JPH04254474A - Production of silicon nitride-based sintered body - Google Patents

Abstract

PURPOSE:To obtain an Si3N4-based sintered body having >=1000MPa strength necessary for a structural material by sintering at a low temp. or <=1,620 deg.C. CONSTITUTION:A uniform powdery mixture of 100 pts.wt., in total, of 97-94wt.% silicon nitride powder as principal starting material and 3-6wt.% sintering aid with 5-80 pts.wt. zirconium oxide is molded, this molded body is heated to 1,350-1,620 deg.C in a nitrogen atmosphere under about 1atm and the pressure of nitrogen is increased to >=1,500atm while holding the molded body at the heating temp.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a silicon nitride sintered body.

0002

[Prior Art] Silicon nitride sintered bodies are expected to be used as structural materials that have both strength and toughness.
A 4-ZrO2-based sintered body has been disclosed (Japanese Patent Application Laid-open No. 1983-
139058). Specifically, ZrO2 20
~40wt%, Al2O3 3~15wt%, ZrO2
and Y2O3 4 to 8 wt% to the total of Y2O3,
The remaining silicon nitride sintered body made of Si3N4 and containing columnar bodies with an aspect ratio of 5 or more was heated for 15 minutes in a non-oxidizing atmosphere.
It is manufactured by sintering at 00 to 1650°C.

0003

[Problems to be Solved by the Invention] Si3N4 is difficult to sinter, but since ZrO2 reacts with Si3N4 at low temperatures, low-temperature sintering becomes possible when ZrO2 is added. However, in the method disclosed in JP-A No. 63-139058, the pressure of 1000 MPa required as a structural material is
A sintered body that exhibits the above strength cannot be obtained. To make it more dense, increasing the sintering temperature causes crystal grains to grow, which also reduces the strength. Therefore, an object of the present invention is to provide a method for manufacturing a silicon nitride sintered body that can be sintered at a low temperature and has a strength of 1000 MPa or more, which is necessary as a structural material.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides that the main raw material powder is silicon nitride, and that the silicon nitride powder contains 97 to 94% by weight and 3 to 6% by weight of a sintering aid. 5 to 80 parts of zirconium oxide per 100 parts by weight
A homogeneous mixed powder containing a weight part of
A silicon nitride sintered body characterized by pre-sintering by heating to a temperature within the range of 50 to 1,620°C, and then main sintering by increasing the pressure to 1,500 atmospheres or more at a temperature within the temperature range. Provides a manufacturing method.

Silicon nitride (Si3N4) as a starting material
has a particle size of 0.6 μm or less, more preferably 0.1 to 0
．． Use one with a diameter of 4 μm. This is because if the particle size of the starting material becomes large, the particle size of the sintered particles becomes large, which causes a decrease in strength. In addition, the purity is 100p total metal impurities.
Use one below pm. If the amount of impurities exceeds this value, the strength will decrease. For similar reasons, zirconium oxide (
ZrO2) has a particle size of 0.1 μm or less, more preferably 0.
．． 02 μm is used. Moreover, purity of 99% or more is used. Further, the sintering aid used has a particle size of 0.5 μm or less and a purity of 99% or more.

[0006] The amount of sintering aid added to the Si3N4 powder is 3 to 6 wt% in total to 97 to 94 wt% of Si3N4.
shall be. If the amount of the sintering aid added is small, densification will not occur and therefore strength will not improve. On the other hand, if the amount of the sintering aid is increased, dense sintering is achieved, but the grain boundary glass phase increases and the strength decreases. Known sintering aids such as Al2O3,
Y2O3, MgO, MgAl2O4, etc. can be used.

In the present invention, 5 to 80 parts by weight of ZrO2 is further added to 100 parts by weight of the Si3N4 powder and sintering aid. The addition of ZrO2 enables dense sintering at low temperatures. If it is less than 5 parts by weight, the effect will be poor, while if it exceeds 40 parts by weight, the strength will decrease. The starting powder can be shaped by conventional methods. That is, typically, the uniform mixed powder is 1000 kg/cm2.
Pressure mold with moderate pressure. Alternatively, pack the molded body in thin rubber, vacuum seal it, and then apply CIP to 3000 kgf/cm2.
Pressurize at a pressure of

[0008] Next, firing is performed, but in the present invention, the firing temperature is set within the range of 1350 to 1620°C.
It is characterized by employing a sintering temperature lower than the normal pressure sintering temperature of 3N4, which is 1700 to 1800°C. That is, conventionally, a pressureless sintering temperature of 1,700 to 1,800°C is used, but at this temperature, the sintered body is not sufficiently densified, and a high-density sintered body reaching 99% of the theoretical density is obtained. I couldn't do that. Therefore, in order to sinter sufficiently at high temperatures,
In order to suppress the thermal decomposition of Si3N4, a method of firing under high pressure (HIP) is used. HI like this
According to the P method, sintering progresses and it is possible to obtain a sintered body with a high density of 99% or more of the theoretical density. However, since it is sintered at a high temperature, the grain size also grows and the strength does not improve as desired. On the other hand, the present inventors first surprisingly found that when using high pressures of 1,500 atmospheres or more, Si3N4 can be sintered even at low temperatures of 1,350 to 1,620 degrees Celsius, which was previously thought not to sinter. Condensation progresses to 99% or more of the theoretical density, and even 99.5%
We have discovered that it is possible to obtain a Si3N4 sintered body with a high density as described above, and that when sintered at low temperatures and high pressures, grain growth is suppressed, making it possible to develop high strength. . In this way, the present invention utilizes high pressure of 1500 atmospheres or more and further adds ZrO2 to achieve 99% reduction even at low temperatures such as 1350°C.
This material was completed after discovering that it can be sintered to a density higher than that and exhibits the high strength required as a structural material.

Therefore, in the present invention, 1350 to 1620
℃, especially below 1600℃, and even below 1500℃, but if the pressure is increased immediately, the pressure of the pores in the sintered body will also increase and the sintered body will not be densified, so it is first prepared under low pressure. Sinter. As long as Si3N4 does not thermally decompose, presintering is preferably performed at a low pressure, but since Si3N4 tends to thermally decompose under reduced pressure, it is generally performed in a N2 atmosphere of 1 atmosphere. However, since it is convenient to perform this preliminary sintering in the HIP equipment,
The actual pressure will be between 1 and 30 atmospheres. In short, the pressure may be lower than the 1,500 atmospheres or more for main sintering, as long as it is around normal pressure. Typically, pre-sintering is performed at around 1 atm of N
2 At a heating rate of about 0.5 to 10℃/min in an atmosphere of 1
The temperature is raised to a temperature within the range of 350 to 1620°C. The temperature increase profile can be varied as desired. One endpoint of pre-sintering is about 90% of the theoretical density.

[0010] When the temperature within the range of 1350 to 1620°C is reached, the pressure is then increased to 1500 atm or more at a rate of increase of about 5 to 20 atm/min, and main sintering is performed while maintaining this pressure. The pressure for main sintering is 1,500 atmospheres or more, typically 1,500 to 2,500 atmospheres. This is because if the pressure is less than 1500 atm, the 1000°C strength of the sintered body decreases. There is no particular upper limit on the high pressure side unless there is a problem with the equipment. In this way, the silicon nitride sintered body sintered at low temperature and high pressure by the method of the present invention is densely sintered while suppressing grain growth, and has a high density of 99% or more of the theoretical density, and even 99.5% or more of the theoretical density. , and exhibits high strength with a four-point bending strength of 1000 MPa or more. The present inventor has conventionally demonstrated that a low-temperature sintered body containing ZrO2 has a relative density of 99% or more and is 1000MP.
I am not aware of any silicon nitride sintered body that exhibits strength greater than a.

[0011]

[Operation] Applying high pressure of 1500 atmospheres or more and ZrO2
By adding Si3N4, it is possible to sinter Si3N4 to a high density of 99% or more at a low temperature of 1620 to 1350°C, suppress grain growth, and reduce the thickness of the grain boundary phase. A sintered body with high density, high strength, and high hardness can be obtained.

Example Si3N4 powder (average particle size 0.2 μm, amount of metal impurities 3
0 ppm, α-ization rate almost 100%), Y2O3 powder (average particle size 0.3 μm, purity 99.9%) was used as the first component of the sintering aid, and MgAl2O4 powder (average particle size 0.3 μm, purity 99.9%) was used as the second component. purity 99.9%), Al2
O3 powder (average particle size 0.12μm, purity 99.9%)
Uniform mixed powder containing any one of the following ingredients: 100
ZrO2 (average particle size 0.02 μm,
(purity 99%) mixed with the composition shown in Table 1 (Si3
N4 ball mill). 200 of these various powders
Pressure molded at a pressure of kg/cm2, vacuum sealed the molded product in thin rubber, and CIPed at a pressure of 3000kg/cm2.
After performing this, the molded body was sintered in a furnace in an N2 atmosphere under the conditions shown in Table 1. The temperature increase rate is 1℃/min,
Under the N2 atmosphere of 0 kg/cm2 until the maximum temperature is reached, and after reaching the maximum temperature, the air flow rate is 15 per minute until the conditions shown in Table 1 are reached.
Pressurization was performed at a pressure increase rate of kg/cm2. Further, the holding time at the maximum temperature was 4 hours. Room temperature of these sintered bodies 4
The point bending strength (JIS R1601) was measured and the results shown in Table 1 were obtained. The relative density of the sintered body is a value obtained by dividing the bulk density determined by the n-butanol substitution method by the theoretical density.

[0013]

[Table 1]

[0014] Comparative Example After molding in the same manner as in the example, the molded product is shown in Table 2.
Sintering was carried out in a furnace in an N2 atmosphere under the conditions shown in Table 2, and the results shown in Table 2 were obtained.

[0015]

[Table 2]

[0016]

[Effects of the Invention] According to the present invention, sintering at a low temperature, which has not conventionally been possible, has become possible, and a sintered body having even finer particles can be obtained. By obtaining a dense sintered body with fine particles, a four-point bending strength value exceeding 1000 MPa is achieved.

Claims (1)

[Claims] Claim 1: The main raw material powder is silicon nitride, and 5 to 8 parts by weight of zirconium oxide is added to 100 parts by weight of a total of 97 to 94 weight % of the silicon nitride powder and 3 to 6 weight % of a sintering aid.
A homogeneous mixed powder to which 0 parts by weight was added was molded, and the molded body was
A silicon nitride sintered body characterized by pre-sintering by heating to a temperature within the range of 350 to 1,620°C, and then main sintering by increasing the pressure to 1,500 atmospheres or more at a temperature within the temperature range. manufacturing method.