JP3142892B2 - Manufacturing method of reaction sintered composite ceramics and manufacturing method of sliding member using it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite ceramic in which boron nitride is dispersed in a sintered body, and more particularly to a composite ceramic obtained by a reaction sintering method.

[0002]

2. Description of the Related Art Generally, engineering ceramics suitable for structural materials such as engines and turbines include:
SiC and Si ₃ N ₄ having excellent heat resistance are known.

[0003] However, in consideration of actual use conditions, there are many insufficient points such as thermal shock resistance, corrosion resistance to molten metal, and machinability. To solve these, processing characteristics,
Si ₃ N _{4 in} which boron nitride having excellent corrosion resistance is mixed and dispersed in Si ₃ N ₄ has been developed (silicon nitride ceramics 2,
197-210, Uchida Lao Tsuruho Publishing). However, using a dispersion is poor boron nitride as a raw material, Si ₃ N ₄ by mixing directly boron nitride to Si ₃ N ₄ - for making boron nitride sintered body, the dispersion of boron nitride There is a disadvantage that it is not always uniform. In addition, there is a problem that the porosity of the sintered body increases as the mixing ratio of boron nitride increases.

On the other hand, the present inventor heated a molded body composed of Si powder and inorganic compound particles such as SiC in nitrogen to remove Si ₃ N ₄ particles as reaction products and / or particles such as SiC with whiskers. A method of manufacturing high strength Si ₃ N ₄ bonded ceramics having a small dimensional change rate during sintering by a bonding method has been proposed (JP-A-61-146754). In this method, when an inorganic compound such as SiC is bonded with Si ₃ N ₄ particles and / or whiskers, the inorganic compound is bonded with Si ₃ N ₄ without being changed. Therefore, even after sintering, the particle shape of the inorganic compound does not change, and Si ₃ N ₄
Is generated in the gas phase reaction and deposited on the inorganic compound particles, so that the dimensional change during sintering is as small as 0.1 to 0.3% and the near net shape is excellent.

[0005]

However, in the above-mentioned method, the voids formed in the compact can be filled only with Si ₃ N ₄ generated from metallic Si. Therefore, when the compounding amount of the inorganic compound is larger than the compounding amount of metal Si, the amount of Si ₃ N ₄ generated is reduced, and the porous body is inevitably formed, and there is a limit in densification.

The present inventor has disclosed in Japanese Patent Application Laid-Open No. 63-2529.
As disclosed in JP-A-73-73, in the production of conductive ceramics, as exemplified in Example 3 of the same publication, Ti
A mixed compact of 80% by weight of B ₂ powder and 20% by weight of Si powder was heated in nitrogen to produce a Si ₃ N ₄ reaction-bonded sintered body. However, this is a heating temperature of 1400 ℃
Since the reaction rate is low, the reaction rate between TiB ₂ particles and nitrogen is low (less than 20%), and the resulting sintered body has a high porosity and is a porous body.

An object of the present invention is to provide a dense composite ceramic.

Another object of the present invention is to provide a dense composite ceramic comprising a compact of a metal powder and a metal boride.

Still another object of the present invention is to provide a sliding member using the above-mentioned dense composite ceramics.

[0010]

The gist of the present invention for solving the above problems is as follows: (1) Metal boride particles and / or whiskers are bonded to each other by metal nitride and boron nitride particles and / or whiskers. A reaction-sintered composite ceramic characterized by being made.

(2) Metal nitride and boron nitride are formed on the surface layer of the metal boride particles and / or whiskers, and these are bonded to each other by the metal nitride and boron nitride particles and / or whiskers. A reaction-sintered composite ceramic characterized by being made.

In the above, the metal nitride and boron nitride particles and / or whiskers are formed in a glass phase and / or an alloy phase. In addition, the volume ratio of the boron nitride to the metal boride is preferably 0.2 or more.

Further, when the content of boron nitride in the sintered body is 5
30% by volume or less, and the pore content is 30% by volume or less, preferably a maximum pore size of 10 μm.
m or less and the pore content is preferably 5% by volume or less. And (3) heating a molded body composed of particles and / or whiskers of metal boride (a) and metal powder (b) at a temperature lower than the melting point of metal powder (b) in a nitriding gas atmosphere. Producing a metal nitride (c) which is a reaction product of the metal powder (b); and heating the metal nitride (d) and boron nitride (b) by heating at a temperature which reacts with nitrogen of the metal boride (a). e) producing the metal boride;
A method of producing a reaction-sintered composite ceramics, characterized in that the metal nitride (d) and the boron nitride (e) are bonded to each other by particles and / or whiskers.

It is preferable to use a molded body in which the mixing ratio of the metal boride (a) and the metal powder (b) is from 95: 5 to 5:95 (weight ratio).

The metal boride (a) is Ti, Zr,
At least one of V, Al, Ta, Cr, Nb, Hf, W
A metal boride selected from the species, and the metal powder (b) is selected from at least one of Si, Ti, Al, and Cr.

The heat treatment method of the present invention is preferably performed in the following two steps as described above.

First step: nitriding in a nitriding gas (nitrogen, ammonia, etc.) atmosphere at a temperature lower than the melting point of the metal powder (b). Second step: temperature (1400) at which the metal boride (a) reacts thereafter. C. to 2000.degree. C.) to obtain a reaction sintered body in which boron nitride is uniformly dispersed.

It is preferable that the volume ratio of the boron nitride / the metal boride is 0.2 or more. If it is smaller than 0.2, the effect of reducing the porosity is small, and the sliding effect and the heat transfer effect, which are characteristics of boron nitride, are reduced. If the amount of boron nitride is too large, the strength of the sintered body is reduced. Therefore, the content of boron nitride in the sintered body after sintering is 3 to 40% by volume, preferably 5% by volume.
-20% by volume.

In the present invention, the sintering aid is a group III, IV
A metal belonging to the group, group V, or group VI, and at least one of oxides, nitrides, carbides, and oxynitrides of the metal can be used. By using the sintering aid, a dense body having a porosity of 5% by volume or less can be obtained.

The composition ratio (a) / (b) of the metal boride (a) TiB ₂ and the metal powder (b) Si is from 20/80 to 7
0/30 (weight ratio) results of porosity of the sintered body produced by changing measured, regardless of the mixing ratio of TiB ₂ 8 to 1
It was found to be as small as 4% by volume. For comparison, the porosity in the case of using metal carbide (SiC) and metal powder Si increased from 12% by volume to 30% by volume with an increase in SiC, resulting in a porous body. This is because the pores (voids) are filled only with the nitride of metal Si.

In the present invention, the average particle size of the metal boride (a) is 100 μm or less, preferably 10 μm or less. This is because if the particle size of the metal boride is large, the reaction rate is low, and the particles of the metal nitride are large. Further, the average particle diameter of the metal powder (b) is 5 μm or less, preferably 1 μm or less, which is suitable for improving the nitriding rate at a low temperature.

According to the study of the present inventors, if the metal powder (b) is heated to a temperature equal to or higher than its melting point before nitriding of the metal powder is completed, the metal is melted to form an alloy with the metal boride (a), It is not preferable because it causes shrinkage and cracks. After the nitriding of the metal is completed, the object of the present invention can be achieved by heating to a temperature (1400 ° C. to 2000 ° C.) at which the metal boride (a) reacts with nitrogen. Furthermore, by using the sintering aid, bonding occurs in the glass phase and the alloy phase, and a denser sintered body can be obtained.

In the present invention, the oxide film on the surface of the metal boride and the metal powder may react with nitrogen to partially synthesize oxynitride and the like, but this has almost no effect on the characteristics of the sintered body. do not do.

The nitriding gas atmosphere is at normal pressure and reduced pressure (10
~ ⁵ Torr) to under pressure (2000 atm). Therefore, an apparatus such as a hot press is not required, since the apparatus does not need to be pressurized.

In the present invention, the maximum pore size of the sintered body is 3
The reason why the diameter is preferably 0 μm or less, preferably 5 μm or less is that a large pore diameter easily becomes a starting point of destruction and causes a decrease in strength. When used as a sliding member, it is preferable that the pore diameter is uniform and small. The pores can be impregnated with resin, particles, oil, solid lubricant, water, metal, and the like. By impregnating the substance, a sliding member having a lower coefficient of friction can be obtained.

The method for molding a sintered body according to the present invention comprises injection molding,
Press molding, casting, rubber press molding, extrusion molding, mold powder molding, etc. are selected according to the purpose, shape, required characteristics, and the like.

It is also possible to obtain an integrally sintered composite of the boron nitride-dispersed ceramic of the present invention and a ceramic made of another inorganic compound.

[0028]

The porosity of the sintered body of the present invention is small for the following reason.

By heating a compact containing metal boride (a) particles and / or whiskers and metal powder (b) in a nitriding gas atmosphere, metal nitride and boron nitride are formed. It is considered that they are uniformly dispersed in the sintered body, are bonded to each other, and are filled with the voids in the molded body to be densified.

[0030]

The present invention will be described more specifically with reference to the following examples.

Example 1 A mixture of TiB ₂ powder having an average particle diameter of 10 μm as a metal boride (a) and Si powder having an average particle diameter of 0.5 μm as a metal powder (b) 10
7 parts by weight of a wax-based binder was added to 0 parts by weight, kneaded with a kneading machine, and pulverized to obtain a raw material for molding. Next, a molded body having a diameter of 50 mm and a thickness of 10 mm was produced using a mold.
After the wax content of the molded body was removed by heating, the Si powder was nitrided from 1100 ° C. to 1350 ° C. in nitrogen gas at 4 ° C./h, and then heat-treated at 1550 ° C. for 5 hours. FIG. 1 shows the relationship between the amount of boron nitride and the porosity of the obtained sintered body.

For comparison, the same molding was performed using boron nitride powder having an average particle size of 5 μm and Si powder having an average particle size of 1 μm.
FIG. 1 shows the relationship between the amount of boron nitride and the porosity of the sintered body obtained by sintering.

As can be seen from FIG. 1, the one using TiB ₂ as the metal boride (a) is as small as 8 to 12% by volume regardless of the amount of boron nitride. As a result, the porosity increases from 15 to 34% by volume with the increase in boron nitride, and it can be seen that the material becomes porous. This is because when the amount of Si is reduced to fill the voids with only the nitride of Si, the amount of Si nitride is also reduced. In addition, aggregates of boron nitride are observed in the sintered body, and the mixing is not uniform.

When TiB ₂ is used to react with nitrogen as described above, TiB ₂ particles form TiN, and free boron produced by this nitriding reaction reacts with nitrogen in the atmosphere. Boron nitride is densified to fill voids in the compact. Here, by controlling the amount of TiB ₂ or the nitriding ratio, the amount of boron nitride generated can be changed. Further, in the present invention, since boron nitride is generated by a chemical reaction in the sintered body, there is no agglomerated portion and the boron nitride is uniformly dispersed.

The composite ceramics of the present invention has pores as small as 5 μm or less regardless of the mixing ratio of the metal boride (a) and the metal powder (b). On the other hand, it was found that the pores of the comparative example were as large as 30 μm or more as the amount of boron nitride was increased.

In the composite ceramics of the present invention, the nitride formed from the Si powder of the metal powder (b) was α, β type silicon nitride particles and whiskers. The dimensional change rate of the obtained composite ceramics during sintering was 0.1%.
Although it expands to 4 to 0.9%, this value is 1/50 to 1/20 of other normal pressure sintered bodies, and is extremely excellent in precision sinterability.

Example 2 Instead of the TiB ₂ particles of Example 1, ZrB ₂ , VB ₂ , ZrB ₁₂ , TaB ₂ , Cr
₂ B, using a _{CrB 2, NbB 2, HfB 2} , and molded in the same manner, the firing heat treatment result, either in addition to silicon nitride, metal nitrides, boron nitride is generated, fill the pores I knew it was. The porosity of each of the sintered bodies was 7 to 13% by volume, and a reaction sintered composite ceramic having a porosity of 5 μm or less was obtained.

Example 3 The same molding and sintering were performed using CrB ₂ whiskers having a length of 50 μm and an aspect ratio of 50 instead of the TiB ₂ particles of Example 1. As a result, a reaction-sintered composite ceramic having low porosity and uniformly dispersed boron nitride was obtained as in Example 1. [Embodiment 4] Instead of Si particles of Embodiment 1, Al, T
Forming and sintering were similarly performed using i and Cr. As a result, a reaction-sintered composite ceramic having low porosity and uniformly dispersed boron nitride was obtained as in Example 1.

[0039] Example 5 and ZrB ₂ powder having an average particle diameter of 3μm as a metal boride (a), a mixture of Si powder having an average particle diameter of 0.5μm as the metal powder (b) ZrB _2: Si
= 20:80 (weight ratio) 8 parts by weight of a wax binder were added to 100 parts by weight, and the diameter was 50 in the same manner as in Example 1.
A molded article having a size of 10 mm x 10 mm was prepared. After removing the wax content of the molded body, the molded body was heated at different temperatures in order to change the reaction rate between the ZrB ₂ powder and nitrogen, thereby preparing a sample having a reaction rate of 0% to 100%. However, the Si powder was almost completely changed to silicon nitride.

Although the porosity does not decrease so much when the conversion is 0% to 15%, the porosity decreases greatly when the conversion is 20% or more. The reason for this is that, for example, when the ZrB ₂ particles react with nitrogen and change to ZrN, the sintered body expands first, so that it has no effect on decreasing the porosity. And the reaction rate is 2
If it is 0% or more, the expansion phenomenon disappears, and the effect of reducing the porosity is obtained.

When the ZrB _{2 of the} present embodiment is reacted with nitrogen, the ZrB ₂ particles are converted into ZrN and boron nitride and are densified to fill voids in the compact.

[0042] Example 6 a mixture of Si powder having an average particle diameter of 0.5 [mu] m CrB as ₂ powder and metal powder (b) having an average particle size of 3μm as a metal boride (a) CrB _2: Si =
20:80 (weight ratio) 100 parts by weight of Y ₂ O ₃ and Al ₂ O ₃ as sintering aids were added in an amount of 2 parts by weight, and 2 parts by weight of polyvinyl butyral binder was added to the mixed powder. And dried to obtain a raw material for molding. Next, a molded body having a diameter of 50 mm and a thickness of 10 mm was produced using a mold. After removing the binder component in the compact, the Si powder was nitrided at 4 ° C./h from 1100 ° C. to 1350 ° C. in nitrogen gas, and then heat-treated at 1550 ° C. for 5 hours and further treated at 1750 ° C. for 3 hours. .

Thus, a chromium nitride / silicon nitride composite ceramic having a porosity of 2% and boron nitride uniformly dispersed was obtained.

Example 7 The sliding surface of the sliding member made of the ceramic sintered body obtained in Example 1 was polished with a grindstone, and the surface roughness was set to 0.1 μm as a ten-point average roughness. did.

The sliding member was assembled in a magnetic disk drive and tested. The test conditions were SUS440 for the bearing.
With C, maximum speed 2.4 m / s, the magnetic head at a frequency 60Hz is reciprocated 10 ⁹ times.

The sliding surface after the test had a ten-point average roughness of 0.1 μm, and it was confirmed that the roughness was not changed from that before the sliding. It was also confirmed that the step between the sliding portion and the non-sliding portion was as small as 0.01 μm or less. From this result, it was found that the sliding member of this example had excellent wear resistance and was suitable for an actuator.

Example 8 The ceramic sintered body obtained in Example 1 was impregnated with glycerin and applied to a valve sliding member for tap water. A test was conducted in which the valve was opened and closed while repeating circulation of hot water 100 ° C. and cold water 10 ° C. As a result, it was found that there was no crack in the valve sliding member, the amount of wear was extremely small and the measurement was not possible, and a valve sliding material excellent in durability was obtained.

Example 9 The sliding surface of the ceramic sintered body obtained in Example 6 was polished with a grindstone to have a ten-point average roughness of 0.1 μm. This is placed in an autoclave with a viscosity of 40.
It was impregnated with 0 centipoise of fluoro oil. The evaluation was performed by assembling the magnetic disk device of Example 7 under the same conditions. The sliding surface after the test had a ten-point average roughness of 0.1 μm, and it was confirmed that there was no change from before sliding. The step between the sliding portion and the non-sliding portion is 0.01 μm or less. It was found that the fluorine oil on the sliding surface after the sliding test was impregnated and adhered to the pores.

Example 10 The Ti obtained in Example 1
The characteristics were examined using a ceramic sintered body having a B ₂ compounding ratio of 60% by weight as a current collector ring and a current collector of an automotive alternator. The test conditions were 30,000 rpm, current density 70 A / cm ^2.
It is. As a result, it was found that the product of the present invention had no wear, had a good condition of the sliding surface, and was suitable for a current collecting member.

[0050] Example 11 a mixture of Si powder having an average particle diameter of 0.5 [mu] m ZrB as ₂ powder and metal powder (b) having an average particle size of 3μm as a metal boride (a) ZrB _2: Si
= 20: 80 (weight ratio): 100 parts by weight, average particle size:
5 to 40 parts by weight of a 5 μm TiC powder and 8 parts by weight of a wax-based binder were added.
A molded body having a size of 0 mm and a thickness of 10 mm was produced. After removing the wax component of the molded product, the temperature was reduced from 1100 ° C to 1 ° C in nitrogen gas.
After nitriding the Si powder at 4 ° C / h up to 350 ° C,
Heat treatment was performed at 0 ° C. for 5 hours.

In this embodiment, ZrB ₂ particles are changed into ZrN and boron nitride, and TiC particles are converted into free carbon, T
It was changed to iN and SiC, and a dense body having a porosity of 7% by volume or less was obtained in order to fill voids in the molded body with other than these Si nitrides. Boron nitride and free carbon which provide a lubricating effect were dispersed in the sintered body.

From the above examples, it can be seen that the reaction sintered composite ceramics of the present invention is suitable for sliding members such as mechanical seals, floating seals, bearings, magnetic head sliders, gears, current collecting members, and reciprocating mechanism parts. I understand.

[0053]

The reaction sintered composite ceramics of the present invention in which boron nitride is uniformly dispersed can provide a dense sintered body having a low porosity, which cannot be obtained by a conventional reaction sintering method. The sintered body has excellent sliding characteristics as a sliding member. In addition, the scope of use of ceramics in fields such as aviation, space, and marine as well as structural members such as engines and turbines is expanded.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of boron nitride in a sintered body and the porosity.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-185864 (JP, A) JP-A-64-5976 (JP, A) JP-A-63-277576 (JP, A) 226767 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/58-35/65

Claims (4)

(57) [Claims] [Claim 1] grain frame other metal boride whiskers
And a compact containing metal powder in a nitriding gas atmosphere.
After heating at lower temperatures than the melting point of the metal powder, a pre-Symbol metal boride said molded body in a nitriding gas atmosphere
A method for producing a reaction-sintered composite ceramics , characterized by heating at a temperature at which nitrogen reacts . 2. A pre-Kikin genus borides is Ti, Zr, V, T
The method for producing a reaction-sintered composite ceramic according to claim 1, which is a nitride of a, Cr, Nb or Hf . 3. The method according to claim 1, wherein the metal nitride is Si, Ti, Al or the like.
Other method of reaction sintering composite ceramic according to 請 Motomeko 1 is a nitride of Cr. 4. A metal boride particle or whisker.
And a compact containing metal powder in a nitriding gas atmosphere.
After heating at a temperature lower than the melting point of the metal powder, the molded body and the metal boride in a nitriding gas atmosphere
A method for manufacturing a sliding member , characterized by using a reaction sintered composite ceramic formed by heating at a temperature at which nitrogen reacts .