Method for preparing high-transmittance AlON transparent ceramic without adding sintering aid

Abstract

The invention relates to a method for preparing high-transmittance AlON transparent ceramic without adding a sintering aid, and belongs to the field of preparation of transparent ceramic materials. The invention relates to a method for preparing high-transmittance AlON transparent ceramic without adding a sintering aid, which comprises the following steps: molding AlON powder with D50 of 0.4-1.2 m and particle size distribution range of 0.1-6.0 m to obtain a green body, and placing the green body in a nitrogen environment for pressureless sintering to obtain an AlON ceramic pre-sintered body; and placing the pre-sintered body in an argon environment, and carrying out hot isostatic pressing sintering to obtain the AlON transparent ceramic. According to the method, the pressureless sintering technology and the hot isostatic pressing sintering technology are combined, sintering aids are not added, the process controllability is high, operation is easy, the sintering temperature is low, the heat preservation time is short, efficiency is high, the cost is low, the energy-saving effect is good, and industrialization is easy to achieve.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing high-transmittance AlON transparent ceramics without adding sintering aids, and belongs to the field of transparent ceramic material preparation. BACKGROUND

[0002] Aluminum oxynitride (gamma-AlON) with a cubic spinel structure has the characteristics of good light transmittance and excellent mechanical properties, and also has the advantage of optical isotropy, and is an ideal structural-functional integrated transparent ceramic material. In addition, compared with single crystal materials, the polycrystalline characteristics of AlON have significant advantages in the preparation of large-size and complex-shaped components. Therefore, AlON transparent ceramics have broad application prospects in military and civilian fields such as infrared windows, transparent armor, transparent panels of precision instruments and meters, safety protection of special equipment, etc.

[0003] Obtaining high density is a necessary condition for realizing high light transmittance of ceramic materials. In the process of sintering transparent ceramics by using AlON powder, sintering aids are often added to reduce the sintering temperature and promote the discharge of pores. However, the reciprocal phase transition behavior between AlON and Al2O3+AlN and the phenomenon of easy grain coarsening undoubtedly increase the difficulty of subsequent pore discharge. In particular, sintering aids often have contradictions in affecting the decomposition degree of AlON and the later densification sintering. For example: Y2O3, which has a significant effect on promoting densification, but it also causes excessive decomposition of AlON in the early sintering and causes particles to coarsen prematurely, thereby making it difficult to densify and sinter in the later stage, and long-time holding is required to obtain high density and high light transmittance; MgO and La2O3 can inhibit the decomposition of AlON in the early sintering, but they are not conducive to the later densification. On the other hand, sintering aids may also remain in the grain boundaries, causing a decrease in transmittance. Therefore, if high densification sintering of AlON is achieved without adding sintering aids, it is very beneficial to obtain high light transmittance ceramics.

[0004] Hot isostatic pressing sintering makes it possible to obtain high-density transparent ceramics without relying on sintering aids, and through hot isostatic pressing sintering, the grain size can also be effectively controlled, which is very beneficial to the mechanical properties of ceramic materials. Zheng et al. prepared AlON transparent ceramics by hot isostatic pressing sintering of AlON powder with different chemical compositions (Al (8+x) / 3 O 4- x N x , x= 0.299~0.575). A pre-calcined body was first prepared by pressureless sintering at 1900°C for 2 h. This was then hot isostatically pressed (HIP) in a 180 MPa nitrogen atmosphere at 1880°C for 5 h to produce a high-density AlON transparent ceramic [Journal of the European Ceramic Society 42(2022) 1362–1369]. This indicates that the use of HIP sintering technology can effectively increase the relative density of AlON ceramics, thereby achieving better light transmittance. However, given the characteristics of HIP equipment, the sintering temperature and holding time should be further controlled to reduce equipment loss, improve efficiency, and reduce costs. Summary of the Invention

[0005] The present invention provides a method for preparing high-transmittance AlON transparent ceramics without adding sintering aids. Specifically, pure-phase AlON powder is used as raw material, its particle size distribution is controlled by ball milling, and no sintering aid is added. A high-density pre-calcined body is first prepared by a pressureless sintering method in a nitrogen environment, and then AlON transparent ceramics with high light transmittance and high mechanical properties are obtained by hot isostatic pressing. This method does not use sintering aids during the sintering process, which can effectively inhibit the growth of particles / grains in the early stage of pressureless sintering, laying a good microstructural foundation for subsequent high-densification sintering to obtain a high-density and fine-grained pre-calcined body; further, the relative density of the ceramic is improved by hot isostatic pressing, and the grain growth is limited. The present invention obtains an AlON ceramic pre-calcined body with a high relative density and a small grain size by pressureless sintering at a relatively low sintering temperature, and after hot isostatic pressing, AlON transparent ceramics with high transmittance, high hardness and good toughness can be obtained. This method has simple process control and is suitable for industrial production.

[0006] A method for preparing high-transmittance AlON transparent ceramics without adding sintering aids comprises the following steps: 50 The green body obtained by forming AlON powder with a particle size distribution range of 0.4-1.2 μm and a particle size distribution range of 0.1-6.0 μm is placed in a nitrogen environment for pressureless sintering to obtain an AlON ceramic pre-calcined body; then the pre-calcined body is placed in an argon environment for hot isostatic pressing sintering to obtain AlON transparent ceramics.

[0007] Preferably, the relative density of the calcined body is 97% to 99%, and the average grain size is 10 to 30 μm.

[0008] Preferably, the AlON powder is first dry-pressed for preforming and then cold isostatically pressed to obtain a green body, wherein the preforming is carried out under 10-60 MPa and the cold isostatic pressing is carried out under 100-150 MPa.

[0009] Preferably, the temperature rising rate of the pressureless sintering is 5-40℃ / min, the sintering temperature is 1780-1850℃, and the holding time is 1.5-3.0 h.

[0010] Preferably, the temperature rising rate of the hot isostatic sintering is 10-30℃ / min, the sintering temperature is 1850-1900℃, the pressure is 150-200 MPa, and the holding time is 1.5-3.0 h.

[0011] Preferably, the pure-phase AlON powder is ball-milled in anhydrous ethanol as a liquid medium and silicon nitride balls as grinding media to regulate the particle size distribution and mixing, thereby obtaining a slurry; the slurry is dried and sieved to obtain AlON powder with D 50 0.4-1.2 µm and a particle size distribution range of 0.1-6.0 µm.

[0012] Further, the D 10 >0.3 µm, and the content of particles with <0.2 µm is <3 vol.%, the D 90 <3 µm, and the content of particles with >3 µm is <1 vol.%.

[0013] Further, the diameters of the grinding balls are 2, 4 and 8 mm, the gradation is 0-8:3:1, the ball-to-material ratio is 10-15:1, the rotation speed of the ball mill is 150-250 rpm, and the ball milling time is 30-60 h.

[0014] Preferably, the method for preparing the AlON transparent ceramic comprises a post-processing step of grinding and polishing the obtained AlON transparent ceramic.

[0015] Another object of the present application is to provide an AlON transparent ceramic prepared by the above method.

[0016] Further, the relative density of the AlON transparent ceramic is 99.4%-99.9%, the average grain size is 12-32 µm, the infrared transmittance is 83%-88%, the HV is 17-19 GPa, the K IC 2-3 MPa·m 1 / 2 .

[0017] The present application has the following beneficial effects: the method uses pure-phase AlON powder, does not add sintering aids, adjusts the particle size distribution of the powder by ball milling to improve the densification sintering ability thereof, then prepares a pre-sintered body with high density and small grain size by low-temperature pressureless sintering, and then uses hot isostatic pressing to prepare AlON transparent ceramic with high light transmittance and excellent mechanical properties. The method does not use sintering aids, which is not only conducive to ensuring the purity of the grain boundary and thus obtaining high light transmittance, but also conducive to controlling the grain growth, which can provide good microstructure conditions for subsequent densification sintering and ensure the mechanical properties of the ceramic. The method effectively improves the densification sintering ability of the AlON powder by adjusting the particle size distribution thereof, and obtains a pre-sintered body with high density and small grain size at a relatively low pressureless sintering temperature, and then obtains AlON transparent ceramic with high transmittance and high mechanical properties at a relatively low temperature and a relatively short holding time of hot isostatic pressing. In addition, the method combines pressureless sintering and hot isstatic pressing technology, has strong controllability, simple operation, low sintering temperature, short holding time, high efficiency, low cost, good energy-saving effect, and is easy to realize industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The phase composition of the AlON powder.

[0019] Figure 2 The particle size distribution and micro-morphology of the AlON powder in Examples 1, 2, 3 and 4: (a) particle size distribution; (b) SEM images of the powder in Examples 1 and 2; (c) SEM images of the powder in Examples 3 and 4.

[0020] Figure 3 The fracture SEM images of the samples in the temperature rising process of pressureless sintering in Examples 1 and 2.

[0021] Figure 4 The densification progress curves of the samples in the temperature rising process of pressureless sintering in Examples 1, 2, 3 and 4.

[0022] Figure 5 The transmittance curves and sample photos of the ceramic after hot isostatic pressing sintering in Examples 1 and 2.

[0023] Figure 6 The fracture SEM images of the samples in the temperature rising process of pressureless sintering in Examples 3 and 4.

[0024] Figure 7 The transmittance curves and sample photos of the AlON transparent ceramic obtained in Examples 3 and 4. DETAILED DESCRIPTION

[0025] The following non-limiting examples can make those skilled in the art more fully understand the present application, but do not limit the present application in any way.

[0026] The test methods described in the following examples are conventional methods; the reagents and materials are commercially available unless otherwise specified.

[0027] One of the embodiments specifically implements the following: A method for preparing high-transmittance AlON transparent ceramic without adding sintering aids, comprising the following steps: (1) Ball milling: Put pure-phase AlON powder into a ball mill tank, use anhydrous ethanol as a liquid medium, and silicon nitride balls as a grinding medium, control the diameter, gradation, and ball-to-material ratio of the grinding balls, control the rotation speed of the ball mill and the ball milling time, and obtain a slurry; dry and sieve the slurry to obtain AlON powder with a particle size D 50 of 0.4-1.2 µm and a particle size distribution range of 0.1-6.0 µm; (2) Forming: dry-press pre-forming and cold isostatic pressing forming are sequentially performed on the AlON powder obtained in step (1) to obtain a green body; (3) Pressureless sintering: the green body obtained in step (2) is placed into a high-temperature atmosphere sintering furnace and sintered under a nitrogen atmosphere without pressure to obtain an AlON ceramic pre-sintered body; (4) Hot isostatic pressing sintering: the pre-sintered body obtained in step (3) is placed into a hot isostatic pressing sintering furnace and sintered under an argon atmosphere to obtain an AlON transparent ceramic; (5) Processing: the AlON transparent ceramic obtained in step (4) is ground and polished.

[0028] The step (1) of the application is preferably performed according to the following method: the pure-phase AlON powder used in step (1) has a particle size D 10 >0.3 µm, and the content of particles with a size <0.2 µm is <3 vol.%; the particle size D 90 <3 µm, and the content of particles with a size >3 µm is <1 vol.%; the diameter of the grinding balls is 2, 4, and 8 mm, the gradation is 0-8:3:1, the ball-to-material ratio is 10-15:1, the rotation speed of the ball mill is 150-250 rpm, and the ball milling time is 30-60 h.

[0029] The pre-forming in step (2) of the application is performed under a pressure of 10-60 MPa, and the cold isostatic pressing forming is completed under a pressure of 100-150 MPa.

[0030] The heating rate of the pressureless sintering in step (3) of the application is 5-40 ℃ / min, the sintering temperature is 1780-1850 ℃, and the holding time is 1.5-3.0 h.

[0031] The relative density of the AlON ceramic pre-sintered body in step (3) of the application is 97%-99%, and the average grain size is 10-30 µm.

[0032] The heating rate of the hot isostatic pressing sintering in step (4) is 10-30 ℃ / min, the sintering temperature is 1850-1900 ℃, the pressure is 150-200 MPa, and the holding time is 1.5-3.0 h.

[0033] Example 1 A method for preparing high-transmittance AlON transparent ceramic without adding sintering aids, comprising the following steps: (1) Ball milling: pure-phase AlON powder is placed in a ball mill tank, anhydrous ethanol is used as a liquid medium, silicon nitride balls with diameters of 2, 4 and 8 mm are used as grinding media, the ball size distribution is 1.6:3:1, the ball-to-material ratio is 10:1, ball milling is carried out at 200 rpm for 30 h to obtain a slurry; the slurry is dried and sieved to obtain AlON powder. The XRD pattern of the pure-phase AlON powder is shown in Figure 1 , only the diffraction peaks of AlON are detected. The particle size distribution and micro-morphology of the powder after ball milling are shown in Figure 2 , it can be seen that the D 50 of the powder after ball milling is 1.1 μm, and the particle size distribution range is 0.3-5.5 μm.

[0034] (2) Forming: the AlON powder obtained after ball milling is first dry-pressed pre-formed at 50 MPa, and then cold isostatic pressed to form a green body.

[0035] (3) Pressureless sintering: the green body is placed in a high-temperature atmosphere sintering furnace, heated at 15 ℃ / min in a nitrogen atmosphere, and held at 1790 ℃ for 2.5 h to obtain an AlON pre-sintered body, the relative density of the obtained pre-sintered body is 98.11%, and the average grain size is 12.65 μm.

[0036] (4) Hot isostatic pressing sintering: the pre-sintered body is placed in a hot isostatic pressing sintering furnace, held at 1850 ℃ for 2 h under the condition of 180 MPa argon, to obtain an AlON transparent ceramic, the relative density of the obtained ceramic is 99.59%, and the average grain size is 22.29 μm. The optical and mechanical property test results show that the AlON transparent ceramic obtained by hot isostatic pressing sintering has very high infrared transmittance, up to 88% (2 mm thick), and at the same time has very good mechanical properties, HV=18.18±0.13 GPa, K IC =2.15±0.21 MPa·m 1 / 2 . Figure 3 and Figure 4 are micro-morphology and densification process curve diagrams of the sample during the heating process, it can be observed that the grains gradually grow during the temperature rising from 1500 ℃ to 1800 ℃, and there is no abnormal growth phenomenon, and the densification process is smooth. Figure 5The transmittance curve and sample photo of the prepared AlON transparent ceramic.

[0037] Example 2 Example 2 was prepared according to the method of Example 1, except that the temperature for preparing the presintered body by pressureless sintering was 1850℃. The relative density of the AlON presintered body obtained by pressureless sintering was 98.87%, the average grain size was 25.04 μm; the relative density of the AlON transparent ceramic obtained after hot isostatic pressing sintering was 99.49%, the average grain size was 29.02 μm, the infrared transmittance was 83%, HV = 17.59±0.25 GPa, K IC = 2.53±0.14 MPa·m 1 / 2 . The transmittance curve and sample photo of the prepared AlON transparent ceramic are shown in Figure 5 .

[0038] Example 3 Example 3 was prepared according to the method of Example 1, except that the pure phase AlON powder was placed in a ball mill tank, anhydrous ethanol was used as the liquid medium, silicon nitride balls with diameters of 2, 4 and 8 mm were used as the grinding medium, the ball size distribution was 7.5 : 3 : 1, the ball-to-material ratio was 14 : 1, and the ball milling was carried out at 230 rpm for 60 h. The particle size distribution and micro morphology of the AlON powder after ball milling are shown in Figure 2 . It can be seen that the D 50 of the powder after ball milling was 0.5 μm, and the particle size distribution range was 0.13~1.35 μm. The micro morphology of the sample during the temperature rising process is shown in Figure 6 . The grains gradually grew during the temperature rising process, there was no abnormal growth phenomenon, and the densification was stable during this process. Figure 4 The relative density of the AlON presintered body obtained by pressureless sintering was 97.38%, the average grain size was 11.71 μm; the relative density of the AlON transparent ceramic obtained after hot isostatic pressing sintering was 99.58%, the average grain size was 14.49 μm, the infrared transmittance was 88%, HV = 18.48±0.31 GPa, K IC = 2.01±0.23 MPa·m 1 / 2 . The transmittance curve and sample photo of the prepared AlON transparent ceramic are shown in Figure 7 .

[0039] Example 4 Example 4 was prepared according to the method of Example 3, except that the pressureless sintering temperature was 1850℃. The micro morphology of the sample during the temperature rising process is shown in Figure 6 . It can be seen that the grains gradually grew during the temperature rising process, there was no abnormal growth phenomenon, and the densification was stable during this process. Figure 4). The relative density of the obtained AlON pre-sintered body was 98.61%, and the average grain size was 16.67 μm; the relative density of the AlON transparent ceramic obtained after hot isostatic sintering was 99.46%, the average grain size was 24.92 μm, the infrared transmittance was 83%, HV = 17.71 ± 0.11 GPa, K IC = 2.42 ± 0.19 MPa·m 1 / 2 . The transmittance curve of the prepared AlON transparent ceramic and the sample photo are shown in Figure 7 .

Claims

1. A method for preparing high-transmittance AlON transparent ceramics without adding a sintering aid, characterized by: D 50 The green body obtained by forming AlON powder with a particle size distribution range of 0.4-1.2 μm and a particle size distribution range of 0.1-6.0 μm is placed in a nitrogen environment for pressureless sintering to obtain an AlON ceramic pre-calcined body; then the pre-calcined body is placed in an argon environment for hot isostatic pressing sintering to obtain AlON transparent ceramics.

2. The preparation method according to claim 1, wherein: The relative density of the AlON ceramic calcined body is 97% to 99%, and the average grain size is 10 to 30 μm.

3. The preparation method according to claim 1, wherein: The heating rate of the pressureless sintering is 5-40°C / min, the sintering temperature is 1780-1850°C, and the holding time is 1.5-3.0 h.

4. The preparation method according to claim 1, wherein: The heating rate of the hot isostatic pressing sintering is 10-30°C / min, the sintering temperature is 1850-1900°C, the pressure is 150-200 MPa, and the holding time is 1.5-3.0 h.

5. The preparation method according to claim 1, wherein: The AlON powder is first dry-pressed to preform, and then cold isostatically pressed to obtain a green body, wherein the preforming is carried out at 10-60 MPa, and the cold isostatic pressing is carried out at 100-150 MPa.

6. The preparation method according to claim 1, wherein: Pure AlON powder was ball-milled with anhydrous ethanol as liquid medium and silicon nitride balls as grinding medium to adjust the particle size distribution and mix to obtain slurry; the slurry was dried and sieved to obtain D 50 The AlON powder has a particle size of 0.4~1.2 μm and a particle size distribution range of 0.1~6.0 μm.

7. The preparation method according to claim 6, characterized in that: The D of the pure phase AlON powder 10 >0.3 µm and <0.2 µm particles <3 vol.%, D 90 <3 µm, and the content of particles >3 µm is <1 vol.%.

8. The preparation method according to claim 6, characterized in that: The diameters of the grinding balls are 2, 4, and 8 mm, the gradation is 0-8:3:1, the ball-to-material ratio is 10-15:1, the ball mill speed is 150-250 rpm, and the ball milling time is 30-60 h.

9. The preparation method according to claim 1, wherein: The preparation method of the AlON transparent ceramic comprises a post-processing step of grinding and polishing the obtained AlON transparent ceramic.

10. An AlON transparent ceramic prepared by the method of claim 1, characterized in that: The relative density of the AlON transparent ceramic is 99.4% to 99.9%, the average grain size is 12 to 32 μm, the infrared transmittance is 83% to 88%, the HV is 17 to 19 GPa, and the K IC 2~3 MPa·m 1 / 2 .

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