JPS59213676A - High strength silicon nitride sintered body and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-strength silicon nitride sintered body suitable for heat-resistant structural materials, machining materials, particularly cutting tools, wear-resistant materials, and corrosion-resistant materials, and a method for producing the same.

Silicon nitride is a compound with strong covalent bonds, and it decomposes and evaporates at high temperatures, has low reactivity due to the small self-diffusion coefficient of grooved atoms, and is more sensitive to grain boundaries than ionic crystals and metal crystals. It is a material that is extremely difficult to sinter due to its large ratio of energy to surface energy. For this reason, even if silicon nitride is sintered by the pressureless ordinary sintering method, a dense sintered body cannot be obtained, and generally IvigO, Y2O:1, Al
No. 203, a dense sintered body is obtained by adding a sintering aid such as AIN and pressure sintering using reaction sintering or liquid phase sintering, or hot isostatic pressing (HIP). In this way, Mg02Y203, Al203, AI
The Si3N4 sintered body to which a sintering aid such as N is added is 5is
Lower silicates are generated in the grain boundary phase of N4, and this lower silicate becomes a liquid phase at low temperatures and promotes the sintering of 5LIN4. On the other hand, it remains in the grain boundary phase even after sintering and reduces the high temperature strength of the sintered viscous material. It has the disadvantage of lowering the

In order to improve this drawback, a method has also been proposed in which lower silicates remaining in the Si3N4 grain boundary phase are crystallized by heat treatment to increase the strength of the sintered body. However, when the Si3N4 sintered body is experimentally sintered in a small shape, the second phase, which is mainly composed of these lower silicates or a sintering aid made by crystallizing these lower silicates by heat treatment, becomes Si3N4 grains. This did not cause any major problems because it was dispersed relatively uniformly in the interfacial phase, but in order to promote industrialization, it was changed (if a shape or a large shape is force-sintered, Si3N4 will sinter and become a tough material). Due to the poor reactivity with the sintering aid, and the problem of cooling speed caused by the enlargement of the sintering furnace, the second phase mainly composed of the oxide-based sintering aid is non-uniform in the Si3N4 grain boundary phase. The problem arises that S is distributed and segregated.
Poor reactivity between i3N4 and sintering aid and sintering aid fii
5i3N4j due to the segregation of the second phase mainly composed of J
, variations in various 4' and r properties within the viscous material become large,
There is a technical problem that it is difficult to industrialize because it causes a decrease in strength.

The present invention solves the above-mentioned drawbacks and problems, and
i By facilitating the reactivity between 3N4 and the sintering aid, the second phase, which is mainly composed of the sintering aid, can be uniformly dispersed in a sintered body with a complex or large shape, and the second phase can be easily dispersed. and Si
The purpose of this invention is to provide a silicon nitride sintered body with improved bonding strength with 3N4 (and thus with improved properties of the sintered body) and a method for manufacturing the same.

The high-strength silicon nitride sintered body of the present invention contains at least L species of rare earth element nitrides and oxynitrides of 0.5 to 252[jit
%, 0.5 to 25% by weight of at least one of oxides, nitrides and oxynitrides of group IIa elements of the periodic table, and the remainder silicon nitride and unavoidable impurities. Among these nitrogen-containing sintering aids, nitrogen-containing compounds of rare earth elements in particular have a lower decomposition temperature than sintering aids based on oxides, and are activated at low temperatures, making them hard. It increases the reactivity with the Si3N4 phase, and since the movement of anion ions is very small in this reaction, the nitrogen-containing sintering aid can be dissolved even partially in 5isN4, and it is sintered at the Si3N4 grain boundaries. The sintering aid is uniformly dispersed to promote sintering, and after sintering, a second phase formed mainly from the nitrogen-containing sintering aid contained in the sintering aid and an Si 3N4 hard phase are formed. Oxide-based sintering aid Q is used to increase the bond strength with the sintering aid.
It is possible to prevent harmful effects such as abnormal growth of 3N4 particles, and the internal stress caused by the crystal anisotropy of the second phase and Si3N4 is also reduced. If sintering is possible, it becomes easy to produce a high-strength sintered body that is dense and has high dimensional accuracy.Among the sintering aids used here, nitrides and oxynitrides of rare earth elements are Because Si3N4 grain boundaries are not uniformly penetrated and dispersed in the sintering process together with the Ha group element compounds shown in the table, Si3N
Formation of a homogeneous second phase mainly composed of sintering aid surrounding the four grains, and mutual diffusion of nitrogen in this second phase and nitrogen in Si3N4 strengthen the bond between Si3N4 and the second phase. It also contributes to the prevention of segregation of the second phase, and after sintering, improves various properties of the sintered body, including improvement in high-temperature strength.On the other hand, the periodic rule used as a sintering aid The oxides, nitrides, and oxynitrides of Group IIa elements shown in the table have a stronger effect of accelerating sintering of 5i3N4 than compounds of rare earth elements, and they promote the formation of a homogeneous second phase mainly composed of sintering aids. It serves as a mediating effect of the bond between the rare earth element in the two phases and the silicon in S i 3N4 and contributes to improving various properties of the sintered body.

In the method for producing a high-strength silicon nitride sintered body of the present invention, it is desirable to use as fine a Si3N4 powder as possible as a starting material, and at least a rare earth element nitride and an oxynitride are added to the Si3N4 powder. 1 type of powder 0.5-・
51% by weight of 25% by weight and 0.5-25% by weight of at least one powder of oxides, nitrides and oxynitrides of group Ila elements of the periodic table, or nitrides and nitrides of rare earth elements. A composite compound powder consisting of at least 1a of oxynitride and at least one of oxides, nitrides and oxynitrides of group Ila elements of the periodic table and Si3N4 powder may be blended as a starting material; A composite compound powder consisting of at least one nitride and oxynitride of a rare earth element, at least one oxide, nitride, and oxynitride of a Tla group element of the periodic table, and Si3N4, and Si3N4 powder as starting materials. In particular, when a composite compound powder is used as a starting material, the structure of the sintered body can be suppressed from becoming columnar or acicular, and the aspect ratio can be reduced and particles can be formed. This is particle shape 21y with small aspect ratio.
：の・）3γ solids have improved thermal shock resistance, so when using them in applications where severe localized thermal shock is applied, such as in cutting tools, it is recommended to use composite compound powder as the starting material. desirable.

In the method for producing a high-strength aged silicon sintered body of the present invention, the 3i3N4 powder used as a starting material is preferably of high purity, and ζ is contained as an impurity in the Si3N4 powder.
If less than 2% by weight of AI, Fe, etc. are mixed in, or if oxygen is adsorbed to the surface of the Si3N4 powder particles to form 5102, or if the blended powder is placed in a container (two people put it in an Al2O3 ball). When mixing and pulverizing with scale balls, round alloy balls, etc. (impurities mixed in from this container and these balls are 5'rR, f-3,:%
If below:! J7J? Adjusting the amount of the i-adjuvant and the nitrogen content of the rare 111 element nitrides and oxynitrides and the oxides, nitrides and oxynitrides of the IIa group elements of the periodic table used as sintering aids. As a result, various properties of the high-strength silicon nitride sintered body of the present invention can be sufficiently maintained. For example, carbides and nitrides of elements of Group A, Group Va, and Group A of the periodic table, which are mixed in from cemented carbide balls used during mixing and pulverization, have no wear resistance in the sintered body of the present invention. 5i02. AI and F
Group e elements promote the interdiffusion reaction between silicon and nitrogen in the hard phase Si3N4, and 5102 in particular promotes the interdiffusion reaction between silicon and nitrogen in Si3N4, which is a hard phase.
In order to lower the original decomposition temperature, the reaction between S i 3N4 and the sintering aid tends to occur on the low temperature side, contributing to the promotion of sintering and densification. In addition, oxides, nitrides, and oxynitrides of L ir Na T K, which are elements of group Ia of the periodic table, can be sintered in the same way as oxides, nitrides, and oxynitrides of elements of group Ila of the periodic table. After contributing to the promotion and densification of silicon nitride, some of it is decomposed and removed and plays an auxiliary role as oxides, nitrides, and oxynitrides of Group Ila elements in the periodic table. They can also be added within a range that does not reduce the various properties of the body. Si as the starting material used here
3] '34 is α-8i3N4, β-3i3N4, amorphous Si3N4, or 3 13 with a different crystal structure of these
A mixture of T cores in any ratio may be used. In addition, among at least L types of nitrides and oxynitrides of rare earth elements as sintering aids and at least 11 gradients, nitrides, and oxynitrides of Ha group elements of the periodic table, nitrogen-containing compounds are Specific compounds or non-stoichiometric compounds ([;selfQ's may be used; among these, nitrogen-containing compounds of rare earth elements are particularly susceptible to oxidation in the atmosphere, so they are handled in the state of inert Ft gases such as nitrogen gas. Although it is necessary, it is desirable to form a complex compound with an element of Group I of the periodic table.

In the manufacturing method of the present invention, various starting F(℃) materials are mixed or mixed and pulverized, and the mixed powder state is packed in a mold for sintering to make a powder compact, or a compact is made into a compact with a forming mold, After making it into a molded body in a mold,
Temperature lower than 1'/1 (sintered at jt degree or formed after preliminary sintering) & form in non-'i, including vacuum
'Sintering in a bicarbonate atmosphere using methods such as normal sintering (including pressureless sintering), high-frequency pressure sintering, energized pressure sintering, gas pressure sintering, and hot pressing; It is also possible to combine the sintering method and the hydrostatic pressing method to promote densification of the sintered body. Although the sintering temperature varies depending on the sintering method or the ingredients, a sufficiently dense sintered body can be obtained at a temperature of 1500°C to 1900°C.

The rare earth elements used here are Sc, Y, and La.

Ce, Pr+Nd, Pm, Sm, Eu, Gd, Tb, D
y, Ho, Er.

A collective term for the 177 elements of Tm, Yb and Lu, in the periodic table]
1. Group a elements are Be + Mg r Ca + Sr
, Ba, and Ra.

The reason for the numerical limitation will be explained here.If at least one of the nitrides and oxynitrides of two rare earth elements is less than 0.5 weight C3, the second
The high temperature strength of the phase is low, and therefore the strength of the sintered body itself is also reduced, and when the amount exceeds 25% by weight, the Si
Since the amount of 3N4 decreases, the hardness of the sintered body decreases, and the wear resistance and heat resistance decrease, so the content was set at 0.5 to 25% by weight.

If at least one of oxides, nitrides, and oxynitrides of Ha group elements in the periodic table is less than 0.5% by weight, Si 3N4
The effect of promoting sintering is weak, and when the amount exceeds 25% by weight, the amount of Si3N4 becomes relatively small, and lower silicates are likely to occur in the second phase formed mainly from the sintering aid. 0.5 to 2 to reduce the hardness and strength of the sintered body.
The content was 5% by weight.

Next, a detailed explanation will be given according to an example.

Example 1 5i3N4 with an average particle size of 1 μIn (a mixture of about 40% amorphous Si3N4, α-3i 3N4 and β-3i3N4), 5i3N4 with an average particle size of 2 pm (about 95% α-3i
3N4 and β-3i 3N4), Si 3N4 with an average particle size of 5 μm (approximately 70% α ~ Si 3N4 and β-3
i 3N4 mixture) and YN, Y303N, MgO
, Mg3N2, and Mg4ON2 (7) Using each powder, mix each sample in the proportions shown in Table 1, and place each blended sample in a stainless steel container with a WC-based cemented carbide ball in a hexane solvent. It was mixed and ground. The obtained mixed powder was coated with BN powder l 00 rymX I
Filled in a 00 turn square carbon mold,
After replacing the furnace with N2 gas, molding pressure of 150 to 400 blades,
Pressure sintering was carried out at a temperature of 1700° C. to 1850° C. and a holding time of 60 to 120 minutes. The manufacturing conditions for each sample are shown in Table 1, and the obtained sintered body was divided into the center and the outer periphery.
The specimens were cut into 13 x 5 mm pieces, and the mechanical properties of each cut sample were determined by comparing with a conventional Y2O3-Al2O3-Si3N4-based sintered body, and the results are shown in Table 2.

As shown in Table 2 below, the high-strength silicon nitride sintered body of the present invention has high hardness, high heat resistance g:IN property, and high fracture toughness (Kic).
Comparison product Y20a -Al 203-3i 3N4
Sialon based sintered compact After holding the sample at each temperature for 2 minutes, the sample is immersed in water at approximately 20°C (room temperature) and the temperature at which the sample can be heated without cracking is shown. It was determined from the length of the crack generated, the size of the indentation, and the Vickers hardness. Also, sample number 3 obtained here
When the outer periphery of the material was confirmed by X-ray diffraction and fluorescent X-rays, it was found that Co and W were contained, and W was thought to form tungsten silicide.

Example 2 1 it m Si 3N4 and Mg used in Example I
SiN2゜YMgON, YSiO2N, YSi402N
5. YMgSi3ON5° different g3N3 and YMg3Si
02Ns was blended as shown in Table 3, and the mixed powder of each sample was prepared in the same manner as in Example I. This mixed powder was sintered according to the manufacturing conditions of Example 1, and various properties of the obtained sintered body were determined in the same manner as in Example 1, and the results are shown in Table 4.

Below is a blank space Example 3 The 1μm5i3N4 used in Example 1, an yttrium compound, and a magnesium compound were further mixed with compounds of Group IIa of the periodic table and compounds of rare earth elements as shown in Table 5, and the same as in Example 1 was carried out. A mixed powder of each sample was prepared. This mixed powder was sintered according to the manufacturing conditions of Example 1, and the properties of the obtained sintered body are shown in Table 6. The properties of the sintered body were determined in the same manner as in Example 1.

Below is the margin Example 4 1μm Si 3N4 used in Example 1 and the non-stoichiometric compound YNo, 85, Y3 (03N) 0.95 and Mg
5(N2) 0.90 and MgO were blended as shown in Table 7, and the mixed powder of each sample was prepared in the same manner as in Example 1. This mixed powder was sintered under the manufacturing conditions of Example 1. The conditions were about 10% N2 pressure sintering or then Ar gas (H
Table 8 shows the properties of the sintered body obtained by IP treatment and sintering. The properties of the sintered body were determined in the same manner as in Example I.

The following margins were used for the sintered bodies of the present invention, sample number 3 of Example I, sample number 13 of Example 2, sample number 19 of Example 3, and sample number 32 of Example 4. A Y20a-Al 203-S i 3N4 sintered body was sintered in the same manner as in Example 1, and each sintered body was cut into the center and outer periphery, and then molded into CIS standard 5NP432 and 5NCN54 ZTN. A cutting test was conducted under the conditions of (G) and ■.
The results are shown in Table 9.

(6) Cutting test conditions by turning Work material Fe12 (350r%rgX] 500m
yθ Cutting speed 600m/min Depth of cut 1.51nm Feed 0.7mm/rev Cutting time 30m1n Chip shape 5NP432 σ3) Cutting test conditions by Noraine He1'kawa Skin hardening 'fi'jl (HRC45) With black skin (sword) Cutting chain 270 rn/min depth of cut 4.5 πm Daple feed G OOtrrrt1/min
--Feed per sword 0.20 +, 'B+, 7 r
eV chip type: L, I (5NCN54.2TN or less Margin shown in Table 9) The high-strength quantified silicon sintered body of the present invention is compared to Y2O3 in terms of wear resistance by turning and chipping resistance by milling. -Al 20i11-8i3N
4 Superior cutting performance and various characteristics between the center and outer periphery of a sintered body that is sintered into a large shape -
Because there is almost no difference and the quality is very stable, it is suitable for industrial production of heat-resistant construction materials that often have large and complex shapes, and materials for mechanical work that require production in large numbers. It was confirmed that the material and manufacturing method were suitable for this purpose.

Claims (1)

[Claims] 25% by weight and the na group elements of the periodic table (Be1Mg, Ca
. A high-strength silicon nitride sintered body comprising 0.5 to 25% by weight of at least one of oxides, nitrides, and oxynitrides of Sr, Ba, and Ra), and the remainder silicon nitride and unavoidable impurities. (2) At least one of nitrides and oxynitrides of rare earth elements (including Sc, Y, and lanthanide elements) 0.5 to 25
0.5 to 25% by weight of at least one of the oxides, nitrides, and oxynitrides of Group IA elements of the periodic table (Be9Mg, Ca, Sr, Ba, and Ra), and the remaining silicon nitride and unavoidable impurities. 1. A method for producing a high-strength silicon nitride sintered body, which comprises forming a mixed powder into a powder compact or compact and heating and sintering it at 1500°C to 1900°C in a non-oxidizing atmosphere.