JPS59223272A - Ceramics structure and manufacture - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a ceramic structural material suitable for use as a high-temperature structural component such as a turbocharger or a gas turbine, and a method for manufacturing the same.

[Background of the invention]

The operating temperature of heat engines tends to be higher and higher in order to improve efficiency, and the structural components that make up heat engines are also required to have even higher temperature characteristics. For example, in a turbocharger for an automobile, the exhaust gas production capacity is 1100 to 1200 tons:'
In addition, high-temperature gas turbines are planned to be used at gas temperatures of about 1,300 to 1,500 c. For this purpose, ceramics such as silicon carbide, silicon nitride, and sialon, which have high temperature and high strength compared to metal materials, have been developed, but these ceramics do not have sufficient heat resistance or high temperature strength. On the other hand, because it is brittle, once a crack develops, it easily grows and breaks, making it unreliable. Furthermore, the strength tends to vary due to defects within the sintered body, surface defects, etc., and it is difficult to design the strength of the material as a structural material.

On the other hand, tool materials such as cermet, sintered bodies mainly made of boron carbide, boron nitride, etc., are tough materials that are difficult to grow even if they crack, and are sticky. These materials have the disadvantage that they change in quality when exposed to high temperatures in an oxidizing atmosphere, resulting in a significant decrease in mechanical strength.

In order to eliminate these drawbacks, a method has also been proposed in which fibers of a heat-resistant, high-strength material such as silicon carbide are mixed into a heat-resistant material such as silicon nitride and then sintered.

However, even with this method, the fibers are generally expensive and the aspect ratio (the ratio of the length of the long axis to the short axis) is usually as large as 50 or more, so the fibers become entangled with each other and are difficult to disperse. Because it is difficult to obtain a uniform sintered body and the fiber does not shrink during sintering, a special sintering method such as the pot press method is required to obtain a dense sintered body without cracks. The mechanical properties of the sintered body vary depending on the direction because mass production is low and it is difficult to apply it to products with complex shapes, and because the fibers tend to line up parallel to each other during processes such as molding and sintering. It has many disadvantages, such as being difficult to use as a general structural component, and lacks reliability and versatility as a structural component.

[Purpose of the invention]

The present invention eliminates the drawbacks of the prior art described above, and provides a ceramic structural material that has high heat resistance and fracture toughness, and is highly reliable and versatile, suitable for use as high-temperature parts such as turbochargers and gas turbines. is intended to provide.

[Summary of the invention]

The ceramic structural material of the present invention includes at least one type selected from hydrogen-resistant silicon, silicon nitride, and sialon;
It is characterized by mainly containing hafnium boride.

In a preferred embodiment of the present invention, the content of the funium boride is selected to be in the range of 5 to 50 volumes.

Furthermore, it is particularly desirable that the ceramic structural material of the present invention contains at least 10% by weight or less of at least one selected from aluminum oxide, magnesium oxide, and yttrium oxide.

As a result of various studies, the present inventors found that in ceramics made by mixing and sintering silicon-based materials such as silicon carbide, silicon nitride, and sialon with hafnium boride,
An oxide film mainly composed of 810x is formed on the surface in a high-temperature oxidizing atmosphere, and this film acts as a barrier to prevent internal oxidation and deterioration. It is dispersed in the base material of silicon-based material, forming a phase with mechanical properties different from those of the base material. Therefore, even if a crack occurs, the crack will branch and bend due to the interaction with the dispersed phase mainly composed of hafnium boride or its sintering reaction product, and as a result, the crack growth will be inhibited. Because of the heat resistance,
It was found that ceramics with high fracture toughness values could be obtained. Furthermore, the silicon ceramics and hafnium boride used may be of the same raw materials as those used in the general ceramics industry, and there is no need to use fibers or the like. Furthermore, a sufficiently dense sintered body can be obtained not only by hot pressing, HIP, etc., but also by ordinary pressureless sintering, and its mechanical properties are substantially isotropic. Therefore, the resulting ceramic structural material has high reliability and versatility.

The amount of hafnium boride contained in the ceramic structural material of the present invention is preferably within the range of 5 to 50 volumes. If the amount of hafnium boride is too small, it will not be effective in improving the fracture toughness value.

When the amount of hafnium boride is 5 volumes or more, the fracture toughness value is 10 MN/H13/2 or more. Furthermore, when the amount of hafnium boride is 10 volumetric or more, the fracture toughness value becomes 15 MN/m''/2 or more. Machining after curing is essential.In this case, surface scratches of up to 100 to 200 μm are often generated, which reduces the strength of conventional ceramics and causes a decrease in reliability. However, if ceramics with a fracture toughness value of 10 MN/m"/" or more are used, even under such conditions, it will show a strength of about 3QK9f/- or more, which is generally required for rotors, etc., and the reliability of ceramic structural materials will be improved. becomes significantly higher.

Furthermore, when the fracture toughness value is 15 MN/mL4 or more, I
The energy required for destruction is more than doubled compared to OMN/rn''/'', and the reliability of the ceramic structural material is further improved.

On the other hand, if the amount of hafnium boride is too large, the heat resistance in an oxidizing atmosphere will decrease, which is not preferable. Heat resistance of 1200 tl' or more is required for safe use in applications such as automobile turbochargers, and for this purpose it is desirable that the amount of hafnium boride is 50 vol tl or less.

When the ceramic structural material of the present invention contains at least one of aluminum oxide, magnesium oxide, and yttrium oxide, these oxides react with hafnium boride during sintering, and part of the material also becomes hafnium Δ arsenide. and form an aggregate of particles with a particle size of about 1 μm or less,
A ceramic structural material having a structure in which this aggregate is dispersed in silicone ceramics is obtained. This aggregate of particles with a particle size of about 1 μm or less is effective in branching cracks and has a great effect in preventing crack propagation. In particular, when about 100 or more particles are aggregated in the aggregate, there is a remarkable effect in preventing crack propagation, and the resulting ceramic structural material exhibits a particularly high fracture toughness value.

The amount of aluminum oxide, magnesium oxide, yttrium oxide, etc. added is preferably 10W1% or less. If the amount added is too large, the strength at high temperatures of 1200C or higher will decrease, which is not preferable.

The ceramic structural material of the present invention includes at least one of silicon carbide, silicon nitride, and sialon, hafnium boride, and Yx Os as necessary.

It is produced by mixing and sintering sintering aids such as A Lx Os 2M g O and B 4C. At this time, the sintering temperature was 16
A range of 00 to 2500C is desirable. If it is less than 1600C, sintering may be insufficient and the strength of the sintered body may be reduced, and if it exceeds 2500C, it may become superphosphoric acid, which may reduce the fracture toughness value.

[Embodiments of the invention]

Hereinafter, the present invention will be explained according to examples.

[Example 1] 8!3N4 powder with an average particle size of 0.7 μm and an average particle size of 2
pm HfB! and Y*O with an average particle size of 0.5/Jm
s.

MgO and AAsOs were blended in the proportions shown in Table 1 to form a uniform mixed powder. Next, add 10 to 15 wt to this
% of an organic binder such as low-polymerized polyethylene was added thereto, and a molded body was obtained by applying a load of 3500 K9/trot by injection molding. After removing the binder from the molded body, the molded body was fired for 1 hour at 1700 to 1800 t:' in N2 gas to obtain a sintered body. Table 1 shows the bending strength, fracture toughness value KIC, and bending strength at room temperature after oxidation at 1200C for 2000 hours of the obtained sintered body.

The fracture toughness value KIC was calculated by scratching the sample with a Vickers hardness meter, measuring the bending strength σ, and using the formula below based on σ and the scratch size C.

As shown in Table 1, ceramic structural materials with excellent fracture toughness and heat resistance can be obtained in the range of HfB2 addition #5 to 50 volumetric, YzOs, MgO, At 20g addition amount≦iowts. You can see what you can get.

Next, a prototype turbocharger rotor with a blade diameter of 40 m was fabricated using the sample shown in Table 1 A3. This rotor was operated at a speed of 300,000 f in a gas temperature of 1,100 to 1,200 C.
Although it was operated continuously for 0 hours, no problems such as damage were observed.

In addition, the amount of H f B2 added to 5isN4 with a particle size of 1 μm was added to 10 volumes, and the amount of H f B2 added to 5isN4 with a particle size of 1 μm was
The amount of tos added is 6wt% and 3wt, respectively, and the temperature is 1750t? The characteristics of the sintered body obtained by hot pressing at a pressure of 200 Kp/crl are shown in Table 2 together with the particle size of the raw material HfB2.

In the samples in Table 2, HfB2 and Y2O5 were present during sintering.

AtzOs etc. react to reduce the particle size to 0.1 to 1 μIn.
The results of SEM observation showed that the 5IsN4 particles formed an aggregate of particles such as Hf&, HfO2, HfSf, etc., and had a structure in which these particles were dispersed in 5IsN4. The number of particles constituting one aggregate depends on the particle size of the raw material HfB2, but Table 2 shows that the fracture toughness value becomes especially large when the number of particles in the aggregate is about 100 or more.
It can be seen that if the particle size of the raw material is too large, the number of pores in the sintered body increases and the bending strength decreases.

α-8iC powder with an average particle size of 1 μm and an average particle size of 5 μm)
-I f B 2 and At203 with an average particle size of 0.5 μm were blended in the proportions shown in Table 2, and polymethylsiloxane was used as a binder at a temperature of 2050 t; a pressure of 200 Kf.
/cd photopress. The characteristics of the obtained sintered body were
Shown in the table.

From Table 3, it can be seen that a ceramic structural material having excellent fracture toughness and heat resistance can be obtained when the amount of Hf132 added is in the range of 5 to 50%.

[Example 3] 5j3N4 powder with an average particle size of 0.7 μm and 5j3N4 powder with an average particle size of 0
．． ALzos particles of 5 μm and AA with an average particle size of 2/4 m
N powder and 5iOz powder with an average particle size of 1 μm were collected so that the value of 2 in the general formula S fa-zAtzOzNs-z of Sialon was 0.2 to 4.2, and then 5iOz powder with an average particle size of 2 μm was collected. HfB2 was added between 1 and 70 volumes to form a uniform mixed powder. The mixed powder was then formed into a compact by applying a load of 1000 Ky/cdl in a mold.

The compact was then fired in N2 gas at a temperature of 1700C for 1 hour. The sintered body obtained in this example also had Hf
When the amount of Bz added is in the range of 5 to 50 at%, the fracture toughness value>
IOMN/m", 15MN/m for 10 volumes or more, bending strength after 2oooh cooling at 1200C ≧40Kp
/- showed excellent properties.

[Example 4] β-8iC powder with an average particle size of 0.5 μm
75 W t % of B4C of μm, 4 wt % of novolak phenolic resin, 15 wt % of low polymerized polyethylene, and 8 vol % of HfB with an average particle size of 5 μm were added.
After injection molding at a pressure of 00 Kg/crA, the binder was removed at a heating rate of 2C/h, and the product was heated at 2300t:' in Ar.
It-yaki D5. sample, and α- with an average particle size of 2 μm.
4wt% of A7N with an average particle size of 2 μm and 28vot% of HfB with an average particle size of 5 μm were added to 8iC powder, and the temperature was 2050C.
Sample grapes were prepared by hot pressing at a pressure of 200 Ky/ctd. The fracture toughness values of these samples are both 11 MN.
/rr13/mi bending strength is 70 Ky/mr for the former
&, the latter was 105KV/-.

In addition, using the former sample, the blade diameter was 40 as in Example 1.
We prototyped a rotor for a turbocharger (blades and shaft integrated). Using this rotor, the waste temperature is 1300
We conducted a continuous test for 1000 hours at a temperature of 300,000 ryam at ~1500C and a cycling test of gas ONiOF, but no problems such as breakage were observed.

〔Effect of the invention〕

As explained above, the ceramic structural material of the present invention has the advantages of high fracture toughness and high heat resistance, and is reliable for applications such as automobile turbochargers and gas turbines. It can be widely applied as a high-temperature structural member with high properties.

Claims (1)

[Scope of Claims] 1. A ceramic structural material, characterized in that the main content thereof is at least one selected from silicon carbide, silicon nitride, and sialon, and a funium boride. 2. A ceramic structural material according to claim 1, characterized in that the content of the funium boride is in the range of 5 to 50 vol. 3. Claim 1 or 2, characterized in that the ceramic structural material further contains at least one selected from aluminum oxide, magnesium oxide, and yttrium oxide by 10 weight or less each. Ceramic structural materials. 4. Claims 1, 2, or 3, wherein the above-mentioned no-funium boride or its reaction product has an aggregate structure in which about 100 or more particles with a particle size of about 1 μm or less are aggregated. A ceramic structural material characterized by being dispersed in a ceramic structural material. 5. At least one selected from silicon carbide, silicon nitride, and sialon and 5 to 50 volumes of hafnium boride are mixed and fired at a temperature within the range of 1600 to 2500G. Method for manufacturing ceramic structural materials.