A high-strength BN-AlN-B 4 C composite ceramic side seal plate and preparation method

Abstract

The present invention discloses a high-strength BN-AlN-B 4 C composite ceramic side seal plate and a preparation method thereof. The technical solution is as follows: Mix 50-90 wt% of hexagonal boron nitride powder and 10-50 wt% of aluminum borocarbide powder, place them in a planetary ball mill for ball milling, drying, and screening to obtain a composite powder. Place the composite powder into a graphite mold, and then place the graphite mold in a hot press sintering device for pre-pressing treatment, vacuum pumping, and then pressurize to 30-70 MPa, heat up to 1500-1800 °C, and finally keep the temperature and pressure at 1500-1800 °C and 30-70 MPa for 60-120 min. After grinding, polishing, and cutting, a high-strength BN-AlN-B 4 C composite ceramic side seal plate is obtained. The production cost of the present invention is low, and the prepared high-strength BN-AlN-B 4 C composite ceramic side seal plate has the characteristics of good densification, high bending strength, high toughness, good thermal shock resistance, and long service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials for side seal plates in thin strip continuous casting. In particular, it relates to a high-strength BN-AlN-B 4 C composite ceramic side seal plate and a preparation method thereof. Background Technique

[0002] The side seal technology is a key technology in the twin-roll casting thin strip continuous casting process. Among them, the comprehensive performance of the side seal plate material directly determines the stability and safety of the thin strip continuous casting process. Hexagonal boron nitride has the advantages of high-temperature self-lubrication, low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, good high-temperature chemical stability, and non-wetting with molten metal, and has become the most promising material for side seal plates used in thin strip continuous casting at present. However, due to the low self-diffusion coefficient of boron nitride, it is easy to form a "card room" layered structure during the sintering process, resulting in a low density and poor mechanical properties of the prepared boron nitride ceramic, which affects its wide application. In addition, the sintering process of pure boron nitride ceramic needs to be sintered densely under high-temperature hot pressing conditions of 2000-2200 °C and 50-90 MPa, which increases the preparation cost of boron nitride ceramic materials and hinders the wide application of boron nitride materials in the engineering field. Therefore, the development of reasonable component compositions and corresponding preparation technologies has become a hot topic of concern for those skilled in the art.

[0003] For the patented technology of "A Modified Boron Nitride Composite Material and Its Preparation Method and a Side Seal Plate" (CN 109704779A), boron nitride is 50-80%, zirconia is 8-20%, sialon is 5-15%, silicon carbide is 5-15%, and additives are 1-5% are mixed and kept warm for 50-70 min by hot press sintering at 1700-1950 °C. Although a modified boron nitride composite material is prepared, this method has a high sintering temperature, a long holding time, and a large equipment investment.

[0004] Miao Yi et al. (Miao Yimin, Liu Liangguang. Influence of Pressure and SiC Content on the Densification and Mechanical Properties of Hot Press Sintered h-BN Ceramics [J]. Journal of Ceramics, 2022, 43(4): 637-643) mixed hexagonal boron nitride powder, nano-cubic boron nitride powder and silicon carbide powder, and through hot press sintering, at 1800 °C and 80 MPa, the c-BN to h-BN crystal form transformation occurred, and an h-BN-based composite ceramic was prepared. The prepared h-BN-based composite ceramic has poor densification and low flexural strength, and cannot meet the use requirements of the side seal plate.

[0005] Fan Zhang et al. (Zhang F, Wang H, Shao G, et al. Effect ofZrO 2on sinteringbehavior and properties of h-BN / ZrO 2 composites by spark plasma sintering[J].Ceramics International,2022,48(23):34877-34884) Adding a certain amount of ZrO 2 as an additive, although h-BN / ZrO 2 composites are prepared by spark plasma sintering, the sintering densification of h-BN composites is low and the toughness is poor, and the addition of oxides leads to an increase in the thermal expansion coefficient of the composites and poor thermal shock resistance. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art, and the purpose is to provide a high-strength BN-AlN-B 4 C composite ceramic side seal plate with good densification, high bending strength, high toughness, good thermal shock resistance, low cost and long service life, and a preparation method thereof.

[0007] To achieve the above purpose, the steps of the technical solution adopted by the present invention are as follows:

[0008] Step 1: Mix 50-90 wt% of hexagonal boron nitride powder and 10-50 wt% of aluminum borocarbide powder to obtain a mixed powder.

[0009] Step 2: Place the mixed powder in a planetary ball mill, use anhydrous ethanol as a dispersant and agate balls as grinding media, with a ball-to-material ratio of 2-6:1, and ball mill for 8-16 h to obtain a mixed slurry.

[0010] Step 3: Dry the mixed slurry at 60-110 °C for 24-48 h, and sieve to obtain a composite powder with a particle size less than 75 μm.

[0011] Step 4: Place the composite powder into a graphite mold, and the inner lining of the graphite mold is provided with graphite paper; place the graphite mold in a hot press sintering device, pre-press it at a pressure of 10-20 MPa, and then evacuate to 0.10-0.2 Pa; then pressurize to 30-70 MPa, and heat it to 1500-1800 °C at a rate of 10-30 °C / min under the pressure holding condition, and keep the pressure and temperature for 60-120 min to obtain a BN-based composite material.

[0012] Step 5: Grind, polish and cut the BN-based ceramic composite material to obtain a high-strength BN-AlN-B 4 C composite ceramic side seal plate.

[0013] The BN content of the hexagonal boron nitride powder is ≥ 98.5 wt%; the particle size of the hexagonal boron nitride powder is 1 - 20 μm.

[0014] The aluminum borocarbide powder's Al 3 BC 3 content is ≥ 99 wt%; the particle size of the aluminum borocarbide powder is 1 - 20 μm.

[0015] Due to the adoption of the above technical solution, the present invention has the following positive effects compared with the prior art:

[0016] The present invention uses hexagonal boron nitride powder as the raw material and aluminum borocarbide powder as the additive, and adopts a hot pressing sintering method, simultaneously pressurizing to 30 - 70 MPa and heating at a rate of 10 - 30 °C / min to 1500 - 1800 °C, holding the pressure and temperature for 60 - 120 min to obtain a BN-based composite material; then the BN-based composite material is polished, ground and cut to prepare a high-strength BN-AlN-B 4 C composite ceramic side seal plate. This method has a low synthesis temperature, a simple process, a low production cost and is easy to industrialize.

[0017] The present invention in-situ generates a high-strength BN-AlN-B with uniform structure through the high-temperature decomposition of aluminum borocarbide and reaction with hexagonal boron nitride 4 C composite ceramic side seal plate, avoiding the complex mixing process and pollution of the high-strength BN-AlN-B 4 C composite ceramic side seal plate by external factors. At the same time, at high temperature, the in-situ generated AlN and B 4 C have better interfacial compatibility with the BN matrix material and are more closely combined, thereby improving the mechanical properties of the high-strength BN-AlN-B 4 C composite ceramic side seal plate. The in-situ generated AlN and B 4 C grains can directly fill the pores between BN grains, effectively promoting the sintering densification of the high-strength BN-AlN-B 4 C composite ceramic side seal plate.

[0018] The present invention uses aluminum borocarbide as an additive to prepare a high-strength BN-AlN-B 4 C composite ceramic side seal plate. The generated AlN and B 4 C have high strength and high toughness, thus improving the disadvantages of poor sinterability and low mechanical properties of BN itself. And AlN and B 4 C belong to non-oxides, ensuring the excellent thermal shock resistance of BN and making the prepared high-strength BN-AlN-B 4 C composite ceramic side seal plate have a long service life.

[0019] The high-strength BN-AlN-B prepared by the present invention 4The C composite ceramic side seal plate was tested: the relative density was 98.4 - 98.7%; the flexural strength was 251 - 259 MPa; the fracture toughness was 3.9 - 4.1 MPa·m 1 / 2 ; the residual flexural strength was 271 - 278 MPa; the ratio of residual flexural strength was 105.4 - 110.8%.

[0020] Therefore, the production cost of the present invention is low, and the prepared high-strength BN-AlN-B 4 C composite ceramic side seal plate has the characteristics of good compactness, high flexural strength, high toughness, good thermal shock resistance and long service life. Specific Embodiments

[0021] The present invention will be further described below in conjunction with specific embodiments, which is not a limitation to its protection scope.

[0022] A high-strength BN-AlN-B 4 C composite ceramic side seal plate and its preparation method. The steps of the preparation method described in this specific embodiment are as follows:

[0023] Step 1: Mix 50 - 90 wt% of hexagonal boron nitride powder and 10 - 50 wt% of aluminum borocarbide powder to obtain a mixed powder.

[0024] Step 2: Place the mixed powder in a planetary ball mill, use anhydrous ethanol as a dispersant and agate balls as grinding media, with a ball-to-powder ratio of 2 - 6:1, and ball mill for 8 - 16 h to obtain a mixed slurry.

[0025] Step 3: Dry the mixed slurry at 60 - 110 °C for 24 - 48 h, and sieve it to obtain a composite powder with a particle size less than 75 μm.

[0026] Step 4: Place the composite powder into a graphite mold, and the inner lining of the graphite mold is provided with graphite paper; place the graphite mold in a hot press sintering device, pre-press it under a pressure of 10 - 20 MPa, and then evacuate to 0.10 - 0.2 Pa; then pressurize to 30 - 70 MPa, and heat it to 1500 - 1800 °C at a rate of 10 - 30 °C / min under the pressure maintaining condition, and keep the pressure and temperature for 60 - 120 min to obtain a BN-based composite material.

[0027] Step 5: Grind, polish and cut the BN-based composite material to obtain a high-strength BN-AlN-B 4 C composite ceramic side seal plate.

[0028] In this specific embodiment:

[0029] The BN content of the hexagonal boron nitride powder is ≥98.5 wt%, and the particle size of the hexagonal boron nitride powder is 1 - 20 μm;

[0030] The Al of the aluminum borocarbide powder 3 BC 3 content ≥ 99 wt%, and the particle size of the aluminum borocarbide powder is 1 - 20 μm.

[0031] Details are not described again in the examples.

[0032] Example 1

[0033] A high-strength BN-AlN-B 4 C composite ceramic side seal plate and its preparation method. The steps of the preparation method in this example are as follows:

[0034] Step 1: Mix 50 wt% of hexagonal boron nitride powder and 50 wt% of aluminum borocarbide powder to obtain a mixed powder.

[0035] Step 2: Place the mixed powder in a planetary ball mill, use anhydrous ethanol as a dispersant and agate balls as grinding media, with a ball-to-material ratio of 6:1, and ball mill for 16 h to obtain a mixed slurry.

[0036] Step 3: Dry the mixed slurry at 60 °C for 48 h, and sieve to obtain a composite powder with a particle size less than 75 μm.

[0037] Step 4: Place the composite powder into a graphite mold, and a graphite paper is provided on the inner lining of the graphite mold; place the graphite mold in a hot press sintering device, pre-press it at a pressure of 10 MPa, then evacuate to 0.15 Pa; then pressurize to 30 MPa, and heat it to 1500 °C at a rate of 30 °C / min under the pressure holding condition, and hold the pressure for 120 min to obtain a BN-based composite material.

[0038] Step 5: Grind, polish and cut the BN-based composite material to obtain a high-strength BN-AlN-B 4 C composite ceramic side seal plate.

[0039] The high-strength BN-AlN-B prepared in this example 4 C composite ceramic side seal plate is detected: the relative density is 98.4%; the flexural strength is 253 MPa; the fracture toughness is 4.1 MPa·m 1 / 2 ; the residual flexural strength is 271 MPa; the residual flexural strength ratio is 107.1%.

[0040] Example 2

[0041] A high-strength BN-AlN-B 4 C composite ceramic side seal plate and its preparation method. The steps of the preparation method in this example are as follows:

[0042] Step 1: Mix 70 wt% of hexagonal boron nitride powder and 30 wt% of aluminum borocarbide powder to obtain a mixed powder.

[0043] Step 2: Place the mixed powder in a planetary ball mill, use anhydrous ethanol as a dispersant and agate balls as grinding media, with a ball-to-material ratio of 4:1, and ball mill for 12 h to obtain a mixed slurry.

[0044] Step 3: Dry the mixed slurry at 110 °C for 24 h and screen it to obtain a composite powder with a particle size less than 75 μm.

[0045] Step 4: Place the composite powder into a graphite mold, and the inner lining of the graphite mold is provided with graphite paper; place the graphite mold in a hot pressing and sintering device, pre-press it at a pressure of 15 MPa, then evacuate to 0.1 Pa; then pressurize to 50 MPa, and heat it to 1700 °C at a rate of 20 °C / min under the pressure-holding condition, and hold the pressure and temperature for 90 min to obtain a BN-based composite material.

[0046] Step 5: Grind, polish and cut the BN-based composite material to obtain a high-strength BN-AlN-B 4 4C composite ceramic side seal plate.

[0047] The high-strength BN-AlN-B 4 4C composite ceramic side seal plate prepared in this example was tested: the relative density was 98.5%; the flexural strength was 251 MPa; the fracture toughness was 4.0 MPa·m 1 / 2 ; the residual flexural strength was 278 MPa; the residual flexural strength ratio was 110.8%.

[0048] Example 3

[0049] A high-strength BN-AlN-B4C composite ceramic side seal plate and a preparation method thereof. The steps of the preparation method in this example are as follows:

[0050] Step 1: Mix 90 wt% of hexagonal boron nitride powder and 10 wt% of aluminum borocarbide powder to obtain a mixed powder.

[0051] Step 2: Place the mixed powder in a planetary ball mill, use anhydrous ethanol as a dispersant and agate balls as grinding media, with a ball-to-material ratio of 2:1, and ball mill for 8 h to obtain a mixed slurry.

[0052] Step 3: Dry the mixed slurry at 90 °C for 36 h and screen it to obtain a composite powder with a particle size less than 75 μm.

[0053] Step 4: Place the composite powder into a graphite mold with a graphite paper lined inside; place the graphite mold in a hot-pressing sintering device, pre-press it under a pressure of 20 MPa, and then evacuate to 0.2 Pa; then increase the pressure to 70 MPa, and heat it to 1800 °C at a rate of 10 °C / min under the condition of maintaining pressure, and keep the pressure and temperature for 60 min to obtain a BN-based composite material.

[0054] Step 5: Grind, polish, and cut the BN-based composite material to obtain a high-strength BN-AlN-B 4 C composite ceramic side seal plate.

[0055] The high-strength BN-AlN-B prepared in this embodiment 4 C composite ceramic side seal plate is tested: the relative density is 98.7%; the flexural strength is 259 MPa; the fracture toughness is 3.9 MPa·m 1 / 2 ; the residual flexural strength is 273 MPa; the residual flexural strength ratio is 105.4%.

[0056] The present specific embodiment has the following positive effects compared with the prior art:

[0057] In the present specific embodiment, hexagonal boron nitride powder is used as the raw material, and aluminum carbide boron powder is used as the additive. By adopting the hot-pressing sintering method, while increasing the pressure to 30 - 70 MPa and heating it to 1500 - 1800 °C at a rate of 10 - 30 °C / min, and keeping the pressure and temperature for 60 - 120 min, a BN-based composite material is obtained; then the BN-based composite material is ground, polished, and cut to prepare a high-strength BN-AlN-B 4 C composite ceramic side seal plate. This method has a low synthesis temperature, a simple process, a low production cost, and is easy for industrial production.

[0058] In the present specific embodiment, through the high-temperature decomposition of aluminum carbide boron, it reacts with hexagonal boron nitride to in-situ generate a high-strength BN-AlN-B with uniform structure 4 C composite ceramic side seal plate, avoiding the complex mixing process and the pollution of the high-strength BN-AlN-B 4 C composite ceramic side seal plate by external factors. At the same time, at high temperature, the in-situ generated AlN, B 4 C has better interfacial compatibility with the BN matrix material and is more closely combined, thereby improving the mechanical properties of the high-strength BN-AlN-B 4 C composite ceramic side seal plate. The in-situ generated AlN and B 4 C grains can directly fill the pores between BN grains, effectively promoting the sintering densification of the high-strength BN-AlN-B 4 C composite ceramic side seal plate.

[0059] This specific embodiment uses aluminum borocarbide as an additive to prepare a high-strength BN-AlN-B 4 C composite ceramic side seal plate. The generated AlN and B 4 C have high strength and high toughness, thus improving the disadvantages of poor sinterability and low mechanical properties of BN itself. Moreover, AlN and B 4 C are non-oxides, ensuring the excellent thermal shock resistance of BN and making the prepared high-strength BN-AlN-B 4 C composite ceramic side seal plate have a long service life.

[0060] The high-strength BN-AlN-B 4 C composite ceramic side seal plate prepared in this specific embodiment is detected: the relative density is 98.4-98.7%; the flexural strength is 251-259 MPa; the fracture toughness is 3.9-4.1 MPa·m 1 / 2 ; the residual flexural strength is 271-278 MPa; the residual flexural strength ratio is 105.4-110.8%.

[0061] Therefore, this specific embodiment has low production cost, and the prepared high-strength BN-AlN-B 4 C composite ceramic side seal plate has the characteristics of good densification, high flexural strength, high toughness, good thermal shock resistance and long service life.

Claims

1. A preparation method of a high-strength BN-AlN-B 4 C composite ceramic side seal plate It is characterized in that The steps of the preparation method are as follows: Step 1: Mix 50-90 wt% of hexagonal boron nitride powder and 10-50 wt% of aluminum borocarbide powder to obtain a mixed powder; Step 2: Place the mixed powder in a planetary ball mill, use absolute ethanol as a dispersant and agate balls as grinding media, with a ball-to-material ratio of 2-6:1, and ball mill for 8-16 h to obtain a mixed slurry; Step 3: Dry the mixed slurry at 60-110 °C for 24-48 h, and sieve to obtain a composite powder with a particle size less than 75 μm; Step 4: Place the composite powder into a graphite mold, and a graphite paper is provided on the inner lining of the graphite mold; place the graphite mold in a hot press sintering device, pre-press it under a pressure of 10-20 MPa, and then evacuate to 0.10-0.2 Pa; then pressurize to 30-70 MPa, and heat it to 1500-1800 °C at a rate of 10-30 °C / min under the pressure holding condition, and keep the pressure and temperature for 60-120 min to obtain a BN-based composite material; Step 5: Grind, polish, and cut the BN-based composite material to obtain a high-strength BN-AlN-B 4 C composite ceramic side seal plate.

2. The preparation method of the high-strength BN-AlN-B 4 C composite ceramic side seal plate as claimed in claim 1 It is characterized in that The BN content of the hexagonal boron nitride powder is ≥98.5 wt%; the particle size of the hexagonal boron nitride powder is 1-20 μm.

3. The preparation method of the high-strength BN-AlN-B 4 C composite ceramic side seal plate as claimed in claim 1 It is characterized in that The Al of the aluminum borocarbide powder 3 BC 3 content ≥ 99 wt%; the particle size of the aluminum borocarbide powder is 1 - 20 μm.

4. A high-strength BN-AlN-B 4 C composite ceramic side seal plate It is characterized in that The high-strength BN-AlN-B 4 C composite ceramic side seal plate is the high-strength BN-AlN-B described in any one of claims 1 to 3 4 C composite ceramic side seal plate prepared by the preparation method of the high-strength BN-AlN-B 4 C composite ceramic side seal plate.