JPH07291722A - Method for manufacturing ceramics sintered body - Google Patents

Abstract

(57) [Summary] [Objective] Alumina and monoclinic zirconia, which have a large particle size and are inexpensive, are used as starting materials to obtain a high-strength and low-cost ceramic sintered body. [Composition] 10 having an average particle size of 1 to 2 μm and a purity of 95% or more.
0% to 10% by weight of monoclinic zirconia (ZrO ₂ )
And yttria (Y ₂ O ₃ ) to ₃ to 5 mol% with respect to zirconia, and 60 to 90 wt% alumina (Al ₂ O ₃ ) having an average particle size of 0.5 to 2 μm and a purity of 99.5% or more. Raw material powder containing 0.1% or less of MgO and SiO ₂ as a co-agent is uniformly dispersed by kneading, and the dried kneading powder is filled in a hot press mold and kept in a temperature range of 1600 to 1700 ° C. for 1 hour or more. While maintaining, a pressure of 30 MPa or more is applied in the temperature range for 0.5 hour or more to sinter.

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 an alumina-zirconia ceramics sintered body.

[0002]

2. Description of the Related Art A piston pin used for a piston of an automobile engine is a component for transmitting an explosive force received by the piston to a crankshaft, and its characteristics are mechanical strength, wear resistance and resistance to repeated stress. Weight reduction is required to improve fuel efficiency. Conventionally, a piston pin made of steel is generally used, and it may be hollowed to reduce the weight, but there is a limit in terms of durability and reliability.

When the piston pin is made of ceramics, materials such as silicon nitride and silicon carbide are not suitable because they have a low coefficient of thermal expansion and produce a clearance due to frictional heat between the piston pin and the metal piston. In recent years, zirconia-dispersed alumina ceramics have been attracting attention as a high-strength structural material. The main uses of this are to increase the toughness and wear resistance of cutting chips, and to commercialize large parts such as pistons. There is no example. A conventional manufacturing process of this alumina-zirconia composite material is shown in FIG. Zirconia powder is added with alumina powder as the main component, and a kneaded mixture of these is added with a molding binder to granulate, and the granules are molded into a predetermined shape, and the molded body is cut if desired. After sintering at normal pressure, and subjecting the sintered body to hot isostatic pressing as necessary,
The finishing grinding process is performed. However, conventional ceramics made of alumina-zirconia composite material have high manufacturing costs, and cannot be applied to large parts such as piston pins in terms of cost.

JP-A-1-172262 discloses that zirconia powder is 1 to 30% by weight and alumina powder is 70 to 99% by weight.
In the composition consisting of at least one metal selected from alkaline earth metals or rare earth metals, the zirconia content is 0.
After being molded into a predetermined shape using a material added with 0 to 1 to 3 mol%, it is further densified by cold isostatic pressing, and the obtained molded body is baked at 1450 ° C. for 6 hours and further at 1400 ° C.
A method for producing a high-strength alumina-based sintered body is described, in which hot isostatic pressing is performed with argon gas at 2000 kg / cm ² .

Further, in Japanese Patent Laid-Open No. 61-117153, an alumina containing 14 to 22.5% by weight of monoclinic zirconia powder is externally coated with yttria as a sintering aid to 0.1 to 1.0. There is described a method for producing an alumina sintered body, in which a molded body which is added by weight% and uniformly ground and molded is fired by an atmospheric pressure sintering method in air in a temperature range of 1500 to 1650 ° C.

[0006]

[Patent Document 1] Japanese Patent Application Laid-Open No. 1-172
In the sintering method described in Japanese Patent No. 262, since the sintering is performed at a temperature of 1500 ° C. or less, the raw material must have a fine particle size of 1 μm or less, and a material having such a particle size is expensive. . Further, since the hot isostatic treatment is performed after the molding, the manufacturing method becomes complicated, and the equipment cost of the hot isostatic device is required, resulting in extremely high manufacturing cost.

Further, in the manufacturing method described in the above-mentioned JP-A-61-117153, since the sintering is carried out by the atmospheric pressure sintering method, the raw material powder to be used must be highly pure and have a small particle size. Instead, expensive raw material powder must be used. Furthermore, even if such expensive raw material powder is used, large parts such as piston pins (for example, φ50 × 100m
In m), densification cannot be achieved during sintering.

The present invention solves the above problems, low cost alumina containing a small amount of flux, which is difficult to sinter by atmospheric pressure sintering as starting materials, and monoclinic zirconia which has not been stabilized. It is an object of the present invention to provide a method for producing a ceramics sintered body, which is capable of producing a large-sized component with high strength and at low cost by using.

[0009]

The present invention has an average particle size of 1 to
10% to 40% by weight of 100% monoclinic zirconia (ZrO ₂ ) having a purity of 95% or more at 2 μm and yttria (Y
₂ O ₃ ) with respect to zirconia in an amount of 3 to 5 mol% and an average particle size of 0.
Alumina with a purity of 99.5% or more at 5 to 2 μm (Al
₂ O ₃ ) 60 to 90 wt% MgO, Si as a sintering aid
The raw material powder containing 0.1% by weight or less of O ₂ was uniformly dispersed by kneading, and the kneaded powder was filled in a hot press mold to prepare 1
This is a method for producing a ceramics sintered body, in which the temperature is maintained in the temperature range of 600 to 1700 ° C. for 1 hour or more and a pressure of 30 MPa or more is applied in the temperature range for 0.5 hour or more to sinter.

[0010]

When the sintering temperature is lower than 1600 ° C, the relative density of the sintered body is insufficient, and the ratio of tetragonal and cubic is insufficient. On the contrary, when the sintering temperature exceeds 1700 ° C., the crystal strength grows and the bending strength becomes insufficient. Therefore, the sintering temperature is 1600 to 1: 1.
A range of 700 ° C is appropriate. The above high temperature holding time is
In the case of a thick part, if the time is less than 1 hour, defects are generated inside the sintered body due to the temperature unevenness inside, and the relative density is reduced, so it is set to 1 hour or more. The pressing force is an important parameter for promoting the flow and diffusion between powders during sintering.
If it is less than Pa, it will not be densified. Further, when the pressure holding time at high temperature is less than 0.5 hours, the relative density of the sintered body sharply decreases, but when it is 0.5 hours or more, the sintered body is sufficiently densified.

[0011]

Embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a manufacturing process diagram, and FIG. 2 is a partial cross-sectional view of a hot press mold. As a raw material powder, 100% monoclinic zirconia 10-20 having an average particle size of 1-2 μm and a purity of 95% or more
% By weight, yttria to zirconia 3 to 5 mol%, and alumina having an average particle size of 0.5 to 2 μm and a purity of 99.5% or more (including 0.1% by weight or less of MgO and SiO ₂ ).
~ 90 wt% is uniformly dispersed by wet or dry kneading,
This kneaded powder is dried and filled in the hot press mold shown in FIG. 2 as it is without being granulated. Hot press
As shown in FIG. 2, a die 1 made of graphite or ceramics.
A void is formed in the center of the piston in accordance with the dimensions of the piston pin to be molded, and the raw material powder 2 is kneaded and dried in this void.
To fill.

The raw material powder 2 filled in the hot press is pressed by a graphite punch 3 and sintered at a high temperature in a vacuum or in an air atmosphere to perform sintering. After sintering, the sintered body taken out from the hot press is put into a piston. Finish the outer diameter so that it is within the tolerance of the external dimensions of the pin. Sintering by hot press is 160
In the temperature range of 0 to 1700 ° C, high temperature holding time 1 hour or more,
Pressurization pressure 30MPa or more, pressure retention time 0.5 in high temperature range
More than time.

The most important characteristic required for a ceramic piston pin is strength, and the strength of a sintered body is determined by the crystal grain size of the sintered body, the tetragonal stabilization ratio of zirconia and the density. The particle size of zirconia is 1-3μ
m, alumina 1 to 4 μm, tetragonal / cubic crystal stabilization ratio of 80% or more, relative density of 99.5% or more, sintering temperature, high temperature holding time, pressure, pressure holding time, etc. It is necessary to set the conclusion conditions. 3 to 5, the relative density, average crystal grain size, tetragonal and cubic of a sintered body obtained by sintering the alumina-zirconia composite material having 80% by weight of alumina by changing the sintering temperature. The crystal ratio and bending strength are shown.

When the sintering temperature is less than 1600 ° C., the relative density of the sintered body is insufficient as shown in FIG. 3 and the ratio of tetragonal and cubic crystals is insufficient as shown in FIG. On the contrary, when the sintering temperature exceeds 1700 ° C., the crystal grains grow as shown in FIG. 3, so that the bending strength decreases as shown in FIG. Therefore, the sintering temperature is appropriately in the range of 1600 to 1700 ° C.

FIG. 6 shows a sintering pattern, and FIGS. 7 to 9 show changes in the relative density of the sintered body when the sintering pattern is changed. It is necessary to set the high temperature holding time (tr) to a parameter that can control the voids generated inside the sintered body. Especially for thick parts such as piston pins, if it is less than 1 hour, the internal temperature Due to the unevenness, defects occur inside the sintered body, and the relative density decreases as shown in FIG. Therefore, the high temperature holding time (tr) is appropriately set to 1 hour or more. The pressurizing force (P) and the pressurizing force holding time (tp) are important parameters for promoting the flow and diffusion between the powder particles, and as shown in FIG. In addition, the pressure holding time (T
As shown in FIG. 8, the relative density of pr) drops sharply in less than 0.5 hours, but if 0.5 hours or more, the sintered body is sufficiently densified.

The pressure holding time (tp-tpr) in the temperature raising process T ₁ -T ₂ is preferably as short as possible from the viewpoint of cost, but the timing T _{1 at} which pressurization is started is
At 1500 ° C. or higher at which diffusion between powders becomes active, self-sintering progresses unevenly before pressurization and crack-like defects occur, so it is desirable to set at 1500 ° C. or lower. The temperature rising rate in the temperature rising process T _{1 to} T ₂ is sufficient if there is no extreme temperature gradient inside the sintered body, and there is no problem if it is 10 to 50 ° C./min. Therefore, as for the sintering pattern, as shown in FIG. 10, the temperature rising rate is 30 ° C./min, the applied pressure (P) of 1200 ° C. to 30 MPa is applied, and the applied pressure holding time (tp) is 0.75 hours. It is appropriate that the temperature is raised to 1650 ° C., the high temperature holding time (tr) is set to 3 hours, and the pressure holding time (Tpr) in the high temperature is set to 0.5 hour.

Next, test examples and test results will be described below. As the raw material powder, zirconia (ZrO ₂ ) having a central particle size of 1.5 μm, a purity of 95%, and 100% of monoclinic crystal,
3 mol% of yttria (Y ₂ O ₃ ) was added with respect to zirconia, and commercially available zirconia that was only subjected to dispersion treatment and not subjected to stabilization treatment, and had a central particle diameter of 0.5 μm and a purity of 99.5%.
Commercially available alumina (Al ₂ O ₃ , MgO as a sintering aid,
SiO ₂ is contained in an amount of 0.1% by weight or less) in various proportions as in the test example shown in Table 1, and methanol is used as a mixed solution for wet mixing for 20 hours in a ball mill. next,
This solution is dried in a 100 ° C. drying cabinet until the methanol content is completely volatilized, and this dried powder is placed in a graphite hot press die having an inner diameter of 50 mm so that the total length of the sintered body after sintering is 100.
Measure and fill to be mm. After filling and enclosing in a hot press, it was sintered in the sintering pattern shown in FIG. Table 2 shows the test results of the characteristic values of the φ50 × 100 mm sintered body thus obtained. In addition, Tables 1 and 2 show the characteristics of hot-pressed alumina sintered bodies and normal-pressure sintered alumina sintered bodies that were molded into the same size by using only the same alumina raw materials as the comparative examples.

[0018]

[Table 1] Note 1: H press indicates sintering by hot pressing. Note 2: In the raw material blending ratio, Test Examples 1 to 5 and Comparative Examples 6 to 7 contain 0.1% or less of MgO and SiO ₂ as auxiliary agents, and Comparative Example 8 contains 4%. Note 3: The mixing ratio (% by weight) of Y ₂ O _{3 in} Test Examples 1 to 5 is
Each corresponds to 3 mol% with respect to ZrO ₂ . Note 4: All sintering temperatures were set to 1650 ° C.

[0019]

[Table 2]

As shown in Table 2, in Test Examples 2 to 5, the bending strength was remarkably improved as compared with Comparative Examples 6 to 8 and the appearance of the sintered body was not defective. Become. The outer diameter dimensional accuracy of the sintered bodies of Test Examples 1 to 5 is shown in Table 3 below. Table 3 shows that since the shrinkage strain due to sintering is extremely small, the stock removal of the grinding process in the post-process can be reduced.

[0021]

[Table 3] Note 1: All units are in mm Note 2: Cylindricity is the value for a total length of 100 mm

As described above, when the piston pin is made into a sintered body by the material and the manufacturing method of the present invention, the weight can be reduced by about 45% as compared with the case where it is made from the conventional steel, and the contraction strain due to the sintering is obtained. Since the size is extremely small, the machining allowance for post-processing can be reduced, so the manufacturing cost is less than twice that of conventional steel piston pins, and the cost can be reduced to the level where ceramics can be used as piston pins for commercial vehicles. It will be possible. Further, the present invention is not limited to piston pins, but can be applied to large-sized shaft parts such as spindles of machine tools.

[0023]

Industrial Applicability According to the present invention, a ceramic sintered body having high strength can be accurately formed by using a relatively inexpensive ceramic raw material, and the process can be simplified as compared with the conventional manufacturing process. It is possible to manufacture a ceramics sintered body with strength and low cost.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of the present invention.

FIG. 2 is a partial cross-sectional view of a hot press used in the present invention.

FIG. 3 is a diagram showing a relationship between a sintering temperature, a relative density of a sintered body, and an average crystal grain size.

FIG. 4 is a diagram showing the relationship between the sintering temperature and the tetragonal / cubic crystal ratio of the sintered body.

FIG. 5 is a diagram showing a relationship between a sintering temperature and a bending strength of a sintered body.

FIG. 6 is a diagram showing a sintering pattern.

FIG. 7 is a diagram showing a relationship between a pressing force and a relative density of a sintered body.

FIG. 8 is a diagram showing a relationship between a pressure holding time at a high temperature and a relative density of a sintered body.

FIG. 9 is a diagram showing the relationship between high temperature holding time and relative density of a sintered body.

FIG. 10 is a diagram showing an example of a sintering pattern.

FIG. 11 is a conventional manufacturing process diagram.

[Explanation of symbols]

 1 Die 2 Raw material powder 3 Punch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masataka Okada 3-25-1, Tonomachi, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Isuzu Motors Limited Kawasaki Plant (72) Shunichi Ito 3-Chome, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture No. 25-1 Inside Isuzu Motors Limited Kawasaki Plant

Claims (1)

[Claims] 1. 10 to 40% by weight of 100% monoclinic zirconia (ZrO ₂ ) having an average particle size of 1 to 2 μm and a purity of 95% or more, and 3 to 5 of yttria (Y ₂ O ₃ ) with respect to zirconia.
Add 0.1% by weight or less of MgO and SiO ₂ as a sintering aid to 60% to 90% by weight of alumina (Al ₂ O ₃ ) having an average particle size of 0.5 to 2 μm and a purity of 99.5% or more. The raw material powder was uniformly dispersed by kneading, and the kneaded powder was filled in a hot press mold and held at a temperature range of 1600 to 1700 ° C. for 1 hour or more, and a pressure of 30 MPa or more at a temperature of 0. A method for producing a ceramics sintered body, which comprises applying and sintering for 5 hours or more.