JPS6077175A - Manufacture of silicon nitride sintered body - 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 method for producing a silicon nitride green body.

Silicon nitride ceramics have excellent mechanical properties such as strength in high-temperature ranges, and are chemically stable, so they are expected to be used as mechanical structural materials in high-temperature applications.

Silicon nitride (8i8N4) has poor self-sintering properties, so when producing a sintered body, it is common to add a sintering aid to promote sintering and improve the performance of the sintered body. . As the sintering aid, for example, magnesia (MgO), alumina (AA'?OR), yttrium oxide (Y2O2), etc. are used singly or in combination.

From the viewpoint of the sintering mechanism, the finer the sintering aid (and silicon nitride, which is the main raw material), the better. Therefore, when using multiple aids together, it is better to simply add them as a mixture.
It is more advantageous to add them as solid solutions or compounds. From this point of view, instead of using a mixture of magnesia and alumina, magnesia alumina (MgO, A1203
) There have also been reports of attempts to improve sinterability by using spinel t-sintering aids.

The MgO and Al2O8 spinels have excellent sintering accelerating effects, and are effective in improving the relative density of the sintered body by improving sinterability. However, the mechanical properties of the sintered body are not necessarily sufficient, and improvements in toughness and strength are particularly desired.

The present invention has been made in view of the above.

The method of the present invention uses MgO, Al2O8 spinel as a sintering aid in combination with other aids to exhibit the excellent sinterability of the spinel and improve the toughness and strength of the sintered body. Its characteristics are that 3 to 10% by weight of MgO.Al 208 spinel and 0.0% of tungsten carbide are added to the silicon nitride powder bed as auxiliaries.
A mixture containing 01 to 1% by weight is prepared, and this is molded.
It consists in sintering.

The present invention will be explained in detail below.

In the present invention, the purpose of adding MgO,'Al□03 spinel as an auxiliary agent is to obtain good sinterability as described above, and in order to fully exhibit this effect, at least 3% of addition is required. is necessary. As the amount added increases, the sinterability improves, but when the amount exceeds 10% by weight, the effect is small compared to the increase in amount, and furthermore, the high temperature strength, which is a characteristic of nitrogen and silicon carbide, decreases.

Therefore, the upper limit of the amount of spinel added is 10% by weight.

On the other hand, tungsten carbide (WC, W2C) is effective in improving the fracture toughness value (KIC) and strength of the sintered body. When only spinel is added, the grain boundary l in the resulting sintered body is
Due to the formation of this glass phase, sufficient performance in terms of strength cannot be expected, but due to the combined addition of tungsten carbide, the grain boundaries become an A I -Mg-8i-W crystal phase, increasing the fracture toughness value. At the same time, it is thought that the strength will improve.

To ensure the above effects of tungsten carbide, it is necessary to add at least 0.01%. The effect increases as the amount added increases, but since tungsten carbide has a higher specific gravity than silicon nitride or the above-mentioned spinel, if a large amount is added, uniform kneading becomes difficult due to the difference in specific gravity, so the amount added Either the effects commensurate with the results are not achieved or the homogeneity of the composition and performance of the resulting fired crystals is impaired. Therefore, the upper limit of the amount added is set at 1% by weight. WC and W2C have the same effect as tungsten carbide, and either one may be used alone or in combination in any proportion.

In addition, instead of using tungsten carbide prepared as a powder with an appropriate particle size, when mixing silicon nitride and sintering aid in a ball mill, use tungsten carbide carbide balls (for example, WC-W2C-GO
It can be added as fine particles that peel off from the surface of the ball. Tungsten carbide has high hardness and it is difficult to obtain fine particles, but according to this method, it is supplied into the kneaded material as an ultrafine powder during the cross-mixing process, which is advantageous in that the effect as an auxiliary agent is increased.

After mixing the sintering aid specified above with the silicon nitride powder bed and adding an appropriate forming aid if necessary, the mixture is kneaded.
The desired sintered body can be obtained by molding and sintering according to a conventional method. Here, "forming and sintering" refers to cases where molding and sintering are performed in one step, such as a hot press method, a hot isostatic sintering method, an atmospheric pressure sintering method, etc. This term includes the case where the step of molding into a required shape and the step of sintering the molded body are carried out separately. Either process may be carried out under normal conditions; for example, in the hot press method, a pressing force of 200 to 400 kg is used.
Sintering is achieved at a f/d, sintering temperature of 1600-1850°C. In the hot isostatic sintering method, for example, the pressing force is 500~
It is carried out at a temperature of 25 ooktif/d1 from 1600 to 1850°C. In addition, in the pressureless sintering method, a mixed wire to which a forming aid such as methylcellulose is added as necessary together with the above-mentioned aids is molded into a desired shape, and the mixture is molded into a desired shape under an inert atmosphere such as nitrogen gas, for example, at an atmospheric pressure of 1 to 1. Knee c sintering may be performed at 10 kgf/cd and temperature L 600-1850'c.

Next, examples will be described.

Example silicon nitride powder bed (gelatinization rate 90% or more, average particle size 0.9μ
MgO-A 420B Schinel was added as a sintering aid to m), pure water was added in an alumina pot, and the mixture was kneaded with a tungsten carbide cemented carbide ball. Dry the slurry to obtain powder, and press the powder into 200 kg f
After molding with a press pressure of /ct4, seal it with a rubber press.
000 kqf/cd to form a disc-shaped compact (-1).Then, it was held at 175°C for 2 hours in a sintering furnace with a nitrogen gas atmosphere of 1 atm to form a disc-shaped sintered compact (diameter 5 Q XTIII ) was obtained.As a comparative example, mixed wires with different sintering aids were prepared, and sintered bodies were obtained by the same molding and sintering process as above.

Table 1 shows the auxiliary components and blending amounts in each kneaded product, as well as the mechanical properties and relative density of the sintered bodies. The blending amount of tungsten carbide among the auxiliary components is a value calculated from the weight change of the tungsten carbide carbide balls before and after kneading. Further, the fracture toughness value (KIC) was measured by the Knoop indentation method.

The bending strength test is 3 mW x 411M x 4 Q.
Using a specimen of ff1l+, the three-point bending method (span distance 3
Qxym).

As shown in Table 1, the sintered bodies of the examples of the present invention have high relative density due to the sinterability of spinel, and have excellent fracture toughness and strength due to the combined effect of adding tungsten carbide. I understand that. The above example is a pressureless sintering method,
It goes without saying that similar improvement effects can be obtained by pressure sintering methods such as the "hot press" method.

As mentioned above, according to the invention, Mg0-J. A sintered body with excellent fracture toughness and strength can be obtained compared to the case where 03 spinel is added alone. In addition, it has a higher relative density compared to conventionally used Mgo additions, and MgO, A/
The fracture toughness value can be improved to the same level as that of 208 spinel without reducing the relative density, making it very useful as a material for mechanical structures.

Agent Patent Attorney Shinhe Miyazaki Procedural Amendments Director General of the Patent Office Kazuo Wakasugi 1. Indication of the case 1984 Patent Application No. 184157 2. Title of the invention Process for producing silicon nitride bisque viscous material 3. Amendment Patent applicant 4, agent 5, date of amendment order (initiated) i, “Detailed description of the invention” column of the specification to be amended, contents of the amendment

Claims (1)

[Claims] (1) Magnesia is added to silicon nitride powder as a sintering aid.
A method for producing a silicon nitride green body, which comprises molding and sintering a mixture containing 3 to 10% by weight of alumina spinel and 0.01 to 1% by weight of tungsten carbide.