JPH0254298B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a high-strength α-sialon sintered body. More specifically, it is a high-strength α-sialon sintered material that can be used for high-temperature structural materials, machine parts such as machine tool bearings, shafts, and mechanical seals that require mechanical strength and wear resistance, and cutting tools. Regarding the body. Prior art Sialon is β- expressed by the general formula Si _6-z Al _z O _z N _8-z (where z represents 0<z4.2).
Sialon was developed, and then α-sialon was discovered as a new sialon. α-Sialon is represented by the general formula M _x (Si, Al) ₁₂ (O, N) ₁₆ , and its crystal structure has Al at the Si position of α-Si ₃ N ₄ .
At the same time as O is substituted at the N position and dissolved in a solid solution, other elements enter the interstitial space and are dissolved in a solid solution. Examples of the interstitial solid solution elements include Li, Ca, Mg, Y, and rare earth elements. Mamoru Mitomo, one of the inventors of the present invention, previously developed the hot press method (Japanese Patent Application Laid-open No. 129667/1983) and the pressureless sintering method (Japanese Patent Application Laid-open No. 129667/1983) to produce α-sialon sintered bodies.
-3769 Publication) was developed. However, the pressureless sintering method, which is simple to manufacture and can easily produce complex molded products, has the problem that 3 to 5% of pores remain, making it impossible to obtain a high-strength sintered body. Purpose of the Invention The present invention was made to solve the above-mentioned problems, and its purpose is to provide a high-strength α-sialon sintered body that can obtain high strength even by pressureless sintering. There is something to do. Structure of the Invention As a result of research to achieve the above object, the present inventors found that there is a range of compositions that yield extremely high strength sintered bodies among the overall compositions containing the α-sialon phase.
In the α-sialon sintered body whose composition is represented by the general formula M _x (Si, Al) ₁₂ (O, N) ₁₆ , M is Li,
When it is selected from Ca, Mg, Y and rare earth elements alone or in a mixture and x is 0<x0.5, it forms a composite structure of α-Sialon crystals and β-Si ₃ N ₄ crystals. It has been found that the sintered body produced by this method has superior mechanical properties and high strength compared to a sintered body composed of only α-sialon. The present invention was completed based on this knowledge. The gist _of the present _invention is _that α-
In the sialon sintered body, M is Li, Ca,
It consists of Mg, Y and a rare earth element selected singly or in a mixture, and the starting material is (Si ₃ N ₄ )-(M oxide or a compound that produces M oxide upon heating)-(AlN) system. and the mixing range is 0<
x0.5, the mineral composition in the sintered body consists of α-sialon and β-Si ₃ N ₄ , and the constituent particles are α-
The present invention is a high-strength α-sialon sintered body that does not contain β-sialon and is characterized by having a composite structure consisting only of sialon crystals and β-Si ₃ N ₄ crystals. In the present invention, when the value of x exceeds 0.5, the sintered body consists only of α-sialon. x value is 0
_{Only in the} range _of becomes. M is selected from Li, Ca, Mg, Y, and rare earth elements alone or in combination. It is necessary that the total amount is within the range of 0<x0.5.
As x becomes smaller, the amount of α-sialon decreases. The α-sialon sintered body of the present invention can also be easily produced by heating to 1600 to 1900°C in a non-oxidizing atmosphere of 1 atm. The manufacturing method is shown by the general formula M _x (Si, Al) ₁₂
(O, N) A raw material powder mixture that produces an α-sialon sintered body represented by ₁₆ (where M is Li, Ca,
x represents 0<x0.5, singly or in combination selected from Mg, Y and rare earth elements; )make. That is, by mixing silicon nitride, aluminum nitride, and an oxide of the above-mentioned M, or an organic acid salt such as a carbonate or an oxalate of these metals, or a hydroxyl salt, which produces an oxide of M by thermal decomposition. to make a mixture. Thoroughly grind and mix these raw material mixtures using a vibration mill, ball mill, or other grinding mixer.
At this time, consideration must be given to preventing the nitride of the raw material from oxidizing and preventing alumina from being mixed into the raw material due to contamination from the material of the raw material mixer.
For this purpose, it is preferable to use an organic solvent such as hexane to prevent oxidation, and to use a vibration mill made of silicon nitride to prevent contamination during mixing. The use of commonly used alumina ball mills should be avoided. If even a small amount of alumina is mixed in, β
- This is because Sialon is generated. The particles are preferably fine particles having an average primary particle diameter of 1 μm or less. This is dried to be used as a molding raw material, or the slurry is made into granules using a spray dryer or the like and used as a molding raw material. The average particle diameter of the granules is preferably 50 to 70 μm. The molding method may be any method such as die molding, slurry casting, isostatic pressing (CIP), or injection molding. The molded body is preferably of high strength. The raw material silicon nitride and the obtained α-SiAlON decompose thermally at high temperatures, so in order to prevent this, the molded body is placed in a graphite crucible, for example, with silicon nitride powder or silicon nitride as its main component, and then nitrided. It is preferable to cover with a mixture of powders of aluminum, Li, Ca, Mg, Y, rare earth elements, etc. that produce an α-sialon sintered body. Sintering is performed under 1 atm in a non-oxidizing atmosphere at 1600 to 1900
℃, preferably 1700-1850℃ for 15 minutes to 3 hours, preferably 1 to 2 hours. However, it goes without saying that sintering may also be performed by a gas pressure sintering method or a hot press method. As a result, a high-density, high-strength α-sialon sintered body can be easily obtained. The density was 95% or more relative to the theoretical density, and the mineral composition was confirmed by X-ray diffraction to be a composite structure of α-sialon phase and β-Si ₃ N ₄ phase. As a result of observation using a scanning electron microscope, it was found that it had a composite structure in which α-sialon crystals and β-Si ₃ N ₄ crystals intersected with each other. The micrograph is shown in FIG. 1. 1st
The figure shows Y _0.5 (Si, Al) ₁₂ (O, N) ₁₆ with 5% MgO
The needle-shaped particles are β-
It is Si ₃ N ₄ , and crystals with small grain growth and small grain size are α-SiAlON. Figure 2 shows the composition of Y _0.6 (Si, Al) ₁₂ (O, N) ₁₆ for comparison, and 100
%α-Sialon phase. α of the present invention
- As a result of measuring the bending strength of the sialon sintered body using the JIS method, it was found that the bending strength was 80 Kg/mm ² or more and more than 100 Kg/mm ² . This strength cannot be obtained by conventional pressureless sintering of α-sialon sintered bodies.
Furthermore, the hardness is comparable to that of alumina, which is conventionally considered to have extremely high hardness, and the fracture toughness value is also improved. Example 1 Raw materials: Si ₃ N ₄ (particle size 1 μm or less, cation impurity 0.5% or less), AlN (particle size 2 μm or less, cation impurity 0.5% or less) Y ₂ O ₃ (1 μm or less, purity 99.8%)
In particular, the AlN raw material was finely ground in a silicon nitride vibration mill (Si ₃ N ₄ boulders) using hexane as a solvent to obtain AlN powder of 1 μm or less. Using these raw materials, the general formula of α-Sialon is
M _x (Si, Al) ₁₂ (O, N) ₁₆ , M=Y
Select x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and
Si ₃ N ₄ , AlN, and Y ₂ O ₃ were blended in a predetermined ratio and mixed for 5 hours in a silicon nitride vibration mill (solvent: hexane, silicon nitride balls) to obtain a mixture. As a result of particle size analysis (SEM and laser method) of the mixture, the particle size was 1 μm or less, and 80% was 0.5 μm or less. The mixture was formed using cold isostatic pressing (CIP) at 2 tons/cm ² □After being processed into 60 x 10 mm, it was sintered under pressure to form a 1750 mm
A sintered body was obtained by firing at ℃ for 2 hours. The sintered body has a density of
Phases were identified by line diffraction, and test pieces of 3 x 4 x 40 mm were prepared by cutting and surface grinding, and the bending strength was measured. Table 1 shows the results. As shown in the results, a sintered body with an average strength of 67 Kg/mm ² or more was obtained in the region of small x with a theoretical density of 95% or more.This value is higher than the strength of conventional pressureless sintered bodies with this type of composition. It is a value.

[Table] Example 2 Si ₃ N ₄ obtained by the same method as Example 1,
In addition to AlN and Y ₂ O ₃ raw materials, MgO (less than 1 μm, purity 99.9
%), the general formula of α-sialon composition M _x
(Si, Al) ₁₂ (O, N) ₁₆ x is in the range of x Total≦0.5, of which Y is _0.2 , and for the rest of x, Mg is x = 0.05, 0.1, 0.15, 0.2, 0.25, A blending composition was prepared to have a composition of 0.3, and mixed for 5 hours using a silicon nitride vibration mill silicon nitride ball (in hexane solvent). Molding was carried out using CIP of 2 ton/cm ² , a sintered body was obtained in the same manner as in Example 1, and the same tests as in Example 1 were conducted. The results were as shown in Table 2. As the results show, the conventional x=
Compared to the 0.2 α-sialon sintered body, the addition of MgO improved density properties, strength, and α-sialon content, but especially in terms of strength, the average
A bending strength of 80 kg/mm ² or more was obtained, and these values are extremely higher than the strength of conventional α-sialon composition sintered bodies.

[Table] Example 3 The α-sialon sintered body produced by the pressureless sintering method according to the method shown in Example 2 was placed in a graphite crucible and covered with silicon nitride powder. The crucible was placed in a pressure container and fired at 1900° C. for 1 hour in nitrogen at 1200 kg/cm ² . The characteristics of the obtained sintered body were investigated by the same test as in Example 2, and the results are shown in FIG. It was confirmed that the α-sialon content, relative density, and bending strength were all improved compared to the results shown in Example 2.

[Table] Example 4 Si ₃ N ₄ and AlN were prepared in the same manner as in Example 1.
The general formula of α- _sialon is M _x (Si, Al) ₁₂ (O,
N) ₁₆ x is in the range x≦0.5, among which Ca is x=0.2, and the rest are Mg 0.05, 0.1, 0.15, 0.2,
A blending composition was prepared so that the amounts were 0.25 and 0.3, and sintered bodies were obtained in the same manner as in Examples 1 and 2. As a result, as shown in Table 4, improvements in density and strength were observed.

[Table] Example 5 By the same method as in Example 1, Si ₃ N ₄ , AlN,
_Y2O3 and _Li2CO3 as Li source (particle size 0.5μ _, purity ₉₉
%), and the general formula of α-Sialon M _x (Si,
Al) ₁₂ (O, N) ₁₆ using Y and Li as M,
A composition having a predetermined ratio of x≦0.5 was prepared, and a sintered body was obtained in the same manner as in Examples 1 and 2. As a result, as shown in Table 5, improvements in density and strength were obtained.

【table】

[Table] Effects of the Invention As described above, the α-sialon sintered body of the present invention is composed of a composite structure in which α-sialon crystals and β-Si ₃ N ₄ crystals intersect with each other. Therefore, compared to conventional α-sialon sintered bodies, it has excellent effects such as higher density, higher strength, and improved hardness and fracture toughness.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph of an α-sialon sintered body of the present invention, and FIG. 2 is an electron micrograph of an α-sialon single crystal for comparison.

Claims (1)

[Claims] 1 α represented by the general formula M _x (Si, Al) ₁₂ (O, N) ₁₆
- In the sialon sintered body, M is Li, Ca,
It consists of Mg, Y and a rare earth element selected singly or in a mixture, and the starting material is (Si ₃ N ₄ )-(M oxide or a compound that produces M oxide upon heating)-(AlN) system. So, the mixing range is 0<
x0.5, the mineral composition in the sintered body consists of α-sialon and β-Si ₃ N ₄ , and the constituent particles are α-
A high-strength α-sialon sintered body comprising a composite structure consisting only of sialon crystals and β-Si ₃ N ₄ crystals.