JPH034514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a silicon carbide composite having excellent dimensional accuracy and wear resistance, and in particular, the present invention relates to a method for producing a silicon carbide composite having excellent dimensional accuracy and wear resistance.
A porous silicon carbide sintered body formed into a desired shape and sintered with virtually no firing shrinkage, with metal silicon filled in the open pores of the product, which has excellent dimensional accuracy and wear resistance. The present invention relates to a method for producing a silicon carbide composite.

[Conventional technology]

Silicon carbide has extremely excellent chemical and physical properties, and is used in catalyst carriers, pump parts, and various jigs used in high-temperature oxidizing atmospheres, strongly corrosive atmospheres such as acids and alkalis, etc. This material is suitable for applications such as.

Conventionally, methods such as a pressure sintering method, an atmospheric pressure sintering method, a reaction sintering method, and a recrystallization sintering method are known as methods for manufacturing silicon carbide sintered bodies.

[Problem that the invention seeks to solve]

By the way, among these methods, a high-density and high-strength sintered body can be obtained according to the pressure sintering method and the pressureless sintering method, but both are sintering methods that involve large firing shrinkage during firing. Since the dimensions of the sintered body are greatly affected by the firing shrinkage and the density of the formed body, it is extremely difficult to manufacture a sintered body with specific dimensional accuracy without special machining.

In addition, both the reaction sintering method and the recrystallization sintering method are sintering methods that do not cause much shrinkage during firing, but the sintered body by the former reaction sintering method is made by converting metallic silicon and carbon powder into SiC during manufacturing. Because the reaction occurs, the surface roughness of the sintered body increases.On the other hand, the latter recrystallization sintering method solidifies coarse and fine silicon carbide particles with an organic binder, and then
This is a method of bonding coarse particles by firing in a recrystallization temperature range of 2400°C to recrystallize fine silicon carbide particles and exert a bonding effect.
Not only does it require an extremely high sintering temperature of ~2400℃, but it also uses coarse particles as a starting material.
The surface roughness is large, and it is difficult to produce a sintered body with particularly high dimensional accuracy without special machining.

As mentioned above, with conventionally known sintering methods, there was no known method for inexpensively and easily manufacturing structural silicon carbide sintered bodies that require high dimensional accuracy without special machining. .

[Means for solving problems]

By the way, the present inventors have developed a sintering method different from the conventionally known sintering methods as described above, that is, sintering a green body formed into a desired shape without substantially causing firing shrinkage, and achieving dimensional accuracy. The aim is to provide a method for manufacturing structural silicon carbide sintered bodies that require strength at low cost without special machining, starting from fine silicon carbide powder that easily shrinks during firing. As a raw material, as a result of various research efforts to develop a sintering method that can suppress firing shrinkage caused by sintering, we have been able to control the impurity components contained in silicon carbide powder and sinter it within a specific atmosphere and temperature range. We discovered a new method for producing a strong silicon carbide sintered body with high surface precision without causing substantial firing shrinkage by sintering the material.
No. 61-122165, "After forming silicon carbide powder with an average particle size of 5 μm or less into a green body, the green body is heated in a non-oxidizing atmosphere within a temperature range of 1700 to 2100°C without substantially shrinking. A method for manufacturing a silicon carbide sintered body having an average bending strength of 7 kg/mm ² or more, which is characterized by sintering, is proposed.

However, the silicon carbide sintered body is a porous body, and it has been difficult to apply it particularly to applications requiring wear resistance or airtightness.

Therefore, with the aim of solving the above-mentioned problems, the present inventor conducted further research on the silicon carbide sintered body, and found that by filling the open pores of the silicon carbide sintered body with metallic silicon. The present invention was completed based on the new finding that it is possible to produce a silicon carbide composite with improved wear resistance and airtightness without impairing dimensional accuracy and surface accuracy.

The present invention provides dimensional accuracy and dimensional accuracy in which metal silicone is filled into the open pores of a porous silicon carbide sintered body that is sintered without substantially shrinking to form open pores in a three-dimensional network structure. This is a method for producing a silicon carbide composite with excellent wear resistance.

The present invention will be explained in detail below.

The porous silicon carbide sintered body needs to be a silicon carbide sintered body sintered without substantially shrinking. The reason is,
A silicon carbide sintered body that is shrunk during sintering is preferable in terms of strength and wear resistance, but the dimensions of a sintered body produced by a sintering method that involves shrinkage depend on the density of the formed body and the time of sintering. It is greatly affected by the amount of shrinkage, so in order to produce a sintered body with excellent dimensional accuracy, it is necessary to cause uniform shrinkage during sintering. By the way, in order to cause the above-mentioned contraction uniformly, it is important to obtain a formed body having a uniform density, but it is extremely difficult to obtain a formed body having such a uniform density. This is because it is difficult to produce a sintered body with excellent dimensional accuracy by causing firing shrinkage.

The sintering shrinkage rate of the silicon carbide sintered body sintered without substantially shrinking is advantageously 2% or less, and more preferably 1% or less.

The silicon carbide composite obtained by the present invention needs to be a porous silicon carbide sintered body whose open pores are filled with metallic silicon.
The reason is that metallic silicon has good compatibility with silicon carbide sintered bodies, and by filling the open pores of porous silicon carbide sintered bodies with metallic silicon, it is possible to form porous silicon carbide sintered bodies. This is because detachment of crystal grains from the body can be prevented, and wear resistance can be significantly improved.

The porous silicon carbide sintered body preferably has an average crystal grain size of 10 μm or less and an open porosity of 18 to 56% by volume. The average grain size of the crystals is 10 μm
The reason why the average grain size of the crystals is preferably less than 10 μm is because the surface roughness of the sintered body becomes large and the dimensional accuracy deteriorates. The reason why the open porosity is preferably 18 to 56% by volume is that if the open porosity is lower than 18% by volume, it is difficult to fill with metallic silicon; This is because if the amount is too high, the strength of the porous silicon carbide sintered body will be low and the particles will be easily detached.

The porous silicon carbide sintered body needs to have excellent dimensional accuracy, and is a silicon carbide sintered body having a three-dimensional network structure composed of silicon carbide crystals with an average aspect ratio of 5 or less. Preferably, it consists of a body.

The silicon carbide composite obtained by the present invention is preferably one in which at least 50 parts by volume of metallic silicon is filled with respect to 100 parts by volume of the open pores of the porous silicon carbide sintered body. The reason is,
This is because if the filling amount of metallic silicon is less than 50 parts by volume, the effect of preventing the detachment of crystal grains from the silicon carbide sintered body will not be sufficient, and it will be difficult to improve the wear resistance.

Next, a method of manufacturing a silicon carbide composite material having excellent dimensional accuracy and wear resistance according to the present invention will be described.

According to the present invention, silicon carbide powder having an average particle size of 5 μm or less is molded into a green body, and then the green body is sintered within a temperature range of 1700 to 2100°C without substantially shrinking to form a three-dimensional A silicon carbide composite with excellent dimensional accuracy and wear resistance is manufactured by manufacturing a porous silicon carbide sintered body having open pores in a network structure, and then filling the open pores with metallic silicon. can do.

The reason why silicon carbide powder with an average particle size of 5 μm or less is used is that silicon carbide with a particle size larger than 5 μm is preferable for suppressing firing shrinkage, but it reduces the number of bonding points between grains in the sintered body. This is because not only is it difficult to obtain a high-strength silicon carbide sintered body, but also the surface roughness is deteriorated.

By the way, the crystal system of silicon carbide has α type and β type.
There are two types: type and amorphous, and any of them or a mixture thereof can be used. Among them, β type is easy to obtain in fine powder form with a diameter of 5 μm or less, and is relatively easy to obtain. It can be advantageously used because a high-strength sintered body can be produced, and in particular, it is advantageous to use silicon carbide powder containing 50% by weight or more of β-type silicon carbide.

Advantageously, the silicon carbide powder has a total content of boron, aluminum and iron of 0.3% by weight or less in terms of elements. The reason for this is that if the total content of boron, aluminum and iron is more than 0.3% by weight in terms of elements, sintering will occur during sintering due to interaction with free carbon contained in silicon carbide powder. This is because it tends to shrink, making it difficult to manufacture a sintered body without causing substantial shrinkage.

In addition, when the content of boron, aluminum, and iron in the silicon carbide powder is within the above range, a carbonaceous substance can be added to make the starting material contain 5% by weight or less of free carbon.
The free carbon has the effect of suppressing the coarsening of crystal grains, and by making it present in the starting raw material, it is possible to make the crystal grain size of the sintered body uniform and obtain a sintered body with relatively high strength. can. The reason why the free carbon content is set to 5% by weight or less is that if it is more than 5% by weight, excessive carbon will exist between the silicon carbide powder particles, which will significantly inhibit the bonding between the particles. This is because the strength of the sintered body deteriorates.

The carbonaceous material may be any material that allows carbon to be present at the start of sintering, such as various organic materials such as phenolic resin, lignin sulfonate, polyvinyl alcohol, cornstarch, sugar, coal tar pitch, and alginate. Alternatively, pyrolytic carbon such as carbon black or acetylene black can be advantageously used.

The silicon carbide powder has a total content of boron, aluminum, and iron of 0.3 in terms of elements.
When the content exceeds 0.6% by weight, it is advantageous that the content of carbonaceous substances and free carbon is 0.6% by weight or less in terms of fixed carbon content. The reason is that when the total content of boron, aluminum and iron exceeds 0.3% by weight in terms of elements, the content of carbonaceous substances and free carbon exceeds 0.6% by weight in terms of fixed carbon content. As I explained earlier, if there are many,
This is because the interaction between boron, aluminum, or iron and carbon tends to cause sintering shrinkage during sintering, making it difficult to obtain a sintered body without substantial shrinkage. In addition, if the contents of boron, aluminum, and iron are too large, they will deteriorate the physical properties of the sintered body, so it is desirable that the contents be as low as possible, and the total content should be 2
% by weight or less.

The resulting body is fired within a temperature range of 1700-2100°C. The reason for this is that if the temperature is lower than 1700°C, it is difficult to sufficiently develop the bonds that connect the grains, making it impossible to obtain a sintered body with high strength, whereas if the temperature is higher than 2100°C, once the Among the nets that have grown, those that are smaller than a certain size become constricted or, in severe cases, disappear, resulting in a decrease in strength, and some particles become coarser, causing the surface to become rougher. This is because the roughness deteriorates.

The resulting shaped body is fired in a non-oxidizing atmosphere without substantial shrinkage. The reason for this is that shrinkage during sintering is preferable for improving the strength of the sintered body, but generally speaking, the amount of shrinkage during sintering has a large effect on the density of the formed body, so it is necessary to generate uniform shrinkage. Therefore, it is important to obtain a formed body with uniform density. However, it is extremely difficult to obtain a formed body having such uniform density, and it is therefore difficult to produce a sintered body with extremely high dimensional accuracy by causing firing shrinkage.

In addition, in order to obtain a sintered body with high dimensional accuracy as described above, the firing shrinkage rate when sintering without substantially shrinking is preferably 2% or less, particularly 1% or less. is more suitable.

In addition, the formed body has a gas partial pressure of at least one of CO or N ₂ in the atmosphere of 100 Pa for at least 10 minutes within a temperature range of 1700 to 2100°C.
It is advantageous that the firing is carried out in an atmosphere maintained above. The reason for this is that by increasing the partial pressure of at least one of CO or _N2 in the atmosphere to 100 Pa or higher for at least 10 minutes within the above temperature range, the growth of the nets can be promoted and the sintering of silicon carbide can be accelerated. This is because shrinkage during firing can be effectively suppressed.

According to the present invention, it is advantageous to charge the green body into a heat-resistant container in which the firing atmosphere can be controlled and fire it. The reason why it is advantageous to charge the material into a heat-resistant container and fire it while controlling the firing atmosphere is because it can promote bonding between adjacent silicon carbide crystals and the growth of nets. . The reason why bonding between adjacent silicon carbide crystals and the growth of nets can be promoted by charging the formed body into a heat-resistant container and firing while controlling the firing atmosphere as described above is because the carbonization This is thought to be because movement of silicon carbide between silicon particles by evaporation-recondensation and/or surface diffusion can be promoted.

As the heat-resistant container, materials such as graphite and silicon carbide, and materials having functions equivalent to these materials can be advantageously used.

Furthermore, it is advantageous to control the volatilization rate of silicon carbide to 5% by weight or less during firing by charging the formed body into a heat-resistant container in which the firing atmosphere can be controlled and firing it.

Advantageously, the product form has a density of 45 to 80% by volume. The reason for this is that if the density of the formed body is lower than 45% by volume, there will be fewer points of contact between the silicon carbide particles, which will inevitably result in fewer bonding points, making it difficult to obtain a high-strength sintered body. , on the other hand, because formed forms with higher than 80 volume % are difficult to manufacture.

Also, in the temperature increase process up to 1700℃ mentioned above,
By maintaining the total gas partial pressure of CO and N ₂ in the atmosphere at 100 Pa or less at 1300℃ or higher for at least 30 minutes, the nets between silicon carbide particles are uniformly generated and bonded firmly. be able to.

According to the present invention, it is necessary to fill the open pores of the porous silicon carbide sintered body with metallic silicon. The reason is that metallic silicon has good compatibility with silicon carbide sintered bodies, and by filling the open pores of porous silicon carbide sintered bodies with metallic silicon, it is possible to form porous silicon carbide sintered bodies. This is because it is possible to prevent the detachment of crystal grains from the steel, and the wear resistance can be significantly improved.

As a method for filling the open pores of the porous silicon carbide sintered body with the metallic silicon, there is a method of impregnating the metallic silicon by heating and melting it, or a method of dispersing pulverized metallic silicon in a dispersion medium and dispersing the metallic silicon. An applicable method is to impregnate a porous silicon carbide sintered body with a liquid, dry it, and then heat it to a temperature higher than the melting temperature of metal silicon.

According to the present invention, the metallic silicon is added to 10 parts by volume of open pores of the porous silicon carbide sintered body.
It is advantageous to fill at least 50 parts by volume.
The reason for this is that if the filling amount of metal-free silicon is less than 50 parts by volume, the effect of preventing the detachment of crystal particles from the silicon carbide sintered body is insufficient, and it is difficult to improve the wear resistance. It is from.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 The silicon carbide powder used as a starting material consisted of 94.6% by weight of β-type crystals and the remainder substantially of 2H-type crystals, and contained 0.29% by weight of free carbon, 0.17% by weight of oxygen, 0.03% by weight of iron, It mainly contained 0.03% by weight of aluminum, had an average particle size of 0.28 μm, and no boron was detected.

5 parts by weight of polyvinyl alcohol and 300 parts by weight of water are blended with 100 parts by weight of the silicon carbide powder,
The mixture was mixed in a ball mill for 5 hours and then dried.

An appropriate amount of the dry mixture was collected, granulated, and then molded using a metal mold at a pressure of 3000 kg/cm ² . The dimensions of this generated feature are 250mm x 250mm x 30mm
The density was 2.0 g/cm ² (62% by volume).

The formed body was placed in a graphite crucible and fired in a Tammann type firing furnace in an atmosphere of mainly argon gas at 1 atm. The temperature was raised to 2000°C at a rate of 450°C/hour and held at the maximum temperature of 2000°C for 10 minutes. CO gas partial pressure during sintering ranges from room temperature to 1700℃
is 80Pa or less, 300±50Pa at higher temperatures than 1700℃
The argon gas flow rate was appropriately adjusted and controlled so that it was within the range of .

The density of the obtained sintered body was 2.05 g/ ^cm2 , and the open porosity was 36%, and its crystal structure, when observed using a scanning electron microscope, was composed of many silicon carbide plate crystals with an average aspect ratio of 2.5. It has a three-dimensional structure that is intricately intertwined in various directions, and the linear shrinkage rate of the formed body is within the range of 0.25 ± 0.02% in any direction, and the dimensional accuracy of the sintered body is within ± 0.05 mm. It was hot. In addition, the average bending strength of this sintered body is 18.5Kg/
It showed an extremely high value of mm ² .

Next, the average particle size is applied to the surface of the porous sintered body.
100 parts by weight of 20μm 99.9% pure metal silico powder and 5
A slurry containing 60 parts by weight of acrylic acid ester/benzene solution was applied, and the surface was coated with 1700 g of metallic silicon. This porous sintered body coated with metallic silicon was heated in an argon gas stream at a heating rate of 450°C/hour, and held at a maximum temperature of 1450°C for about 1 hour to coat the surface of the sintered body. Metallic silicon was infiltrated into the sintered body to obtain a silicon carbide composite.

The porosity of the obtained silicon carbide composite was 1.6%, and the dimensional change was only 0.005 mm larger than before filling with metal silicon. Furthermore, the average bending strength was 35.5 Kgf/mm ² , which was significantly increased by filling with metallic silicon.

Example 2 Same as Example 1, but as silicon carbide powder
92.8% by weight of β-type crystals and the remainder essentially of 2H-type crystals, 0.21% by weight of free carbon, 0.17% by weight
of oxygen, 0.05% by weight of iron, 0.1% by weight of aluminum, 0.2% by weight of boron,
Using silicon carbide powder having an average particle size of 0.27 μm, a novolak type phenolic resin with a fixed content of 51.6% by weight based on 100 parts by weight of the silicon carbide powder.
0.4 parts by weight and 300 parts by weight of benzene were mixed in a ball mill for 5 hours and then dried. The resulting dry mixture was used to form a 250 x 250 x 50 mm shaped body, and then sintered to form a porous sintered product. I got a body.

The density of the obtained sintered body was 2.05 g/cm ² , the open porosity was 36%, and the linear shrinkage rate for the formed body was
Although it was slightly larger at 0.52±0.03%, the dimensional accuracy was ±
It was 0.08mm, which was relatively good. The average bending strength of this sintered body was 32.5 Kg/mm ² , which was a significantly high value.

Next, the porous sintered body was placed in a graphite crucible, and after 99.9% pure bulk metal silicon was placed around the porous sintered body, it was heated at 1450°C for 1 hour to form a silicon carbide composite. Obtained.

The obtained silicon carbide composite had a porosity of 2.2%, and almost no dimensional change was observed. The dimensional accuracy of this composite was within ±0.05 mm, and the average bending strength was 42.6 Kgf/mm ² .

〔Effect of the invention〕

As described above, the silicon carbide composite obtained by the present invention has extremely excellent dimensional accuracy and wear resistance, and is suitable for semiconductor diffusion and oxidation treatment, diode bonding, glass sealing, and package lead frame loading. Silicon carbide is suitable for applications such as materials for heat-resistant jigs in the electronics industry, wear-resistant materials such as mechanical seals and bearings, and corrosion-resistant materials such as pump parts for highly corrosive solutions such as acids and alkalis. It is possible to provide a quality composite at a low cost and is extremely useful industrially.

Claims (1)

[Claims] 1. After molding silicon carbide powder with an average particle size of 5 μm or less into a green body, CO or N ₂ in the atmosphere is heated for at least 10 minutes within a temperature range of 1700 to 2100°C.
A porous sintered body having open pores with a three-dimensional network structure is produced by sintering without substantially shrinking in an atmosphere in which the partial pressure of at least one of the gases is maintained at 100 Pa or more, and then the open pores are sintered without substantially shrinking. A method for producing a silicon carbide composite with excellent dimensional accuracy and wear resistance, characterized by filling pores with metallic silicon. 2. The manufacturing method according to claim 1, wherein the silicon carbide powder has a total content of boron, aluminum, and iron of 0.3% by weight or less in terms of elements. 3 The silicon carbide powder has a total content of boron, aluminum, and iron exceeding 0.3% by weight and 2.0% by weight or less in terms of elements, and a content of carbonaceous substances in terms of fixed carbon content. 0.6% by weight
The manufacturing method according to claim 1, which is as follows. 4. The manufacturing method according to any one of claims 1 to 3, wherein the porous silicon carbide sintered body has a shrinkage rate of 2% or less during sintering. 5. At least 50% of the metal silicon is added to 100 parts by volume of open pores of the porous silicon carbide sintered body.
The manufacturing method according to any one of claims 1 to 4, wherein the manufacturing method is filled by volume.