WO2021014693A1 - Ceramic matrix composite material - Google Patents

Abstract

A ceramic matrix composite material according to the present invention is provided with: reinforcing fibers; and a matrix which contains SiC and a dispersoid that is composed of a silicide of one or more elements that are selected from among Zr, Yb, Y and Hf, and which is complexed with the reinforcing fibers so as to bind the reinforcing fibers with each other.

Description

Ceramic-based composite material

The following disclosure relates to ceramic-based composite materials applied to equipment that requires high-temperature strength, such as jet engines for aircraft.

Ceramics have extremely high heat resistance, but on the other hand, many ceramics have the drawback of being brittle. In order to overcome brittleness, attempts have been made conventionally to combine ceramic fibers with a base material (matrix) made of other ceramics or metals.

For compounding, methods such as vapor phase impregnation (CVI), liquid phase impregnation (for example, polymer melt impregnation thermal decomposition (PIP)), solid phase impregnation (SPI), and molten metal impregnation (MI) have been proposed. For example, according to the MI method, a woven fabric made of reinforcing fibers such as silicon carbide (SiC) is impregnated with carbon powder, and ingots of silicon are attached to the woven fabric, and the carbon powder and silicon are reacted by melting. A silicon carbide matrix is formed, whereby a silicon carbide-silicon carbide composite material can be produced.

Patent Documents 1 and 2 disclose related technologies.

Japanese Unexamined Patent Publication No. 2013-147366 International Publication No. 2018/047419

The MI method inevitably uses a high temperature, so a rapid reaction can be expected, and since the matrix does not shrink with the reaction, there is no noticeable defect in the product. However, it is a problem that a small amount of unreacted carbon and silicon remain.

According to the studies by the present inventors, when the composite material is exposed to high temperature again, unreacted carbon and silicon are vapor-oxidized and gradually evaporated, and then defects such as fine cavities remain. It became clear that it would be done.

What is disclosed below was created in view of the above problems.

According to one aspect, the ceramic-based composite is one or more elements selected from SiC and Zr, Yb, Y, Hf, which combine with the reinforcing fibers and bond the reinforcing fibers to each other. It comprises a dispersion of the silices of the above, and a matrix containing.

Provided is a ceramic-based composite material that repairs defects in the matrix by itself at high temperatures.

FIG. 1 is a flowchart illustrating a method for manufacturing a ceramic-based composite material according to an embodiment. FIG. 2 is a diagram schematically showing the excitation process. FIG. 3 is a schematic view showing a process in which an ingot impregnates a molded product in a melting / impregnation step. FIG. 4 shows the X-ray diffraction results of the ceramic-based composite material after melting and impregnation. FIG. 5 is a photograph of a cross section of the ceramic-based composite material after melting and impregnation observed with a scanning electron microscope. FIG. 6 is a graph showing the relationship between the volume fraction of ZrC in the slurry and the volume fraction of ZrSi _{2 in} the matrix. FIG. 7 shows the high temperature strength measurement results of the ceramic-based composite material. FIG. 8 shows the fatigue test results of the ceramic-based composite material in the atmosphere at 1400 ° C.

Some exemplary embodiments will be described below with reference to the accompanying drawings.

Suitable uses of the ceramic-based composite material according to the present embodiment are mechanical parts exposed to a high temperature environment such as components of an aircraft jet engine, and examples thereof include turbine blades, combustors, and afterburners. Of course, it can be applied to other uses.

The ceramic-based composite material according to the present embodiment generally consists of reinforcing fibers made of ceramics such as silicon carbide (SiC) and a matrix composited with the reinforcing fibers to bond the reinforcing fibers to each other, and the matrix is SiC and this. It is provided with a dispersion made of a silicified material such as zirconium silicate (ZrSi ₂ ) dispersed in. Examples of the silicified product include ZrSi ₂ as well as ytterbium silicate (YbSi ₂ ), yttrium silicate (YSi ₂ ), and hafnium silicate (HfSi ₂ ). Such a composite material can also be produced by melt-impregnating a molded product containing reinforcing fibers and raw material powder with pure silicon (Si) or a silicon alloy. Here, the raw material powder is mainly composed of SiC and carbon (C), and further contains zirconium carbide (ZrC). Alternatively, or in addition to ZrC, the raw material powder may contain any one or more carbides of ytterbium (Yb), yttrium (Y), and hafnium (Hf).

The matrix formed by impregnating silicon or a silicon alloy bonds the SiC fabrics to each other, thereby forming a ceramic-based composite material. At this time, the reaction between Si and C produces SiC, which occupies a major part of the matrix, but the added ZrC produces ZrSi ₂ . When oxidized at high temperatures, it expands in volume to fill defects and integrate with the matrix, thus restoring the strength of the composite. Yb, Y, and Hf also have similar properties.

In order to form the matrix, any one or more of gas phase impregnation (CVI), liquid phase impregnation (for example, polymer melt impregnation thermal decomposition (PIP)), and solid phase impregnation (SPI) can be further combined.

The manufacturing method of the ceramic-based composite material will be mainly described with reference to FIG.

The raw material fiber such as SiC may be used as it is, or may be coated. Examples of the coating include, but are not limited to, C, BN, and rare earth silicates. For example, the BN coating prevents the propagation of cracks from the matrix to the fibers and increases toughness. Alternatively, the rare earth silicate coating enhances the water vapor oxidation resistance of the fiber. Further, two or more coatings may be applied in layers. As a coating method, any known method such as a vapor phase method or a dip method can be used.

As referred to FIG. 2 in combination with FIG. 1, the raw material fibers may remain as bundles of fibers, but are preferably woven two-dimensionally or three-dimensionally to form a woven fabric 10, and a shape determined according to the application. (Fabric molding step S1). As the raw material fiber, commercially available ones can be applied, and those available under the name of Tyranno fiber ZMI grade (Ube Industries, Ltd.) and those available under the name of Nicalon or Hainalon (NGS Advanced Fiber Co., Ltd.) can be used. .. Further, as the raw material fiber, in addition to silicon carbide (SiC), it can be appropriately selected and contained from the group of other inorganic substances according to the required characteristics.

The raw material powder can be contained in the raw material fiber or the woven fabric 10 in advance, but in the present embodiment, an impregnation step using a liquid phase is used instead of or in addition to this. Therefore, in parallel with the above-mentioned step, the mixture 20 for impregnating the woven fabric 10 is prepared (impregnated liquid preparation step S3). As described above, the mixture 20 is a mixture of SiC and C powder containing ZrC or an equivalent thereof and a medium made of an organic solvent and suspended, and may take the form of a so-called slurry. Alternatively, the medium can include a polymeric raw material that produces a matrix by heating.

As the C powder, any of those produced by vapor phase synthesis, powdered graphite synthesized by firing, natural graphite powder, etc. can be used, and commercially available powders can be used. Can be done. The particle size of the C powder is not particularly limited, but is, for example, an average particle size of 1 μm or more and 10 μm or less, and more preferably an average particle size of about 6 μm. The smaller the particle size, the easier it is to impregnate the fine voids in the woven fabric, and conversely, the larger the particle size, the easier it is to handle.

The organic solvent is not particularly limited, but methanol, ethanol, xylene and the like can be exemplified. When the mixture 20 contains a polymer raw material, an appropriate organic solvent for dissolving the polymer raw material is preferable, and for example, xylene is preferable. Further, if the slurry has an appropriate viscosity, it is easy to suppress the agglutination of the powder and maintain an appropriate dispersed state, and the impregnation of the powder is promoted in the vibration step described later. Therefore, the medium may contain a viscosity modifier.

The above-mentioned raw material powder is added to an organic solvent or an organic solution having an adjusted viscosity, and mixed so as to be sufficiently uniform to form a mixture 20.

The mixture 20 may be allowed to stand for an appropriate period of time to cause precipitation 30 if precipitation occurs (precipitation step S5). The mixture 20 may also be placed under reduced pressure for defoaming.

The woven fabric 10 is buried in the mixture 20 or in the precipitate 30 when the precipitate 30 is formed, and is vibrated from the outside (vibration step S7). The conditions for vibration are not particularly limited, but it is desirable to use an ultrasonic vibration device. An example of an ultrasonic vibration device is one that is generally available under the trade name of Sonoquick (Ultrasonic Engineering Co., Ltd.). With this device, for example, an ultrasonic wave having a vibration frequency of 38 kHz and an output of 250 W is applied to the mixture 20 for 10 minutes. This vibration step can be carried out in the atmosphere under normal temperature and pressure, but may be carried out under reduced pressure or pressurized. By the vibration step, the raw material powder impregnates the gaps between the fibers of the woven fabric 10.

Next, the woven fabric 10 containing the powder is pulled up from the mixture 20 and dried by, for example, exposing it to an appropriate high temperature to obtain the molded product 1 shown in FIG.

Alternatively, instead of or in addition to the above steps, the raw material powder is kneaded in a binder containing an appropriate thermoplastic resin, which is made into a sheet, laminated with the woven fabric 10, and rolled down through a press or a rolling mill. A step of impregnating the woven fabric 10 with the raw material powder together with the binder may be adopted. The binder decomposes and disappears in the melt impregnation step described later. Alternatively, the binder may be eliminated by heating before the melt impregnation step.

In parallel with the above process, an ingot of Si or Si alloy to be melt-impregnated is prepared. The ingot can contain elements that improve oxidation resistance, such as titanium (Ti) and hafnium (Hf), and can also contain elements that exclusively contribute to melting point reduction, such as yttrium (Y). Alternatively, other elements may be included for other purposes. The ingot is formed into an appropriate shape and size in consideration of the shape of the ceramic molded body to be adhered.

As shown in FIG. 3 in combination with FIG. 1, the produced ingot 3 is attached to the ceramic molded body 1 and inserted into the reaction furnace. Preferably, the furnace is evacuated to vacuum or purged with an inert gas such as argon.

The molded body 1 and the ingot 3 are heated in the furnace so that the ingot 3 is melt-impregnated in the molded body 1 (melt impregnation step S9). The heating temperature profile can be appropriately determined. For example, the temperature is raised to the maximum temperature at which the ingot 3 is melted at a heating rate of 10 ° C./min, held for a sufficient time for melt impregnation, and then slowly cooled. It can depend on the profile. In the process of raising the temperature, a step of temporarily stopping the raising of the temperature to maintain the temperature may be included. Further, as the temperature approaches the maximum temperature, the rate of temperature rise may be suppressed to, for example, 5 ° C./min.

Depending on the composition of the ingot 3, the maximum temperature should be high enough to cause its melting and an appropriate temperature to prevent deterioration of the reinforcing fibers. For example, the melting point of the ingot 3 + 100 ° C. may be appropriately determined.

When the melting point is reached, the ingot 3 starts melting and gradually impregnates the molded product 1 as shown by reference numeral 5, as schematically shown in the middle part of FIG. The Si melted in parallel with the impregnation reacts with C in the raw material powder to form SiC, which combines with the SiC in the raw material powder to form a matrix. Carbides such as ZrC in the raw material powder produce silicified products such as ZrSi ₂ , which become dispersions in the matrix. When this process proceeds sufficiently, the matrix fills the voids between the fibers and bonds the fibers to each other, and as schematically shown in the lower part of FIG. 3, the ceramic-based composite material 100 is obtained.

In order to cause a sufficient reaction, it is better to keep it at the maximum temperature for a long time. On the other hand, if it is too long, the reinforcing fibers will deteriorate, so the holding time should be shortened appropriately. The holding time can be determined in consideration of these, and is, for example, 60 to 120 minutes.

Then, after gradually cooling, the ceramic-based composite material 100 is taken out from the furnace. An appropriate cooling rate can be set to avoid a sudden thermal shock.

The obtained ceramic-based composite material is usually subjected to finish processing to make a final product. Further coating may be applied after the finishing process for the purpose of preventing corrosion, improving heat resistance, or preventing the adhesion of foreign substances.

Several tests were conducted to verify the effect of this embodiment.

The raw material powders having each composition listed in Table 1 were prepared, mixed with an organic solvent having an adjusted viscosity (methanol in this case), suspended to form a slurry, and impregnated into a woven fabric made of SiC fibers.

Each sample L-1 to L-6 and H-1 to H-6 were combined with an ingot made of pure Si and heated in vacuum for melt impregnation. The temperature profile was as described above, and the maximum temperature was 1450 ° C. for samples L-1 to L-6 and 1600 ° C. for samples H-1 to H-6. The time to maintain the maximum temperature was 100 minutes in each case.

Each of the obtained ceramic-based composite materials was cut, the phase was identified by X-ray diffraction, the cross section was polished, and the cross section was observed with a scanning electron microscope (SEM).

With reference to FIG. 4, the curves a1 to a6 are the X-ray diffraction results obtained from the samples L-1 to L-6, respectively. Strong peaks derived from SiC were observed in both curves, which are considered to be derived from reinforcing fibers and matrix. Further, since peaks derived from Si are observed in all the curves, it is considered that unreacted Si remains even after melt impregnation. Except for the curves a1 and a2, peaks derived from ZrSi ₂ were observed, which is considered to indicate that ZrC mixed with the raw material powder reacted with Si to generate ZrSi ₂ .

With reference to FIG. 5, each phase can be identified as a contrast difference by SEM observation. In FIG. 5, a relatively dark region is a SiC phase, a relatively bright region is a Si phase, and the brightest region is a ZrSi ₂ phase. A relatively small amount of ZrSi ₂ phase is dispersed in the ground SiC phase, and the rest is a residual Si phase recognized as an unavoidable impurity.

The area ratio of each phase was measured by image analysis, and the relationship between the volume fraction of ZrC in the raw material slurry and the volume fraction of ZrSi ₂ in the obtained matrix was investigated as shown in FIG. In each case, it can be seen that if the volume fraction of ZrC in the raw material slurry is increased, the volume fraction of ZrSi _{2 in} the matrix also tends to increase. However, in the case of heating at 1450 ° C., even if the volume fraction of ZrC in the raw material slurry is increased from 0 to 34% by volume, the volume fraction of ZrSi _{2 in} the matrix tends to be saturated at a level lower than 10% by volume. On the other hand, when heated at 1600 ° C., the volume fraction of ZrSi _{2 in} the matrix does not saturate to a level of at least 34% by volume. That is, from the viewpoint of obtaining a larger volume fraction of ZrSi ₂ , the maximum temperature is preferably higher, and it is possible to produce a matrix in which the dispersion accounts for more than 0% by volume and 35% by volume or less.

With reference to FIG. 7, a high temperature tensile test was performed on each sample. In the figure, the white squares and black squares correspond to the prior art described in the 2005 edition of "Handbook of Ceramic Compositions" (Coleman, Rusla), and the white circles and white triangles. Corresponds to sample L-1, and the black triangle mark corresponds to sample L-3. In the sample L-3 containing ZrSi ₂ in the matrix, the tensile strength is improved at any temperature as compared with other examples.

With reference to FIG. 8, a fatigue test was performed in the air at 1400 ° C. The white circles correspond to the sample L-1, and the black circles correspond to the sample L-3. Sample L-3 containing ZrSi ₂ in the matrix has an improved fatigue limit as compared with Sample L-1 not containing it.

According to the present embodiment, a ceramic-based composite material that repairs defects by itself at a high temperature is obtained, and as is clear from the above-described embodiment, the present embodiment improves its high-temperature strength and high-temperature fatigue limit.

Although some embodiments have been described, it is possible to modify or modify the embodiments based on the above disclosure contents.

Provided is a ceramic-based composite material that repairs defects in the matrix by itself at high temperatures.

Claims (4)

1. Reinforcing fiber and
   A matrix comprising SiC and a dispersion of silices of one or more elements selected from Zr, Yb, Y, Hf, which are composited with the reinforcing fibers to bond the reinforcing fibers to each other.
   Ceramic-based composite material with.
2. The ceramic-based composite material according to claim 1, wherein the dispersion accounts for more than 0% by volume and 35% by volume or less in the matrix.
3. The ceramic-based composite material according to claim 1, wherein the matrix comprises SiC, the dispersion, and unavoidable impurities in the balance.
4. The ceramic-based composite material according to any one of claims 1 to 3, wherein the silicified wood is ZrSi ₂ .

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