JP2003286069A - Alumina sintered compact having machinability and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alumina sintered compact which has machinability, and to provide a method of producing the same. <P>SOLUTION: The alumina sintered compact contains, by weight, 90 to 99.99% alumina and 0.01 to 10% magnesium oxide, and in which the mean crystal grain size and the maximum crystal grain size of the alumina are 10 to 50 μm and ≤70 μm, respectively, and three-point bending resistance deflective strength is 250 to 450 MPa. In the method of producing the sintered compact, 90 to 99.99% easily sinterable alumina powder having a mean crystal grain size of ≤1.0 μm is blended with 0.01 to 10% magnesium oxide, and, a binder for molding is added thereto, and the blend is compacted so as to be a prescribed shape, and subsequently, firing is performed in an oxidizing atmosphere heated at 1,620 to 1,800°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an alumina-based sintered body having free-cutting properties and a method for producing the same.

[0002]

2. Description of the Related Art Alumina-based sintered bodies are excellent in wear resistance, heat resistance, chemical resistance and the like among ceramic sintered bodies, and alumina as a raw material is relatively inexpensive. It is widely used as an industrial material such as crushing members and structural members.

In recent years, semiconductor manufacturing equipment such as vacuum chamber inner wall material, microwave introduction window, focus ring, clamp ring, susceptor, etc. exposed to halogen-based corrosive gases such as fluorine-based and chlorine-based or their plasma atmospheres. It has been proposed to use an alumina-based sintered body as the corrosion-resistant member (see JP-A-5-217946).

[0004]

However, the alumina-based sintered body has higher strength and hardness as compared with metal materials and the like, and generally has a high fracture toughness value, so that the processing load during grinding becomes high. Since it takes time to process, there is a problem that the structural member cannot be manufactured at low cost. In particular, when the structural member becomes large in size, the processing area increases, and it takes a lot of time for processing. Therefore, there is a problem that the processing cost increases and the structural member becomes expensive.

Therefore, an object of the present invention is to provide an alumina-based sintered body having a free-cutting property (high processability) capable of reducing the processing load and the processing cost, and a method for producing the same.

[0006]

The alumina-based sintered body of the present invention for solving the above-mentioned problems is alumina 90-99.
99% by weight and 0.01 to 10% by weight of magnesium oxide, the average crystal grain size and the maximum crystal grain size of the alumina are 10 to 50 μm and 70 μm or less, respectively, and the three-point bending transverse strength is 250 to It is characterized by being 450 MPa.

As a result, the alumina sintered body of the present invention is
High free machinability (high workability) is obtained while maintaining sufficient mechanical strength.

Further, the alumina-based sintered body of the present invention is destroyed.
Toughness value is 4.5-6.0 MPa · m ^1/2Like to be
Good Further, the alumina-based sintered body of the present invention has a grinding resistance.
The value is preferably 25 N or less. This grinding resistance value is
It is an index to evaluate the workability of alumina sintered body.
is there.

According to the production method of the present invention for obtaining the above-mentioned alumina sintered body, 90 to 99.99% by weight of easily sinterable alumina powder having an average crystal grain size of 1.0 μm or less is added to magnesium oxide of 0.01 to 10%. 16 wt% after blending the weight% and adding a molding binder to mold into a predetermined shape
It is characterized by firing in an oxidizing atmosphere of up to 1800 ° C. Here, the “sinterable alumina powder” refers to an alumina powder that has a large particle growth energy and is easy to sinter even at a low temperature because the individual particle size is small and the specific surface area is large.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below. The alumina sintered body of the present embodiment has a three-point bending bending strength of 250 to 450 M, which is an index of mechanical strength.
It is in the range of Pa and has a fracture toughness value of 4.5 to 6.0 MPa.
・ It is in the range of m ^1/2 .

If the three-point bending bending strength is less than 250 MPa, there is a possibility that it cannot be used as a structural member requiring mechanical strength. On the other hand, if the three-point bending transverse strength exceeds 450 MPa, the workability may decrease. The three-point bending transverse strength is measured according to the method specified in JIS R 1601.

The fracture toughness value is 4.5 MPa · m ^1/2
If it is less than the range, it may not be used as a structural member requiring mechanical strength. On the other hand, if the fracture toughness value exceeds 6.0 MPa · m ^1/2 , the workability may decrease. The fracture toughness value is measured according to the method specified in JIS R1607.

Since the alumina sintered body of the present invention has the three-point bending transverse strength and the fracture toughness value within the above ranges, it has excellent workability. This workability can be represented by the following grinding resistance value, and the alumina-based sintered body of the present invention preferably has a grinding resistance value of 25 N or less.

<Measurement Method of Grinding Resistance Value> First, the vertical 150
An alumina sintered body having a size of mm × width 30 mm × thickness 10 mm is prepared. Then, using a metal wheel diamond grinding tool (diameter 300 mm) of a surface grinder, a surface (surface to be ground) of length 150 mm × width 30 mm, wheel peripheral speed 1800 m / min, surface grinder table moving speed 150 m
Grind at m / min and cut depth of 0.5 mm. A resistance value applied to the grinding tool in the normal direction of the surface to be ground during this grinding is defined as a grinding resistance value (N).

The average crystal grain size and the maximum crystal grain size of alumina in the alumina sintered body are 10 to 5 respectively.
It should be 0 μm and 70 μm or less.

When the average crystal grain size exceeds 50 μm, a large number of pores are present in the sintered body, and the three-point bending resistance strength, fracture toughness value and hardness of the sintered body may be excessively lowered. is there. On the other hand, when the average crystal grain size is less than 10 μm, the three-point bending resistance strength, fracture toughness value and hardness of the sintered body become excessively high, which may impair free-machining property.

If the maximum crystal grain size exceeds 70 μm, the three-point bending resistance strength, fracture toughness value and hardness may be excessively reduced.

To obtain an alumina-based sintered body having such a particle size characteristic, 90% of alumina is contained in the sintered body.
~ 99.99 wt%, magnesium oxide 0.01-1
It is necessary that the content is 0% by weight.

The content of magnesium oxide is 0.01 to 1
By being in the range of 0% by weight, 1620 to 1800
Even when firing is performed at a high temperature of ° C, partial grain abnormal grain growth can be suppressed, and the maximum crystal grain size can be within the above range.

When the content of alumina is less than 90% by weight, the mechanical properties and thermal properties of the sintered body are other than alumina, and other components (magnesium oxide, and silicon oxide, calcium oxide added as necessary) are added. Sintering aids, etc.)
The ratio controlled by the characteristics of 1) becomes high, and the three-point bending bending strength, fracture toughness value and hardness of the sintered body may be excessively lowered. On the other hand, the content of alumina is 99.99% by weight
If it exceeds, the content of magnesium oxide will decrease,
Since the above-described effect of suppressing abnormal grain growth is reduced, it may not be possible to suppress an excessive decrease in the three-point bending bending strength, fracture toughness value and hardness of the sintered body.

The alumina-based sintered body to which the above-mentioned mechanical characteristics and free-cutting property are given can be produced by the following manufacturing method.

First, an easily sinterable alumina powder as a raw material,
Prepare magnesium oxide powder and, if necessary, auxiliary components such as a sintering auxiliary. As the easily sinterable alumina powder,
Alumina purity is 95% or more, average crystal grain size is 1.0
It is preferably not more than μm.

The average crystal grain size of the alumina powder is 1.0 μ
When it exceeds m, the specific surface area is reduced and the activity for promoting sintering is reduced, so that the energy for grain growth is reduced. It is difficult to adjust the average crystal grain size and the maximum crystal grain size of the alumina powder having such low activity to the above-mentioned ranges by simply adjusting the firing temperature. On the other hand, since the alumina powder having an average crystal grain size of 1.0 μm or less has a large specific surface area and thus has a large energy for grain growth, the average crystal grain size and the maximum crystal grain size can be easily adjusted by adjusting the firing temperature. .

Next, easily sinterable alumina powder 90-99.
Magnesium oxide 0.01 to 10.0% by weight is added to 99% by weight, and a wax emulsion (wax +
Emulsifier), PVA (polyvinyl alcohol), PEG
An organic binder (molding binder) such as (polyethylene glycol) is added and kneaded to prepare a slurry, or kneaded and dried to prepare granulated powder.

When the slurry is prepared, it is molded into a predetermined shape by a tape molding method such as a casting method, an injection molding method, a doctor blade method or the like. On the other hand, when producing granulated powder, a uniaxial pressure molding method such as press molding in which the powder is filled into a mold is used, or a predetermined pressure molding method such as rubber press molding is used. To shape.

Then, if necessary, the obtained molded body is subjected to 3
Degreased at 00-600 ° C, and further 1620-1800
Baking in an oxidizing atmosphere at ℃.

Here, the easily sinterable alumina powder used in the present invention is usually fired at a firing temperature of about 1400 to 1600 ° C. When firing in this temperature range, the average crystal grain size becomes as small as 10 μm or less, and a highly densified sintered body can be obtained, but the fracture toughness value is 6.0 M.
Three-point bending bending strength of 450 MPa over Pa · m ^1/2
As described above, the workability at the time of grinding the sintered body decreases. When the firing temperature is lower than 1400 ° C, an undensified alumina sintered body is obtained, the water absorption rate is increased, and the fracture toughness value is 4.5 MPa · m ^1/2 or less.
The bending resistance against point bending is reduced to 250 MPa or less, and it cannot be used as a structural member requiring mechanical strength. On the other hand, if the firing temperature exceeds 1800 ° C., the alumina powder causes abnormal grain growth, and the bending strength, hardness, and
Since mechanical properties such as fracture toughness value are extremely lowered, there is a possibility that it cannot be used as a structural member requiring mechanical strength.

Therefore, in the production method of the present invention, the firing temperature of the easily sinterable alumina powder is set to the normal firing temperature (1400 to 1400).
Higher temperature (1620-180)
By setting the temperature to 0 ° C.), the particle size of the obtained sintered body is appropriately increased, and sufficient mechanical strength and high workability required for structural members and the like are provided.

The alumina sintered body thus obtained has a three-point bending bending strength of 250 to 450 MPa, a fracture toughness value of 4.5 to 6.0 MPa · m ^1/2 , and a grinding resistance value. Since it is 25N or less, it has excellent workability, and has a Vickers hardness of 15 GPa or more and a thermal shock resistance (ΔT) of 150 ° C. or more, so even if it is used in an environment where heat is applied, it is not subject to thermal shock. It is less likely to crack and can be used stably. Further, the alumina-based sintered body of the present invention is an inner wall material of a vacuum chamber exposed to a halogen-based corrosive gas such as a fluorine-based or chlorine-based gas or its plasma atmosphere, a microwave introduction window, a focus ring, a clamp ring, a susceptor. It can also be used as a corrosion resistant member for semiconductor manufacturing equipment such as.

Further, the alumina-based sintered body of the present invention is less likely to be chipped or cracked when it is handled by a fastener in various processing devices for processing into a predetermined shape, and is also subjected to grinding,
Since it has excellent free-cutting properties when it is cut, it can be cut in a relatively short time.

The alumina-based sintered body having free-cutting property of the present invention has other auxiliary components, for example, a sintering aid for the alumina-based sintered body, as long as alumina and magnesium oxide are within the above-mentioned ranges. It may contain silicon oxide, calcium oxide or the like used as.

[0032]

[Examples] The average crystal particle size of alumina as a raw material, the content of alumina, the content of magnesium oxide and the firing temperature were set to the respective conditions shown in Table 1, and the alumina sintered bodies of Sample Nos. 1 to 15 were set. Was prepared by the following procedure, and the three-point bending bending strength, fracture toughness value, and grinding resistance value of each sample were measured.

[Table 1]

<Production Method of Alumina Sintered Body> Alumina powder having a purity of 99.5% or more and magnesium oxide powder were mixed in the proportions shown in Table 1, and ion-exchanged water and a wax emulsion (wax) as a binder were mixed. And a mixture of emulsifier) and PVA (polyvinyl alcohol)
And PEG (polyethylene glycol) were added and kneaded and dried to prepare granulated powder.

Next, the obtained granulated powder was filled in a mold, and a disk-shaped molded body having a diameter of 100 mm and a thickness of 10 mm was prepared by the CIP molding method.
By firing for about 5 hours at the firing temperature shown in Table 1,
Each of the alumina-based sintered bodies of Sample Nos. 1 to 15 shown in FIG.

Each of the alumina-based sintered bodies obtained by the above method was observed with a scanning electron microscope, and the average crystal grain size and the maximum crystal grain size of alumina in the sintered body were measured by an image analyzer (Nireco Corporation). It was measured by using Luzex manufactured by the company. The measurement results are shown in Table 1.

The three-point bending bending strength and fracture toughness of each alumina sintered body obtained by the above method were measured. The three-point bending strength was measured under the above conditions according to JIS R 1601, and the fracture toughness value was JIS R 1607.
The measurement was performed under the above conditions according to The measurement results are shown in Table 1.

Further, in order to confirm the workability during grinding, the alumina sintered bodies of Sample Nos. 1 to 15 were produced by the same method as above, and the grinding resistance values of these were measured. The grinding resistance value was measured by the method described above. The measurement results are shown in Table 1.

In Table 1, the average crystal grain size and the maximum crystal grain size are 10 to 50 μm and 70, respectively.
Samples within the range of μm or less are marked with “◯” in the evaluation column, and samples outside the above range are marked with “x” in the evaluation column.

Further, in Table 1, the samples whose three-point bending transverse strength and fracture toughness are in the ranges of 250 to 450 MPa and 4.5 to 6.0 MPa · m ^1/2 , respectively, are marked with "○" in the evaluation column. "," And "x" was entered in the evaluation column for samples outside the above range.

Further, in Table 1, the grinding resistance value is 25
Samples that were judged to have excellent workability because they were as small as N or less were marked with "O" in the evaluation column, and samples with poor workability were marked with "X" in the evaluation column. For the other samples with "-" entered, the above-mentioned three-point bending bending strength or fracture toughness value was lower than the proper range and could not be used as an alumina-based sintered body. No measurement was performed.

From Table 1, samples No. 1, No. 6 and No. 8
Nos. 15 to 15 could not be used as an alumina-based sintered body because the three-point bending strength and fracture toughness values were lower than the proper ranges. Although the fracture toughness value of Sample No. 7 was within the proper range, the three-point bending transverse strength was higher than the proper range, and the grinding resistance value was large and the workability was poor. On the other hand, sample Nos. 2 to 5 according to the present invention
The three-point bending resistance strength and fracture toughness value were both within proper ranges, the grinding resistance value was low, and the workability was excellent.

[0042]

According to the present invention, the raw material is mainly composed of relatively inexpensive alumina, and the obtained sintered body has the free-cutting property, so that the processing time is shortened to reduce the processing cost. Therefore, it is possible to provide an inexpensive structural member, and there is an effect that it has sufficient mechanical strength even when used as a large structural member.

Claims (4)

[Claims] 1. Alumina containing 90 to 99.99% by weight and 0.01 to 10% by weight of magnesium oxide, wherein the alumina has an average crystal grain size and a maximum crystal grain size of 10 to 50 μm and 70 μm or less, respectively. A free-cutting alumina sintered body having a three-point bending transverse strength of 250 to 450 MPa. 2. A fracture toughness value of 4.5 to 6.0 MPa.m.
The alumina sintered body according to claim 1, which is ^1/2 . 3. The alumina sintered body according to claim 1, which has a grinding resistance value of 25 N or less. 4. 90 to 99.99% by weight of easily sinterable alumina powder having an average crystal particle size of 1.0 μm or less is mixed with 0.01 to 10% by weight of magnesium oxide, and a molding binder is further added. After molding into a predetermined shape, 1620-
A method for producing an alumina-based sintered body having free-cutting properties, which comprises firing in an oxidizing atmosphere at 1800 ° C.