JPS5957965A - Manufacture of fiber reinforced silicon nitride sintered bo-dy - 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 (a) Background Art The present invention relates to a method for producing a heat-resistant heptadramic sintered body, particularly a silicon nitride sintered body.

Among heat-resistant ceramics, silicon nitride has excellent +11 heat resistance, thermal shock resistance, and corrosion resistance, so it is suitable for use in turbines, diesel engines, etc. used in high-temperature gases.

It is a promising material for parts and is being developed with great interest.

When the one-side thermal ceramic sintered body is used in these structural phases, physical and chemical stability at high temperatures is required. In particular, high mechanical properties at high temperatures are desired.

However, silicon nitride and silicon carbide are both covalent compounds and are considered difficult to read binding materials.

Therefore, silicon nitride and silicon carbide are not sintered alone, but are sintered by adding several percent to several tens of percent of a sintering aid to form a low melting point compound.

For example, in the case of silicon nitride, MgO・A is used as a sintering aid.
/, -z03. A sintered body with a density close to the theoretical density is obtained by adding 5 to 20% of Yp+Oa or the like alone or in combination and hot pressing.

However, the sintered body thus obtained has insufficient strength at high temperatures.

That is, while MgO, AL203, Y2O5, etc. added as a sintering aid have the advantage of forming a low melting point compound and promoting sintering as described above, on the other hand,
This low melting point compound causes a decrease in strength at high temperatures.

For this reason, efforts are being made to minimize the type and amount of sintering aids used during the production of silicon nitride and silicon carbide sintered bodies, but the drawback of reduced strength at high temperatures still remains. The current situation is that it has not been resolved.

In view of the above points, the present inventors conducted extensive studies to obtain a silicon nitride sintered body that has excellent heat-reducing properties and high-temperature strength.
We have previously discovered and applied for a method for producing a silicon nitride sintered body reinforced with fibrous whiskers.

(Patent application No. 171844= and Patent application No. 17184-2)
(No. 293) Whiskers are single-crystal fibers that are generally called cat's whiskers, and the strength of these fibers is said to be several tens to hundreds of times stronger than polycrystalline materials.

Furthermore, since the whisker is a single crystal, there is no strength deterioration at high temperatures, and it is strengthened by the entanglement of single crystal fibers, and even if it contains a sintering aid, the high temperature strength can be improved.

” - The application filed by the inventors provides an industrially easy manufacturing method for dispersing these whiskers in a sintered body of silicon nitride, and provides a sintered product with high strength, particularly with little loss of strength even at high temperatures. It's what the body gets.

However, in the conventional manufacturing method, whiskers are mixed during powder mixing and then press-molded, which causes the whiskers to be mixed unevenly or aligned only in a specific direction, resulting in the strength of the sintered body varying depending on the direction. was there.

(b) Disclosure of the Invention The present invention provides a method for producing a silicon nitride sintered body that can eliminate all of the various drawbacks and problems described in "--" in addition to the characteristics of silicon nitride sintered bodies produced by conventional methods. The present invention relates to an improvement in the manufacturing method of silicon nitride whisker-reinforced silicon nitride sintered bodies.

To explain the present invention in detail below, a mixed powder of silicon nitride, a whisker-forming material that becomes whiskers through heat treatment, a whisker-formation accelerator, and a sintering aid is heat-treated to form whiskers in a non-oxidizing atmosphere having a partial pressure of nitrogen gas. Then,
4. Press molding into a predetermined shape and then sintering in a non-oxidizing atmosphere. This is a manufacturing method with the following characteristics.

The conventional method of mixing granular raw material powders and sintering aids with fibrous whiskers has the disadvantage that it is difficult to mix uniformly and in large quantities. Furthermore, a method is adopted in which the whisker-forming phase, which becomes whiskers through heat treatment, is mixed in granular form and then sintered after the whisker-forming heat treatment, which eliminates the drawbacks of the conventional method. However, it has the disadvantage of being non-uniform. In the present invention, in order to uniformly make the whiskers the optimum length, a whisker generation accelerator is mixed at the same time as the raw materials are mixed.

By this addition, the whisker length can be made uniform and the strength of the sintered body and its distribution can be improved.

That is, whisker generation It that becomes whiskers by granular raw material powder, sintering aid, and heat treatment.

Further, a whisker generation promoter is mixed, and the powder is heated under a non-oxidizing atmosphere with a partial pressure of nitrogen gas to give 14.O0=1.
After heat treatment at a temperature of 650°C, fibrous whiskers are uniformly generated in the powder using a whisker-forming material and a generation accelerator, and then formed into a predetermined shape, and then sintered in a non-oxidizing atmosphere. This is a method for producing fiber-strength silicon nitride (reinforced silicon nitride) L aggregates by performing the following steps.

In the present invention, the raw material powder and sintering aid are not particularly limited, and may have a generally known crystal structure and chemical composition.

The whisker generating material to be mixed is one that generates gaseous silicon oxide in a non-oxidizing atmosphere having a partial pressure of nitrogen gas, and the inventors have selected an inorganic compound containing 51 such as metal Si, SiO, 5iOz, etc. Organic compounds containing Si such as silicone rubber and silicone resin, as well as amorphous Si3N,
It has been found that any combination of one or more of powder, a mixture of 5102 and carbon or Si, etc. can have similar effects.

The whisker formation promoter of the present invention includes Fe and Ni.

One or more metals or alloys of C(1, Cr, V, Ti, Ta, W, Mo) are added in an amount of 0.01 to 5 wt%.

The addition of these metals and alloys generates a liquid phase containing Si and Nz in solid solution at the whisker generation treatment temperature, and
Promotes the growth of Na whiskers and increases the concentration of about ・1・O~5 (+
Whiskers with a uniform length of 1 tm are produced in the powder. Furthermore, by manipulating the amount, type, and generation treatment conditions of the whisker generation accelerator, even longer whiskers can be generated.

The present invention will be explained in detail below with reference to Examples.

Example Crystalline Si3N of the types shown in Table 1, + powder, sintering aid, whisker forming material, and whisker accelerator were mixed and ground in a ball mill for 50 hours. Add this mixed powder to 14.5
After heat treatment was performed at 0'C in a nitrogen atmosphere of 400 Torr for 2 hours, it was molded at a pressure of 1.5t/C♂ using a mold of a predetermined shape. The molded body was placed in a nitrogen atmosphere of 1 atm.
The temperature was raised to 1750°C and held for 1 hour to perform densification and sintering.

A test piece measuring 4 mm x 3 mm x 4 O mm was cut out from the sintered body, transverse rupture strength was measured over a 30 mm span, and the fracture surface was observed. The measurement and observation results are summarized in Table 1.

Including whisker generation phase for comparison! Those that do not contain whisker-forming materials, but those that are not according to the present invention, such as those that do not contain the formation accelerator shown in Table 1, were similarly heat-treated in a nitrogen atmosphere at 14.50°C, and sintered after forming. Those are shown in Table 1 as Nos. ]~8.10~12.

In the case of the method of the present invention, the transverse rupture strength at room temperature was improved, and the high temperature strength at 1200°C was also improved by 11'', indicating that the effect of the present invention is high. If the content of the whisker-generating material is less than 196% or more than 75%, the effect will be small, so it is judged that a content of 1% or more and 75% or less is effective.

If the whisker formation promoter is less than 0.01%, the effect will be small, and if it exceeds 5%, the amount of metal will increase and the high temperature characteristics will deteriorate.
5% or less is appropriate.

The whisker generation heat treatment temperature range is 14.00°C.
Below this, the whisker generation speed becomes extremely slow and is not practical. Furthermore, since densification and sintering proceed at temperatures above 1650°C, densification progresses during whisker growth, resulting in little effect. Therefore, over 1400°C16
A range of 14.50°C to 1550°C with a temperature below 50°C is best.

Transverse rupture strength i1 of the sample of the present invention! When the fracture surface after II treatment was observed under a microscope, the diameter was about ]/7+11 mm and the length was 40 μm.
Wisnono fibers with uniform lengths of m to 507 tm were intertwined three-dimensionally. rJh, kll: Enhanced 111J
I was able to confirm that C was built.

Claims (1)

[Scope of Claims] (+) In the method of manufacturing a silicon nitride sintered body in which silicon nitride whiskers are dispersed, a whisker generating material, a whisker generation promoting agent, and a sintering aid that become whiskers by heat treatment with silicon nitride powder After mixing these, they are subjected to whisker growth heat treatment in a non-oxidizing atmosphere with nitrogen gas partial pressure, then molded into a predetermined shape, and the molded body is densified and sintered in a non-oxidizing atmosphere. A method for manufacturing a fiber-reinforced silicon nitride sintered body, which is characterized by being fused. (2. Whisker generation according to claim 1)
Fiber-reinforced nitriding characterized in that 4 is a combination of Si or an inorganic compound containing Si, an organic compound containing Si, an amorphous silicon nitride powder, a mixture of Sing and carbon or Si, or a combination of these. Method for manufacturing silicon sintered bodies. (3) Particularly ii'l' The whisker generation promoting material according to claim 1 is Fe, Ni, Co, Cr, V, Ti.
, Ta, W, MO, or an alloy thereof. (4) The whisker generation heat treatment temperature described in claim 1 is 14. A method for producing a fiber-reinforced silicon nitride sintered body, characterized in that the temperature is O0°C to 1650°C. (5) In the manufacturing method according to claim 1, the whisker-generating material is 1% by weight or more and 75% by weight or less,
Whisker generation accelerator is 0.01% by weight or more”-5%
A method for producing a fiber-reinforced silicon nitride sintered body, characterized by the following.