Near-net-shape preparation process of high-transmittance large-size magnesium-aluminum spinel ceramics

Abstract

The application discloses a near-net forming preparation process of high-transmittance large-size magnesium-aluminum spinel ceramics, and belongs to the technical field of preparation of high-performance transparent ceramics. The process is characterized by the following steps: firstly, magnesium-aluminum spinel raw material powder is mixed with lithium-free composite sintering additives according to a mass ratio; the composite sintering additives are composed of magnesium fluoride, ytterbium fluoride and ytterbium oxide in a molar ratio; the mixed powder is cold isostatic pressed into a preform; after being crushed, the preform is subjected to high-low pressure cycle pressing near-net forming; the obtained blank is first hot-pressed and pre-sintered, then is treated in a fluorine-containing atmosphere, and finally is subjected to hot isostatic pressing sintering; and finally, the finished product is obtained through post-processing. The process successfully overcomes the bottleneck in the preparation of large-size components, realizes the net forming of the magnesium-aluminum spinel ceramic with a diagonal size greater than 400 mm, the transmittance of the finished product is more than 93% in the wavelength range of 400 nm to 800 nm, the bending strength is more than 194 MPa, and the raw material cost and equipment dependence are significantly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of high-performance transparent ceramics, and particularly relates to a near-net forming preparation process of high-transmittance large-size magnesia-alumina spinel ceramics. BACKGROUND

[0002] High-performance transparent ceramics have increasingly prominent strategic value in the field of national defense and cutting-edge technology, especially in scenarios such as super-fast aircraft observation windows and laser weapon systems. Magnesia-alumina spinel (MgAl2O4) has become a key material in the high-performance transparent ceramic system due to its excellent optical transmittance, outstanding mechanical strength and extreme environmental stability. However, the core bottleneck in the industrialization of this material is the controllable preparation of large-size components. Existing technologies are difficult to stably prepare components with a diagonal size of more than 400 mm, which seriously restricts the application and promotion of the material in key scenarios such as large-size bulletproof observation windows and infrared optical systems.

[0003] In the current technical route, the hot pressing / hot isostatic pressing composite method can realize the preparation of optical-grade ceramics (see patent CN201710520821.1), but its process design is mainly aimed at small and medium-sized products, and there is no effective solution for the shrinkage control of large-size green bodies. The research literature "Preparation and Performance of Magnesia-Alumina Spinel Transparent Ceramics" further points out that even if the above method is used, it still needs to rely on high-purity sub-micron raw materials and special forming equipment, resulting in a surge of more than 300% in the cost of single production. This technical and economic defect greatly limits the feasibility of batch production.

[0004] The more prominent technical obstacle is the traditional sintering aid system. The widely used lithium fluoride can cause three negative effects during densification: first, it forms a low-melting-point grain boundary phase, inducing abnormal grain growth; second, it increases the density of micro-cracks in the grain boundary due to residual lithium ions; and third, it causes material loss of transparency due to high-temperature volatilization, ultimately causing the bending strength of the component to decay to below 160 MPa. These defects make it difficult for existing materials to meet the mechanical requirements of various scenarios. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a near-net forming preparation process for high-transmittance large-size magnesia-alumina spinel ceramics with low cost and excellent mechanical properties.

[0006] The technical solution adopted by the present application to solve the technical problem is: a near-net forming preparation process for high-transmittance large-size magnesia-alumina spinel ceramics, characterized in that it comprises the following steps:

[0007] 1) Magnesia-alumina spinel raw material powder and sintering aid are mixed in a mass ratio of 95-99:1-5 to form ceramic powder; the ceramic powder is subjected to cold isostatic pressing in a mold to form a preform;

[0008] 2) the preform is secondarily crushed into a preform powder with a particle size of 0.1mm-2mm; the preform powder is subjected to near-net forming to obtain a green body;

[0009] 3) the green body is subjected to hot-pressing pre-sintering at 600-610℃ and 100-120MPa for 2-4h to increase the strength and density of the green body and reduce deformation in the subsequent sintering process; then the green body is subjected to hot isostatic pressing sintering at 1350-1380℃ and 180-200MPa for 3-5h to realize high densification under high temperature and high pressure; and the sintering is performed to prevent oxidation and volatilization and ensure the purity and transparency of the material;

[0010] 4) post-processing: the basic post-processing includes machining and polishing, rough grinding of the transparent ceramic that passes the preliminary detection, and then precise optical polishing on a super-precision grinding machine to improve the surface smoothness and transparency of the ceramic through rough grinding and precise optical polishing.

[0011] The present application breaks through the core bottleneck of large-size component preparation by the innovative combination of lithium-free sintering aid combination and cold isostatic pressing preform crushing process. The method completely eliminates the risk of low-melting phase and micro-cracks at the grain boundary, greatly improves the bending strength of the finished product; the innovative "crushing and recombination" near-net forming technology significantly improves the uniformity of the green body, realizes the net forming of large-size components with a diagonal size of ≥400mm, and relaxes the requirements for the particle size of raw materials to the conventional level; the two-stage precise pressure control (hot-pressing pre-sintering + hot isostatic pressing) ensures that the material density reaches more than 99.8% of the theoretical value, the visible light transmittance is improved to 86%±0.5%, and the process greatly reduces the equipment dependency and raw material cost, thereby reducing the production cost of a single piece.

[0012] The present application prepares magnesium-aluminum spinel ceramic by sintering magnesium-aluminum spinel powder. The main raw material, magnesium-aluminum spinel powder, can be pre-prepared according to traditional basic formulations, such as pre-mixing MgO and Al2O3 powder in a molar ratio of 1:0.98-3; or directly purchased from enterprises such as Zhongci High-tech, Shandong Guocai, Shanghai Haohong, etc. The process can improve the yield of large-size magnesium-aluminum spinel transparent ceramic.

[0013] Preferably, the mixing of the magnesium-aluminum spinel raw material powder and the sintering aid in step 1) of the above preparation process is carried out in a ball mill, the rotation speed of the ball mill is 220-280r / min, and the mixing time is 20-26h. The ball milling parameters promote the uniform dispersion of the sintering aid to the sub-micron level, eliminate the risk of local agglomeration, reduce the composition gradient in the large-size green body, and lay a structural foundation for eliminating grain boundary impurity segregation and deformation defects in the subsequent sintering.

[0014] Preferably, the sintering aid in step 1) of the above preparation process is a MgF2-YbF3-Yb2O3 composite sintering aid; the molar ratio of the three crystal forms of MgF2, YbF3 and Yb2O3 in the composite sintering aid is 2.5-7.5:4.5-5.5:2.5.

[0015] The synergistic mechanism of the composite sintering aid achieves densification and optical optimization through three steps:

[0016] 1. Liquid phase activation: YbF3 melts first to form a low-viscosity liquid phase in the pre-sintering at 600-610°C, wets the interstitial gaps between spinel particles, promotes mass transfer and diffusion, significantly reduces the densification temperature, and provides a basis for uniform shrinkage of large-size green bodies.

[0017] 2. Grain boundary pinning: MgF2 decomposition produces MgF2 and Yb2O3, which pin the grain boundaries and hinder abnormal grain growth, reducing light scattering sources. 2+ suppresses Al2O3 phase transition, and the nanoscale MgF2-Yb2O3 composite phase pins the grain boundaries, preventing abnormal grain growth and reducing light scattering sources.

[0018] 3. Atmosphere purification: Yb2O3 reacts with residual oxygen to form Yb-O compounds, removing oxygen impurities from the grain boundary pores; fluorine ions from the decomposition of YbF3 further gasify and encapsulate oxygen vacancies, reducing porosity. The molar ratio of the three ensures a balance between liquid phase amount, grain boundary pinning force and oxygen removal efficiency, making the 400-800 nm transmittance breakthrough 93%, and achieving the unity of high light transmittance and high strength of large-size ceramics.

[0019] Specifically, the preparation process of the composite sintering aid is as follows: mix YbF3, MgF2 and Yb2O3 raw material powders according to the ratio, then add alcohol or deionized water for ball milling; then heat treat at 600-610°C for 110-130 minutes under a protective atmosphere, and cool to obtain the product. Through precise heat treatment, multiple functions are synergistically optimized: MgF2-YbF3 forms a eutectic body to pre-fill the lattice gaps, and Yb2O3 is simultaneously converted into active oxygen removal units; an inert gas barrier effectively inhibits the volatilization of fluorides at high temperatures, improving the stability of the crystal structure of the composite aid. The aid prepared in this way can ensure uniform light transmittance in the entire area of large-size components during subsequent sintering.

[0020] Preferably, in the preparation process of the above composite sintering aid, the ball-to-material ratio for ball milling is 17-20:1, the rotation speed is 200-250 r / min, and the time is 20-24 hours. By controlling the ball-to-material ratio, rotation speed and time, the MgF2-YbF3-Yb2O3 ternary system is atomically mixed, component segregation is eliminated, and uniformly dispersed active units are pre-constructed, ensuring the consistency of liquid phase formation and oxygen removal reactions during subsequent heat treatment

[0021] Preferably, in the preparation process of the composite sintering aid, the mixed powder after ball milling is dried, sieved through a 200-mesh screen, and then heat treated.

[0022] Preferably, in step 1) of the preparation process, the temperature of the cold isostatic pressing process is 20-30℃, the pressure is 305-315 MPa, and the cold isostatic pressing time is 5-20 min. Precise control of the temperature and pressure at room temperature enables the preform to achieve ultra-high density and ultra-low density gradient, completely eliminates the defects of dense edges and loose centers of the large-size blank body in traditional pressing, greatly reduces the sintering deformation rate, and guarantees the dimensional stability of the component.

[0023] Specifically, in step 2) of the preparation process, the near-net forming adopts a high-low pressure cyclic pressing process, wherein the pressure in the high-pressure stage is 35-45 MPa, the pressure in the low-pressure stage is 3-7 MPa, and the high-low pressure cycle number is 8-10. The cyclic pressing of high and low pressures promotes the interlayer densification and reconstruction of the preform powder, the high-pressure stage breaks through the friction barrier between the powders, and the skeleton particles are densely packed; the low-pressure stage releases elastic stress and avoids micro-cracks caused by local overpressure; the cycle number precisely controls the relative density gradient of the blank body, reduces the critical defect size of the green body, and provides a core guarantee for eliminating large-size shrinkage deformation in subsequent sintering.

[0024] Preferably, in the high-low pressure cyclic pressing process, the pressure increasing rate from the low-pressure stage to the high-pressure stage is 0.5-1 MPa / s, and the pressure holding time in the low-pressure stage is 1.5-2 times that in the high-pressure stage. Slow pressure increase avoids stress concentration in the powder skeleton and eliminates layered cracks; long-time low-pressure holding promotes the full slip of fine particles to fill the mesopore space, while releasing elastic strain energy, which further reduces the internal closed porosity of the green body and significantly improves the sintering deformation resistance of large-size blanks.

[0025] Specifically, in step 3) of the preparation process, after the hot-pressing pre-sintering, the blank body is placed in a fluorine-containing atmosphere (such as CF4 or SF6) at 550-580℃ for 30-60 min, and then subjected to hot isostatic pressing sintering. The reaction of fluorine atmosphere with residual oxygen generates volatile gas, which removes grain boundary oxygen impurities, reduces porosity, activates grain boundary migration channels, and makes the grain size more uniform in subsequent hot isostatic pressing.

[0026] In addition, the post-processing in step 4) can also include ultrasonic-assisted polishing in a polishing liquid containing nano YbF3 and annealing in an argon atmosphere (400℃, 2 h). Nano YbF3 fills the surface micro-cracks, further improving the transmittance; annealing eliminates processing stress, and the bending strength is improved.

[0027] The protective atmosphere is an inert gas, such as argon or nitrogen, which can achieve the desired effect.

[0028] The transmittance of the obtained magnesium-aluminum spinel ceramic is not less than 80% in the wavelength range of 400nm-800nm, and the average grain size is less than 5um.

[0029] Compared with the prior art, the near-net forming preparation process of the high-transmittance large-size magnesium-aluminum spinel ceramic has the beneficial effects that the high optical performance, the super large size and the excellent mechanical properties are synergistically improved. The lithium-free MgF2-YbF3-Yb2O3 composite sintering aid is innovatively adopted, and the technical bottleneck of the YbF3 forming low-viscosity liquid phase activation densification in the pre-sintering in the traditional lithium fluoride system is completely solved through a triple synergistic mechanism; the MgF2-Yb2O3 nano composite phase pins the grain boundary to inhibit abnormal grain growth; the Yb2O3 / YbF3 decomposition products efficiently remove oxygen vacancies, so that the transmittance of the finished product in the wavelength range of 400-800nm is broken through, and the bending strength is improved. The gradient densification control system is created on the forming process: the super-low density gradient is realized through the suitable cold isostatic pressing of the preform; the preform powder is subjected to 8-10 times of high-low pressure cycle pressing, combined with the low-speed pressure rising and the long low-pressure holding strategy, to eliminate the layered cracks and reduce the closed porosity pressure, so as to guarantee the deformation rate of the diagonal line size of the green body; the pre-sintering is combined with the hot isostatic pressing to greatly improve the density.

[0030] The raw material particle size requirement of the application is relaxed to the conventional level, the dependence on special equipment is reduced, the production cost is reduced, and an industrial-level solution is provided for the batch manufacturing of large-size transparent ceramic components under extreme working conditions. DETAILED DESCRIPTION

[0031] The application will be further described below in combination with specific embodiments, and the embodiment 1 is the best embodiment. The magnesium-aluminum spinel powder used in the embodiment is the pre-mixed material of MgO and Al2O3 powder in a molar ratio of 1:2. Other mixing ratios are not shown one by one in the embodiment.

[0032] Preparation of YbF3-MgF2-Yb2O3 composite sintering aid A: YbF3, MgF2 and Yb2O3 powders are mixed in a molar ratio of 5.0:5.0:2.5, alcohol is added in a ball-to-material ratio of 18:1, and then ball milling is carried out at a speed of 230r / min for 22h; after drying treatment, the powder is sieved through a 200-mesh screen, and then heat treatment is carried out at 605℃ for 120min in a nitrogen protective atmosphere to obtain the YbF3-MgF2-Yb2O3 composite sintering aid A.

[0033] Preparation of YbF3-MgF2-Yb2O3 composite sintering aid B: YbF3, MgF2 and Yb2O3 powders were mixed in a molar ratio of 4.5:7.5:2.5, alcohol was added in a ball-to-material ratio of 20:1, and then ball milling was performed at a speed of 250 r / min for 20 h; after drying treatment, the mixture was sieved through a 200 mesh screen, and then heat treatment was performed at 600°C for 130 min in a nitrogen atmosphere to obtain YbF3-MgF2-Yb2O3 composite sintering aid B.

[0034] Preparation of YbF3-MgF2-Yb2O3 composite sintering aid C: YbF3, MgF2 and Yb2O3 powders were mixed in a molar ratio of 5.5:2.5:2.5, alcohol was added in a ball-to-material ratio of 17:1, and then ball milling was performed at a speed of 200 r / min for 24 h; after drying treatment, the mixture was sieved through a 200 mesh screen, and then heat treatment was performed at 610°C for 110 min in a nitrogen atmosphere to obtain YbF3-MgF2-Yb2O3 composite sintering aid C.

[0035] Preparation of YbF3-MgF2-Yb2O3 composite sintering aid D: YbF3, MgF2 and Yb2O3 powders were mixed in a molar ratio of 1:1:1, alcohol was added in a ball-to-material ratio of 18:1, and then ball milling was performed at a speed of 230 r / min for 22 h; after drying treatment, the mixture was sieved through a 200 mesh screen, and then heat treatment was performed at 605°C for 120 min in a nitrogen atmosphere to obtain YbF3-MgF2-Yb2O3 composite sintering aid D.

[0036] Example 1

[0037] 1) Magnesium aluminate spinel powder and YbF3-MgF2-Yb2O3 composite sintering aid A were mixed in a ball mill at a speed of 240 r / min for 24 h in a mass ratio of 98:2;

[0038] 2) The mixed ceramic powder was placed in a mold and cold isostatic pressed at 25°C and 310 MPa for 10 min to obtain a green compact, which was crushed by a crusher and sieved to obtain a green powder with a particle size of 0.1 mm to 2 mm;

[0039] 3) The green powder was placed in a mold and subjected to high-low pressure cycle pressing to obtain a compact, which was subjected to a high pressure stage at a pressure increasing rate of 0.6 MPa / s to a high pressure of 40 MPa for 10 min, and then was subjected to a low pressure stage at a pressure of 5 MPa for 18 min; the high-low pressure cycle was repeated 9 times;

[0040] 4) The obtained compact was heat pressed and pre-sintered at 605°C and 110 MPa for 3 h in a nitrogen atmosphere, and then was treated in a CF4 atmosphere at 560°C for 40 min;

[0041] 5) After pre-sintering, the green body is subjected to hot isostatic pressing sintering at 1360℃ under nitrogen protective atmosphere, 190MPa pressure for 4h;

[0042] 6) After sintering, the transparent ceramic is polished, the rough shape of the transparent ceramic that passes the preliminary detection is coarsely ground, and then precisely polished on a super-precision grinding machine. Through coarse grinding and precise optical polishing, a 450mmx750mm large-size magnesia-alumina spinel transparent ceramic is obtained, with a forming rate of 100%, a transmittance of 93.2% in the wavelength range of 400nm-800nm, an average grain size of 2.1μm, a compressive strength of 392.6MPa, and a bending strength of 194.3MPa.

[0043] Example 2

[0044] The basic preparation process is the same as that of Example 1, except that the sintering aid used is YbF3-MgF2-Yb2O3 composite sintering aid B. The obtained 450mmx750mm large-size magnesia-alumina spinel transparent ceramic has a forming rate of 100%, a transmittance of 92.8% in the wavelength range of 400nm-800nm, an average grain size of 2.2μm, a compressive strength of 392.3MPa, and a bending strength of 194.1MPa.

[0045] Example 3

[0046] The basic preparation process is the same as that of Example 1, except that the sintering aid used is YbF3-MgF2-Yb2O3 composite sintering aid C. The obtained 450mmx750mm large-size magnesia-alumina spinel transparent ceramic has a forming rate of 100%, a transmittance of 92.7% in the wavelength range of 400nm-800nm, an average grain size of 2.1μm, a compressive strength of 392.2MPa, and a bending strength of 193.8MPa.

[0047] Example 4

[0048] The basic preparation process is the same as that of Example 1, except that the sintering aid used is YbF3-MgF2-Yb2O3 composite sintering aid D. The obtained 450mmx750mm large-size magnesia-alumina spinel transparent ceramic has a forming rate of 100%, a transmittance of 92.1% in the wavelength range of 400nm-800nm, an average grain size of 2.2μm, a compressive strength of 390.7MPa, and a bending strength of 189.6MPa.

[0049] Example 5

[0050] 1) Magnesia-alumina spinel powder and YbF3-MgF2-Yb2O3 composite sintering aid A are put into a ball mill with a rotation speed of 280r / min and mixed for 20h;

[0051] 2) Put the mixed ceramic powder into the mold, and cold isostatic press at 25℃, 305MPa for 12min to press into a preform, and the preform is crushed by a crusher and sieved to obtain a preform powder with a particle size of 0.1mm-2mm;

[0052] 3) Put the preform powder into the mold again, and perform high-low pressure cycle pressing to prepare a green body, and the pressure is increased to 35MPa at a pressure increasing rate of 0.5MPa / s, and the pressure is maintained for 15min in the high pressure stage, and the pressure is released to 3MPa in the low pressure stage, and the pressure is maintained for 30min; the high-low pressure cycle is 9 times;

[0053] 4) The obtained green body is heat pressed and pre-sintered at 600℃, 120MPa for 4h in a nitrogen protection atmosphere; and the green body is placed in a CF4 atmosphere and treated at 550℃ for 60min;

[0054] 5) The pre-sintered green body is heat isostatic pressed and sintered at 1350℃, 200MPa for 5h in a nitrogen protection atmosphere;

[0055] 6) After sintering is completed, the transparent ceramic is processed and polished, the rough shape of the transparent ceramic which passes the preliminary detection is coarsely ground, and then the transparent ceramic is precisely optically polished on a super-precision grinding machine, and through the coarse grinding and precise optical polishing, a large-size magnesia-alumina spinel transparent ceramic with a forming rate of 100% is prepared, the transmittance reaches 88.4% in the wavelength range of 400nm-800nm, the average grain size is 2.4μm, the compressive strength is 392.6MPa, and the bending strength is 194.8MPa.

[0056] Example 6

[0057] 1) Put the magnesia-alumina spinel powder and YbF3-MgF2-Yb2O3 composite sintering aid A with a mass ratio of 99:1 into a ball mill with a rotating speed of 220r / min for 26h;

[0058] 2) Put the mixed ceramic powder into the mold, and cold isostatic press at 25℃, 315MPa for 8min to press into a preform, and the preform is crushed by a crusher and sieved to obtain a preform powder with a particle size of 0.1mm-2mm;

[0059] 3) Put the preform powder into the mold again, and perform high-low pressure cycle pressing to prepare a green body, and the pressure is increased to 45MPa at a pressure increasing rate of 1MPa / s, and the pressure is maintained for 8min in the high pressure stage, and the pressure is released to 7MPa in the low pressure stage, and the pressure is maintained for 12min; the high-low pressure cycle is 8 times;

[0060] 4) The obtained green body is heat pressed and pre-sintered at 610℃, 100MPa for 2h in a nitrogen protection atmosphere; and the green body is placed in a SF6 atmosphere and treated at 580℃ for 30min;

[0061] 5) After pre-sintering, the green body is subjected to hot isostatic sintering at 1380℃ under a nitrogen protective atmosphere at a pressure of 180MPa for 3h;

[0062] 6) After sintering, the transparent ceramic is processed and polished, and the transparent ceramic that passes preliminary detection is roughly ground into a shape, and then subjected to precise optical polishing on a super-precision grinding machine. Through rough grinding and precise optical polishing, a 450mm×750mm large-size magnesia-alumina spinel transparent ceramic is obtained, with a forming rate of 100%, a transmittance of 93.3% in the wavelength range of 400nm~800nm, an average grain size of 2.7μm, a compressive strength of 388.7MPa, and a bending strength of 188.1MPa.

[0063] Example 7

[0064] The basic preparation process is the same as that of Example 1, except that the sintering aid used is a traditional Y2O3-MgO composite sintering aid with an equal mass, and the molar ratio of Y2O3 and MgO is 3:6. The obtained 450mm×750mm large-size magnesia-alumina spinel transparent ceramic has a forming rate of 100%, a transmittance of 83.4% in the wavelength range of 400nm~800nm, an average grain size of 2.3μm, a compressive strength of 385.6MPa, and a bending strength of 167.5MPa.

[0065] Example 8

[0066] The basic preparation process is the same as that of Example 1, except that the cold isostatic pressing process pressure in step 2) is 400MPa. The obtained 450mm×750mm large-size magnesia-alumina spinel transparent ceramic has a forming rate of 100%, a transmittance of 85.5% in the wavelength range of 400nm~800nm, an average grain size of 4.1μm, a compressive strength of 387.3MPa, and a bending strength of 174.7MPa.

[0067] Example 9

[0068] The basic preparation process is the same as that of Example 1, except that the pressure in the high-low pressure cycle pressurization in step 3) is 80MPa in the high-pressure stage and 1MPa in the low-pressure stage. The obtained 450mm×750mm large-size magnesia-alumina spinel transparent ceramic has a forming rate of 100%, a transmittance of 86.6% in the wavelength range of 400nm~800nm, an average grain size of 4.5μm, a compressive strength of 387.8MPa, and a bending strength of 177.4MPa.

[0069] Example 10

[0070] The basic preparation process is the same as that of Example 1, except that the green body is not subjected to two-dimensional treatment in a fluorine atmosphere in step 4). The forming rate of the obtained 450 mm x 750 mm large-size magnesia-alumina spinel transparent ceramic is 100%, the transmittance in the wavelength range of 400 nm to 800 nm reaches 93.0%, the average grain size is 2.1 μm, the compressive strength is 392.3 MPa, and the bending strength is 193.1 MPa.

[0071] Comparative Example 1

[0072] The basic preparation process is the same as that of Example 1, except that the treatment in step 2) is not performed. When the 450 mm x 750 mm large-size magnesia-alumina spinel transparent ceramic is prepared, the forming rate is low, only 76%, the transmittance in the wavelength range of 400 nm to 800 nm reaches 84%, the average grain size is 4.1 μm, the compressive strength is 367.9 MPa, and the bending strength is 145.3 MPa.

[0073] Comparative Example 2

[0074] The basic preparation process is the same as that of Example 1, except that the crushing in step 2) and the treatment in step 3) are not performed. When the 450 mm x 750 mm large-size magnesia-alumina spinel transparent ceramic is prepared, the forming rate is low, only 46%, the transmittance in the wavelength range of 400 nm to 800 nm reaches 85%, the average grain size is 3.8 μm, the compressive strength is 328.4 MPa, and the bending strength is 102 MPa.

[0075] Comparative Example 3

[0076] The basic preparation process is the same as that of Example 1, except that LiF is used to replace the YbF3-MgF2-Yb2O3 composite sintering aid A. The forming rate of the obtained 450 mm x 750 mm large-size magnesia-alumina spinel transparent ceramic is 86%, the transmittance in the wavelength range of 400 nm to 800 nm is 83.3%, the average grain size is 3.6 μm, the compressive strength is 363.4 MPa, and the bending strength is 127.8 MPa.

[0077] Comparative Example 4

[0078] The basic preparation process is the same as that of Example 1, except that the high-low pressure cyclic pressurization is replaced by single pressurization with the same high-low pressure. The forming rate of the obtained 450 mm x 750 mm large-size magnesia-alumina spinel transparent ceramic is 86%, the transmittance in the wavelength range of 400 nm to 800 nm is 86.4%, the average grain size is 2.7 μm, the compressive strength is 384.3 MPa, and the bending strength is 185.3 MPa.

[0079] The above merely describes preferred embodiments of the present application, but is not intended to limit the present application to other forms, and any person skilled in the art can make changes or modifications to the above disclosed technical contents into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution content of the present application and according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. A process for near-net-shape preparation of high-transparency large-size magnesium aluminate spinel ceramics, characterized by, The method comprises the following steps: 1) mixing magnesium-aluminum spinel raw material powder and sintering aids in a mass ratio of 95-99:1-5 to obtain ceramic powder; and cold isostatic pressing the ceramic powder in a mold to obtain a preform; 2) secondary crushing the preform into preform powder with a particle size of 0.1-2 mm; and near-net forming the preform powder to obtain a green body; 3) hot-pressing pre-sintering the green body at 600-610 DEG C and 100-120 MPa for 2-4 h; and then hot isostatic pressing sintering the green body at 1350-1380 DEG C and 180-200 MPa for 3-5 h; 4) post-processing; the sintering aids in step 1) are MgF2-YbF3-Yb2O3 composite sintering aids; the molar ratio of the three crystal forms of MgF2, YbF3 and Yb2O3 in the composite sintering aids is 2.5-7.5:4.5-5.5:2.5; and the preparation process of the composite sintering aids is as follows: mixing raw material powders of YbF3, MgF2 and Yb2O3 according to the ratio, then adding alcohol or deionized water for ball milling; after ball milling, hot-treating at 600-610 DEG C for 110-130 min under a protective atmosphere, and cooling to obtain the composite sintering aids; in step 2), the near-net forming adopts a high-low pressure cyclic pressurization process, wherein the pressure in the high pressure stage is 35-45 MPa, the pressure in the low pressure stage is 3-7 MPa, and the high-low pressure cycle number is 8-10.

2. The process for near net shape fabrication of high optical transparency large size magnesium aluminate spinel ceramics according to claim 1, characterized in that: in step 1), the mixing of the magnesium-aluminum spinel raw material powder and the sintering aids is performed in a ball mill, the rotation speed of the ball mill is 220-280 r / min, and the mixing time is 20-26 h.

3. The process for near net shape fabrication of high optical transparency large size magnesium aluminate spinel ceramics according to claim 1, characterized in that: the ball milling is performed at a ball-to-material ratio of 17-20:1, a rotation speed of 200-250 r / min, and a time of 20-24 h.

4. The process for near net shape fabrication of high optical transparency large size magnesium aluminate spinel ceramics according to claim 1, characterized in that: the mixed powder obtained by ball milling is first dried and then sieved through a 200-mesh sieve before being heat-treated.

5. The process for near net shape fabrication of high optical transparency large size magnesium aluminate spinel ceramics according to claim 1, characterized in that: in step 1), the cold isostatic pressing process is performed at a temperature of 20-30 DEG C and a pressure of 305-315 MPa for 5-20 min.

6. A process for near net shape fabrication of high light transmittance large size magnesio-alumina spinel ceramics according to any one of claims 1, characterized by: the pressure increasing rate from the low pressure stage to the high pressure stage is 0.5-1 MPa / s, and the pressure holding time in the low pressure stage is 1.5-2 times the pressure holding time in the high pressure stage.

7. A process for near net shape fabrication of high light transmittance large size magnesio-alumina spinel ceramics according to any one of claims 1, characterized by: after the hot-pressing pre-sintering in step 3), the green body is placed in a fluorine-containing atmosphere and treated at 550-580 DEG C for 30-60 min before being subjected to hot isostatic pressing sintering.