JPS59107967A - Zirconia ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to high-strength and high-toughness zirconia porcelain used as structural materials for machine parts, wear-resistant materials, cutting tools, and the like.

Conventionally, zirconia porcelain has been stabilized by Y2O6 and Mg.
It is known as completely stabilized zirconia consisting only of cubic crystals in which O, CaQ, etc. are dissolved. These have been particularly used as solid electrolytes in oxygen sensors and the like.

However, these cubic zirconia porcelains are weak in strength,
In particular, it has poor thermal shock resistance, and its service life as a sensor has become a problem.

On the other hand, it was subsequently discovered that by partially stabilizing zirconia, its basic physical properties such as strength and thermal shock resistance were improved, and it came to be used in sensors and the like. Further developing this idea, the strength properties of partially stabilized zirconia,
Research has been conducted to improve its toughness and use it as a mechanical material.

Conventionally, itria has been generally used as a stabilizer in such high-strength zirconia, and its content has been substantially 3 mol. Ta. In other words, when the amount of ittria is less than 3 molt, it becomes difficult to control the abundance ratio of the crystalline phase, which is a factor that affects strength, by the usual manufacturing method, and desirable results cannot be obtained from an industrial standpoint.

By the way, as stabilizers for zirconia, Y2O3, C
Although aO, MgO, etc. are known, zirconia porcelain partially stabilized with Y2O3 is superior in strength, toughness, etc.

Zirconia porcelain partially stabilized by Y2O3 is called phase transition strengthened zirconia, and absorbs stress (fracture energy) by transitioning the remaining tetragonal crystals to monoclinic crystals. It is said to improve strength properties.

In addition to these findings, the present inventors conducted further intensive studies and found that if the abundance ratio of cubic, tetragonal, and monoclinic crystals in zirconia porcelain is within a certain range, strength and toughness are significantly increased. I discovered that.

That is, the zirconia porcelain of the present invention has three phases: cubic, tetragonal, and monoclinic, and contains 30 to 55% by weight of cubic, 30 to 60% by weight of tetragonal, and 5 to 20% by weight of monoclinic. It is characterized by being % by weight.

In the present invention, the abundance ratio of cubic crystals, tetragonal crystals, and monoclinic crystals in the zirconia porcelain is limited to the above range because if it deviates from the above range, a zirconia porcelain with high strength and high toughness cannot be obtained.

Further, in the Norphea porcelain of the present invention, in order to maintain high strength and high toughness, and further consider heat resistance, it is desirable that the total amount of impurities is 0.85% by weight or less.

In addition, in the zirconia porcelain of the present invention, internal stress increases significantly because tetragonal crystals, which are stable at high temperatures, remain at room temperature.In order to withstand this internal stress and maintain high strength, the porcelain itself must It is desirable that the crystal structure be extremely fine. For this purpose, it is desirable that the average crystal grain size of the matrix portion of the ceramic is 2 μm or less.

Furthermore, for the same reason, it is desirable that the area occupied by the coarse grains within the porcelain is 5 inches or less.

The present invention will be explained in detail below.

The table below consists of Examples 1-11 and Comparative Examples 1-4.

Monoclinic norconia powder with an average particle size of 0.9 μm and a purity of 99.8%, an average particle size of 0.9 μm obtained by coprecipitation method,
Sorconia compound (nY2O5(
100n) ZrO2, n=10) powder were mixed in a mortar so that the final ittria content was as shown in the table below. Next, polyvinyl alcohol was mixed with these mixed powders as a binder, and after granulation, 2.0t
On, pressure molding was performed under the conditions of 2. Subsequently, these molded bodies were fired in the atmosphere for 2 hours at each temperature shown in the same table, and then cooled to obtain zirconia porcelain.

For each obtained zirconia porcelain, the abundance ratio of its crystal phase, average crystal grain size, coarse grain area, impurity content, bending strength,
Fracture toughness values (KIC values) and evaluation results are also listed in the same table.

Incidentally, the quantitative determination of the crystal phase, the measurement of the crystal grain size, the measurement of bending strength, and the measurement of KIc value were performed as follows.

(1) Quantification of crystal phase Monoclinic is determined based on the X-ray diffraction intensity of the lapped surface of the sintered body.
It was calculated using the following formula.

Tetragonal crystals are obtained by pulverizing the above measurement sample to a size of 5 μm or less, and assuming that the tetragonal crystals undergo a phase transition and are all converted to monoclinic crystals due to this pulverization. Based on the X-ray diffraction intensity of this powder, the above formula The crystal was calculated, and the difference from the monoclinic crystal in the lapped plane mentioned above was defined as the tetragonal crystal.

The cubic crystal was determined by the following formula based on the X-ray diffraction intensity of the above-mentioned pulverized powder having a size of 5 μm or less.

(11) Crystal Grain Size Using a scanning electron microscope, the sample was observed at a magnification of 8,000 to 10,000 times, and the area of the micrograph was calculated at 10 random locations.

(Iiii) Bending strength The bending strength was measured by a three-point bending test on a test piece with dimensions of 5 x 5 x 60- obtained by polishing a rectangular sintered body.

(Cut fracture toughness value (KIC value)) An indentation was formed on the test piece using the Vickers method under a load of 30 kg, and the length of the crack extending from the end of the indentation was measured.
It was calculated using the calculation method proposed by Vana et al.

As is clear from the above table, the zirconia porcelains of Comparative Examples 1 to 4 have monoclinic, tetragonal, and cubic crystal phases outside the scope of the present invention, so they have high bending strength and high fracture toughness. I couldn't get it. In contrast, Example 1
All of the zirconia porcelains No. 1 to 11 exhibited high strength and high toughness.

In fact, what about the zirconia porcelain of the present invention? - It was a high-performance product that could be used as a pole for remills or bearings, spikes for rubber tires, fasteners such as bolts and nuts, and tiles for lining mills.

For example, the zirconia porcelain of the present invention is shaped into a cylinder with a diameter of about 10 cm, and placed in an alumina pot with a volume of 2 cm.
Approximately 1ki9 alumina balls with a diameter of 8 mm, 500 g of alumina powder with a particle size of 5 μm, and 800 m7 of water were added and subjected to wet pulverization to measure the abrasion loss, and the weight loss rate after 200 hours was 1.1 to 1.4 C. Comparing this value with conventional zirconia porcelain, it was found that the wear resistance was very good.

Furthermore, even if the ittria content in the zirconia porcelain of the present invention is less than 3 mo1%, it has high strength and high toughness, and compared to conventional zirconia porcelain, the amount of expensive ittria used is small, so the cost is low. It can be manufactured in

As detailed above, according to the present invention, it is possible to provide zirconia porcelain that has high strength and high toughness and is low in cost.

Claims (1)

[Claims] The crystal grains are composed of three phases of cubic, tetragonal and monoclinic,
A zirconia porcelain characterized in that the cubic crystal content is 30 to 55 weight %, the tetragonal crystal content is 30 to 60 weight %, and the monoclinic crystal content is 5 to 20 weight %.