JPH0359032B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical field The present invention relates to a method for manufacturing extremely high-strength zirconia sintered bodies at low cost. (b) Technical background Partially stabilized zirconia (ZrO ₂ ) sintered body is ZrO ₂
It has long been well known as a strong ceramic that utilizes the phase transition of That is, by dissolving an appropriate amount of Y ₂ O ₃ , CaO, MgO, etc. in ZrO ₂ , ZrO ₂ in the sintered body exists in a metastable state as a tetragonal crystal. This tetragonal ZrO ₂
is transferred to monoclinic crystal due to stress concentration,
Stress relaxation at the crack tip occurs, and a significant improvement in toughness is achieved. However, although the fracture toughness is significantly higher than that of other ceramic materials, the reality is that pressureless sintering can only yield a transverse rupture strength of 1 GPa or less. This is because the cavities remaining in the sintered body serve as starting points for destruction. In order to make this into a high-strength ceramic with a strength of 1.5 GPa, it is necessary to perform hot press sintering, but the drawback is that this increases the cost. (C) Disclosure of the Invention In view of the above-mentioned drawbacks, the present inventors have conducted various studies on methods for manufacturing high-strength zirconia sintered bodies at low cost. By pre-sintering the zirconia sintered body until it runs out, and then sintering it in a hot isostatic press without canning, it is possible to obtain a zirconia sintered body that has higher strength than that obtained by conventional hot press sintering and is also cheaper. This is what I discovered. Partially stabilized _ZrO2 exists in the form of metastable tetragonal crystals, so it is necessary to make it into a sintered body with the smallest particle size possible, and the raw material used must be fine powder of 1μ or less. For this reason, the compactability was extremely poor, and pores often remained in the sintered body. Conventionally, these drawbacks have been solved by hot-press sintering, but hot-press sintering is expensive and has large size and shape restrictions, which limits its applications. The present inventors succeeded in obtaining an extremely high-strength zirconia sintered body with no pores by optimizing the manufacturing conditions when performing hot isostatic pressing after preliminary sintering. . The method will be explained in detail below. First, add Y ₂ O ₃ , MgO or CaO to zirconia powder.
A zirconia powder compact is obtained by a known molding method using a known composition (Japanese Unexamined Patent Publication No. 54-4913) in which, for example, 2 to 4 moles of Y ₂ O ₃ are dissolved in solid solution. . After that, this molded body is placed in a vacuum atmosphere.
Pre-sintering is performed at a temperature of 1390-1600℃ until there are no open pores. In order to perform canning-less hot isostatic pressing (HIP), the theoretical density ratio is preferably 95% to 98%.
It is necessary to sinter it. Temperature conditions: 1390~1600℃
The reason why the range is set is that below 1390°C, the disappearance of open pores is not achieved, and above 1600°C, _two ZrO grains grow, resulting in particles of 1μ or more, resulting in a significant decrease in strength. Furthermore, by sintering in a vacuum atmosphere, adsorbed gas can be smoothly removed during sintering, and open pores can easily disappear. The obtained pre-sintered body was further heated for 200 min by hot isostatic pressing (HIP) in an inert gas atmosphere.
Sintering at 1200-1600℃ under pressure of more than Kg/ ^cm2 . The reason why the pressure is set at 200 Kg/cm ² or higher in this HIP is that if the pressure is 200 Kg/cm ² or lower, there is no effect of removing residual pores, and therefore, densification does not occur. Also 1200-1600
The reason for limiting the degree Celsius and temperature conditions is the same as the reason for pre-sintering. In other words, at temperatures below 1200°C, densification progresses slowly, and at temperatures above 1600°C, ZrO ₂ grain growth significantly causes a decrease in strength and a decrease in tetragonal crystals. It is desirable that the zirconia sintered body thus obtained has a density of 98% or more and a tetragonal content as large as possible. In particular, the ratio of tetragonal to monoclinic is calculated as tetragonal (111) / tetragonal (111) + monoclinic (111) + monoclinic (111), but according to the above formula, if it is less than 0.9, A significant decrease in strength is undesirable. Furthermore, if the average particle size of ZrO ₂ is 1 μ or more, the strength will be significantly lowered, so it is preferable to suppress it to 1 μ or less, and more preferably 0.5 μ or less. The dizirconia sintered body obtained by this invention has a transverse rupture strength of 1.5 GPa, the production cost is lower than that of the hot press method, and it has extremely practical industrial value in terms of properties such as chemical stability. It's expensive. The present invention will be explained in detail below with reference to Examples. Example 1 Partially stabilized zirconia powder obtained by coprecipitating ZrO ₂ and 3 moles of Y ₂ O ₃ (manufactured by Daiichi Kigenso Kogyo Co., Ltd.)
HSY-3) was wet-pulverized in a ball mill for 24 hours,
The obtained slurry solution was dried in the air. Further, after molding with a hydrostatic press at a pressure of 1 t/cm ² , a 7 mm x 6 mm x 45 mm test piece was cut out as a test piece. This molded specimen was tested under the conditions shown in Table 1.
After sintering for an hour, the sintered body with an average grain size of 1μ or less was further heated with Ar at 1400℃ for 1 hour without canning.
Hot isostatic pressing was carried out at a pressure of 1 t/cm ² in gas. Table 1 shows the results of examining the characteristic values of each sintered body, such as specific gravity, transverse rupture strength (GPa), fracture toughness (K _IC ), and amount of tetragonal ZrO ₂ . From Table 1, it was recognized that the method of the present invention is superior. Note that the numbers marked with 〓 in Table 1 are outside the scope of the claims of this invention.

[Table] Example 2 The pre-sintered body of sample number 3 shown in Example 1 was subjected to various HIP conditions shown in Table 2 without canning.
When HIP sintered, the characteristic values shown in Table 2 were obtained. From this result, it was recognized that the HIP conditions had a large influence on the properties of the sintered compact. Note that the numbers marked with 〓 are outside the scope of the claims of this invention.

[Table] Example 3 ZrO ₂ powder containing 5 mol MgO and ZrO ₂ powder containing 8 mol CaO were subjected to preliminary sintering and HIP sintering without canning under the conditions shown in sample number 3 of Example 1. The properties shown in Table 3 were obtained.

【table】

Claims (1)

[Claims] 1. Molding ceramic powder whose main component is zirconium oxide with a grain size of 1μ or less and excellent sinterability.
Theoretical density ratio is 95% in vacuum atmosphere at 1390-1600℃
After sintering to a state with no open pores ^, X
The peak intensity ratio by line diffraction is 0.9 or more for tetragonal crystals,
Production of a high-strength zirconia sintered body with a transverse rupture strength of 1.0 GPa or more, characterized by obtaining a zirconia sintered body in which the monoclinic and/or cubic crystals are 0.1 or less and the average grain size of ZrO ₂ is 1 μm or less. Method.