JPH0686331B2 - High-strength sialon-based sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-strength sialon-based sintered body useful for producing various engineering ceramics having high temperature high strength, high hardness and high toughness.

(Prior Art and Its Problems) α-sialon is a substance in which Al is dissolved in the Si position of α-type silicon nitride and O is substituted in the N position of the α-type silicon nitride, and at the same time, the modified dissolved cation M is invaded in the interstitial position. Yes, the formula Mx (Si, Al) ₁₂ (O, N) ₁₆ [I] (In the formula, M is Li, Mg, Ca, Y and a lanthanide element (however, La
And Ce are excluded), and x is a number satisfying 0 <x ≦ 1. ) Is represented. This Mα-sialon has characteristics as an engineering ceramics such as high hardness, low coefficient of thermal expansion, and excellent corrosion resistance.

However, one of the causes of the Mα-sialon crystal single-phase sintered body is that the crystal shape is granular, but the properties such as strength and fracture toughness as engineering ceramics cannot be said to be sufficient. Therefore, in order to improve this drawback, JP-A-58-185484, 58-204875,
No. 63-233082 discloses a formula Si ₆ -zAlzOzN _8- z [II] (formula) in which Mα-sialon crystal phase and Al in the Si position of β-type silicon nitride and O in the N position are replaced by solid solution. In the above, z is a number satisfying 0 <z ≦ 4.2.) And a sialon-based sintered body is proposed which is compounded with a needle-like β-sialon crystal phase.

However, the mechanical properties of this sialon-based sintered body are not practically sufficient for use as a high temperature material. Further, yttrium Y is generally used as the modifying cation M, but a sialon-based sintered body containing Y is said to have inferior oxidation resistance at high temperatures, and it is difficult to remove the slag used under severe conditions. It is expected to be difficult to use for turbine parts.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems and to provide a novel sialon-based sintered body having excellent oxidation resistance, high temperature strength and high toughness.

(Summary of the Invention) According to the present invention, microcrystals of RE ₂ M _2- uO _7-2 u having a fluorite type crystal structure (wherein R is H
Rare earth element selected from o, Er, Tm, Yb and Lu, M is Hf
And / or Zr, and u is a number satisfying -1 <u <1. ), A microcrystal of M'Nv having a salt-type crystal structure (wherein M'represents Hf and / or Zr, and v is 0.7≤v≤
It is a number that satisfies 1.2. ), The formula REx (Si, Al) ₁₂ (O, N) ₁₆ [III] (wherein RE represents a modifying rare earth element selected from Ho, Er, Tm, Yb and Lu, and x is 0 <A number satisfying x <1.) RE α-sialon crystal represented by the formula, β-sialon crystal represented by the above formula [II], AlN polytype crystal of a composite oxynitride containing Al and Si. , And a high-strength sialon-based sintered body composed of a crystalline phase other than the above and / or a glass phase containing RE.

(Detailed Description of the Invention) The content ratio of each phase in the sialon-based sintered body of the present invention is preferably in the range shown below.

1 <RE ₂ M _2- uO _7-2 u microcrystalline phase <20 wt% 0.5 M'Nv microcrystalline phase <10 wt% 5 <RE α-sialon crystalline phase <50 wt% 30 <β-sialon Crystal phase <90 wt% 0.5 <AlN polytype crystalline phase of composite oxynitride containing Al, Si <10 wt% 1 <Crystalline phase containing RE and / or glass phase <10 wt% However, for RE α-sialon The crystal phase and the crystal phase of β-sialon have the compositions represented by the formulas [III] and [II], respectively, and the respective phases do not necessarily have to have a constant composition between the crystal grains, and are different from each other. It may have a composition. Ho, Er, Tm, Yb or Lu having a smaller ionic radius than Y penetrates into the α-sialon lattice to form a solid solution, which improves the oxidation resistance of the obtained sialon-based sintered body and improves the oxygen content at high temperature. It can be used stably even in an atmosphere. In particular, when the invading solid solution element is Er, Tm, Yb or Lu, the oxidation resistance is excellent.

If the proportions of the microcrystalline phases of RE ₂ M _2- uO _7-2 u and M′Nv deviate from the above range, the mechanical strength of the obtained sialon-based sintered body is lowered and its variation is increased, which is preferable. Absent.

In the present invention, RE ₂ M _2- uO _7-2 u microcrystals are RE ₂ Hf ₂ O ₇ ,
RE ₂ Zr ₂ O ₇ , a solid solution of both, or these and RE ₂ O
₃ , a solid solution with HfO ₂ or ZrO _2, and -1 <u <1
Is.

The M'Nv microcrystals represent HfN, ZrN, or a solid solution of both, or a nonstoichiometric compound thereof,
7 ≦ v ≦ 1.2.

Further, in the sialon-based sintered body of the present invention, it is preferable that the major axis of RE α-sialon crystal is 0.05 to 10 μm and the major axis of β-sialon crystal is 1 to 100 μm.

The AlN polytype crystal of the composite oxynitride containing Al and Si represents a crystal group having a composition near AlN having a long period structure such as 15R, 21R, 27R, 8H, 12H, and 12Hδ.

As the crystal phase containing RE, for example, a melilite type RE ₂ Si ₃
O ₃ N ₄ , apatite type RE ₁₀ (SiO ₄ ) ₆ N ₂ , wollastonite type RESiO ₂ N, warrelite type RE ₄ Si ₂ O ₇ N ₂ , garnet type RE ₃ Al ₅ O ₁₂ , Mullite type RE ₄ Al ₂ O ₉ , RE ₃ Al
Examples thereof include Si ₂ O ₇ N ₂ , RE ₂ Si ₂ O ₇ , and RE ₂ SiO _5, but the present invention is not limited to these crystal groups.

In the sialon-based sintered body of the present invention, β-sialon crystals, Al, AlN polytype crystals of complex oxynitride containing Si, crystalline phase and / or glass phase containing RE, and crystals at grain boundaries Fine-grained crystals of RE ₂ M _2- uO _7-2 u having a fluorite-type crystal structure and M′Nv fine-grained crystals having a salt-type crystal structure are present together with the RE α-sialon crystals.

In the present invention, RE ₂ M _2- uO existing in this sintered body is used.
_The grain boundary phase (RE ₂ M _2- uO
_7-2 u and crystalline phase containing RE and / or glass phase) have improved strength characteristics. In particular, the heat resistance of the grain boundary glass phase, which is said to soften at high temperatures, is improved, and excellent mechanical properties can be maintained up to high temperatures. In addition, the composition in the sintered body,
There are various phases having different crystal phases, particle shapes, particle diameters and coefficients of thermal expansion, and after sintering, minute cracks due to minute strain occur in the sintered body. This improves mechanical properties such as fracture toughness of the obtained sialon-based sintered body in combination with the matrix strengthening effect due to the three-dimensional intersection of needle-like crystals and granular crystals and the crack growth inhibiting effect. it is conceivable that.

As a method for producing the sialon-based sintered body of the present invention,
Any method may be used as long as a sintered body having the above structure is obtained.

An example of the method for producing the sialon-based sintered body of the present invention will be described below.

The sialon-based sintered body of the present invention has REα-sialon represented by the above formula [III] as a main phase, and has the formula [II
60% by weight or less of REα-sialon powder containing 8% by weight or less of excess oxygen with respect to the theoretical oxygen amount specified in [I],
Hafnium oxide powder and / or zirconium oxide powder 15
It is obtained by heating and sintering a raw material mixed powder having a weight percentage of not more than the rest and α-silicon nitride powder as the balance, in the maximum temperature range of 1600 to 2100 ° C.

As the REα-sialon powder, any powder may be used as long as it is a powder having REα-sialon represented by the formula [III] as a main phase, and the applicant has previously proposed JP-A-62- A powder prepared according to the invention of 223009 is preferred.

The method of this proposal is as follows: (a) amorphous silicon nitride powder, (b) metallic aluminum or aluminum nitride, (c) RE interstitial solid solution of RE α-sialon.
Is a metal salt forming an oxide of a modifying rare earth element selected from Ho, Er, Tm, Yb or Lu, and, if necessary, (d) an oxygen-containing compound of aluminum or silicon, It is a method for producing REα-sialon powder by mixing so as to have a REα-sialon composition and heating the mixture to a temperature in the range of 1300 to 1900 ° C. under a nitrogen-containing atmosphere. The REα-sialon powder obtained by this method is a fine and uniform particle size powder having a primary particle size of 0.2 to 2 μm and contains almost no free carbon and metallic impurities, and therefore has no pores or abnormal grain growth. You can give a union.

REα-To improve the sinterability of sialon powder and at the same time to obtain a high-strength sialon-based sintered body, REα of the sintering raw material is used.
-It is necessary that the sialon powder contains 8% by weight or less of excess oxygen with respect to the theoretical amount of oxygen defined by the formula [III].

As a method of containing excess oxygen in REα-sialon powder, for example, in the step of preparing REα-sialon powder,
A method of adding an excessive amount of an oxygen-containing compound of silicon, aluminum or a specific rare earth element RE to amorphous silicon nitride, REα-
A method of heating the sialon powder in an oxygen-containing atmosphere is adopted. As an example of the latter, there is a method of heating the REα-sialon powder to a temperature in the range of 800 to 1200 ° C. in an oxygen-containing atmosphere so that the REα-sialon powder contains oxygen in excess of the theoretical amount. Heating time is usually 0.5 ~
5 hours. This treatment can be carried out by, for example, a method of thinly placing REα-sialon powder on a holding plate and leaving it in an oxygen-containing atmosphere, or a method of fluidizing REα-sialon powder in an oxygen-containing atmosphere.

The excess oxygen content is 8% by weight or less, preferably 1 to 6.5% by weight, particularly preferably 2 to 4% by weight. If the amount of excess oxygen is excessively large, many phases with a low melting point remain in the sintered body,
The mechanical properties at high temperature become impaired.

The α-silicon nitride powder preferably has an average particle size of 1 μm or less in terms of sinterability, and further impairs strength, corrosion resistance, and oxidation resistance of the obtained sintered body at high temperatures. The content of impurities is preferably 0.1% by weight or less.

The blending ratio of α-silicon nitride powder in the raw material mixed powder is 40
It is at least wt%, preferably 50 to 90 wt%, more preferably 60 to 80 wt%. Within the above range, the proportion of the β-sialon phase in the produced sialon-based sintered body increases as the blending proportion of the silicon nitride powder increases. When the blending ratio of the α-silicon nitride powder exceeds 90% by weight, the sinterability of the mixture is lowered and the densification of the sintered body does not proceed.

Further, in the present invention, the α-silicon nitride powder may further contain aluminum or a modifying rare earth element RE as a component. Also in this case, aluminum or the modifying rare earth element RE may be present inside or on the surface of the particles of the α-silicon nitride powder, or aluminum or the modifying rare earth element.
Powders such as RE oxides, nitrides, and oxynitrides may be mixed. In addition, the content of metal impurities other than the main metal components is 0.
It is preferably 1% by weight or less.

Furthermore, if necessary, 10% by weight may be added to the raw material mixed powder.
The following hafnium nitride powder and / or zirconium nitride powder can also be added. For example, the M'Nv crystallites in the sialon-based sintered body of the present invention are obtained by reacting hafnium oxide and / or zirconium oxide in the raw material mixed powder with nitrogen gas in the atmosphere during the sintering process. Since it is generated by reduction nitriding, it is possible to increase the generation ratio of M′Nv microcrystals by adding hafnium nitride powder and / or zirconium nitride in advance.

The method for preparing the raw material mixed powder is not particularly limited, and a method known per se, for example, a method of dry mixing individual raw material powders, a method of wet mixing in an inert liquid, and then removing the inert liquid, etc. Can be appropriately adopted.
A V-type mixer, a ball mill, a vibration mill or the like is conveniently used as the mixing device.

The heat-sintering of the raw material mixed powder is performed by, for example, molding the mixed powder as it is into a predetermined shape by a dry method or a wet method. A method of sintering in a gas atmosphere, a method of filling raw material powder into a die having a predetermined shape and hot pressing, and the like can be adopted. Further, the physical properties of the sintered body can be further enhanced by further hot isostatic pressing of the sintered body obtained by the above method.

Molding of the mixed powder prior to the atmospheric pressure or atmospheric pressure sintering can be performed by a known method, for example, a rubber pressing method, a uniaxial molding method, a casting molding method, an injection molding method, an explosive compression molding method, or the like.

Sintering temperature is usually 1600 ~ 2100 ℃, sintering time is usually 0.
5-10 hours. If the sintering temperature is excessively low, the sintering will not proceed, and if the sintering temperature is excessively high, the composition of the sintered body will change due to thermal decomposition.

According to the method, a crystal of β-sialon believed to be produced by the reaction of RE α-sialon and α-silicon nitride, Al, an AlN polytype crystal of a composite oxynitride containing Si, a crystalline phase containing RE and / or RE ₂ M _2- uO _7-2 u having a fluorite crystal structure crystallized at the glass phase and grain boundaries, and M′Nv having a salt crystal structure, are composed of RE α-sialon as a raw material. As a result, a sialon-based sintered body can be obtained which is present together with REα-sialon crystals in which x in the formula [III] is slightly lower.

In particular, in order to form a crystal phase or a glass phase having high heat resistance at the grain boundaries of the sialon-based sintered body, under sintering conditions, Al and Si which can coexist with these heat resistant grain boundary phases are contained. Precipitation of AlN polytype crystals of complex oxynitride is essential. Therefore, for example, by using a raw REα-sialon powder having an excess oxygen content of 5% by weight or less, adding aluminum nitride powder, or increasing the nitrogen gas pressure in the sintering atmosphere, the AlN polytype It is desirable to promote the precipitation of crystals.

(Effects of the Invention) The sialon-based sintered body obtained by the present invention has not only mechanical properties such as high-temperature strength and fracture toughness, but particularly remarkable oxidation resistance, as compared with the conventional sialon-based sintered body. Since it is improved, it can be suitably used as a highly reliable structural material, particularly as a heat-resistant component such as a rotor, a stator, and a combustor for a gas turbine engine.

(Example) An example and a comparative example are shown below.

Examples 1 to 15 and Comparative Examples 1 to 7 Amorphous silicon nitride powder, rare earth oxide (RE ₂ O ₃ ) powder and metallic Al powder having the compounding ratios shown in Table 1 were oscillated under a nitrogen gas atmosphere with a vibration mill. Mix for 1 hour. Fill the carbon crucible with the mixed powder, set it in a resistance heating type high temperature furnace, and from room temperature to 1200 ° C for 1 hour from 1200 ° C in a nitrogen gas atmosphere.
Crystallize by heating up to 1400 ° C for 4 hours, and further from 1400 ° C to 1600 ° C for 2 hours on a heating schedule.
REα-sialon powder was obtained. The properties of the obtained RE α-sialon powder are shown in Table 1.

REα-sialon powder synthesized as above, specific surface area: 11.5m ² / g Particle shape: equiaxed crystal Producing phase: α phase> 95% Oxygen content: 1.3% by weight Metal impurities: <500ppm α-silicon nitride powder (Ube Industries, Ltd.)
), Hafnium oxide powder, zirconium oxide powder, hafnium nitride powder, and zirconium nitride powder (all manufactured by Hermann C. Starck Co., Ltd.) at a blending ratio shown in Tables 2 and 3, and ethanol as a medium. Used,
After wet ball milling for 48 hours, it was vacuum dried at 80 ° C. 150 g of the obtained raw material powder was filled in a graphite die having an inner diameter of 100 mm whose surface was coated with boron nitride, and set in a hot press sintering device, and then from room temperature under a pressure of 250 kg / cm ^2.
The temperature was raised to 750 ° C. at 200 ° C./hour and maintained at the same temperature for 1 hour.

The results of measuring the bulk density and the ratio of the produced phase of the obtained sintered body are shown in Tables 2 and 3. The ratio of the generated phase was calculated from the X-ray diffraction peak intensity. FIG. 1 shows an X-ray diffraction chart of the sintered body obtained in Example 5.

Also, a test piece of 3 x 4 x 40 mm from the created sintered body
Cut out 100 pieces and use 30 mm for outer span and 10 mm for inner span
Then, the bending strength was measured at room temperature and 1400 ° C. The fracture toughness value K ₁ c was measured by the SEPB method. Further, as an oxidation resistance test of the obtained sintered body, a test piece was heat-treated in air at 1350 ° C. for 100 hours to measure the weight increase due to oxidation and the bending strength at room temperature after oxidation. These results are shown in Tables 2 and 3. When the Weibull coefficient was calculated for the room temperature strength value (the number of samples: 50), in Examples 1 to 15, all 20 to 30 were obtained.
And in Comparative Examples 1 to 7, it was 6 to 10.

Examples 16 to 30 and Comparative Examples 8 to 15 RE α-sialon powder, α-silicon nitride powder, hafnium oxide powder, zirconium oxide powder and aluminum nitride powder used in Examples 1 to 15 are shown in Tables 4 and 5. Ethanol was used as a medium at the blending ratio shown in (1), and wet ball milling was performed for 48 hours, followed by vacuum drying at 80 ° C.

The powder mixture was preformed into a rectangular shape using a die having a cross section of 50 × 80 mm and then rubber-pressed at a pressure of 1.5 ton / cm ² . Using the electric furnace, the obtained molded body was heated under the temperature-nitrogen gas pressure conditions shown in Tables 4 and 5 and kept at the same temperature for 2 hours to carry out atmospheric pressure sintering or atmosphere. Pressure sintering was performed.

Various characteristics of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Tables 4 and 5. In addition, when the Weibull coefficient was calculated for the room temperature strength value (50 samples), it was 18 to 28 in Examples 16 to 30 and 6 to 10 in Comparative Examples 8 to 15.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of the sintered body obtained in Example 5 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Shintoku 5 1978 Kogushi, Ube City, Yamaguchi Prefecture 5 750, Ube Institute of Industrial Research, Ube Research Co., Ltd. Kazuko Yanagi (56) References JP-A-59-199579 ) JP-A-3-208866 (JP, A) JP-A-3-290373 (JP, A)

Claims (1)

[Claims] 1. A microcrystal of RE ₂ M _2- uO _7-2 u having a fluorite crystal structure (wherein RE is a rare earth element selected from Ho, Er, Tm, Yb and Lu, and M is Hf and / or Zr, u is -1 <u <1
Is a number that satisfies. ), A microcrystal of M'Nv having a salt-type crystal structure (wherein M'represents Hf and / or Zr, and v is 0.7≤v≤
It is a number that satisfies 1.2. ), The formula REx (Si, Al) ₁₂ (O, N) ₁₆ (where RE is a rare earth element for modification selected from Ho, Er, Tm, Yb and Lu, and x is 0 <x ≦ A crystal of RE α-sialon represented by the formula: Si _6- zAlzOzN _8- z (wherein z is a number satisfying 0 <z ≦ 4.2) A high-strength sialon-based sintered body comprising a sialon crystal, an AlN polytype crystal of a composite oxynitride containing Al and Si, and a crystal phase and / or a glass phase other than the above containing RE.