JPH03208866A - High strength sialon-based sintered body - Google Patents

Abstract

PURPOSE:To obtain a sialon-based sintered body having high strength and toughness at high temp. by forming a beta-sialon crystal phase as a principal phase, a Yalpha-sialon crystal phase and other crystal phases. CONSTITUTION:This sialon-based sintered body is composed of a phase (1) of microcrystals of Y2M2-uO7-2u (M is Hf and/or Zr and -1<u<1) having fluorite structure, a phase (2) of microcrystals of M'Nv (M' is Hf and/or Zr and 0.7<=v<=1.2) having sodium chloride structure, a phase (3) of crystals of Yalpha-sialon represented by a formula Yx(Si,Al)12-(O,N)16 (0<x<1), a phase (4) of crystals of beta-sialon represented by a formula Si6-zAlzOzN8-z (0<=z<=4.2), a phase (5) of AlN type crystals of a multiple oxynitride contg. Al and Si and other Y-contg. crystal phase (6) and/or a glass phase.(7).

Description

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

(Prior art and its problems) Yα-Sialon is a substance in which Ai is substituted in the St position of α-type silicon nitride and 0 is substituted in the N position, and at the same time Y enters into solid solution, and has the formula Yx (St, It is expressed as A/ri+t(0,N)+h(1) (wherein, X is a number satisfying O<x≦1).

This Yα-sialon has characteristics as an engineering ceramic, such as high hardness, low coefficient of thermal expansion, and excellent corrosion resistance.

However, since the sintered body of the single Yα-sialon phase has a granular crystal shape, it does not have sufficient properties such as strength and fracture toughness as an engineering ceramic.
In order to improve this drawback, Japanese Patent Application Laid-Open No. 58-185484
No. 58-204875, No. 63-233
Publication No. 082, etc. describes the formula S 1 h-mA j! in which Af is substituted in the Si position and 0 is substituted in the N position of Yα-sialon crystal and β-type silicon nitride. gosNs-s (I
A sialon-based sintered body has been proposed that is a composite of acicular β-sialon crystals represented by I) (in the formula, 2 is a number satisfying O<z≦4.2). .

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, YtMz-,0-1- with a fluorite crystal structure
1u of microcrystals (where M is I(f and/or Zr, -1
< u < 1 ), microcrystals of M'Nv with a salt-type crystal structure (wherein M' is Hf and/or Zr, 0.7≦v≦
1, 2), a crystal of Yα-sialon represented by the formula (I), a crystal of β-sialon represented by the formula (It), Aj! A high-strength sialon-based sintered body is provided, which is composed of an A2N polytype crystal of a composite oxynitride containing St, and a crystal phase other than the above and/or a glass phase containing Y.

(Detailed 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<YgHf--0? - Microcrystalline phase of 〈20% by weight
Microcrystalline phase with 0.5<M'Nv <10〃5<
Crystalline phase of Yα-Sialon <5ON30<Crystalline phase of β-Sialon <90〃0.5<Crystalline phase containing Y and/or Glass phase<10〃Y z M z −uO?
If the ratio of the microcrystalline phase of -t u and M'Nv 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.

In the present invention, Y, M! -, O, -uO7-2u microcrystals are YgHf rich Oq, YIZr! O? Or a solid solution of both, or these and Y! 0. represents a solid solution with
-1ku<1.

Moreover, the microcrystal of M'Nv represents HfN, ZrN, a solid solution of both, or a non-stoichiometric compound of these, and 0
．． 7≦v≦1.2.

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

Aj! , St-containing composite oxynitride AfN polytype crystals are 15R, 21R, 27R, and 8H.

It represents a crystal group with a composition near AfN having a long-period structure such as 12H12Hσ.

As the crystal phase containing Y, for example, melilite type Yt
SisOsNa, apatite type Y+a(Si04)J
z, wollastonite type YSiO,N, wolerite type YaSizOJt, garnet type Y3A1. O
□, mullite type YaAlzO*, Y3AISizOt
Examples include Ng, YxSi20g, YlSiOl, etc., but the material is not limited to these crystal groups.

The sialon-based sintered body of the present invention contains β-sialon crystals, Aj! , an AfN polytype crystal of a composite oxynitride containing Si, a crystal phase and/or a glass phase containing Y, and a YxMx-got with a fluorite-type crystal structure crystallized at grain boundaries.
-zs microcrystals and M'Nv microcrystals with a salt-type crystal structure are present together with Yα-sialon crystals.

The grain boundary phase (YtMx-Oy
-z.

(crystal phase and/or glass phase containing Y). In addition, the composition, crystal phase, particle shape,
There are seven types of phases with different particle sizes and coefficients of thermal expansion, and after sintering, microcranks occur in the sintered body due to microstrains. It is thought that this, together with the matrix strengthening effect and crack propagation inhibiting effect of the acicular crystals mainly composed of β-sialon, improves the mechanical properties such as fracture toughness of the obtained sialon-based sintered body. It will be done.

The method for producing the sialon-based sintered body of the present invention includes:
Any method may be used 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 Yα-sialon represented by the formula (1) as a main phase, and contains 8% by weight or less of excess oxygen with respect to the theoretical oxygen amount defined by the formula (I). A raw material mixed powder containing 50% by weight or less of Yα-SiAlON powder, 15% by weight or less of hafnium oxide powder and/or zirconium oxide powder, and the balance consisting of α-silicon nitride powder is heated to a maximum temperature in the range of 1400 to 2100°C. ,
Obtained by sintering.

As the Yα-sialon powder, Y expressed by the formula (13)
Any powder may be used as long as it has α-sialon as its main phase.
Powders prepared according to the invention of No. 223009 are preferred. This proposed method consists of (a) amorphous silicon nitride powder, (b) metallic aluminum or aluminum nitride, (c)
A metal salt that produces an oxide of Y that forms an interstitial solid solution between the lattices of Yα-sialon, and, if necessary, (d) an oxygen-containing compound of aluminum or silicon, is mixed to obtain a desired Yα-sialon composition. This is a method for producing Yα-sialon powder by heating the mixture to a temperature in the range of 1300 to 1900° C. in a nitrogen-containing atmosphere. The Yα-sialon powder obtained by this method is a fine and uniform powder with a particle size of 0.2 to 2 μm, and contains almost no free carbon and metal impurities, so it does not have pores or abnormal grain growth. It is possible to provide a sintered body without

In order to improve the sinterability of the Yα-sialon powder and at the same time obtain a high-strength sialon-based sintered body, it is necessary to increase the sintering raw material Yα.
- It is necessary that the Sialon powder contains 8% by weight or less of excess oxygen relative to the theoretical oxygen amount defined by formula (I).

Examples of methods for containing excess oxygen in the Yα-sialon powder include a method of adding an excessive amount of an oxygen-containing compound of silicon, aluminum, or yttrium to amorphous silicon nitride in 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 theoretical amount. Heating time is usually 0.5-5
It's time. 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 to 6.5% by weight, particularly preferably 2 to 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.

The α-silicon nitride powder preferably has a particle size of 1 μm or less in terms of sinterability, and further contains impurities that impair the strength, corrosion resistance, and oxidation resistance of the resulting sintered body at high temperatures. It is preferable that the content is lli% or less.

The blending ratio of α-silicon nitride powder in the raw material mixed powder is 3
It is 0% by weight or more, preferably 50 to 90% by weight, more preferably 60 to 80% by weight.

Within the above range, as the blending ratio of silicon nitride powder increases, 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, 10% by weight may be added to the raw material mixed powder.
The following hafnium nitride powder and/or zirconium nitride powder, 15% by weight or less of aluminum nitride powder, or 1
For example, M' in the sialon-based sintered body of the present invention may contain 0% by weight or less of yttrium oxide powder.
Nv microcrystals are generated by the hafnium oxide and/or zirconium oxide in the raw material mixed powder reacting with nitrogen gas in the atmosphere and being reduced and nitrided during the sintering process. By adding/or adding zirconium nitride, it is possible to increase the generation rate of M'Nv microcrystals.

There are no particular restrictions on the method for preparing the raw material mixed powder (
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 employed. 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 it, etc. can be adopted. 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 -axial molding method, a cast molding method, an injection molding method, an explosive compression molding method, and the like.

The sintering temperature is usually 1400-2100"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, As a result, composition changes occur in the sintered body due to thermal decomposition.

By the above method, crystals of β-sialon, which are thought to be produced by the reaction of Yα-sialon and α-silicon nitride, Aj! , a /IN polytype crystal of a composite oxynitride containing 33, a crystal phase and/or a glass phase containing Y, and a fluorite-type crystal structure crystallized at grain boundaries.
w Oq −* M of fine grain crystal and salt type crystal structure of w
A sialon-based sintered body is obtained in which fine crystals of 'Nv exist together with crystals of Yα-sialon whose X in formula (I) is slightly lower than the composition of the raw material Yα-sialon.

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, A7!, which can coexist with these heat-resistant grain boundary phases under sintering conditions, is required. , precipitation of AfN polytype crystals of complex oxynitrides containing Si is essential. Therefore, for example, the above-mentioned AlN polyamide can be produced by using a raw material Yα-SiAlON powder having an excess oxygen content of 5% by weight or less, by adding aluminum nitride powder, by increasing the nitrogen gas pressure in the sintering atmosphere, etc. It is desirable to promote the precipitation of type 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 Amorphous silicon nitride powder 500 g, Y, O, powder 62 g
and 65.7 g of All metal powder were mixed in a vibrating 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 from room temperature to 1200°C for 1 hour at 1200°C in a nitrogen gas atmosphere.
It was crystallized by heating from 1,400° C. to 1,400° C. for 4 hours and then from 1,400° C. to 1,400° C. for 2 hours to obtain Yα-sialon powder.

The properties of the obtained Yα-sialon powder are shown below.

Theoretical composition Yo, 551w, tsAlz, zso
o, ysN+s, zs Specific surface area 25 po/g Particle shape Equiaxed crystal formation phase α phase ≧90% Product composition (wtχ) Y near, 2 Si: 44.2 Al: 9.8 0:
4.9 N: 33.9 Excess oxygen amount 2.9% by weight The above Yα-sialon powder, α-silicon nitride powder (5N-EIOs manufactured by Ube Industries ■ Specific surface area: 11 po/g, oxygen content: 1.3 wt %), hafnium oxide powder, zirconium oxide powder, hafnium nitride powder, and zirconium nitride powder (all manufactured by Hermann C. Starck ■).
Wet ball milling was performed for 48 hours using ethanol as a medium at the ratio shown in the table, followed by vacuum drying at 80°C. 40 g of the obtained raw material powder was filled into a graphite die with an inner diameter of 100 m and whose surface was coated with boron nitride, and after setting it in a hot press sintering device, it was heated at 200°C from room temperature to 1750°C under a pressure of 250 kg/cd. The temperature was raised at a rate of 1/2 hr. 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. The proportion of the formed phase was determined 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 cm were cut out from the produced sintered body, and subjected to a 4-point bending strength test with an outer span of 30II and an inner span of 10.
00°C) intensity and Weibull coefficient were determined. Also, 5E
c was measured by the PB method.

The results are shown in Table 1.

Examples 8 to 14 and Comparative Example 2 The Yα-sialon powder, α-silicon nitride powder, hafnium oxide powder, zirconium oxide powder, and aluminum nitride powder used in Examples 1 to 7 were used as a medium in the proportions shown in Table 2. After wet ball milling using ethanol for 48 hours, it was vacuum dried at 80°C.

The powder mixture was preformed using a mold with a cross section of 50 x 80 squares, and then rubber pressed at a pressure of 1.5 ton/cj. The obtained molded product was heated using an electric furnace under the temperature and atmospheric gas pressure conditions listed in Table 2, held at the same temperature for 2 hours, and subjected to normal pressure sintering or atmospheric pressure sintering. went.

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 drawings]

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

Claims (1)

[Claims] Y_2M_2_-_uO_7_-_ with fluorite crystal structure
2_u microcrystals (in the formula, M is Hf and/or Zr, u is a number satisfying -1<u<1), M'Nv microcrystals with a salt-type crystal structure (in the formula, M' is Hf and/or Zr, v is 0.7≦v≦
This is a number that satisfies 1.2. ), formula Y_x(Si,Al)_1_2(O,N)_1_4(
In the formula, x is a number satisfying 0<x≦1. ); β-sialon crystal represented by the formula Si_6_-_zAl_zO_zN_8_-_z (wherein, z is a number satisfying 0<z≦4.2);Al; A high-strength sialon-based sintered body comprising an AlN polytype crystal of a composite oxynitride containing Si, and a crystal phase other than the above and/or a glass phase containing Y.