KR950008606B1 - Process for the production sintering of tetragonal zirconia - Google Patents

Abstract

The tetragonal zirconia polycrystalline sintered body added yttria is manufactured by (a) mixing tetragonal zirconia powder of the particle size of 0.5-1.0 micrometer and the sphericity of 0.7-1.0 and 5-30 vol% one or more than two metallic powders which comprise molybdenum, cobalt and nickel powder of the particle size of less than 1.0 micrometer and molding, (b) firing the molded body at 1,300-1,450 deg.C for 0.5-1.5 hrs. in inert or reduction atmosphere. The tetragonal zirconia polycrystalline sintered body has good property of fracture toughness and uses as an abrasion resistant parts and cutting tools etc.

Description

Method for producing tetragonal zirconia polycrystalline sintered body

1 is an optical micrograph showing the microstructure of a tetragonal zirconia polycrystalline sintered body prepared according to the present invention and a comparative method.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ceramics for use in wear resistant members, chips for cutting tools, and the like, and more particularly, to a method for producing tetragonal zirconia polycrystalline sintered bodies having excellent fracture toughness.

Ceramics have high strength and high hardness, which are used in wear-resistant members and cutting tool chips. Such ceramics include tetragonal zirconia polycrystalline sintered body, alumina zirconia composite sintered body, or silicon nitride sintered body. have.

However, since the ceramics are brittle, cracking may occur in the wear-resistant member and the cutting tool chip, which may cause breakage.

The above-mentioned fatal disadvantage of ceramics is that brittleness is due to the intrinsic chemical bonds of ceramics, that is, ionic bonds and covalent bonds. In order to overcome the brittleness of ceramics, complex studies have been actively conducted.

Until now, in the case of zirconia ceramics, a method of improving fracture toughness of zirconia ceramics by adding an oxide such as alumina or a carbide such as silicon carbide as a secondary phase has been proposed.

As an example, Japanese Patent Application Laid-Open No. 59-45969 can be cited, which includes adding alumina to stabilized and unstabilized zirconia powder or simultaneously adding alumina and graphite to calcination at 1600 ° C. under carbon monoxide and nitrogen atmosphere. A method for producing a zirconium oxide-based ceramics having high toughness having a fracture toughness of 9.8-10.3 MN / m ^3/2 is provided.

However, the above-mentioned conventional methods have a disadvantage that it is difficult to manufacture a sintered body composed of only tetragonal zirconia polycrystals because the calcination temperature is higher than 1550 ° C. to obtain partial stabilization zirconia.

The present invention seeks to provide a tetragonal zirconia polycrystalline sintered body having excellent fracture toughness by dispersing the metal powder in a tetragonal zirconia polycrystalline sintered body to induce cracks to propagate across the metal particles and simultaneously using plastic deformation of the metal. There is a purpose.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention provides a method for producing a tetragonal zirconia polycrystalline sintered body, wherein the tetragonal zirconia powder is selected from the group consisting of Mo, Co, Ni, Nb, Ta, Ti, V and W metal powders having an average particle diameter of 1.0 μm or less. Alternatively, the mixed powder to which two or more metal powders are added, 5-30 vol%, is formed as a starting material in a conventional manner, and then the molded body is calcined at a temperature of 1300-1450 ° C. under an inert atmosphere or a reducing atmosphere for 0.5-1.5 hours. The present invention relates to a method for producing a tetragonal zirconia polycrystalline sintered body having excellent fracture toughness.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, when the particle size of the tetragonal zirconia powder is 1.0 µm or more, local sintering occurs, the microstructure becomes uneven, and large residual pores are formed in the sintered body, making densification difficult. Since the grain growth is not possible to predict the microstructure and the reproducibility of the microstructure is difficult, the particle size of the tetragonal zirconia powder is preferably limited to 0.5-1.0 μm.

On the other hand, in order to narrow the particle size distribution and uniformize the microstructure of the tetragonal zirconia polycrystalline sintered body, it is preferable to perform pretreatment such as classification before molding. The tetragonal zirconia powder form is better as the spherical shape is better, and when the sphericity (shortening of the powder: the ratio of the major axis) is 0.7 or less, a lot of voids are generated during molding, so that the molding density and the sintering density are decreased. The sphericity of the positive zirconia powder is preferably limited to 0.7-1.0.

The higher the purity of the tetragonal zirconia powder for sintering is better, and the purity is preferably 99% or more.

The average particle size of the Mo, Co, Ni, Nb, Ta, Ti, V and W metal powder is preferably 1.0 μm or less, because if the average particle size is 1.0 μm or more, the specific gravity of the metal powder compared to the tetragonal zirconia powder This is because it is about 2-3 times so that uniform dispersion is difficult and the sinterability of tetragonal zirconia polycrystal sintered compact is reduced.

The amount of the Mo, Co, Ni, Nb, Ta, Ti, V and W metal powder is preferably limited to 530 vol%, because when the addition amount is less than 5 vol%, the additive metal powder acts as an inclusion and tetragonal It is because the strength of a zirconia polycrystal sintered compact falls, and when the addition amount becomes 30 vol% or more, the sinterability of a tetragonal zirconia polycrystal sintered compact will fall, and strength will fall rapidly.

The higher the purity of the metal powder is, the better it is, in particular, preferably 99% or more.

On the other hand, when the firing temperature is 1300 ° C. or less, a fine tetragonal zirconia polycrystal sintered body cannot be obtained. When the firing temperature is 1450 ° C. or higher, grain growth of tetragonal zirconia occurs, resulting in nonuniform microstructures. Co, Ni is melted in the powders of Ni, Nb, Ta, Ti, V, and W, elutes on the surface of the tetragonal zirconia polycrystalline sintered body, and consequently, large pores remain inside the tetragonal zirconia polycrystal sintered body, and thus the strength decreases. The firing temperature is preferably limited to 1300-1450 ° C.

When firing at the firing temperature of 1300-1450 ° C., the firing time is preferably about 0.5 to 1.5 hours. The reason for this is that when the baking time is 0.5 hours or less, a dense sintered body cannot be obtained due to the presence of many residual pores, In this case, it is because coalescence of tetragonal zirconia powder and the metal powder added in the secondary phase occurs, resulting in uneven structure and lowering of strength.

In addition, as the minor component, an inert atmosphere of nitrogen and / or argon or a reducing atmosphere such as hydrogen is preferable. The reason for this is that when firing in air, the metal is oxidized and the tetragonal zirconia polycrystalline sintered compact is deteriorated due to volume change. This is because the effect of adding the powder is not exerted.

The sintering method is not particularly limited and may be one or two mixing methods of atmospheric pressure sintering, gas pressure sintering, hot pressure sintering and hot hydrostatic sintering.

The method of mixing the tetragonal zirconia powder and the metal powder is not particularly limited, however, in consideration of the specific gravity difference between the tetragonal zirconia powder and the metal powder, it is preferable to use an ultrasonic mixing method or the like rather than a mechanical mixing method such as a ball mill. Do.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

To a tetragonal zirconia powder having a particle size distribution of 0.5-1.0 μm and a sphericity of 0.7-1.0 having 3.0 mol% of Y ₂ O ₃ added thereto, a metal Ni, Mo or Co powder having an average particle size as shown in Table 1 below The mixture is added at the same volume% as 1, mixed, preformed into 50mm in diameter and 10mm in height, followed by cold hydrostatic molding at 20MPa pressure to prepare a molded product, and 0.5-1.5 hours in an arcon atmosphere at a temperature range of 1300-1450 ° C. Gas sintered at a pressure of 10 MPa to prepare a sintered body, and then the relative density, the four-point bending strength, and the fracture toughness of the sintered bodies were measured, and the measurement results are shown in Table 1 below.

On the other hand, in the tetragonal zirconia polycrystal sintered body manufactured by the invention example (4) and the comparative example (6), the dispersion form of the metal Co powder and Mo powder was observed with the optical microscope, and the observation result of the invention example (4) In FIG. 1 (a), the comparative example (6) is shown in FIG. 1 (b), respectively.

In FIG. 1 (a) and (b), the white part is a metal powder, and the black part is a tetragonal zirconia polycrystal.

Table 1

Note 1) Under all conditions of the examples, zirconia has only tetragonal crystal phase.

** Note 2) Relative density is [measurement density / theoretical density] × 100

As shown in Table 1, Inventive Example (1-4) prepared according to the present invention is superior in relative density, four-point bending strength and fracture toughness as compared to Comparative Example (1-9) outside the scope of the present invention. It can be seen.

That is, the fracture toughness is enhanced by the addition of the metal powder. When the amount of the metal powder added is 5 vol% or less in volume ratio, the additive metal powder acts as an inclusion and the strength of the tetragonal zirconia polycrystalline sintered body is lowered. The sinterability of the positive zirconia polycrystal sintered compact fell and the strength fell rapidly.

In addition, when the firing temperature is 1300 ° C. or less, the densification was not performed. When 1450 ° C. or more, Co was melted and eluted to the surface of the crystalline zirconia polycrystalline sintered body. And the strength was lowered.

In addition, when firing in air, the metal oxidizes and the tetragonal zirconia polycrystal sintered body is deteriorated due to the volume change, and the sintered body is opened so that the effect of the addition of the metal powder is not exerted. In the case of 1.5 hours or more, the structure of the sintered body became nonuniform and the strength decreased.

On the other hand, as can also be seen in Figures 1 (a) and (b), when the average particle size of the metal powder is 1.0 µm or more, the specific gravity of the metal powder is about 2-3 times larger than that of the tetragonal zirconia powder, which leads to uniformity. Since dispersion was difficult, the sinterability of the tetragonal zirconia polycrystal sintered compact fell.

As described above, the present invention provides a tetragonal zirconia polycrystalline sintered body in which the metal powder is uniformly dispersed in the secondary phase to enhance fracture toughness, thereby improving the design of mechanical structural components such as cutting tools, wear-resistant parts, and sealing materials. There is an easy effect.

Claims (2)

In the method for producing tetragonal zirconia polycrystalline sintered body to which Y ₂ O ₃ is added, at least one metal selected from the group consisting of Mo, Co, and Ni metal powders having an average particle size of 1.0 μm or less in tetragonal zirconia powder The mixed powder to which 5-30 vol% of the powder is added is molded by a conventional method, and then the molded body is calcined for 0.5 to 1.5 hours at a temperature of 1300-1450 ° C. under an inert atmosphere or a reducing atmosphere. Method for producing sintered body. The method for producing a tetragonal zirconia polycrystalline sintered compact according to claim 1, wherein the particle size of the tetragonal zirconia powder is 0.5-1.0 mu m, and the sphericity is 0.7-1.0.