JPS6176628A - Ceramics-metal composite material - Google Patents

Abstract

PURPOSE:To provide a ceramics-metal composite material consisting of ceramics and metal hydride, capable of being sintered at a lower temp. compared with simple substance of ceramics, and yet still having toughness at the same time by using a chemical reaction between them. CONSTITUTION:Ceramics such as Si3N4, SiC, and BN, and metal hydride e.g. TiH2 are mixed selectively in a powdery state to form a ceramics-metal composite material. At this time, in order to attain toughening, the effective amount of the metallic element which is to be added to the ceramics is 2-60%, by weight ratio. And further, the finer the particle size of metal hydride to be used becomes, the higher the sintered density of sintered body also becomes. That is, when the particle size of ceramics is 10mum, for example, the particle size of metal hydride is preferably <=50mum. According to this invention, by the use of hydride-type powder instead of metal powder which is apt to form an oxide film thereon, a ceramics material having high density and toughness equal to those of conventional sintered body which is manufactured at high temp. and pressure can be obtained at lower temp. and pressure.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a ceramic-metal composite material, which is particularly suitable for heat-resistant structural materials that require toughness, and which utilizes the reactivity between ceramics and metal. The present invention relates to a ceramic-metal composite material that can be sintered at a relatively low temperature and under normal pressure because of its properties.

[Background of the invention]

Conventional methods for mixing starting raw material powders in ceramic-metal composite materials include: A method has been used in which metal powder is added to ceramic powder and mixed mechanically (Japanese Patent Application Laid-Open No.
No. 8-194775). Although this method is simple, it has the disadvantage that the surface of the added metal powder oxidizes during the process of forming the final green compact. This oxidation causes a reaction between the ceramic and the metal, which requires pressure sintering at high temperatures. In addition, as a method for producing mixed powder, there is a method of mixing ceramic powder in the form of a metal solution and reducing it to create a ceramic-metal mixed powder (Ceramic Bvlletin Vo.
t, 61A9 (1982)). This method can obtain a very uniform mixed powder, but it is difficult to completely reduce metals that have a strong affinity for oxygen, such as Cr, Ti, and Zr, and it is not possible to obtain a clean metal powder. .

[Purpose of the invention]

The purpose of the present invention is to utilize the chemical reaction between ceramics and metal hydrides. It can be sintered at a lower temperature than ceramics alone,
Ceramics that also have toughness
Our objective is to provide metal composite materials.

[Summary of the invention]

Ceramics have excellent heat resistance and corrosion resistance. In particular, non-oxide ceramics such as Sr3N4 and SiC have better mechanical strength at high temperatures than oxide ceramics, so they are used for applications such as gas turbine blades and nozzles. It is being considered for use as a high-temperature member.

However, since these ceramics have fracture toughness values that are more than one order of magnitude lower than metals, they have not reached the point where they can be used as structural materials. If such ceramics can be made tougher, they can be widely used as structural materials.

One possible method for toughening ceramics is to add metal powder to ceramics to make them into composite materials. However, the added metal generally has a very strong affinity for oxygen, and the surface is covered with a thin surface oxygen film. This oxide film is extremely stable and becomes a major hindrance when reacting ceramics and metals, especially at low temperatures. Further, it takes a long time to mix the added metal to uniformly disperse it in the ceramic, and the powder becomes considerably contaminated due to surface oxidation.

From this point of view, the present invention was devised to keep money powder active. The present invention will be explained in detail below. Instead of pure Ti or pure Zr, which are used to keep metal surfaces active, we tried adding hydrides such as TiT and ZrH. Since the surface of this hydride powder is stable at room temperature, there is no fear of powder surface oxidation even if mixing is performed for a long time. However, since hydrides decompose at temperatures of 4.50 DEG C. to 500 DEG C., the hydride-based powder in the green compact is decomposed during the rise in sintering temperature and becomes metal powder with a clean surface. Since the metal surface can be kept active during sintering, it is possible to sinter at a lower temperature than conventional high sintering temperatures.

Further, such hydrides have a lighter specific gravity than pure metals, and a sufficiently small particle size. The specific gravity of ceramics is approximately 3 g/
cm", whereas the specific gravity of conventionally added metals is about 4.5 to 9 g/cm", which is a large difference. Therefore, by replacing the conventional additive metal with hydride, Ti (4,51g/cm”)−+Ti
H, (3,76g/cm”), Z r (6,49g
/cm2) −+ZrH, (5,6g/cm”)
The difference in specific gravity between metal and ceramics can be reduced.

The smaller the difference in the specific gravity of the powder, the more uniformly the powder can be mixed in a shorter time, so by substituting a hydride, the powder can be mixed more uniformly even under the same mixing conditions. However, no matter how stable the surface of the hydride powder is, it has a very strong affinity for oxygen, so it is possible that the surface may be partially oxidized, so it is better to avoid contact with oxygen during mixing as much as possible. In order to prevent oxidation, it is best to perform wet mixing to suppress contact with air during mixing, and select a solvent that has as low a solid solubility of water and oxygen as possible. The mixed powder of metal and ceramics, which has been coughed to retain its activity, is sintered in nitrogen or vacuum.

As an additive metal, it itself has a high melting point. An element that reacts with ceramics to produce high melting point carbides and nitrides.
In addition, a hydride-based powder was selected as the activated powder, and 'I' iHv was selected in consideration of reactivity with ceramics.
and Zr) (, powders were studied. Ceramic powders include SiS N4 + 8' among carbide-based and nitride-based powders that are generally used for heat-resistant ceramics.
CT people chose tN and BN.

The sintered density was investigated under various conditions and it was found that the sintered density increases rapidly from the temperature at which ceramics and metals start to form. When TiHl is added to st, N, the following reaction occurs. First, Ttax → T l + Ht around 400℃, then s like SisN4+4'l'i → 4TiN+38i from around tooC.
TiN and 3i are generated by decomposing t and N. SiC
When TrHt is added to 5ic-+'ri4'ii
SiC decomposes to produce TiC and Sif as shown in c+si.

Not all of the 3i produced during this reaction exists alone, but a portion reacts with Ti to produce TiSi. The actual sintering temperature is 1400°C to 1600°C. At this time, TiSi is melted and liquid phase sintering occurs using this liquid phase, improving the sintered density.

In order to improve the toughness of a ceramic-metal composite material, in addition to the type of ceramic and the combination of metal elements added, the amount of metal elements added is important. If the amount of the added metal element is less than 2% by weight, the sintered density will not increase. Also 60wt
If one or more is added, all of the T i 3N4 will react. From this, it is effective for the amount of metal elements added to ceramics to be in the range of 2 to 60% by weight for toughening.

- Yoshikawa The particle size of the powder also has a large effect on toughening. If the particle size of the ceramic powder is 10 μm or more, there will be many sintered holes even after sintering, and a sintered density of 90% or more will not be achieved.

The smaller the grain size, the higher the sintered density and the finer the crystal grains.

Therefore, it is also effective in terms of strength. The particle size of the metal powder is determined by the particle size of the ceramic powder used. For example, if the ceramic particle size is 10 μm, if the particle size of the metal powder added is 50 μm or more, the difference in particle size from the ceramic powder will be large. This makes it difficult to mix uniformly, and furthermore, the contact area between the metal powder and the ceramic powder becomes small, making it impossible to sinter by fully utilizing the reaction between the two. On the other hand, it was found that as the particle size of the metal hydride added becomes finer, the sintered density of the sintered body increases. Therefore, the finer the particle size of the ceramic powder and metal powder used, the more effective the toughening will be.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

Example 1゜Si, N, powder with a particle size of 0.5 μm and a weight ratio of 50 wt.
%, Ti powder with an average particle size of 5 μm was added, mixed for 1 hour in a Raikai machine, molded at 2 tons/cm”, and sintered at 1500°C under normal pressure in a vacuum atmosphere.
The sintered density was 69.4% in relative density.

Compared to the commonly used sintering temperature, the temperature is 160°C.
It can be seen that when the sintering temperature is as low as 0° C., the sintered density hardly increases.

Example 2 S with a particle size of 0.5 μm; weight ratio of 50wt4 to N4 powder
TiH1 powder with an average particle size of 5 μm was added, mixed for 1 hour in a Raikai machine, molded in a 2 ton mold, and
As a result of pressureless sintering in a vacuum atmosphere at 0°C, the sintered density was 9.
It reached 0.9%. As can be seen from the comparison with Example 1, the use of TiH2 powder significantly increases the sintered relative density even at a low sintering temperature.

Example 3゜Particle size: 0.5 μm (7) Average particle size: 5 μm for Si3N4 powder
The sintered density at each sintering temperature when 5Qwt% of Ti powder and 7) TiH powder with an average particle diameter of 5 μm + 7) was added in a weight ratio and sintered in vacuum at normal pressure was converted to a relative density. Shown in Figure 1. As shown in Figure 1, the sintered density of the molded body added with metal Tl does not increase even at high temperatures;
The sintered density of the molded body to which TiH2 is added increases from around 1300°C, and reaches a sintered relative density of 90- or more at a sintering temperature of 1500°C to 1600°C. In this way, TiH
It can be seen that by using 1 powder, sintering can be performed at a lower temperature than in the case of adding metal Ti powder.

Example 4 Powder with the same composition as in Example 2 was mixed in the same manner as in Example 2 and then mixed in the bottom of a ball mill-I494 to examine the effect of the mixing method on sinterability. . These powders were formed into a mold at 2 ton/cm" and sintered in a vacuum at 1600°C, resulting in a sintered density of 99.8. It can be seen that the sintered relative density is much improved compared to machine mixing.

Example 5 TiH with an average particle size of 5 μm and metal Ti with an average particle size of 5 μm were added in a weight ratio of 50 wt to SiC powder with a particle size of 0.5 μm, and the same method as in Example 1 was carried out. After mixing, it was molded at 2 ton/cm" and heated at 150 ton/cm in vacuum.
As a result of pressureless sintering at 0°C for 2 hours, it was found that the Ti)IT-based sintered material had a sintered density of 91%, whereas the metal Ti
The sintered density of the system sintered material is as low as 75%, indicating that hydride addition is also effective for Si/C powder.

Example 6゜St with a particle size of 0.5 μm, N, powder with an average particle size of 5 μm
of Ti powder and TiH powder with an average particle size of 5 μm at a weight ratio of 0.5, 10, 20, 30, 40°50.6, respectively.
0% was added, mixed for 1 hour in a Raikai machine, mixed for 244 hours in a centrifugal ball mill, sintered in a vacuum atmosphere at 1600°C for 2 hours, and the fracture toughness value +c was measured using the 5ENB method. The results are shown in FIG. (a) is T iH
(b) is the case where Ti is added. This is it, 9
It can be seen that addition of TiH (addition of Ti is much more effective than addition of Ti), and its addition amount reaches its maximum value at about 30 Ti.

Example 7 Si, N, powder with a particle size of 0.5 μm and a weight ratio of 50wt4
ZrI (with an average particle size of 5 μm) and metal 7.r with an average particle size of 5 μm were added, mixed in the same manner as in the example, molded at 2 tons/cm2, and
As a result of pressureless sintering at 00°C for 2 hours, ZrH2-added ceramics had a sintered density of 90%, whereas metals had a sintered density of 7. R-added ceramics have a low sintered density of 70%,
It can be seen that hydride addition is effective in Zr addition.

〔Effect of the invention〕

In conventional methods for producing ceramic-metal composite materials, the surface of the metal powder added to the ceramic is covered with an oxide film, so the molded body is sintered at high temperature while being pressurized to obtain a high-density ceramic material.

According to the present invention, by using a hydride-based powder instead of a metal powder that tends to form an oxide film on the powder surface, a high-density and tough ceramic material equivalent to that of conventional pressurized and high-temperature sintered bodies can be produced. It can be obtained at low temperature and without pressure.

[Brief explanation of the drawing]

FIG. 1 shows an example of an 8'a N4T of the present invention.
iH is a graph showing the sintered density of the composite material at each temperature, and Figure 2 is a graph showing the dependence of the fracture toughness value of the iHs and Ti composite materials on the amount of metal added (a )...In the case of TtH addition, (b)...In the case of Ti addition.

Claims (1)

[Claims] 1. A ceramic-metal composite material comprising ceramic powder and metal powder, characterized in that a metal hydride is added instead of a metal.