JP3472802B2 - Manufacturing method of Sialon sintered body - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sialon sintered body used in the fields of automobile engines, chemical plants, cutting tools, precision machines and the like.

[0002]

2. Description of the Related Art Sialon is a solid solution of silicon nitride and is a material having excellent wear resistance and corrosion resistance. In particular, α-
Α-sialon, which is a solid solution of type silicon nitride, has high hardness and is excellent as a wear resistant material. Metals that form a solid solution in α-type silicon nitride to stabilize its structure include Li, Mg, and C.
A, Y, and lanthanide metals (excluding La and Ce) are known, and they form an interstitial solid solution in a part of two large holes existing in the unit cell of α-type silicon nitride.

The α-sialon containing Y as a solid solution has been most studied, and the invention (Japanese Patent No. 1628374) of one of the inventors of the present patent application (Sanyu) has already been put to practical use.
Thereafter, it has been reported that La or Ce partially forms a solid solution when co-added with the above-mentioned known metal. For example, when Ce is added at the same time as Y, α-sialon stabilized with Y and Ce is obtained (Journal of E
European Ceramic Society, Volume 8, pp. 3-9 (1991)). However, the hardness of this material has not been reported.

Since the lattice size of α-sialon does not change significantly due to solid solution, it is expected that a metal having a larger ionic radius has a higher atomic density and a higher hardness. Therefore, studies have been conducted for the purpose of synthesizing α-sialon stabilized by La or Ce alone. Recently, it has been reported that α-sialon stabilized with Ce (Ce-α-sialon) can be synthesized by rapidly cooling from high temperature (Journal of Materials Science Letters, Volume 15,
1435-1438 (1996)). However, the content of Ce-α-sialon was about 20%, most of the remaining was β-sialon, and part was 21R which is a polytype of AlN.

As described above, a sintered body having a high hardness containing α-sialon stabilized with La or Ce as a main component has not been synthesized. Further, in the prior art, the synthesis of α-sialon is carried out at a high temperature, and it is inevitable that a by-product having low oxidation resistance such as 21R is mixed.

Α-Sialon is Si ₃ N ₄ -AlN-A
A mixed powder of a predetermined ratio of l ₂ O ₃ -metal oxide is heated to a high temperature in a nitrogen atmosphere to cause a solid solution reaction at the same time as sintering to produce a sintered body. When CeO ₂ is used as the oxide, α-sialon cannot be synthesized by the usual sintering method. Further, even if it is rapidly cooled from a high temperature, a sintered body containing α-sialon stabilized by Ce as the main component cannot be synthesized, and the coexistence of the 21R polytype is unavoidable.

[0007]

DISCLOSURE OF THE INVENTION The present invention is directed to a sialon calcination having high hardness and excellent wear resistance, which is composed only of β-sialon and a glass phase of grain boundaries in addition to α-sialon stabilized by Ce. It is intended to provide a method for producing a tie.

[0008]

In order to solve the above problems, the present inventors have examined the reaction process of Ce-α-sialon and found that the formation of a solid solution largely depends on the nucleation stage. . That is, it was clarified that the reason why the conventional sintering method could not synthesize was not because the solid solution was not thermodynamically stable, but because the driving force for nucleation was insufficient. Then, a predetermined ratio of Si ₃ N ₄ -AlN-
If a pre-synthesized α-sialon powder is added to Al ₂ O ₃ -CeO ₂ -based raw material powder as a nucleus for grain growth, Ce-α-
Since the sialon grew, the intended sialon sintered body could be manufactured.

In the present invention, a sialon sintered body containing Ce-α-sialon is produced by adding α-sialon powder as a nucleus to a raw material powder corresponding to Ce-α-sialon and sintering at high temperature. It is a thing.

That is, the present invention is based on Si ₃ N ₄ -AlN
0.2 to 30% by weight of α-sialon powder was added to the mixed powder of the —Al ₂ O ₃ —CeO ₂ system, and α was stabilized with Ce by sintering at 1500 to 2000 ° C. in a nitrogen atmosphere. A method for producing a sialon sintered body containing sialon.

Further, according to the present invention, silicon nitride (Si ₃ N ₄ ): aluminum nitride (AlN): alumina (Al ₂ O ₃ ): cerium oxide (CeO ₂ ) in the raw material powder is 3 in molar ratio.
It is a manufacturing method of the said sialon sintered compact which is within the range of -12: 4-6: 0-0.5: 1.

The present invention also relates to Ce-stabilized α-
It is a method for producing the above sialon sintered body, in which the substance other than sialon is β-sialon and the glass phase of the grain boundary.

The present invention also uses a plasma sintering furnace,
1 at 1500 to 1850 ° C in nitrogen at 1 atm or less
It is a method for producing the above-mentioned sialon sintered body, which is carried out for 60 minutes.

The present invention also provides 165 in 1 atmosphere of nitrogen.
It is a method for producing the above sialon sintered body, which is pressureless sintering or hot press sintering at 0 to 1850 ° C.

In the present invention, when sintering is carried out under pressure nitrogen , 1650 to 1750 ° C. in nitrogen at 2 atm and 1750 to 1850 ° C. in nitrogen at 5 atm and 1 nitrogen in nitrogen at 10 atm.
It is a method for producing the above sialon sintered body, which comprises gas pressure sintering in any of the temperature ranges of 850 to 2000 ° C.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. Raw material _{powder, Si 3 N 4 -AlN-Al} 2 O 3 -CeO
Set to ₂ series. CeO ₂ is thermally decomposed at a high temperature to Ce ₂ O ₃ and, like other trivalent lanthanide metals, can form a solid solution within a certain composition range. Its composition range is
The molar ratio is 3 to 12: 4 to 6: 0 to 0.5: 1, respectively. Outside this composition ratio range, α-sialon is not formed in the sintered body, and β-sialon or β-Si ₃ N ₄ is not produced.
Is the main component of the sintered body.

Further, α-sialon is not formed even if the raw materials are controlled within the above composition range and sintered at high temperature. Ce-α
The reason why sialon is not produced has been considered to be that the structure is unstable because the radius of Ce ³⁺ ions is too large. Therefore, 0.2 to 3 of the previously synthesized α-sialon was used.
When 0% by weight is added, α-sialon in which Ce is solid-dissolved grows on it.

As is clear from the present invention, a large activation energy is required for nucleation, and it is considered that generation was impossible because the nucleation step was rate-determining. The nucleus may be α-sialon. If the amount of α-sialon added is 0.2% by weight or less, the effect of the addition will not be obtained, and 3
If it is 0% by weight or more, the product becomes expensive. Desirable amount is 3 ~
It is 10% by weight.

Since Ce-α-sialon is expected to have high hardness, the higher the content in the sintered body, the more desirable. However, at present, a sintered body containing only α-sialon as a crystal phase cannot be obtained. The rest is the β-sialon and the glass phase remaining at the grain boundaries. As previously reported, when thermal decomposition proceeds at high temperature sintering, not only α-sialon and β-sialon but also polytypes such as 21R having poor oxidation resistance and wear resistance are by-produced. In order to suppress the production of 21R, it is necessary to heat under a sufficient nitrogen gas pressure in order to suppress the progress of thermal decomposition in the sintering process.

In the sintering method, sintering and reaction proceed sufficiently,
In addition, plasma sintering, hot pressing, atmospheric pressure sintering, and gas pressure sintering are suitable as long as the generation of 21R can be suppressed. Since plasma sintering can be rapidly heated, it can be densified by relatively low temperature and short time sintering. Plasma sintering is 1
Sintering is performed at 1500 to 1850 ° C., preferably 1600 to 1850 ° C. in nitrogen under atmospheric pressure for 1 to 60 minutes, but it is necessary to heat at a lower temperature for a longer time. 45 to 60 minutes at 1600 to 1700 ° C, 10 to 30 at 1700 to 1800 ° C
1 minute at 1850 ° C.

In the hot pressing or atmospheric pressure sintering method, sintering is performed at 1650 to 1850 ° C. in nitrogen at 1 atm. In gas pressure sintering, it is necessary to increase the nitrogen pressure in the atmosphere so that the sintering is performed at a higher temperature. 1650 to 1750 ° C in nitrogen at 2 atm,
A temperature range of 1750 to 1850 ° C. in nitrogen at 5 atmospheres and a temperature range of 1850 to 2000 ° C. in nitrogen at 10 atmospheres is desirable.

[0022]

EXAMPLES The present invention will be described more specifically with reference to examples. Examples 1-3 Commercially available β-type fine powder (manufactured by Denki Kagaku, SN-P21
FC) by sedimentation method and centrifugal classification 0.2
A 5 micron fine powder was separated. To 13 mol of this powder, 9 mol of aluminum nitride and 2 mol of cerium oxide (CeO ₂ ) were added. Furthermore, Y-α-sialon powder (manufactured by Ube Industries, SN-S manufactured by Ube Industries, Ltd.) in the amount of each example shown in Table 1 was added to this powder.
Y5) was added and dispersed with hexane as a solvent, and then mixed with a planetary ball mill made of silicon nitride for 2 hours.

After the mixture was dried, BN was applied to the inside of a graphite mold, carbon films were applied on the top and bottom, and a discharge plasma was generated in nitrogen of 1 atm under a pressing pressure of 300 atm to perform heat sintering. The heating and cooling rate was about 300 ° C / min.

The relative density of the sintered body was 99% or more.
As for the crystal phase in the sintered body, the crushed sample was examined by X-ray diffraction, and it was confirmed that all were only α-sialon and β-sialon. The hardness was measured by pressing a diamond (Vickers) indenter with a load of 1 kg. As shown in Table 1, the results are 15-16 GPa of all silicon nitride-based materials.
Higher values were obtained.

[0025]

[Table 1]

Examples 4 to 6 Commercially available α type fine powder (manufactured by Ube Industries, SN-E1)
0), aluminum nitride and cerium oxide (CeO ₂ ) and alumina used in Example 1 (manufactured by Sumitomo Chemical, AKP
-20) was mixed in a predetermined ratio. Furthermore, a predetermined amount of Y-α-sialon (SN-SY5 manufactured by Ube Industries, Ltd.) was added to this powder.
Was added and dispersed with hexane as a solvent, and then mixed with a planetary ball mill made of silicon nitride for 2 hours. After the mixture was dried, it was treated by the sintering method shown in Table 2.

[0027]

[Table 2]

In the hot breath method, a graphite mold coated with BN was filled and a pressing pressure of 200 atm was applied. The nitrogen pressure of the atmosphere was 1 atm for hot pressing and atmospheric pressure sintering, and 10 atm for gas pressure sintering. The heating rate was 30 ° C / min. The sintering method and sintering conditions are shown in Table 2. As a result, as shown in Table 3, high hardness Ce-α-sialon was obtained.

[0029]

[Table 3]

Comparative Example When plasma sintering was performed under the same conditions as in Example 1 without adding α-sialon powder to the raw material powders of Examples 1 and 4, a sintered body having a relative density of 99% or more was obtained. When the crystal composition was examined by X-ray diffraction, it was only β-sialon. In this way, if the core α-sialon is not added, Ce-α
-No sialon was produced.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-62-46966 (JP, A) JP-A-2-263764 (JP, A) JP-A-8-208341 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C04B 35/599

Claims (6)

(57) [Claims] 1. Si ₃ N ₄ —AlN—Al ₂ O ₃ —C
To the mixed powder of eO ₂ system, 0.2 to α-sialon powder
Add 30 wt% and sinter in nitrogen atmosphere
Containing Ce-stabilized α-sialon characterized by
Sialon sintered body manufacturing method. 2. Silicon nitride (Si ₃ N ₄ ) in the raw material powder:
Aluminum Nitride (AlN): Alumina (Al ₂ O ₃ ):
Cerium oxide (CeO ₂ ) in a molar ratio of 3 to 12: 4
The method for producing a sialon sintered body according to claim 1, which is in the range of 6: 0 to 0.5: 1. 3. The method for producing a sialon sintered body according to claim 1, wherein the substance other than the α-sialon stabilized with Ce comprises β-sialon and a glass phase of a grain boundary. 4. The method for producing a sialon sintered body according to claim 1, wherein the sintering is performed in a nitrogen atmosphere at 1 atm or less at 1500 to 1850 ° C. for 1 to 60 minutes using a plasma sintering furnace. 5. 1650 to 1850 ° C. in 1 atmosphere of nitrogen
The method for producing a sialon sintered body according to claim 1, wherein the pressureless sintering or hot press sintering is performed. 6. When sintering under pressure nitrogen, nitrogen pressure of 2 atm is used.
1650 to 1750 ° C in nitrogen, 175 in nitrogen at 5 atm
0 to 1850 ° C, 1850 to 200 in nitrogen at 10 atm
The method for producing a sialon sintered body according to claim 1, wherein gas pressure sintering is performed in any of the temperature ranges of 0 ° C.