JPH09295869A - Sialon ceramic excellent in impact resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem an weak impact resistance with a sialon ceramic in which the growth of particles in a sintered product are accelerated to form columnar particles or which is mixed with short fibers to form a composite material. SOLUTION: This sialon ceramic comprises a sintered product containing β-sialon in an amount of 80-90wt.%. Therein, a volume occupied with columnar particles constituting the sintered product and having minor axis diameters of >=1μm and aspect ratios of >=3 and further with uniaxial particles having particle diameter of <1μm and aspect ratios of <3 is >=70% based on the total volume of the β-sialon, and the area ratio of the columnar particles to the uniaxial particles is 1:1 to 3:1 in the same cross section. This method for producing the sialon ceramic comprises adding the oxide of the group IIIa element in the periodic table in an amount of 3-8wt.% as a sintering auxiliary to sialon powder, preparing the mixture into particles having a specific surface area of 12-15m<2> /g, molding the particles, sintering the molded product at the atmospheric pressure and further subjecting the sintered product to a HIP treatment, or hot-pressing the molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sialon ceramics and a method for manufacturing the same, and more particularly to sialon ceramics having excellent impact resistance and a method for manufacturing the same.

[0002]

2. Description of the Related Art Sialon ceramics have high strength and are excellent in oxidation resistance, thermal shock resistance, corrosion resistance, wear resistance, etc., and are suitable for parts used under high temperature and high load conditions such as gas turbines. Promising as a material.

However, this sialon ceramics
Since it has the disadvantage of low fracture toughness, in order to improve it, there is a method of promoting grain growth and columnarizing the grains in the sintered body, or a method of adding short fibers such as silicon carbide whiskers to form a composite. Is being attempted.

[0004]

However, although the above-mentioned method is effective in improving the static fracture toughness,
There is a problem that it is less effective in dynamically improving fracture toughness and weak in impact resistance. Therefore, for example, when particles collide with a ceramic component used in a gas turbine during operation, the ceramic may be easily cracked, resulting in large strength deterioration.

The present invention has been made in view of the problems of the above-described conventional sialon ceramics and the manufacturing method thereof, and an object thereof is to provide a sialon ceramic having improved impact resistance and a manufacturing method thereof. It is in.

[0006]

Means for Solving the Problems As a result of earnest studies to achieve the above-mentioned object, the present inventors have found that the ratio of relatively large-diameter columnar particles and extremely small-diameter equiaxed particles constituting a sintered body is determined. The present invention has been completed based on the finding that sialon ceramics having improved impact resistance can be obtained by using a suitable sintered body.

That is, according to the present invention, (1) a sialon ceramic is a sintered body containing 80 to 90% by weight of β-sialon, and the minor axis diameter of the sintered body is 1 μm or more and the aspect ratio is The volume occupied by 3 or more columnar particles and equiaxed particles having a particle size of less than 1 μm and an aspect ratio of less than 3 is 70% or more of the whole β-sialon, and the columnar particles and the equiaxed particles have the same cross section. The ratio of the area occupied by is 1: 1 to 3:
Sialon ceramics excellent in impact resistance (claim 1) characterized by being 1 and further (2) one or more kinds of periodic table 3a as a sintering aid in the sialon powder.
Addition of 3 to 8% by weight of oxide of group 3 element and specific surface area of 12
After adjusting to a fineness of ˜15 m ² / g, the powder compact is subjected to normal pressure sintering in nitrogen gas at a temperature of 1700 to 1800 ° C., and the sintered body is further compressed with nitrogen gas having a pressure of 150 MPa or more. In the method for producing sialon ceramics excellent in impact resistance, which is characterized in that HIP treatment is carried out at a temperature of 1650 to 1750 ° C. (Claim 2).
(3) To the sialon powder, 3 to 8% by weight of an oxide of one or more elements of Group 3a of the periodic table is added as a sintering aid, and the specific surface area is adjusted to 12 to 15 m ² / g. After that, the powder compact is 1800-185 in nitrogen gas.
The gist of the present invention is to provide a method for producing sialon ceramics having excellent impact resistance, which comprises hot pressing at a temperature of 0 ° C. by applying a pressure of 200 kg / cm ² or more (claim 3). Further details will be given below.

The reason why the impact resistance is improved by appropriately adjusting the ratio of the columnar particles and the equiaxed particles constituting the sintered body is not clear in detail, but it can be inferred as follows. A momentary stress such as collision of particles causes a crack on the surface of the material. In the case of brittleness such as ceramics, the crack usually becomes a fracture starting point and causes a large deterioration in strength. If the sintered body is composed of extremely small-diameter equiaxed particles as in the present invention, the interfacial strength is high, so that cracks are less likely to occur and the occurrence of fracture starting points can be suppressed. Also,
Even if a crack occurs, if the sintered body is composed of relatively large-diameter columnar particles as in the present invention, the progress of the crack is inhibited so that the crack does not significantly progress, and the strength deterioration is reduced. You can In this way, if the columnar particles having an appropriate particle diameter and the equiaxed particles are appropriately mixed in the sintered body,
It is thought that the impact resistance will be high because cracks are unlikely to occur and even if they do, they do not become large defects.

The columnar particles are columnar particles having a minor axis diameter of 1 μm or more and an aspect ratio of 3 or more, and the equiaxed particles are equiaxed particles having a particle size of less than 1 μm and an aspect ratio of less than 3. Particles (claim 1). Columnar particles have a minor axis diameter of 1 μm
If it is less than 1, the resistance to crack growth is low, which is not desirable. Further, if the aspect ratio is less than 3, crack deflection does not occur and it does not hinder crack growth, which is not desirable.
When the particle size of the equiaxed particles is 1 μm or more, the thickness of the grain boundary phase becomes thick and the interfacial strength becomes low, so that cracks easily occur upon impact. Further, even if the aspect ratio is 3 or more, cracks are likely to occur along the particles, which is not desirable.

The ratio of the columnar particles to the equiaxed particles is 1: 1 to 3: 1 in terms of the ratio of the areas occupied by the same cross section,
The volume ratio of the both particles to the total amount of β-sialon particles was 70% or more (claim 1). If the ratio is larger than 3: 1, that is, if the number of columnar particles is too large, the grain boundary area becomes small, the grain boundary phase becomes too thick, and the grain boundaries become weak, resulting in low impact resistance. On the other hand, if it is smaller than 1: 1, that is, if the number of equiaxed particles is too large, only the crack growth inhibiting effect of the long-axis particles is present, and the cracks easily propagate, so that the impact resistance decreases as a whole, which is not desirable. When the ratio of the total of both particles is less than 70% of the total amount of β-sialon particles, the effect of inhibiting the generation and propagation of cracks is also lost, which is not desirable.

Further, the proportion of the entire β-sialon particles in the whole sintered body is set to 80 to 90% by weight (claim 1). This means that if the β phase is too low, there are many particles of the equiaxed α phase, which is not desirable for the reason described above. Conversely, if the proportion of the β phase is too high, rare earth elements are incorporated into the sialon particles. The grain boundary phase becomes thicker,
Impact resistance is lowered, which is not preferable.

As a method for producing the sialon ceramics having the above-mentioned structural constitution, 3 to 8% by weight of an oxide of a Group 3a element of the periodic table is added to a sialon powder as a sintering aid, Specific surface area of 12 to 15 m ² / g
After that, the powder compact is subjected to atmospheric pressure sintering in nitrogen gas at a temperature of 1700 to 1800 ° C., and the sintered body is further exposed to nitrogen gas having a pressure of 150 MPa or more from 1650 to 1750. The HIP treatment is performed at a temperature of ℃ (Claim 2). If the amount of the sintering aid is less than 3% by weight, the liquid phase generated during firing will be too small and the densification will not proceed. If it is more than 8% by weight, a large amount of the glass phase will remain in the sintered body and the grain boundary strength will be weak. Therefore, the impact resistance is significantly reduced, which is not desirable.

The raw material powder has a specific surface area of 12 m ² / g.
If it is coarser, there is no effect in promoting grain growth by dissolution and reprecipitation, and if it is finer than 15 m ² / g, the growth of columnar particles due to dissolution and reprecipitation proceeds too much, which is not preferable.

Further, if the sintering temperature at normal pressure is lower than 1700 ° C., the densification is not sufficiently performed, and if it is higher than 1800 ° C., the decomposition reaction of sialon occurs, and the densification is also hindered, which is not desirable. At the temperature of HIP treatment, if it is lower than 1650 ° C, the effects of densification and grain growth are not recognized, and 1750 ° C.
If it is higher, rapid grain growth and decomposition reaction occur, so that a desired sintered body structure cannot be obtained.

As another production method other than the above, one or more kinds of periodic table 3a as a sintering aid may be added to the sialon powder.
Addition of 3 to 8% by weight of oxide of group 3 element and specific surface area of 12
After adjusting to a fineness of ˜15 m ² / g, the powder compact is molded in nitrogen gas at a temperature of 1800 to 1850 ° C. for 2 minutes.
It was decided to apply a pressure of not less than 00 Kg / cm ² for hot pressing (Claim 3). In this hot press method, 2
It is not necessary to carry out stage sintering, and if the sintering temperature is lower than 1800 ° C., densification does not occur, and if it is higher than 1850 ° C., dissolution reprecipitation proceeds too much to obtain a desired structure. If the pressing pressure is less than 200 Kg / cm ² , the effect of pressing is not observed and the desired structure cannot be obtained.

BEST MODE FOR CARRYING OUT THE INVENTION

The method for producing the sialon ceramics will be described in more detail.
-Prepare sialon powder or powder in which silicon nitride, aluminum nitride and alumina are blended so as to have a chemical composition of β-sialon. If the amount of impurities contained in these powders is large, the strength of the sialon particles will be weakened and the impact resistance will be lowered, so 0.1% by weight or less is preferable. However, for silicon nitride and aluminum nitride powder, it is desirable that the amount of oxygen does not exceed 2% by weight.
If it exceeds 2% by weight, the amount of the grain boundary glass phase generated in the sintered body increases, which causes a reduction in impact resistance.

As the sintering aid to be added, the third group of the periodic table is used.
Y ² O ³ , Sc ² O ³ , Yb ² O ^{3 and the} like, which are oxides of group a elements, are used, and 3 to 8 wt% is added by internal division. The purity of the sintering aid is preferably 99.9% or more. In addition, it is preferable to use not only one kind of the sintering aid but also two or more kinds in combination, which often gives good results. It is considered that this is because the multi-component liquid phase generated during sintering promotes grain growth due to dissolution and reprecipitation to some extent.

The sialon powder to which the sintering aid was added was
Alcohols such as methanol and isopropyl alcohol are used as the dispersion medium to suppress the oxidation of the powder, and beads made of silicon nitride or sialon ceramics are used as the medium to prevent the inclusion of impurities. ~
Mix and grind to a fineness of 15 m ² . Using this slurry, molding is performed by a conventional method such as a method of drying and CIP molding, a method of adding a binder and casting, or a method of adding a resin and injection molding.

Next, the formed body was subjected to 1 in nitrogen gas.
Normal pressure sintering is performed at a temperature of 700 to 1800 ° C., and the sintered body is subjected to HIP treatment at a temperature of 1650 to 1750 ° C. in nitrogen gas at a pressure of 150 MPa or more, or the formed body is made to 1800 in nitrogen gas. Sialon ceramics are produced by hot press sintering at a temperature of ˜1850 ° C. and a pressure of 200 Kg / cm ² or more.

When the sialon ceramics are manufactured by the above method, the sialon ceramics excellent in impact resistance can be obtained.

[0021]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
The present invention will be described in more detail.

(Examples 1 to 9) (1) Preparation of sialon ceramics Silicon nitride, aluminum nitride and alumina powders were blended so as to be β-sialon having a Z value of 0.3, and then shown in Table 1. The oxides were added in the amounts shown in Table 1, dispersed in isopropyl alcohol, and mixed and pulverized using beads made of Sialon ceramics by a medium stirring mill until the specific surface area became fine as shown in Table 1.

After drying the obtained slurry, 65 × 65 ×
It was uniaxially pressure-molded to 8 mm, and then CIP-molded at a pressure of 1.5 t. The compact was subjected to normal pressure sintering in nitrogen gas at a temperature shown in Table 1, and then subjected to HIP treatment in nitrogen gas at a pressure of 180 MPa at a temperature shown in Table 1 to produce a sialon ceramic.

(2) Evaluation The β-conversion rate of the obtained sintered body was determined from the intensity ratio of the peaks obtained by X-ray diffraction of the powder obtained by disintegrating the sintered body into powder. Further, the ratio of the proportion of the columnar particles and the equiaxed particles is determined by taking a photograph of the same cross section obtained by cutting the sintered body with an electron microscope and subjecting the photograph to image processing to make it equiaxed with the columnar particles having the particle diameter of the present invention. The area with particles was calculated and calculated. Further, the particle volume fraction was calculated by obtaining the area of the entire β-sialon particles in addition to the areas of the columnar particles and the equiaxed particles from the electron micrograph of the same cross section. Regarding the fracture toughness value of the obtained sintered body, the sintered body was ground to 8 × 6 ×
A 50 mm test piece was processed and the impact fracture toughness value was obtained by a one-point bending impact fracture test. Table 1 shows the results.

(Examples 10 to 14) Sinters were produced and evaluated in the same manner as in Examples except that hot pressing was performed at the temperatures and pressures shown in Table 1. The results are shown in Table 2.

(Comparative Examples 1 to 8) For comparison, as shown in Table 1, the specific surface area of the sialon powder, the addition amount of the sintering aid, the atmospheric pressure or the sintering temperature of the HIP treatment was used in the present invention. Sialon-based ceramics were produced by the same method as that of the example except that it was out of the range and evaluated in the same manner. The results are also shown in Table 1.

Comparative Examples 9 to 11 Sialon ceramics were prepared and evaluated in the same manner as in Examples except that the pressure or sintering temperature of hot press sintering was set outside the range of the present invention. Table 2 shows the results.

[0025]

[Table 1]

[0026]

[Table 2]

As is clear from Tables 1 and 2, in the examples in which the sintered bodies were produced under the conditions within the scope of the present invention,
The β ratio of the sintered body, the particle volume fraction, and the ratio of the columnar particles to the equiaxed particles are all within the scope of the present invention, and as a result, the impact fracture toughness value is larger than 8.5 MPa√m. Has become. This indicates that if a sintered body is manufactured under the conditions of the present invention, a sialon ceramic having excellent impact resistance can be manufactured.

On the other hand, in the comparative example, since the sintered body was manufactured under the conditions outside the scope of the present invention, all the β conversion of the sintered body,
1 of particle volume fraction and ratio of columnar particles to equiaxed particles
Three or more were out of the scope of the present invention, and as a result, the impact fracture toughness values were all significantly lower than those of the examples.

[0029]

As described above, when sialon ceramics are produced by the method according to the present invention, sialon ceramics in which columnar particles having a relatively large diameter and equiaxed particles having an extremely small diameter are mixed in an appropriate ratio can be produced. As a result, sialon ceramics having excellent impact resistance can be obtained.

Claims (3)

[Claims] 1. Sialon ceramics is a sintered body containing 80 to 90% by weight of β-sialon, and columnar particles having a minor axis diameter of 1 μm or more and an aspect ratio of 3 or more and a particle diameter which compose the sintered body. The volume fraction occupied by equiaxed particles having a diameter of less than 1 μm and an aspect ratio of less than 3 is 70% or more of the whole β-sialon, and the ratio of the area occupied by the columnar particles and the equiaxed particles in the same cross section is 1 : Sialon ceramics excellent in impact resistance, which is characterized by being 1 to 3: 1. 2. A fine powder having a specific surface area of 12 to 15 m ² / g when 3 to 8% by weight of an oxide of one or more elements of Group 3a of the Periodic Table is added to a sialon powder as a sintering aid. After that, the powder compact was molded in nitrogen gas at 1700 to 1700.
Pressureless sintering is performed at a temperature of 1800 ° C., and the sintered body is further subjected to a pressure of 150 MPa or more in a nitrogen gas of 1650 to 175.
A method for producing sialon ceramics having excellent impact resistance, which comprises performing HIP treatment at a temperature of 0 ° C. 3. A fine powder having a specific surface area of 12 to 15 m ² / g by adding 3 to 8% by weight of an oxide of an element of Group 3a of the periodic table as a sintering aid to a sialon powder. Then, the powder compact is prepared in nitrogen gas at 1800 to
A method for producing sialon ceramics excellent in impact resistance, which comprises hot pressing at a temperature of 1850 ° C. at a pressure of 200 kg / cm ² or more.