Method for preparing high-transmittance AION transparent ceramic through hot isostatic pressing sintering
By controlling the particle size of AlON powder and using Y2O3 additives, combined with pressureless and hot isostatic pressing sintering, the problem of unfavorable grain growth during the AlON ceramic sintering process was solved, and the preparation of AlON transparent ceramics with high light transmittance and high hardness was achieved, which is suitable for industrial production.
Patent Information
- Application Number
- CN202511253228.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-03
- Publication Date
- 2025-11-18
AI Technical Summary
In the existing sintering process of AlON transparent ceramics, the high temperature and long duration cause grain growth that is not conducive to mechanical properties. Furthermore, the pressureless sintering process is demanding, consumes a lot of equipment and energy, and is inefficient, making it difficult to achieve both high light transmittance and high hardness.
By controlling the particle size of AlON powder and using Y2O3 sintering aid, combined with pressureless and hot isostatic pressing sintering, grain growth can be controlled, and sintering temperature and time can be reduced to obtain AlON transparent ceramics with high transmittance and high hardness.
High density and small grain size of AlON transparent ceramics were achieved at lower temperatures and in a shorter time, which improved light transmittance and hardness, reduced cost and energy consumption, and made them suitable for industrial production.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a method for preparing high-transmittance AlON transparent ceramic by hot isostatic pressing sintering, and belongs to the field of transparent ceramic material preparation. BACKGROUND
[0002] AlON transparent ceramic has excellent light transmittance in the 0.2-6.0 µm wave band, and also has good mechanical properties, and is one of the most potential structural-functional integrated transparent ceramic materials in the 21st century, and has very broad application prospects in dual-mode guidance, transparent armor, infrared detection, and safety protection of special equipment.
[0003] When light passes through transparent ceramic, pores will cause scattering of light, which is one of the important factors leading to the decrease of light transmittance of transparent ceramic. Therefore, improving the relative density is an important goal of sintering of transparent ceramic. Among many sintering technologies, pressureless sintering is a preparation technology of AlON pre-sintered body which is simple in process, low in cost, and suitable for preparation of special-shaped and large-size components. However, during the sintering process of AlON ceramic, the reciprocal phase transformation behavior between AlON and Al2O3+AlN often easily causes premature particle agglomeration / coarsening, which brings great difficulty to the densification sintering in the later stage.
[0004] Hot isostatic pressing sintering technology is an effective means to improve the relative density of materials, and is also a technical approach to improve the light transmittance of AlON transparent ceramic and guarantee the mechanical properties. Therefore, based on the preparation of pre-sintered body by pressureless sintering, the densification is improved by hot isostatic pressing sintering, so as to obtain high light transmittance. Moreover, through this way of pressureless sintering combined with hot isostatic pressing treatment, the grain growth of AlON can be controlled, so as to guarantee the mechanical properties. However, the process requirement is still harsh during the process of pressureless sintering preparation of AlON pre-sintered body and hot isostatic pressing: the preparation of pre-sintered body is generally at ≥1900℃ for 4-20 h; hot isostatic pressing sintering needs to be at ≥1880℃ for 3-6 h. The harsh process requirement not only increases the equipment and energy consumption, and has the problems of low efficiency and high cost, but also the high sintering temperature and long holding time will lead to the grain growth of AlON ceramic, which is not conducive to the improvement of mechanical properties.
[0005] Recent research results show that the unique phase transformation behavior during the preparation of AlON by pressureless sintering is affected by the coupling effect of powder particle size and sintering aid. It can be seen that adjusting the particle size of AlON powder and using appropriate sintering aid are feasible ways to promote the densification sintering of AlON. Therefore, through the synergistic effect of AlON powder particle size and sintering aid, it is expected to accelerate the densification process, so as to reduce the process requirement of the whole process of preparation of high light transmittance AlON ceramic, and promote the wide application of AlON transparent ceramic. SUMMARY
[0006] The application aims to provide a method for preparing high-transmittance AlON transparent ceramic by hot isostatic pressing sintering, specifically, the particle size distribution of AlON powder is regulated by ball milling, the sintering aid Y2O3 and its content control are used, and the AlON transparent ceramic with high transmittance and high hardness from visible to infrared waveband is obtained by pressureless and hot isostatic pressing sintering. In the application, the pressureless and hot isostatic pressing sintering is completed under the condition of lower temperature and shorter holding time, the process is simple, the sintering effect is good, the equipment loss is small, the efficiency is high, the cost is low, the obtained AlON ceramic has good light transmittance and high hardness, and is suitable for industrial production.
[0007] The application is based on the particle size regulation of AlON powder, the AlON powder with large particle size is used, the sintering aid Y2O3 and its content control are used, and the synergistic effect promotes the densification process, so that the pre-sintered body with high density and small grain size is prepared under the condition of lower pressureless sintering temperature and shorter holding time (1790-1850 ℃, 2.5 h), and a good microstructure foundation is laid for subsequent hot isostatic pressing sintering. Further, in the hot isostatic pressing sintering stage, the good effect of improving the density is achieved under the condition of lower temperature and shorter holding time (1850 ℃, 2.0 h), and the grain growth is limited, so that the AlON transparent ceramic with high light transmittance and high hardness is obtained.
[0008] A method for preparing high-transmittance AlON transparent ceramic by hot isostatic pressing sintering, comprising the following steps: ball milling pure-phase AlON powder and sintering aid Y2O3, drying and sieving to obtain AlON and Y2O3 mixed powder, dry pressing forming, pressureless sintering in a nitrogen atmosphere to obtain AlON pre-sintered body, and hot isostatic pressing sintering in an argon atmosphere to obtain AlON transparent ceramic, wherein the D 50 of the AlON and Y2O3 mixed powder is 0.8-2.2 µm, and the particle size distribution range is 0.3-10.0 µm.
[0009] Further, the D 10 of the AlON and Y2O3 mixed powder is >0.5 µm, and the content of the particles with <0.4 µm is <2 vol.%, the D 90 >5 µm is <2 vol.%.
[0010] Further, the chemical purity of the pure-phase AlON powder is >99.9%.
[0011] Preferably, the content of the sintering aid Y2O3 is 0.35%-0.45% of the mass of the AlON powder.
[0012] Preferably, pure phase AlON powder and sintering aid Y2O3 are first ball-milled at 170 rpm for 12 h, then ball-milled again at 210 rpm for 18 h, dried, and sieved to obtain D. 50 It is a 1.1 µm mixed powder of AlON and Y2O3.
[0013] Preferably, pure phase AlON powder and sintering aid Y2O3 are ball-milled at 170 rpm for 12 h, dried, and sieved to obtain D. 50 It is a 2.0 µm mixed powder of AlON and Y2O3.
[0014] In the method described in this invention, the mixed powder of AlON and Y2O3 is first pre-formed under a condition of 20~70 MPa, and then cold isostatically pressed under a condition of 100~180 MPa.
[0015] In the method described in this invention, the heating rate of the pressureless sintering is 5~50℃ / min, the sintering temperature is 1790~1850℃, and the holding time is 2.0~3.0 h.
[0016] In the method described in this invention, the relative density of the AlON pre-burnt body is 99.4%~99.6%, and the average grain size is 40~55 µm.
[0017] In the method described in this invention, the heating rate of the hot isostatic pressing sintering is 10~20℃ / min, the sintering temperature is 1830~1880℃, the pressure is 150~200 MPa, and the holding time is 1.5~2.5 h.
[0018] The method described in this invention includes a post-processing step: grinding and polishing the obtained AlON transparent ceramic.
[0019] Another object of the present invention is to provide AlON transparent ceramics prepared by the above method.
[0020] Furthermore, the AlON transparent ceramic has a relative density of 99.7%~99.9%, an average grain size of 55~70µm, a maximum transmittance of 85%~87% in the wavelength range of 3500 nm~3900 nm, a transmittance of 77%~81% at a wavelength of 500 nm, and a Vickers hardness of 18~20 GPa.
[0021] The beneficial effects of this invention are: This invention improves the densification and sintering ability of AlON powder by controlling its particle size distribution and combining it with Y2O3 sintering aid. This allows for pressureless sintering, achieving a pre-sintered body with high density and small grain size at lower temperatures and shorter holding times. Based on this, hot isostatic pressing (HIP) is used to further improve density at lower temperatures and shorter holding times, while controlling grain growth. This results in the preparation of transparent AlON ceramics with both high light transmittance and high hardness from the visible to mid-infrared range.
[0022] The key to this invention lies in the synergistic effect of AlON powder particle size control and Y2O3 sintering aid. The AlON powder has a moderate particle size, is readily available, and the process is simple and highly controllable, avoiding the problem of reduced light transmittance caused by excessive impurities introduced during fine powder preparation. Simultaneously, it improves powder preparation efficiency and reduces costs. In terms of results, the synergistic effect of AlON powder particle size and Y2O3 sintering aid significantly enhances the densification and sintering ability of AlON, effectively lowering the pressureless sintering temperature for pre-sintered body preparation. A pre-sintered body with a relative density of 99.48% can be obtained with a holding time as low as 1790℃ for a short time (2.5 h). This pre-sintered body also features a small grain size (average grain size of 45 µm). Subsequent hot isostatic pressing (HIP) sintering significantly improved the relative density of the pre-sintered body and effectively controlled grain growth. The resulting ceramic had a relative density of 99.80% and an average grain size of 58 µm. Performance tests showed that its maximum transmittance was 85.7% (3600 nm) and its transmittance at 500 nm wavelength was 80.3%. It also exhibited high hardness, with a Vickers hardness of 19.48 ± 0.31 GPa.
[0023] The method described in this invention is simple to operate, with low temperatures and short holding times for both pressureless and hot isostatic pressing sintering, resulting in high efficiency, good energy-saving effect, low cost, and easy industrialization. Attached Figure Description
[0024] Figure 1 The images show the phase composition, particle size distribution, and microstructure of AlON powder in Examples 1 and 2, where (a) is an XRD pattern; (b) is a particle size distribution diagram; (c) is a SEM image of the AlON and Y2O3 mixed powder in Example 1; and (d) is a SEM image of the AlON and Y2O3 mixed powder in Example 2.
[0025] Figure 2 The grain morphology of the pre-fired body (PS) and the AlON ceramic (PS+HIP) after hot isostatic pressing sintering in Example 1 is shown.
[0026] Figure 3 The images show the transmittance curves and sample photographs of the pre-fired body and the AlON ceramic after hot isostatic pressing sintering in Example 1.
[0027] Figure 4 The fracture morphology of the pre-fired body and the AlON ceramic after hot isostatic pressing sintering in Example 1 is shown.
[0028] Figure 5 The image shows the grain morphology of the pre-fired body and the AlON ceramic after hot isostatic pressing sintering in Example 2.
[0029] Figure 6 The images show the transmittance curves and sample photographs of the pre-fired body and the AlON ceramic after hot isostatic pressing sintering in Example 2.
[0030] Figure 7 The fracture morphology of the pre-fired body and the AlON ceramic after hot isostatic pressing in Example 2 is shown.
[0031] Figure 8 The transmittance curves and sample photographs of the pre-fired body and the AlON ceramic after hot isostatic pressing in Comparative Example 1 are shown.
[0032] Figure 9 The transmittance curves and sample photographs of the pre-fired body and the AlON ceramic after hot isostatic pressing in Comparative Example 2 are shown.
[0033] Figure 10 The transmittance curves and sample photographs of the pre-fired body and the AlON ceramic after hot isostatic pressing in Comparative Example 3 are shown. Detailed Implementation
[0034] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.
[0035] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.
[0036] One of the specific implementation methods: A method for preparing high-transmittance AlON transparent ceramics by hot isostatic pressing sintering includes the following steps: (1) Preparation: Weigh AlON and Y2O3 powders, pour them into a ball mill jar, add anhydrous ethanol, and ball mill with silicon nitride balls as the grinding medium to obtain a slurry; dry the slurry and sieve it to obtain a mixed powder of AlON and Y2O3; (2) Molding: The dry pressing method is used for molding. First, the mixed powder obtained in step (1) is pre-formed by unidirectional pressure, and then cold isostatic pressing is used to obtain the blank. (3) Pressureless sintering: The green body obtained in step (2) is placed in a high-temperature atmosphere sintering furnace and pressureless sintering is carried out in a nitrogen atmosphere to obtain AlON ceramic pre-sintered body; (4) Hot isostatic pressing sintering: The pre-sintered body obtained in step (3) is placed in a hot isostatic pressing sintering furnace and hot isostatic pressing sintering is carried out in an argon atmosphere to obtain AlON transparent ceramic. (5) Grind and polish the AlON transparent ceramic obtained in step (4).
[0037] Step (1) of the present invention is preferably carried out according to the following method: In step (1), the chemical purity of the pure phase AlON powder is >99.9%; the amount of sintering aid Y2O3 is 0.35%~0.45% of the mass of AlON powder; the D of AlON powder in the AlON and Y2O3 mixed powder is... 50 The particle size is 0.8~2.2 µm, and the particle size distribution ranges from 0.3~10.0 µm; further, the D in the AlON and Y2O3 mixed powder is... 10 The content of particles >0.5 µm and <0.4 µm is <2 vol.%, D 90 The content of particles <5 µm and >5 µm is <2 vol..
[0038] In step (1) of this invention, the ball milling operation is preferably carried out as follows: the pure phase AlON powder and the sintering aid Y2O3 are first ball milled at 170 rpm for 12 h, and then ball milled at 210 rpm for 18 h. After drying, the powder is sieved to obtain D. 50 The desired product is a 1.1 µm mixed powder of AlON and Y2O3; or, pure phase AlON powder and sintering aid Y2O3 are ball-milled at 170 rpm for 12 h, dried, and sieved to obtain D. 50 It is a 2.0 µm mixed powder of AlON and Y2O3.
[0039] In step (2) of the present invention, the mixed powder of AlON and Y2O3 is first pre-formed under 20~70 MPa conditions, and then cold isostatically pressed under 100~180 MPa conditions.
[0040] In step (3) of the present invention, the heating rate of the pressureless sintering is 5~50℃ / min, the sintering temperature is 1790~1850℃, the holding time is 2.0~3.0 h, the relative density of the obtained AlON pre-sintered body is 99.4%~99.6%, and the average grain size is 40~55 µm.
[0041] In step (4) of the present invention, the heating rate of hot isostatic pressing sintering is 10~20℃ / min, the sintering temperature is 1830~1880℃, the pressure is 150~200 MPa, and the holding time is 1.5~2.5 h.
[0042] Example 1 A method for preparing high-transmittance AlON transparent ceramics by hot isostatic pressing sintering includes the following steps: (1) Material preparation: Weigh out single-phase AlON powder with a purity of 99.94% and sintering aid Y2O3, wherein the amount of Y2O3 is 0.4% of the mass of AlON powder; pour the above powder into a ball mill jar, add anhydrous ethanol, use silicon nitride balls as the grinding medium, first ball mill at 170 rpm for 12 h, and then continue ball milling at 210 rpm for 18 h to obtain a slurry; dry the slurry and sieve it to obtain a mixed powder of AlON and Y2O3, the phase composition, particle size distribution and microstructure of which are shown in the figure. Figure 1 ; (2) Molding: The AlON and Y2O3 mixed powder obtained after ball milling is first pre-formed in a steel mold under unidirectional pressure of 50 MPa, and then cold isostatically pressed at 120 MPa to obtain the blank; (3) Pressureless sintering: The green body obtained in step (2) is placed in a high-temperature atmosphere sintering furnace and heated at a rate of 15℃ / min in a nitrogen atmosphere. It is then held at 1790℃ for 2.5 h to obtain an AlON ceramic pre-sintered body, denoted as PS. Its grain morphology is shown in [reference needed]. Figure 2 Transmittance curves and sample photos can be found here. Figure 3 The fracture morphology is shown Figure 4 ; (4) Hot isostatic pressing sintering: The pre-sintered body obtained in step (3) is placed in a hot isostatic pressing sintering furnace and hot isostatic pressing sintering is carried out in an argon atmosphere. The sintering pressure is 180 MPa, the sintering temperature is 1850℃, and the holding time is 2 h.
[0043] (5) The AlON ceramic obtained in step (4) is ground and polished to obtain AlON transparent ceramic, denoted as PS+HIP. Its grain morphology is shown in [reference needed]. Figure 2 Transmittance curves and sample photos can be found here. Figure 3 The fracture morphology is shown Figure 4 .
[0044] Results analysis: Figure 1 (a) is the XRD pattern of AlON powder, where only AlON diffraction peaks were detected and no second phase was observed. Figure 1 (b) is a particle size distribution diagram of AlON powder with added Y2O3 after ball milling. It can be seen that: the D of the powder 50 The particle size is 1.1 μm, with a particle size distribution range of 0.3~5.5 μm, D 10 The content of particles with a diameter of 0.6 µm and a diameter <0.4 µm was 0.5 vol.%, D 90 The content of particles with a diameter of 2.1 µm and a particle size >5 µm is <0.1 vol.%. Figure 1(c) shows that the microstructure SEM image indicates that the powder dispersed well after ball milling.
[0045] Figure 2 The images show the grain morphology of the pre-fired body (PS) and the AlON ceramic (PS+HIP) after hot isostatic pressing. It can be seen that the relative density of the obtained AlON pre-fired body is 99.48% and the average grain size is 45 μm. After hot isostatic pressing, the relative density of the ceramic obtained from the pre-fired body is increased to 99.80% and the average grain size is 58 μm.
[0046] Figure 3 The images show the transmittance curves and sample photos of AlON ceramics after pre-sintering and hot isostatic pressing. It can be seen that hot isostatic pressing significantly improves the transmittance of AlON ceramics, with a maximum transmittance of 85.7% (3600 nm). Moreover, it also has high transmittance in the visible light band, with a transmittance of 80.3% at a wavelength of 500 nm.
[0047] Figure 4 The fracture morphology of the pre-fired body and the AlON ceramic after hot isostatic pressing (HIP) sintering shows that HIP reduces the porosity and pore size of the ceramic, which is the main reason for its improved light transmittance. Simultaneously, this transparent AlON ceramic also exhibits high hardness, with a Vickers hardness of 19.48 ± 0.31 GPa.
[0048] Example 2 Example 2 follows the method of Example 1, except that: In step (1), the ball milling conditions for AlON and Y2O3 powders were 170 rpm for 12 h to obtain the D of the mixed AlON and Y2O3 powder. 50 The particle size is 2.0 μm, and the particle size distribution ranges from 0.4 to 9 μm. 10 The content of particles with a size of 0.9 µm and <0.4 µm was 0 vol.%, D 90 The content of particles with a diameter of 3.8 µm and >5 µm was 1.4 vol.%. Figure 1 (b) and Figure 1 (d)); In step (3), the pressureless sintering temperature is 1850℃.
[0049] Figure 5 The images show the grain morphology of the pre-sintered body and the AlON ceramic after hot isostatic pressing (HIP). It can be seen that the relative density of the pre-sintered AlON body is 99.51% and the average grain size is 52 μm. The relative density of the ceramic after HIP is 99.75% and the average grain size is 67 μm. Figure 6The images show the transmittance curves and sample photographs of the pre-sintered AlON ceramic and the AlON ceramic after hot isostatic pressing (HIP). It can be seen that the maximum transmittance of the AlON ceramic obtained by HIP reaches 86.6% (3800 nm), and the transmittance at 500 nm wavelength is 77.5%. Figure 7 The fracture morphology shows that hot isostatic pressing reduces the porosity and pore size of the ceramic. The Vickers hardness of the AlON transparent ceramic obtained in this embodiment is 18.61 ± 0.26 GPa.
[0050] Comparative Example 1 Comparative Example 1 follows the method of Example 1, except that in step (1), the amount of Y2O3 is 0.2 wt.%. The transmittance curves and sample photographs of the pre-fired body and the AlON ceramic obtained by hot isostatic pressing sintering in this comparative example are shown below. Figure 8 It can be seen that the maximum transmittance of AlON ceramics obtained by hot isostatic pressing sintering is 76.3%, and the transmittance at a wavelength of 500 nm is 68.1%.
[0051] Comparative Example 2 Comparative Example 2 follows the method of Example 1, except that in step (1), the amount of Y2O3 is 0.5 wt.%. The transmittance curves and sample photographs of the pre-sintered body and the AlON ceramic obtained by hot isostatic pressing sintering in this comparative example are shown below. Figure 9 It can be seen that the maximum transmittance of AlON ceramics obtained by hot isostatic pressing sintering is 85.4%, and the transmittance at a wavelength of 500 nm is 25.7%.
[0052] Comparative Example 3 Comparative Example 3 follows the method of Example 1, except that: in step (1), the amount of Y2O3 is 0.1 wt.%; AlON and Y2O3 powders are first ball-milled at 170 rpm for 12 h, then ball-milled at 210 rpm for 18 h, and finally ball-milled at 250 rpm for 24 h to obtain D of the mixed powder of AlON and Y2O3. 50 The transmittance is 0.5 μm. The transmittance curves and sample photographs of the pre-sintered body and the AlON ceramic obtained by hot isostatic pressing sintering in this comparative example are shown below. Figure 10 It can be seen that the maximum transmittance of AlON ceramics obtained by hot isostatic pressing sintering is 85.1%, and the transmittance at a wavelength of 500 nm is 44.9%.
Claims
1. A method for preparing high-transmittance AlON transparent ceramics by hot isostatic pressing sintering, characterized in that: Pure-phase AlON powder and sintering aid Y2O3 were ball-milled, dried, and sieved to obtain a mixed AlON and Y2O3 powder. This powder was then dry-pressed and pressurelessly sintered in a nitrogen atmosphere to obtain an AlON pre-sintered body. Finally, it was hot isostatically pressed in an argon atmosphere to obtain AlON transparent ceramics. The D of the AlON and Y2O3 mixed powder... 50 The particle size ranges from 0.8 to 2.2 µm, with a particle size distribution range of 0.3 to 10.0 µm.
2. The preparation method according to claim 1, characterized in that: D in AlON and Y2O3 mixed powder 10 The content of particles >0.5 µm and <0.4 µm is <2 vol.%, D 90 The content of particles <5 µm and >5 µm is <2 vol.%.
3. The preparation method according to claim 1, characterized in that: The sintering aid Y2O3 is added at a concentration of 0.35% to 0.45% of the AlON powder mass.
4. The preparation method according to claim 1, characterized in that: The relative density of the AlON pre-burnt body is 99.4%~99.6%, and the average grain size is 40~55 µm.
5. The preparation method according to claim 1, characterized in that: The mixed powder of AlON and Y2O3 was first pre-formed under 20~70 MPa conditions, and then cold isostatically pressed under 100~180 MPa conditions.
6. The preparation method according to claim 1, characterized in that: The pressureless sintering process involves a heating rate of 5~50℃ / min, a sintering temperature of 1790~1850℃, and a holding time of 2.0~3.0 h.
7. The preparation method according to claim 1, characterized in that: The heating rate of the hot isostatic pressing sintering is 10~20℃ / min, the sintering temperature is 1830~1880℃, the pressure is 150~200 MPa, and the holding time is 1.5~2.5 h.
8. The preparation method according to claim 1, characterized in that: The preparation method of the AlON transparent ceramic includes a post-processing step: grinding and polishing the obtained AlON transparent ceramic.
9. The AlON transparent ceramic prepared by the method according to any one of claims 1 to 8.
10. The AlON transparent ceramic according to claim 9, characterized in that: The AlON transparent ceramic has a relative density of 99.7%~99.9%, an average grain size of 55~70 µm, a maximum transmittance of 85%~87% in the 3500~3900 nm wavelength band, a transmittance of 77%~81% at a wavelength of 500 nm, and a Vickers hardness of 18~20 GPa.