JPH0559077B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a sialon-based sintered body useful for producing various engineering ceramics having high-temperature high strength, high hardness, and high toughness, and a method for producing the same. (Prior art and its problems) α-Sialon has an A
is a substance in which O is substituted and dissolved in the N position, and at the same time, a modifying cation M enters and forms a solid solution in the interstitial position, and the formula M _x (Si, A) ₁₂ (O, N) ₁₆ [] (in the formula , M represents Li, Mg, Ca, Y and lanthanide elements (excluding La and Ce), x is 0
It is a number that satisfies <x≦2. ). This Mα-SiAlON has characteristics as an engineering ceramic, such as high hardness, low coefficient of thermal expansion, and excellent corrosion resistance. However, one reason for this is that the single-phase Mα-sialon crystal sintered body has a granular crystal shape, but it cannot be said that its properties such as strength and fracture toughness are sufficient for engineering ceramics.
Therefore, in order to improve this drawback, JP-A-58-
Publication No. 185485, Publication No. 58-204875, Publication No. 63-
Publication No. 233082, etc. describes the Mα-sialon crystal phase, A at the Si position, and O at the N position of β-type silicon nitride.
was substituted and dissolved. It is combined with an acicular β-sialon crystal phase represented by the formula Si _6-z A _z O _z N _8-z [] (wherein, z is a number satisfying 0<z≦4.2). A sialon-based sintered body has been proposed. However, the mechanical properties of these sialon-based sintered bodies are still not sufficient for use as high-temperature materials. In addition, yttrium Y is commonly used as the cation M for modification, but sialon-based sintered bodies containing Y are said to have poor oxidation resistance at high temperatures, and are used under harsh conditions. It is expected that it will be difficult to use it for turbine parts, etc. (Object of the Invention) An object of the present invention is to solve the above problems and provide a novel sialon-based sintered body having excellent oxidation resistance, high temperature strength and toughness, and a method for manufacturing the same. ( _{Summary of} the Invention) According to the present invention, the formula _RE Indicates the rare earth element used, and x is 0<
This is a number that satisfies x≦2. ) The crystalline phase of REα-sialon represented by the formula [], the crystalline phase of β-sialon represented by the above formula [],
Melilite crystal phase of RE ₂ Si ₃ N ₄ O ₃ and/or 15R
A sialon-based sintered body composed of a type AN polytype sialon crystal phase and a glass phase and a method for producing the same are provided. (Specific Description of the Invention) The content ratio of each phase in the sialon-based sintered body of the present invention is preferably within the range shown below. 5<REα-Sialon crystal phase <50 wt% 40<β-Sialon crystal phase <95 wt% 0<Melilite crystal phase and/or 15R type AN
Polytype Sialon crystal phase <10% by weight 0<Glass phase <5% by weight However, REα-Sialon crystal phase and β-
The crystal phases of Sialon have compositions represented by formulas [) and [], and each phase does not necessarily have to have a constant composition between each crystal grain, and may have different compositions. . α−
By interstitial solid solution of Ho, Er, Tm, Yb, or Lu, which has a smaller ionic radius than Y, between the lattices of Sialon, the oxidation resistance of the resulting Sialon-based sintered body is improved, and it can be used even in high-temperature oxygen-containing atmospheres. , it becomes possible to use it stably. In particular, when the element entering solid solution is Er, Tm, Yb or Lu, the oxidation resistance is excellent. If the proportion of the melilite crystal phase and/or the 15R type AN polytype sialon crystal phase is out of the above range, the mechanical strength of the obtained sialon-based sintered body will decrease and its dispersion will increase, which is not preferable. Most of the sialon-based sintered bodies of the present invention have a diameter of 0.2
It consists of granular and rod-shaped crystals of ~2μm, which are 3
They intertwine and intertwine dimensionally. Moreover, it consists of a mixed phase of several crystals with slightly different coefficients of thermal expansion, and there is extremely little grain boundary glass phase, which is said to be one factor that adversely affects mechanical properties at high temperatures. Therefore, it has excellent mechanical properties at high temperatures, and produces a composite effect of whisker strengthening effects such as particle dispersion effect, microcracking effect, and pullout effect, resulting in high fracture toughness. The method for manufacturing the sialon-based sintered body of the present invention will be described below. The sialon-based sintered body of the present invention has the above formula []
The main phase is REα−Sialon expressed by
and 8 for the theoretical oxygen amount specified by the formula []
REα-Sialon powder containing 60% by weight or less of excess oxygen and the balance being silicon, oxygen, and nitrogen, with an oxygen content of 1.0 to 5.0% by weight.
It is obtained by heating and sintering a raw material mixed powder consisting of powder in the amount of % by weight to a maximum temperature in the range of 1600 to 2200°C. Any powder may be used as the REα-sialon powder as long as it has REα-sialon as the main phase represented by the formula [].
Powders prepared according to the invention of JP-A-62-223009 previously proposed by the present applicant are preferred. This proposed method consists of (a) amorphous silicon nitride powder, (b) metallic aluminum or aluminum nitride, and (c) RE interstitial solid solution in the interstitials of REα-Sialon (RE is Ho, Er, Tm, (Yb or Lu) and, if necessary, (d) an oxygen-containing compound of aluminum or silicon to give the desired REα-Sialon composition, and the mixture is heated under a nitrogen-containing atmosphere. at 1300~1900
By heating to a temperature in the range of °C, REα−
This is a method for producing sialon powder. The REα-sialon powder obtained by this method is a fine and uniform powder with a primary particle size of 0.2 to 2 μm, and contains almost no free carbon or metal impurities, so it is sintered without pores or abnormal grain growth. It can give unity. In order to improve the sinterability of REα-sialon powder and to obtain a high-strength sialon-based sintered body, the REα-sialon powder as a sintering raw material has a It is necessary to contain less than 8% by weight of excess oxygen. Examples of methods for incorporating excess oxygen into the REα-Sialon powder include adding an excessive amount of an oxygen-containing compound of silicon, aluminum, or RE to amorphous silicon nitride in the preparation stage of the REα-Sialon powder; A method is adopted in which sialon powder is heated in an oxygen-containing atmosphere. An example of the latter is heating REα-Sialon powder to a temperature in the range of 800-1200°C in an oxygen-containing atmosphere;
One method is to include oxygen in excess of the theoretical amount in the REα-Sialon powder. Heating time is usually
It is 0.5 to 5 hours. This process is performed, for example, by REα−
This can be carried out by placing a thin layer of sialon powder on a holding plate and leaving it in an oxygen-containing atmosphere, or by fluidizing REα-sialon powder in an oxygen-containing atmosphere. The amount of excess oxygen is 8% by weight or less, preferably 1~
6.5% by weight, particularly preferably 2-4% by weight.
If the amount of excess oxygen is too large, many phases with low melting points remain in the sintered body, and mechanical properties at high temperatures are impaired. Powders containing silicon, oxygen, and nitrogen whose oxygen content is 1.0 to 5.0% by weight may be powders containing all of silicon, oxygen, and nitrogen within the particles, or It may be a mixture of powders containing either of them in the particles. Examples of such powder include powders mainly composed of silicon nitrides, oxides, and oxynitrides. In the present invention, in particular, as the powder, 1.0
α-silicon nitride powder containing ~5.0% by weight of oxygen is preferably used. Such α-silicon nitride powder has an average particle size of 1 μm or less in terms of sinterability, and
More than 80% of the oxygen content is unevenly distributed within 50 nm of the surface layer of each particle, and the content of metal impurities other than Si impairs the strength, corrosion resistance, and oxidation resistance of the resulting sintered body at high temperatures. It is preferably 0.1% by weight or less. Further, in the present invention, the powder containing the silicon, oxygen, and nitrogen components may further contain aluminum or a modifying rare earth element RE as a component. In this case as well, aluminum or the rare earth element RE for modification may be included in the particles of the powder, or powders of oxides, nitrides, oxynitrides, etc. of aluminum or the rare earth element RE for modification may be mixed. Further, it is preferable that the content of metal impurities other than the main metal components is 0.1% by weight or less. The blending ratio of the powder containing each component of silicon, oxygen, and nitrogen in the raw material mixed powder is 40% by weight or more, preferably 60 to 90% by weight. As the blending ratio of the powder increases within the above range, the ratio of the β-sialon phase in the produced sialon-based sintered body increases. When the blending ratio of the powder exceeds 90% by weight, the sinterability of the mixture decreases, and the densification of the sintered body does not proceed. There is no particular restriction on the method for preparing the raw material mixed powder, and methods known per se may be used, such as 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. may be adopted as appropriate. As a mixing device, a V-type mixer, a ball mill, etc. are conveniently used. For heating and sintering of raw material mixed powder, for example, the mixed powder is directly shaped into a predetermined shape using a dry or wet method, and if the mixed powder is formed using a wet method, it is dried and then sintered with a nitrogen-containing non-oxidizing material under normal pressure or pressurized. A method of sintering in a gas atmosphere, a method of filling a die of a predetermined shape with raw material powder and hot pressing, etc. can be employed. Further, by further subjecting the sintered body obtained by the above method to hot isostatic pressing, the sintered body can be further densified. Molding of the mixed powder prior to normal pressure or atmospheric pressure sintering can be performed by a known method, such as a rubber press method, a uniaxial molding method, a cast molding method, an injection molding method, an explosive compression molding method, etc. . The sintering temperature is usually 1600-2200°C, and the sintering time is usually 0.5-10 hours. If the sintering temperature is too low, sintering will not proceed, and if the sintering temperature is too high, a compositional change will occur in the sintered body due to thermal decomposition. By the above method, REα-sialon and silicon,
The β-sialon crystals, melilite crystal phase and/or 15R type AN polytype sialon crystal phase, and glass phase, which are thought to be produced by the reaction with powder containing oxygen and nitrogen components, are the raw material REα-sialon. From the composition of the formula [], x
A Sialon-based sintered body is obtained in which REα-SiAlON crystals exist together with a slightly low REα-Sialon crystal. (Effects of the Invention) Compared to conventional sialon-based sintered bodies, the sialon-based sintered body obtained by the present invention not only has excellent mechanical properties such as high-temperature strength and fracture toughness, but also has particularly remarkable oxidation resistance. As a result, it can be suitably used as a highly reliable structural material, particularly as heat-resistant parts such as rotors, stators, and combustors for gas turbine engines. (Example) Examples and comparative examples are shown below. Examples 1 to 15 and Comparative Examples 1 to 7 Amorphous silicon nitride powder with the blending ratio shown in Table 1,
Rare earth oxide (RE ₂ O ₃ ) powder and metal A powder were mixed in a vibratory mill for 1 hour under a nitrogen gas atmosphere. The mixed powder was filled into a carbon crucible, set in a resistance heating high temperature furnace, and heated under a nitrogen gas atmosphere.
It was crystallized by heating on a heating schedule from room temperature to 1200°C for 1 hour, from 1200°C to 1400°C for 4 hours, and then from 1400°C to 1600°C for 2 hours to obtain REα-Sialon powder. obtained
Table 1 shows the characteristic values of REα-Sialon powder. The REα-Sialon powder synthesized as described above has the following characteristics: specific surface area: 17.5 m ² /g particle shape: equiaxed crystal formed phase: α phase >95% oxygen content: 2.3% by weight metal impurities: <500ppm The α-silicon nitride powder was subjected to wet ball milling for 48 hours using ethanol as a medium at the ratios shown in Tables 2 and 3, and then heated at 80°C.
It was vacuum dried. After the obtained raw material powder was molded by cold isostatic pressing, the temperature was raised from room temperature to 1800°C at a rate of 2°C/min in a nitrogen atmosphere at normal pressure, and maintained at the same temperature for 4 hours. The properties of the obtained sialon-based sintered body are shown in Tables 2 and 3. Examples 16 to 25 and Comparative Examples 8 to 14 REα-sialon powder used in Examples 1 to 15, Specific surface area: 10.0 m ² /g Particle shape: Equiaxed crystal Formation phase: α phase > 95% Oxygen content: 0.5% by weight Metal impurities: <500 ppm α-silicon nitride powder and specific surface area: 8.0 m ² /g particle shape: equiaxed crystal metal impurities: <700 ppm were prepared as shown in Table 4 and Wet ball milling was carried out for 48 hours using ethanol as a medium at the ratio shown in Table 5, followed by vacuum drying at 80°C. After the obtained raw material powder was molded by cold isostatic pressing, the temperature was raised from room temperature to 1800°C at a rate of 2°C/min in a nitrogen atmosphere at normal pressure, and maintained at the same temperature for 4 hours. The properties of the obtained sialon-based sintered body are shown in Tables 4 and 5. In addition, in Tables 2 to 5, the bending strength is as follows:
The fracture toughness value K _IC was measured by the SEPB method using a four-point bending test with an outer span of 30 mm and an inner span of 10 mm.

【table】

[Table] β-sa: β-sialon Melilite: RE ₂ Si ₃ N ₄ O ₃
AlN: 15R type AlN polytype Sialon *: The rest of the generated phase is a glass phase **: Value measured after heat treatment in air at 1350℃ for 100 hours

[Table] β-sa: β-sialon Melilite: RE ₂ Si ₃ N ₄ O ₃
AlN: 15R type AlN polytype Sialon *: The rest of the generated phase is a glass phase **: Value measured after heat treatment in air at 1350℃ for 100 hours

[Table] β-sa: β-sialon Melilite: RE ₂ Si ₃ N ₄ O ₃
AlN: 15R type AlN polytype Sialon *: The rest of the generated phase is a glass phase **: Value measured after heat treatment in air at 1350℃ for 100 hours

[Table] β-sa: β-sialon Melilite: RE ₂ Si ₃ N ₄ O ₃
AlN: 15R type AlN polytype Sialon *: The rest of the generated phase is a glass phase **: Value measured after heat treatment in air at 1350℃ for 100 hours

Claims (1)

[Claims] 1 Formula: RE _x (Si, A) ₁₂ (O, N) ₁₆ (wherein, RE represents a rare earth element for modification selected from Ho, Er, Tm, Yb and Lu, x is 0<
This is a number that satisfies x≦2. ) The crystal phase of REα-sialon is expressed by the formula Si _6-z A _z O _z N _8-z (where z is a number satisfying 0<z≦4.2). crystalline phase, melilite crystalline phase of RE ₂ Si ₃ N ₄ O ₃ and/or
15R type AN polytype consisting of sialon crystal phase and glass phase, density 2.5g/
Sialon-based sintered body of cm ³ or more. 2 Formula RE _x (Si, A) ₁₂ (O, N) ₁₆ (In the formula, RE represents a rare earth element for modification selected from Ho, Er, Tm, Yb, and Lu, and x represents 0<
This is a number that satisfies x≦2. ), with REα-Sialon as the main phase,
and a powder containing 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 by the above formula, and the balance containing each component of silicon, oxygen, and nitrogen, and its oxygen content. is 1.0~5.0
The method for producing a sialon-based sintered body according to claim 1, characterized in that a raw material mixed powder consisting of a powder of 1,600 to 2,200° C. is heated to a maximum temperature of 1,600 to 2,200° C. and sintered.