JPH0559075B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a high-strength sialon-based sintered body useful for manufacturing various engineering ceramics having high-temperature high strength, high hardness, and high toughness.

(Prior art and its problems) Yα-Sialon is a solid solution in which A is substituted at the Si position of α-type silicon nitride and O is substituted at the N position.
It is a substance that has entered into a solid solution, and has the formula Y _x (Si, A) ₁₂ (O, N) ₁₆ [] (In the formula, x is a number that satisfies 0<x≦1.)
It is expressed as This Yα-sialon has high hardness,
It has properties suitable for engineering ceramics, such as a low coefficient of thermal expansion and excellent corrosion resistance.

However, the sintered body of Yα-sialon phase alone is
Because the crystal shape is granular, it does not have sufficient properties such as strength and fracture toughness for engineering ceramics. Therefore, in order to improve this drawback, Japanese Patent Laid-Open No. 58-185484, No. 58-204875, No. 63-233082, etc., disclose Yα-SiAlON crystal and β-type silicon nitride at the Si position. A is represented by the formula Si _6-z A _z O _z N _8-z [] (where z is a number satisfying 0<z≦4.2) where A is substituted with O in the N position as a solid solution. A sialon-based sintered body has been proposed, which is a composite of acicular β-sialon crystals.

However, the mechanical properties of this sialon-based sintered body are not sufficient for practical use.

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

(Summary of the Invention) According to the present invention, Y ₂ M _2-u O _7-2u with a fluorite crystal structure
Microcrystals of (where M is Hf and/or Zr, -1<u
<1), a microcrystal of M′N _v with a salt-type crystal structure (in the formula,
M' is Hf and/or Zr, 0.7≦v≦1.2), Yα-sialon crystal represented by the above formula [], β-sialon crystal expressed by the above formula [], A,
A high-strength sialon-based sintered body is provided that is composed of an AN polytype crystal of a composite oxynitride containing Si, and a crystal phase other than the above and/or a glass phase containing Y.

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

1<Y ₂ M _2-u O _7-2u microcrystalline phase <20 wt% 0.5<M′N _v microcrystalline phase <10 wt% 5<Yα−Sialon crystalline phase <50 wt% 30<β− Sialon crystal phase <90% by weight 0.5<A, AN of composite oxynitride containing Si
Polytype crystalline phase <10% by weight 1<Crystalline phase containing Y and/or glass phase
<10% by weight If the proportion of the microcrystalline phase of Y ₂ M _2-u O _7-2u and M'N _v is out of the above range, the mechanical strength of the obtained sialon-based sintered body will decrease and its dispersion will decrease. This is not desirable as it also increases the size.

In the present invention, the microcrystals of Y ₂ M _2-u O _7-2u are
It represents _Y2Hf2O7 , _{Y2Zr2O7 , a} solid solution of both, or _a solid solution of these and _{Y2O3 ,} and -1<u< ₁ .

Further, the microcrystal of M′N _v represents HfN, ZrN, a solid solution of both, or a non-stoichiometric compound of these, and satisfies 0.7≦v≦1.2.

Moreover, in the sialon-based sintered body of the present invention,
Yα-Sialon crystal long axis is 0.05 to 10 μm, β
- It is preferable that the long axis of the Sialon crystal is 1 to 100 μm.

The AN polytype crystals of composite oxynitride containing A, Si are 15R, 21R, 27R, 8H, 12H,
It represents a crystal group with a composition near AN and having a long-period structure such as 2H〓.

Examples of crystal phases containing Y include melilite type Y ₂ Si ₃ O ₃ N ₄ , apatite type Y ₁₀ (SiO ₄ ) ₆ N ₂ ,
Wollastonite type YSiO ₂ N, wallerite type Y _{4 Si 2} O ₇ N ₂ , garnet type Y ₃ Al ₅ O ₁₂ , mullite type Y ₄ Al ₂ O ₉ , Y ₃ AlSi ₂ O ₇ N _{2 , Y2Si2O7 ,}
Examples include Y ₂ SiO ₅ , but the crystal group is not limited to these crystal groups.

The sialon-based sintered body of the present invention contains a β-sialon crystal, an AN polytype crystal of a composite oxynitride containing A and Si, a crystal phase containing Y, and/or
Or, the glass phase and fine crystals of Y ₂ M _2-u O _7-2u with a fluorite-type crystal structure crystallized at grain boundaries and fine-grain crystals of M'N _v with a salt-type crystal structure are Yα-sialon crystals. exist with

Y ₂ M _2-u O _7-2u and
The fine crystals of M′N _v improve the strength properties of the grain boundary phase (crystal phase and/or glass phase containing Y ₂ M _2-u O _7-2u and Y). In addition, the composition, crystal phase,
There are seven types of phases with different particle shapes, particle diameters, and coefficients of thermal expansion, and after sintering, microcracks occur in the sintered body due to microstrains. This, together with the matrix strengthening effect and crack propagation inhibiting effect of the acicular crystals mainly composed of β-sialon, is thought to improve the mechanical properties such as fracture toughness of the resulting sialon-based sintered body. .

Any method may be used to produce the sialon-based sintered body of the present invention as long as a sintered body having the above structure can be obtained.

An example of a method for manufacturing the sialon-based sintered body of the present invention is shown below.

The sialon-based sintered body of the present invention has the above formula []
50% by weight or less of Yα-sialon powder, which has Yα-sialon as the main phase and contains 8% by weight or less of excess oxygen with respect to the theoretical oxygen amount defined by formula [], hafnium oxide powder and/or Alternatively, it can be obtained by heating and sintering a raw material mixed powder consisting of 15% by weight or less of zirconium oxide powder and the balance consisting of α-silicon nitride powder at a maximum temperature in the range of 1600 to 2100°C.

The Yα-sialon powder may be any powder as long as it has Yα-sialon as the main phase represented by the formula []. Powders prepared accordingly are suitable. This proposed method consists of: (a) amorphous silicon nitride powder; (b) metallic aluminum or aluminum nitride; (c) a metal salt that generates an oxide of Y that forms an interstitial solid solution between the lattices of Yα-sialon; and optionally (d) by mixing an oxygen-containing compound of aluminum or silicon to the desired Yα-sialon composition and heating the mixture to a temperature in the range of 1300-1900°C under a nitrogen-containing atmosphere. , a method for producing Yα-sialon powder. The Yα-sialon powder obtained by this method is a fine and uniform powder with a primary particle size of 0.2 to 2 μm,
Contains almost no free carbon and metal impurities, so
A sintered body without pores and abnormal grain growth can be provided.

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

Examples of methods for incorporating excess oxygen into the Yα-sialon powder include adding an excessive amount of an oxygen-containing compound such as silicon, aluminum, or yttrium to amorphous silicon nitride during the preparation stage of the Yα-sialon powder; A method is employed in which the powder is heated in an oxygen-containing atmosphere. An example of the latter is a method in which Yα-sialon powder is heated to a temperature in the range of 800 to 1200° C. in an oxygen-containing atmosphere to cause the Yα-sialon powder to contain oxygen in excess of the stoichiometric amount. Heating time is usually 0.5
~5 hours. This treatment can be carried out, for example, by placing Yα-sialon powder thinly on a holding plate and leaving it in an oxygen-containing atmosphere, or by fluidizing α-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 a low melting point remain in the sintered body, which impairs the mechanical properties at high temperatures.

α-Silicon nitride powder is 1 μm in terms of sinterability.
It is preferable that the particles have the following particle size, and further preferably that the content of impurities that impair the strength, corrosion resistance, and oxidation resistance at high temperatures of the obtained sintered body is 1% by weight or less.

The blending ratio of α-silicon nitride powder in the raw material mixed powder is 30% by weight or more, preferably 50 to 90% by weight,
More preferably, it is 60 to 80% by weight. As the blending ratio of silicon nitride 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 α-silicon nitride powder exceeds 90% by weight, the sinterability of the mixture decreases and the densification of the sintered body does not proceed.

In addition, if necessary, add 10% to the raw material mixed powder.
It is also possible to add up to 15% by weight of hafnium nitride powder and/or zirconium nitride powder, up to 15% by weight of aluminum nitride powder, or up to 10% by weight of yttrium oxide powder. For example, during the sintering process, hafnium oxide and/or zirconium oxide in the raw material mixed powder reacts with nitrogen gas in the atmosphere to reduce the M′N _v microcrystals of the sialon-based sintered body of the present invention. Since it is produced by nitriding, by adding hafnium nitride powder and/or zirconium nitride in advance,
The generation rate of microcrystals of M′N _v can be increased.

There is no particular restriction on the method for preparing the raw material mixed powder, and methods known per se, 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. Can 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. Moreover, by further subjecting the sintered body obtained by the above method to hot isostatic pressing, the physical properties of the sintered body can be further improved.

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, and the like.

The sintering temperature is usually 1600-2100°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, β-
Sialon crystal, AN polytype crystal of composite oxynitride containing A and Si, crystal phase and/or glass phase containing Y, and Y ₂ M _2-u with fluorite-type crystal structure crystallized at grain boundaries Sialon group sintering in which fine crystals of O _7-2u and fine crystals of M′N _v with a salt-type crystal structure exist together with crystals of Yα-sialon, where x in formula [] is slightly lower than the composition of the raw material Yα-sialon. You get a body.

In particular, in order to form a highly heat-resistant crystal phase or glass phase at the grain boundaries of the sialon-based sintered body, a composite containing A and Si that can coexist with these heat-resistant grain boundary phases under sintering conditions is required. Precipitation of oxynitride AN polytype crystals is essential. Therefore, for example, the above-mentioned AN It is desirable to promote precipitation of polytype crystals.

(Effect of the invention) The sialon-based sintered body obtained by the present invention has improved mechanical properties such as high-temperature strength and fracture toughness compared to conventional sialon-based sintered bodies, so it is highly reliable. It can be suitably used as a structural material, especially as a wear-resistant and heat-resistant material for gas turbine parts, cutting chips, rolls, dies, nozzles, etc.

(Example) Examples and comparative examples are shown below.

Examples 1 to 7 and Comparative Example 1 500 g of amorphous silicon nitride powder, 62 g of Y ₂ O ₃ powder, and 65.7 g of metal A powder were mixed for 1 hour in a vibration mill under a nitrogen gas atmosphere. The mixed powder was filled into a carbon crucible, set in a resistance heating high temperature furnace, and heated from room temperature to 1200℃ for 1 hour at 1200℃ under a nitrogen gas atmosphere.
to 1400℃ for 4 hours, then from 1400℃ to 1600℃
The mixture was crystallized by heating on a 2-hour temperature rising schedule to obtain Yα-Sialon powder.
The properties of the obtained Yα-sialon powder are shown below.

Theoretical composition Y _0.5 Si _9.75 Al _2.25 O _0.75 N _15.25 Specific surface area 2.5 m ² /g Particle shape Equiaxed crystal formation phase α phase ≥ 90% Product composition (wt%) Y: 7.2 Si: 44.2 Al: 9.8 O: 4.9 N: 33.9 Excess oxygen amount 2.9% by weight Above Yα-sialon powder, α-silicon nitride powder (SN-E10 manufactured by Ube Industries, Ltd.; specific surface area: 11 m ² /g,
Oxygen content: 1.3wt%), hafnium oxide powder, zirconium oxide powder, hafnium nitride powder and zirconium nitride powder (all Hermann C.
(manufactured by Starck Co., Ltd.) at the ratios shown in Table 1, using ethanol as a medium, wet ball milling was performed for 48 hours, and then vacuum-dried at 80°C. Obtained raw material powder
After filling 40 g into a graphite die with an inner diameter of 100 mm whose surface is coated with boron nitride and setting it in a hot press sintering device, it is heated from room temperature under a pressure of 250 kg/cm ^2.
The temperature was raised to 1750°C at a rate of 200°C/hour and maintained at the same temperature for 1 hour.

Table 1 shows the results of measuring the bulk density and proportion of the formed phase of the obtained sintered body. Note that the proportion of the generated phase was calculated based on the X-ray diffraction peak intensity. FIG. 1 shows an X-ray diffraction chart of the sintered body obtained in Example 5.

In addition, 50 test pieces of 3 x 4 x 50 mm were cut out from the produced sintered body, and the outer span was 30 mm.
A 4-point bending strength test with an inner span of 10 mm was performed (at room temperature and 1400°C) to determine the strength and Weibull coefficient. In addition, K _1C was measured by the SEPB method. Results first
Shown in the table.

Examples 8 to 16 and Comparative Example 2 Yα-sialon powder used in Examples 1 to 7,
α-silicon nitride powder, hafnium oxide powder, zirconium oxide powder and aluminum nitride powder
48 using ethanol as the medium in the proportions shown in the table.
After wet ball milling for an hour, it was vacuum dried at 80°C.

The powder mixture was preformed using a mold with a square cross section of 50 x 80 mm, and then rubber pressed at a pressure of 1.5 ton/cm ² . The obtained molded product is heated to a second temperature using an electric furnace.
The temperature was raised under the temperature-atmosphere gas pressure conditions listed in the table and maintained at the same temperature for 2 hours to perform normal pressure sintering or atmospheric pressure sintering.

The properties of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Table 2.

[Brief explanation of the drawing]

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

[Table] β-sa: β-sialon
YMO: _{Y2M2 - uO7-2u}
M′N：M′N _v
ANP: AlN polytype crystal generated in the Al-Si-O-N system (
Mainly composed of 15R type crystal phase)
*: Weight % of the formed phase excluding the crystalline phase containing Y and/or the glass phase
**: Weibull coefficient of room temperature strength value (number of samples: 50)

[Table] β-sa: β-sialon
YMO: _{Y2M2 - uO7-2u}
M′N：M′N _v
ANP: AlN polytype crystal generated in the Al-Si-O-N system (
Mainly composed of 15R type crystal phase)
*: Weight % of the formed phase excluding the crystalline phase containing Y and/or the glass phase
** Weibull coefficient of room temperature strength value (50 samples)

Claims (1)

[Claims] 1. Microcrystals of Y ₂ M _2-u O _7-2u with a fluorite crystal structure (where M is Hf and/or Zr, and u is -1<u
It is a number that satisfies <1. ), microcrystals of M′N _v with a salt-type crystal structure (where M′ is Hf and/or Zr, and v is 0.7≦v≦
This is a number that satisfies 1.2. ), Yα-sialon crystal expressed by the formula Y _x (Si, A) ₁₂ (O, N) ₁₆ (where x is a number satisfying 0<x≦1), the formula Si _{6- z} A _z O _z N _8-z (In the formula, z is a number satisfying 0<z≦4.2) A high-strength sialon-based sintered body composed of a polytype crystal and a crystal phase other than the above containing Y and/or a glass phase.