JP3061573B2 - Manufacturing method of multilayer ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of ceramics which are excellent in mechanical properties such as strength, and which are excellent in oxidation resistance and corrosion resistance at high temperatures, and which are suitable as a mechanical component material and a structural material.

[0002]

2. Description of the Related Art Silicon carbide (SiC) ceramics have excellent heat resistance, thermal shock resistance and creep resistance, and have an oxide film formed on the surface in an oxidizing atmosphere to act as a natural protective film. Also excellent in chemical properties. For this reason,
It is expected to be used as a material for mechanical parts such as gas turbines and automobile engines. However, in a high-temperature environment exceeding 1500 ° C., since the ambient temperature is close to the melting point of silicon oxide, the effect as a protective film can no longer be expected, and deterioration due to the progress of oxidation cannot be avoided.

[0003]

Therefore, it is anticipated that forming an oxide layer which can act as a protective film even in a high temperature environment on the surface of silicon carbide ceramics will result in a mechanical component material that can withstand use at high temperatures. You.

However, it is usually difficult to join / integrate non-oxide ceramics and oxide ceramics, and even if they are joined, they are separated immediately. Also, even in the case of joining, the heat treatment accompanying the integration operation causes tensile or compressive residual stress to occur in the cooling process due to the difference in physical properties between the two, especially the difference in the coefficient of thermal expansion, and the cracks Often occurs. Therefore, it is difficult to integrate the silicon carbide ceramic and the oxide layer by the conventional method.

The present invention has been made in order to solve such problems of the prior art, and provides a mechanical component material which has excellent strength and heat resistance and can sufficiently cope with oxidation and corrosion at high temperatures. It is intended for.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have conducted intensive studies, and as a result, a ceramic having silicon carbide as a main component and a layer of a silicate compound of a rare earth element have been integrated. Laminated ceramics can be suitably manufactured,
They have found that they can sufficiently cope with use at high temperatures, and have invented a method for producing a laminated ceramic of the present invention.

[0007] The method for producing a laminated ceramic of the present invention comprises:
In the first layer containing silicon carbide, a rare earth oxide represented by a general formula: RE ₂ O ₃ (wherein RE represents a rare earth element selected from the group consisting of Y, Yb, Er and Dy) The second layer is laminated to form a laminate, and the laminate is heated in an oxidizing atmosphere to oxidize the silicon carbide of the first layer to produce silicon oxide and to form a rare earth element of the second layer. From the oxide and the silicon oxide, a general formula: RE ₂ SiO ₅ (R in the formula)
E represents a rare earth element selected from the group consisting of Y, Yb, Er and Dy).

[0008] The formation of the laminate is performed by charging the first layer into a rare earth oxide dispersion and attaching the rare earth oxide to the surface of the first layer by electrophoresis. Heating is performed at 1400-1700 ° C.

Further, the first layer is a sintered body layer obtained by molding and sintering a powder containing silicon carbide, and the rare earth silicate compound layer having a thickness of 100 μm or less is formed by heating the laminated body. By the above method of forming a layer containing a rare earth silicate compound and a rare earth oxide, a layer of a rare earth silicate compound is favorably formed on the surface of silicon carbide, and oxidation of silicon carbide is prevented by the rare earth silicate compound. As a result, the obtained laminated ceramic has both high-temperature strength, oxidation resistance, and corrosion resistance. In addition, since silicon carbide and a silicate compound of a rare earth element have similar thermal expansion coefficients, the residual stress generated between the layers is low, cracks are prevented, and the mechanical parts such as gas turbines and automobile engines are exposed to high temperatures. It has the performance to withstand use.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Silicon carbide is a ceramic excellent in high-temperature strength, and if it is improved in oxidation resistance and corrosion resistance at high temperatures, it is a suitable material for mechanical parts. This improvement is realized by coating the surface of silicon carbide with an oxide ceramic having oxidation resistance and corrosion resistance. As an oxide for this purpose, a silicate compound of a rare earth element which is a composite oxide:
RE ₂ SiO ₅ (where RE is Y, Yb, Er and D
The present inventors have found that a rare earth element selected from the group consisting of y is suitable. The above-mentioned rare earth silicate compound: RE ₂ SiO ₅ (hereinafter simply referred to as silicate in the present application) has excellent heat resistance, has a thermal expansion coefficient close to that of silicon carbide, and is similar in thermal expansion behavior. However, the silicon carbide and the silicate are not joined even if they are brought into contact and heated, and they are not integrated by simultaneous sintering. That is, it is not possible to obtain a laminate in which these are integrated by simply performing the heat treatment.

According to the present invention, a silicate is produced by utilizing a reaction between a rare earth oxide and silicon oxide (SiO ₂ ) in order to produce a laminated ceramic in which silicon carbide and silicate are joined. After forming the rare earth oxide layer on the surface, the silicon carbide surface is oxidized to generate silicon oxide, and thereby a layer containing silicate is formed by a reaction between the generated silicon oxide and the rare earth oxide.
As a result, the two layers are joined with sufficient strength, and a laminated ceramic that can withstand use at high temperatures without a problem of residual stress caused by a difference in thermal expansion behavior can be obtained. Although there are many kinds of rare earth oxides, a general formula: RE ₂ O ₃ (wherein RE
Represents a rare earth element selected from the group consisting of Y, Yb, Er and Dy).

Hereinafter, the present invention will be described in more detail.

First, in order to form a silicate layer on the surface of a silicon carbide sintered body manufactured according to a conventional method, a rare earth oxide layer is laminated and coated on the silicon carbide sintered body. The thickness of the laminated rare earth oxide layer must be such that oxygen in the atmosphere can reach the silicon carbide layer in order to oxidize the internal silicon carbide through the rare earth oxide layer in the next stage. is there. The method for laminating the rare-earth oxide layer is not particularly limited, and can be applied by applying a paste of a rare-earth oxide. Particularly effective in the present invention is a lamination method utilizing an electrophoretic effect. The lamination by electrophoresis is a method capable of suitably forming a thin layer having a thickness of several hundred μm or less, and the oxidation of silicon carbide sufficiently proceeds through the rare earth oxide layer formed thereby. Since silicon carbide ceramics is conductive, lamination using electrophoresis can be performed.

As shown in FIG. 1, powder P of rare earth oxide
When the electrodes 3 and 5 are put into a dispersion liquid 1 in which ethanol is dispersed in ethanol, and a voltage is applied by a DC power supply 7,
, The rare earth oxide powder P moves and adheres. Therefore,
Lamination of the rare earth oxide by electrophoresis is performed by charging the silicon carbide sintered body into a dispersion liquid in which the rare earth oxide powder is dispersed, and applying a negative voltage to the silicon carbide sintered body.
As an apparatus for actually performing this, for example, the apparatus shown in FIG. This apparatus 10 includes an electrodeposition tank 11, an annular electrode 13, and a DC power supply 15, and is provided with rare earth oxide powder P.
Is dispersed in a dispersion medium such as alcohol, and the dispersion liquid 17 is charged into the electrodeposition tank 11. The ring electrode 13 connected to the anode of the DC power supply 15 is immersed in the dispersion liquid 17, and a voltage is applied while the silicon carbide sintered body S connected to the cathode of the DC power supply 15 is placed at the center of the ring electrode 13. As a result, the rare earth oxide powder P is attracted to the silicon carbide sintered body S and adheres to the surface, and the rare earth oxide layer is laminated. This is dried to obtain a laminate. Depending on the dispersion medium to be used, a rare earth oxide may be laminated on the positive electrode side, so that the sign of the applied voltage is appropriately set in consideration of the dispersion medium and the like.

In the lamination by electrophoresis, the silicon carbide sintered body as the base does not need to be flat, and the rare earth oxide can be uniformly laminated even in a complicated shape. It is possible to use a silicon carbide sintered body.
In addition, the time required for lamination is short, and the operation is simple.

The thickness of the rare earth oxide layer laminated on the silicon carbide sintered body may be at least 100 μm or more. If the laminated rare earth oxide layer is excessively thick, cracks occur during drying. It is desirable to laminate to a thickness. Approximately 10 to 1
It is preferable to control the lamination of rare earth oxides so that a silicate layer having a thickness of 00 μm can be formed.

The laminate in which the rare earth oxide is laminated on the silicon carbide sintered body is subjected to an oxidation treatment. The condition of the oxidation treatment may be a condition under which silicon carbide forms a silicon oxide film, and specifically, heating may be performed at 1400 to 1700 ° C. in an oxidizing atmosphere for at least one hour. At a temperature lower than 1400 ° C., oxidation of silicon carbide hardly proceeds. If the temperature exceeds 1700 ° C., the silicon carbide is excessively vigorously oxidized to a foamed state, and a dense silicate film is not formed. By this oxidation treatment, oxidation of silicon carbide in silicon carbide sintered body S on which rare earth oxide P is laminated as shown in FIG. 3A progresses, and as shown in FIG. 3B, rare earth oxide P And the silicon oxide 19 is mixed in the stacking. In this state, the silicon oxide 19 reacts with the rare earth oxide P,
As shown in FIG. 3C, the general formula: RE ₂ SiO ₅
(Wherein RE in the formula represents a rare earth element selected from the group consisting of Y, Yb, Er and Dy), and a silicate-containing layer 21 represented by the formula (1) is generated. The thickness of the generated silicate-containing layer 21 increases as the time for performing the oxidation treatment increases, and increases as the heating temperature increases. The silicate-containing layer may be a single layer of silicate or a layer of a mixture of silicate and rare earth oxide, depending on the conditions of the oxidation treatment and the state of the laminate. When the rare earth oxide layer laminated on the silicon carbide sintered body is thin, the rare earth oxide layer does not remain on the surface of the laminated ceramic after the oxidation treatment, and a mixture layer of silicate and rare earth oxide is formed, and the laminated rare earth oxide is formed. When the thickness of the oxide layer is greater than or equal to the predetermined thickness, the laminated ceramic after the oxidation treatment has a rare earth oxide layer on the surface and a layer of substantially silicate alone. The thickness of the silicate-containing layer is at least 10 μm
If it is on the order, it can play a role of protecting the silicon carbide sintered body, and it is preferably about 10 to 100 μm. The layer of the rare earth oxide P remaining on the surface is a silicate-containing layer 2
The silicon carbide sintered body coated with silicate can be obtained by removing the layer of the rare earth oxide remaining after the oxidation treatment because it is easy to peel off from silicon oxide. When the oxidation treatment conditions and the like are adjusted so that unreacted rare earth oxides remain, when the multilayer ceramic obtained after the oxidation treatment is placed in a high-temperature environment, the oxidation newly generated along with the further oxidation of silicon carbide is performed. Since the generation of silicate by silicon proceeds, an effect such as self-repair can be obtained.

In the multilayer ceramic obtained by the above-described oxidation treatment, the silicon carbide layer and the silicate layer are closely bonded, and have the same strength as that of the integrated material. This is considered to be because the silicate-containing layer to be formed is formed by oxidation of silicon carbide, so that the interface between the two layers is continuously bonded without breaking, resulting in a stable bond. Further, since the thickness of the coating layer is small, the material has both heat resistance and oxidation resistance without substantially impairing the thermal shock resistance and creep resistance of silicon carbide. Silicon carbide and silicate have very similar thermal expansion changes,
Even if it is cooled, cracks are hardly generated, and it can withstand use at a high temperature. The silicate-containing layer of the multilayer ceramic obtained by the production method according to the present invention may be further subjected to a coating treatment with a heat-resistant oxide.

In the present invention, in producing a silicon carbide sintered body, additives such as sintering aids, lubricants and the like which are usually used can be used according to a general method. Even if it is a composite material using a reinforcing material or the like, a suitable laminated ceramic can be obtained by applying the method of the present invention.

The laminated ceramics joined by the heat treatment is a stable laminate having little residual stress due to a difference in thermal expansion coefficient. However, in order to prevent the occurrence of cracks due to a rapid temperature change, the heat treatment is performed. The subsequent cooling is preferably performed gently.

[0021]

EXAMPLES Examples of the present invention will be described below in more detail with reference to experimental results.

(Operation 1) Y ₂ O ₃ powder was added to ethanol at a ratio of 15% by weight and mixed in a ball mill for 24 hours to prepare a slurry dispersion. Using the configuration of FIG. 1, a dispersion liquid of Y ₂ O ₃ is charged into the apparatus, and the electrode 3 of the silicon carbide sintered body and the electrode 5 of the carbon plate are placed in the dispersion liquid at an interval of 1.5 cm. Then, a voltage of 50 V was applied from the DC power supply 7 for 10 seconds. After applying the voltage, the electrode 3 was taken out, and the thickness of the Y ₂ O ₃ powder covering the surface of the electrode 3 was measured. Thereafter, the electrode 3 coated with Y ₂ O ₃ is placed on an alumina flooring plate and heated at 1550 ° C. for 24 hours in the air to promote oxidation of silicon carbide, thereby forming a silicate layer and forming a laminated ceramic. Obtained. The thickness of the silicate layer was measured by observing the laminated ceramic with a scanning electron microscope.

Table 1 shows the thickness of the Y ₂ O ₃ powder and the thickness of the silicate layer measured above.

(Operations 2 to 4) The same operation as in operation 1 was repeated except that the voltage application time of electrophoresis was set to 20 seconds, 40 seconds and 60 seconds, respectively, to obtain a laminated ceramic. Y ₂ O ₃
The thickness of the powder and the thickness of the silicate layer were measured in the same manner. Table 1 shows the results.

(Operation 5) A multilayer ceramic was obtained by repeating the same operation as in Operation 1 except that Yb ₂ O ₃ powder was used instead of Y ₂ O ₃ powder as the rare earth oxide. Yb ₂ O
₃ The thickness of the powder and the thickness of the silicate layer were measured in the same manner.
Table 1 shows the results.

[0026]

Table 1 Electrophoretic silicate Thickness Operation Voltage application Rare earth film thickness Time (seconds) Oxide (μm) (μm) --------------------------------------------------- 110 Y ₂ O ₃ 100 Y ₂ SiO ₅ 10 220 Y ₂ O ₃ 150 Y ₂ SiO ₅ 15 340 Y ₂ O ₃ 400 Y ₂ SiO ₅ 30 460 Y ₂ O ₃ 480 Y ₂ SiO ₅ 30 540 Yb ₂ O ₃ 500 Yb ₂ SiO ₅ 35 ----------------------------------------------------------- Obtained by operations 2-4. The laminated ceramics had a white thin layer formed on the surface layer, and as a result of analysis by X-ray analysis, it was Y ₂ O ₃ , which could be easily peeled off. Below the white thin layer was a dense gray layer that was firmly bonded to silicon carbide. This gray layer was found by X-ray diffraction to be a single phase of Y ₂ SiO ₅ . The multilayer ceramic obtained in operation 1 has no white layer on the surface layer,
It was a phase of Y ₂ O ₃ and Y ₂ SiO ₅ . In operation 5,
A white Yb ₂ O ₃ thin layer and a Yb ₂ SiO ₅ layer were formed thereunder.

When the laminated ceramics obtained in the above operations 1 to 5 were heated in the air at 1600 ° C. for 24 hours,
In each of the laminated ceramics, there was almost no change in weight, and there was no change in structure or composition. That is, it was found that the silicon carbide base material was protected by the silicate coating, and the temperature range in which the silicon carbide base material could be used stably could be improved.

[0028]

As described above, the method for producing a laminated ceramic according to the present invention is capable of obtaining a laminated ceramic excellent in high-temperature strength, high-temperature oxidation resistance and corrosion resistance, and its industrial value is extremely large. It is. Moreover, the laminated ceramics obtained by the production method of the present invention is suitable as a material for mechanical parts used at high temperatures due to its excellent heat resistance, and enables the supply of high-quality mechanical parts.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the operation of electrophoresis used in the method for producing a laminated ceramic according to the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of an apparatus used in the method for producing a laminated ceramic according to the present invention.

3A and 3B are diagrams illustrating steps in a method for manufacturing a multilayer ceramic according to the present invention, wherein FIG. 3A illustrates a step of laminating a rare earth oxide, FIG. 3B illustrates an oxidation step, and FIG.
FIG. 3 is a view showing a laminated ceramic obtained by an oxidation treatment.

[Explanation of symbols]

 Reference Signs List 1,17 Dispersion liquid 3,5 Electrode 7,15 DC power supply 11 Electrodeposition tank 13 Ring electrode P Powder of rare earth oxide S Sintered silicon carbide

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C04B 41/87 C25D 13/02 Z C25D 13/02 C04B 35/56 101X (56) References JP-A-7-277861 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 41/87, 41/89

Claims (3)

(57) [Claims] The first layer containing silicon carbide has a general formula:
A second layer containing a rare earth oxide represented by RE ₂ O ₃ (where RE represents a rare earth element selected from the group consisting of Y, Yb, Er and Dy) is laminated to form a laminate. Heating the laminated body in an oxidizing atmosphere to oxidize the silicon carbide of the first layer to produce silicon oxide;
From the rare earth oxide of the layer and the silicon oxide, a general formula: RE ₂ S
A method for producing a laminated ceramic, comprising producing a rare earth silicate compound represented by iO ₅ (wherein RE represents a rare earth element selected from the group consisting of Y, Yb, Er and Dy). 2. The formation of the laminate is performed by charging the first layer into a rare earth oxide dispersion and attaching the rare earth oxide to the surface of the first layer by electrophoresis,
The method according to claim 1, wherein the heating of the laminate is performed at 1400 to 1700C. 3. The first layer is a sintered body layer obtained by molding and sintering a powder containing silicon carbide, and the rare earth silicate compound layer having a thickness of 100 μm or less by heating the laminate. 3. The method according to claim 1, wherein a layer containing a rare earth silicate compound and a rare earth oxide is formed.