JPS6212670A - Fiber reinforced ceramics - 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 Field of Application of the Invention The present invention relates to high-strength, high-toughness fiber-reinforced ceramics suitable for use as high-temperature structural materials such as gas turbine blades and various engine parts.

[Background of the invention]

Heat-resistant alloys have traditionally been used for parts such as gas turbine blades that are exposed to high temperatures or harsh environments. However, in recent years, in order to improve performance, higher temperature use has been desired, and the use limit of heat-resistant alloys is being reached. Therefore, as materials to replace these heat-resistant alloys, silicon carbide, silicon nitride, and Sialon (trade name of Lucas Corporation), which have high heat resistance, oxidation resistance, and thermal shock resistance, have begun to attract attention as high-temperature structural materials. However, as is well known, these materials have the major drawback of being brittle, and have not been put into full-scale practical use to date.

Methods of compounding and toughening ceramics include: (1) A method of dispersing particles of ceramics, metals, and metal carbon, nitrogen, silicides, etc.

(2) Possible methods include whisker and fiber dispersion. However, in any of the above methods, when metal and metal carbon, nitrogen, and silicide are combined, the toughness at room temperature is improved, but since it contains a metal phase, there is a problem with oxidation resistance at high temperature, and when used at high temperature. The lifespan of the parts is short and impractical, so it has excellent oxidation resistance even at high temperatures.
BACKGROUND ART Research is actively being conducted on composite ceramics in which ceramic particles, whiskers, fibers, etc., which can maintain strength, are dispersed. Whiskers and fibers are particularly promising. In other words, when a crack occurs in ceramics, it is thought that the force to absorb the progress of the crack is greater than that of particle dispersion. An example of using whiskers is JP-A-59-54680. In this case, SiC whiskers are composited into Si3N4, resulting in a ceramic with little strength deterioration even at high temperatures. However, it is impossible to significantly improve the toughness of ceramics using whiskers alone. The main reason is 25vo
If the content exceeds Q%, the whisker dispersion becomes non-uniform, the density decreases significantly and a normal sintered body cannot be obtained, and the diameter of SiC whiskers obtained by the commonly available gas phase method is 0.5 to 1.0 μm. This is because the grain size is very thin and almost the same as the matrix grain size, so it has a weak ability to absorb the progression of one crack. On the other hand, for fibers, metal
metal.

Some combinations of metal and ceramics have been put into practical use. However, ceramics - FRC of ceramics
There are various discussions about this.

The characteristics have not yet been sufficiently improved.

For example, M.W. Lindly, D.J.

Godfrey) Nature229, 192~
193 (1971) reported that Si3N ceramics reinforced with silicon carbide fibers with a diameter of 80 to 100 μm have a relatively large fracture energy, but since Si3N is sintered by a reaction sintering method, Si
3N.

There are pores left inside, and the strength is 127MPa (approximately 13k).
g/a+”), which is small for a ceramic.

In addition, in this case, SiC CVD was applied to the W line as the fiber.
is used, and when used at high temperatures for long periods of time, W and SiC may react, resulting in deterioration of fiber properties.

Also, Bee Knee Bender (B, Mu, Bander)
Proceedings of the 8th Annual Conference of Composites and
Advanced Ceramic Materials (Proc,
of 8th Annual Conference
ofComposites and Advances
d Ceramic Materials) p51
3-529 Jan, 15-18 (1984), ZrO reinforced with SiC fibers with a diameter of 10-12 μm.
Reports on mullite, cordierite, etc. However, the strength of these ceramics is 80 to 180 MPa, which is not sufficient. Also, since the ceramics are oxides, the strength may decrease due to softening at high temperatures, and the SiC fibers used are 130 to 180 MPa.
There is also the problem that characteristics deteriorate due to heat treatment at temperatures above 0'C.

[Purpose of the invention]

An object of the present invention is to significantly improve the toughness of silicon nitride and sialon, and to provide a silicon nitride sintered body and a sialon sintered body that have high strength and excellent toughness even at high temperatures.

[Summary of the invention]

Problems to be Solved by the Invention In order to significantly improve the toughness of ceramics using fibers, compatibility between the ceramics and the fibers becomes a problem. Even if the fiber's elastic modulus and breaking force are large,
When combined, it does not necessarily have the same effect. That is, the effect varies greatly depending on the reactivity of the ceramic and fiber during sintering, the coefficient of thermal expansion, etc. Even if fibers of a substance that reacts with the matrix ceramic during sintering are combined, not only will the effects of the fibers not be exhibited, but the properties of the ceramics themselves will deteriorate. Toughening of ceramics using fibers is achieved by pulling the aligned fibers out of the ceramics with a moderate amount of force.

However, if the surface layer or all of the fiber reacts with the ceramic and becomes integrated, this pull-out effect will not work and the toughness will not improve.

Even non-reactive substances have different coefficients of thermal expansion.

Cracks occur in the ceramics or fibers, making it impossible to obtain a healthy sintered body. Furthermore, even if no cracks occur, the sintered body is highly distorted, and gaps are created between the ceramic and the fibers, which can be pulled out with extremely weak force, making it impossible to expect an improvement in toughness.

Means for Solving the Problems In consideration of the above, the present inventors have studied how to strengthen ceramics using fibers. As mentioned above, S i C and S i3N are used as high temperature structural materials.

and Sialon has heat resistance at high temperatures, thermal shock resistance,
It is promising because of its excellent corrosion resistance. Among these, SiC, which exhibits little strength deterioration even at high temperatures, is particularly promising as a high-temperature material. However, a sintered body cannot be produced unless the sintering temperature is extremely high, such as 2000° C. or higher. Therefore, the heat resistance of the fibers that are composited to make them tougher becomes a problem.

Therefore, the present inventors used 1500 as matrix ceramics.
Si3N4 or Sialon (
It was considered to strengthen S is-xAQxoxNm-x*O<z≦4) with fibers. First SL3N
We investigated the reactivity of 4 and cyclone with various substances and found that C and SiC fibers do not react with the sintered body during sintering. Among these, C fiber has a large difference in thermal expansion coefficient in the long axis direction and short axis direction, and the long axis direction is Si3N
It is about the same as 4, but the short axis direction is very large. Therefore, what expanded during sintering contracts during cooling and becomes S.
SiC fibers are unfavorable because they create gaps between them and the i3N4 or sialon, which reduces the strength and lacks the pull-out force as described above.On the other hand, in the case of SiC fibers, the coefficient of thermal expansion is about the same as that of sintered bodies, It was found to be effective in increasing strength and improving fragility.

In other words, it has been found that when SiC fibers are composited into Si3N or Sialon, pull-out occurs with a moderate force, and as a result, the toughness of Si3N or Sialon increases significantly.

Here, the diameter of the SiC fiber needs to be five times or more the particle diameter of Si3N or Sialon. If the diameter is too large, the fibers will not have sufficient mechanical strength and will break during drawing, resulting in insufficient improvement in toughness.If the diameter is too large, the fibers will burn due to the difference in thermal expansion. Sharpness tends to occur at the interface of the aggregate, which is undesirable.

Specifically, a range of 10 to 200 μm is preferable.

Further, in order for the fiber to be sufficiently drawn out to be effective, its length must be at least 30 times the diameter.

Further, the amount of fiber added is preferably in the range of 20 to 50 voQ% in the case of random orientation.

If there is too little fiber, it will not be effective in improving toughness, and if there is too much fiber, strength will tend to decrease.

Furthermore, the density of the matrix Si3N4 and Sialon is 9.
It is necessary that the sintered body has a content of 5% or more.

When the density of the sintered body is low, the strength of the sintered body decreases and the force required to pull out the fibers becomes extremely small, so that the strength and toughness of the composite sintered body are not sufficient.

From this point of view, reaction sintering such as Si3N4 is not preferable because it tends to leave pores, and a method of sintering Si3N4 or SiAlON together with a sintering aid and fiber is preferable.Furthermore, since the fiber does not shrink during sintering, In order to particularly increase the density of the composite sintered body, it is particularly preferable to use HP or HIP.

The SiC fibers to be added may have short fibers oriented randomly, or long fibers may be arranged one-dimensionally, two-dimensionally, or three-dimensionally. Toughness is particularly improved when the fibers are oriented perpendicular to the direction of crack propagation.

In this case, the fiber arrangement interval is 0 of the fiber diameter.
．． This objective can be achieved by multiplying by 5 to 2 times. In other words, when the fiber arrangement spacing exceeds twice the diameter, the improvement in toughness is slight, and when it becomes less than 0.5 times, fiber pull-out does not occur, and cracks connect between adjacent fibers and occur along the fibers. As the condition progresses, the toughness decreases. From this, the fiber arrangement spacing is
0.5 to 2 times the diameter is effective for improving toughness, especially 1
．． 0 times is desirable.

As a SiC fiber, from the viewpoint of strength and heat resistance, C
It is preferable to use the VD method, and from the viewpoints of light weight, high strength, and heat resistance, it is especially good to use CVD on C fibers.This fiber does not change its properties even when Si3N4 or Sialon is sintered, and The Si3N4 or Sialon composite sintered body to which this fiber is added has high strength up to high temperatures, and its mechanical properties do not change even if it is used for a long time at 1000°C.

In addition, this fiber not only pulls out the interface between the fiber and the sintered body when the sintered body breaks, but also engages in CVD between the C fiber and the sintered body within the fiber.
Since it also causes pull-out at the interface with SiC, it also has the advantage of being particularly effective in improving toughness.

On the other hand, CVD of SiC onto metal fibers such as W is performed.

Although SiC fibers are also known, if they are used at high temperatures for a long time, the metal and SiC will react and the mechanical strength of the SiC fibers will deteriorate, which is not preferable.

When using SiC fibers made by the CVD method, the surface of the fibers may be damaged during processes such as mixing, molding, and firing, and the strength in the sintered body may be lower than its initial strength. This is the opening movement. At this time, the effect of the C film not only keeps the SiC fiber high in strength, but also makes it easier for Si3N4 or Sialon to pull out the SiC fiber, and the composite ceramic exhibits a particularly large tensile strength value.

Note that if the thickness of the C film becomes too thick, the interface with the sintered body tends to peel off due to the difference in thermal expansion, so the film thickness needs to be 1 μm or less. On the other hand, if the C film becomes too thin, its effect will be small.

The SiC fiber has a diameter of 5 to 1
A thick whisker of approximately 0 μm or more may be formed and used.

At this time, the aspect ratio of the whisker needs to be 30 or more, and it is desirable that a C film with a thickness of 0.1 to 1 μm is provided on the surface.

Generally, when a crack occurs in ceramics, it breaks instantly. In order to prevent this, the purpose can be achieved by selecting the matrix ceramic and fiber materials.

[Embodiments of the invention]

Examples of the present invention will be described below.

Example I A predetermined amount of Si3N4 (average particle size: 2 μm) powder and sintering aid powder were weighed and thoroughly mixed in a sintering machine. There are various well-known sintering aids, but as a result of investigation, we found AI2. O,
In this example, it has been confirmed that a suitable amount of Al220. (
Particle size 0.5-1.0 μm) 2% by volume, Yaks (particle size 2
~5 μm) was fixed at 3% by volume, but it has been confirmed that similar results can be obtained within the above addition range. After adding an appropriate amount of a 5% polyvinyl alcohol aqueous solution to this mixed powder, the powder was sized using a 16-mesh sieve.

On the other hand, the SiC fiber is first deposited onto the 35 μm C fiber.
A diameter of 140 μm obtained by CVD of iC was used. Note that Cll1 with a thickness of 1 μm is formed on the surface of this fiber. The length can be cut arbitrarily, but the diameter is 3
Unless it is 0 times or more, there is no sufficient effect. The row spacing is 0.3, 0.5, 1.0, 1.5, 2.
A jig for 0 and 2.5 times alignment was prepared and uniaxially oriented. The spacing in the thickness direction was controlled by placing Si3N4 powder and SiC fibers into the mold alternately and changing the amount of powder.

After that, it was pressurized to 400 kg/+f to a thickness of 6 cm.
A green body with a diameter of 60 f11φ was produced.

This was set in a hot press using a well-known graphite die, and sintered at a maximum heating temperature of 1800° C. under a pressure of 300 kg/cd in nitrogen gas. This sintered body was cut parallel to the SiC fiber to a width of 3 cm x 41 cm. il thickness x36
A test piece of +m+ length was taken. After polishing this, a cut with a width of 0.01 m and a depth of 0.5 m was made in the center at right angles to the fiber, and SENB (Single Ed
A test piece was prepared using the GE Notched Beam) method, and the fracture toughness value was determined to be 1o. Figure 1 shows how the fibers are arranged, and Figure 2 shows the horizontal axis as Ω/d, where d is the diameter of the SiC fiber, and Q is the shortest length occupied by Si'3N4 between the fibers. , c. As is clear from Figure 2, Q/d
The maximum value is shown when Q/d is 1.0, and Q/d is 0.3.
In this case, the amount occupied by fibers is large and it is not effective in improving toughness, but when it is 0.5 or more, the increase of 1° is remarkable.
When /d exceeds 2.0, the amount of fiber is small and the influence on toughness is small. Due to this, Ω/d is 0.5~
A value in the range of 2.0 is preferable, and in particular, a value of 1.0 shows excellent toughness.

Using the same method, the fiber arrangement direction was alternately 90'
A sample was prepared in which the fibers were oriented differently in two dimensions. This sample also had a large square in the range of Q/d=0.5 to 2.0. was gotten.

Example 2 As in Example 1, a green body with Q/d of 1.0 and -axis orientation was produced. Si3N, -8iC fiber-composite sintered bodies having different densities were prepared by changing the sintering conditions, and a fracture toughness value of 1° was determined using the same method as in Example 1. Figure 3 shows the results. Sintered bodies with a relative density of 95% or more have a remarkable improvement in settlement, but lower relative densities have no effect. In other words, in order to increase toughness with fibers, the density of a composite sintered body must be 95%. In addition, in Figure 3, the bending strength of the sample with a relative density of 100% is RT ~ 1100.
It was over 80 kg/m'' in the range of ℃.

Example 3 In order to improve the toughness of ceramics using fibers, it is important that the fibers can be pulled out of the ceramics. If SiC fibers with a C film on the surface are used, pullout will occur easily and the toughness will improve. . Fourth
The figure shows a fracture toughness value of 1° (d/Ω = 1. Si3N with a density of 100%, sintered Cl is significantly increased due to the presence of a carbon film between the sintered body and the fiber. However, those without C film. The improvement is small. In addition, as a result of the fracture surface me, it was found that for fibers coated with C film, pull-out occurred mainly at the interface between Si3N4 and SiC fibers, and for fibers coated with C film, pull-out occurred at the interface between SiC and C fibers. was confirmed. Further, the length of the fiber required to be pulled out must be at least 30 times the diameter.

FIG. 5 shows the relationship between the fracture toughness value of 1° and the aspect ratio, indicating that the pull-out effect is small when the aspect ratio is less than 30. That is, the surface of the SiC fiber is coated with a C film of 1 μm or less, and the aspect ratio is 3.
When 0 or more SiC fibers are composited, Si3
The toughness of N4 or Sialon can be greatly improved.

Example 4 The toughness of Si3N or Sialon made of SiC fibers is particularly high when the fibers are arranged perpendicular to the direction of propagation of a single crack. However, in the present invention, the effect is not lost even if they are mixed randomly. Figure 6 shows the relationship between the amount added and the fracture toughness value of 1o when SiC fibers with an aspect ratio of 30 or more are arranged randomly. 15
Below voQ%, the effect is small, but above 20voQ%, the toughness is greatly improved. When added in an amount of 60 to 4 QvoQ%, the contribution to toughness is small. Therefore, the appropriate amount for random compounding is 20 to 50 VOQ%, and 30 to 4 Qvou% is particularly effective.

At this time, the 1 bending strength was also 50 kg/m'' or more.

Example 5 Si3N with an average particle size of 1.5 pm, powder with a diameter of 5. o.

10.50, 140, 200 and 300 μm SiC
fibers (CVDL on all C fibers, 0.1 on the surface
A composite sintered body was prepared in the same manner as in Example 1, and its fracture toughness value was determined to be 1°. Note that since it is impossible to arrange fibers of 10 μm or less individually, more than 10 fibers were arranged together. The results are shown in Table 1.

Si3N4 average particle size 2. Opm From these results, the toughness cannot be improved unless the particle size of the matrix is 5 times or more, and the effect is lost even if the fiber diameter exceeds 200 μm.

In order to improve the toughness with fibers.

The diameter is 5 to 100 times the particle size of the matrix (10 to 20
0 μm) is good.

Example 6 A test was carried out in the same manner as in Example 1 using Sialon as the matrix. That is, using SiC fiber with a diameter of 140 μm in SiAlON having the composition of Si, AQON,
A Sialon-8iC fiber composite sintered body was produced.

The measurement results of 6 are shown in Table 2, and the matrix is Si3
Similar to the case of N4, it showed excellent fracture toughness values.

The single bending strength was also a large value of 10 kg/■8 or more.

Table 2 (Matrix sialon composition Si, AQON,) Example 7 Using the HI P method (in Ar, 2000 atm, 1800°C), the tip was formed with a structure in which SiC fibers were arranged two-dimensionally as shown in Figure 7. Sialon (S L s, S
A gas turbine blade manufactured by AQ6,@06,sN7,5) was prototyped. This blade showed extremely high reliability, with no damage observed during rotation tests in gas at a temperature of 1350°C (100,000 rpm) and thermal shock tests in which hot gas and air were alternately sent. .

〔Effect of the invention〕

According to the present invention, SiC is added to 513N4 or Sialon.
By combining fibers, fiber-reinforced ceramics with high strength, especially high toughness values at high temperatures can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram schematically representing the fiber spacing, Figure 2 is a curve diagram showing the relationship between the fracture toughness value and fiber spacing of a Si3N, -8iC fiber-composite sintered body, and Figure 3 is a diagram showing the relationship between the fiber spacing and the fracture toughness of the composite sintered body. A curve diagram showing the relationship between the relative density of the sintered body and the fracture toughness value. Figure 4 is a comparison diagram of the fracture toughness value with and without C film on the fiber surface. Figure 5 is a diagram showing the relationship between the aspect ratio and the fracture toughness value. FIG. 6 is a curve diagram showing the relationship between the amount of fiber added and the fracture toughness value, and FIG. 7 is a perspective view of a gas turbine blade made using the sintered body of the present invention.

Claims (1)

[Claims] 1. Si_3N_4 or Si_6_ with a density of 95% or more
−_zAl_zO_zN_3_-_z (However, 0<z≦4
) A fiber-reinforced ceramic characterized in that the ceramic matrix contains SiC fibers having a particle diameter of 5 times or more and a fiber length of 30 times or more of the diameter of the ceramic matrix. 2. The fiber-reinforced ceramic according to claim 1, wherein the SiC fibers are oriented one-dimensionally, two-dimensionally, or three-dimensionally. 3. In claim 1 or 2, the above S
A fiber-reinforced ceramic characterized in that the inter-fiber spacing (l) of iC fibers is l/d of 0.5 to 2 (where d=fiber diameter). 4. In any one of claims 1 to 3, the SiC fiber has C fiber as its core and S on it.
A fiber-reinforced ceramic characterized by having an iC layer. 5. The fiber-reinforced ceramic according to any one of claims 1 to 4, wherein the SiC fiber has a C coating layer on its surface. 6. In claim 1 or 2, the fibers are randomly oriented and the content is 20 to 5.
Fiber-reinforced ceramics characterized by being 0 vol%.