JPH05330926A - Boride-based composite ceramic sintered compact - Google Patents

Abstract

PURPOSE:To improve hardness, strength and toughness by making up the fine structure of a sintered compact with TiB2 self-crystallized prism grains and ZrC crystal grains. CONSTITUTION:To a mixture powder containing a ZrB2 powder and a TiC powder in 0.2 to 2.0 molar ratio, as necessary, 0.5 to 20wt.% one or more kinds of transition metals selected from among Ti, Zr, Cr, Mo, W, Mn, Fe, Co, Ni, etc., and having <=10mum average particle diameter and 1 to 30wt.% oxide ceramics such as zirconia or alumina each partly stabilized with yttria and having <=2mum average particle diameter or 5 to 30wt.% non-oxide ceramics such as ZrB2, TiC or B4C having <=5mum average particle diameter are added. The resultant mixture is sintered in a non-oxidative atmosphere at 1200 to 1900 deg.C, thus producing the objective sintered ceramics having a fine structure composed of TiB2 self-crystallized prism grains and ZrC crystal grains, exhibiting an Alchimedean density value of >=98% theoretical density, >=50kg/mm<2> three-point bending strength and >=70kg/mm<2> three-point bending strength at 1000 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug, a turbine wheel of a turbocharger, a piston cap, a cylinder liner, a cam surface of a cam shaft, a tappet, a rocker arm tip, an intake / exhaust valve, a hot plug of a sub combustion chamber of a diesel engine. Such as automotive internal combustion engine components, jet engine fans, jet engine air compression chambers and combustion chamber housings, aerospace components such as orbiter and nose cone insulation tiles, and vane and plunger components such as pumps. , Other, dice, mold,
The present invention relates to a boride-based composite ceramics sintered body suitable for applications requiring heat resistance, wear resistance, strength and toughness, such as tools, blades, and thread guides.

[0002]

2. Description of the Related Art Boride ceramics are materials that are difficult to sinter, and it has been difficult to obtain a dense sintered body. For example, TiB ₂ simple substance requires a high temperature of about 2000 ° C. for sintering, but it is known that the sintered body obtained even with this has a high porosity and is decomposed above this temperature. Therefore, Elsevier Science Publishers
Journal of European Ceramic Society published by Ltd.
(1989), pages 23-27, 200
For the purpose of promoting densification at 0 ° C. or lower, a method is known in which a metal such as Fe or Ni and an oxide ceramics such as alumina or zirconia are added in appropriate amounts as sintering aids.

The titanium boride ceramics obtained by such a method are dense and have improved mechanical properties at room temperature, but the excellent hardness inherent in titanium boride and the high temperature properties near 1000 ° C. Is significantly impaired. Further, when the fine structure of the sintered body is observed with an electron microscope or the like, it is known that the particles are coarse and that the particles are agglomerated with each other. For this reason,
Its strength and impact resistance are low, and its practical use is also hindered from the viewpoint of reliability.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of conventional boride composite ceramics sintered compacts, and is composed of fine microcrystalline particles. Combines high strength and toughness, 1000 ° C
It is an object of the present invention to provide an epoch-making boride-based composite ceramics sintered body having substantially no deterioration in mechanical properties even at high temperatures.

[0005]

In order to achieve the above object, the boride-based ceramics sintered body of the present invention is substantially composed of composite ceramics composed of TiB ₂ and ZrC, and TiB ₂ is columnar self-shaped. It is characterized by being a sintered body having a structure.

This sintered body is obtained by sintering powders of ZrB ₂ and TiC as a raw material in a non-oxidizing atmosphere and advancing the reaction shown by the following equation at the time of the sintering. ZrB ₂ + TiC → TiB ₂ + ZrC

In this method, as in the conventional method, T
Unlike the method of using iB ₂ powder and ZrC powder to densify mainly by diffusion sintering of particles, a method of accelerating densification by precipitation of crystals through a solid solution by the reaction represented by the above formula. .. Hereinafter, the boride-based composite ceramics sintered body of the present invention will be described in detail.

Preparation Step of Raw Material Powder In this step, a powder obtained by mixing ZrB ₂ powder and TiC powder is prepared. However, since the present invention is premised on causing a substitution reaction during sintering, the above ZrB ₂ and TiC powders are used as raw materials so that the reaction proceeds more quickly and more uniformly. It is desirable that the particle diameter be 5.0 μm or less. This 5.0 μm
The following range is much wider than the case of using a ceramic mixed powder having the same composition as the composite ceramic composition produced by the conventional method, and larger powder particles can be used.

The mixing ratio of the respective ceramics is a molar ratio such that ZrB ₂ / TiC is 0.2 to 2.0. Within this range, it is determined according to the average particle size, the presence or absence of the addition of the third component described later, the addition amount, and the sintering conditions. The reaction takes place equimolarly as ZrB ₂ + TiC → TiB ₂ + ZrC. However, even if some of ZrB ₂ and / or TiC used as a raw material remains unreacted, the properties of the composite ceramics are not significantly impaired. Further, in the present invention, it is also possible to control the heat of reaction generation and prevent coarsening of the crystal grain size by intentionally adjusting the mixing ratio and causing a partial substitution reaction. ..

The mixing operation may be dry or wet. In the case of wet mixing, for example, an organic dispersion medium such as isopropyl alcohol, ethyl alcohol, ethylene glycol, dimethylsulfoxide is added to the mixed powder, and well mixed and pulverized with a ball mill, an attrition mill or the like. As a result, the secondary agglomeration is deflocculated, and a mixed powder in which the primary particles are extremely uniformly dispersed is obtained. If a rotary evaporator is used after mixing and pulverizing, segregation due to a difference in specific gravity, which is likely to occur in natural drying or constant temperature drying, can be prevented. Further, in the case of the dry method, it is effective to use various surface modification devices to obtain a mixed powder having good uniformity. this is,
This is a method of producing uniform composite particles by applying mechanical energy to the powder surface and utilizing the mechanochemical effect to cause surface fusion between particles. In order to apply mechanical energy to the particle surface, there is a method of generating compressive force, frictional force or impact compressive force on the powder by a rotating body such as an Ong mill.

By the way, if necessary, the mixed powder may contain
Furthermore, a third component can be added. By adding the third component, the properties such as density, strength, toughness, hardness, thermal conductivity and electric conductivity of the composite ceramic can be changed.

That is, the average particle size of the mixed powder is 10 μm.
Hereinafter, desirably, Ni, Mo, Co, W, and 7 μm or less,
At least one metal selected from the group IIIa, IVa, and Va metals such as Cr is added in an amount of 0.5 to 20% by weight, or Z having an average particle size of 2 μm or less, preferably 1 μm or less.
1 to 30% by weight of at least one compound selected from oxide ceramics such as rO ₂ , AI ₂ O ₃ , spinel, and mullite, or ZrB ₂ having an average particle size of 5 μm or less, preferably 1 μm or less, SiC, B ₄ C, Ti
Add 5 to 30% by weight of one or more compounds among non-oxide ceramics such as C, Si ₃ N ₄ and BN,
And / or 5 to 40% by volume of whiskers having an average diameter of 0.1 to 2.5 μm and an average length of 0.5 to 5 μm.
It can be added. Si as a whisker
Ceramic whiskers such as C and Si ₃ N ₄ can be used. Above all, it is desirable to use SiC whiskers which have high Young's modulus and rigidity and which are excellent in oxidation resistance at high temperatures. The amount of whiskers added is preferably selected in the range of 5 to 40% by volume.
This is because if it is less than volume%, the effect of improving fracture strength and toughness cannot be expected because it is too small, and if it exceeds 40 volume%, the density of the composite ceramics tends to decrease. In addition, when adding whiskers, it is previously dispersed in an organic solvent such as ethyl alcohol, isopropyl alcohol, or toluene with a dispersant such as polyethyleneimine or trichlorooctadecylsilane, and well dispersed by ultrasonic dispersion or the like. It is desirable to keep it.

The third component is selected according to the characteristics required for the composite ceramic as described above. In order to improve the mechanical properties of ceramics, when plastic deformation of metal is used, particles with high Young's modulus (including whiskers) are dispersed, and partially stabilized zirconia or tetragonal zirconia polycrystal is added. , There is a case to utilize the peculiar phase transformation.

For example, when it is desired to improve the strength of the composite ceramics at room temperature, it is suitable to add a metal of group IVa or VIII, AI ₂ O ₃ , ZrO ₂ or the like. Further, when it is desired to improve the toughness, addition of IVa or VIII group metal, ZrO ₂ , whiskers or the like is suitable.
Furthermore, especially when it is desired to improve hardness and wear resistance,
The addition of B ₄ C, SiC, TiC, Va, VIa, VIIa metals, Si ₃ N ₄ and ZrB ₂ is effective.

Forming Step and Sintering Step In the present invention, next, the mixed powder prepared as described above is sintered, and there are two methods. One is to mold the mixed powder into a desired shape using a dry hydrostatic molding method, a die molding method, a wet slip casting molding method, an injection molding method, etc., and then press the molded body under pressure or without pressure. Is a method of sintering. The other is hot pressing or hot isostatic pressing (H
This is a method of pressure sintering using the IP method. In any case, the sintering is performed in a non-oxidizing atmosphere, for example, an atmosphere of an inert gas such as nitrogen gas or argon gas. The sintering temperature is selected in the range of 1200 to 1900 ° C. according to the composition of the mixed powder, the presence or absence of the addition of the third component, and the addition amount.

In the case of sintering with pressurization, the temperature is raised to the sintering temperature at a rate of 5 to 10 ° C./min, and the temperature is maintained for a desired period of time so as to prevent temperature distribution. At this time, the pressurization may be performed before the sintering, or may be gradually increased according to the sintering speed, and the pressurization may be performed when the sintering temperature is reached without pressing during the temperature increase. You can Also in the case of sintering without pressure, it is desirable that the rate of temperature rise be the same as in the case of sintering with pressure.

(Characteristics of Sintered Body) In the present invention, a mixed powder of ZrB ₂ and TiC is used as a raw material powder, and at the time of sintering, an element substitution reaction, a reaction formula represented by ZrB ₂ + TiC → TiB ₂ + ZrC Different from the starting material, TiB
_{A 2} / ZrC composite ceramic is produced. Hereinafter, this sintered body is referred to as a substitution reaction sintered body. Next, the features of the boride composite ceramics sintered body of the present invention will be described in detail.

(1) Physical Properties of Sintered Body A bending test piece was cut from the sintered body obtained as described above to a predetermined size by a diamond cutter and a grindstone, and was ground. The size of the test piece is JIS-R1
Processed as described in 601 and span 30 mm
Bending at 3 points at a load application speed of 0.5 mm / m
in. As a result of a bending test, it was found that the obtained sintered body had a higher strength than the conventional method.

Furthermore, 0.6 μ for the sample after fracture
Polished with diamond abrasive grains of m to give a mirror finish. A Vickers indenter was pressed into this sample, and the hardness (H) was measured according to JIS-Z2244 and the fracture toughness value (hereinafter referred to as K _IC ) was obtained from the obtained indentation diameter and crack length according to JIS-R1607. ..

The strength at high temperature was measured by a three-point bending test in accordance with JIS-R1601 at room temperature. The heater was a silicon knit furnace, and the temperature control such as elevating temperature was JIS-R (platinum). -Platinum / Rhodium) was used for the thermocouples with PID control. After holding at the measurement temperature for 20 minutes, the measurement was started after waiting for the inside of the electric furnace to reach a constant temperature.

(2) Microstructure of Sintered Body The obtained sintered body was observed for its structure by a scanning electron microscope and a transmission electron microscope. When observed by a scanning electron microscope, the sintered body structure formed through the substitution reaction is dense and has almost no remaining pores, and fine crystal particles are uniformly dispersed. On the other hand, when observing a sintered body obtained by a conventional sintering method for comparison, a large number of pores remained and the agglomerated secondary particles were segregated.

Further, observing the fine structure with a transmission electron microscope, the TiB ₂ particles in the present sintered body had an average particle size of 1
It exhibited fine columnar automorphic crystals of ˜3 μm, and the ZrC particles were other-shaped crystals with an average particle size of 1 μm or less. Usually, the automorphic structure precipitates from a liquid phase or a solid solution. From this, it is considered that the ZrB ₂ and TiC particles formed a solid solution at the stage of initial sintering. Then, in the cooling process, TiB ₂ first nucleates and grows into self-shaped particles,
Next, ZrC precipitates, but it is considered that the self-form was not taken due to the spatial constraint and the particles became other-shaped particles. Furthermore, detailed observation of the grain interface revealed that there was a clear grain boundary phase. This grain boundary phase indicates that there was a solid solution state, and is considered to be a quaternary compound of Ti, Zr, B and C. When electron diffraction is performed on this interface compound, a regular pattern may appear, but a halo may appear to show an amorphous state.

The above-mentioned automorphic structure is extremely special in the TiB ₂ sintered body. The automorphic structure has already been preceded by cemented carbide and the like, but is most ideal in the sintered structure. It is considered that the reason is that the precipitation phase is preferentially formed from the thermodynamically stable crystal plane, so that the grain boundary interface has good compatibility and the grain boundary bonding force is large. This indicates that the sintered body has both hardness and toughness.

Further, according to the conventional method, in the case of a hardly sinterable ceramic such as boride ceramics, it is extremely difficult to obtain a dense sintered body. That is, since the sintering process by the conventional method is solid-phase diffusion of atoms, bonding between atoms is strong (strong covalent bond), and ceramics such as boride having a small diffusion coefficient are difficult to densify. For some reason. Therefore, in the boride, as described above, the agglomerated state of the powder is observed as it is in the structure of the sintered body, and the joint part of the interface due to sintering is also fragile, which is harmful to various characteristics of the sintered body including strength. Make up. However, as described above, the sintered body according to the present invention has a dense and fine automorphic structure as compared with the conventional method, and can be a sintered body having high hardness and toughness.

(3) Structural Analysis of Sintered Body X-ray diffraction reveals that the crystals of the composite ceramic obtained by the substitution reaction sintering method are subjected to a large compressive strain. Due to the presence of compressive stress in the sintered body, the progress of fracture of the sintered body can be prevented, and high mechanical properties can be achieved. The amount of strain is usually less than 1%, but the effect on mechanical properties is extremely large. However, if 0.1% or less, there is almost no effect, and if it exceeds 1% and reaches several%, the crystal structure becomes unstable.
Therefore, the amount of lattice strain effective in improving mechanical properties is in the range of 0.1 to several percent.

Throughout the measurement, the crystal lattice strain of the present composite ceramics sintered body was 0.1% or less, with almost no shrinkage on the a and b axes of TiB ₂ , but 0 on the c axis. A very large shrinkage of 0.5 to 2.0% was observed. With respect to ZrC, shrinkage of about 0.2 to 1.0% was observed, and since the lattice constants of both TiB ₂ and ZrC were smaller than the literature values, this sintered body was subjected to compressive stress. It was confirmed. Also, the TiB ₂ axial ratio, c
/ A is 1.064, which is almost the literature value (National B
Monogr., 21 (1984) issued by ureau of Standards (US))
It was good.

By the way, the present sintered body is produced by a substitution reaction during sintering, and the solid solution state of the sintered body by the substitution reaction is understood as follows. In addition to TiB ₂ , TiB, Ti ₃ B ₄ , ZrB ₂ , ZrB, Z
Although the existence of rB ₁₂ is known, TiB ₂ and ZrB
₂ has an AlB ₂ type hexagonal structure, whereas TiB has a FeB type and ZrB has a NaCl type cubic structure. Therefore, crystallinely, Ti
It is considered that B ₂ , ZrB ₂ have the same structure as TiC, ZrC, and ZrB, and substitution of metal atoms can be performed between the same crystals. Therefore, it is possible to have (Ti, Zr) B ₂ and (Zr, Ti) C solid-solved crystals in the same crystal system.

Considering in this way, the crystal lattice strain is T
It can be understood that it is caused by a small amount of solid solution of Zr and Ti in the main constituent compounds of iB ₂ and ZrC, respectively. Regarding ZrC, from the literature value of TiC, ZrC
It is calculated that Ti is a solid solution of 10% or more in C. Also, Z
The lattice constant of rB ₂ is a literature value, and a = b = 3.169, c
= 3.530, and ZrB is found in TiB ₂ from the lattice constant.
It is unlikely that ₂ is in solid solution. Therefore, TiB
₂ is considered to be a non-stoichiometric composition represented by (Ti, Zr) B _2-X .

Since the fracture of ceramics is promoted by the tensile stress perpendicular to the crack direction, if there is some compressive strain in the sintered body, this tensile stress is consumed for releasing the strain. For this reason, the tensile stress required for fracture becomes larger than usual when there is compressive strain in the material.
The presence of compressive stress strengthens the grain boundary bonds between the crystals in the sintered body and has the effect of restraining the crystals.
It appears to have excellent mechanical properties.

The literature values of each compound used here are shown below. Literature value TiB ₂ lattice constant ¹⁾ hexagonal a = b: 3.
03034, c: 3.22953 ZrB ₂ ²⁾ hexagonal a = b: 3.16870, c:
3.53002 TiC ³⁾ cubic a: 4.3274 ZrC ⁴⁾ cubic a: 4.6930 Each literature value is (1) TiB ₂ published by National Bureau of Standards (USA) is Monogr. 21st volume (1984).
(2) ZrB ₂ was published in Monogr.
Page 13 (1983), (3) TiC, Monogr. Magazine, Vol. 18, page 73 (1981), (4) ZrC.
In Monogr. Magazine, Vol. 21, page 25 (1984),
I referred to the ones described in each.

(4) Elemental analysis of sintered body The TiB ₂ / ZrC composite sintered body of the present invention was subjected to elemental analysis as follows. Energy Dispersive X-ray Spectroscopy, ED
X) and electron beam energy loss spectrometer (Electron Ener
Elemental analysis was performed on individual particles in the sintered body by using a transmission electron microscope (TEM) equipped with gy Loss Spectroscopy (EELS). The former is used for quantitative analysis of Ti and Zr present in crystal grains, and the latter is also used for semi-quantitative analysis of B and C as well.

As seen in the elemental analysis by EELS, the BK absorption edge is around 190 eV, the CK absorption edge is around 290 eV, and the C tail is almost erased around 330 eV, but Zr-M ₂
The absorption edge, around 450 eV, is the Ti-L absorption edge. Within the analyzed range, reaction-sintered TiB ₂ / ZrC is a high-contrast particle of ZrC (having a very high Zr / Ti ratio), Ti (B> C) particle (having a very low Zr / Ti ratio). , Consists of two types of particles. Various morphologies were observed in the grain boundaries due to these combinations, but they were various.

The sintered body of the present invention comprises (Ti, Zr) B ₂ containing Ti and Zr in an average particle size of 5 μm or less and an average particle size of 4
exist in the form of (Zr, Ti) C particles of less than μm, (T
The abundance ratio of particles having an elemental ratio of Ti / Zr present in i, Zr) B ₂ particles of 60% or more is 40% or more of the entire particles, and Ti / Zr present in (Zr, Ti) C particles.
The abundance ratio of the particles having the element ratio of 30% or less must be 30% or more of the entire particles. Outside this range, a dense sintered body having excellent mechanical properties cannot be obtained. Furthermore, the average particle diameter of 3 μm or less (Ti, Z
r) B ₂ and Ti existing in the form of (Zr, Ti) C particles having an average particle size of 3 μm or less, and Ti existing in the (Ti, Zr) B ₂ particles.
The abundance ratio of particles having an element ratio of / Zr of 70% or more is
It is more preferable that the abundance ratio of the particles is 30% or more of the total particles, and the Ti / Zr element ratio present in the (Zr, Ti) C particles is 20% or less, of 30% or more of the total particles. .. In the normal sintering method, since element substitution does not occur, it is understood that TiB ₂ particles and ZrC particles are simply sintered by a general diffusion model instead of the complex structure in which Ti and Zr are mixed as described above. be able to.

The ZrB ₂ / TiC ratio as a raw material is preferably 0.2 to 2.0, more preferably 0.3 to 1.5. Within this range, the sintered body has a (T
i, Zr) B ₂ and (Zr, Ti) C or (Ti,
It has a structure in which Zr) C or (Zr, Ti) B ₂ coexists.

Furthermore, as a result of energy dispersive elemental analysis by X-ray of this reaction sintered body, Zr and Ti were detected from TiB ₂ and ZrC particles, and (T
It was confirmed that they were mixed in the form of i, Zr) B ₂ and (Zr, Ti) C. Quantitative analysis revealed that TiB ₂ contains Zr atoms of from several atomic% to several tens of atomic%, and ZrC contains Ti atoms of several atomic% to 20 atomic%.

Although the characteristics of the sintered body have been described above, there are still many unclear points regarding the mechanism of formation of the reaction sintered body itself. However, at present, as a mechanism that can be considered from the factual relationship, ZrB ₂ and TiC become active from a relatively low temperature of about 1000 ° C. during sintering, and Ti and Z
Substitution reaction between r atoms is actively carried out, and once Ti--Z
It is considered that the r-B-C goes through a solid solution state in which the r-B-C are separated to form a thermodynamically crystallographically equilibrium stable state. T
It is possible that B and C move predominantly because iB ₂ is generated and grows near or inside the TiC particles, but it is not clear.

[0037]

EXAMPLES Next, examples and comparative examples will be described. Example 1 ZrB ₂ powder having an average particle diameter of 0.8 μm and TiC powder having an average particle diameter of 1.4 μm were prepared so that the molar ratio was 1: 1, and the powder was used to form a SiC ball having a diameter of 10 mm. Use, after ball milling and mixing in ethanol for 12 hours,
It dried under reduced pressure using the rotary evaporator and the mixed powder was obtained. Next, the above powder was treated at 1800 ° C. for 1 hour to give a 0.1.
Hot press sintering under reduced pressure of 1 Torr or less, (T
An i, Zr) B ₂ / (Zr, Ti) C sintered body was obtained. The pressure applied at this time was 20 MPa.

The mechanical properties of this sintered body were examined.
The measuring method was as follows. The density was based on the Archimedes method. The strength was measured according to JIS-R1601, with a span length of 30 mm, 3-point bending, and a load application speed of 0.
It was performed at 5 mm / min. The hardness was measured according to JIS-Z2244 with a load of 10 kg. Furthermore, the K _IC was measured by the microindentation method according to JIS-R1607. As a result of these measurements, a density of 5.45 g
/ Cm ³ , 3-point bending strength 675 MPa, Vickers hardness 2380 kg / mm ² , and K _IC 5.4 MPa · m ^1/2 . Furthermore, as a result of measurement of high temperature strength, 105 at 800 ° C
0 MPa, 980 MPa at 1000 ° C, 8 at 1200 ° C
It was 90 MPa.

Next, the crystal lattice strain was measured. Pure Si powder was adhered to the surface of the present composite ceramics sintered body polished to a mirror surface (maximum roughness of 0.1 μm or less), and the lattice constants of TiB ₂ and ZrC were measured by the internal standard method. As a result, TiB ₂ : a = b = 3.027410
(0.09% shrinkage), c = 3.205220 (0.7
5% shrinkage), ZrC: a = 4.665182 (0.5
9%), and the lattice constants of both TiB ₂ and ZrC shrink more than those of ordinary powders, confirming that the sintered body is subjected to compressive stress. The axial ratio of TiB ₂ , c / a, was 1.05996, which was slightly smaller than the literature value (1.06573). Zr
As for C, TiC is calculated from the literature value in which 2 to 13% of Ti is solid-solved in ZrC.

Further, the individual crystal grains of the obtained sintered body were subjected to elemental analysis by an analytical electron microscope.
Table 1 shows the results of analysis on six locations.

[0041]

[Table 1]

In Table 1, half of the particles have a Ti / Zr ratio of 60% or more, and about 30% of the particles have a Ti / Zr ratio of 30% or less. For example, in analysis place 1-1,
Zr / Ti≈75 / 25, EELS C> B, which is considered to be a crystal having a considerably high ZrC property, but 20% or more means that Ti is contained. In 1-2, Zr
The particles have a ratio of / Ti of about 70/30 and contain B and C in substantially the same amount. In 1-3, Zr / Ti≈7
At 0/30, it can be seen from the EELS results that the particles have a high ZrC property. The peaks at 213 eV and 244 eV in the figure are absorptions of Zr-M _4.5 . In 1-4, Zr / Ti
≈60 / 40, EELS has a small B peak and C
Was rich. It is considered to have ZrC property. In 1-5, Zr / Ti≈15 / 85 is Ti-rich, and B>
Crystallographically, it is considered to be TiB ₂ in C. In 1-6, Zr / Ti≈5 / 95 and almost only Ti,
B and C were present in almost the same amount instead of TiB ₂ . TiB
_{Although 2} is usually columnar, it was not columnar here. The presence of ZrC alone was not found in the dozens of analyses.

Further, as a result of energy dispersive elemental analysis by X-ray of this reaction sintered body, Zr and Ti were detected from TiB ₂ and ZrC particles, and (T
It was confirmed that they were mixed in the form of i, Zr) B ₂ and (Zr, Ti) C. Quantitative analysis revealed that TiB ₂ contained 12 at% Zr atoms and ZrC contained 17 at% Ti atoms.

Example 2 ZrB ₂ powder having an average particle diameter of 0.8 μm and TiC powder having an average particle diameter of 1.4 μm were prepared in a molar ratio of 1: 1 and the average particle was used as a metal binder. Diameter 3
5 μm of Ni powder of μm is added. This powder was made into 1 in ethanol using a SiC ball with a diameter of 10 mm.
After pulverizing and mixing with a ball mill for 2 hours, it was dried under reduced pressure using a rotary evaporator to obtain a mixed powder. Next, the powder was sintered by hot pressing at 1600 ° C. for 1 hour under a reduced pressure of 0.1 Torr or less, and TiB ₂ / ZrC /
A Ni-based sintered body was obtained. The applied pressure at this time is 20MP
It was a.

When the mechanical properties of this sintered body were examined, the results were as follows. Density 5.48 g / cm ³ , 3
Point bending strength 960 MPa, Vickers hardness 2090 kg
/ Mm ² and K _IC 509 MPa · m ^1/2 . As a result of high-temperature strength measurement, it was 1130 MPa at 1000 ° C.

Next, the crystal lattice strain was measured. Pure Si powder was adhered to the surface of the present composite ceramics sintered body polished to a mirror surface (maximum roughness of 0.1 μm or less), and the lattice constants of TiB ₂ and ZrC were measured by the internal standard method. As a result, TiB ₂ has a = b = 3.030275
Is almost the same as the literature value, and c = 3.17853 is 1.5
Shrinkage of 8% was seen. ZrC has a = 4.65762
It was found that the shrinkage was 0.75%, and TiB ₂ , Z
It was confirmed that both rC were subjected to compressive stress. The axial ratio of TiB ₂ , c / a, was 1.07231, which was slightly larger than the literature value (1.06573). Regarding ZrC, from the literature value of TiC, Ti in ZrC is 15 to
It was calculated that the solid solution was 16%.

Further, the individual crystal grains of the obtained sintered body were subjected to elemental analysis by an analytical electron microscope.
The results of analysis of 6 places are shown below.

[0048]

[Table 2]

Example 3 ZrB ₂ powder having an average particle diameter of 0.8 μm and TiC powder having an average particle diameter of 1.4 μm were prepared so that the molar ratio was 1: 1, and the average diameter was 1.2 μm. , Average length 5.5
μm SiC whiskers are added at 30% by volume of the whole. This powder was put into ethanol using a SiC ball with a diameter of 10 mm.
After milling and mixing in a ball mill for 12 hours, the mixture was dried under reduced pressure using a rotary evaporator to obtain a mixed powder. next,
The above powder was sintered by hot pressing at 1900 ° C. for 1 hour under reduced pressure of 0.1 Torr or less to obtain TiB ₂ /
A ZrC / SiC whisker composite sintered body was obtained. The pressure applied at this time was 20 MPa.

When the mechanical properties of this sintered body were examined, the results were as follows. Density 5.13 g / cm ³ , 3
Point bending strength 898 MPa, Vickers hardness 2260 kg
/ Mm ² and K _{IC were} 5.7 MPa · m ^1/2 . 100
The result of high temperature strength measurement at 0 ° C. was 962 MPa.

Further, the individual crystal grains of the obtained sintered body were subjected to elemental analysis by an analytical electron microscope. 6
Table 3 shows the results of analysis of two locations.

[0052]

[Table 3]

Example 4 ZrB ₂ powder having an average particle size of 0.8 μm and TiC powder having an average particle size of 1.4 μm were prepared in a molar ratio of 1: 2, and the powder having a diameter of 10 mm was prepared. Using a SiC ball, ball milling and mixing in ethanol for 12 hours,
It dried under reduced pressure using the rotary evaporator and the mixed powder was obtained. Next, the above powder was treated at 1800 ° C. for 1 hour to give a 0.1.
Hot press sintering under reduced pressure of 1 Torr or less, Ti
To obtain a B ₂ / TiC / ZrC sintered body. The pressure applied at this time was 20 MPa.

When the mechanical properties of this sintered body were examined, the results were as follows. Density 5.31, 3-point bending strength 795 MPa, Vickers hardness 2190, K _IC 5.9M
It was as good as Pa · m ^1/2 . The high temperature strength measurement result at 1000 ° C. was 940 MPa. Further, when the sintered body was observed by SEM, TiB ₂ crystal particles were found to be Zr.
The structure was columnar precipitation at the grain boundaries and in the grains of C particles.

Comparative Example 1 TiB ₂ powder having an average particle size of 0.9 μm and ZrC powder having an average particle size of 1.2 μm were prepared in a molar ratio of 1: 1, and the prepared powder having a diameter of 10 mm was prepared. A SiC ball was used for ball mill pulverization and mixing in ethanol for 12 hours, followed by vacuum drying using a rotary evaporator to obtain a mixed powder. The above powder was hot-press sintered in vacuum at 1800 ° C. for 1 hour under a reduced pressure of 0.1 Torr or less to obtain a TiB ₂ / ZrC sintered body.

When the mechanical properties of this sintered body were examined, the results were as follows. Density 5.41 g / cm ³ , 3
Point bending strength 345 MPa, Vickers hardness 2090 kg
/ Mm ² , and K _{IC was} 3.9 MPa · m ^1/2 . This sintered body has the same composition as that found in Example 1, but the structure has a large number of residual pores, agglomeration of particles is also observed, and the mechanical performance is remarkably poor.

Comparative Example 2 ZrB ₂ powder having an average particle diameter of 0.8 μm and TiC powder having an average particle diameter of 1.4 μm were prepared in a molar ratio of 2: 1, and the prepared powder having a diameter of 10 mm was prepared. After using a SiC ball to pulverize and mix in a ball mill for 12 hours in ethanol, it was dried under reduced pressure using a rotary evaporator to obtain a mixed powder. Next, the above powder was heated at 1750 ° C. for 1 hour,
Hot press sintering under reduced pressure of 0.1 Torr or less,
As a result of X-ray diffraction, a TiB ₂ / ZrB ₂ / ZrC sintered body was obtained. This sintered body was extremely fragile and was destroyed during processing of the test piece. The structure shows almost no columnarization of TiB ₂ particles, and has low mechanical properties.

[0058]

EFFECTS OF THE INVENTION According to the present invention, since a mass transfer of an element occurs between crystals due to a substitution reaction at the time of sintering, a sintered body which is well densified even if the grain size of the raw material powder is relatively large. Is obtained.

A large number of composite ceramics have been studied so far, but these were mostly due to the grain boundary diffusion of the powder particles, which is based on the classical powder sintering theory. However, in the present invention, a new solid solution state is once formed by chemical reaction between particles, not by simply sintering the powder, and then a stable equilibrium compound is formed in the closed system. Therefore, particles that are denser and have an automorphic form a structure than in the past, and exhibit properties significantly superior to those of the sintered body obtained by the conventional method.

Claims (11)

[Claims] 1. The microstructure of the sintered body is substantially TiB ₂
A boride-based composite ceramics sintered body, characterized in that it is composed of columnar self-assembled crystal grains composed of and crystal grains substantially composed of ZrC. 2. A clear crystal grain boundary exists between crystal grains of TiB ₂ and ZrC, and Ti and Z are present at the grain boundary.
The boride-based composite ceramics sintered body according to claim 1, wherein a quaternary compound having a crystalline or amorphous structure composed of r, B and C is formed. 3. Of the crystal grains constituting the sintered body, Ti
The B ₂ particles are (Ti, Zr) B ₂ in which Ti and Zr are mixed, having an average particle diameter of 5 μm or less, and the abundance ratio of particles having a Ti / Zr element ratio of 60% or more is 40% or more, ZrC particles are present in the form of (Zr, Ti) C particles having an average particle size of 4 μm or less, in which Zr and Ti are mixed, and the Ti / Zr element ratio is 30% or less. The boride-based composite ceramics sintered body according to claim 1 or 2, wherein the abundance ratio is 30% or more of the entire particles. 4. Among the crystal particles constituting the sintered body, (Ti, Zr) B ₂ particles having an average particle size of 5 μm or less are a small amount of C.
The boride-based composite ceramics sintered body according to claim 3, wherein the (Zr, Ti) C particles having an average particle diameter of 4 μm or less contain a minute amount of B. 5. The boron according to claim 1, wherein the (Ti, Zr) B ₂ particles and (Zr, Ti) C particles constituting the sintered body have a lattice strain in the compression direction. Compound ceramics sintered body. 6. As a third component, Ti, Zr (IVa
Group), Cr, Mo, W (VIa group), Mn (VIIa)
Group) and 0.5 to 20% by weight of at least one kind of transition metal such as Fe, Co, Ni (group VIII), and the like, according to any one of claims 1 to 5. Union. 7. As a third component, at least one compound of at least one kind selected from oxide ceramics such as zirconia and alumina partially stabilized by yttria is used.
The boride-based composite ceramics sintered body according to any one of claims 1 to 5, wherein the boride-based composite ceramics sintered body contains the same. 8. ZrB ₂ , SiC, B as a third component
6. The boride-based composite ceramic according to claim 1, which contains 5 to 30% by weight of at least one compound among non-oxide ceramics such as ₄ C, TiC, Si ₃ N ₄ and BN. Sintered body. 9. A whisker as a third component is 5-40.
The boride-based composite ceramics sintered body according to any one of claims 1 to 5, wherein the boride-based composite ceramics sintered body contains the same. 10. The boride-based composite ceramics sintered body according to claim 1, wherein the density of the sintered body obtained by the Archimedes method is 98% or more of the theoretical density. 11. The three-point bending strength of the sintered body at room temperature is 5
The boride compound ceramics sintered body according to any one of claims 1 to 10, which has a strength of 0 kg / mm ² or more and a strength at 1000 ° C of 70 kg / mm ² or more.