating rate is 30~50℃ / min; when the temperature is above 1000℃, the heating rate is 10~15℃ / min.

[0061] Sintering is carried out using a gradient pressure method. The initial pressure is 10 MPa, and when the temperature reaches above 700℃, the sintering pressure is increased to 20 MPa. When the temperature reaches 1300℃, the sintering pressure is increased to 50 MPa.

[0062] The sintering temperature is 1550℃, and the sintering is ended after holding at that temperature for 3 minutes. After holding at that temperature, the pressure is released to 0MPa, and the furnace is cooled to below 100℃ before being removed.

[0063] 5. Post-processing: Sampling: The sample is taken out using a hydraulic press, and sandblasting is used to remove the graphite from the sample surface.

[0064] This yields optical mold products with a surface free of white spots and chipping after precision machining. The surface has a hardness of 1800 HV30, is free of pores, and has a fracture toughness greater than 6.7 MPa·m. 1 / 2 The coefficient of thermal expansion is 9.0 × 10⁻⁶. -6 / K (600℃), density is 6.99g / cm³ 3 .

[0065] Samples of the obtained aspherical chalcogenide glass pressing optical mold products were taken, and the coefficient of thermal expansion from room temperature to 800°C was measured. The results are shown below. Figure 1 In the middle. For example Figure 1 As shown, the coefficient of thermal expansion at 600℃ is 9.036 × 10⁻⁶. -6 / K, meeting the requirements of chalcogenide glass molding technology.

[0066] Example 2

[0067] Optical mold material with a diameter of φ100mm×55mm was prepared, wherein the mass ratio of niobium carbide:chromium carbide:nickel powder in the composite powder was 30:70:0.

[0068] 1. Raw material powder mixing and drying: 30 kg of powder weighed according to the above mass ratio is placed in a wet drum mill and wet-milled under a nitrogen atmosphere. The abrasive is cemented carbide balls, the ball-to-powder ratio is 4:1, the milling speed is 42 r / min, and the milling time is 18 h. The milled powder is then dried and sieved at 100℃ and stored under a nitrogen atmosphere.

[0069] 2. Molding and pre-pressing: Take 3 kg of the dried composite powder and put it into the graphite negative mold. Use a hydraulic press to pre-press it. The pre-pressing pressure is 20 MPa. After pre-pressing, adjust the height of the upper and lower pressure heads so that they are exposed at the same height in the negative mold.

[0070] 3. Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation;

[0071] 4. Spark plasma sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 5 MPa, evacuate to below 10 Pa, and start sintering by powering on; during the sintering process, use a gradient heating method for sintering, from room temperature to 1000℃, the heating rate is 30~40℃ / min; when the temperature is above 1000℃, the heating rate is 10~13℃ / min.

[0072] Sintering is carried out using a gradient pressure method. The initial pressure is 5 MPa. When the temperature reaches above 600℃, the sintering pressure is increased to 25 MPa. When the temperature reaches 1300℃, the sintering pressure is increased to 60 MPa.

[0073] The sintering temperature is 1530℃. After holding at this temperature for 5 minutes, the sintering is completed. After holding at this temperature, the pressure is released to 0MPa, and the furnace is cooled to below 100℃ before being removed.

[0074] 5. Post-processing: Sampling: The sample is taken out using a hydraulic press, and sandblasting is used to remove the graphite from the sample surface.

[0075] This yields optical mold products with a surface free of white spots and chipping after precision machining. The surface has a hardness of 1850 HV30, is free of pores, and has a fracture toughness greater than 6.6 MPa·m. 1 / 2 The coefficient of thermal expansion is 9.1 × 10⁻⁶. -6 / K (600℃), density is 7.01g / cm³ 3 .

[0076] Example 3

[0077] An optical mold material with a diameter of φ80mm×30mm was prepared, wherein the mass ratio of niobium carbide:chromium carbide:nickel powder in the composite powder was 32:67:1.

[0078] 1. Raw material powder mixing and drying: 30 kg of powder weighed according to the above mass ratio is placed in a wet drum mill and wet-milled under a nitrogen atmosphere. The abrasive is cemented carbide balls, the ball-to-powder ratio is 4:1, the milling speed is 42 r / min, and the milling time is 18 h. The milled powder is then dried and sieved at 100℃ and stored under a nitrogen atmosphere.

[0079] 2. Molding and pre-pressing: Take 1.1 kg of the dried composite powder and put it into the graphite negative mold. Use a hydraulic press to pre-press it at a pressure of 20 MPa. After pre-pressing, adjust the height of the upper and lower pressure heads so that they are exposed at the same height in the negative mold.

[0080] 3. Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation;

[0081] 4. Spark plasma sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 5 MPa, evacuate to below 10 Pa, and start sintering by powering on; during the sintering process, use a gradient heating method for sintering, from room temperature to 1000℃, the heating rate is 30~40℃ / min; when the temperature is above 1000℃, the heating rate is 10~13℃ / min.

[0082] Sintering is carried out using a gradient pressure method. The initial pressure is 5 MPa. When the temperature reaches above 600℃, the sintering pressure is increased to 25 MPa. When the temperature reaches 1300℃, the sintering pressure is increased to 60 MPa.

[0083] The sintering temperature is 1600℃, and the sintering is ended after holding at that temperature for 8 minutes. After the holding period, the pressure is released to 0MPa, and the furnace is cooled to below 100℃ before being removed.

[0084] 5. Post-processing: Sampling: The sample is taken out using a hydraulic press, and sandblasting is used to remove the graphite from the sample surface.

[0085] This yields optical mold products with a surface free of white spots and chipping after precision machining. The surface has a hardness of 1700 HV30, no porosity, and a fracture toughness greater than 6.8 MPa·m. 1 / 2 The coefficient of thermal expansion is 9.1 × 10⁻⁶. -6 / K (600℃), density is 6.98g / cm³ 3 .

[0086] Comparative Example 1

[0087] Optical mold material with a diameter of φ100mm×55mm was prepared, wherein the mass ratio of niobium carbide:chromium carbide:nickel powder in the composite powder was 30:65:5.

[0088] 1. Raw material powder mixing and drying: 30 kg of powder weighed according to the above mass ratio is placed in a wet drum mill and wet-milled under a nitrogen atmosphere. The abrasive is cemented carbide balls, the ball-to-powder ratio is 4:1, the milling speed is 42 r / min, and the milling time is 18 h. The milled powder is then dried and sieved at 100℃ and stored under a nitrogen atmosphere.

[0089] 2. Molding and pre-pressing: Take 3 kg of the dried composite powder and put it into the graphite negative mold. Use a hydraulic press to pre-press it. The pre-pressing pressure is 20 MPa. After pre-pressing, adjust the height of the upper and lower pressure heads so that they are exposed at the same height in the negative mold.

[0090] 3. Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation;

[0091] 4. Sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 5 MPa, evacuate to below 10 Pa, and start sintering by powering on; during the sintering process, use a gradient heating method for sintering, from room temperature to 1000℃, the heating rate is 30~40℃ / min; when the temperature is above 1000℃, the heating rate is 10~13℃ / min.

[0092] Sintering is carried out using a gradient pressure method. The initial pressure is 5 MPa. When the temperature reaches above 600℃, the sintering pressure is increased to 25 MPa. When the temperature reaches 1300℃, the sintering pressure is increased to 60 MPa.

[0093] The sintering temperature is 1530℃. After holding at this temperature for 5 minutes, the sintering is completed. After holding at this temperature, the pressure is released to 0MPa, and the furnace is cooled to below 100℃ before being removed.

[0094] 4. Sampling: The sample is taken out using a hydraulic press, and the graphite on the sample surface is removed by sandblasting.

[0095] This yields optical mold products with a surface free of white spots and chipping after precision machining. The surface has a hardness of 1550 HV30, is free of pores, and has a fracture toughness greater than 6.6 MPa·m. 1 / 2 The coefficient of thermal expansion is 8.3 × 10⁻⁶. -6 / K (600℃), density is 6.4 g / cm³ 3 Its hardness and coefficient of thermal expansion do not meet the requirements of chalcogenide glass molding technology.

[0096] Comparative Example 2

[0097] Optical mold material with a diameter of φ100mm×55mm was prepared, wherein the mass ratio of niobium carbide:chromium carbide:nickel powder in the composite powder was 30:70:0.

[0098] 1. Raw material powder mixing and drying: 30 kg of powder weighed according to the above mass ratio is placed in a wet drum mill and wet-milled under a nitrogen atmosphere. The abrasive is cemented carbide balls, the ball-to-powder ratio is 4:1, the milling speed is 42 r / min, and the milling time is 18 h. The milled powder is then dried and sieved at 100℃ and stored under a nitrogen atmosphere.

[0099] 2. Molding and pre-pressing: Take 3 kg of the dried composite powder and put it into the graphite negative mold. Use a hydraulic press to pre-press it. The pre-pressing pressure is 20 MPa. After pre-pressing, adjust the height of the upper and lower pressure heads so that they are exposed at the same height in the negative mold.

[0100] 3. Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation;

[0101] 4. Spark plasma sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 5 MPa, evacuate to below 10 Pa, and start sintering by powering on; during the sintering process, use a gradient heating method for sintering, from room temperature to 1000℃, the heating rate is 30~40℃ / min; when the temperature is above 1000℃, the heating rate is 10~13℃ / min.

[0102] Sintering is carried out using a gradient pressure method. The initial pressure is 5 MPa. When the temperature reaches above 600℃, the sintering pressure is increased to 25 MPa. When the temperature reaches 1300℃, the sintering pressure is increased to 60 MPa.

[0103] The sintering temperature is 1450℃, and the sintering is ended after holding at that temperature for 5 minutes. After the holding period, the pressure is released to 0MPa, and the furnace is cooled to below 100℃ before being removed.

[0104] 5. Post-processing: Sampling: The sample is taken out using a hydraulic press, and sandblasting is used to remove the graphite from the sample surface.

[0105] This yields optical mold products with a surface free of white spots and chipping after precision machining. The surface has a hardness of 1700 HV30, is free of pores, and has a fracture toughness greater than 6.0 MPa·m. 1 / 2 The coefficient of thermal expansion is 7.8 × 10⁻⁶. -6 / K (600℃), density is 6.7g / cm³ 3 The coefficient of thermal expansion does not meet the requirements of the molding technology for chalcogenide glasses.

[0106] As can be seen from the above embodiments and comparative examples, the aspherical chalcogenide glass molding optical mold material prepared by the present method using a spark plasma sintering equipment has high hardness, high strength and low coefficient of thermal expansion, as well as good processing performance and excellent surface finish, and is radially uniform.

[0107] The embodiments described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention. The technical content for which protection is sought in this invention has been fully described in the claims.

Claims

1. A mold core material for molding chalcogenide glass aspherical lenses, characterized in that, The composite powder, made from niobium carbide powder, chromium carbide powder, and nickel powder, is produced by spark plasma sintering. The nickel powder has a mass content of 0 wt% to 2 wt%, with the remainder being niobium carbide powder and chromium carbide powder. The mass ratio of niobium carbide powder to chromium carbide powder is 30~35:65~70; The coefficient of thermal expansion of the mold core material at 600℃ is 8.5×10⁻⁶. -6 / K~9.5×10 -6 / K, fracture toughness is 6.0~7.0 MPa·m 1 / 2 Its hardness is 1700~1900HV30, and its density is 6.8~7.0g / cm³; The mold core material for molding chalcogenide glass aspherical lenses is prepared by the following method: (1) Mixing and drying of raw material powders: Niobium carbide powder, chromium carbide powder and nickel powder are mixed in an inert atmosphere to obtain composite powder, which is then dried, sieved and stored in an inert atmosphere; (2) Molding and pre-pressing: The composite powder is loaded into the graphite mold and pre-pressed. The pre-pressing pressure is 10~20MPa. After pre-pressing, the height of the upper and lower pressure heads is adjusted so that the height of the exposed part of the mold is consistent. (3) Insulation wrapping: Wrap two to three layers of 5mm thick carbon felt around the graphite mold for insulation; (4) Spark plasma sintering: The graphite mold treated in step (3) is placed in the spark plasma sintering system. After vacuuming, the power is turned on for gradient heating sintering. The maximum sintering temperature is 1530℃~1650℃, and the temperature is held for 3~10 minutes. The maximum sintering pressure is 40~100MPa. After sintering, the current is cut off for cooling until the mold temperature is below 100℃ before taking it out of the furnace. (5) Post-processing: Take out the sintered sample and remove the surface deposits; In step (4), the gradient heating is specifically as follows: the heating rate from room temperature to 1000℃ is 30~50℃ / min, and after the temperature is higher than 1000℃, the heating rate is adjusted to 10~15℃ / min; In step (4), sintering is carried out by gradient pressurization, specifically including: the initial pressure is 5~10MPa; when the temperature reaches above 700℃, the sintering pressure is increased to 20MPa; when the temperature reaches 1300℃, the sintering pressure is increased to 40~100MPa; after the heat preservation is completed, the sintering pressure is adjusted to 0MPa.

2. The mold core material for molding chalcogenide aspherical lenses according to claim 1, characterized in that, The nickel powder has a mass content of 0 wt% to 1.5 wt%; the purity of the nickel powder is ≥99.5%, and the particle size is ≤1 μm.

3. The mold core material for molding chalcogenide glass aspherical lenses according to claim 1, characterized in that, The coefficient of thermal expansion of the mold core material at 600℃ is 8.9 × 10⁻⁶. -6 / K~9.4×10 -6 / K.

4. The mold core material for molding chalcogenide aspherical lenses according to claim 1, characterized in that, In step (1), the particle size of the niobium carbide powder and the chromium carbide powder are both 1 to 2 micrometers, and the purity is both 99.5 wt.% to 99.9 wt.%.

5. The mold core material for molding chalcogenide aspherical lenses according to claim 1, characterized in that, In step (1), the mixing process adopts planetary ball milling, drum wet milling or tilting wet milling; the grinding balls are cemented carbide balls, the ball-to-material ratio is 3~5:1, the ball milling speed is 30~200r / min, and the ball milling time is 12~48h.

6. The mold core material for molding chalcogenide aspherical lenses according to claim 1, characterized in that, In step (1), the inert atmosphere is a nitrogen atmosphere, and the nitrogen purity is greater than 99.999%.

7. An optical mold for molding aspherical chalcogenide glass lenses, characterized in that, It is prepared from the mold core material as described in any one of claims 1 to 3.

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