JPH11139874A - Silicon nitride-base ceramics and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce silicon nitride-base ceramics excellent also in workability while having excellent mechanical characteristics. SOLUTION: The silicon nitride-base ceramics contains a titanium compd. chiefly in the grain boundaries and has <=100 nm average grain diameter. The Vickers hardness of the ceramics is >=1,200 at room temp. and lowers to <=300 at >1,000 deg.C. The ceramics is produced as follows; silicon nitride powder and titanium powder are mixed and communicated to <=50 nm average particle diameter by a mechanical alloying method and the resultant composite powder is heated until <=100 nm average grain diameter is attained and the titanium compd. is distributed chiefly in the grain boundaries.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a silicon nitride structural ceramic material used for a mechanical structural member such as an automobile part, which has excellent hardness and flexural strength from room temperature to 900.degree. While having the mechanical properties of
The present invention relates to a silicon nitride-based ceramic having a novel function in which hardness is extremely lowered in a high temperature range of 1000 ° C. or more and processing becomes easy, and a method for producing the same.

[0002]

2. Description of the Related Art Silicon nitride ceramics are well-balanced materials in strength, fracture toughness, corrosion resistance, abrasion resistance, thermal shock resistance, oxidation resistance, etc., and can be used in a wide range from cutting tools to engine parts. Used as a structural material. In particular, recently, it has attracted attention as a structural material for automobile engines and gas turbines.

However, the mechanical properties of silicon nitride ceramics, such as high hardness, are conversely inferior in workability, leading to an increase in manufacturing costs. For this reason, ultra-high-speed grinding has been studied to increase grinding efficiency, or superplastic processing or near-net forming technology has been developed to reduce grinding, and silicon nitride ceramic parts can be manufactured at lower cost. Technology development for fabrication is being attempted.

[0004]

As described above, attempts have been made to reduce the production cost of silicon nitride ceramics. However, it is difficult to omit the finishing process even by a superplastic working method or a near net forming technique. Yes, ultra-high-speed grinding requires special machine tools and grinding wheels,
Innovative low-cost manufacturing technology has not yet been realized.

The present invention has been made in view of such a conventional situation,
An object of the present invention is to provide a silicon nitride-based ceramic which can be manufactured by a fundamental and simple method, has excellent mechanical properties, and is also excellent in workability, and a method for manufacturing the same.

[0006]

Means for Solving the Problems In order to achieve the above object, the silicon nitride-based ceramic provided by the present invention mainly contains a titanium compound at a grain boundary and has an average crystal grain size of 100 n.
m or less, the Vickers hardness at room temperature is 1200 or more, and when it exceeds 1000 ° C., the Vickers hardness becomes 3
It is characterized by being reduced to 00 or less.

[0007] In the above-mentioned method for producing silicon nitride ceramics, silicon nitride powder and titanium powder are mixed and pulverized to a mean particle size of 50 nm or less by a mechanical alloying method, and the obtained composite powder is mixed with an average particle size of 100 nm or less and titanium powder. It is characterized by heating until the compound is mainly distributed at the grain boundaries.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The silicon nitride-based ceramic of the present invention comprises a silicon nitride sintered body mainly containing a titanium compound in a grain boundary, and has a characteristic structure in which the average crystal grain size is 100 nm or less. doing. With such a configuration, it has excellent mechanical properties such as high Vickers hardness in a medium to low temperature range, and at the same time exhibits excellent workability at a high temperature of 1000 ° C. or higher.

That is, the silicon nitride-based ceramic of the present invention has a hardness equivalent to that of a conventional silicon nitride sintered body in a temperature range from around room temperature to 800 ° C. or lower, and has abrasion and wear resistance.
It also has excellent performance in bending strength and fatigue strength. Specifically, when the Vickers hardness is 1200 or more at room temperature, and when the Vickers hardness is less than 120, particularly wear resistance cannot be maintained, and characteristics equivalent to those of a conventional silicon nitride sintered body cannot be exhibited. . For this reason, the silicon nitride-based ceramics of the present invention is intended for use in medium to low temperatures such as sliding parts.

At the same time, the hardness of the silicon nitride-based ceramic of the present invention rapidly decreases when the temperature exceeds 1000 ° C.
The Vickers hardness at 00 ° C. is 300 or less. In the grinding of silicon nitride ceramics, the temperature at the grinding point is 100
Since the temperature exceeds 0 ° C., the hardness at 1000 ° C. or more greatly affects the grindability, and according to the study of the present inventors, the removal processing is high when the hardness at 1000 ° C. is 300 or less. It turned out that it can be done with efficiency.

The silicon nitride ceramic of the present invention can be manufactured, for example, by the following method. First, commercially available silicon nitride powder and titanium metal powder are mixed and pulverized by a ball mill to form a composite powder of silicon nitride particles and titanium powder having an average particle diameter of 50 nm or less. When the addition amount of the metal titanium powder is too small, there is no effect of improving the workability by addition, and when it is too large, the metal titanium may remain in the sintered body without being nitrided. It is preferable to be about weight%.

Thereafter, the composite powder is densified in a short time by a hot press method or the like, and is controlled so that the average crystal grain size does not exceed 100 nm. When the mixing and grinding of the raw material powder is insufficient, the average particle size of silicon nitride in the obtained composite powder is 50%.
When sintered, the sintered body comprising silicon nitride and titanium compound particles having an average crystal grain size of 100 nm or less cannot be obtained.

When the average crystal grain size of the silicon nitride and titanium compound in the obtained silicon nitride-based sintered body exceeds 100 nm, even if the Vickers hardness at room temperature is 1200 or more, the Vickers hardness at 1000 ° C. The hardness does not become 300 or less, and a silicon nitride ceramic having excellent workability cannot be obtained.

[0014]

EXAMPLE An α-type Si ₃ N ₄ powder having an average particle size of 0.6 μm was
Metal Ti powder having an average particle size of 5.0 μm in the amount shown in Table 1 below and 1% by weight of MgO as a sintering aid were added, and mixed and pulverized using a ball mill. The conditions (acceleration and time) for the mixing and pulverization are as shown in Table 1.

[0015] The composite powder obtained by co-grinding, measuring the particle size of silicon nitride using a TEM, Si ₃
Table 1 shows the average particle size of N ₄ . Next, each composite powder was pressure-sintered at a temperature shown in Table 1 under 1 atm of nitrogen to be densified. As a comparative example in which the sintering temperature was lowered, Sample 1 was used.
0 was prepared.

[0016]

[Table 1] Ti addition amount Mixing and grinding conditions In composite powder Sintering temperature Sample (wt%) Acceleration (G) Time (hr) Si ₃ N ₄ Particle size (nm) (° C) 1 * − 100 4 200 1400 2 5 100 4 40 1400 3 20 100 4 10 1400 4 50 100 4 10 1400 5 * 70 100 4 60 1400 6 * 20 2 4 400 1600 7 20 150 8 10 1300 8 * 20 150 4 10 1900 9 * 20 100 8 15 1700 10 * 20 100 8 15 1200 (Note) Samples marked with * in the table are comparative examples.

The Vickers hardness of each of the obtained Si ₃ N ₄ based sintered bodies was measured at room temperature and at 1000 ° C. The measurement of Vickers hardness was carried out in vacuum under a condition of holding at a load of 200 g for 10 seconds. Regarding the microstructure of the sintered body,
A thin film sample was prepared by ion etching, and the particle diameters of the matrix silicon nitride particles and the dispersed TiN particles were evaluated using a transmission electron microscope. These results are also shown in Table 2. Except for Sample 10, the TiN particles were mainly distributed at the crystal grain boundaries.

[0018]

[Table 2] (Note) Samples marked with * in the table are comparative examples.

As can be seen from the above results, the average particle diameter of the Si ₃ N ₄ particles and the TiN particles in the Si ₃ N ₄ based sintered body is 1
Each sample of the present invention having a size of 00 nm or less had a Vickers hardness at room temperature of 1200 or more and a Vickers hardness at 1000 ° C. of 300 or less.

[0020]

According to the present invention, while having excellent mechanical properties in the middle and low temperature range, the hardness sharply decreases at a temperature of 1000 ° C. or more, and therefore, it is difficult to perform grinding such as grinding at 1000 ° C. or more. Silicon nitride ceramics with excellent workability,
And a simple manufacturing method thereof can be provided.

Claims (2)

[Claims] 1. A titanium compound mainly containing at a grain boundary, an average crystal grain size of 100 nm or less, a Vickers hardness at room temperature of 1200 or more, and a Vickers hardness of 300 or less at 1000 ° C. or more. A silicon nitride-based ceramic characterized by a decrease. 2. A silicon nitride powder and a titanium powder are mixed and pulverized by a mechanical alloying method to an average particle diameter of 50 nm or less, and the obtained composite powder has an average particle diameter of 100 nm or less and a titanium compound is mainly distributed at grain boundaries. A method for producing silicon nitride-based ceramics, wherein heating is performed until the temperature of the ceramics increases.