JPH0243809B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field The present invention improves toughness and strength by dispersing in a ceramic matrix spherical metal particles that are chemically strongly bonded to the ceramic of the matrix. The present invention relates to ceramics made of ceramics and a method for producing the same. The energy required to sinter this metal dispersion strengthened ceramic is
It is supplied by the reaction heat generated when synthesizing ceramics by combining metal and non-metal elements, and is unique in that the synthesis, sintering, and dispersion of metal particles of ceramics are completed simultaneously in one process. .

(b) Problems with the conventional technology Ceramics generally have higher hardness and better wear resistance than metals, so they are used for processing tools and sliding parts that are subject to significant wear compared to metals.

At this time, the most important issues when using ceramics are strength and toughness. Strength and toughness, in turn, lead to material reliability.

Most ceramics are covalently bonded, have a modulus of elasticity several times higher than metals, and hardly experience elastic or plastic deformation.

For this reason, it is extremely sensitive to defects inside the sintered body, and once cracks begin to develop, it is almost impossible to stop them midway, resulting in destruction all at once. This is the biggest difference from metal,
Various attempts have been made to date to improve the brittleness of ceramics.

One of these attempts to stop the growth of cracks by applying compressive stress to the crack tips by utilizing the volumetric expansion associated with the phase transformation of ceramic dispersed phases, such as partially stabilized ZrO ₂ . However, with this method, phase transformation occurs before stress is applied as the temperature rises, and the toughening mechanism disappears.

Another method is to strengthen ceramic particles such as cermet by bonding them through metal grain boundary phases. This method has a strong impact buffering effect due to the presence of a highly tough metal phase between the ceramic particles, but when used at high temperatures, the softening of the grain boundary phase greatly affects the overall strength of the cermet. reflected, causing a rapid decrease in strength.

Furthermore, research has been conducted on strengthening the ceramic matrix by dispersing different types of ceramic fibers in a ceramic matrix to branch out the propagation of cracks and increase fracture energy. The dispersion technology is difficult, and the wettability of the ceramic matrix and ceramic fibers is not fully understood, so it has not yet reached the stage of practical use.

As mentioned above, various measures have been taken to improve the toughness of ceramics currently in use, but these are still insufficient or properties other than toughness are sacrificed.

Considering the conventional technology from the viewpoint of manufacturing methods, in order to obtain ceramics with a structure in which spherical metal particles are dispersed in a ceramic matrix, as in the present invention, the conventional method involves mixing ceramic powder and metal. It would be common to sinter the powder mixture under high pressure. However, the sintering temperature of ceramics is often higher than the melting point of metals, and in that case, the metal melts during sintering, resulting in a structure in which the metal fills the spaces between ceramic particles, resulting in a ceramic matrix like the one of the present invention. A structure in which spherical metal particles are dispersed cannot be obtained. Conversely, even if the melting point of the metal is higher than the sintering temperature of the ceramic, poor wettability between the ceramic particles and the metal particles will inhibit the densification of the ceramic and leave many pores in the sintered body. Further, as the volume fraction of the metal increases, the coalescence of the added metal particles progresses, and there is a high possibility that a structure in which the metal is finely and uniformly distributed will not be obtained, but a structure in which coarse metal particles are unevenly distributed.

As described above, with conventional sintering methods, it has been difficult to obtain high toughness ceramics in which spherical metal particles are finely and uniformly dispersed as in the present invention. In view of the above problems, the present inventors conducted research and development on a method for sintering high-toughness ceramics dispersion-strengthened with metal particles, and as a result, they arrived at the present invention.

(C) Disclosure of the Invention The biggest difference between the present invention and conventional ceramic composite materials is that the composite material is not obtained by sintering a mixture of ceramic powder and a dispersion material such as a metal, but by sintering a mixture of a metal powder and a nonmetallic element. When simultaneously sintering ceramics from
The purpose is to uniformly disperse unreacted metal particles into the ceramic matrix after sintering.

As mentioned in the section on problems with conventional technology, when a mixture of ceramic powder and metal powder is used as a starting material, there are problems with the melting point and sintering temperature of the metal, and problems with the wettability of ceramic particles and metal particles. There are many problems such as the formation of coarse particles due to coalescence of metal particles. In contrast, in the present invention, these problems can be solved by utilizing simultaneous sintering of ceramics.

First, there is the issue of the melting point and sintering temperature of metals. Even if the simultaneous sintering temperature of ceramics is higher than the melting point of metals, metal particles that are in contact with nonmetallic elements during the ceramics synthesis process are sequentially removed from the surface. Ceramicization progresses toward the inside, so even if the temperature temporarily exceeds the melting point of metal,
The metal melts inside the ceramic shell and does not flow out of the shell. Therefore, after cooling, a structure in which spherical metal particles are dispersed in the ceramic matrix can be obtained.

This application is for ceramic group a, group a, group a
A ceramic matrix is made of at least one metal element selected from Group A, Group A, and at least one non-metal element selected from the group consisting of B, C, N, and Si. Metal dispersion-strengthened ceramics characterized in that approximately spherical metal particles identical to the metal constituting the metal particles are dispersed in a volume fraction of 70% or less (not including 0), and both are strongly chemically bonded. It is something.

For example, spherical metal Ti is placed in a TiB ₂ matrix.
Considering the case of manufacturing a composite material in which TiB 2 is dispersed, Ti + 2B → TiB ₂ + 70.0Kcal/mol (298〓K) ... (1) As shown in equation (1), as TiB ₂ is generated,
A heat of reaction of 70.0 Kcal/mol is generated. For this reason, if a powder mixture of Ti and B, in which Ti is added in excess of the stoichiometric composition, is consolidated under pressure, a portion of the mixture is heated and ignited to force the reaction of equation (1) to start. Next, the reaction heat generated causes adjacent parts to start reacting one after another, and the chain reaction progresses to the entire powder compact, completing the synthesis and sintering of the ceramic at the same time. When TiB ₂ is formed, the temperature is thought to exceed 2000°C, albeit temporarily. For this reason, metallic Ti that does not participate in the synthesis reaction of TiB ₂ added in excess of the stoichiometric composition may be temporarily melted, but the outer shell of metallic Ti changes to TiB ₂ and melts. This prevents Ti from flowing out between particles.
After cooling, a structure in which spherical metallic Ti particles are dispersed in a gray ceramic matrix as shown in FIG. 1 is obtained. Figure 1 shows the state in which metallic Ti particles are dispersed in a TiB ₂ matrix.

Regarding wettability between the ceramic of the matrix and the dispersed metal particles, ceramicization progresses from the surface of the metal particles inward, and this outer ceramic shell is sintered to form a matrix. It has very good wettability and is chemically bonded strongly.

As shown in Fig. 1, the TiB ₂ matrix and the metallic Ti dispersed particles are firmly bonded without any gaps.

Furthermore, according to the simultaneous synthesis and sintering method of the present invention, there is no excess Ti that does not contribute to the synthesis reaction of ceramics during sintering.
Since the parts are separated by the TiB ₂ outer shell, there is a low probability of direct contact, which has the advantage that the metal particles are less likely to become coarse. As shown in FIG. 1, most of the dispersed particles of metallic Ti exist independently.

When the volume ratio of metal dispersed particles exceeds 70%, there is a high probability that the metal dispersed particles will come into direct contact with each other.
Since the structure in which spherical metal particles exist independently in the ceramic matrix of the present invention cannot be maintained, the volume ratio of the metal dispersed particles must be suppressed to 70% or less.

The metal dispersion-strengthened ceramics produced as described above has extremely high hardness and excellent abrasion resistance because the matrix is ceramic, and at the same time, the dispersed metal particles resist impact force. Because of this role, impact resistance has been greatly improved. In addition, by dispersing metal particles with low hardness in a matrix with high hardness,
There is a high possibility that the sliding properties will be improved. In fact, the coefficient of friction is smaller than that of ceramics alone, which does not contain dispersed metal particles.

Regarding high-temperature strength, cermets have the disadvantage that high-temperature strength rapidly decreases due to the softening of the metal grain boundary phase existing between ceramic particles, but in the metal dispersion-strengthened ceramic of the present invention, the high-temperature strength Since the skeleton present in the material is ceramic, the rate of decrease in strength and hardness at high temperatures is much smaller than that of cermets.

Regarding corrosion resistance, when metal exists in continuous grain boundaries like in cermets, the metal grain boundary phase is preferentially corroded by acids and alkalis, making it impossible to hold the ceramic particles together. However, in the metal dispersion-strengthened ceramic of the present invention, the matrix is made of ceramic with excellent corrosion resistance, and metals that are susceptible to corrosion are protected by the ceramic matrix, so they cannot be used directly. Since it does not come into contact with corrosive atmospheres, corrosion resistance is also greatly improved.

As described above, the metal dispersion-strengthened ceramics of the present invention have high hardness and excellent wear resistance.
It is a material that combines the advantages of ceramics, which have excellent high-temperature properties and corrosion resistance, and the advantages of metals, which have high toughness and excellent impact resistance.

The present invention will be explained below with reference to Examples.

Example 1 -71.85 g (1.5 mol) of metallic Ti powder of 325 mesh
After mixing 21.62 g (2 moles) of B powder with an average particle size of 1.0 μm, a portion of this powder was molded into a cylinder with a diameter of 5 mm and a height of 5 mm using a mold press at a pressure of 2 tons/cm ² . did. After storing this molded body in a BN container, it was placed in an ultra-high pressure generator with the upper end of the molded body in contact with a carbon heater, and while pressurized to 30,000 atmospheres, the carbon heater was energized and ignited. . The current was interrupted immediately after the TiB ₂ production reaction started.

Metal Ti dispersion strengthening obtained as above
The density of the TiB ₂ sintered body was 99.4% of the theoretical density.
The structure inside the sintered body at this time is shown in FIG.

As a result of EPMA analysis, the particles dispersed in Figure 1 were metallic Ti, and the matrix was _TiB2 .

All of the added B powder reacted with Ti. In order to evaluate the characteristics of the sintered body thus obtained, a cutting test was conducted.

The work material used was a 100φ cast iron bar, and the cutting speed was
Dry cutting was performed at 250 m/min, depth of cut 0.4 mm, and feed rate 0.1 mm/rev. When measuring the time required for flank wear to reach 0.2 mm, it was 6 minutes for a commercially available Al ₂ O ₃ cutting tool and 5 minutes for a TiN-TiC-WC-Co based cermet, but the time required for flank wear to reach 0.2 mm was obtained with the present invention. What I had
It had a lifespan of 20 minutes.

Example 2 239.85 g (2.5 mol) of metal Mo powder of -325 mesh and 12.01 g (1 mol) of C powder with an average particle size of 1.0 μm were mixed and then vacuum-sealed in a sealed container made of Mo. A carbon heater is built into this sealed container as an ignition device, and a lead wire is taken out of the container. This sealed container was placed in a high pressure generator, and while the sealed container was preheated to 800°C and pressurized with Ar gas at 2000 atm, electricity was applied to the carbon heater to ignite it. The current was interrupted immediately after the Mo ₂ C production reaction started.

Metal Mo dispersion strengthening obtained as above
The density of the Mo ₂ C sintered body was 99.1% of the theoretical density.
As a result of X-ray diffraction of this sintered body, peaks of Mo ₂ C and Mo corresponding to approximately the molar ratio appeared.

The sintered body thus obtained was processed into a cutting tool, and a cutting test was conducted under the same conditions as in Example 1. As a result, the life span was 10 minutes.

Example 3 -117.8 g (2 mol) of metal Y powder of 325 mesh
After mixing 28.1 g (1 mol) of Si powder with an average particle size of 1.0 μm, a part of this powder was molded into a cylinder with a diameter of 5 mm and a height of 5 mm using a mold press at a pressure of 2 tons/cm ² . did. After storing this molded body in a BN container, it was placed in an ultra-high pressure generator with the upper end of the molded body in contact with a carbon heater, and while pressurized to 10,000 atmospheres, the carbon heater was energized and ignited. . The current was interrupted immediately after the YSi production reaction started.

The density of the metal Y dispersion strengthened YSi sintered body obtained as described above was 98.6% of the theoretical density. As a result of X-ray diffraction of this sintered body, the molar ratio is approximately equivalent to
YSi and Y peaks appeared.

When the sintered body thus obtained was processed into a tool and cut under the same conditions as in Example 1, the tool life was 14 minutes.

Example 4 After mixing 452.37 g (2.5 mol) of metallic Ta powder of −325 mesh and 12.01 g (1 mol) of C powder with an average particle size of 1.0 μm, a portion of this powder was pressed into 2 tons using a die press. It was molded into a cylindrical shape with a diameter of 5 mm and a height of 5 mm under a pressure of /cm ² . The molded body was placed in a high pressure generator with its upper end surface in contact with a carbon heater, and while the molded body was preheated to 900°C and pressurized with 2000 atmospheres of N ₂ gas, the carbon heater was energized and ignited. The current was interrupted immediately after the TaC production reaction started.

Metal Ta dispersion strengthening obtained as above
As a result of X-ray diffraction of TaC sintered body, TaC and
TaCN and Ta peaks were observed. The atomic ratio of C and N was 9:1.

When the sintered body thus obtained was subjected to a cutting test under the same conditions as in Example 1, the tool life was 15 minutes.

[Brief explanation of drawings]

FIG. 1 was produced according to an embodiment of the present invention.
This is a 1000 times enlarged micrograph of a structure in which metallic Ti is dispersed in TiB ₂ of TiB ₂ −Ti-based dispersion-strengthened ceramics.

Claims (1)

[Claims] 1 Powder of at least one metal element selected from Groups a, a, a, and a of the periodic table and at least one nonmetallic element selected from B, C, Si, and N. After molding a mixed powder containing more metal powder than the stoichiometric composition of ceramics obtained from both,
A part of this molded body is heated to start a ceramic synthesis reaction, and the reaction heat generated at this time induces a synthesis reaction in the adjacent part, and it is possible to synthesize ceramics without applying external heat or by using ordinary ceramic synthesis. The entire molded body is reacted to sintering at a temperature much lower than the above temperature, and the ceramic that remains unreacted due to being added in excess is formed in the ceramic matrix produced by the reaction. A method for producing metal dispersion-strengthened ceramics, which is characterized in that roughly spherical metal particles identical to the metal are dispersed in a volume percentage of 70% or less (not including 0), and the two are strongly chemically bonded.