An in-situ self-generated YAG phase reinforced AlON ceramic material and its preparation method

Abstract

This invention discloses an in-situ self-generated YAG phase reinforced AlON ceramic material and its preparation method. The method uses Al₂O₃ and AlN as raw materials and Y₂O₃ as an additive, successfully preparing high-performance AlON ceramics using a three-stage SPS process. Through precise control of the sintering process, a YAG liquid phase is generated during ceramic preparation. Further process optimization ensures that this liquid phase is uniformly distributed between powder particles and completely dissolved in the ceramic matrix at the end of sintering. The introduction of the YAG liquid phase significantly lowers the reaction temperature between Al₂O₃ and AlN, accelerates material densification, and induces a grain refinement strengthening effect. Simultaneously, the YAG liquid phase dissolves in the ceramic matrix in the later stages of sintering, triggering a solid solution strengthening effect. While significantly improving the mechanical properties of AlON ceramics, this method achieves low-temperature and rapid material preparation, reducing energy consumption and production costs, and has broad industrial application prospects.

Description

Technical Field

[0001] This invention relates to an in-situ self-generated YAG phase reinforced AlON ceramic material and its preparation method, belonging to the field of ceramic material preparation. Background Technology

[0002] Aluminum oxynitride (AlON) ceramics have shown great application potential in fields such as police explosion protection, safety gear, high-pressure sodium lamps, and special instrument manufacturing due to their high hardness, high strength, excellent wear resistance, good corrosion resistance and oxidation resistance, as well as excellent optical transparency (covering the near ultraviolet to mid-infrared band). They are also one of the ideal materials for making transparent armor and infrared windows.

[0003] Currently, the mainstream method for preparing AlON ceramics is a two-step process: first, AlON powder is synthesized, and then AlON ceramics are obtained through high-temperature densification sintering. The common sintering method is pressureless sintering, with sintering temperatures typically above 1800℃. Patent CN112299861A synthesizes pure-phase AlON powder using the traditional carbothermal reduction nitridation method. After ball milling the powder, a certain amount of γ-Al₂O₃ is added and mixed uniformly. AlON ceramic green bodies are then prepared by dry pressing, followed by pressureless sintering at 1880℃ for 8 hours to obtain AlON ceramics. Patent CN109516813A discloses a method for preparing high-transmittance AlON ceramics through direct water injection molding. This method disperses pure-phase AlON powder in deionized water containing a dispersant to prepare a slurry, then prepares a green body through slurry injection molding, and finally performs pressureless sintering in a carbon furnace at 1850–1900℃ for 1.5–8 hours to obtain AlON ceramics. Patent CN113135759A discloses a method for preparing AlON ceramic powder using solution combustion synthesis, followed by pressureless sintering at 1800–2000℃ for 1–20 hours to prepare AlON ceramics. However, these methods generally suffer from drawbacks such as complex processes, high costs, and low production efficiency. Furthermore, limitations imposed by excessively high sintering temperatures and prolonged holding times during preparation result in large ceramic grain sizes and poor mechanical properties, failing to meet practical application requirements. To obtain high-quality AlON ceramics, sintering aids are typically added during the preparation process. However, due to the limited amount of sintering aids added, the problem of their uniform distribution within the ceramic matrix is ​​difficult to solve, thus affecting the performance of the final product. Moreover, the effectiveness of sintering aids is closely related to the sintering process of AlON ceramics.

[0004] In recent years, spark plasma sintering (SPS) technology has gradually become an important method for preparing high-performance ceramic materials due to its advantages such as rapid heating rate, short sintering time, low sintering temperature, rapid cooling, energy saving, and environmental friendliness. Compared with traditional pressureless sintering, hot pressing, and hot isostatic pressing, SPS technology can achieve the preparation of high-density ceramic materials at lower temperatures and has better microstructure control capabilities. Although SPS technology has shown significant potential in reducing sintering temperature and suppressing grain growth, how to further optimize the SPS process flow and parameters to meet the preparation requirements of AlON ceramics under specific sintering aid conditions remains an urgent technical challenge. Summary of the Invention

[0005] This invention aims to provide an in-situ self-generated YAG phase reinforced AlON ceramic material and its preparation method, overcoming the shortcomings of existing technologies. By precisely controlling the SPS process, the Y2O3 sintering aid reacts with Al2O3 during sintering to generate a YAG liquid phase, ensuring that this liquid phase is uniformly distributed among the powder particles. The introduction of the YAG liquid phase significantly lowers the reaction temperature between Al2O3 and AlN, accelerating the densification process of AlON ceramics and enabling successful preparation at lower sintering temperatures. This effectively inhibits grain growth and significantly enhances the grain refinement strengthening effect of the material. Simultaneously, the YAG liquid phase dissolves into the AlON ceramic at the end of sintering, further triggering the solid solution strengthening effect and significantly improving the mechanical properties of the AlON ceramic.

[0006] The present invention discloses a method for preparing in-situ self-generated YAG phase reinforced AlON ceramic materials, which mainly includes the following steps:

[0007] Step 1) Select Al2O3 powder and AlN powder with a purity greater than 99% and a particle size range of 20-500nm as raw materials, with a mass ratio of 0.79:0.21.

[0008] Step 2) Add Y2O3 with a purity greater than 99% and a particle size range of 10-100nm as a single sintering aid, with a content of 0.2wt% to 2wt%.

[0009] Step 3) Place the raw material powder and sintering aid together into a ball mill jar, and use an alternating forward and reverse ball milling process to mix and disperse the powder. The ball mill speed is 100-400 r / min, the ball milling time is 5-30 h, and the ball mill rotation direction is changed every 30 min;

[0010] Step 4) Load the uniformly dispersed mixed powder or compact after ball milling into a carbon-carbon mold;

[0011] Step 5) Place the assembled mold into the SPS furnace chamber for vacuum sintering to prepare AlON ceramics. The SPS sintering process consists of three stages. In the first stage, the temperature is raised to a predetermined value at a relatively fast heating rate to ensure the smooth formation of the YAG liquid phase. In the second stage, while maintaining the temperature of the first stage, pressure is applied to the sintered body at a certain pressurization rate to ensure that the YAG liquid phase is uniformly distributed between the powder particles. In the third stage, the temperature and pressure are further increased to a predetermined value at a slower heating rate and a faster pressurization rate, and held at that temperature for a certain time to ensure the smooth solidification of the YAG liquid phase and finally obtain single-phase AlON ceramics. The specific sintering parameters are as follows: First, the temperature is increased to 1200–1400℃ at a heating rate of 150–300℃ / min; then, while keeping the temperature constant, the pressure is increased to 10–30MPa at a pressurization rate of 0.02–0.06MPa / s; finally, the temperature and pressure are increased to 1500–1700℃ and 50–100MPa respectively at a heating rate of 30–80℃ / min and a pressurization rate of 0.1–0.3MPa / s, and held for 5–20 min.

[0012] The density of the in-situ self-generated YAG phase reinforced AlON ceramic materials is greater than 99.8%, and the hardness is greater than 17.5 GPa.

[0013] The beneficial effects of this invention include:

[0014] (1) Through precise control of the SPS process, the YAG liquid phase was successfully generated and uniformly distributed in the gaps between Al2O3 and AlN powder particles during the preparation of AlON ceramics. The introduction of the YAG liquid phase significantly reduced the reaction temperature between Al2O3 and AlN, accelerated the densification process of AlON ceramics, and thus achieved rapid preparation of high-density AlON ceramics at a lower temperature, effectively inhibiting grain growth and promoting a significant fine-grain strengthening phenomenon in the material. In the first stage of SPS sintering, a relatively fast heating rate was used to rapidly heat the material to the required temperature, which stimulated the sintering driving force, enhanced the diffusion on the surface of the powder particles, improved the reactivity, and ensured that the Y2O3 sintering aid reacted with the Al2O3 powder to generate the YAG liquid phase. In the second stage, by slowly increasing the pressure while keeping the temperature of the first stage constant, the generated YAG liquid phase was dispersed to the maximum extent and uniformly distributed in the gaps between the powder particles. This process fully utilized the wettability and fluidity of the YAG liquid phase, promoted the rearrangement of powder particles and the elimination of pores, and accelerated the densification process of the material. Meanwhile, it can significantly reduce the sintering activation energy of the powder, effectively ensuring a decrease in the solid-phase reaction temperature between Al2O3 and AlN. In the third stage of sintering, while ensuring a uniform distribution of the liquid phase, further heating and pressurization are applied to ensure the formation of the AlON phase. The slower heating rate in this stage helps stabilize the thermal field, ensuring the uniformity of the internal temperature of the material and preventing over-burning and melting of AlON ceramics. Simultaneously, the slower heating rate provides sufficient time for the solid-phase reaction between Al2O3 and AlN, ensuring the complete progress of the reaction. The rapid pressurization process provides a strong mechanical driving force for the sintering of AlON ceramics, accelerating the densification process of the powder and promoting the solid solution of the YAG liquid phase, thus avoiding the residue of the second phase in the AlON ceramic.

[0015] (2) Due to the differences in lattice constant and ionic radius between YAG and AlON ceramics, the incorporation of YAG into AlON ceramics causes lattice distortion, thereby increasing the internal stress of the material. Furthermore, the solid solution of YAG also forms localized chemical inhomogeneities or atomic clusters in the lattice. These regions can act as barriers to dislocation movement, hindering dislocation slip and increasing dislocation density. These mechanisms work together to significantly improve the mechanical properties of AlON ceramics. Attached Figure Description

[0016] Figure 1 The fracture morphology of AlON ceramic after the first stage of SPS sintering in Example 1;

[0017] Figure 2 The fracture morphology of AlON ceramic after the second stage of SPS sintering in Example 1;

[0018] Figure 3The fracture morphology of AlON ceramic after the third stage of SPS sintering in Example 1;

[0019] Figure 4 The fracture morphology of AlON ceramic after the first stage of SPS sintering in Example 2;

[0020] Figure 5 The fracture morphology of AlON ceramic after the second stage of SPS sintering in Example 2;

[0021] Figure 6 The fracture morphology of AlON ceramic after the third stage of SPS sintering in Example 2 is shown.

[0022] Figure 7 The fracture morphology of AlON ceramic after the first stage of SPS sintering in Example 3;

[0023] Figure 8 The fracture morphology of AlON ceramic after the second stage of SPS sintering in Example 3;

[0024] Figure 9 The fracture morphology of AlON ceramic after the third stage of SPS sintering in Example 3; Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but these descriptions are not intended to limit the scope of the invention.

[0026] Example 1

[0027] Step 1) Select Al2O3 and AlN powders with a purity of 99.99% and a particle size of 20nm as raw materials, with a mass ratio of 0.79:0.21;

[0028] Step 2) Add Y2O3 with a purity of 99.99% and a particle size of 10nm as a sintering aid, with a content of 2wt%.

[0029] Step 3) Place the raw material powder and sintering aid together into a ball mill jar, and use an alternating forward and reverse ball milling process to mix and disperse the powder. The ball mill speed is 100 r / min, the ball milling time is 30 h, and the ball mill rotation direction is changed every 30 min;

[0030] Step 4) The uniformly dispersed mixed powder after ball milling is loaded into a carbon-carbon mold, and the mold and the powder are separated by graphite paper.

[0031] Step 5) Place the assembled mold into the SPS furnace chamber for vacuum sintering to obtain AlON ceramic. The SPS sintering process adopts a three-stage sintering method. In the first stage of sintering, the temperature is increased to 1400℃ at a heating rate of 300℃ / min; in the second stage of sintering, while keeping the temperature constant at 1400℃, the pressure is increased to 30MPa at a pressurization rate of 0.06MPa / s; in the third stage of sintering, the temperature and pressure are increased to 1500℃ and 100MPa respectively at a heating rate of 30℃ / min and a pressurization rate of 0.3MPa / s, and held for 20min.

[0032] The AlON ceramics prepared in this embodiment were tested, and the results are as follows:

[0033] (1) After the first stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 1 As shown, although there is a clear YAG liquid phase inside the sample (the white phase marked by the white dashed line), this liquid phase is not uniformly dispersed in the gaps between the powder particles, and there is obvious agglomeration.

[0034] (2) After the second stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 2 As shown in the figure, the YAG liquid phase is uniformly distributed among the powder particles.

[0035] (3) After the third stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 3 As shown, the overall structure of the ceramic is uniform and dense, and no YAG phase was found, indicating that YAG has been completely dissolved into the AlON ceramic.

[0036] (4) In this embodiment, the density of AlON ceramic is 99.91% and the hardness is 17.7 GPa.

[0037] Example 2

[0038] Step 1) Select Al2O3 and AlN powders with a purity of 99.99% and a particle size of 200nm as raw materials, with a mass ratio of 0.79:0.21;

[0039] Step 2) Add Y2O3 with a purity of 99.99% and a particle size of 50nm as a sintering aid, with a content of 1wt%.

[0040] Step 3) Place the raw material powder and sintering aid together into a ball mill jar, and use an alternating forward and reverse ball milling process to mix and disperse the powder. The ball mill speed is 250 r / min, the ball milling time is 20 h, and the ball mill rotation direction is changed every 30 min;

[0041] Step 4) is the same as in Example 1;

[0042] Step 5) Place the assembled mold into the SPS furnace chamber for vacuum sintering to obtain AlON ceramic. The SPS sintering process adopts a three-stage sintering method. In the first stage of sintering, the temperature is increased to 1300℃ at a heating rate of 200℃ / min; in the second stage of sintering, while keeping the temperature constant at 1300℃, the pressure is increased to 20MPa at a pressurization rate of 0.04MPa / s; in the third stage of sintering, the temperature and pressure are increased to 1600℃ and 75MPa respectively at a heating rate of 50℃ / min and a pressurization rate of 0.2MPa / s, and held for 10min.

[0043] The AlON ceramics prepared in this embodiment were tested, and the results are as follows:

[0044] (1) After the first stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 4 As shown, although there is a clear YAG liquid phase inside the sample (the white phase marked by the white dashed line), this liquid phase is not uniformly dispersed in the gaps between the powder particles, and there is obvious agglomeration.

[0045] (2) After the second stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 5 As shown in the figure, the YAG liquid phase is uniformly distributed among the powder particles.

[0046] (3) After the third stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 6 As shown, the overall structure of the ceramic is uniform and dense, and no YAG phase was found, indicating that YAG has been completely dissolved into the AlON ceramic.

[0047] (4) In this embodiment, the density of AlON ceramic is 99.89% and the hardness is 17.6 GPa.

[0048] Example 3

[0049] Step 1) Select Al2O3 and AlN powders with a purity of 99.99% and a particle size of 500nm as raw materials, with a mass ratio of 0.79:0.21;

[0050] Step 2) Add Y2O3 with a purity of 99.99% and a particle size of 100nm as a sintering aid, with a content of 0.2wt%.

[0051] Step 3) Place the raw material powder and sintering aid together into a ball mill jar, and use an alternating forward and reverse ball milling process to mix and disperse the powder. The ball mill speed is 400 r / min, the ball milling time is 5 h, and the ball mill rotation direction is changed every 30 min;

[0052] Step 4) is the same as in Example 1;

[0053] Step 5) Place the assembled mold into the SPS furnace chamber for vacuum sintering to obtain AlON ceramic. The SPS sintering process adopts a three-stage sintering method. In the first stage of sintering, the temperature is increased to 1200℃ at a heating rate of 150℃ / min; in the second stage of sintering, while keeping the temperature constant at 1200℃, the pressure is increased to 10MPa at a pressurization rate of 0.02MPa / s; in the third stage of sintering, the temperature and pressure are increased to 1700℃ and 50MPa respectively at a heating rate of 80℃ / min and a pressurization rate of 0.1MPa / s, and held for 5 minutes.

[0054] The AlON ceramics prepared in this embodiment were tested, and the results are as follows:

[0055] (1) After the first stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 7 As shown, although there is a clear YAG liquid phase inside the sample (the white phase marked by the white dashed line), this liquid phase is not uniformly dispersed in the gaps between the powder particles, and there is obvious agglomeration.

[0056] (2) After the second stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 8 As shown in the figure, the YAG liquid phase is uniformly distributed among the powder particles.

[0057] (3) After the third stage of SPS sintering, the fracture morphology of AlON ceramics is as follows: Figure 9 As shown, the overall structure of the ceramic is uniform and dense, and no YAG phase was found, indicating that YAG has been completely dissolved into the AlON ceramic.

[0058] (4) In this embodiment, the density of AlON ceramic is 99.90% and the hardness is 17.6 GPa.

[0059] The foregoing description describes the embodiments of the present invention in conjunction with the accompanying drawings. However, the present invention includes, but is not limited to, the above embodiments. Any modifications, additions, equivalent substitutions, or partial improvements made under the spirit and principles of the present invention shall be considered to be within the protection scope of the present invention.

Claims

1. A method for preparing in-situ self-generated YAG phase reinforced AlON ceramic materials, characterized in that, The process includes the following steps: 1) Nanoscale Al2O3 powder and AlN powder were selected as raw materials; 2) Add Y2O3 as a single sintering aid, with an addition amount of 0.2–2 wt%; 3) Place the raw material powder and sintering aid together into a ball mill jar, and use a ball mill to mix the powder; 4) Load the uniformly dispersed mixed powder or pressed blank after ball milling into a carbon-carbon mold; 5) Place the assembled mold into an SPS sintering furnace and sinter under vacuum conditions to obtain AlON ceramics; The SPS sintering process employs a three-stage sintering method. In the first stage, the temperature is raised to 1200–1400℃ at a heating rate of 150–300℃ / min. In the second stage, while maintaining a constant temperature, the pressure is increased to 10–30MPa at a pressurization rate of 0.02–0.06MPa / s. In the third stage, the temperature and pressure are increased to 1500–1700℃ and 50–100MPa respectively at a heating rate of 30–80℃ / min and a pressurization rate of 0.1–0.3MPa / s, and then held at these temperatures for 5–20 minutes.

2. The method for preparing in-situ self-generated YAG phase reinforced AlON ceramic material according to claim 1, characterized in that, In step 1), the purity of both Al2O3 powder and AlN powder is greater than 99%, the particle size range is 20-500 nm, and the mass ratio of the two is 0.79:0.

21.

3. The method for preparing in-situ self-generated YAG phase reinforced AlON ceramic material according to claim 1, characterized in that, In step 2), the purity of the Y2O3 sintering aid is greater than 99%, and the particle size range is 10-100 nm.

4. The method for preparing in-situ self-generated YAG phase reinforced AlON ceramic material according to claim 1, characterized in that, In step 3), the ball mill speed is 100-400 r / min, the ball milling time is 5-30 h, and the entire ball milling process is carried out by alternating forward and reverse rotation, changing the direction of rotation every 30 min.

5. An in-situ self-generated YAG phase reinforced AlON ceramic material, characterized in that, Prepared by the method according to any one of claims 1 to 4.

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