JPH03232773A - Production of sintered base of silicon nitride base having high toughness and high strength - Google Patents

Abstract

PURPOSE:To obtain a sintered material of Si3N4 base having both high toughness and high strength, exhibiting excellent cutting performances as a cutting tool, by press molding a powder mixture of raw material of Si3N4, ZrN, SiO2 and MgO and burning in a nitrogen atmosphere at two stages by heating under pressure. CONSTITUTION:Mixed powder comprising (A) 1-27wt.% ZrN powder, (B) 0.1-5wt.% SiO2 powder, (C) 1-10wt.% MgO powder and (D) the rest of Si3N4 (preferably consisting essentially of alpha type) powder is molded into pressed powder, primarily sintered in a N2 gas atmosphere at 1,500-2,000 deg.C under 1-50atm. Successively the sintered material is secondarily sintered in a N2 gas atmosphere at 1,700-2,000 deg.C under 100-2,000atm. once or twice continuously or intermittently. By the secondary sintering, ZrO2 is formed as a dispersed phase, needle formation of Si3N4 as a hard layer is promoted to improve toughness and O content in a bonded phase of Mg-Si-O-N or Mg-Si-Zr-O-N is reduced and N content is increased to improve heat resistance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a nitrided material that has high toughness and high strength and exhibits excellent cutting performance especially when applied as a cutting tool that requires these properties. The present invention relates to a method for producing a silicon (hereinafter referred to as Si3N4)-based sintered material.

[Conventional technology]

Conventionally, as a method for producing 513N four-base sintered material, for example, the method described in Japanese Patent Publication No. 60-2034Ei is known.

This conventional method uses 513N4 powder, zirconium oxide (hereinafter referred to as Z r O2) powder, and magnesium oxide (hereinafter referred to as MgO) powder as raw material powders,
These raw material powders are blended into a predetermined composition, mixed under normal conditions, and formed into a green compact.The green compact is then heated at a temperature of 160 in an atmosphere of nitrogen or nitrogen + inert gas.
This is a method for producing an 813N4-based sintered material by sintering under the conditions of 0 to 2100°C and a pressure of 1.5 to 130 atm.

[Problem to be solved by the invention]

However, SiaN4 produced by the above conventional method
Although the base sintered material has high strength, it does not have sufficient toughness, so when it is used as a cutting tool for, for example, wet continuous high-speed cutting of cast iron or rough milling,
Due to lack of toughness, the cutting edge is prone to breakage and chipping, and the current usage life is reached in a relatively short period of time.

[Means to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to develop a SisN4-based sintered material that has both high toughness and high strength. powder, zirconium nitride (hereinafter referred to as ZrN) powder, silicon oxide (hereinafter referred to as Si
Using O2) powder and MgO powder, these raw material powders are blended into a predetermined composition, mixed under normal conditions, and then shaped into a bowl or green compact. , when primary sintering is performed at a relatively low pressure,
In this primary sintering, α-813N4 or slightly acicular β
Mg-5jO-N or Mg-Si- which changes to -8i3N4 and has low viscosity and good wettability as a binder phase
Good sinterability is ensured due to the formation of a Zr-0-N liquid phase, and subsequently, when secondary sintering is performed at a relatively high pressure in the same nitrogen atmosphere, as a dispersed phase. ZrN
A part of ZrN+5IO2+N2→ Z r O2+ S ia N4− ...
(1) ZrN ten bonded phase (primary sintering) ten N2 → Z r O2 + bonded phase (secondary sintering)・(2) Above (1)
The reaction (2) results in ZrO2, and when Zr02 is produced from ZrN, the inherent micropores are absorbed and densified, and β-3iaN4
The needle-like shape of the particles further progresses, and a binder phase with a lower oxygen content and an increased nitrogen content is formed compared to the binder phase formed during the primary sintering. The resulting Si3N4-based sintered material has excellent thermal shock resistance and wear resistance due to the residual ZrN with high thermal conductivity and high hardness, and is chemically stable and has improved oxidation resistance. High toughness is ensured by ZrO2, which contributes to the structure and absorbs fracture energy through martensitic transformation when a crack develops, and β-8i3N4, which has become extremely acicular, and includes high densification. It also has high strength, and in this case, Z'02 has Mg in solid solution (St and N may also be in solid solution) and exhibits cubic or tetragonal crystals. Research results showed that a bonded phase with a high nitrogen content and a low oxygen content contributes to improved heat resistance, and that this bonded phase consists of a glass phase, forsterite phase, or unstedtite phase.

This invention was made based on the above research results, and raw material powders include 513N4 powder, preferably α-Si3N4 powder, ZrN powder, SiO2 powder,
and MgO powder, these raw material powders are blended into a composition of ZrN: 1 to 27%, SiO2: 0.5 to 5%, MgO: 1 to 10%, Si3N4: remainder, in weight percent, After mixing under normal conditions and forming into a green compact, the green compact is heated in a nitrogen (N2) atmosphere at a temperature of 1500 to 20 oo℃.
Primary sintering was carried out under the conditions of pressure = 1 to 50 atm to obtain good sinterability, and then the temperature was 1700 to 2000°C in a N2 atmosphere.
Secondary sintering is performed once or twice at a pressure of 100 to 2000 atmospheres higher than the pressure in the secondary sintering, either continuously following the primary sintering or separately from the primary sintering. In addition, when secondary sintering is performed two or more times, it is performed intermittently separately from the first secondary sintering, and in this secondary sintering, the ZrN to Z
r O2 is generated as a dispersed phase, and at this point, the internal bores are absorbed and densified, further promoting the acicular formation of β-813N4, thereby ensuring high toughness and high strength. MgSi formed by primary sintering
-0-N or Mg -Si -Zr -0-N
This method is characterized by a method for producing a 513N4-based sintered material, which aims to improve heat resistance by reducing the oxygen content and increasing the nitrogen content in the binder phase of the system.

Therefore, the SiaN four-based sintered material produced by the method of the present invention has the following content in volume %: ZrO2: 0.1-20%, ZrN: 0.1-14%, Mg-Si-0-N or Mg -5j -Z
rO-N type bonded phase: 1 to 1596, with the remainder consisting of β-8i3N4 and inevitable impurities.

Next, the reason why the manufacturing conditions are limited as described above in the method of this invention will be explained.

(1) Blend composition (a) ZrN powder ZrN is either present as it is in the primary sintering to ensure good sinterability, or ZrO2 is added to a part of it in the secondary sintering. The remaining ZrN imparts excellent thermal shock resistance and wear resistance to the sintered material, while the generated ZrO has the effect of absorbing fracture energy to improve toughness. If the content is less than 0.1% by weight, the content of ZrO2 in the sintered material will be less than 0.1% by volume, and the content of remaining ZrN will also be less than 0.1% by volume, thereby achieving the desired effect on the above action. On the other hand, if the blending ratio exceeds 27% by weight, Z in the sintered material
r The content of O2 becomes too large, exceeding 20% by volume, and the hardness decreases, making it impossible to secure the desired wear resistance, and at the same time, the content of ZrN also increases, exceeding 14% by volume, Since this causes a decrease in oxidation resistance, the blending ratio was set at 1 to 27% by weight.

(b) SiO2 and MgO powder SIO2 and MgO contain SiO2 present on the surface of the SiN powder during primary sintering, and if necessary reacts with a part of the ZrN powder to create a relative amount of oxygen. Mg -5t -0-N or Mg -Si with high content and low nitrogen content, which results in low viscosity
-Zr-0-N system liquid phase is generated, and this liquid phase promotes good sintering and has the effect of forming a binder phase, and in the secondary sintering, the binder phase is relatively oxygen-containing. The nitrogen content decreases, the nitrogen content increases, and the heat resistance improves, but the blending ratio is SiQ2: o, 1
If the weight is less than 96% and MgO: less than 1% by weight, the content of the binder phase in the sintered material will be less than 1% by volume, making it impossible to secure the desired excellent sinterability. SiO2: 5% by weight and MgO:
If it exceeds 10% by weight, the binder phase content will exceed 15% by volume and the heat resistance of the sintered material will decrease.
: 0.1 to 5% by weight, and MgO: 1 to 10% by weight.

(c) Si3N4 powder Si3N4 has SiO present on the powder surface during primary sintering.
2, other auxiliary components MgO and SiO2, and if necessary, ZrN to form β-8i3N4 particles by dissolution and precipitation in the liquid phase, and the growth of these β-813N4 particles is slight in the primary sintering. However, in secondary sintering, the grains grow into acicular shapes due to the above (+) reaction, significantly improving toughness, and the bores inherent in the sintered material are absorbed and become densified. In this case, in order to ensure uniformity and good sinterability, it is preferable to use fine particles with a narrow particle size distribution.

(2) Primary sintering conditions As mentioned above, in the primary sintering, it is necessary to form a binder phase with low viscosity and relatively high oxygen content and low nitrogen content to promote good sintering. If the temperature is less than 1500°C or the pressure is less than 1 atm, the formation of the binder phase will be insufficient and satisfactory sintering cannot be achieved, while if the pressure exceeds 50 atm, high pressure N2
Gas is trapped inside the sintered body, and this N2 gas not only impairs sintering properties, but also
Densification and βSi3N4 due to bore absorption in secondary sintering
Acicular growth of particles is also suppressed, and 200
Temperatures exceeding 0°C require extensive equipment, so
The conditions are temperature: 1500~2000℃, pressure = 1~
The pressure was set at 50 atm.

(3) Secondary sintering conditions In the secondary sintering, the reactions in (1) and (2) above are carried out to improve the heat resistance of the binder phase by reducing oxygen and increasing nitrogen. rO2 is generated, and the acicularization of β-8i3N4 particles is significantly promoted, and the bores inherent in the sintered body are absorbed and densified, thereby ensuring high toughness and high strength, but at a temperature of 1700℃. Even if the pressure is less than 100 atmospheres, the above (1) and (2)
) reaction was not carried out sufficiently, and as a result, the sintered material could not be given the above-mentioned excellent properties;
Temperatures exceeding 0℃ and pressures exceeding 2000 atm require large-scale equipment and increase costs, so the conditions are: temperature: 1700 to 2000℃, pressure crab 100
~2000 atm.

Although the primary and secondary sintering conditions are determined by the composition, it goes without saying that the pressure under the actual conditions is relatively higher in the secondary sintering than in the primary sintering.

〔Example〕

Next, the method of the present invention will be specifically explained using examples.

As raw material powder, 813N4 (α/β: 97 in volume ratio) has an average particle size within the range of 0.1 to 0.5
/3, oxygen = 2% by weight) powder, ZrN (oxygen = 3
(% by weight) powder, S L 02 powder, MgO powder, and Z r O2 powder were prepared, and these raw material powders were blended into the composition shown in Table 1, and wet mixed for 72 hours in a ball mill. , after drying, plane:
A green compact with dimensions of 30 mm x 30 m 11% thickness =]Ow and a green compact in the shape of a cutting tip according to JIS 5NGN432 were press-formed, and then these green compacts were subjected to the same conditions shown in Table 1. Methods 1 to 4 of the present invention, comparative methods 1 to 8, and conventional methods were carried out by sintering with
Present invention Si N -based sintered materials 1 to 14, comparative Si3
N44-based sintered materials 1 to 8 and conventional SiaN4-based sintered materials were manufactured, respectively.

Next, the component compositions of the various Si3N4-based sintered materials obtained as a result were measured. In this case, the proportions of Zr02 and ZrN were determined by X-ray diffraction.
The intensity of the diffraction 34' peak of ZrO2 and ZrN was measured and calculated based on the measurement results.
The proportion of the Si-Zr-0-N bonded phase was determined by observing the mirror-polished surface using an EPMA (X-ray microanalyzer), and was also determined by theoretical density ratio and Rockwell hardness (A
scale), transverse rupture strength, and fracture toughness values by the 1M method (indentation method) were measured. In addition, using a vertical milling machine, workpiece material: width: 150m + eX length: 300
FC25 perforated square material with dimensions +nm, Cutting speed: 200m / 1ins Depth of cut: 2mm
.

Feed: 0.25mm/rev.

Cutting edge: A wet milling (intermittent) cutting test was conducted on cast iron under the conditions of 0.15mm x -25'', and the cutting time until a breakage occurred on the cutting edge was measured.These results are summarized in Table 2. Indicated.

In addition, Comparative Methods 1 to 8 were all conducted under one of the manufacturing conditions (marked with * in Table 1) or under conditions outside the scope of the present invention.

〔Effect of the invention〕

From the results shown in Tables 1 and 2, it can be seen that methods 1 to 1 of the present invention
Invention Si3N4-based sintered materials 1 to 14 produced in 14
All have a theoretical density ratio of 99% or more, are dense,
The formation of bores is extremely small, and it exhibits superior toughness compared to conventional Si3N4-based sintered materials manufactured by conventional methods, and has high strength and hardness that are equal to or greater than this, so it has excellent strength and hardness. In addition, when used as a cutting tool for cutting under conditions that require particularly high toughness, it exhibits excellent performance over a long period of time.
Comparative 813N four-base sintered material 1 produced by comparative methods 1 to 8
-8, if any of the manufacturing conditions deviates from the scope of the present invention, at least one of the above characteristics will be inferior, and when used as a cutting tool. It is clear that the same also has a short service life.

As described above, according to the method of the present invention, it is possible to produce a Si3N4-based sintered material that has high toughness and strength, and also has excellent thermal shock resistance and wear resistance. For example, when used as a cutting tool that requires these characteristics, it exhibits excellent cutting performance over a long period of time and has industrially useful effects such as a long service life.

Out wish Man Mitsubishi Metals Corporation teenager Reason Man Akira Field sum husband 1 other person

Claims (1)

[Claims] (1) Silicon nitride powder, zirconium nitride powder, silicon oxide powder, and magnesium oxide powder are used as raw material powders, and these raw material powders are divided into the following by weight%: zirconium nitride: 1 to 27%, silicon oxide: 0 .1 to 5%, magnesium oxide: 1 to 10%, and silicon nitride: the remainder, mixed under normal conditions, molded into a compact, and then placed into the compact in a nitrogen atmosphere. , temperature: 1500-2000℃, pressure: 1
Primary sintering is performed under good sintering conditions of ~50 atm, followed by conditions of temperature: 1700~2000°C and pressure: 100~2000 atm higher than the pressure in the primary sintering in a nitrogen atmosphere. Secondary sintering is performed continuously or intermittently one or more times, and in the secondary sintering, zirconium oxide is produced as a dispersed phase, and silicon nitride as a hard phase is made into needles. In order to improve the toughness by further promoting the
- A method for producing a silicon nitride-based sintered material having high toughness and strength, which improves heat resistance by reducing oxygen content and increasing nitrogen content in an N-based binder phase.