Complex-phase nitride ceramic mold plate with high thermal conductivity and high strength and toughness and preparation method of complex-phase nitride ceramic mold plate

Abstract

The preparation method comprises the following steps: taking hexagonal boron nitride, aluminum nitride and beta-silicon nitride as main phases, taking 3Y-zirconium oxide and alpha-aluminum oxide as auxiliary phases, adding yttrium oxide, lithium fluoride and aluminum fluoride glass phase raw materials capable of promoting sintering densification, adding nano-scale carbon black powder, and uniformly mixing to obtain the composite nitride ceramic mold plate with high thermal conductivity and high strength and toughness. The invention relates to the technical field of ceramic mold materials, in particular to a composite nitride ceramic mold plate. According to the high-thermal-conductivity and high-strength-toughness complex-phase nitride ceramic mold plate and the preparation method thereof, high-volume-fraction flaky h-BN and AlN-Si3N4 are co-fired to form a highly-oriented nacre-like microstructure, and the h-BN lamellae are parallel to the working surface of the mold, so that a thermal-conductivity high-speed channel is constructed, and a solid lubrication effect is also provided; and the mechanical property is greatly improved through a dual toughening mechanism of introducing 3-12wt% of nano 3Y-ZrO2.

Description

Technical Field

[0001] This invention relates to the field of ceramic mold materials technology, specifically to a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, and its preparation method. Background Technology

[0002] Against the backdrop of the booming development of consumer electronics and automotive displays, 3D curved glass is a core component in these fields, and its forming relies on high-temperature hot bending molds. Currently, the mainstream mold material in the industry is high-strength graphite, which has good thermal conductivity and is easy to process, but it has drawbacks such as low strength, easy oxidation, and short service life. With the large-scale application of microcrystalline and semi-microcrystalline curved glass, the hot bending temperature has risen sharply, significantly reducing the lifespan of traditional high-strength graphite molds. Furthermore, the molds can lead to a deterioration in the surface quality of the hot-bent glass in later stages, increasing subsequent processing costs.

[0003] Traditional nitride ceramics, such as aluminum nitride and silicon nitride, have the advantages of good thermal conductivity, high hardness, strong resistance to high temperature oxidation, and non-reaction with glass. However, these ceramics have excessive hardness and insufficient thermal conductivity, and are not machinable. They require expensive diamond tools for fine grinding, resulting in extremely high processing costs.

[0004] Referring to the prior art publication number CN108726987A, a high thermal conductivity boron nitride-aluminum nitride multiphase ceramic and its preparation method are described. The ceramic uses h-BN and AlN as the main phases, adds Y2O3 as a sintering aid, and adopts a single hot pressing sintering process to prepare a thermally conductive substrate for electronic packaging. However, the existing technology has insufficient toughening mechanism and cannot withstand the mechanical load and thermal shock during the hot bending process. The h-BN orientation is not controlled, and the h-BN is randomly distributed, failing to form a high-speed thermal channel, resulting in low thermal conductivity. In addition, the application scenarios are limited, and it is only suitable for low-stress electronic packaging substrates, and is completely unsuitable for high-load hot bending molds.

[0005] Referring to the existing technology publication CN109534892B, which discloses a high-strength and tough silicon nitride-based ceramic mold material and its preparation method, β-Si3N4 is used as the main phase, with the addition of Y2O3-Al2O3 sintering aid and 3Y-ZrO2 toughening phase. Gas pressure sintering is then employed to prepare ceramics for hot bending molds. However, Si3N4 has low intrinsic thermal conductivity, and the grain boundary phase introduced by gas pressure sintering further hinders heat conduction. This low thermal conductivity leads to a large temperature gradient inside the mold, resulting in concentrated thermal stress. In practical use, this easily causes microcracks and unstable lifespan. Furthermore, the ceramic mold material has high hardness, making it difficult to process. Slow machining with diamond tools is required, resulting in a long processing cycle and high cost per mold.

[0006] In summary, the current market urgently needs a mold material that combines excellent machinability, ultra-high thermal conductivity, sufficient high-temperature strength, and long service life to break through existing technological bottlenecks. Summary of the Invention

[0007] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, as well as its preparation method. This solves the problems of short lifespan of traditional graphite molds and high processing cost of traditional hard nitride ceramic molds. The material can be used for a long time at ≥900℃, while possessing ultra-high thermal conductivity, excellent mechanical properties, and can be precisely cut and mirror polished by ordinary cemented carbide tools.

[0008] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, comprising hexagonal boron nitride, aluminum nitride, and β-silicon nitride as the main phases, 3Y-zirconium oxide and α-alumina as auxiliary phases, and the addition of yttrium oxide, lithium fluoride and aluminum fluoride glass phase raw materials that promote sintering densification, and the addition of nano-sized carbon black powder, thereby producing a multiphase nitride ceramic mold plate, wherein the weight parts of each component are as follows: The mixture contains 7-35 parts hexagonal boron nitride, 20-40 parts aluminum nitride, 10-40 parts β-silicon nitride, 3-12 parts 3Y-zirconium oxide, 1-5 parts α-alumina, 2-4 parts yttrium oxide, 0.5-1.5 parts lithium fluoride, 0.3-0.8 parts aluminum fluoride, and a small amount of carbon black powder.

[0009] Preferably, the percentage of carbon black powder in the total raw materials of the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate is calculated based on the weight percentage of hexagonal boron nitride added and the oxygen content of the raw materials. The specific calculation formula is as follows: Hexagonal boron nitride weight percentage × raw material oxygen content × K; Where K is the carbon black weight coefficient required to remove oxygen (taken as 0.75). Although aluminum nitride and silicon nitride require the participation of surface oxides in the formation of the glass phase to promote shrinkage and densification, carbon black is generally not considered for removing oxygen. However, if the oxygen content of these two nitrides exceeds the standard, the amount of carbon black added should be calculated according to this formula to remove excess oxygen. Generally speaking, the oxygen content of aluminum nitride and silicon nitride should be less than 1%, and excess oxygen should be removed with carbon black.

[0010] Preferably, the hexagonal boron nitride is highly oriented and parallel to the working surface of the mold during the casting and hot pressing sintering process, forming a high-speed thermal conduction channel and a solid lubrication layer.

[0011] Preferably, the 3Y-zirconium oxide undergoes monoclinic and tetragonal phase transformations during sintering to achieve stress-induced toughening, while simultaneously reacting in situ with aluminum nitride and α-alumina to generate nano-zirconium nitride and spinel-type aluminum oxynitride, pinning grain boundaries to enhance strength and toughness (during sintering, some 3Y-ZrO2 reacts in situ with AlN to generate nano-ZrN, and some AlN reacts with Al2O3 in liquid phase to generate spinel-type AlON).

[0012] This invention also provides a method for preparing a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, specifically including the following steps: S1. Batching and pulverizing process: The required weight parts of hexagonal boron nitride, aluminum nitride, β-silicon nitride, 3Y-zirconium oxide, α-alumina, yttrium oxide, lithium fluoride and aluminum fluoride are measured separately by batching equipment and then pulverized in sequence by pulverizing equipment to obtain powder. S2. Ball milling and mixing: The raw material powders obtained in step S1 are mixed with anhydrous ethanol, and then ball milled for 48 hours using a planetary ball mill. The mixture is then passed through a 400-mesh sieve to obtain a mixed slurry. S3. Adding and drying of molding agent: Add molding agent to the mixed slurry in step S2, stir evenly, and then dry to remove solvent to obtain powder containing molding agent. S4. Compression molding: Place the powder containing the molding agent obtained in step S3 into a mold, hold it under pressure of 30 MPa for 5 minutes, and compress it into a blank. S5. Wax and glue removal: Place the blank pressed in step S4 in a vacuum environment, heat it to 300℃ at 0.5℃ / min, then heat it to 350℃ at a slow heating rate and keep it at that temperature for 4-10 hours to complete wax removal. Continue to heat it to 500℃ at 0.5℃ / min, then slowly heat it to 600℃ and keep it at that temperature for 4 hours to complete glue removal. S6. Composite hot pressing sintering: includes three stages: vacuum low-pressure sintering, high-temperature hot pressing sintering and low-temperature hot pressing sintering. S7. Finishing: Using ordinary carbide tools, the sintered blank is CNC machined and mirror polished at a cutting speed of 60-80m / min to obtain a multiphase nitride ceramic mold plate with a surface roughness Ra≤0.2μm.

[0013] Preferably, the molding agent in step S3 is one or more of rubber, paraffin wax, or polyethylene glycol.

[0014] Preferably, during the wax and adhesive removal process in step S5, the heating rate from 300°C to 350°C and from 500°C to 600°C is controlled at 0.1 to 0.2°C / min.

[0015] Preferably, the composite hot pressing sintering in step S6 specifically includes the following steps: T1. Vacuum low-pressure sintering: After dewaxing and debinding, multiple blanks are stacked and placed together in the hot press mold of the hot press furnace, separated by a 2-10mm thick graphite plate. Sintering is carried out under nitrogen atmosphere at 1600-1650℃ and axial pressure of 5MPa for 1.5 hours to promote phase transformation and densification and remove gas. T2. High-temperature hot pressing sintering: Maintain the temperature at 1700-1800℃, increase the axial pressure to 30-40MPa, and hold for 1.5-2 hours to make the hexagonal boron nitride highly oriented and compress the pores. T3. Low-temperature hot pressing sintering: The temperature is reduced to 1600-1650℃, the pressure is maintained at 30-40MPa, and the pressure is held for 30 minutes to refine the pores, eliminate secondary porosity caused by volume shrinkage during cooling, and improve density.

[0016] Preferably, in step T1, when multiple billets are stacked and loaded into the furnace, a graphite plate is used to separate each pair of billets, and the surface of the graphite plate is coated with boron nitride slurry and covered with graphite paper.

[0017] Preferably, the graphite plate is a porous graphite plate with a large number of through holes with a diameter of 1-1.5 mm distributed on it, 1-4 holes per square centimeter. All partitions in contact with the powder are required, but partitions between powders are not required.

[0018] Preferably, the hot bending mold for 3D curved glass processed by CNC in step S7 can be used for a long time at a temperature below 800°C. After 10,000 continuous hot bending of 3D glass, the dimensional change is <7μm and there is no glass sticking to the surface.

[0019] Hexagonal boron nitride provides solid lubrication, ease of machining, and the formation of highly thermally conductive channels. Aluminum nitride, as the framework phase, exhibits excellent thermal conductivity. β-Silicon nitride provides a high-strength, high-toughness fibrous interlocking structure. 3Y-zirconia is used for phase transformation toughening and in-situ reaction to generate AlON / ZrN. α-Alumina promotes liquid-phase sintering and controls grain boundary phases. Yttrium oxide serves as the primary sintering aid. Lithium fluoride acts as a low-temperature volatilization aid, promoting densification. Aluminum fluoride assists in deoxygenation, promoting direct contact between AlN particles. Carbon black removes excess oxygen, significantly improving the material's thermal conductivity.

[0020] (III) Beneficial Effects This invention provides a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, and its preparation method. Compared with the prior art, it has the following advantages: (1) The high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate and its preparation method are achieved by co-firing high volume fraction flake h-BN with AlN-Si3N4 to form a highly oriented nacre-like microstructure. The h-BN flakes are parallel to the working surface of the mold, which not only constructs a high-speed thermal conductivity channel, but also provides solid lubrication, making the material machinability close to that of graphite, while its temperature resistance is better than that of graphite. The mechanical properties are greatly improved by introducing a dual toughening mechanism of 3-12 wt% nano 3Y-ZrO2. Stress-induced toughening is achieved by monoclinic tetragonal phase transformation during sintering. At the same time, ZrO2 reacts in situ with AlN and Al2O3 to generate nano ZrN and AlON second phase, which pins the grain boundaries and achieves simultaneous improvement of strength and toughness.

[0021] (2) The high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate and its preparation method, by using the Y2O3-LiF-AlF3 low-temperature liquid phase sintering aid system to reduce the sintering temperature to 1700-1800℃, which is lower than that of traditional silicon nitride ceramics, avoids severe decomposition of h-BN at high temperature; at the same time, the volatilization of LiF removes the surface oxide layer, promoting direct contact of AlN particles to form a high thermal conductivity skeleton. By adopting a composite process of vacuum low-pressure sintering, high-temperature hot-pressing sintering and low-temperature hot-pressing sintering, high densification is achieved, ensuring the structural stability and thermal conductivity of the material.

[0022] (3) The high thermal conductivity and high strength and toughness of the multiphase nitride ceramic mold plate and its preparation method achieve the characteristics of precision cutting and mirror polishing in nitride ceramics. It can be precisely cut and processed, which greatly reduces the cost. It can be processed to Ra≤0.2μm using ordinary cemented carbide tools, which solves the pain point of traditional cemented ceramic molds relying on diamond tools for fine grinding. At the same time, it has an ultra-long service life, improves production efficiency, and has no glass adhesion phenomenon on the surface. Its service life is greatly improved compared with traditional graphite molds, which greatly reduces the mold replacement frequency and production cost. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the nacreous layer-like microstructure of the multiphase nitride ceramic mold plate of the present invention; Figure 2 This is a flowchart of the multiphase nitride ceramic mold plate and its preparation method according to the present invention; Figure 3 This is a comparison diagram of the porosity of the multiphase nitride ceramic mold plate of the present invention and the traditional high-strength graphite mold in the comparative experiment of the present invention; Figure 4 This is a comparison diagram of the room temperature thermal conductivity of the multiphase nitride ceramic mold plate of the present invention and the traditional high-strength graphite mold in the comparative experiment of the present invention. Figure 5This is a comparison diagram of the bending strength of the multiphase nitride ceramic mold plate of the present invention and the traditional high-strength graphite mold in the comparative experiment of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see Figures 1 to 5 The present invention provides three technical solutions: a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness and its preparation method, specifically including the following embodiments: Example 1: A multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, characterized in that: it is made of hexagonal boron nitride, aluminum nitride, and β-silicon nitride as the main phases, 3γ-zirconium oxide and α-alumina as auxiliary phases, and yttrium oxide, lithium fluoride and aluminum fluoride glass phase raw materials that can promote sintering densification are added, and nano-sized carbon black powder is added to form a multiphase nitride ceramic mold plate, wherein the weight parts of each component are as follows: The mixture consists of 15 parts hexagonal boron nitride, 50 parts aluminum nitride, 25 parts β-silicon nitride, 5 parts 3Y-zirconium oxide, 2 parts α-alumina, 2 parts yttrium oxide, 0.5 parts lithium fluoride, 0.5 parts aluminum fluoride, and carbon black powder added according to the weight percentage of hexagonal boron nitride and the oxygen content of the raw materials.

[0026] In this embodiment of the invention, the percentage of carbon black powder in the total raw materials of the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate is calculated based on the weight percentage of added hexagonal boron nitride and the oxygen content of the raw materials. The specific calculation formula is as follows: Hexagonal boron nitride weight percentage × raw material oxygen content × K; Where K is the weight coefficient of carbon black required to remove oxygen, and its value is 0.75.

[0027] In this embodiment of the invention, the multiphase nitride ceramic mold plate has a thermal conductivity of 78.5 W / m·K, a porosity of 0.2%, a flexural strength of 625 MPa, and a fracture toughness of 6.5 MPa·m. 1 / 2 The surface roughness Ra of the machined material is 0.08 μm. After the raw material is prepared by composite molding process, the bulk density of the mold plate is 3.12 g / cm³. 3 The thermogravimetric loss at 800℃ for 1000 hours is 0.09%. Carbon black removes excess oxygen, greatly improving the thermal conductivity of the material.

[0028] In this embodiment of the invention, hexagonal boron nitride is highly oriented and parallel to the working surface of the mold during the tape casting and hot pressing sintering process, forming a high-speed thermal conduction channel and a solid lubrication layer.

[0029] In this embodiment of the invention, 3Y-zirconia undergoes monoclinic and tetragonal phase transformations during sintering to achieve stress-induced toughening. At the same time, it reacts in situ with aluminum nitride and α-alumina to generate nano-zirconia and spinel-type aluminum oxynitride, which pin grain boundaries to improve strength and toughness.

[0030] This invention also provides a method for preparing a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, specifically including the following steps: S1. Batching and pulverizing process: The required weight parts of hexagonal boron nitride, aluminum nitride, β-silicon nitride, 3Y-zirconium oxide, α-alumina, yttrium oxide, lithium fluoride and aluminum fluoride are measured separately by batching equipment and then pulverized in sequence by pulverizing equipment to obtain powder. S2. Ball milling and mixing: The raw material powders obtained in step S1 are mixed with anhydrous ethanol, and then ball milled for 48 hours using a planetary ball mill. The mixture is then passed through a 400-mesh sieve to obtain a mixed slurry. S3. Adding and drying of molding agent: Add molding agent to the mixed slurry in step S2, stir evenly, and then dry to remove solvent to obtain powder containing molding agent. S4. Compression molding: Place the powder containing the molding agent obtained in step S3 into a mold, hold it under pressure of 30 MPa for 5 minutes, and compress it into a blank. S5. Wax and glue removal: Place the blank pressed in step S4 in a vacuum environment, heat it to 300℃ at 0.5℃ / min, then heat it to 350℃ at a slow heating rate and keep it at that temperature for 7 hours to complete wax removal. Continue to heat it to 500℃ at 0.5℃ / min, then slowly heat it to 600℃ and keep it at that temperature for 4 hours to complete glue removal. S6. Composite hot pressing sintering: includes three stages: vacuum low-pressure sintering, high-temperature hot pressing sintering and low-temperature hot pressing sintering. S7. Finishing: Using ordinary carbide tools, the sintered blank is CNC machined and mirror polished at a cutting speed of 70m / min to obtain a multiphase nitride ceramic mold plate with a surface roughness Ra≤0.2μm.

[0031] In this embodiment of the invention, the molding agent in step S3 is rubber, paraffin wax, and polyethylene glycol.

[0032] In this embodiment of the invention, during the wax and adhesive removal process in step S5, the heating rate from 300°C to 350°C and from 500°C to 600°C is controlled at 0.15°C / min.

[0033] In this embodiment of the invention, step S6, composite hot pressing sintering, specifically includes the following steps: T1. Vacuum low-pressure sintering: After dewaxing and debinding, multiple blanks are stacked and placed together in the hot pressing mold of the hot press furnace, separated by a 6mm thick graphite plate. Under nitrogen atmosphere, sintering is carried out at 1650℃ and axial pressure of 5MPa for 1.5 hours to promote phase transformation and densification and remove gas. T2. High-temperature hot pressing sintering: Maintain the temperature at 1740℃, increase the axial pressure to 35MPa, and hold for 1.5h to make the hexagonal boron nitride highly oriented and compress the pores. T3. Low-temperature hot pressing sintering: The temperature is reduced to 1600℃, the pressure is maintained at 35MPa, and the pressure is held for 30min to refine the pores, eliminate secondary porosity caused by volume shrinkage during cooling, and improve density.

[0034] In this embodiment of the invention, when multiple billets are stacked and loaded into the furnace in step T1, graphite plates are used to separate each pair of billets. The surface of the graphite plates is coated with boron nitride slurry and then covered with graphite paper. This invention also considers the issue that during the densification hot-pressing sintering process, the internal gas of the product is obstructed from escaping onto the surface. Therefore, the partitions between the hot-pressing mold and the powder are all made of porous graphite plates with numerous through holes of 1.25 mm in diameter, three holes per square centimeter. All partitions in contact with the powder are required, but partitions between individual powder particles are not necessary.

[0035] In this embodiment of the invention, in step S7, a hot bending mold for 3D curved glass is manufactured by CNC. After long-term use at temperatures below 800°C and continuous hot bending of 3D glass for 12,500 times, the dimensional change is 10 μm, and there is no glass sticking to the surface.

[0036] Example 2: A multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, characterized in that: it is made of hexagonal boron nitride, aluminum nitride, and β-silicon nitride as the main phases, 3γ-zirconium oxide and α-alumina as auxiliary phases, and yttrium oxide, lithium fluoride and aluminum fluoride glass phase raw materials that can promote sintering densification are added, and nano-sized carbon black powder is added to form a multiphase nitride ceramic mold plate, wherein the weight parts of each component are as follows: The mixture consists of 15 parts hexagonal boron nitride, 40 parts aluminum nitride, 35 parts β-silicon nitride, 5 parts 3Y-zirconium oxide, 2 parts α-alumina, 2 parts yttrium oxide, 0.6 parts lithium fluoride, 0.4 parts aluminum fluoride, and carbon black powder added according to the weight percentage of hexagonal boron nitride and the oxygen content of the raw materials.

[0037] In this embodiment of the invention, the percentage of carbon black powder in the total raw materials of the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate is calculated based on the weight percentage of added hexagonal boron nitride and the oxygen content of the raw materials. The specific calculation formula is as follows: Hexagonal boron nitride weight percentage × raw material oxygen content × K; Where K is the weight coefficient of carbon black required to remove oxygen, and its value is 0.75.

[0038] In this embodiment of the invention, the multiphase nitride ceramic mold plate has a thermal conductivity of 71.2 W / m·K, a porosity of 0.3%, a flexural strength of 633 MPa, and a fracture toughness of 7.1 MPa·m. 1 / 2 The surface roughness Ra of the machined material is 0.11 μm. After the raw material is prepared by composite molding process, the bulk density of the mold plate is 3.10 g / cm³. 3 The thermogravimetric loss at 800℃ for 1000 hours is 0.12%. Carbon black removes excess oxygen, greatly improving the thermal conductivity of the material.

[0039] In this embodiment of the invention, hexagonal boron nitride is highly oriented and parallel to the working surface of the mold during the tape casting and hot pressing sintering process, forming a high-speed thermal conduction channel and a solid lubrication layer.

[0040] In this embodiment of the invention, 3Y-zirconia undergoes monoclinic and tetragonal phase transformations during sintering to achieve stress-induced toughening. At the same time, it reacts in situ with aluminum nitride and α-alumina to generate nano-zirconia and spinel-type aluminum oxynitride, which pin grain boundaries to improve strength and toughness.

[0041] This invention also provides a method for preparing a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, specifically including the following steps: S1. Batching and pulverizing process: The required weight parts of hexagonal boron nitride, aluminum nitride, β-silicon nitride, 3Y-zirconium oxide, α-alumina, yttrium oxide, lithium fluoride and aluminum fluoride are measured separately by batching equipment and then pulverized in sequence by pulverizing equipment to obtain powder. S2. Ball milling and mixing: The raw material powders obtained in step S1 are mixed with anhydrous ethanol, and then ball milled for 48 hours using a planetary ball mill. The mixture is then passed through a 400-mesh sieve to obtain a mixed slurry. S3. Adding and drying of molding agent: Add molding agent to the mixed slurry in step S2, stir evenly, and then dry to remove solvent to obtain powder containing molding agent. S4. Compression molding: Place the powder containing the molding agent obtained in step S3 into a mold, hold it under pressure of 30 MPa for 5 minutes, and compress it into a blank. S5. Wax and glue removal: Place the blank pressed in step S4 in a vacuum environment, heat it to 300°C at 0.5°C / min, then heat it to 350°C at a slow heating rate and keep it at that temperature for 4 hours to complete wax removal. Continue to heat it to 500°C at 0.5°C / min, then slowly heat it to 600°C and keep it at that temperature for 4 hours to complete glue removal. S6. Composite hot pressing sintering: includes three stages: vacuum low-pressure sintering, high-temperature hot pressing sintering and low-temperature hot pressing sintering. S7. Finishing: Using ordinary carbide tools, the sintered blank is CNC machined and mirror polished at a cutting speed of 60m / min to obtain a multiphase nitride ceramic mold plate with a surface roughness Ra≤0.2μm.

[0042] In this embodiment of the invention, the molding agent in step S3 is rubber and polyethylene glycol.

[0043] In this embodiment of the invention, during the wax and adhesive removal process in step S5, the heating rate from 300°C to 350°C and from 500°C to 600°C is controlled at 0.1°C / min.

[0044] In this embodiment of the invention, step S6, composite hot pressing sintering, specifically includes the following steps: T1. Vacuum low-pressure sintering: After dewaxing and debinding, multiple blanks are stacked and placed together in the hot press mold of the hot press furnace, separated by a 2mm thick graphite plate. Under nitrogen atmosphere, sintering is carried out at 1700℃ and axial pressure of 5MPa for 1.5 hours to promote phase transformation and densification and remove gas. T2. High-temperature hot pressing sintering: Maintain the temperature at 1700℃, increase the axial pressure to 30MPa, and hold for 2 hours to make the hexagonal boron nitride highly oriented and compress the pores. T3. Low-temperature hot pressing sintering: The temperature is reduced to 1650℃, the pressure is maintained at 30MPa, and the pressure is held for 30min to refine the pores, eliminate secondary pores caused by volume shrinkage during cooling, and improve density.

[0045] In this embodiment of the invention, when multiple billets are stacked and loaded into the furnace in step T1, graphite plates are used to separate each pair of billets. The surface of the graphite plates is coated with boron nitride slurry and then covered with graphite paper. This invention also considers the issue that during the densification hot-pressing sintering process, the internal gas of the product is obstructed from escaping onto the surface. Therefore, the partitions between the hot-pressing mold and the powder are all made of porous graphite plates with numerous 1mm diameter through holes distributed on the graphite plates, four holes per square centimeter. All partitions in contact with the powder are required, but partitions between powder particles are not necessary.

[0046] In this embodiment of the invention, in step S7, a hot bending mold for 3D curved glass is manufactured by CNC. After long-term use at temperatures below 800°C and continuous hot bending of 3D glass for 10,000 times, the dimensional change is 7μm, and there is no glass sticking to the surface.

[0047] Example 3: A multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, characterized in that: it is made of hexagonal boron nitride, aluminum nitride, and β-silicon nitride as the main phases, 3γ-zirconium oxide and α-alumina as auxiliary phases, and yttrium oxide, lithium fluoride and aluminum fluoride glass phase raw materials that can promote sintering densification are added, and nano-sized carbon black powder is added to form a multiphase nitride ceramic mold plate, wherein the weight parts of each component are as follows: The mixture consists of 15 parts hexagonal boron nitride, 35 parts aluminum nitride, 40 parts β-silicon nitride, 5 parts 3Y-zirconium oxide, 1.5 parts α-alumina, 2.5 parts yttrium oxide, 0.5 parts lithium fluoride, 0.5 parts aluminum fluoride, and carbon black powder added according to the weight percentage of hexagonal boron nitride and the oxygen content of the raw materials.

[0048] In this embodiment of the invention, the percentage of carbon black powder in the total raw materials of the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate is calculated based on the weight percentage of added hexagonal boron nitride and the oxygen content of the raw materials. The specific calculation formula is as follows: Hexagonal boron nitride weight percentage × raw material oxygen content × K; Where K is the weight coefficient of carbon black required to remove oxygen, and its value is 0.75.

[0049] In this embodiment of the invention, the multiphase nitride ceramic mold plate has a thermal conductivity of 70.6 W / m·K, a porosity of 0.3%, a flexural strength of 671 MPa, and a fracture toughness of 7.6 MPa·m. 1 / 2 The surface roughness Ra of the machined material is 0.09 μm. After the raw material is prepared by composite molding process, the bulk density of the mold plate is 3.09 g / cm³. 3 The thermogravimetric loss at 800℃ for 1000 hours is 0.13%. Carbon black removes excess oxygen, greatly improving the thermal conductivity of the material.

[0050] In this embodiment of the invention, hexagonal boron nitride is highly oriented and parallel to the working surface of the mold during the tape casting and hot pressing sintering process, forming a high-speed thermal conduction channel and a solid lubrication layer.

[0051] In this embodiment of the invention, 3Y-zirconia undergoes monoclinic and tetragonal phase transformations during sintering to achieve stress-induced toughening. At the same time, it reacts in situ with aluminum nitride and α-alumina to generate nano-zirconia and spinel-type aluminum oxynitride, which pin grain boundaries to improve strength and toughness.

[0052] This invention also provides a method for preparing a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, specifically including the following steps: S1. Batching and pulverizing process: The required weight parts of hexagonal boron nitride, aluminum nitride, β-silicon nitride, 3Y-zirconium oxide, α-alumina, yttrium oxide, lithium fluoride and aluminum fluoride are measured separately by batching equipment and then pulverized in sequence by pulverizing equipment to obtain powder. S2. Ball milling and mixing: The raw material powders obtained in step S1 are mixed with anhydrous ethanol, and then ball milled for 48 hours using a planetary ball mill. The mixture is then passed through a 400-mesh sieve to obtain a mixed slurry. S3. Adding and drying of molding agent: Add molding agent to the mixed slurry in step S2, stir evenly, and then dry to remove solvent to obtain powder containing molding agent. S4. Compression molding: Place the powder containing the molding agent obtained in step S3 into a mold, hold it under pressure of 30 MPa for 5 minutes, and compress it into a blank. S5. Wax and glue removal: Place the blank pressed in step S4 in a vacuum environment, heat it to 300°C at 0.5°C / min, then heat it to 350°C at a slow heating rate and keep it at that temperature for 10 hours to complete wax removal. Continue to heat it to 500°C at 0.5°C / min, then slowly heat it to 600°C and keep it at that temperature for 4 hours to complete glue removal. S6. Composite hot pressing sintering: includes three stages: vacuum low-pressure sintering, high-temperature hot pressing sintering and low-temperature hot pressing sintering. S7. Finishing: Using ordinary carbide tools, the sintered blank is CNC machined and mirror polished at a cutting speed of 80m / min to obtain a multiphase nitride ceramic mold plate with a surface roughness Ra≤0.2μm.

[0053] In this embodiment of the invention, the molding agent in step S3 is rubber.

[0054] In this embodiment of the invention, during the wax and adhesive removal process in step S5, the heating rate from 300°C to 350°C and from 500°C to 600°C is controlled at 0.2°C / min.

[0055] In this embodiment of the invention, step S6, composite hot pressing sintering, specifically includes the following steps: T1. Vacuum low-pressure sintering: After dewaxing and debinding, multiple blanks are stacked and placed together in the hot press mold of the hot press furnace, separated by a 10mm thick graphite plate. Under nitrogen atmosphere, sintering is carried out at 1750℃ and axial pressure of 5MPa for 1.5 hours to promote phase transformation and densification and remove gas. T2. High-temperature hot pressing sintering: Maintain the temperature at 1780℃, increase the axial pressure to 40MPa, and hold for 1.5h to make the hexagonal boron nitride highly oriented and compress the pores. T3. Low-temperature hot pressing sintering: The temperature is reduced to 1650℃, the pressure is maintained at 40MPa, and the pressure is held for 30min to refine the pores, eliminate secondary porosity caused by volume shrinkage during cooling, and improve density.

[0056] In this embodiment of the invention, when multiple billets are stacked and loaded into the furnace in step T1, graphite plates are used to separate each pair of billets. The surface of the graphite plates is coated with boron nitride slurry and then covered with graphite paper. This invention also considers the issue that during the densification hot-pressing sintering process, internal gas escape from the product is obstructed on the surface. The partitions between the hot-pressing mold and the powder are all made of porous graphite plates with numerous 1.5mm diameter through holes distributed on the graphite plates, one hole per square centimeter. All partitions in contact with the powder are required, but partitions between powder particles are not necessary.

[0057] In this embodiment of the invention, in step S7, a hot bending mold for 3D curved glass is manufactured by CNC. After long-term use at temperatures below 800°C and continuous hot bending of 3D glass for 11,600 times, the dimensional change is 9 μm, and there is no glass sticking to the surface.

[0058] Depend on Figure 1 It can be seen that the highly oriented h-BN sheets are parallel to the working surface, forming a nacre-like structure, while AlN and β-Si3N4 are uniformly distributed.

[0059] Comparative Experiment: A traditional high-strength graphite mold with the same dimensions as the examples was selected as a comparative example. The bulk density, porosity, room temperature thermal conductivity, flexural strength, fracture toughness, Vickers hardness, surface roughness, and thermogravimetric loss at 800℃ for 1000 hours were tested on the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the traditional high-strength graphite mold of the comparative example, respectively. The details are as follows: Bulk density and porosity tests: Five cuboid samples with dimensions of 10.0±0.1mm×10.0±0.1mm×50.0±0.5mm were prepared for each of the four test objects: the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example. The working surfaces were precision ground with diamond wheels (Ra≤0.8 μm). The specific test steps are as follows: 1. Dry at 110±5℃ to constant weight (weigh twice consecutively at 2-hour intervals with a difference of <0.05%), to obtain dry weight W. d ; 2. Vacuum impregnation (vacuum degree ≤ 5 Pa) for 24 hours. After saturation and water absorption, remove the product and quickly wipe the surface dry with a damp cloth to obtain the saturated surface dry weight W. w ; 3. The sample is suspended in distilled water and weighed (water temperature 23±1℃), obtaining the weight W in the water. s ; 4. Then, according to the bulk density ρ=W d The formula for calculating the volume density ρ and porosity is 1-(measured density / theoretical density)×100% (theoretical density is calculated according to the mixing rule). Outliers are removed from 5 parallel samples of each test object and the arithmetic mean is taken. The standard deviation is marked. The specific test results are shown in Table 1.

[0060] Room temperature thermal conductivity test: Each of the four test objects, namely the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example, was made into a circular piece with a diameter of 12.7±0.1 mm and a thickness of 2.5±0.1 mm. Both sides were polished to a mirror finish (Ra≤0.1μm), and a high-purity graphite coating (thickness≈10μm) was sprayed on. The room temperature thermal conductivity was tested using a laser flash thermal conductivity meter equipped with an InSb infrared detector under argon protection (purity ≥99.999%), room temperature 25.0±0.5℃, laser energy 15J, pulse width 0.45ms. Each sample was tested 5 times. The specific test results are shown in Table 1.

[0061] Bending strength test: Each of the four test objects, namely the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example, was made into a sample with a size of 3.0±0.1mm×4.0±0.1mm×45.0±0.5mm and Ra≤0.2μm. Then, the bending strength was tested using an Instron 5985 universal testing machine and a three-point bending fixture (span 30.0±0.1 mm). The specific test results are shown in Table 1.

[0062] Fracture toughness test: For each of the four test objects, namely the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example, a sample with a pre-cut depth of a=1.25±0.05mm×5.0±0.1mm×25.0±0.2mm and a pre-cut kerf depth of a=1.25±0.05mm (diamond wire cutting, kerf width ≤0.12 mm) was prepared. Then, the fracture toughness test was carried out using the same bending strength test equipment equipped with a high-precision displacement sensor (resolution 0.1μm). The specific test results are shown in Table 1.

[0063] Vickers hardness test: Each of the four test objects, namely the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example, was made into a 15mm×15mm×15mm block polished to a mirror finish (Ra≤0.05μm). Then, the Vickers hardness test was performed using a Wilson VH3300 microhardness tester and a diamond square pyramid indenter (with an included angle of 136° between the two opposite faces). The specific test results are shown in Table 1.

[0064] Surface roughness test: Each of the four test objects, namely the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example, was made into a sample. The surface roughness was tested using a Taylor Hobson Surtronic S-100 roughness tester. The specific test results are shown in Table 1.

[0065] Experimental test of thermogravimetric loss at 800℃ for 1000h: For each of the four test objects—the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the conventional high-strength graphite mold in the comparative example—samples measuring 10.0±0.1mm × 10.0±0.1mm × 2.0±0.1mm were prepared. The samples were first ultrasonically cleaned (acetone → anhydrous ethanol → deionized water), then dried at 110℃ for 2h. The experiments were then conducted using a high-temperature muffle furnace (Carbolite Gero HTRH 16 / 18, temperature control accuracy ±1℃) and a high-precision balance (0.01 mg). The specific experimental steps are as follows: 1. Weigh the initial mass m0 (accuracy 0.01 mg); 2. Place in the constant temperature zone of the furnace, in an air atmosphere, and raise the temperature to 800±2℃ at a rate of 5℃ / min; 3. Maintain constant temperature for 1000 hours (during which the furnace door is briefly opened for <30 seconds every 200 hours for observation); 4. Cool the furnace to room temperature and weigh the final mass m1. The mass loss rate is calculated as [(m0-m1) / m0]×100%. The specific test results are shown in Table 1.

[0066] Table 1 Performance Indicators of Multiphase Nitride Ceramics As shown in Table 1, the multiphase nitride ceramic mold plates prepared using the methods of Examples 1-3 of this invention exhibit superior bulk density, porosity, flexural strength, fracture toughness, Vickers hardness, surface roughness, and thermogravimetric loss at 800℃ for 1000h compared to the conventional high-strength graphite molds. Their thermal conductivity is also comparable to that of high-strength graphite. Furthermore, the performance indicators of the multiphase nitride ceramics of Example 1 are superior to those of Example 2. While the thermal conductivity increases significantly with increasing AlN content at a given boron nitride content, the mechanical properties, particularly fracture toughness, are insufficient.

[0067] The mold life was tested: Four test objects—the multiphase nitride ceramic mold plates prepared in Examples 1-3 and the comparative traditional high-strength graphite mold—were used to simulate a 3D curved glass hot bending forming device. The multiphase nitride ceramic mold plates prepared in Examples 1-3 and the comparative traditional high-strength graphite mold were heated to 800℃ and continuously hot-bent 3D glass. A high-precision displacement sensor was used to measure the mold dimensional changes, and the presence of glass sticking to the mold surface was observed. The number of consecutive hot bending cycles, mold dimensional changes, and surface quality were tested. Specific test data are shown in Table 2.

[0068] Table 2 Comparison of lifespan between multiphase nitride ceramic molds and traditional graphite molds As shown in Table 2, the multiphase nitride ceramic mold plate prepared by the preparation method of Example 2 of the present invention exhibits a dimensional change of only 7 μm after 10,000 continuous hot bending at 800℃, with no glass adhesion on the surface. In contrast, the conventional high-strength graphite mold of the comparative example exhibits a dimensional change of >15 μm after 2,500 continuous hot bending of 3D glass at 800℃, rendering it unusable. Therefore, the service life of the multiphase nitride ceramic mold plate prepared by the preparation methods of Examples 1-3 of the present invention is significantly better than that of the conventional high-strength graphite mold of the comparative example. Furthermore, the multiphase nitride ceramic mold plate prepared by Example 1 of the present invention has a service life of up to 12,500 cycles with a dimensional change of only 10 μm. Therefore, Example 1 is the optimal solution.

[0069] In summary, this invention co-fires high-volume-fraction flake-like h-BN with AlN-Si3N4 to form a highly oriented nacre-like microstructure. The h-BN flakes are parallel to the working surface of the mold, creating both high-speed thermal conductivity channels and providing solid lubrication. This makes the material's machinability approach that of graphite, while its temperature resistance is superior to graphite. Furthermore, by introducing 3-12... The dual toughening mechanism of wt% nano-3Y-ZrO2 significantly improves mechanical properties. During sintering, a monoclinic tetragonal phase transformation occurs, achieving stress-induced toughening. Simultaneously, ZrO2 reacts in situ with AlN and Al2O3 to generate nano-ZrN and AlON second phases, pinning grain boundaries and achieving simultaneous improvement in strength and toughness. By lowering the sintering temperature using a Y2O3-LiF-AlF3 low-temperature liquid phase sintering aid system, the sintering temperature is reduced to 1700-1800℃, which is lower than that of traditional silicon nitride ceramics, avoiding severe decomposition of h-BN at high temperatures. At the same time, the volatilization of LiF removes the surface oxide layer, promoting direct contact between AlN particles to form a high thermal conductivity framework. By employing a composite process of vacuum low-pressure sintering, high-temperature hot-pressing sintering, and low-temperature hot-pressing sintering, high densification is achieved, ensuring the structural stability and thermal conductivity of the material. This enables precision machining and mirror polishing in nitride ceramics. Precision machining significantly reduces costs, allowing for machining to Ra≤0.2μm using ordinary carbide tools. This solves the problem of traditional hard ceramic molds relying on diamond tools for precision grinding. It also features an ultra-long service life, improving production efficiency, and eliminating glass adhesion to the surface. The lifespan is significantly longer than that of traditional graphite molds, greatly reducing mold replacement frequency and production costs.

[0070] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness, characterized in that: A multiphase nitride ceramic mold plate is prepared by adding hexagonal boron nitride, aluminum nitride, and β-silicon nitride as the main phases, 3Y-zirconium oxide and α-alumina as auxiliary phases, and yttrium oxide, lithium fluoride, and aluminum fluoride glass phase raw materials to promote sintering densification, along with nano-sized carbon black powder. The weight parts of each component are as follows: The mixture contains 7-35 parts hexagonal boron nitride, 20-40 parts aluminum nitride, 10-40 parts β-silicon nitride, 3-12 parts 3Y-zirconium oxide, 1-5 parts α-alumina, 2-4 parts yttrium oxide, 0.5-1.5 parts lithium fluoride, 0.3-0.8 parts aluminum fluoride, and a small amount of carbon black powder.

2. The high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 1, characterized in that: The percentage of carbon black powder in the total raw materials of the high thermal conductivity and high strength multiphase nitride ceramic mold plate is calculated based on the weight percentage of hexagonal boron nitride added and the oxygen content of the raw materials. The specific calculation formula is as follows: Hexagonal boron nitride weight percentage × raw material oxygen content × K; Where K is the weight coefficient of carbon black required to remove oxygen, and its value is 0.

75.

3. The high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 1, characterized in that: The hexagonal boron nitride is highly oriented during the tape casting and hot pressing sintering process, parallel to the working surface of the mold, forming a high-speed thermal conduction channel and a solid lubrication layer.

4. The high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 1, characterized in that: During sintering, the 3Y-zirconia undergoes monoclinic and tetragonal phase transformations to achieve stress-induced toughening. Simultaneously, it reacts in situ with aluminum nitride and α-alumina to generate nano-zirconia and spinel-type aluminum oxynitride, which pin grain boundaries and enhance strength and toughness.

5. A method for preparing a multiphase nitride ceramic mold plate with high thermal conductivity and high strength and toughness according to any one of claims 1-4, characterized in that: Specifically, the following steps are included: S1. Batching and pulverizing process: The required weight parts of hexagonal boron nitride, aluminum nitride, β-silicon nitride, 3Y-zirconium oxide, α-alumina, yttrium oxide, lithium fluoride, aluminum fluoride, and carbon black powder are measured separately by batching equipment and then pulverized sequentially by pulverizing equipment to obtain powder. S2. Ball milling and mixing: The raw material powders obtained in step S1 are mixed with anhydrous ethanol, and then ball milled for 48 hours using a planetary ball mill. The mixture is then passed through a 400-mesh sieve to obtain a mixed slurry. S3. Adding and drying of molding agent: Add molding agent to the mixed slurry in step S2, stir evenly, and then dry to remove solvent to obtain powder containing molding agent. S4. Compression molding: Place the powder containing the molding agent obtained in step S3 into a mold, hold it under pressure of 30 MPa for 5 minutes, and compress it into a blank. S5. Wax and glue removal: Place the blank pressed in step S4 in a vacuum environment, heat it to 300℃ at 0.5℃ / min, then heat it to 350℃ at a slow heating rate and keep it at that temperature for 4-10 hours to complete wax removal. Continue to heat it to 500℃ at 0.5℃ / min, then slowly heat it to 600℃ and keep it at that temperature for 4 hours to complete glue removal. S6. Composite hot pressing sintering: includes three stages: vacuum low-pressure sintering, high-temperature hot pressing sintering and low-temperature hot pressing sintering. S7. Finishing: Using ordinary carbide tools, the sintered blank is CNC machined and mirror polished at a cutting speed of 60-80m / min to obtain a multiphase nitride ceramic mold plate with a surface roughness Ra≤0.2μm.

6. The method for preparing the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 5, characterized in that: In step S3, the molding agent is one or more of rubber, paraffin wax, or polyethylene glycol.

7. The method for preparing the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 5, characterized in that: During the wax and adhesive removal process in step S5, the heating rate from 300°C to 350°C and from 500°C to 600°C is controlled at 0.1–0.2°C / min.

8. The method for preparing the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 5, characterized in that: The composite hot-pressing sintering in step S6 specifically includes the following steps: T1. Vacuum low-pressure sintering: After dewaxing and debinding, multiple blanks are stacked and placed together in the hot press mold of the hot press furnace, separated by a 2-10mm thick graphite plate. Sintering is carried out under nitrogen atmosphere at 1600-1650℃ and axial pressure of 5MPa for 1.5 hours to promote phase transformation and densification and remove gas. T2. High-temperature hot pressing sintering: Maintain the temperature at 1700-1800℃, increase the axial pressure to 30-40MPa, and hold for 1.5-2 hours to make the hexagonal boron nitride highly oriented and compress the pores. T3. Low-temperature hot pressing sintering: The temperature is reduced to 1600-1650℃, the pressure is maintained at 30-40MPa, and the pressure is held for 30 minutes to refine the pores, eliminate secondary porosity caused by volume shrinkage during cooling, and improve density.

9. The method for preparing the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 8, characterized in that: In step T1, when multiple billets are stacked and loaded into the furnace, a graphite plate is used to separate each pair of billets, and the surface of the graphite plate is coated with boron nitride slurry and covered with graphite paper.

10. The method for preparing the high thermal conductivity and high strength and toughness multiphase nitride ceramic mold plate according to claim 9, characterized in that: The graphite plate is a porous graphite plate with a large number of through holes with a diameter of 1-1.5 mm distributed on it, with 1-4 holes per square centimeter.

Images