JPH0872032A - Manufacture of fiber reinforced ceramics - Google Patents

Abstract

PURPOSE: To provide a manufacturing method of fiber reinforced ceramics, by which uniform orienting properties can be given to short reinforcing fibers, neither deformation nor crack and the like develops at sintering and homogeneous material characteristics can be obtained even in the direction of the thickness even in a thicker member. CONSTITUTION: Slurry S, which is prepared by dispersing ceramics powder and short reinforcing fibers in solvent solution, is poured in a casting mold 1, in which a gypsum mold 3 is arranged, and, at the same time, applied with back pressure P so as to discharge the solvent solution through the gypsum mold 3 in order to grow a cast layer LA of the ceramics powder and short reinforcing fibers for producing a formed body. After that, by sintering the formed body, fiber reinforced ceramics are manufactured. The back pressure P applied to the slurry S at the production of the formed body is increased in proportion to the increase of the thickness L of the cast layer LA or to the time elapsed since the start of pressurizing. Thus, the solution absorbing rate of the gypsum mold at the production of the formed body can be made constant, resulting in giving uniform orienting properties to the short reinforcing fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fiber-reinforced ceramic suitable for use as a corrosion-resistant structural member, a cutting tool, an abrasion-resistant jig, a member for high temperature, and the like. The present invention relates to a method for producing a fiber-reinforced ceramic that is uniform and has excellent toughness and strength.

[0002]

2. Description of the Related Art In recent years, application of composite materials such as ceramic bases has been widely promoted for members and parts which require high strength under high temperature, corrosion and abrasion environments. On the other hand, addition of reinforcing fibers such as whiskers and short carbon fibers has been attempted in order to improve the toughness and strength of these composite materials, and in particular, great expectations are placed on improving the toughness of monolithic ceramics. This is because the pull-out mechanism of the reinforcing fiber improves the toughness and the presence of the fiber suppresses the coarsening of the crystal grains to improve the strength. Although various attempts have been made as methods for producing such fiber-reinforced ceramics, conventionally, if whiskers or short fibers (hereinafter abbreviated as short fibers including whiskers) are added to ceramics, the sinterability is poor. Therefore, the manufacturing by the hot press method dominated. However, although the hot pressing method is effective for imparting a two-dimensional orientation of short fibers and densifying it when manufacturing a member having a relatively small thickness,
Thick ones tend to have random short fiber orientation,
Further, there is a problem that it is difficult to form a complicated shape.

Therefore, in recent years, the slip casting method and the filter pressing method, which can give orientation to the added short fibers, have a higher degree of freedom in shape than the hot pressing method, and have a low die manufacturing cost, have been attracting attention. , Its application has been tried variously. Then, in a normal slip casting method, a raw material powder dispersed in a solvent liquid such as water (which is called slip or slurry) is filled in a hygroscopic mold such as a gypsum mold, The mold is made to absorb the solvent liquid to obtain a molded body under normal pressure.In the fiber reinforced ceramics, for example, as proposed in JP-A-63-288973, raw material powder is mixed in the solvent liquid. The dispersed slurry (slip) is filled into a mold made of a porous material such as a filter, and then the slurry is pressed toward the porous material of the mold with a constant pressure and passed through the porous material. The method of discharging the solvent liquid to obtain a molded body, and then sintering the molded body, that is, the application of the pressure slip casting method and the filter press method, improves the two-dimensional orientation degree of the added short fibers. Is said to be effective

[0004]

However, when the above-mentioned conventional slip cast method or filter press method is used to sinter the molded body, the following problems occur. That is, in these molding methods, as shown in the conceptual diagram [Fig. 3], the solvent liquid (F) in the slurry (S) in which the ceramic powder (C) and the short fibers (W) are dispersed, Porous mold
Discharge through (21) and give orientation to short fibers (W) in the process of growing ceramic powder (C) and infiltration layer (LA) of short fibers (W) on liquid absorbing surface (21a). However, the orientation is largely influenced by the liquid absorption speed v of the mold (21). However, since the inking layer (LA) that grows on the liquid absorption surface (21a) itself becomes a consolidated layer having liquid passage resistance, the solvent liquid that goes toward the liquid absorption surface (21a) as it grows. The resistance against the flow of (F) is increased, and the liquid absorption speed v of the mold (21) is rapidly reduced.
Therefore, as shown in Fig. (A), in the place near the liquid absorption surface (21a), that is, in the inking layer (LA) formed in the initial stage, although there is an extremely high orientation of the short fibers (W), While the thickness L of the meat layer (LA) does not grow very much (for example, when slip casting at 1 atm has grown to a thickness of about 5 mm), the mold (2
The liquid absorption speed v of 1) drops sharply, and short fibers
The orientation of (W) is also lost, and as shown in the result (b), the obtained molded product (B) is one in which the orientation of the short fibers (W) in the thickness direction is not uniform. It is easy to become. This also occurs in the pressure slip casting method or the filter pressing method in which a constant back pressure is applied, and becomes more remarkable as the thickness of the molded body increases.

FIG. 4 is an explanatory view of sintering a molded body produced by a normal powder method which does not contain short fibers.
As shown in Fig. (a), a sintered body (B1 ") in which the molded body (B") isotropically and uniformly contracted is obtained. Further, when a molded body in which short fibers are randomly oriented is sintered, similarly, although a sintered body having no anisotropy in shrinkage rate during sintering is obtained, it is difficult to increase the density of the sintered structure. The problem arises. On the other hand, as shown in the same figure (b), when the compact (B ') in which the short fibers (W) are oriented in a certain direction is sintered, the sintering shrinkage amount is
The sintered body (B1 ′) is large in the direction orthogonal to the orientation direction of the short fibers and small in the orientation direction. In other words, in a powder compact containing oriented short fibers, the higher the orientation of the short fibers, the lower the shrinkage rate in the orientation direction and the greater the shrinkage rate in the orthogonal direction to the orientation direction. There is anisotropy. Therefore, as described above, when a compact (B) in which the orientation of the short fibers (W) is not uniform in the thickness direction is sintered, as shown in the same figure (c), it is sintered according to the orientation. Since the shrinkage rate changes anisotropically, the resulting sintered body (B1) is significantly deformed or cracked in some cases. In addition, the various characteristics are also affected by the non-uniform orientation of the short fibers, and it is difficult to obtain homogeneous material characteristics. Moreover, these problems become remarkable when manufacturing a thick member.

The present invention has been made to solve the above-mentioned problems of the prior art, and even if the member is thicker,
The added reinforcing short fibers can be given a uniform orientation, so even if anisotropic shrinkage occurs during sintering, there is no significant deformation or cracking, excellent toughness and strength, and even in the thickness direction. It is an object of the present invention to provide a method for producing a fiber-reinforced ceramics that can obtain a member having uniform material properties.

[0007]

In order to achieve the above object, the present invention has the following constitution. That is, the method for producing a fiber-reinforced ceramics according to the present invention is such that a slurry formed by dispersing and mixing a ceramic powder serving as a base material and a reinforcing short fiber in a solvent liquid is filled in a mold formed of a porous body. After that, a back pressure is applied to the slurry to apply pressure toward the porous body, and the solvent liquid is discharged through the porous body to grow a ceramic powder and a thin fiber infiltration layer on the surface. Then, in the method for producing a fiber-reinforced ceramics, which comprises forming a molded body made of ceramic powder and reinforcing short fibers in the mold, and thereafter sintering the molded body at a high temperature, a slurry is formed when the molded body is formed. The back pressure to be applied is increased in proportion to an increase in the thickness of the inking layer or an elapsed time from the start of pressurization.

[0008]

In the present invention, back pressure is applied to the slurry obtained by dispersing and mixing the ceramic powder, which is the base material, and the reinforcing short fibers in the solvent liquid, and is applied toward the porous body of the filled mold. By pressing and discharging the solvent liquid through this porous body to grow a layer of ceramic powder and short fibers on the surface of the porous body, a molded body made of ceramic powder and reinforced short fibers is formed in the mold. However, the following equation (1) is established from the relationship between the liquid absorption speed of the porous body, the thickness of the inking layer, and the back pressure at that time. v = ds / dt = K / η · Δp / L ------- (1) where v is the liquid absorption rate of the porous body, s is the liquid absorption amount, t is the liquid absorption time, and K is the liquid absorption time. Liquid permeability of the meat layer, η is the slurry concentration, L is the thickness of the meat layer, and Δp is the pressure difference between the back pressure and the outlet pressure of the porous body. On the other hand, it has been confirmed by experiments that K and η hardly change even when the differential pressure Δp changes when ordinary base material particles or short fibers are used. Therefore, the value of K / η in the equation (1) becomes constant, and by setting this as a constant A, the following equation (2) is obtained. v = A · Δp / L ------- (2) From the above formula (2), to keep the liquid absorption speed v constant, Δp /
It is understood that the value of L should be constant. Further, if the value is used as a constant B and the above equation (2) is modified, the following equation (3) is obtained. Δp = B · L ------- (3) Furthermore, since the thickness L of the inking layer is proportional to the elapsed time T from the start of pressurization, the above equation (3) is expressed as It can be replaced by equation (4). Δp = B · T ------- (4) That is, if the pressure difference Δp is proportional to the thickness L of the inking layer or the elapsed time T from the start of pressurization, then from the above equation (2), The liquid absorption speed v becomes constant. Further, if the liquid absorption speed v of the porous body becomes constant, as described above, the orientation of the short fibers of the inking layer formed on the surface also becomes constant. Here, in the present invention, the back pressure applied to the slurry at the time of forming the molded body is increased in proportion to the increase in the thickness of the inking layer or the elapsed time from the start of pressurization. It is possible to impart uniform orientation to the added reinforcing fibers by keeping the liquid absorption rate v of the body constant, so that there is no deformation or cracking during sintering, and the fiber characteristics are uniform after sintering. Ceramics can be obtained.

As the means for sintering and densifying the molded body in the present invention, there are generally used pressureless sintering and pressure sintering, and generally HIP and capsule HIP after sintering and hot pressing. The method used can be applied depending on the purpose.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. - the α-Al ₂ 0 ₃ powder of Example 1 average particle diameter 0.5μm 79.5wt%, an average diameter
11.5wt% of SiC whiskers with 1.0μm and aspect ratio of 10,
A mixture containing an oxide sintering aid of 9 wt% was wet mixed in a ball mill for 10 hours to prepare a slurry (S). Further, pure water was used as the solvent liquid, and the concentration of solid content was
It was added so as to be 64%, and 0.3 wt% of a dispersant was further added to improve the dispersibility of the slurry (S).

On the other hand, as shown in FIG. 1 which is a schematic diagram thereof, a grid is formed on the inner bottom portion of an inverted cup-shaped steel mold (2) having a pressure medium gas introduction hole (2a) in the upper part. A casting mold (1) was prepared in which a gypsum mold (3) held on a plate-shaped support plate (4) was placed. This casting mold (1) has a structure used for ordinary pressure slip casting, and has a pressure medium gas introduction hole on the upper part thereof.
(2a) is connected to a high-pressure air supply device (not shown), while the lower parts of the plaster mold (2) and the support plate (3) are open to the atmosphere. Also, in this embodiment, the formwork above the plaster mold (3)
(2) The cross-sectional shape of the inner hole is a square cross-sectional shape that can form a flat plate of 40 mm in length and width.

Then, the slurry (S) is poured into the casting mold (1) so that the infiltration layer (LA) is formed on the surface of the gypsum mold (2).
At the time when about mm was formed, high-pressure air was introduced through the pressure medium gas introduction hole (2a), a back pressure (P) was added to the slurry (S), and the slurry (S) was pressed toward the gypsum mold (2). Also at this time, the slurry
The back pressure (P) to (S) was made proportional to the elapsed time from the start of pressurization by adjusting the pressure of high pressure air to be introduced, and increased with a proportional constant of 0.2 MPa / min per unit area. .

[0013] The pressurization is continued under the above conditions to grow the inking layer (LA) on the surface of the gypsum mold (2).
A molded body having a thickness of 12 mm was obtained. Then, the molded body was demolded and sufficiently dried, and then 1 mm of the lower surface portion corresponding to the first inking layer was scraped off, and then sintered at a temperature of 1800 ° C.

As a result, a sound sintered body having no bending deformation was obtained. Further, subsequently, the obtained sintered body was ground, and the orientation of the SiC whiskers was investigated by X-ray diffraction on the two front and back surfaces parallel to the gypsum mold (2) surface and the central surface.
The orientation was evaluated by determining the strength ratio between the (002) plane and the (111) plane of the SiC whiskers and comparing the strength of the surface with 1. As a result, as shown in [Table 1], the orientation of the SiC whiskers in the sintered body obtained in this example was
It was confirmed to be uniform within the error of the experiment.

[0015]

[Table 1]

Here, in this embodiment, the slurry (S) is used.
The back pressure (P) that was added to the pressure was increased in proportion to the elapsed time from the start of pressurization, because this is compensated for by the increase in the liquid flow resistance of the growing infiltration layer (LA) and it is eliminated. Therefore, it is needless to say that the back pressure (P) may be increased in proportion to the thickness (L) of the thickness of the layer (LA).

-Example 2- 79.5 wt% α-Si ₃ N ₄ powder having an average particle size of 0.8 μm, average diameter
11.5 wt% of SiC whiskers with an aspect ratio of 10 at 0.9 μm,
4.5 wt% of Y ₂ O ₄ as a sintering aid and Al ₂ 0 ₃ and 4.5 wt%
The added mixture was wet mixed in a ball mill for 10 hours to prepare a slurry (S). In addition, pure water was used as the solvent liquid, and added so that the solid content concentration became 64%.
0.3 wt% of a dispersant was added to improve the dispersibility of the slurry.

Then, this slurry (S) was poured into the same casting mold (1) as in Example 1 above, and when the inking layer (LA) was formed on the surface of the gypsum mold (2) by about 1 mm. Then, as in Example 1, back pressure (P) was applied to the slurry (S), and the back pressure (P) was proportional to the elapsed time from the start of pressurization to 0.4 per unit area. It was increased with a proportional constant of MPa / min.

[0019] Pressurization is continued under the above conditions to grow an inking layer (LA) on the surface of the gypsum mold (2).
A molded body having a thickness of 12 mm was obtained. Then, the molded body was demolded and sufficiently dried, and, similarly to the first embodiment, the lower surface portion 1 mm corresponding to the first inking layer was scraped off, and thereafter, 1800
Sintered at a temperature of ° C.

As a result, a sound sintered body having no bending deformation was obtained. In addition, subsequently, the SiC in the obtained sintered body
The orientation of the whiskers was investigated by the same procedure as in the first example. As a result, as shown in [Table 2], the orientation of the SiC whiskers in the sintered body obtained in this example is uniform within the error of the experiment, as in the case of the first example. Was confirmed.

[0021]

[Table 2]

[0022] - The α-Al ₂ 0 ₃ powder of Example 3 the average particle diameter of 0.8μm 79.5wt%, an average diameter
11.5wt% of SiC whiskers with 1.0μm and aspect ratio of 10,
A mixture containing an oxide sintering aid of 9 wt% was wet mixed in a ball mill for 10 hours to prepare a slurry. Further, pure water was used as the solvent liquid, and was added so that the concentration of the solid content was 64%. Further, 0.3 wt% of a dispersant was added to improve the dispersibility of the slurry.

On the other hand, as shown in the schematic diagram [FIG. 2], the upper metal mold (12) has a cylindrical upper mold (12) and a large number of vertical water passage holes (13a) at the center. The lower die (13) fitted in the lower opening of the die (12) is placed in close contact with the upper surface of the lower die (13), and the outer peripheral edge portion is located above the lower die (13). A casting mold (11) comprising a metal mesh filter (14) sandwiched between the mold (12) and a pressure ram (15) press-fitted into the upper mold (12) from above. I prepared. This casting mold (11) has a structure used in a usual filter press method.
(15) is connected to a pressure device (not shown), while the lower mold
The lower part of the water passage hole (13a) of (13) is open to the atmosphere. Further, in this embodiment, as in the first embodiment, the filter (14)
The cross-sectional shape of the upper mold (12) inner hole above the
It has a square cross-section so that a flat plate of 40 mm can be formed.

Then, the slurry (S) is injected into the casting mold (11), and the infiltration layer (LA) is formed on the surface of the filter (14).
When about 1 mm was formed, the pressure ram (15) was pressed down and the back pressure (P) was applied to the slurry (S) to filter the filter (14).
Pressurized towards. The back pressure (P) by the pressure ram (15) at this time is proportional to the elapsed time from the start of the pressure,
It was increased with a proportional constant of 0.4 MPa / min per unit area.

Continue pressurization under the above conditions, and filter (14)
Growing an infiltration layer (LA) on the surface of the
Then, a molded body having a thickness of 12 mm was obtained. Next, after demolding the molded body and sufficiently drying it, as in the first embodiment,
1 mm of the lower surface corresponding to the first inking layer was scraped off, and then sintered at a temperature of 1800 ° C.

As a result, a sound sintered body having no bending deformation was obtained. In addition, subsequently, the SiC in the obtained sintered body
The orientation of the whiskers was investigated by the same procedure as in the first example. As a result, as shown in [Table 3], the orientation of the SiC whiskers in the sintered body obtained in this example is uniform within the error of the experiment, as in the case of the first example. Was confirmed.

[0027]

[Table 3]

Here, for comparison with the above three embodiments,
Based on the conventional pressure slip casting method, a sintered body having the same composition and size as in Example 1 was manufactured. In First same manner as in Example 1, the α-Al ₂ 0 ₃ powder having an average particle diameter of 0.5μm
A mixture of 79.5 wt%, 11.5 wt% SiC whiskers with an average diameter of 1.0 μm and an aspect ratio of 10 and 9 wt% oxide sintering aid was mixed by a ball mill for 10 hours to prepare a slurry. Also, pure water is used as the solvent liquid,
A solid content concentration of 64% was added, and 0.3 wt% of a dispersant was further added to improve the dispersibility of the slurry.

Then, this slurry (S) was poured into the same casting mold (1) as in Example 1, and at the time when the inking layer (LA) was formed on the surface of the plaster mold (2) by about 1 mm. Then, high-pressure air was introduced through the pressure medium gas introduction hole (2a), and a back pressure (P '), which was a constant pressure of 0.6 MPa per unit area, was added to the slurry (S) and directed toward the gypsum mold (2). And pressurized.

The gypsum mold (2) is continuously pressed under the constant pressure.
Growing an infiltration layer (LA) on the surface of the
Then, a molded body having a thickness of 12 mm was obtained. Then, after demolding the molded body and drying it sufficiently, the lower surface portion 1 mm corresponding to the first inking layer was scraped off and sintered at a temperature of 1800 ° C. as in Example 1. .

As a result, the obtained sintered body was deformed like a part of a spherical surface. Further, subsequently, the orientation of the SiC whiskers in the obtained sintered body was investigated by the same procedure as in the first example. As a result, as shown in [Table 4], the orientation of the SiC whiskers in the sintered body obtained in this comparative example was remarkably changed in the thickness direction.

[0032]

[Table 4]

That is, in the conventional technique in which the back pressure applied to the slurry is constant, the water absorption rate of the mold decreases in inverse proportion to the thickness of the growing inking layer, and the orientation degree of the whiskers rapidly deteriorates accordingly. . Moreover, this is supported by the above-mentioned equation (1). On the other hand, in the present invention, since the back pressure applied to the slurry is increased in proportion to the thickness of the inking layer, the increase in the liquid passage resistance of the growing inking layer itself is eliminated and the water absorption speed of the mold is eliminated. Can be kept constant, and as confirmed in the above-mentioned three examples, the degree of orientation of the whiskers added as the reinforcing fibers can be made uniform.

The particle diameters of the α-Al ₂ O ₃ powder and α-Si ₃ N ₄ powder used in the above three examples, the SiC whiskers as reinforcing fibers, and the diameter and aspect ratio thereof are preferable examples. However, the present invention is not limited to these. For example, when the particle size of the raw material ceramic powder is 1 μm or more, sufficient sintering strength cannot be obtained, so the average particle size is preferably 1 μm or less. In addition to SiC whiskers, Si ₃ N ₄ whiskers, TiC whiskers, TiN whiskers, Al ₂ 0 ₃ whiskers, Zr 0 ₂ whiskers, and the like can be used as the short fibers added as the reinforcing fibers. Is also suitable, but from the viewpoint of current availability, strength and toughness development
SiC whiskers are preferred. Also, its aspect ratio is
If it is 4 or less, the toughness is not sufficiently strengthened by the pull-out mechanism or the like, so it is set to 4 or more, and if the length is 20 μm or more, the short fiber itself is a starting point of fracture, so the length is 20 μm or less and the diameter is 0.2 μm or less In the case of 5 μm or more, the
Since it will be 20 μm or more, 0.2 μm to 5 μm is desirable. Further, the addition amount is preferably 8 vol% or more because the toughness is not sufficiently strengthened at 8 vol% or less, and if a raw material satisfying these conditions is used and an appropriate solvent liquid or dispersion liquid is selected, A healthy slurry is obtained which is compatible with the invention.

[0035]

As described above, according to the present invention,
Even for thicker members, it is possible to impart uniform orientation to the added reinforcing short fibers, and even if anisotropic shrinkage occurs during sintering, significant deformation or cracking does not occur, and toughness and It is possible to obtain fiber-reinforced ceramics having excellent strength and uniform material properties in the thickness direction.

[Brief description of drawings]

FIG. 1 is a schematic view of a casting mold used in an example of the present invention.

FIG. 2 is a schematic view of another casting mold used in the embodiment of the present invention.

FIG. 3 is a conceptual explanatory view of a molding method of a powder compact by a slip casting method and a filter pressing method.

FIG. 4 is an explanatory diagram of a shrinkage form that occurs during sintering of the powder compact.

[Explanation of symbols]

 (1) --Casting mold (2) --Form frame (2a) --Pressurized gas introduction hole (3) --Gypsum mold (4) --Support plate (LA) --Inking layer (L)- -Thickening layer thickness (P) --Back pressure (S) --Slurry

Claims (1)

[Claims] 1. A slurry obtained by dispersing and mixing ceramic powder, which is a base material, and reinforced short fibers in a solvent liquid, is filled in a mold made of a porous material, and a back pressure is applied to the slurry. By adding and pressurizing toward the porous body, discharging the solvent liquid through the porous body and growing a ceramic powder and an infiltration layer of short fibers on the surface thereof, the ceramic powder in the mold is obtained. In the method for producing a fiber-reinforced ceramics, in which a molded body composed of a reinforced short fiber is formed, and thereafter, the molded body is sintered at a high temperature, a back pressure applied to the slurry when the molded body is formed A method for producing fiber-reinforced ceramics, which comprises increasing the thickness of a layer or increasing it in proportion to the time elapsed from the start of pressurization.