JP3738784B2 - Method for producing interface control ceramics - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing ceramics having high strength and high toughness.
[0002]
[Prior art]
Ceramics are used as a material for parts exposed to high temperatures in the field of energy-related equipment such as high-temperature gas turbines and rockets. However, since ceramics generally have low toughness and are easily cracked, it is necessary to control the characteristics of the crystal grain interface in order to increase the toughness and increase the strength, and techniques such as dispersing different kinds of particles at such an interface are used. Conventionally, such an additive for controlling the interface is mixed with the raw material powder simultaneously with other components such as a sintering aid.
[0003]
[Problems to be solved by the invention]
However, when additive ingredients for interfacial control are mixed with the raw material powder together with the sintering aid, reaction between them or mass transfer may occur during firing, adding for interfacial control. Since the components cannot be arranged at the target interface portion, the interface characteristics cannot be sufficiently controlled, and the performance improvement of the ceramics must be limited.
[0004]
The present invention has been devised in view of the above problems, and it is possible to manufacture a ceramic with high toughness and high strength by reliably controlling the interface by localizing additives for interface control at the interface of the ceramic crystal. The purpose is to do.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing an interface-controlling ceramic according to the present invention comprises a step of coating a surface of a ceramic particle serving as a core with a sintering aid, and a ceramic particle serving as a core on the surface coated with the sintering aid From the step of coating a ceramic raw material of the same material, the step of attaching ceramic particles for interface control to the surface, or the step of coating the ceramic raw material for interface control, and the step of sintering after molding Become.
[0006]
It is preferable to perform heat treatment for solid solution or precipitation after sintering the ceramic. Silicon nitride or silicon carbide may be adopted as the ceramic material. The process of coating the sintering aid, the same ceramic material as the core ceramic, and the ceramic raw material for interface control is impregnated with a liquid phase raw material such as a vapor phase reaction such as CVD, a sol-gel method or a ceramic precursor resin. A method may be adopted. The step of attaching ceramic particles for interface control may utilize agglomeration of solid powder.
[0007]
Hereinafter, the production method of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing each step of the present invention.
[0008]
As shown in FIG. 1 (A), the surface of the ceramic particles 1 serving as the core is coated with the sintering aid 2. As the heat-resistant ceramic as a core, silicon carbide and silicon nitride are targeted, and short fibers such as particles and whiskers are used as the core. These surfaces are coated with ceramics as a sintering aid. When the core ceramics are silicon nitride, oxide ceramics such as alumina and yttria are used, and the core ceramics are silicon carbide. In this case, alumina, yttria, boron, carbon, aluminum or the like is used. As a coating method, a gas phase reaction such as CVD may be used, or a liquid phase reaction may be used as in the sol-gel method.
[0009]
Next, the raw material particle phase 3 is formed on the surface of the sintering aid 2 as shown in FIG. The raw material particle phase 3 is a ceramic made of the same material as the core 1. As a method for forming the raw material particle phase 3, a sintering aid is applied to the core 1 produced in the step of FIG. 1A in a solution of a silicon carbide or silicon nitride precursor resin such as polycarbosilane or polysilazane. There is a method in which particles coated with the agent 2 are dispersed and dried and fired.
[0010]
The raw material particle phase 3 may be formed by a method other than those described above. For example, the core particle 1 produced in the step of FIG. 1A and the powder particles coated with the firing aid 2 and the raw material powder particles are dispersed in the solution. Then, the surface charge of the coated particles may be controlled by a method such as controlling PH, and the raw material powder particles may be aggregated on the surface of the coated particles, or may be aggregated during drying.
[0011]
Next, as shown in FIG. 1C, an additive component for controlling the interface is attached to or coated on the surface of the raw material particles 3. When the additive component is a powder, it is adhered to the surface of the raw material particles 3, and the method is preferably to use agglomeration as in the step (B). Alternatively, it may be performed by a gas phase reaction such as CVD, or a liquid phase reaction such as a sol-gel method or a precursor resin may be used.
[0012]
Next, molding is performed as shown in FIG. A plastic material obtained by adding the powder obtained in the step (D) into the solution and mixing is molded by applying a usual method such as extrusion molding or CIP.
[0013]
Next, as shown in FIG. 1 (E), the molded body obtained in the step (D) is sintered. A commonly used sintering method is applied depending on the material. For example, normal pressure sintering may be used, or pressure sintering such as hot pressing or HIP may be used. As shown in FIG. 1E, an interface control component 4 is arranged at the interface of the ceramic particles 5. Thereafter, heat treatment for controlling solid solution and precipitation is performed as necessary for controlling the interface phase.
[0014]
[Action]
Manufacture of interface control ceramics by the above manufacturing method is performed by the following operation. Since the surface of the core particle 1 is coated in the order of the sintering aid 2, the raw material powder 3, and the interface control component 4, densification progresses sequentially from the vicinity of the sintering aid during sintering, and the final stage of sintering. It reaches the interface control component 4. For this reason, the reaction between the interface control component and the sintering aid that occurs when these components are uniformly mixed as in the prior art is prevented, and the interface control component 4 can be reliably disposed at the interface. As a result, the desired interface control is accurately performed, and the improvement of the material properties such as the fracture toughness and the strength can be expressed.
[0015]
[Example 1]
An α-type silicon carbide powder having an average diameter of 2 μm is dispersed in an aqueous solution containing aluminum nitrate and urea, heated to 90 ° C. with stirring, and maintained for 6 hours to thereby form aluminum hydroxide on the surface of the silicon carbide powder. Was deposited and coated. This reaction occurs as follows.
[0016]
This was fired at 1300 ° C., and aluminum hydroxide was used as alumina (sintering aid).
[0017]
Next, this powder was dispersed in a tetrahydrofuran solution in which polycarbosilane was dissolved. After passing through a furnace, the powder was dried and infusible to coat the surface with polycarbosilane. This was baked in an argon gas at 1300 ° C., and polycarbosilane was converted to silicon carbide. This treatment was repeated 10 times to obtain a raw material particle phase.
[0018]
The obtained powder and titanium boride powder were made into an aqueous slurry and then spray-dried to adhere the titanium boride powder to the surface of the raw material particle phase powder. This was molded by CIP and fired at 1900 ° C., 200 MPa for 1 hour using HIP sintering to obtain a sintered body.
[0019]
The strength of the obtained sintered body is 500 MPa (3-point bending strength in JIS R1601 “Bending strength test method of fine ceramics”), and the fracture toughness is 7 MPa√m (JIS R1601 “Fracture toughness test of fine ceramics”). An excellent value of SEPB method in “Method” was shown.
[0020]
[Example 2]
A slurry containing an α-type silicon carbide powder having an average diameter of 2 μm, a water-soluble phenolic resin and boric acid was spray-dried to coat the surface of the silicon carbide powder with a mixture of the phenolic resin and boric acid. This was fired in an argon gas at 1500 ° C., and the surface of the silicon carbide powder was coated with boron carbide (sintering aid). Next, after the silicon carbide raw material phase was coated, alumina was coated in the same manner as in Example 1. This powder was mixed with pitch quinoline solution, dried and then treated in 1350 ° C. N ₂ gas for 3 hours to convert alumina to aluminum nitride (additional component for interface control). Then, it was calcined at 500 ° C. in air for 3 hours to remove excess carbon.
[0021]
The obtained powder was CIP-molded, calcined in a 1500 ° C. vacuum, and then calcined at 1900 ° C. and 200 MPa for 1 hour by the HIP method. Thereafter, heat treatment was performed at 2100 ° C. for 5 hours in order to dissolve aluminum nitride, and then heat treatment was performed at 1750 ° C. for 10 hours. The obtained sintered body had excellent strength of 590 MPa and fracture toughness of 7.4 MPa√m. The method for measuring strength and toughness is the same as in Example 1.
[0022]
[Comparative Example 1]
A compact obtained by adding alumina and titanium boride as sintering aids to commercially available silicon carbide powder was densified under the same firing conditions as in Example 1. As a result, the strength was 450 MPa and the fracture toughness was 5.5 MPa√m. there were.
[0023]
[Comparative Example 2]
A material obtained by adding the same amount of boron carbide and aluminum nitride to commercially available silicon carbide powder was densified under the same firing conditions as in Example 2. As a result, the strength was 400 MPa and the fracture toughness was 4.5 MPa√m. .
[0024]
As is clear from the comparison of the examples and the comparative examples corresponding thereto, it is clear that the ceramic obtained by the production method of the present invention has high toughness and large strength.
[0025]
【The invention's effect】
As described above, the interface control ceramic obtained by the production method of the present invention is formed by sequentially forming a raw material ceramic as a core, a sintering aid, a ceramic raw material of the same quality as the core, and a powder coated with additive components for interface control in order. Since it is sintered and densified, the interface control component is localized at the ceramic crystal interface without reacting or diffusing with other components such as a sintering aid during sintering. Yes. Therefore, it is possible to obtain a ceramic having excellent properties such as fracture toughness and strength by reliably performing the desired interface control.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a method of manufacturing an interface control ceramic according to the present invention in the order of steps.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic particle | grains used as nucleus 2 Coating | covering of sintering auxiliary agent 3 Raw material particle phase of ceramic same material as ceramic particle used as nucleus 4 Additive component for interface control 5 Composition particle of interface control ceramics

Claims (5)

The step of coating the surface of the ceramic particles that are the core with the sintering aid, the step of coating the surface coated with the sintering aid with the ceramic raw material of the same material as the core ceramic particles, and the interface control on the surface A method for producing interface-controlling ceramics comprising the steps of adhering ceramic particles for coating or coating a ceramic raw material for interface control and sintering after molding. The method for producing an interface-controlled ceramic according to claim 1, wherein after the ceramic is sintered, heat treatment for solid solution or precipitation is performed. The method for producing an interface-controlled ceramic according to claim 1 or 2, wherein the core particles and the raw material ceramics are silicon nitride or silicon carbide. The step of coating the surface of the ceramic particles as the core with the sintering aid, the step of coating the surface coated with the sintering aid with the ceramic raw material of the same material as the core ceramic particles, and the surface for controlling the interface 4. The method for producing an interface-controlled ceramic according to claim 1, wherein the step of coating the ceramic raw material is a method of impregnating a liquid phase raw material such as a vapor phase reaction such as CVD or a solgen method or a ceramic precursor resin. 4. The method for producing an interface-controlling ceramic according to claim 1, wherein the step of attaching ceramic particles for controlling the interface is a method utilizing agglomeration of solid powder.

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