JPS59162173A - Zirconia sintered body - 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 provides Zr02 with high mechanical strength and fracture toughness.
The present invention relates to a -0θO1-based zirconia sintered body.

The sintered body according to the present invention can be used for cutting or cutting tools.

It is suitable for use as a constituent material for individual dies, nozzles, sliding parts, etc.

Pure zirconia has a reversible phase transition between 900 and 1200°C, which causes a large volume change. Such abnormal volume changes cause cracks in the sintered body, making the production of the sintered body difficult. Therefore, when making a sintered body, various stabilizers such as Mc70.
It is common practice to use so-called stabilized zirconia (hereinafter referred to as FSZ), which has a cubic crystal structure that does not cause phase transition by dissolving OaO, 'Y2O3, etc. as a solid solution. However, such a FSZ sintered body
It has a disadvantage in that it is inferior in mechanical strength such as bending strength and thermal shock strength, and is not suitable for applications requiring such properties.

Recently, this drawback has been fundamentally improved with high strength.

Research is being conducted on zirconia sintered bodies with high toughness. This sintered body differs from the FSZ sintered body in its composition and crystal structure. That is, in terms of composition, the amount of stabilizer added is smaller than that of FSZ.

On the other hand, in terms of crystal structure, while FSZ has a cubic system, it consists of a tetragonal system or a mixed phase of a tetragonal system and a cubic system.

Such a sintered body is made of partially stabilized zirconia (hereinafter referred to as ps
(denoted as z) is called a sintered body. This psz sintered body is
It has high strength and high toughness, and the reason for this is explained below.

In other words, when mechanical stress concentration is applied to the tip of a crack in a sintered body, the surrounding tetragonal particles undergo stress-induced transformation to monoclinic, and the volume expansion that accompanies this causes the crack to open. By inhibiting the progress, fracture toughness and fracture strength are increased. Therefore, in order for the PSz sintered body to have high strength and high toughness, it is extremely important that it contains particles having a tetragonal crystal phase.

However, this tetragonal crystal phase is the high temperature phase in most zirconia-stabilizing component systems and does not exist as a stable phase at room temperature. Therefore, it is allowed to exist as a metastable phase at room temperature, but in this case, the method of manufacturing the sintered body and the selection of the type and amount of stabilizer added are important.

Currently, Mg0-Z is used as a high-strength, high-toughness psz sintered body.
rO, system, 0aO-ZrO, system, Y, 03-ZrO
Two types of sintered bodies have already been mentioned.

The present inventors have developed the above-mentioned stabilizer MgO, Oak.

As a result of intensive research aimed at obtaining a sintered body with excellent mechanical properties using stabilizers other than Y and O, we found that ZrO
The present inventors have discovered that the 2-0eO system is extremely effective and have accomplished the present invention. According to previous research, ZrO2
It was said that the J3e02 type Akatsuki compact does not exhibit the high strength and toughness known from the ZrO, -Y2O2 type. The present invention has succeeded in obtaining a dense sintered body based on a sintered body manufacturing technology, especially a unique raw material powder preparation technology,
This was achieved because by further examining the composition in detail, they were able to derive a result that differs from the conventional theory.

That is, the present invention provides a zirconia sintered body mainly composed of Zr01 and Coo, and whose crystal phase is mainly a tetragonal system or a mixed phase of a tetragonal system and a cubic system.

In order to manufacture the sintered body of the present invention, ZrOt-CeO is used.

After molding the raw material powder into a desired shape by a rubber press method or the like, it may be sintered by firing at a temperature of 1300 to 1600° C. for several hours.

ZrO, -CeO, raw material powder can be prepared by the so-called dry synthesis method, in which zirconia powder and Ceria powder are mixed, calcined, and pulverized repeatedly. In order to obtain a sintered body with high strength, it is preferable to use the wet synthesis method described below.

For example, an aqueous solution of a zirconium salt such as zirconium oxychloride or zirconium nitrate and an aqueous solution of a cerium salt such as cerium nitrate are mixed to a desired composition, and aqueous ammonia is added to the resulting precipitate, which is then split and dried. This method involves calcining to obtain the desired powder.

Alternatively, a method may be used in which a mixed solution of the zirconium salt and cerium salt is heated for several tens of hours to cause a hydrolysis reaction, and the resulting sol is dried and calcined to obtain the desired powder. Furthermore, the mixed solution of the zirconium salt and cerium salt is evaporated to dryness under normal pressure or reduced pressure, pulverized, and calcined at a temperature of 500°C to 900°C to obtain the desired powder. Good way to get it too.

Powders obtained by these so-called wet synthesis methods have excellent sinterability and are suitable as raw materials for producing the sintered body of the present invention. □ In addition, it is not necessary to use high-purity cerium oxide or cerium salt as the ceria raw material;
If the amount is 1 or more, the remainder may be an oxide or salt made of a light rare earth metal such as samarium or tan. Such raw materials are inexpensive and suitable as raw materials for industrial products.

Therefore, in the present invention, a zirconia sintered body mainly composed of ZrO2 and Oe02 means a sintered body mainly using CeO as a stabilizer of zrO,
In addition to Coo1, other rare earth oxides, such as y, o
, , Yb203 , La, O,, am, O@
etc., or alkaline earth metal oxide MgO, c
Furthermore, metal oxides of Group 3 and Group 4 of the periodic table, such as aO, sc
, o3°TiO2, HfO, and the like.

For example, in a ZrO2-Coo, -Y, 01-based sintered body, Y, 0. If the added amount is 2 molt or less and partial stabilization is achieved, the added Coo can be considered to be making an important contribution to the partial stabilization, and therefore falls within the scope of the sintered body of the present invention.

Zr02-C of the present invention! so, in the system sintered body (!e
The molar ratio of o2/ZrO must be in the range of 8/92 to 3o/7o. This CeO2/ZrO, molar ratio is 8
When the amount is less than /92, it is extremely difficult to obtain a sintered body having a tetragonal crystal phase. In this case,
After the sintered body is fired, a phase transition from a tetragonal system to a monoclinic system occurs during the cooling process to room temperature, and cracks may even occur due to the volumetric expansion. Also, the molar ratio is 5
If it exceeds 0770, a sintered body with the desired crystalline phase consisting of coexisting tetragonal and cubic crystal phases can be obtained, but the proportion of the tetragonal system is decreasing, which is expected. It is not possible to obtain such high fracture toughness and fracture strength.

The crystalline phase of the sintered body of the present invention is mainly composed of a tetragonal system or a mixed phase of a tetragonal system and a cubic system. However, in addition to these crystal phases, a small amount of monoclinic phase may coexist.

The permissible monoclinic proportion is 30 wt% or less.

The measurement was carried out by X-ray diffraction method, and monoclinic crystal (11
1) plane, the (111) plane, the (200) plane of the tetragonal crystal, and the (200) plane of the cubic crystal, respectively, as M(111).
), M(11 completed), T(200,>.

When 0 (2U O), (M<111>+M<111>)/(T<200.>+
Let the intensity ratio of c(200)+M(111>+M(1tr>) be the weight percent of the monoclinic system.

The particle size of the sintered body of the present invention is preferably 2 μm or less, and at a firing temperature of 1400°C, the particle size is 111L2 to 05 μm, and at a temperature of 160°C.
At 0°C, it is 1 to 2 μm. Conventionally, it has been known that when a Ps2 sintered body is exposed to high temperatures for a long time, it deteriorates over time and the sintered body breaks. For example, a Y, O, -P8Z sintered body with a particle size of 2 μm or more is heated at 200°C to 3
When left at a temperature of 00° C. for a long time, the tetragonal crystal transforms to monoclinic crystal, and cracks are observed in the sintered body. That is,
The finer the particle size, the less thermal deterioration occurs over time. The particle size of the sintered body of the present invention can be easily controlled to 2 μm or less, and such a sintered body is preferable because it has excellent thermal stability.

Furthermore, the sintered body of the present invention has a mechanical strength of 3-point bending strength of 50 kg/m" or more and a fracture toughness of 4 MN*m"".
It has characteristics greater than or equal to t and s. If the characteristic values are below these values, the sintered body of the present invention cannot withstand use as a useful industrial member, which is not preferable.

Next, the sintered body of the present invention will be described in detail based on Examples.

Three-point bending strength and fracture toughness in Examples were measured by the following methods.

Three-point bending strength measurement is performed by cutting and grinding a plate-shaped sintered body for 3 seconds.
A rectangular bar-shaped test piece of as+X 4 sn

Fracture toughness is measured by the indentation method, in which a Vickers indenter is driven into the mirror-polished sintered sample surface and the value is calculated from the ratio of the indentation length to the crack length generated from the indentation. The driving load of the indenter is 20 kg. The formula used for calculation is D, B, Marshall a
ndA+G, Evans, Oomm, Am.

The following formula described in Oeram, Soc, 0-182 (1981) is used.

Kxo= 0.036 K"P"'a-'・'(O
/a)-'・5KXO; Fracture toughness (N-re'-")
E: Modulus of elasticity (Nsm-") P: Load (Nsm-") a: Diagonal length of indentation (m) C: Length of crack generated from indentation (m) Examples 1 to 6. Comparative Example 1 An aqueous solution of zirconium oxychloride and an aqueous solution of nitric acid consisting of 80% cerium, the balance, and a light rare earth metal such as lanthanum, samarium, and neodymium were mixed to a desired composition and heated at 100° C. for 60 hours.

Heating was continued to obtain a hydrolyzed sol. The powder obtained by evaporating to dryness was calcined at 900° C. and further ground in a ball mill for 48 hours to prepare a ZrO, -0θO7-based raw material powder. Next, the raw material powder was processed by a rubber press method to a thickness of 9 width and a length of 43111.40 mm and 5 mm, respectively.
A plate-shaped molded product having a size of 6 tu was obtained.

This molded body was fired at a temperature of 1,400 to 1,500°C for 2 hours, and 7. A rof-c8o-based sintered body was obtained.

The crystal phase content, crystal grain size 1 bending strength, and fracture toughness were measured for the seven sets of sintered bodies prepared in this way. These results are shown in Table 1.

Examples 7 and 8. Comparative Example 2 An aqueous solution of zirconium oxychloride and an aqueous solution of cerium nitrate with a purity of 99% or more were mixed to a desired composition,
According to the method described in Example 1, a ZrO2-0eO raw material powder was prepared. This powder was molded by a rubber press method and held at a temperature of 1400° C. for 2 hours to obtain the desired sintered body. Measurements similar to those described in Example 1 were performed on the three sets of sintered bodies thus produced.

The measurement results are shown in Table 1.

Example 9.10 Water bath solutions of zirconium oxychloride, cerium nitrate, and yttrium nitrate were mixed to give the desired composition, and aqueous ammonia was added thereto to adjust the pH of the solution to 8 to obtain a precipitate. This was cut into pieces, dried, calcined at 800℃, and further ground in a ball mill for 24 hours to form Zr02.
-0θ02-Y, 03 series raw material powder was obtained. The above raw material powder was molded and fired in the same manner as described in Example 1 to obtain a sintered body of the present invention. Regarding the two sets of sintered bodies created in this way, the crystal phase content, crystal grain size 9, bending strength,
Fracture toughness was measured.

The measurement results are shown in Table 2.

It is clear from the above results that the zirconia sintered body of the present invention mainly contains OeO as a stabilizer and mainly consists of tetragonal crystals or tetragonal crystals and cubic crystals as a crystal phase, and has high strength, It has high toughness.

Applications that require mechanical strength and thermal/mechanical durability, such as cutting tools, extrusion or wire drawing dies, cutters, spray nozzles, grinding balls, ball bearings, mechanical seals, hydraulic equipment structural parts, and internal combustion engines. It is suitable as an industrial material for structural parts, etc., and is extremely useful industrially.

Patent applicant: Toyo Soda Kogyo Co., Ltd. 446-1

Claims (1)

[Scope of Claims] (1) A zirconia sintered body mainly consisting of Z r02 and Coo, and a crystal phase mainly consisting of a tetragonal system or a mixed phase of a tetragonal system and a cubic system. (The molar ratio of 210e 02 /Z r 02 is 8/
Claim No. (1) which is in the range of 92 to 30/70
The zirconia sintered body described in . (3) The 6-point bending strength of the zirconia sintered body is 50 k
p) m” or more, and the fracture toughness is 4 M N m
-'' or more, the zirconia sintered body according to claim No. +11 or (2).