JPS60245739A - Manufacture of tough ceramic - Google Patents

Abstract

PURPOSE:To manufacture a tough ceramic having high strength and high reliability by mixing an element of group IVa, etc. in the periodic table and an oxide such as Al2O3 in powder state with silicon nitride as a main body, and sintering said mixture to a specified relative density. CONSTITUTION:With silicon nitride as the main body, 5.5-45wt% metal (especially, V is preferable) of one kind or more selected from groups IVa or Va elements in the periodic table, and 1-20wt% metal oxide (especially, Al2O3, Y2O3 is preferable) of one kind or more selected from Al2O3, MgO, Y2O3, rare earth element oxide are mixed in powder state. Said mixture is sintered thoroughly in nonoxidizing atmosphere at about >=1,650 deg.C temp. to obtain >=95% relative density. In this way, the tough ceramic suitable for gas turbine blade, turbo-charger, etc. for automobile is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for manufacturing structural ceramics, and particularly to a method for manufacturing strong ceramics suitable for use in gas turbine blades, automotive turbine blades, and the like.

[Background of the invention]

BACKGROUND ART There is a tendency for heat engines to be used and temperatures to become higher and higher for the purpose of increasing efficiency, and the structural members that make up heat engines are also required to have even higher temperature characteristics. For example, a car tar? Charsha is required to be used at an exhaust gas temperature of 1100 to 1200°C, and gas turbines are planned to be used at a gas temperature of about 1300 to 1500°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 cracks occur, cracks easily grow and break, making it unreliable as a structural material. Further, the strength of the sintered body tends to vary due to defects in the sintered body, surface defects, etc., and it is difficult to design the strength of the sintered body.

On the other hand, tool materials such as ceramics, sintered bodies made mainly of boron carbide, boron nitride, etc., are tough materials that do not easily develop cracks even after being stained. However, 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, methods have also been proposed in which fibers of inorganic compounds or metals are dispersed in ceramics. However, with the former method, it is difficult to obtain a uniform sintered body because it is difficult to disperse the fibers, and the fibers do not shrink during sintering, so a special sintering method such as hot pressing is required. However, it has many disadvantages such as low mass production and difficulty in applying it to products with complex shapes.

Further, as the latter method, for example, Japanese Patent Application Laid-Open No. J1851-4
No. 1011 2% 1982-10815, 1973-
Examples are known in which various metals are added to silicon nitride, such as in Japanese Patent Application Laid-open No. 154417, Japanese Patent Application Laid-Open No. 194775-1982, and Japanese Patent Publication No. 1569-1987. However, in these examples, the toughness of the obtained sintered bodies was low for one of the reasons described below, and it was not possible to obtain a sufficiently reliable sintered body as a structural material.

(1) Since the amount of metal added to silicon nitride is small at 5% or less, the toughness of the sintered body does not increase.

(2) Because metal is only added to silicon nitride and no oxide to act as a sintering aid is added, sintering of the silicon nitride does not progress sufficiently, resulting in oxidation resistance at high temperatures of the resulting sintered body. The strength and toughness are not sufficiently large.

(3) An oxide that serves as a sintering aid is added to silicon nitride along with a metal, but the combination of metal and oxide types is not appropriate, and reactions between silicon nitride, metal, and oxide occur during sintering. The grain boundary phase formed by this process cannot be sufficiently tough and dense. Therefore, the oxidation resistance of the sintered body at high temperatures is 1
Strength and toughness are not sufficiently large.

[Purpose of the invention]

An object of the present invention is to provide a method for producing high-strength, highly reliable, tough ceramics suitable for use as high-temperature components such as turbocharts and gas turbines.

[Summary of the invention]

The method for producing tough ceramics of the present invention includes silicon nitride as a main component, one or more metals selected from elements of group IVa or group Va of the periodic table, and aluminum oxide, magnesium oxide, yttrium oxide, It is characterized in that one or more metal oxides selected from rare earth element oxides are mixed in powder form and sintered to a relative density of 95% or more.

In an advantageous embodiment of the invention, panasium is selected as the metal and one or more of aluminum oxide or isothrium oxide is selected as the metal oxide.

As a result of various studies by the present inventors, silicon nitride, metals from group fVa or group VA of the periodic table, aluminum oxide, magnesium oxide, and yttrium oxide.

Metal oxides selected from rare earth element oxides are mixed and the relative density is 9 at a temperature of 1650℃ or higher in a non-oxidizing atmosphere.
Ceramics that have been sufficiently sintered to 5% or more not only have excellent strength and oxidation resistance, but also have a high fracture toughness value of 10MN/rn% or more when evaluated with a stress intensity factor of 1c, making it suitable for structural ceramics. It was found that it has particularly excellent properties as a camphorax.

The fracture toughness value is a value indicating toughness, and it is known that the larger the value, the tougher the ceramic is, and the more reliable it is as a structural material.

In particular, when Klc exceeds IOMN/□ζ, defects of 100 μm can occur inside or on the surface, which can become a starting point for ceramic fracture.
Even if there is a defect of approximately 30 m, its strength is 30
With a length of 7 or more, it satisfies the strength design tolerances of rotating structures such as turbocharts and gas turbines, and does not cause problems such as breakage during use. Furthermore, even if there are defects in ceramics that are 100 μm or larger, they can be found and removed non-destructively on the production line by means such as X-ray transmission, ultrasonic flaw detection, and visual inspection. It's easy. In this way, Klc is 10 MN
By using ceramics with a content of /rn% or more, damage accidents due to inevitable internal defects or surface scratches in ceramics can be prevented, and the reliability of ceramic structures as structural materials can be greatly improved.

Furthermore, when Klc is large, a large amount of energy is required for the cracks existing in the ceramic to grow, and as a result, the growth of cracks is inhibited, so the properties of the ceramic are stable over a long period of time, and reliability is improved. The value will be high. 1c of ceramics produced by the manufacturing method of the present invention
is greater than l Q MN/'72, while silicon carbide and silicon nitride, which are typical structural ceramics, are
．． are at most 6MN/:4 and 13MN/, , 5 respectively.
It is 4. Accordingly, the energy required to grow the tough two-mix ceramics by the manufacturing method of the present invention is 1.5 to 2.5 times higher than that of these silicon carbide and silicon nitride ceramics.

In the tough ceramic produced by the production method of the present invention,
The reason why such a large fracture toughness value is obtained is that some of the added metals in Group A or Group Va of the periodic table react with silicon nitride during sintering, forming nitrides and silicides. At the same time as increasing the adhesion between silicon nitride particles and metal particles,
A part of it mixes with or reacts with aluminum oxide, magnesium oxide, ivtrium oxide, and rare earth element oxides to form a dense and tough phase, which precipitates at the grain boundaries of silicon nitride and causes cracks. This is thought to be to completely prevent the growth of

In the present invention, the reason why it is essential to make the relative density of the ceramic 95% or more is that if the relative density decreases further and the number of pores increases in the ceramic, cracks may grow along the pores. This is because it is difficult to inhibit the growth of cracks and cracks, making it impossible to obtain a large fracture toughness value.Also, when the relative density decreases, oxidation resistance at high temperatures decreases, and the strength tends to change over time. This is because it occurs. Here, the relative density means the ratio between the theoretical density calculated from the density and addition amount of silicon nitride, the added metal, and the metal oxide, and the actual density.

It is desirable that the amount of the metals of group IVa and group Va of the periodic table added is 5.5% by weight or more and 45% by weight or less. If the amount added is less than 5% by weight, it is not effective in improving the fracture toughness value;
If it exceeds 5% by weight, the sinterability will decrease and the relative density will decrease.
It will be difficult to have more than 5 sections. It should be noted that when the amount added is less than 30%, the strength and oxidation resistance at high temperatures of 1100° C. or higher are advantageous. In turbocharts and gas turbines, the temperature of ceramics is generally about 100 to 150°C lower than the gas temperature, and the amount added is 55 to 30°C.
It can be used at a gas temperature of 1200 to 1250° C. within the range of % by weight. In addition, the amount of the metal added is 5.5% by weight.
Above, 15 weight - or less, gas temperature 1300-135
It can be used at 0°C.

Among the metals of groups IVa and Va of the periodic table, the use of vanadium is particularly preferred. The use of vanadium particularly increases the oxidation resistance of the resulting ceramics at high temperatures.

Aluminum oxide, magnesium oxide, yttrium oxide, and rare earth element oxides act as sintering aids that promote densification of silicon nitride during sintering, but the amount added is
The total amount of metal oxides is preferably in the range of more than 1% by weight and less than 20% by weight. If the amount added is less than this range, sintering will be insufficient, the relative density will decrease, and the fracture toughness value will not be large enough. On the other hand, if it exceeds 20% by weight, the strength and oxidation resistance at high temperatures of 1,1200°C or higher will decrease. Note that in order to maintain high strength at high temperatures, it is particularly preferable to use aluminum oxide and/or yttrium oxide as the metal oxide.

The additive raw materials for the F/a group and Va group metals in the periodic table may be anything as long as they can be converted into metals during sintering, such as metal powders, alloy powders of metals, metal hydrides, organometallic compounds, etc. I can do it. Alternatively, it may be added in the form of a metal oxide or the like and then reduced to a metal.

In addition, as raw materials for adding aluminum oxide, magnesium oxide, and rare earth element oxides, anything can be used as long as it becomes an oxide during sintering. Composite oxides such as, metal salts such as nitrates, etc. can be used.

Examples of the present invention will be described below along with comparative examples.

[Embodiments of the invention]

Example: Si3N4 powder with an average particle size of 0.5 μm has an average particle size of 10 μm.
μm vanasome powder and Y2O3 with average particle size 07μm
゜At203. MgO, CeO,..., La2O3 powders were blended in the proportions shown in Table 1 to form a uniform mixed powder. Next, 10 to 15% by weight of an organic binder such as low polymerized polyethylene was added to this, and the mixture was molded using an injection molding method.
kg/cm2. A molded body was obtained by applying a load of . The molded body was then heated at a rate of 2° C./h to remove the binder, and then fired in N2 gas at 1650 to 1800° C. for 1 to 10 hours to obtain a sintered body. Table 1 shows the relative density, bending strength, and fracture toughness of the obtained sintered body, c, and the bending strength at room temperature after oxidation at 1100° C. for 1000 hours in air.

In addition, the fracture toughness value 1c is determined by making a semi-circular scratch with an area A on the sample using a Bizkaas hardness tester, and then measuring the bending strength σ.
Calculated using the formula below.

At σ=0.84, c4 horoscope Moreover, the bending strength was measured by the JIS three-point bending method.

As seen in Table 1, companies 1 to 23 who implemented the present invention
The tough ceramics have high bending strength and fracture toughness values, especially those with metal addition of more than 5% by weight and 30% by weight or less, and those with metal oxide addition of more than 1% by weight and 20% by weight. % or less, it can be seen that the high temperature strength and oxidation resistance are particularly high.

Using the blending ratios of A2, 8, and 12.13 in Table 1, all prototype rotors for turbocharts (blades and shaft integrated) with a blade diameter of 40 mm were manufactured in the manner described above. The prototype rotor was heated at a speed of 30,000 rpm at a gas temperature of 1,200 to 1,300°C.
After continuous operation, turn the gas ON and OFF. t
I ran the artdstop repeat test sound, but I couldn't find any problems such as damage.

Example 2 515N4 powder with an average particle size of 0.5 μm was added with metal powder from group A and Va of the periodic table (particle size 1 to 20 μm) and an average particle size of 0
．． 7 tim's At205. Y2O3, MgO, and rare earth element oxide powders were blended in the proportions shown in Table 2, mixed with 5% polyvinyl alcohol aqueous solution, and then placed in a carbine mold at a pressure of 350 kg/crn2 and a maximum temperature of 1750 ml. Hot-dose sintering was carried out under the conditions of 2 hours of holding time at °C. The properties of the obtained sintered body are shown in Table 2.

It is clear from Table 2 that the fracture toughness and bending strength of the tough ceramics (diameters 24 to 57) obtained by the manufacturing force method of the present invention are large.

〔Effect of the invention〕

As explained above, the present invention not only has excellent high-temperature strength and oxidation resistance, but also has a fracture toughness value of 10.
This is a large value of MN/-5, or more, and therefore, a strong ceramic that is highly reliable as a structural ceramic or glass can be obtained.

Claims (1)

[Claims] 1. Mainly silicon nitride, and one or more metals selected from Group A or Group I/A elements of the periodic table, and aluminum oxide, magnesium oxide, Ivtrium oxide, one selected from rare earth element oxides
More than one metal oxide is mixed in powder form, and the relative density is 95.
% or more. 2. The method for producing tough ceramics according to claim 1, wherein the total amount of metal added is within the range of 5.5 to 45% by weight. 3. The method for producing tough ceramics according to claim 1 or 2, wherein the total amount of metal oxides added is within the range of 1 to 20 parts by weight. 4. The method for producing tough ceramics according to claim 1, 2, or 3, wherein the metal is panzoum, and the metal oxide is aluminum oxide, ivtrium oxide, or both.