JPH10330734A - Silicon carbide composited silicon nitride abrasive and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-cost silicon carbide composite silicon nitride abrasive having high hardness and being useful in high performance precision grinding. SOLUTION: This material is prepared by mixing 60-92 wt.% silicon nitride powder having a mean crystal grain diameter of 1 μm or below with 3-10 wt.% Al2 O3 having a mean crystal grain diameter of 1 μm or below and, at least one rare earth oxide and Y2 O3 , and 5-30 wt.% silicon carbide powder having a mean crystal grain diameter of 1 μm or below and firing the mixture and has a Vickers hardness of above 22 GPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates to a silicon carbide composite silicon nitride based abrasive used as a grinding wheel, abrasive cloth or the like, and a method for producing the same.

[0003]

2. Description of the Related Art A silicon nitride sintered body has heat resistance, wear resistance,
Because of its excellent corrosion resistance, fracture toughness, etc., it is expected to be used as a structural material in place of metal materials, and has achieved remarkable development. For example, silicon nitride focused on technology for growing columnar crystals peculiar to silicon nitride for the purpose of improving fracture toughness for the purpose of using it as a structural material, and achieving high strength and high toughness by controlling the columnar crystals (“Diversification of Si ₃ N ₄ ceramics by controlling the structure”, silicon nitride ceramics (2), pages 135 to 146).

However, when attention is paid to the hardness required as an abrasive, the growth of crystal grains is not as excellent as other characteristic values, because the distance between the crystals is increased to reduce the intercrystalline bonding force. Vickers hardness is at most about 18 GPa, which is slightly lower than that of the alumina sintered body. Therefore, as a high-hardness abrasive used for a grinding wheel, abrasive cloth, etc., the performance of a conventional silicon nitride sintered body is insufficient, and alumina,
Silicon carbide is used.

Further, in recent years, diamond and cubic boron nitride (cBN) have been increasingly used as ultra-hard abrasives for higher precision grinding.

[0006] The hardness of the alumina-based abrasive is insufficient to cope with precision grinding, and the silicon-carbide-based abrasive is liable to react with iron and cannot be used as a work material containing iron. There are serious drawbacks. On the other hand, diamond and cubic boron nitride (cBN) have a sufficient performance as a super-hard abrasive, but are very expensive, 100 to 200 times as expensive as general abrasives such as alumina and silicon carbide. is there. Therefore, improvement and development of general abrasives that can sufficiently cope with precision grinding are desired.

Under these circumstances, the present inventor has already developed an abrasive obtained by adding a sintering aid powder selected from alumina and rare earth oxides to silicon nitride powder, molding, crushing and firing. It is disclosed that when this is used for a grinding wheel or the like, an extremely high grinding ratio, which cannot be achieved with conventional general abrasive grains, can be realized in precision grinding, particularly wet grinding (Japanese Patent Laid-Open No. 3-287687).

[0008]

The present invention is a further improvement of the above invention (Japanese Patent Application Laid-Open No. 3-287687), which has high hardness and is useful for high-performance precision grinding, and realizes low cost. Silicon carbide composite silicon nitride abrasive,
And a method for manufacturing the same.

[0009]

The present inventors Means for Solving the Problems], the above invention (Japanese Patent Laid-Open 3-287687) As a result of intensive studies in order to improve, the silicon nitride powder, A1 ₂ 0 ₃ powder and rare earth oxides It has been found that a sintered body obtained by mixing and firing one or more kinds of powder, Y ₂ O ₃ powder, and further silicon carbide powder has high hardness, and has completed this invention.

[0010] Namely, the present invention according carbide composite silicon nitride abrasive silicon nitride as a main component, and a one or more and Y ₂ O ₃ of A1 ₂ 0 ₃ and rare earth oxide as an auxiliary component, further carbonized It is essentially characterized by having silicon as a constituent and having a Vickers hardness of greater than 22 GPa.
In particular, 60 to 92 wt% silicon nitride powder having an average grain size below 1 [mu] m, A1 ₂ 0 ₃ and one or more rare earth oxides having an average grain size below 1 [mu] m and Y ₂ O ₃ is 3
It is characterized in that silicon carbide powder having an average crystal grain size of 1 to 10% by weight is mixed and fired at a component ratio of 5 to 30% by weight (preferably 10 to 20% by weight).

In this case, the firing temperature is 1500 to 1800
It can be fired at a temperature of 1550C, more preferably 1550C to 1750C, and more preferably 1700C or lower and 1600C or higher. The firing conditions are preferably performed by pressure firing.

Further, the silicon carbide composite silicon nitride abrasive has a microstructure of 1 μm or less.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In obtaining a novel silicon carbide composite silicon nitride based abrasive of the present invention, an auxiliary component, that is, a component selected from Al ₂ O ₃ (alumina) and a rare earth oxide as a sintering aid. The above and Y ₂ O ₃ (yttria) are added so that the total amount is 3% by weight (hereinafter referred to as “%”) or more. Rare earth oxides include Nd, Pr, Ce,
Oxides of Gd and other rare earth oxides (lanthanoids with atomic numbers 57 to 71) or mixtures thereof can be used. On the other hand, even with the addition of this auxiliary agent, it is necessary that the abrasive can have sufficient high temperature, high strength and high hardness as an abrasive for precision grinding. Therefore, auxiliary components (sintering aids)
Is 10% or less. In particular, the ratio of alumina to yttria is preferably about 1: 1. It is preferable that the ratio of alumina to yttria be 1: 1, (Si ₃ N ₄ +
Al ₂ O ₃ + Y ₂ O ₃ )
0% is preferable, 3 to 8% is more preferable, and 4 to 5% is most preferable.

Further, in order to obtain the silicon carbide composite silicon nitride based abrasive of the present invention, it is preferable to add 5% or more of silicon carbide. By adding a significant amount of silicon carbide, the hardness of the sintered body can be increased, and the Vickers hardness is 22GP.
It can be larger than a. On the other hand, if the amount of silicon carbide is too large, structural defects occur due to a difference in the coefficient of thermal expansion from silicon nitride, so the amount of silicon carbide is set to 30% or less.
Silicon carbide is preferably from 10 to 25%, particularly preferably from 10 to 20%. Silicon nitride is Si ₃ N ₄ + Al ₂ O ₃ + Y ₂ O ₃
The ratio of the three components is preferably 80 to 98%, more preferably 84 to 94%, and most preferably 88 to 90%.

The average crystal grain size of this raw material powder is as follows: silicon nitride as a main component, Al ₂ O ₃ and a sub-component
Each of ₂ O ₃ and silicon carbide has a thickness of 1 μm or less. The resulting silicon carbide composite silicon nitride-based sintered grains have a fine crystal structure of 1 μm or less, and exhibit a high grinding ratio as an abrasive. The average particle size of the raw material powder is preferably 0.2 to 0.4 μm.

The molding after mixing the raw materials can be performed by various known methods,
For example, pressure molding and slip casting can be selected and used according to the purpose. The cold formed article is subsequently crushed and before firing. Therefore, the shape of the molded product is massive,
There is no particular limitation on the shape of a sheet or a string.

The molded product is pulverized (crushed) to a particle size substantially corresponding to a particle size suitable as an abrasive. In the case of precision grinding of steel, for example, it is preferably about 250 μm to 350 μm (# 60 to # 80).

In firing the pulverized material, a solid pressure medium is mixed in order to apply uniform pressure to each powder and obtain sintered particles having desired particle size as abrasive particles. As the solid pressure medium, hexagonal boron nitride (hBN) having low hardness, low reactivity and low cost is preferable, and its average particle size is not particularly limited, but is 1 to 5 μm (further, 3.5 μm or less, or 2 μm or less). It is preferable that the mixed amount is about 80 to 120% by weight based on the above pulverized material. The sintering method may be either normal pressure sintering or pressure sintering. However, in order to increase the sinterability and obtain a high-density, high-hardness abrasive, pressure sintering, that is, hot pressing (HP) sintering, is employed. Sintering, isostatic hot pressing (HIP) sintering, or a predetermined nitrogen partial pressure (for example, 9
kg / cm ² ).
The firing temperature is 170 from the viewpoint of preventing the growth of silicon nitride grains.
The temperature is preferably set to 0 ° C. or lower.

The silicon carbide composite silicon nitride-based sintered particles thus obtained are polycrystals having an extremely fine average crystal grain size of 1 μm or less, particularly about 0.2 to 0.5 μm. There is a grain boundary phase mainly composed of an auxiliary. This grain boundary phase is, for example, Si ₃ N ₄ —nY ₂ O ₃ —mAl ₂
It exists as a crystal phase composed of the compound represented by O ₃ or a glass phase such as nitrided glass.

In the present invention, the compact is crushed in advance before sintering and sintered in the presence of a solid pressurized medium. Therefore, the sintered body is sintered very densely with a particle size of, for example, about 200 to 300 μm. It can be obtained as aggregates. Therefore, it is not necessary to separately pulverize the sintered body that requires high breaking energy.

Using the silicon carbide composite silicon nitride-based abrasive, a grinding wheel and abrasive cloth are manufactured according to a conventional method. When manufacturing a general vitrified grinding wheel as a grinding wheel for precision grinding, which is the object of the present invention, it is preferable to use a vitreous binder having a firing temperature of about 1000 ° C. The grinding wheel thus obtained has a grinding performance equal to or higher than that of a grinding wheel using conventional general abrasives (alumina, silicon carbide). As a work material, it can be applied to metals in general, and is particularly effective for heat-resistant alloys and super tool steels.
Although it contains silicon carbide as a component, it is needless to say that the present abrasive is difficult to weld to iron.

[0022]

【Example】

[First Example] As a first example, the following raw materials were mixed at the following mixing ratio. Using raw silicon nitride: (Ube Industries, Ltd.) E-10 (average particle size 0 · 3 [mu] m) Sintering: Sumitomo Chemical (Co.) A1 ₂ 0 ₃ (average particle size 0 · 4 [mu] m) Mitsubishi Chemical (Co.) Y ₂ 0 ₃ (average particle size 0 · 8 [mu] m) silicon carbide: Ibiden (Ltd.) UltraFine (average particle size 0.3 [mu] m) blended proportion of the raw material _{Si 3 N 4: A1 2 0} 3: Y 2 0 3: SiC = 81: 4 5.5: 4.5: 10 (% by weight)

40 g of a mixture comprising the above-mentioned raw material composition was
Put into a rectangular parallelepiped mold (bottom 60 mm x 25 mm) and have a surface pressure of 30
The molded product is preformed by uniaxial pressing at 0 kg / cm ² , and the molded product is packed in a vinyl bag for cold isostatic pressing (CIP), evacuated, and a vacuum pack is formed. gave. Then, a pressure of 2000 kg / cm ² was applied to each of the bags of the vacuum pack, and C.I.
I. P. did.

C. I. P. Thereafter, the molded product was taken out of the plastic bag, crushed in an alumina mortar or the like, and sieved to a desired particle size. The particle size to be selected was 250 to 350 μm. In order to finally obtain an abrasive having a particle size of about 200 to 300 μm, shrinkage due to firing is expected.

The molding powder sieved to the desired particle size and hexagonal boron nitride (hBN) powder having an average particle size of 3.5 μm as a pressure medium were mixed in an amount of 100 g each. This mixed powder is filled in a rectangular parallelepiped graphite mold (bottom surface 90 mm x 50 mm), and the hot press firing furnace (Fuji Denki Kogyo Co., Ltd.)
(Manufactured by Co., Ltd.) at a heating rate of 13 ° C./min.
Heat to 0 ℃, uniaxial mechanical pressure 400kg / c at the same temperature
m ² and baked under pressure for 60 minutes. Then 5 ℃ / min
The temperature was lowered to 1000 ° C. at the temperature lowering rate, and then allowed to cool to room temperature.

Next, the fired body was lightly ground in an alumina mortar. Since hexagonal boron nitride (hBN) has low reactivity, it is easy to grind. After that, hexagonal boron nitride (hBN) was completely removed by sieving and further washing with an ultrasonic cleaner. Although water may be used for washing, it is preferable to use a detergent. The washed sintered particles were dried in a drier to completely remove water, and particles having an average of 250 μm (about # 60) were selected by sieving to obtain an abrasive of the first embodiment.

This abrasive had a microcrystalline structure (fine structure) having an average crystal grain size of 0.5 μm, and had a Vickers hardness of 24 GPa. For comparison, a composition (weight% ratio that does not contain silicon _{carbide, Si 3 N 4: A1 2} 0 3: Y 2 0 3 = 9
0: 5: 5), the Vickers hardness of these abrasives was determined as Comparative Example 1, and the abrasives having the same composition as Comparative Example 1 but having different firing temperatures were defined as Comparative Example 2. Are shown in Table 1.

[0028]

[Table 1]

A vitrified grinding wheel (referred to as a first grinding wheel) was prepared using the abrasive of the first embodiment. On the other hand, the comparative examples 1 and 2 and a conventionally known fused alumina single crystal were prepared. Abrasives (Pacific Random Co., Ltd .; 32
A), Sintered alumina polycrystalline abrasive (3M; Cubitron)
321) was also prepared (comparative grinding wheels 1 to 4). Specifically, the grinding wheel is composed of abrasive grains 8
8.1 parts by weight of ceramic binder component 11.9 parts by weight,
After adding and mixing 3.1 parts by weight of dextrin, the mixture was pressurized to form a molding density of 1.88 g / cm ³ . Next, the raw whetstone before firing is heated at 50 ° C./Hr in an electric furnace at 1000 ° C.
Until heated. The ceramic binder used was composed of feldspar, clay and frit glass. The grindstone after firing was 47.2% by volume of the abrasive (abrasive) and 8.9% by volume of the binder. Table 2 shows the properties of the grinding test whetstone. The dimensions of the grindstone were 178 mm in outer diameter × 12.7 mm in thickness × 76.
It was 2 mm.

[0030]

[Table 2]

Next, a grinding test was performed on the grinding wheels shown in Table 2. The grinding test conditions are as follows. Machine: Okamoto TairaKen CFG-52AN grindstone peripheral speed: 2000 m / min cut: Δ ^R 20μm / pass dry plunge cut down Workpiece: SKD-1 (HRC60: tool steel) (dimension): Length 100 × height 50 x width 10 (mm) (cut width): 100mm Dress: single stone dresser

Table 3 shows the results.

[0033]

[Table 3]

As is clear from Table 3, even when compared with the comparative grinding wheel 1 using the silicon nitride abrasive (Comparative Example 1) produced with the same component ratio as in the example except that silicon carbide was not added. A grinding ratio of 1.7 times is obtained.

Further, a conventional silicon nitride abrasive having crystal grains grown for the purpose of structural material, a known fused alumina single crystal abrasive (32A), and a sintered alumina polycrystalline abrasive (Cubitron 321) are used. As compared with the comparative grinding wheels 2 to 4 used, a grinding ratio of 4 to 10 times can be obtained.

[Second to Fourth Embodiments] Further, the same raw materials as in the first embodiment were mixed at the following mixing ratios to prepare the second, third and fourth embodiments. . Formulation ratio of the raw material of the second embodiment _{Si 3 N 4: A1 2 0} 3: Y 2 0 3: SiC = 85.5: 4.
75: 4.75: 5 wt% third formulation ratio of the raw material of Example _{Si 3 N 4: A1 2 0} 3: Y 2 0 3: SiC = 72: 4: 4:
Formulation proportion of 20 wt% raw materials fourth embodiment _{Si 3 N 4: A1 2 0} 3: Y 2 0 3: SiC = 63: 3.5:
3.5: 30% by weight

40 g of the mixture having the above-mentioned raw material composition was
Forming, crushing, firing, crushing,
After washing to obtain an abrasive, a vitrified grinding wheel was prepared and a grinding test was performed. Each condition is the same as in the first embodiment. Table 4 shows the hardness of the abrasive, and Table 5 shows the grinding ratio of the grinding wheel, together with the results of the first embodiment.

[0038]

[Table 4]

[0039]

[Table 5]

As is clear from Tables 4 and 5, all of the second, third, and fourth embodiments achieve high performance as an abrasive similarly to the first embodiment. .

Fifth Embodiment In order to examine the relationship between the amount of added SiC and Vickers hardness, Si ₃ N ₄ , Al ₂ O ₃ , and Y ₂ O _{3 were used.}
Is maintained at 90: 5: 5 wt%, and the mixture
33% by weight of SiC was blended as shown in Table 6, and an abrasive was produced in the same manner as in the first example, and Vickers hardness was measured. Table 6 shows the results.

[0042]

[Table 6]

[0043]

According to the present invention, a dense silicon carbide composite silicon nitride abrasive having high hardness and fine crystals can be obtained.
A grinding wheel using such an abrasive can be suitably used for precision grinding of tools, dies, and the like made of heat-resistant alloys and the like, and exhibits extremely excellent performance as compared with conventional grinding wheels. Therefore, in precision grinding, it is extremely useful as a polishing material to replace a very expensive super-hard polishing material. In particular, the present invention relates to Si
Despite containing the C component, it was found to be effective for grinding hard-to-cut iron-based steel such as tool steel. This is surprising.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a manufacturing method according to an embodiment of the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kenji Ito 3-36 Noritake Shinmachi, Nishi-ku, Nagoya-shi, Aichi Prefecture Noritake Co., Ltd.

Claims (7)

[Claims] 1. A method according to claim 1, wherein the main component is silicon nitride, and A1
₂ 0 ₃ and includes a one or more and Y ₂ O ₃ of a rare earth oxide,
Furthermore, a silicon carbide composite silicon nitride-based abrasive characterized by essentially having silicon carbide as a constituent component and having a Vickers hardness of greater than 22 GPa. 2. A 1μm or less in average crystal grain size of silicon nitride powder 60 to 92 wt% with one or more A1 ₂ 0 ₃ and rare earth oxide having an average grain size below 1μm and Y ₂
A silicon carbide composite silicon nitride material characterized in that O3 is mixed at a component ratio of ₃ to 10% by weight, silicon carbide powder having an average crystal grain size of 1 [mu] m or less at 5 to 30% by weight, and fired. Abrasive material. 3. The silicon carbide composite silicon nitride based abrasive according to claim 1, which has a microstructure of 1 μm or less. 4. A polishing whetstone or abrasive cloth made by using the abrasive according to claim 1. 5. 1μm or less in average crystal grain size of silicon nitride powder 60 to 92 wt% with one or more A1 ₂ 0 ₃ and rare earth oxide having an average grain size below 1μm and Y ₂
A silicon carbide composite silicon nitride characterized in that silicon carbide powder having an O ₃ content of ₃ to 10% by weight and an average crystal grain size of 1 μm or less is mixed at a component ratio of 5 to 30% by weight, and the mixture is fired. Method for producing high quality abrasives. 6. The method according to claim 5, wherein the firing temperature is 1700 ° C. or less. 7. The method for producing a silicon carbide composite silicon nitride based abrasive according to claim 5, wherein the firing is performed by pressure firing.