JPS59207879A - High tenacity 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-toughness silicon nitride sintered body suitable for heat-resistant grooving materials, machining materials, particularly cutting tools, wear-resistant materials, and corrosion-resistant materials, and a method for producing the same. , it is a compound with strong covalent bonding, and it decomposes and evaporates at high temperatures, and its reactivity is low because the self-diffusion coefficient of the constituent atoms is small. Furthermore, it has low grain boundary energy and surface properties compared to ionic crystals and metal crystals. It is an extremely sinterable and strong material because of its large energy ratio. For this reason, even if silicon nitride is sintered using a pressureless ordinary sintering method, a dense sintered body cannot be obtained, and generally MgO, Y2O3, Al203,
Pressure sintering using reactive sintering or liquid phase sintering with the addition of a sintering aid such as AIN, or hot isostatic pressing (HIP)
) etc. to obtain a dense sintered body. Among these, a silicon nitride sintered body to which a sintering agent consisting of Y2O3, which is an oxide of a rare earth element, and MgO, which is an oxide of an element of group I [a of the periodic table], was published in JP-A-49-113803. is being attempted. In this way, when a green compact or compact made of a mixed powder of silicon nitride to which Y2O3 and MgO are added as sintering aids is sintered experimentally in a small shape, the sintering aid is mainly contained in the Si3N4 grain boundary phase. Since the second phase is relatively uniformly dispersed, no major problems occur, but in order to promote industrialization, when sintering complex or large shapes, Si
Because 3N4 is a material that is difficult to sinter, it has poor reactivity with sintering aids, and because of problems with cooling speed caused by larger sintering furnaces, a second phase containing oxide-based sintering aids is used. is Si
A problem arises in that it is unevenly distributed and segregated in the 3N4 grain boundary phase. In this way, S
There is a problem that it is difficult to commercialize the i3N4 sintered body because the variation in properties within the i3N4 sintered body becomes large and causes a decrease in strength.

The present invention solves the above-mentioned problems and facilitates the reactivity between Si3N4 and the sintering aid, thereby making it possible to use a secondary sintering aid-based product in complex-shaped products or large-sized products.
The object of the present invention is to provide a silicon nitride sintered body and a method for manufacturing the same, in which phase distribution is made uniform within the SiN4 sintered body and the strength, heat resistance, and toughness of the sintered body are improved.

The high toughness silicon nitride sintered body of the present invention contains at least 0.5 to 25% of rare earth element oxides and n of the periodic table.
At least l IN of nitrides and oxynitrides of group a elements
It is a silicon nitride sintered body consisting of 5 to 25% by weight of O, and the remainder silicon nitride and unavoidable impurities. In this way, when a nitrogen-containing compound of the llana group elements of the periodic table is present in the sintering aid, the decomposition temperature is lower than that of the llana group element compounds of the periodic table, and it becomes activated at low temperatures. In addition, since the movement of anion ions is small in this reaction, Si3N4 is partially oxidized (with nitrogen element intervening to aid sintering). At the same time, the sintering aid is uniformly dispersed in the S i 3N4 grain boundaries, promoting sintering, and after sintering, the nitrogen contained in the sintering aid becomes a sintering aid. In order to increase the bonding strength between the second phase formed mainly of Si3N4 and the hard phase of Si3N4, the segregation of the sintering aid, uneven firing, residual pores, and Si3N4 found in the sintering aid made of oxide are used. It is possible to prevent harmful effects such as abnormal growth of particles, and the second phase and S
The internal stress caused by the crystal anisotropy with i3N4 is also reduced, so even products with complex or large shapes can be sintered easily and homogeneously. It becomes easy to produce a body. Among the sintering aids used here, at least one of nitrides and oxynitrides of elements in the group NA of the periodic table is used together with oxides of rare earth elements to uniformly form Si3N4 grain boundaries during the sintering process. Without penetrating and dispersing, a homogeneous second phase mainly composed of the sintering aid is formed surrounding the Si3N4 particles, and the nitrogen in the second phase supplied from the compound of group IIa of the periodic table and the nitrogen in the Si3N4 It contributes to strengthening the bond between Si3N4 and the second phase through interdiffusion with nitrogen, promotes sintering, prevents segregation of the second phase, and thereby contributes to improving the properties of the sintered body. . On the other hand, rare earth element oxides used as sintering aids are 1. It improves the properties of the sintered body, mainly improving high-temperature strength.

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. 5 to 25% by weight and at least 0.5 to 25% by weight of one type of powder of an Ilana group element of the periodic table and an oxynitride,
Alternatively, a composite compound powder consisting of at least one oxide of a rare earth element and at least one nitride or oxynitride of an element in the Na group of the periodic table and Si3N4 powder may be blended as a starting material, and may be blended as starting materials with Si3N4 powder and a composite compound powder consisting of at least an oxide of a rare earth element, at least one of an llana group element of the periodic table and an oxynitride, and Si3N4 powder. When powder is used as a starting material, the structure of the sintered body is prevented from becoming columnar or acicular, and when a nitrogen-containing compound of the Ilana group of the periodic table is used as a sintering aid, the composition of the sintered body is improved. tends to become plate-like and form particles with a small aspect ratio, and sintered bodies with a particle shape with a small aspect ratio have improved heat resistance, so they are subjected to locally severe thermal shock such as with cutting tools. When used for purposes (this is suitable.

Method for manufacturing a high-strength silicon nitride sintered body of the present invention (herein,
It is desirable that the Si3N4 powder used as a starting material be of high purity, but it may contain less than 2% by weight of Al, Fe, etc., which are contained as impurities in the Si3N4 powder.
Or, the surface heat of Si3N4 powder particles can be adsorbed to form Si02. When mixing and pulverizing with a bowl, etc., there will be a lot of waste mixed in from the container and these bowls.
If it is less than 5% by weight, the amount of sintering aid and sintering aid 1.
By adjusting the nitrogen content (1), the various properties of the high-strength silicon nitride sintered body of the present invention can be more fully maintained. For example, Group Ia elements of the periodic table, ■ Group A elements, and ■
Carbides, nitrides, etc. of Group A elements tend to help improve the wear resistance of the sintered body of the present invention.
02. AI and Fe group elements are hard phase 5iaN4
It promotes the interdiffusion reaction between silicon and nitrogen in Si
Oz is S to lower the original decomposition temperature of 343N4.
There is a tendency for the reaction between i3N4 and the sintering aid to occur on the low temperature side, contributing to the promotion of sintering and densification. In addition, oxides, nitrides, and oxynitrides of Li, Na, and other Group Ia elements of the periodic table contribute to improved sintering and densification by promoting liquid phase formation, and then some of them are decomposed and removed. I[a of the periodic table
Since it assists some of the roles of group compounds, it can be added within a range that does not reduce the various properties of the high-strength silicon nitride sintered body of the present invention. Si as the starting material used here
3N4 is α-3i3N4. β-3i3N4゜Amorphous Si3N4 or these Si with different crystal structures
A mixture of 3N4 in any ratio may be used.

Further, the nitrides and oxynitrides of Group Ia elements of the periodic table used as sintering aids may be polymeric compounds or non-stoichiometric compounds. Since these nitrogen-containing compounds are easily oxidized in the atmosphere, it is preferable to handle them in a state filled with an inert gas such as nitrogen gas, but it is even better to handle them in the state of a composite compound.

In the manufacturing method of the present invention, various starting materials are mixed or mixed and pulverized, and the powder is packed in a mixed powder state into a sintering mold to form a powder green compact, or a molded body is formed into a compact, or The compact is pre-sintered at a temperature lower than the post-sintering temperature, or the compact is formed after pre-sintering and is normally sintered in a non-oxidizing atmosphere including vacuum (including pressureless sintering). , high-frequency pressure sintering, current pressure sintering, gas pressure sintering, hot press, etc., or by combining these sintering methods with hydrostatic pressing to densify the sintered body. There are also ways to promote this. The sintering temperature varies depending on the sintering method or blended ingredients, but is between 1500 and 1900.
A sufficiently dense sintered body can be obtained within a temperature range of .

The rare earth elements used here are Sc T Y
+L a r Ce + P r + N d + P
mt Sm+ E u * G d + T b +
D y tHo, Er, Tm, Yb, and Lu are the 177 elements, and group Ia elements of the periodic table are Be, Mg,
Ca, Sr.

It is a general term for six elements: Ba and Ra.

The reason for limiting the numerical value will be explained here.

Low amount of oxides of rare earth elements (0.5% by weight for each type)
If the temperature is less than 2, the high-temperature strength of the second phase formed mainly from the sintering aid will be low, and the strength of the sintered body itself will also decrease.
If the amount exceeds 5% by weight, the amount of S i 3N4 becomes relatively small and the hardness of the sintered body decreases, resulting in a decrease in wear resistance and heat resistance.

If at least one group IIaIa element compound and oxynitride of the periodic table is less than 0.5% by weight, the effect of promoting sintering of Si 3N4 is weak, and if it exceeds 25% by weight, the relative amount of Si 3N4 decreases. 0.5 to 0.5 to l/), and lower silicates tend to remain in the second phase formed mainly from the sintering aid, resulting in a decrease in the hardness and strength of the sintered body. 2
The content was 5% by weight.

Example 1 5isN4 (approximately 40% amorphous S) with an average particle size of 1 μm
i3N4 and α-3i 3N4 and β-3i3N4 mixture)
, 5iaN4 (approximately 95% (!-Si
3N4 and β-3i3N4), with an average particle size of 5 μm,
5i3N4 (approximately 70% α-3i 3N4 and β-8i3N
4) and Y2O3, MgaN2 and Mg4O
Using each powder of N2, each sample was blended in the ratio shown in Table 1 (Table 1), and each blended sample was mixed and ground in a Nutenless container with WC-based cemented carbide balls in a hexane solvent. The obtained mixed powder was filled into a 100mm x 100+++m square carbon mold coated with N powder, and after replacing the inside of the furnace with N2 gas,
Molding pressure of 0'M, temperature of 1700°C to 1850°C, 6
Pressure sintering was performed with a holding time of 0 to 120 minutes. The manufacturing conditions for each sample are shown in Table 1, and the obtained sintered body is
Cut approximately 13X13X5si4 pieces into the outer periphery, and
The characteristics of each cut sample of the 2O3-MgO-S i 3N4 based sintered body were determined and the results are shown in Table 2.

The results shown in Table 2 below show that the high-toughness silicon nitride sintered body of the present invention has high hardness, heat-resistant cylinder qP properties, and fracture toughness (Kic), and is superior to the Y2O3-Mg O-Si 3N4-based sintered body, which is a comparative product. It was confirmed that there was less variation in the properties of the core and outer periphery of the sintered body compared to the solid body, and that even large-sized products could be sintered homogeneously. In the thermal shock test conducted here, the sample was held at each temperature for 2 minutes and then immersed in water at approximately 20℃ (room temperature), and the sample showed the temperature it could withstand without cracking, and the fracture toughness value was 301cg load. It was determined from the length of the crack generated from the Vickers indentation, the size of the indentation, and the Vickers hardness.

Furthermore, when the outer periphery of the trial fitting number +j-2 obtained here was confirmed by Xa diffraction and fluorescence It was considered.

Example 2 I tt m Si3N4 and MgS used in Example 1
iN2゜Y2Mg303N2. Y2O3, Mg5N2
．． Mg4ON2 and other rare earth oxides and periodic table na
Compounds according to Table 3 are used, and the actual flow side 1
A mixed powder of each sample was prepared in the same manner as above. This mixed powder was sintered according to the manufacturing conditions of Example 1, and the opening property of the obtained sintered body was measured in the same manner as in Example 1. The measurement results are shown in Table 4.

Below is the margin Example 3 Sample numbers 2 and 3 of Example 1 and sample number IO of Example 2
The Y2O3-Mg O-S 13N4-based sintered bodies shown in Table 2 were used for comparison in the sintered bodies of the present invention and No. 11, and each uQ body was cut into the center and the outer periphery.
It was molded into IS standard 5NP432 and 5NCN54ZTN and subjected to trowel cutting tests under the following conditions (A) and 0, and the results are shown in Table 5.

(a) Cutting test conditions by turning Work material Fe25 (350ψ Cutting test conditions with milling cutter Work material Case hardened steel (HRc40) Cutting speed with black scale 250 m/min Depth of cut 4.5 rr, rtt Table feed 600 mm/min - Feed per knife 0.20 my'rev Chip shape
5NCN54ZTN As shown in Table 5, the high-toughness silicon nitride sintered body of the present invention exhibits stable performance in both wear resistance by turning and chipping resistance by milling, and is particularly superior to Y2O3-MgO-3i3N4-based sintered body. Because there is almost no difference between the center and the outer periphery of the sintered body, it is suitable for industrial use in heat-resistant structural materials, which often have large and complex shapes, and materials for mechanical work, which require production in large numbers. It was confirmed that the material and manufacturing method are suitable for annual production.

Margin below 45i

Claims (2)

[Claims] (1) 0.5 to 25% by weight of at least one kind of oxide of rare earth elements (including Sc, Y and lanthanide elements) and elements of Group I of the periodic table (Be, Mg, Ca, Sr, Ba and Ra) A high toughness silicon nitride sintered body comprising 0.5 to 25% by weight of at least one of nitrides and oxynitrides, and the remainder silicon nitride and unavoidable impurities. (2) 0.5 to 25% of at least one oxide of rare earth elements (including Sc, Y, and lanthanide elements) and group a elements (Be, Mg, Ca, Sr, Ba, and At least one of nitrides and oxynitrides of Ra) 0.5
High-toughness silicon nitride sintering, characterized in that a mixed powder consisting of ~25% by weight, the remainder silicon nitride, and unavoidable impurities is made into a powder compact or molded body and heated and sintered at 1500°C to 1900°C in a non-oxidizing atmosphere. Method for producing solids.