JPH0725658A - Gradient-functional molded material and sintered product therefrom - Google Patents

Abstract

PURPOSE:To obtain the molded material through specific modes using plural particle groups differing in particle diameter from one another to enable large- sized molded products with continuously gradient diversified composition and sintered products thereof to be produced at a low cost. CONSTITUTION:At least two kinds of particle groups differing in particle diameter from one another where the mean particle diameter ratio for the groups of greater particle size and the group of the minimum mean particle size is <=1/5 and the corresponding volume ratio >=2 is mixed with water into a slip >=30wt.% in solid concentration, which is then cast into a porous mold to produce a molded form with the composition ratio for the different particle groups altered in a continuous way, thus obtaining the molded material, which is composed of two or more kinds of particle groups whose composition ratio is continuously altered at least unidirectionally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a functionally graded molding material and a sintered product thereof. More specifically, the present invention is a molded article for a functionally graded material having continuously changing properties, which is useful as a highly heat resistant material used in an extreme environment such as aerospace, chemical industry, and nuclear industry. Or, it relates to a sintered product.

[0002]

2. Description of the Related Art In recent years, in various fields such as aerospace, chemical industry, nuclear industry, etc., various characteristics have been continuously improved as a highly heat resistant material that is effectively used under extreme environmental conditions. Gradient functional materials that change are attracting attention. Then, regarding this functionally graded material, in order to realize the continuous change of the characteristics, it is technically very important to make the composite of different materials into a state where the composition ratio is continuously different. It is an issue.

To date, various measures have been studied to deal with this problem and have been proposed as a concrete means. That is, as a typical one, CV
D, a gas phase method such as a plasma spraying method, a self-combustion synthesis method (SHS), and a thin film lamination method are known. In the case of a vapor phase method such as CVD or plasma spraying method, although there is an advantage that it is possible to control in a very small area, it is difficult to increase the size, the target material is limited, and the cost is high. The disadvantage of becoming unavoidable. Further, in the self-combustion synthesis method (SHS), although the high melting point material can be graded, the target material is limited, and in the case of the thin film laminating method, for example, a sheet by a doctor blade method is used. The composition distribution is graded by forming and stacking it, and then sintering, and relatively low cost and good productivity, and it is easy to obtain a variety of compositions, but it is difficult to obtain a thick product, which is troublesome. However, since the composition is gradually graded, inconveniences such as deterioration and peeling easily occur at the laminated interface.

Therefore, each of the conventional methods has practical disadvantages. In particular, the thickness, gradient, etc. of the graded layer can be freely changed, the cost is low, and the composition is diverse.
Moreover, the issue of being able to provide large-scale products was still unsatisfactory. An object of the present invention is to provide a new functionally graded material capable of solving the above-mentioned drawbacks of the conventional technology and solving the above-mentioned problems.

[0005]

Means for Solving the Problems The present invention is, in order to solve the above-mentioned problems, a functionally gradient material composed of at least two kinds of particle groups having different particle diameters, and is most suitable for a particle group having a larger particle diameter. Average particle size ratio of particles with small particle size is 1 /
Provided is a functionally gradient material, characterized in that the volume ratio is 5 or less, the volume ratio is 2 or more, and the composition ratio of each particle group is continuously different in at least one direction.

The present invention also provides a functionally graded material made of a sintered product of this molded material. The molded product of the present invention, and further the sintered product, can be defined as having the above-mentioned characteristics. As a manufacturing method therefor, the inventor of the present invention has already proposed. The slip casting method can be preferably used.

The present invention also provides a method for producing the above-mentioned molded body and sintered product by this slip casting method.

[0008]

With respect to the functionally graded material of the present invention, various ceramics such as alumina, zirconia, silica, titania, magnesia, boria, thoria, etc., and composite oxides such as titanates and zirconates, It can be constituted by using various kinds of particles such as carbides and nitrides, and various kinds of metals and alloys, powders, etc. In that case, at least two kinds of particle groups having different particle sizes are used. Use is essential in this invention.

In order to continuously change the composition in the molded body, the average particle size ratio of the larger particle size particle group (coarse particles) to the smallest particle size particle group (fine particles) is as described above. 1
/ 5 or less. If it is larger than this, it becomes difficult to obtain a desired molded product. Further, the volume ratio of the coarse particles to the fine particles is set to 2 or more. If the ratio is less than 2, it becomes difficult to obtain a desired molded product.

Usually, the molded article of the present invention is manufactured by the slip casting method as described above. In this method,
First, powders having different particle diameters, for example, ceramics and metal powders are mixed in a required volume ratio so as to satisfy the particle ratio as described above, and water and, if necessary, surface active Dispersants such as agents and celluloses are added and mixed to form a slip (slurry).

Regarding the particle concentration of the slip at this time,
Usually, it is preferably 40% by weight or less, more preferably 30% by weight or less. If the concentration exceeds 40%, it becomes difficult to obtain a desired molded product. Then, the obtained slip is cast by pouring it into a porous mold such as gypsum.
Inside a porous mold such as gypsum, the slip water is rapidly removed, and at the same time, the composition ratio changes continuously in the thickness direction, that is, along the water removal direction (green body) due to the sedimentation of the particle groups. Will be obtained. A desired molded product is obtained by drying this.

FIG. 1 of the accompanying drawings is a schematic diagram showing this slip casting method in principle. For example, as illustrated in FIG. 1, a water-impermeable mold (2) is placed in a porous mold (1) such as gypsum, and the slip (3) is injected into the mold (1). Then, the water is removed through the porous thin tube portion (11) of the porous type (1), and the casting layer (5) is formed together with the settling of the particles (4) in the slip (3). At the stage where most of the water is removed, the formed molded body (green body) is demolded from the mold (1) and the mold (2) and dried to obtain a desired molded body.

In this molded article, the settling direction of particles,
That is, the composition ratio continuously changes in the thickness direction. The change pattern of the composition ratio is of course influenced by the difference due to the specific gravity of the particles, but the factors that have a greater effect are the water absorption rate of the porous type, the particle size of the particles, and the particle size distribution. .

As long as the particle size ratio of the particles is 1/5 or less and the volume ratio is 2 or more, it is difficult to form the gradient composition itself. The pattern of change in composition ratio is generally two types of patterns (A) as schematically illustrated in FIG.
(B) will be shown. If two kinds of particle groups (a, b) having different particle diameters are used for slip casting, the composition ratio of the particles a will be as shown in the patterns (A) and (B) of FIG. 2 along the casting direction. Will be shown.

Pattern (A) shows a forward gradient composition.
However, in the case of the pattern (B), the gradient layer (L₁)
(L₂) Shows the opposite slope, and in the initial stage,
Inverted layer (L₁) Has been generated. Such a reverse tilt
Layer (L₁), And sintered products thereof,
It enables unique applications as it is, and also has a reverse gradient layer.
(L ₁) And the forward graded layer (L₂) And cut appropriately and apply
You can also do it.

The pattern (B) has a relatively uniform particle size distribution and is easily produced by using particles having a small average particle size. The reason is that, for example, as illustrated in FIG. 3, in the cast layer of the particles (a) and the particles (b) having a uniform composition formed by the water-absorption filtration action of the porous type (1), the inter-particle It is considered that the fine particles (a) enter the gaps, which easily forms the reverse gradient layer.

In any of the patterns (A) and (B),
In the present invention, it can be arbitrarily selected, and it becomes possible to manufacture a functionally gradient material having more flexibility. Further, in the present invention, in slip casting,
As an external force that acts on the sedimentation of particles, it is possible to form a characteristic change pattern of the composition ratio by an electrophoretic means using a mesh electrode or a means such as magnetic field application in the case of metal particles.

Examples will be shown below to describe the functionally graded material of the present invention and its sintered product in more detail.

[0019]

Example 1 Yttria was added in an amount of 3 mol%, and the average particle size was about 0.3 μm.
m tetragonal zirconia (Tosoh: TZ-3YS) powder and nickel having an average particle size of about 8 μm (Sumitomo Metal Mining: S
NP-130) powder was used, an appropriate amount of water and a dispersant were added thereto, and the mixture was mixed in a ball mill for 24 hours to form a slip.
Table 1 shows the slip composition.

Subsequently, this slip was poured into a glass tube placed on a plaster mold, and was inscribed in one direction (moving direction).
The obtained molded body was dried and then sintered under normal pressure.
After sintering, a functionally graded sintered product having a graded composition was obtained.

[0021]

[Table 1]

The sintering temperature is set to 1400 ° C. or lower, specifically, from room temperature to 1000 ° C. for 3 hours, 1000 ° C. to 14 ° C.
The temperature was raised to 00 ° C. for 4 hours, baked at 1400 ° C. for 2 hours, and then naturally cooled. Argon gas was used in the atmosphere as a gas that does not cause oxidation of nickel. FIG. 4 shows changes in the content of zirconia in the obtained molded body. Table 1
It can be seen that when the A and B slips are used, the structure is continuously changed, but the composition is not inclined in the C slip. Thus, if the slip concentration is too high, the composition and inclination cannot be achieved, and if it is too thin, it is difficult to produce a thick product, so it is desirable to use a slip having an appropriate concentration. Example 2 In Example 1, various investigations were made on the action factors for the formation of the graded composition layer. 1) Volume Ratio A molded body was manufactured by using powder of average particle diameter 0.3 μm ZrO ₂ and Ni having average particle diameter 8 μm and changing the volume ratio at a slip concentration of 5%. The result at this time is shown in FIG. The black part in the figure is a mixed layer of ZrO ₂ and Ni,
The shaded portion indicates the graded composition layer, and the white portion indicates the ZrO ₂ layer. As is clear from FIG. 5, when the volume ratio of ZrO ₂ / Ni is 80/20, the graded composition layer is formed, and when it is less than that, that is, when the volume ratio of ZrO ₂ is decreased, the graded composition layer is formed. It can be seen that the layers are not clearly created. 2) ZrO ₂ particle size The Ni powder had an average particle size of 8 μm, and only ZrO _{2 having} a different average particle size was slip-cast. As a result, as shown in FIG. 6, it was found that the smaller the average particle size of ZrO ₂ , that is, the smaller the particle size ratio with respect to the Ni powder, the clearer the formation of the graded composition layer.

The slip concentration is 5%, ZrO ₂ / N
The volume ratio of i was 80/20. 3) Slip Concentration At a volume ratio of 80/20, slip casting was performed by changing only the slip concentration. The results are shown in Fig. 7. As is clear from FIG. 7, the formation of the graded composition layer was observed only when the concentration was 5% or 10%. Example 3 A molded body was manufactured by slip casting using alumina and tungsten powder. The volume ratio of alumina to tungsten powder was 80/20. Slip density is 1
It was set to 0%.

At this time, as the alumina, the average particle size is 0.
Using 2 μm particles (A) and particles (B) having an average particle size of 0.56 μm, the difference in generation of the gradient composition layer in the molded body was examined. 8A and 8B show the particle size distribution of the alumina particles (A) and (B). FIG. 9 shows the particle size distribution of tungsten (average particle size 2.8 μm).

FIG. 10 shows the composition ratio of alumina in the obtained molded body. It can be seen that when the alumina particles (B) having a larger average particle size and a relatively broad particle size distribution are used, the reverse gradient layer formed in the case of the particles (A) is not recognized. Note that FIG. 12 shows a sintered product (sintering temperature 1450) in the case of the alumina particles (A) of FIG.
The hardness is measured at (° C. × 3 hours), and the results are shown. It can be seen that it has a tilt characteristic.

[0026]

As described in detail above, according to the present invention, it is possible to manufacture a molded product whose composition is continuously graded and a sintered product thereof. Moreover, it is possible to freely change the thickness and the inclination pattern of the inclined layer, and it is possible to manufacture large-sized products with various compositions at low cost.

[Brief description of drawings]

FIG. 1 is a sectional view showing a principle method of a manufacturing method of the present invention.

FIG. 2 is a schematic view illustrating a generation pattern of a gradient composition.

FIG. 3 is an estimation diagram illustrating a mechanism in which an anti-gradient layer is generated.

FIG. 4 is a diagram showing a gradient composition as an example.

FIG. 5 is a cross-sectional view of generation of a graded composition layer in which the volume ratio is examined.

FIG. 6 is a cross-sectional view of formation of a graded composition layer in which the grain size of zirconia was examined.

FIG. 7 is a cross-sectional view of generation of a graded composition layer examined for slip concentration.

FIG. 8 is a particle size distribution diagram of alumina.

FIG. 9 is a particle size distribution diagram of alumina.

FIG. 10 is a particle size distribution chart of tungsten.

FIG. 11 is a diagram showing a gradient composition as an example.

FIG. 12 is a diagram showing an example of hardness characteristics.

[Explanation of Codes] 1 porous type 2 form 3 slip 4 particles 5 casting layer 11 porous thin tube part

Claims (4)

[Claims] 1. A functionally gradient molding material comprising at least two kinds of particle groups having different particle sizes, wherein the average particle size ratio of the smallest particle size to the larger particle size is 1/5.
A functionally gradient material having a volume ratio of 2 or more and a composition ratio of each particle group continuously different in at least one direction. 2. A functionally graded sintered product, which is a sintered product of the molded material according to claim 1. 3. A particle group having at least two different particle sizes, wherein the average particle size ratio of the particle group having the smallest average particle size to the particle group having the larger average particle size is 1/5 or less, and ,
A particle group whose volume ratio is 2 or more is mixed with water to obtain a concentration of 3
A method for producing a functionally gradient molded product, which comprises forming a slip having a slip of 0% or less, and injecting it into a porous mold to continuously produce a composition having different composition ratios of different particle groups. 4. A method for producing a functionally graded sintered product, which comprises sintering the compact produced by the method of claim 3.