JP2581936B2 - Alumina sintered body and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintered body containing alumina and zirconia as a main component and a method for producing the same, and particularly useful as a cutting tool, a high temperature material, or an industrial machine material. It relates to improvement of a sintered body.

(Prior art)

A tool made of ceramic has advantages such as excellent hardness, wear resistance, and heat resistance, but has a problem that chipping and chipping easily occur, and its use has been limited to finishing and the like.

However, recently, with the advent of high-strength ceramics such as silicon nitride, medium to heavy cutting with a ceramic tool has been increasingly performed. As such high-strength ceramics, silicon nitride and zirconia are typical, but both have poor wear resistance and are therefore used only in some fields of cutting.

Alumina (hereinafter referred to as Al ₂ O ₃ ) has been attracting attention as a useful material for cutting tools because of its low reactivity with metals and excellent wear resistance.
₁ c) there has been a problem that low. Zirconia (hereinafter referred to as ZrO ₂ ) has high bending strength and fracture toughness, but shows a sharp decrease in strength at 200 to 300 ° C, is thermally unstable, and has low hardness and large deformation, so cutting tools Was unsuitable for practical use.

Therefore, by dispersing containing ZrO ₂ in Al ₂ O _3, it has been made to improve the fracture toughness of the Al ₂ O _3. Conventionally, two types of methods for improving the fracture toughness have been proposed. One is a material in which monoclinic ZrO ₂ is dispersed in an Al ₂ O ₃ -based sintered body, which generates microcracks due to the phase transition of ZrO ₂ . The other one is Al ₂ O
₃ by dispersing in quality sintered tetragonal ZrO ₂ is intended to absorb the energy of the crack tip at the phase transition of ZrO _2.

[Problems to be solved by the invention]

According to the above prior art, the particle size of the dispersed ZrO ₂ is 1
It is pointed out that the effect of improving the toughness described above weakens below μm. This is because the phase transition from tetragonal to monoclinic of ZrO ₂ hardly occurs.

On the other hand, from the viewpoint of the transverse rupture strength, ZrO ₂ is more preferably fine, and if the ZrO ₂ particles are larger than 1 μm, ZrO ₂ particles of ₂ to 3 μm serve as breaking sources and the transverse rupture strength is reduced. As described above, with the Al ₂ O ₃ -ZrO ₂ material, both the fracture toughness and the bending strength could not be improved.

[Object of the invention]

An object of the present invention is to solve the above-mentioned disadvantages of the Al ₂ O ₃ —ZrO ₂ based sintered body, and to provide a sintered body excellent in both fracture toughness and bending strength and a method for producing the same.

[Means for solving the problem]

The present inventors have conducted studies on the above problems, and as a result,
When a mechanical or thermal shock is applied to the Al ₂ O ₃ sintered body in which ZrO ₂ is dispersed, a high toughness layer having a fracture toughness larger than the center is generated near the surface of the sintered body, and ZrO ₂ particles It was found that the phase transition of ZrO ₂ becomes easy even when the value is small, and the fracture toughness can be improved without lowering the bending strength.

That is, the present invention is an alumina-based sintered body comprising 1 to 30% by weight of zirconia and the remainder mainly composed of alumina, wherein the fracture toughness of the surface is higher than that of the center. The production method is characterized in that a mechanical or thermal shock is applied to an alumina sintered body containing 1 to 30% by weight of zirconia.

 Hereinafter, the present invention will be described in more detail.

Normally, in an Al ₂ O ₃ sintered body in which ZrO ₂ having a particle diameter of 1 μm or less is dispersed, ZrO ₂ particles are present around the ZrO ₂ particles due to the presence of Al ₂ O ₃ particles.
_{2 is in} a state where the phase transition is unlikely to occur.

However, if a suitable mechanical or thermal shock is given to such a sintered body, the phase transition of ZrO ₂ becomes easy. Although the mechanism that facilitates the phase transition is not clear, the present inventor has found that the applied shock causes distortion in the ZrO ₂ particles or increases defects such as transitions in the particles, thereby causing the phase transition. It is presumed that the amount of energy up to that point was reduced.

By such a treatment, a high toughness layer having a fracture toughness larger than the central portion is formed on the surface of the sintered body, and the toughness value decreases almost continuously from the surface portion to the central portion. It has a gradient. The difference in toughness between the high toughness layer and the central portion is related to the transverse rupture strength, as is clear from the examples described later, and the larger the difference, the higher the transverse rupture strength. Therefore, according to the sintered body of the present invention, it is desirable that the fracture toughness value at a position (measurement limit) specifically at 5 μm from the surface is larger than the fracture toughness value at the center by 10% or more, particularly 20% or more.

Further, according to the present invention, ZrO ₂ is 1 to 30 wt% in the composition of the sintered body, in particular 10 to 25 wt%, it is important that the balance being mainly of Al ₂ O _3, the amount of ZrO ₂ Is 1% by weight
If the amount is less than 30%, the toughness decreases. If the amount exceeds 30% by weight, the bending strength and the toughness decrease.

Further, the ZrO ₂ particles in the sintered body of the present invention are preferably 1.5 μm or less, particularly preferably dispersed in Al ₂ O ₃ as fine particles of 0.5 μm, and the particle size of ZrO ₂ is larger than 1.5 μm. In such a case, the effect of increasing the surface toughness tends not to be expected. It is desirable that these ZrO ₂ particles exist in the sintered body as tetragonal or cubic.
Zr between 22.0 and 63.5 ° in the α-ray analysis chart
O ₂ peak (H ₆₃ ), 2θ peak of ZrO ₂ between 27.5-29 ° (H ₂₈ ), 2θ peak of 59.5-61 °, ZrO ₂ peak (H
₆₀ ) Each intensity (peak height) of the ZrO ₂ peak (H ₄₃ ) whose 2θ is between 42.5 and 44 ° is H ₆₃ / H ₂₈ > 0.1 H ₆₀ / H
It is desirable to satisfy ₄₃ > 0.07.

In producing the sintered body of the present invention, a method of applying a mechanical or thermal shock to form a tough layer on the surface of the sintered body is as follows. (In this case, the effect may vary slightly depending on the material of the grindstone and the degree of clogging.) (2) A method of heating the sintered body to 300 to 400 ° C. and then dropping it in water (3) ) Shot peening method and the like.

In addition, the sintered body before performing the above-mentioned processing is 1 to 30% by weight of ZrO ₂ powder, and the rest is required to use a raw material powder mainly composed of Al ₂ O ₃ powder. Manufactured, specifically, first, the mixed powder obtained by mixing the above Al ₂ O ₃ and ZrO ₂ fine powders in the above ratio is formed by press molding, cold molding (CIP), injection molding, slurry casting molding, etc. After that, sintering is performed in the atmosphere at 1250 to 1600 ° C., preferably 1350 to 1500 ° C. or in an inert gas by normal pressure sintering, hot pressing or the like for 1 to 6 hours. In order to further increase the density, the sintered body thus obtained can be subjected to hot isostatic firing at a temperature of 1200 to 1500 ° C.

In addition, as a sintered body before this treatment, ZrO ₂ is particularly 1.5 μm.
m or less, and preferably in the form of a cubic or cubic crystal similar to these.For this purpose, for example, as disclosed in JP-A-57-100976, the particle size is 1.
Using high purity ZrO ₂ powder and Al ₂ O ₃ powder of 5 μm or less and adding additives such as MgO, Y ₂ O ₃ , Cr ₂ O ₃ , NiO,
In a system to which no additives are added, ZrO ₂ can be dispersed as tetragonal and cubic by grinding fine raw material powder with high energy as proposed by the present inventors in Japanese Patent Application No. 62-247413. The latter is particularly desirable from the viewpoint of mechanical properties.

 Hereinafter, the present invention will be described with reference to the following examples.

(Example) Al ₂ O ₃ powder having an average particle size of 1 μm or less and a purity of 99% or more and Z
rO ₂ was blended at the ratios shown in Table 1 and blended for 36 hours in a ball mill. Add binder to raw material after mixing, 4t / c
A test piece was formed by a CIP (Cold Isostatic Press) treatment at a pressure of m ² . After debinding the obtained molded body at 350 ° C., it was preliminarily calcined at 1450 ° C. for 2 hours in the air, and then 1500 kg / c.
Hot isostatic pressure treatment was performed in an m ² Ar gas atmosphere.

A 3 × 4 × 40 mm test piece was cut out from the obtained sintered body,
Was analyzed, Al ₂ O ₃ Average particle size 0.5 [mu] m, ZrO ₂ in ZrO ₂ mean particle size 0.3μm whereas tetragonal ZrO ₂ out of the total amount 5%
Was monoclinic and the rest consisted of tetragonal and cubic.

After performing the treatment shown in Table 1 on the test piece,
A point bending bending test was performed. Note that, among the treatments, the grinding treatment using a diamond grindstone was performed only on the surface to which a tensile stress was applied during the bending test.

In each process, grinding is performed at a depth of cut of 10 μm and a feed of 6 m / min.
The samples were dropped in water, and the surfaces of the samples were further polished with a No. 325 diamond grindstone, heated to a predetermined temperature, and dropped into water at 20 ° C. In addition, shot peening was performed for 1 minute using a steel ball having a diameter of 1 mm after polishing the surface with a No. 325 diamond grindstone.

As is clear from Table 1, in No. 8 where no treatment was applied, the bending toughness was 65 kg / mm ² and the fracture toughness hardly changed from the position of 5 μm to the center. In the case of 1, no tough layer is formed and the impact is excessive.
In No. 4, the sample cracked. All of the specimens which had been subjected to appropriate treatments formed high toughness layers. However, in the case of No. 12 in which the amount of ZrO ₂ exceeded 30% by weight, the transverse rupture strength was extremely low.

Sample Nos. ² , 3, 5, 6, 7, 9, 10, and 11 of the present invention all had a transverse rupture strength of 65 kg / mm ² or more, and an effect of improving the toughness of the surface was observed. The effect is not so significant when dropped from ° C. When ZrO ₂ is 3% by weight (No.
In 9), it is understood that the bending strength tends to be low.

〔The invention's effect〕

Described above in detail streets, to the surface of the Al ₂ O ₃ -ZrO ₂ based sintered body according to the present invention, by providing a mechanical or thermal shock, high toughness of the layer is formed on the surface portion In addition, when this is applied to, for example, a tool or the like, the toughness can be improved to prevent chipping of the cutting edge and extend the life of the tool.

Claims (2)

(57) [Claims] 1. An alumina-based sintered body comprising 1 to 30% by weight of zirconia and a balance mainly composed of alumina, wherein the surface portion has a higher fracture toughness than a central portion. 2. A mechanical or thermal shock is applied to an alumina-based sintered body containing 1 to 30% by weight of zirconia and the remainder mainly composed of alumina to make the surface part tougher than the center part. For producing an alumina sintered body.