Tetragonal zirconia ceramic powders, tetragonal...

Details Tetragonal zirconia ceramic powders, tetragonal... Tetragonal zirconia ceramic powders, tetragonal...

2000-04-10

2002-04-30

Koslow, C. Melissa (Department: 1755)

Compositions: ceramic

Ceramic compositions

Refractory

C501S103000, C501S127000, C501S153000, C264S666000, C264S664000

Reexamination Certificate

active

06380113

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zirconia ceramic powder and a tetragonal zirconia-alumina composite using the ceramic powder which have a low temperature degradation resistance as well as a high strength and high toughness, and to a method of a preparation for the same, and in detail, to a tetragonal zirconia ceramic powder having a triangle composition range formed of three composition points of 92 mol % ZrO
2
-4 mol % Y
2
O
3
-4 mol % Nb
2
O
5
(or Ta
2
O
5
), 89 mol % ZrO
2
-7 mol % Y
2
O
3
-4 mol % Nb
2
O
5
(or Ta
2
O
5
), 86 mol % ZrO
2
-7 mol % Y
2
O
3
-7 mol % Nb
2
O
5
(or Ta
2
O
5
) in which the composition ratio of the tetragonal zirconia is in the ternary system of ZrO
2
—Y
2
O
3
—Nb
2
O
5
, or a zirconia/alumina composite comprising the above-described tetragonal zirconia and 5~50% (v/v) alumina and a manufacturing method of the same, which has a low temperature degradation resistance as well as a high toughness and high strength.
2. Description of the Background Art
A pure zirconia has three polymorphic forms of a monoclinic phase, tetragonal phase and cubic phase based on a temperature under an atmospheric pressure. In the case the pure zirconia, it is known to have a cubic phase from a melting point of zirconia to 2370° C. when cooling the same at a high temperature, a tetragonal phase from about 2370° C. to about 1170° C., and a monoclinic phase below 1170° C. When cooling a high temperature tetragonal phase above 1170° C., the phase is transformed to the monoclinic phase at 950° C., so that a volume is expanded by 3~5% for thereby forming cracks over the entire portions of a sintered body. In order to prevent a martensitic phase transformation, an oxide such as MgO, CaO, Y
2
O
3
, CeO
2
, etc. is added as a stabilizing agent for thereby stabilizing a cubic phase or tetragonal phase which is stable in high temperature. The stabilized Y—TZP(YO-stabilized Tetragonal Zirconia Polycrystalline) in which all ceramic grains are formed in the tetragonal phases by sintering under a condition that the tetragonal phase is stable by adding Y
2
O
3
is a material having a high strength above 1000 MPa by decreasing the flaw size due to a crystal control effect. However, when this material is exposed at 100~400° C. for a long time, the tetragonal phase is transformed to the monoclinic phase for thereby causing cracks, so that the mechanical characteristics (for example, strength) of the material are degraded. In order to prevent the low temperature degradation phenomenon and strength decrease, an alumina is added into the zirconia for thereby manufacturing a composite. In the case when adding the alumina, the alumina acts to minimize the flaw size and acts as a grain-growth inhibits of the zirconia, so that the zirconia-alumina composite have a high strength compared to the zirconia monolith. Namely, since the strength of the zirconia is in reverse proportional to the grain size, the alumina added into the zirconia prevents a grain growth of the zirconia during a sintering operation for thereby increasing the strength of the tetragonal zirconia.
Various zirconia/alumina ceramics are disclosed. For example, according to the U.S. Pat. No. 4,298,385 by Claussen, it is known that a composite of alumina, zirconia and HfO
2
has high toughness. However, in the U.S. Pat. No. 4,298,385, it is difficult to maintain a tetragonal phase as the amount of zirconia is increased, and the grain size of the zirconia must be maintained below 0.5 &mgr;m.
According to the U.S. Pat. No. 4,316,964, a zirconia and alumina composite into which Y
2
O
3
, CeO
2
, La
2
O
3
, Eu
2
O
3
, etc. are added for stabilizing the tetragonal phase is disclosed by Lange. According to the U.S. Pat. No. 4,533,647, different composition of the alumina/zirconia composite is disclosed by Tien. A zirconia and HfO
2
are added into the alumina into which Cr
2
O
3
is dissolved to increase the phase transformation temperature from the tetragonal phase to the monoclinic phase for thereby increasing the toughness. However, in this patent, it was known later that the toughness was not increased.
According to the U.S. Pat. No. 4,552,852, a composite manufactured by adding a zirconia or HfO
2
and glass phase into the alumina is disclosed by Manning. The thusly manufactured material has an increased thermal shock resistance.
According to the U.S. Pat. No. 4,587,225, a zirconia/alumina composite into which Y
2
O
3
is added by Hot isostatic press method is disclosed by Tsukuma. This composite has a high strength and is sintered for a short time at a lower temperature compared to other composite.
According to the U.S. Pat. No. 4,666,467, a high strength zirconia/alumina composite is disclosed by Matsumoto. The composition of the same is formed of a zirconia 50%~98% added by 1.5~5 mol % Y
2
O
3
and an alumina or spinel of 50%~2 weight %. According to the U.S. Pat. No. 4,659,680, a method for manufacturing a zirconia which is partially stabilized by adding yttria and implementing a secondary stabilized phase. In this method, the sintered body is quickly cooled from a temperature range of 1000° C.-1475° C. and is maintained for a long time at a temperature at which the zirconia is precipitated inside a cubic grain.
According to the U.S. Pat. No. 4,760,038 by Kinney et al., a composite is manufactured by adding 5~35% ZrO
2
as a first additive and 0.25 through 5% TiO
2
and MnO
2
as a second additive and a third additive respectively using the alumina as a main component. The above-described additives are used to increase a thermal shock resistance of the ceramic composition and prevent a decrease of the strength in a high temperature.
According to the U.S. Pat. No. 4,829,028 by Ichiro, et al., an alumina/zirconia composite having an excellent mechanical strength is manufactured using a Bayer alumina or bauxite for alumina and a vedellate mineral rock for a zirconia. In addition, according to the U.S. Pat. No. 5,061,665 by Ichiro, et al., a molten body is manufactured using the alumina and zirconia and then is rapidly cooled, and at least one ceramic powder selected from the group comprising CeO
2
and TiO
2
having an average diameter of 0.5 through 1.5 &mgr;m is added to the resultant solid material and is ground and sintered for thereby manufacturing an alumina/zirconia composite. This composite has an excellent strength and thermal shock resistance characteristic depending on the amount of ZrO
2
, CeO
2
, and TiO
2
.
According to the U.S. Pat. No. 5,556,816, a new zirconia among the compositions ternary system of ZrO
2
—Y
2
O
3
—Nb
2
O
5
or Ta
2
O
3
, is disclosed. This zirconia has a high toughness and a phase transformation does not occur from the tetragonal phase to the monoclinic phase. However in this patent, the physical strength in which the grain size acts as one of the important factors is very low die to the large grain growth.
As described above, there are various patents and reports on the zirconia/alumina composite for the reason that the zirconia's grain in which the martensitic phase transformation occurs enhances a lower mechanical properties of the alumina, and the alumina having a large Young's modulus restricts the low temperature degradation of the zirconia. However, as shown in
FIG. 1
, adding the alumina to the tetragonal zirconia does not restrict the low temperature degradation of the tetragonal zirconia under the autoclave processing condition at a temperature of 200° C. and 200 MPa vapor pressure. Only when heat-treating in the air at a temperature of 100~400° C., the low temperature degradation is delayed.
SUMMARY OF THE INVENTION
The present invention is directed to a zirconia/alumina composite and a manufacturing method of the same which provide a high strength and toughness and a low temperature degradation resistance.
Accordingly, it is an object of the present invention to provide a tetragonal zirconia having a triangle composition range formed of three composition points of 92 mol % ZrO
2
-4 mol % Y
2
O
3
-4 mol % Nb
2
O
5
(

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