JPH0822775B2 - Zirconia sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zirconia sintered body which is excellent in mechanical properties such as strength, fracture toughness, and creep resistance, and is excellent in translucency.

(Prior Art) In recent years, a high toughness sintered body containing tetragonal zirconia as a main constituent has been developed. Generally, the tetragonal zirconia particles contained in this sintered body should be fine. For example, Japanese Unexamined Patent Publication No. 56-134564 describes the condition that the Y ₂ O ₃ —ZrO ₂ system must be tetragonal. If the particle size is larger than 2 μm, the stability of the tetragonal crystal becomes low and it transforms into a monoclinic crystal. For example, 200
If it is left in the vicinity of ° C for a long time, a thermal deterioration phenomenon due to this transformation will be exhibited. That is, there was no known sintered body having large tetragonal grains and good stability.

(Problems to be Solved by the Invention) A conventional zirconia sintered body composed of tetragonal grains has a drawback that mechanical deformation easily occurs at high temperature because of fine grains, Had a drawback in that it was difficult to obtain sufficient translucency. It is an object of the present invention to improve the above two drawbacks by using a sintered body having high stability even though the size of tetragonal grains is large.

(Means for Solving Problems) That is, the present inventors have found that CeO ₂ -ZrO ₂ system has CeO ₂
It was found that by setting the / ZrO ₂ molar ratio to 14/86 to 20/80, it is sufficiently stable even if the average particle size of the tetragonal crystal particles is 5 μm or more.

When the above molar ratio is less than 14/86, the tetragonal crystal becomes unstable and is transformed into a monoclinic crystal, while when it exceeds 20/80, the cubic crystal is mixed.

Here, the average particle size is a value obtained by observing with a scanning electron microscope after etching the polished surface of the sample and using the following formula.

r = 1.5 r: average particle size l: average length of 50 or more particles crossing an arbitrary drawn line segment The sintered body of the present invention can be manufactured as follows.

It is desirable that the raw material powder be of high purity and that ZrO ₂
It may be either a solid solution of CeO ₂ or a mixture of ZrO ₂ powder and CeO ₂ powder. CeO ₂ / ZrO _{2 in it}
The molar ratio should be between 14/86 and 20/80. This powder is molded into a predetermined shape by a molding method such as rubber pressing or slip casting, and then fired. The higher the firing temperature and the longer the firing time, the larger the particles in the sintered body obtained. For example, when the firing temperature is 1550 ° C., the firing time is 10 hours or longer, and when the firing temperature is 1650 ° C., 1 hour or longer, so that a sintered body composed of tetragonal grains having an average grain size of 5 μm or more can be obtained. In order to obtain high translucency, firing in oxygen is better than in air. It is also possible to perform hot isostatic treatment in order to obtain a higher transparency. In that case, it is preferable to select a pressure medium of argon gas, a pressure of 50 MPa or more, and a temperature of 1400 to 1600 ° C. as processing conditions. The CeO ₂ -ZrO ₂ system sintered body is easily reduced and stabilized by hot isostatic treatment,
It must be processed by embedding it in a powder such as CeO ₂ .

(Effects of the Invention) The sintered body of the present invention has excellent mechanical properties and good translucency. The mechanical properties are particularly excellent in fracture toughness and creep resistance. Therefore, the nozzle,
It can be used as high-temperature structural materials such as machine structural parts such as dies and sliding parts, and heat insulating engine parts. Further, since it has a light-transmitting property and is superior to the light-transmitting alumina in mechanical properties, it is more useful than the light-transmitting alumina in the fields where the light-transmitting alumina is used, such as electronic jig parts. It can be used to advantage.

(Example) In the following examples, the bending strength is JIS R 1601 (198
It is the room temperature three-point bending strength value according to 1), and the fracture toughness is the room temperature fracture toughness value measured by the indentation method.

<Production of powder> By hydrolyzing a mixed aqueous solution of zirconium oxychloride and cerium chloride in a predetermined ratio, the resulting sol is dried and pulverized to obtain a CeO ₂ -ZrO ₂ -based fine powder. The composition and particle size of the fine powder are shown in the table below.

<Test Example 1> The powder thus obtained is formed into a plate-shaped compact by a die and a rubber press, placed in a tubular furnace, and the temperature is raised in the atmosphere at a rate of 100 ° C / hr to 1650 ° C. After holding for 2 hours, the temperature was lowered.

The crystal phases of the obtained sintered bodies were all tetragonal crystals. The average particle size, bending strength and fracture toughness are shown in the table below.

<Test Example 2> The powder in Example 2 was made into a thin compact by the same method as in Test Example 1 above, put in a tubular furnace, and the temperature was raised at a rate of 50 ° C / hr while flowing oxygen to 1650 ° C. After holding for 4 hours, the temperature was lowered. The obtained sintered body was mirror-polished to have a thickness of 0.5 mm.

The polished product had translucency. Further, the light transmittance in the visible light range was 13%, and the transmission wavelength range was 0.35 to 7 μm.

<Test Example 3> Using a bending test piece manufactured from the sintered body obtained in Example 2 of Test Example 1, a temperature of 1200 ° C and a crosshead speed of 0.005 mm /
The bending test was conducted under the condition of min, and the particle size was 0.5 for comparison.
A zirconia sintered body containing μm and Y ₂ O ₃ 3 mol% was also tested under the same conditions. After the test, the Y ₂ O ₃ -containing sintered body was largely plastically deformed and bent, but the one of the present invention elastically fractured and showed no plastic deformation. This shows that the sintered body of the present invention is superior in creep resistance as compared with the conventional high toughness sintered body having a minute grain size.

Claims (1)

[Claims] 1. A CeO ₂ / ZrO ₂ molar ratio of CeO ₂ and ZrO _{2 of} 14/86 to
A zirconia sintered body composed of tetragonal grains having an average grain size of 5 μm or more, which is contained in a ratio of 20/80.