CN1062542C - Composite ceramics and production thereof - Google Patents

Abstract

A sialon composite phase ceramic and a preparation method thereof belong to silicon nitride-based materials. In the present invention, the values of m and n in the general formula Y _m/3 Si _12-(m+n) Al _m+n O _n N _16-n of α-sialon are used as the main crystal phase α-sialon of the design sialon composite phase ceramics and the main parameters of β-sialon content, when m=0.3, n=1.0, the ratio of α-sialon: β-sialon is equal to 50:50, the fluctuation range is 40:60, and the content of grain boundary phase YAG is the main crystal phase weight 9%. Its preparation method is a general ceramic method. After batching, it is uniaxially formed at 20MPa and then cold isostatically formed at 200MPa. The green body is sintered at 1800°C under 1 atmosphere of N ₂ airflow for 2 hours without pressure or at 1900-2000°C for 1.5-3.0 hours under a high nitrogen pressure of 1.5MPa. The embedded powder is Si ₃ N ₄ :AlN:BN = 6:3:1 (wt%). The strength of the prepared composite ceramics at a high temperature of 1350°C is greater than 500MPa, up to 715MPa.

Description

Sialon composite ceramics and preparation method thereof

The invention relates to a high-strength and high-hardness Sialon composite ceramics prepared by a pressureless and high-nitrogen pressure sintering process with excellent high-temperature mechanical properties, which belongs to the field of silicon nitride-based materials.

Sialon is a solid solution of Si ₃ N ₄ , which was first proposed by KHJack et al. in 1972. Si ₃ N ₄ has two variants of α-Si ₃ N ₄ and β-Si ₃ N ₄ , and solid solutions with the same structure They are called α-Sialon and β-Sialon respectively. Like Si ₃ N ₄ , these solid solutions have their own characteristics and advantages in grain morphology and properties. For example: α-sialon has high hardness and excellent thermal shock resistance, and β-sialon has high strength and high fracture toughness. Sialon composite ceramics composed of α-sialon and β-sialon can be formed by learning from each other. Sialon composite ceramics with both high hardness and high strength (especially at high temperature) have always been the goal pursued by ceramic workers.

However, since the Si ₃ N ₄ material is a material with strong covalent bonds, it is difficult to sinter and densify, so metal oxides such as La ₂ O ₃ , Y ₂ O ₃ , and Al ₂ O ₃ are often added as additives during the sintering process , and densify the ceramics by liquid phase sintering. Unfortunately, the liquid phase exists in the grain boundary of the ceramic in the form of a glass phase during the cooling process, and the low softening point of the glass phase affects the high-temperature mechanical properties of the ceramic, thus limiting the scope of application.

The purpose of the present invention is to apply the existing knowledge of the phase relationship of Y, Si, Al, O, N five-element system to find out the component area with good sintering performance, and to prepare the excellent performance by using the pressureless and high nitrogen pressure sintering process. Sialon composite ceramics.

The object of the present invention is to use high melting point YAG (Y ₃ Al ₅ O ₁₂ ) as the grain boundary phase, and utilize the advantages of high hardness and high strength of α-sialon and β-sialon, respectively, to prepare it with pressureless and high nitrogen pressure technology Sialon multiphase ceramic implementation.

Specifically:

(1) The m and n values in the general formula Y _m/3 Si _12-(m+n) Al _m+n O _n N _16-n of α-sialon are used as the main crystal phase of α-sialon composite ceramics The main parameters of the content of sialon and β sialon, when m=0.3, n=1.0, the ratio of α sialon: β sialon is equal to 50:50, and the fluctuation range is 40:60.

(2) The sinterability of α-sialon and β-sialon composite ceramics depends on the content of YAG (Y ₃ Al ₅ O ₁₂ ) in the original components. The present invention controls the content of YAG to 9% of the main crystal phase weight, and YAG is the grain boundary phase.

(3) The original powder Si ₃ N ₄ is UBE-10 produced by Ube Shinsan Co., Ltd., the purity of AlN, Al ₂ O ₃ , Y ₂ O ₃ is 99.9%, and the average grain size is 1-2 μm. After weighing according to the composition ratio of (1) and (2) above, mix in an Al ₂ O ₃ ball mill cylinder with absolute ethanol as the dispersion medium and Si ₃ N ₄ balls as the ball mill medium for 24 hours, take out the slurry and dry it, Sieve through a 75-mesh sieve, shape it under 20MPa uniaxial pressure, and then make a green body by 200MPa cold isostatic pressing.

(4) The green body is sintered _under pressureless sintering at 1800°C under 1 atmospheric pressure of N ₂ airflow, and kept for 2 hours _. After sintering, it is sintered at a temperature of 1900-2000° C. for 1.5-3.0 hours under a high nitrogen pressure of 1.5 MPa.

(5) The fired samples were heat-treated at 1350°C for 24 hours under N ₂ conditions for crystallization treatment.

The advantages of the present invention are:

(1) In the main crystal phase, α-sialon: β-sialon = 50:50, and the fluctuation range is 40:60. The sintered composite ceramic has both high strength and high hardness.

(2) Since YAG with a high melting point is used as the grain boundary phase, the material also has excellent high-temperature mechanical properties (see Examples 1-5 for details).

(3) The dense Sialon composite ceramics can be obtained under the conditions of no pressure and high nitrogen pressure, which is beneficial to industrial production.

Example 1

Using Si ₃ N ₄ (UBE-10) produced by Japan Zibu Shinsan Co., Ltd. as the Si ₃ N ₄ raw material, the purity of AlN, Al ₂ O ₃ , Y ₂ O ₃ powder is 99.9%, and the average particle size is 1-2 μm. And considering the oxygen content on the surface of nitrogen-containing particles such as Si ₃ N ₄ and AIN, the ingredients are prepared according to m=0.3, n=1.0, and the weight of YAG is 9% of the weight of the main crystal phase. The green body flows at 1800 ° C and 1 atmosphere Under nitrogen, pressureless sintering for 2 hours, the embedding powder is Si ₃ N ₄ :AIN:BN=6:3:1 (wt%), after firing the sample, it was crystallized at 1350°C under N ₂ for 24 hours. The room temperature strength of the sample is 612MPa, the fracture toughness is 3.9 (MPa·m ^1/2 ), the Vickers hardness (HV ₁₀ ) is 1594, the strength at 1000°C is 595MPa, and the strength at 1350°C is 500MPa.

Example 2

Use the same raw materials as in Example 1 to sinter the sample in a high-nitrogen pressure furnace. First, keep it at 1800°C for 2 hours under flowing nitrogen at 1 atmosphere pressure, and then keep it at 1900°C for 15 hours under a high nitrogen pressure of 1.5MPa. The powder embedding is the same as in the example 1. The room temperature strength of the sample is 840MPa, the fracture toughness is 6.1 (MPa·m ^1/2 ), the Vickers hardness (HV ₁₀ ) is 1820, the strength at 1000°C is 740MPa, and the strength at 1350°C is 620MPa.

Example 3

Use the same raw materials as in Example 1 to sinter the sample in a high-nitrogen pressure furnace. First, keep it warm at 1800°C for 2 hours under 1 atmosphere of flowing nitrogen, and then keep it at 1900°C for 3.0 hours under a high nitrogen pressure of 1.5MPa. Example 1, the room temperature strength of the sample is 890MPa, the fracture toughness is 6.9 (MPa·m ^1/2 ), the Vickers hardness (HV ₁₀ ) is 1850, the strength at 1000°C is 780MPa, and the strength at 1350°C is 660MPa.

Example 4

Use the same raw materials as in Example 1 to sinter the sample in a high-nitrogen pressure furnace. First, keep the temperature at 1800 ° C for 2 hours under 1 atmospheric pressure of flowing nitrogen, and then keep it at 1950 ° C for 1.5 hours under a high nitrogen pressure of 1.5 MPa. The powder embedding is the same as the implementation Example 1, the room temperature strength of the sample is 860MPa, the fracture toughness is 6.5 (MPa·m ^1/2 ), the Vickers hardness (HV ₁₀ ) is 1820, the strength at 1000°C is 775MPa, and the strength at 1350°C is 650MPa.

Example 5

Use the same raw materials as in Example 1 to sinter the sample in a high-nitrogen pressure furnace. First, keep the temperature at 1800 ° C for 2 hours under 1 atmospheric pressure of flowing nitrogen, and then keep it at 2000 ° C for 15 hours under a high nitrogen pressure of 1.5 MPa. Example 1, the room temperature strength of the sample is 925MPa, the fracture toughness is 7.2 (MPa·m ^1/2 ), the Vickers hardness (HV ₁₀ ) is 1884, the strength at 1000°C is 830MPa, and the strength at 1350°C is 715MPa.

Claims (2)

1. A kind of sialon composite phase ceramic, is made up of Y, Si, Al, O, N quinary system, is characterized in that (1) The m and n values in the general formula Y _m/3 Si _12-(m+n) Al _m+n O _n N _16-n of α-sialon are used as the main crystal phase of α-sialon composite ceramics The main parameters of the content of sialon and β-sialon; (2) When m=0.3, n=1.0, the ratio of α-sialon and β-sialon is equal to 50:50, and the fluctuation range is 40:60; (3) The content of the grain boundary phase YAG (Y ₃ Al ₅ O ₁₂ ) is 9% of the weight of the main crystal phase; (4) The original powder Si ₃ N ₄ is UBE-10 produced by Ube Shinsan Co., Ltd., the purity of AlN, Al ₂ O ₃ , Y ₂ O ₃ is 99.9%, and the average grain size is 1-2 μm. 2. The preparation method of the sialon composite ceramics according to claim 1, characterized in that: (1) According to the main crystal phase α-sialon:β-sialon ratio is equal to 50:50, the fluctuation range is 40:60, the content of the grain boundary phase YAG is 9% of the weight of the main crystal phase; (2) Using absolute ethanol as the dispersion medium and Si ₃ N ₄ balls as the ball milling medium in the ball milling cylinder, mix for 24 hours, dry and sieve, form under 20MPa uniaxial pressure, and then 200MPa cold isostatic pressing; (3) The green body was sintered under pressureless sintering at 1800°C and 1 atmospheric pressure N ₂ for 2 hours, and the embedded powder was Si ₃ N ₄ :AlN:BN=6:3:1 (wt%) or after pressureless sintering Insulate at 1900-2000°C for 1.5-3.0 hours under 1.5MPa high nitrogen pressure; (4) After the sample is fired, it is crystallized at 1350 ° C under the condition of N ₂ for 24 hours.