An in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material and its preparation method

Abstract

The present invention relates to the field of ceramic matrix composites, and specifically to an in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material and a preparation method thereof. First, hexagonal boron nitride powder, ytterbium oxide powder, aluminum oxide powder, and silicon oxide powder are weighed according to the ratio, and mixed by physical and mechanical methods for 6 to 12 hours. The dried and sieved mixed powder is loaded into a graphite mold and cold pressed into shape, cold pressed at a pressure of 5 to 15 MPa for 1 to 10 minutes, and then hot pressed and sintered in a hot pressing furnace with a protective atmosphere. The heating rate is 5 to 20 °C / min, the sintering temperature is 1500 to 2000 °C, the sintering time is 1 to 10 hours, and the sintering pressure is 10 to 40 MPa, and it is cooled to room temperature with the furnace. By using the method of the present invention, a ytterbium aluminosilicate (YbAS) glass reinforced hexagonal boron nitride ceramic matrix composite material with high density, good machinability, and excellent room temperature strength can be obtained. In the ytterbium aluminosilicate glass phase, there are two existing forms, namely glass fibers and glass dispersed phases, and the proportion of glass fibers is ≥20 vol.%.

Description

Technical Field

[0001] The present invention relates to the field of ceramic matrix composites, and specifically to an in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material and a preparation method thereof. Background Art

[0002] Hexagonal boron nitride (h-BN) has a layered structure similar to that of graphite. The B-N atoms within the layers are bonded by strong covalent bonds, and the layers are bonded by weak van der Waals forces. The unique structural characteristics of h-BN determine that it has a series of excellent physical and chemical properties, such as high temperature resistance, oxidation resistance, chemical corrosion resistance, self-lubrication, high thermal conductivity, electrical insulation, etc. In addition, h-BN also has a special property, namely good processability, and can be processed by ordinary processing equipment. This enables it to be widely used in many fields. However, pure h-BN ceramic materials are not easy to sinter, have poor strength and low hardness, thus limiting their scope of use. The method of preparing h-BN ceramic matrix composites by adding a second phase can well solve this problem. In Document 1: Journal of the European Ceramic Society. 2000, 20: 1923-1928, Wen et al. prepared h-BN / fused quartz composites. The h-BN flaky grains were preferentially oriented under hot pressing and were uniformly distributed in the fused quartz matrix, achieving obvious co-reinforcement. In Document 2: Journal of the European Ceramic Society. 2018, 38: 3210-3216, Chen et al. prepared h-BN-based composites containing amorphous silica and Yb-Si-Al-O glass phases by in-situ hot pressing. The results showed that the h-BN-based composites containing double glass phases had obvious strengthening effects due to the presence of fine spherical Yb-Si-Al-O glass particles. In Document 3: Journal of the European Ceramic Society. 2020, 40: 2260-2267, Qiu et al. prepared h-BN / La-Al-Si-O composites. The research showed that a La-Al-Si-O ternary liquid phase was formed during the sintering process, which had good wettability with h-BN grains, could effectively fill the pores, improve the densification of the composite ceramic, and nanocrystals would precipitate in the liquid phase, thereby improving the mechanical properties of the composite material. In previous work, materials for in-situ synthesizing glass fibers to reinforce hexagonal boron nitride ceramics have not been reported. Summary of the Invention

[0003] The object of the present invention is to provide an in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material and a preparation method thereof. By adding an oxide sintering aid, ytterbium aluminosilicate glass fibers and a glass phase are formed in the hexagonal boron nitride ceramic matrix, and a hexagonal boron nitride ceramic matrix composite material with high density and excellent mechanical properties is prepared.

[0004] The technical solution of the present invention is as follows:

[0005] An in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, which is composed of a hexagonal boron nitride phase and a ytterbium aluminosilicate glass phase; in the ytterbium aluminosilicate glass phase, there are two existing forms, namely glass fibers and a glass dispersion phase, and the proportion of the glass fibers is ≥ 20 vol.%.

[0006] For the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material described above, by volume percentage, the content of the hexagonal boron nitride phase in this material is 50 - 95 vol.%, and the content of the ytterbium aluminosilicate glass phase is 5 - 50 vol.%.

[0007] For the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material described above, preferably, the proportion of the glass fibers in the ytterbium aluminosilicate glass phase is 20 - 30 vol.%.

[0008] For the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material described above, the size range of the glass fibers is as follows: the length is 2 μm - 30 mm, and the diameter is 0.2 - 10 μm.

[0009] For the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material described above, in the ytterbium aluminosilicate, the content of ytterbium oxide (Yb2O3) is 3 - 24 mol%, the content of aluminum oxide (Al2O3) is 5 - 30 mol%, and the content of silicon dioxide (SiO2) is 52 - 92 mol%.

[0010] A preparation method of an in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, the specific steps are as follows:

[0011] (1) Raw material composition and component range:

[0012] The raw materials are composed of hexagonal boron nitride powder, ytterbium oxide powder, aluminum oxide powder and silicon dioxide powder, and the content of the hexagonal boron nitride powder is 50 - 95 vol.%; in the raw materials for forming ytterbium aluminosilicate, the content of ytterbium oxide powder is 3 - 24 mol%, the content of aluminum oxide powder is 5 - 30 mol%, and the content of silicon dioxide powder is 52 - 92 mol%;

[0013] (2) Preparation process:

[0014] First, weigh hexagonal boron nitride powder, ytterbium oxide powder, aluminum oxide powder, and silicon oxide powder according to the ratio, mix them by physical and mechanical methods for 6 - 12 h, load the dried and sieved mixed powder into a graphite mold for cold pressing and forming, cold press for 1 - 10 min at a pressure of 5 - 15 MPa, and conduct hot pressing and sintering in a hot pressing furnace with a protective atmosphere. The heating rate is 5 - 20 °C / min, the sintering temperature is 1500 - 2000 °C, the sintering time is 1 - 10 h, the sintering pressure is 10 - 40 MPa, and then cool it to room temperature with the furnace.

[0015] In the preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, in step (1), the particle size of the hexagonal boron nitride powder is 0.5 - 10 μm, the particle size of the ytterbium oxide powder is 3 - 30 μm, the particle size of the aluminum oxide powder is 5 - 50 μm, and the particle size of the silicon oxide powder is 1 - 20 μm.

[0016] In the preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, in step (2), the physical and mechanical method is ball milling in a silicon nitride ball milling tank with anhydrous ethanol as the medium.

[0017] In the preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, in step (2), when drying and sieving, the drying temperature is 100 - 200 °C, the drying time is 12 - 24 h, and it is sieved through a 100-mesh sieve.

[0018] In the preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, in step (2), the protective atmosphere is high-purity nitrogen, and the volume purity of the high-purity nitrogen is above 99.999%.

[0019] The design concept of the present invention is:

[0020] The hexagonal boron nitride ceramic matrix composite material of the present invention is composed of a hexagonal boron nitride phase and a ytterbium aluminosilicate (YbAS) glass phase. For the first time, the method of synthesizing ytterbium aluminosilicate glass fibers is used to reinforce the hexagonal boron nitride-based ceramic material, so as to improve the disadvantages of poor sintering performance and low strength of the hexagonal boron nitride ceramic material.

[0021] The advantages and beneficial effects of the present invention are:

[0022] 1. The present invention in-situ synthesizes ytterbium aluminosilicate glass fibers to reinforce hexagonal boron nitride ceramics, and prepares a composite material with excellent mechanical properties.

[0023] 2. The preparation process of the present invention is simple, and a hexagonal boron nitride ceramic matrix composite material with high density and good processability can be prepared only by one-step hot pressing and sintering. Description of the Drawings

[0024] Figure 1X-ray diffraction pattern of the composite material obtained in Example 1. In the figure, the abscissa 2θ is the diffraction angle (°), and the ordinate Intensity is the relative intensity (arb.units).

[0025] Figure 2 Fracture morphology of the composite material obtained in Example 2. Detailed implementation manners

[0026] In the specific implementation process, the present invention first weighs hexagonal boron nitride powder, ytterbium oxide powder, alumina powder and silica powder according to the ratio, mixes the raw material powders in appropriate proportions by physical and mechanical methods for 6 - 12 h, loads the dried and sieved mixed powder into a graphite mold for cold pressing and forming, cold presses at a pressure of 5 - 15 MPa for 1 - 10 min, sinters in a hot pressing furnace with a protective atmosphere, the heating rate is 5 - 20 °C / min, the sintering temperature is 1500 - 2000 °C, the sintering time is 1 - 10 h, the sintering pressure is 10 - 40 MPa, and cools to room temperature with the furnace.

[0027] The technical indexes of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic matrix composite material of the present invention are as follows: the density is 2.24 - 3.03 g / cm 3 , the room temperature bending strength is 252 - 436 MPa, the fracture toughness is 3.0 - 4.2 MPa﹒m 1 / 2 , the compressive strength is 628 - 1072 MPa, and the Vickers hardness is 1.37 - 2.41 GPa.

[0028] Next, the present invention will be further described in detail through examples.

[0029] Example 1

[0030] In this example, 0.86 g of 30-μm Yb2O3 powder, 0.37 g of 50-μm Al2O3 powder, 0.52 g of 20-μm SiO2 powder and 18.25 g of 10-μm h-BN (content 95 vol%) powder are loaded into a silicon nitride ball milling tank and ball milled with absolute ethanol for 12 h, dried at 120 °C for 24 h, sieved through a 100-mesh sieve, then loaded into a graphite mold for cold pressing and forming, the applied pressure is 15 MPa, after holding the pressure for 10 minutes, it is then put into a hot pressing furnace for hot pressing sintering, the heating rate is 20 °C / min, start to pressurize when heating to 100 °C, pressurize to 40 MPa at a rate of 2 kN / min, heat to 2000 °C and hold for 10 h, and the whole sintering process is carried out under nitrogen protection.

[0031] As Figure 1As shown, the obtained 95h-BN-5YbAS (vol%) composite material was subjected to X-ray diffraction analysis. The composite material included h-BN crystal phase and ytterbium aluminosilicate glass phase. In the ytterbium aluminosilicate glass phase, the proportion of glass fibers was about 20 vol.%, and the dimensions of the glass fibers were as follows: length 2 μm to 10 mm, diameter 0.2 to 3 μm. The density of the composite material was measured to be 2.24 g / cm 3 , the room temperature flexural strength was 252 MPa, and the fracture toughness was 3.0 MPa·m 1 / 2 , the compressive strength was 628 MPa, and the Vickers hardness was 1.37 GPa.

[0032] Example 2

[0033] In this example, 3.06 g of 3-μm Yb2O3 powder, 1.32 g of 5-μm Al2O3 powder, 1.87 g of 1-μm SiO2 powder, and 13.75 g of 0.5-μm h-BN (content 80 vol.%) powder were loaded into a silicon nitride ball mill jar and ball milled with absolute ethanol for 12 h, dried at 120 °C for 24 h, passed through a 100-mesh sieve, and then loaded into a graphite mold for cold pressing. The applied pressure was 10 MPa. After holding the pressure for 5 minutes, it was put into a hot press furnace for hot press sintering. The heating rate was 10 °C / min. The pressure was applied starting from 100 °C and increased to 30 MPa at a rate of 2 kN / min, heated to 1800 °C and held for 5 h. The entire sintering process was carried out under nitrogen protection. As Figure 2 shown, the fracture morphology of the 80h-BN-20YbAS (vol.%) composite material. In it, in-situ synthesized glass fibers can be seen, and their proportion in the ytterbium aluminosilicate glass phase is about 30 vol.%. The dimensions of the glass fibers are as follows: length 4 μm to 30 mm, diameter 0.5 to 5 μm. The density of the composite material was measured to be 2.48 g / cm 3 , the room temperature flexural strength was 436 MPa, and the fracture toughness was 4.2 MPa·m 1 / 2 , the compressive strength was 1072 MPa, and the Vickers hardness was 2.41 GPa.

[0034] Example 3

[0035] In this embodiment, 6.33 g of 15-μm Yb2O3 powder, 2.72 g of 20-μm Al2O3 powder, 3.86 g of 10-μm SiO2 powder, and 7.09 g of 5-μm h-BN (content 50 vol.%) powder were loaded into a silicon nitride ball mill jar and ball milled with absolute ethanol for 12 h, dried at 120 °C for 24 h, passed through a 100-mesh sieve, and then cold-pressed into a mold in a graphite mold. The applied pressure was 5 MPa. After holding the pressure for 1 min, it was put into a hot press furnace for hot press sintering. The heating rate was 5 °C / min. Pressurization started when the temperature was raised to 100 °C, and the pressure was increased to 10 MPa at a rate of 2 kN / min. It was heated to 1500 °C and held for 1 h. The entire sintering process was carried out under nitrogen protection. The obtained 50h-BN-50YbAS (vol.%) composite material included h-BN crystal phase and ytterbium aluminosilicate glass phase. In the ytterbium aluminosilicate glass phase, the proportion of glass fibers was about 25 vol.%. The dimensions of the glass fibers were as follows: length 3 μm to 20 mm, diameter 1 to 10 μm. The density of the composite material was measured to be 3.03 g / cm 3 , the room temperature bending strength was 378 MPa, and the fracture toughness was 3.5 MPa﹒m 1 / 2 , the compressive strength was 960 MPa, and the Vickers hardness was 2.12 GPa.

[0036] The implementation results show that the ytterbium aluminosilicate glass-reinforced hexagonal boron nitride ceramic matrix composite material with high density, good processability, and excellent room temperature strength can be obtained by using the method of the present invention.

[0037] The raw materials listed in the present invention, the upper and lower limit values of each raw material, and the upper and lower limit values of each process parameter can all implement the present invention, and the embodiments are not listed one by one here.

Claims

1. An in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material, characterized in that, It is composed of a hexagonal boron nitride phase and a ytterbium aluminosilicate glass phase; in the ytterbium aluminosilicate glass phase, there are two existing forms, namely glass fibers and a glass dispersed phase, and the proportion of the glass fibers is ≥20 vol. %.

2. The in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 1, characterized in that, By volume percentage, the content of the hexagonal boron nitride phase in this material is 50 - 95 vol. %, and the content of the ytterbium aluminosilicate glass phase is 5 - 50 vol. %.

3. The in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 1, characterized in that, The proportion of the glass fibers in the ytterbium aluminosilicate glass phase is 20 - 30 vol. %.

4. The in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 1, characterized in that, The size range of the glass fibers is as follows: the length is 2 μm - 30 mm, and the diameter is 0.2 - 10 μm.

5. The in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 1, wherein In the ytterbium aluminosilicate, the content of ytterbium oxide (Yb2O3) is 3 - 24 mol%, the content of alumina (Al2O3) is 5 - 30 mol%, and the content of silicon dioxide (SiO2) is 52 - 92 mol%.

6. A method for preparing an in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to any one of claims 1 to 5, characterized in that, The specific steps are as follows: (1) Raw material composition and composition range: The raw materials are composed of hexagonal boron nitride powder, ytterbium oxide powder, alumina powder, and silicon dioxide powder. Among them, the content of the hexagonal boron nitride powder is 50 - 95 vol. %; in the raw materials for forming the ytterbium aluminosilicate, the content of the ytterbium oxide powder is 3 - 24 mol%, the content of the alumina powder is 5 - 30 mol%, and the content of the silicon dioxide powder is 52 - 92 mol%. (2) Preparation process: First, weigh the hexagonal boron nitride powder, ytterbium oxide powder, alumina powder, and silicon dioxide powder according to the ratio, mix them by physical and mechanical methods for 6 - 12 h, load the dried and sieved mixed powder into a graphite mold for cold pressing and forming, cold press for 1 - 10 min at a pressure of 5 - 15 MPa, and conduct hot pressing and sintering in a hot pressing furnace with a protective atmosphere. The heating rate is 5 - 20 ℃ / min, the sintering temperature is 1500 - 2000 ℃, the sintering time is 1 - 10 h, the sintering pressure is 10 - 40 MPa, and then cool to room temperature with the furnace.

7. The preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 6, characterized in that, In step (1), the particle size of the hexagonal boron nitride powder is 0.5 - 10 μm, the particle size of the ytterbium oxide powder is 3 - 30 μm, the particle size of the alumina powder is 5 - 50 μm, and the particle size of the silicon dioxide powder is 1 - 20 μm.

8. The preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 6, characterized in that, In step (2), the physical and mechanical method is ball milling in a silicon nitride ball milling tank with anhydrous ethanol as the medium.

9. The preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 6, characterized in that, In step (2), when drying and sieving, the drying temperature is 100 - 200 ℃, the drying time is 12 - 24 h, and it is sieved through a 100 - mesh sieve.

10. The preparation method of the in-situ synthesized glass fiber reinforced hexagonal boron nitride ceramic material according to claim 6, characterized in that, In step (2), the protective atmosphere is high - purity nitrogen, and the volume purity of the high - purity nitrogen is above 99.999%.

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