Calcium zirconate-silicon nitride-boron carbide composite refractory and method for producing the same

Abstract

This invention provides a calcium zirconate-silicon nitride-boron carbide multiphase refractory material and its preparation method. The preparation method includes the following steps: (1) weighing 60-65 parts of calcium zirconate powder, 20-25 parts of silicon nitride powder, and 10-20 parts of boron carbide powder, and mixing them to obtain a mixed powder; (2) adding 3-5 parts of binder and stirring to obtain a mixture, pressing the mixture into a blank; (3) placing the pressed blank into a drying oven for drying, and sintering the dried blank under a nitrogen atmosphere to obtain the calcium zirconate-silicon nitride-boron carbide multiphase refractory material. Compared with the existing calcium zirconate single-phase material, this invention utilizes the low thermal expansion and high bending strength of silicon nitride and the high toughness and strong corrosion resistance of boron carbide to compensate for the shortcomings of calcium zirconate single-phase material, such as insufficient mechanical properties, poor thermal shock resistance, and low high-temperature erosion resistance.

Description

Technical Field

[0001] This invention relates to the field of refractory materials, and in particular to a calcium zirconate-silicon nitride-boron carbide multiphase refractory material and its preparation method. Background Technology

[0002] Nickel-based superalloys are the preferred material for turbine blades in aero-engines. Due to the high-temperature, vacuum melting technology used in their preparation, the melting environment is high and complex, often requiring crucibles with high thermal shock resistance and good corrosion resistance. With the continuous development of superalloys, melting temperatures and the content of highly reactive elements are constantly increasing, subjecting crucibles to increasingly demanding service environments. Conventional alumina and magnesia crucibles are prone to reacting with the alloys, leading to a decrease in alloy purity and performance. Calcium zirconate, with its perovskite crystal structure in the CaO-ZrO2 binary system, has a melting point above 2300℃. It possesses characteristics such as a high melting point, stable chemical properties, high mechanical strength, low coefficient of thermal expansion, strong resistance to alkaline slag corrosion, and unique electrical properties. It can be used as a refractory material in smelting; for example, calcium zirconate refractories are commonly used in continuous casting submerged entry nozzles to prevent alumina nodule blockage. It is also currently used in the smelting of nickel-based superalloys.

[0003] Currently, commercially available calcium zirconate is mainly prepared through solid-state reaction and electrofusion methods. For example, the solid-state reaction method uses calcium carbonate and monoclinic zirconium oxide as raw materials, and hot-presses them together to form calcium zirconate. Because calcium zirconate is difficult to sinter, small amounts of sintering aids are often added to react with it to form a solid solution or a low-melting-point phase, promoting sintering and thus increasing density. Commonly used sintering aids include cobalt oxide, titanium oxide, and iron oxide. Current research on calcium zirconate refractories is limited to improvements in single-phase calcium zirconate materials. For instance, stepwise calcination processes are used to improve density and strength, and sintering aids are added to improve density and erosion resistance. However, the performance improvement of single-phase calcium zirconate materials is limited.

[0004] Multiphase refractories refer to refractory material systems composed of two or more crystalline / glassy phases. They optimize mechanical strength, thermal shock resistance, and slag erosion resistance through multiphase synergy, distinguishing them from single-phase refractories with a single main crystalline phase. The core design principle is to utilize the complementary properties of each phase to address the shortcomings of single-phase materials. Therefore, there is an urgent need to provide a calcium zirconate multiphase refractories and its preparation method to further improve the mechanical properties, thermal shock resistance, and melt erosion resistance of calcium zirconate.

[0005] It should be noted that the above description of the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of this invention. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a calcium zirconate-silicon nitride-boron carbide multiphase refractory material and its preparation method with high mechanical properties, thermal shock resistance and melt erosion resistance, so as to solve the problems of poor mechanical properties, insufficient thermal shock resistance and poor melt erosion resistance in the prior art.

[0007] To achieve the above and other related objectives, the present invention provides a calcium zirconate-silicon nitride-boron carbide multiphase refractory material, which is composed of the following components in parts by weight: 60-65 parts of calcium zirconate powder, 20-25 parts of silicon nitride powder, 10-20 parts of boron carbide powder, and 3-5 parts of binder.

[0008] This invention also provides a method for preparing a calcium zirconate-silicon nitride-boron carbide multiphase refractory material, comprising the following steps:

[0009] (1) Weigh 60-65 parts of calcium zirconate powder, 20-25 parts of silicon nitride powder, and 10-20 parts of boron carbide powder. First, mix the calcium zirconate powder and boron carbide powder evenly, then add the silicon nitride powder and mix evenly to obtain a mixed powder.

[0010] (2) Add the mixed powder obtained in step (1) into a mixing mill, add 3-5 parts of binder and stir to obtain a mixture, press the mixture at 150~250MPa to obtain a blank;

[0011] (3) Place the pressed blank into a drying oven to dry it, and sinter the dried blank under a nitrogen atmosphere, that is, heat it to 800-900℃ at a heating rate of 4-6℃ / min, hold it for 2-4h, then heat it to 1200-1350℃ at a heating rate of 3-5℃ / min, hold it for 3-5h, then heat it to 1600-1650℃ at a heating rate of 2-3℃ / min, and hold it for 1-2h to obtain calcium zirconate-silicon nitride-boron carbide multiphase refractory material.

[0012] Optionally, weigh out 60 parts of calcium zirconate powder, 20 parts of silicon nitride powder, and 20 parts of boron carbide powder.

[0013] Optionally, weigh out 65 parts of calcium zirconate powder, 25 parts of silicon nitride powder, and 10 parts of boron carbide powder.

[0014] Optionally, the adhesive is polyvinyl alcohol or polyvinyl butyral.

[0015] Optionally, the particle size D50 of the calcium zirconate powder is 8~10μm, the particle size D50 of the boron nitride powder is 2~4μm, and the particle size D50 of the boron carbide powder is 1~2μm.

[0016] Optionally, in step (1), the mixing time of calcium zirconate powder and boron carbide powder is 30-40 min, and the mixing time of silicon nitride powder is 20-30 min.

[0017] Optionally, the stirring time in step (2) is 40~60 min.

[0018] Optionally, the pressing pressure in step (2) is 200~250MPa.

[0019] Optionally, the drying temperature in step (3) is 80~100℃ and the drying time is 40~60min.

[0020] The calcium zirconate-silicon nitride-boron carbide multiphase refractory material and its preparation method of the present invention have the following beneficial effects:

[0021] (1) Compared with the existing single-phase calcium zirconate materials, the present invention utilizes the low thermal expansion and high bending strength of silicon nitride and the high toughness and strong corrosion resistance of boron carbide to make up for the shortcomings of the single-phase calcium zirconate materials, such as insufficient mechanical properties, poor thermal shock resistance and low high-temperature corrosion resistance.

[0022] (2) Silicon nitride particles are uniformly dispersed in the calcium zirconate matrix. When the material is subjected to external force, the crack propagation needs to bypass the dispersed particles, consuming more energy. At the same time, silicon nitride particles are adsorbed at the calcium zirconate grain boundaries, inhibiting the abnormal growth of calcium zirconate grains during sintering, refining the matrix grains, thereby improving compressive strength and fracture toughness. In addition, silicon nitride and boron carbide have lower coefficients of thermal expansion than calcium zirconate, thereby improving the thermal shock resistance of the material.

[0023] (3) Silicon nitride and boron carbide will undergo a slight interfacial reaction with calcium zirconate at high temperature to generate a Ca-Si-ONB glass phase. The generated glass phase fills the intergranular gaps, increases the material density, improves the erosion resistance of the melt, and at the same time improves the wettability of silicon nitride / boron carbide and calcium zirconate matrix, increases the interfacial strength, and thus improves the overall performance of the material.

[0024] (4) When mixing raw materials, calcium zirconate and boron carbide are mixed first, so that boron carbide is coated on calcium zirconate. When silicon nitride is added and mixed, boron carbide is at the interface between calcium zirconate and silicon nitride. The boron carbide coating layer acts as a buffer phase to reduce the thermal stress caused by the thermal expansion mismatch between calcium zirconate and silicon nitride and reduce microcracks. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] Calcium zirconate powder, boron nitride powder, and boron carbide powder were selected as raw materials for the calcium zirconate-silicon nitride-boron carbide multiphase refractory material. The particle size D50 of the calcium zirconate powder was 8 μm, the particle size D50 of the boron nitride powder was 4 μm, and the particle size D50 of the boron carbide powder was 2 μm.

[0027] Example 1

[0028] A method for preparing a calcium zirconate-silicon nitride-boron carbide multiphase refractory material, comprising the following steps:

[0029] (1) Weigh 60 parts of calcium zirconate powder, 20 parts of silicon nitride powder and 20 parts of boron carbide powder. First, add calcium zirconate powder and boron carbide powder to a mixer and stir for 40 minutes to mix evenly. Then add silicon nitride powder and stir for 30 minutes to mix evenly to obtain a mixed powder.

[0030] (2) Add the mixed powder obtained in step (1) into a mixing mill, add 4 parts of polyvinyl alcohol and stir for 50 minutes to obtain a mixture. Press the mixture at 200 MPa to obtain a green body.

[0031] (3) Place the pressed blank into a drying oven and dry it at 100°C for 60 min. Then, sinter the dried blank in a high-temperature sintering furnace under a nitrogen atmosphere. The sintering temperature is increased to 900°C at a heating rate of 5°C / min and held for 2 h. Then, the temperature is increased to 1350°C at a heating rate of 3°C / min and held for 3 h. Then, the temperature is increased to 1600°C at a heating rate of 2°C / min and held for 2 h. The temperature is then reduced to room temperature to obtain calcium zirconate-silicon nitride-boron carbide multiphase refractory material.

[0032] Example 2

[0033] A method for preparing a calcium zirconate-silicon nitride-boron carbide multiphase refractory material, comprising the following steps:

[0034] (1) Weigh 65 parts of calcium zirconate powder, 25 parts of silicon nitride powder and 10 parts of boron carbide powder. First, add calcium zirconate powder and boron carbide powder to a mixer and stir for 40 minutes to mix evenly. Then add silicon nitride powder and stir for 30 minutes to mix evenly to obtain a mixed powder.

[0035] (2) Add the mixed powder obtained in step (1) into a mixing mill, add 4 parts of polyvinyl alcohol and stir for 50 minutes to obtain a mixture. Press the mixture at 200 MPa to obtain a green body.

[0036] (3) Place the pressed blank into a drying oven and dry it at 100°C for 60 min. Then, sinter the dried blank in a high-temperature sintering furnace under a nitrogen atmosphere. The sintering temperature is increased to 900°C at a heating rate of 5°C / min and held for 2 h. Then, the temperature is increased to 1350°C at a heating rate of 3°C / min and held for 3 h. Then, the temperature is increased to 1600°C at a heating rate of 2°C / min and held for 2 h. The temperature is then reduced to room temperature to obtain calcium zirconate-silicon nitride-boron carbide multiphase refractory material.

[0037] Comparative Example 1

[0038] The only difference between this comparative example and Example 1 is that only calcium zirconate powder is used as raw material to prepare single-phase calcium zirconate refractory material.

[0039] Comparative Example 2

[0040] The only difference between this comparative example and Example 1 is that in step (3), the sintering temperature is increased to 1600°C at a rate of 5°C / min, held for 2 hours, and then cooled to room temperature to obtain calcium zirconate-silicon nitride-boron carbide multiphase refractory material.

[0041] Comparative Example 3

[0042] The only difference between this comparative example and Example 1 is that in step (1), calcium zirconate powder, boron carbide powder, and silicon nitride powder are added together to the mixer and stirred evenly during the mixing of raw materials.

[0043] Performance Testing: Performance tests were conducted on the samples obtained in Examples 1-2 and Comparative Examples 1-3. The room temperature compressive strength of the multiphase refractories was tested according to GB / T5072. The room temperature flexural strength was measured using the three-point bending method. The sample size was 8 mm × 8 mm × 45 mm, the span was 20 mm, and the indenter moving speed was 0.05 mm / min. Thermal shock resistance was tested using the water quenching method. A strip sample of a specific size (8 mm × 8 mm × 45 mm) was placed in the test furnace. After the furnace temperature stabilized at 1000℃, it was held at that temperature for 15 min. After the holding period, the sample was removed with a clamp and placed in a container filled with cold water for water quenching for 20 min. This process was repeated three times. After the sample cooled to room temperature, the flexural strength after thermal shock was measured, and the residual flexural strength rate after thermal shock was calculated to evaluate the thermal shock resistance of the sample. Detailed test results are shown in Table 1.

[0044] Table 1

[0045]

[0046] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a calcium zirconate-silicon nitride-boron carbide multiphase refractory material, characterized in that, Includes the following steps: (1) Weigh 60-65 parts of calcium zirconate powder, 20-25 parts of silicon nitride powder, and 10-20 parts of boron carbide powder. First, mix the calcium zirconate powder and boron carbide powder evenly, then add the silicon nitride powder and mix evenly to obtain a mixed powder. (2) Add the mixed powder obtained in step (1) into a mixing mill, add 3-5 parts of binder and stir to obtain a mixture, press the mixture at 150~250MPa to obtain a blank; (3) Place the pressed blank into a drying oven to dry it, and sinter the dried blank under a nitrogen atmosphere, that is, heat it to 800-900℃ at a heating rate of 4-6℃ / min, hold it for 2-4h, then heat it to 1200-1350℃ at a heating rate of 3-5℃ / min, hold it for 3-5h, then heat it to 1600-1650℃ at a heating rate of 2-3℃ / min, and hold it for 1-2h to obtain calcium zirconate-silicon nitride-boron carbide multiphase refractory material.

2. The method for preparing the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, In step (1), weigh out 60 parts of calcium zirconate powder, 20 parts of silicon nitride powder, and 20 parts of boron carbide powder.

3. The preparation method of the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, In step (1), weigh out 65 parts of calcium zirconate powder, 25 parts of silicon nitride powder, and 10 parts of boron carbide powder.

4. The preparation method of the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, The adhesive is polyvinyl alcohol or polyvinyl butyral.

5. The preparation method of the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, The particle size D of the calcium zirconate powder 50 The particle size D of boron nitride powder is 8~10 μm. 50 The particle size D of boron carbide powder is 2~4μm. 50 It is 1~2μm.

6. The preparation method of the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, In step (1), the mixing time for calcium zirconate powder and boron carbide powder is 30-40 min, and the mixing time for silicon nitride powder is 20-30 min.

7. The method for preparing the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, The stirring time in step (2) is 40~60 min.

8. The method for preparing the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, The pressing pressure in step (2) is 200~250MPa.

9. The method for preparing the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to claim 1, characterized in that, In step (3), the drying temperature is 80~100℃ and the drying time is 40~60min.

10. The calcium zirconate-silicon nitride-boron carbide multiphase refractory material prepared by the preparation method of the calcium zirconate-silicon nitride-boron carbide multiphase refractory material according to any one of claims 1-9.

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