JPS589784B2 - Zirconia cutting tool material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal cutting tool material comprising a sintered body of a zirconia solid solution in which zirconia is doped with one or more of oxides of yttrium, calcium, and magnesium.

Ceramics have been attracting attention as tool materials for high-speed cutting, and Al2O3, Al2O3-Tic,
Tools using Al2O3-TiN, cermet, etc. have been developed.

However, although these tools exhibit excellent cutting performance on cast iron, steel, etc., they have the disadvantage that they are prone to chipping due to the poor toughness of the material.

In addition, it has been difficult to cut aluminum alloys, copper alloys, etc. because of its high affinity with the metal to be cut.

As a result of conducting research on tool materials for high-speed cutting, the present inventors focused on zirconia sintered bodies.

As is well known, a 100% zirconia sintered body has approximately 100%
At temperatures below 0°C, it has a monoclinic structure, but at around 1200°C, it reversibly transforms into a tetragonal phase with a large volume change and collapses.

Therefore, zirconia solid solutions with an equiaxed crystal phase in which the dislocation is suppressed by adding alkaline earth metal oxides, rare earth oxides, etc. are used in some fields, but these sintered bodies also have low strength. Due to its low strength and lack of toughness, it has not been used as a cutting tool material.

In addition, abrasive grains were developed in which a two-component mixture of zirconia and alumina was melted and then rapidly supercooled to form a eutectic of alumina and monoclinic and tetragonal phase zirconia, and these were used as grinding wheels. However, the operating temperature of this abrasive grain is 80℃.
When the temperature reaches 0°C or higher, the tetragonal phase transforms to the monoclinic phase during cooling from this high temperature, causing large cracks and collapsing.Since it is a eutectic of Al2O3 and ZrO2,
There are drawbacks such as low strength of the boundary.

Therefore, it is difficult to process this zirconia-alumina material into cutting tools, and during high-speed cutting,
It cannot be used for metal cutting tools that reach temperatures close to 00°C.

However, according to the research of the present inventor, a sintered body of a zirconia solid solution containing at least one of oxides of yttrium, calcium, and magnesium, which has a monoclinic system, a tetragonal system, and an equiaxed system. When using a zirconia-based material that has a tricrystalline phase and the total amount of the two phases of tetragonal and equiaxed crystal systems is within a specific range, it is also possible to use so-called difficult-to-cut metals such as aluminum alloys. Demonstrates high-speed machinability,
It has been found that a cutting tool is obtained which allows for extended tool life and a smooth finished surface.

That is, the present invention comprises a sintered body of a zirconia solid solution containing one or more oxides of yttrium, calcium, and magnesium, and the crystals of the sintered body are monoclinic, tetragonal, and equiaxed. The present invention provides a zirconia cutting tool material which contains a trigonal crystal system and has a two-phase content of tetragonal and equiaxed crystal systems of 60 to 95% by weight.

When the cutting tool material of the present invention comes into contact with the metal to be cut, it instantly becomes heated to a high temperature of 1000°C or more, is subjected to large thermal stress and mechanical stress, and even a chemical reaction occurs with the metal to be cut. It can exhibit excellent cutting performance and durability even under severe cutting conditions.

Further, its bending strength is at least 50 kg/mm2, and depending on manufacturing conditions, it is possible to achieve an ultra-high strength exceeding 100 kg/mm2.

The yttria content in the material of the present invention is usually 1.0 to 6.0 mol% based on zirconia, more preferably 1.0 to 6.0 mol%.
It is 5 to 5.0 mol%.

In addition, the calcia content is usually 2.0 to 8.0 to zirconia.
0 mol%, more preferably 2.5 to 6.0 mol%
It is.

Furthermore, the magnesia content is usually 3.0 to 3.0 to zirconia.
10.0 mol%, more preferably 4.0 to 9.0 mol%
It is.

When using a mixture of two or more of these, the content may be within the above range in the mixing ratio of each.

For example, when using equal amounts of yttria and calcia, the amount of yttria used is (1.0 to 6.0 x 1/2) = 0
．． 5 to 3.0 mol%, and the amount of calcia used is (2.0 to 8.0 mol%).
0×1/2)=1.0 to 4.0 mol%.

When these contents are below the above-mentioned lower limit amounts, the monoclinic phase tends to increase, leading to a transition to a tetragonal phase at high temperatures and collapse due to the accompanying volume change.

On the other hand, if the content exceeds the above upper limit, the bending strength tends to decrease significantly.

If the total content of the two phases, the tetragonal phase and the equiaxed phase, is less than 60% by weight, the thermal shock resistance will be low, and if it exceeds 95% by weight, the content of the tetragonal phase will be relatively low, resulting in poor durability. deteriorates.

The zirconia cutting tool material of the present invention is manufactured, for example, as follows.

First, add a predetermined amount of one or more of yttria, calcia, and magnesia to zirconia within the above range,
A powder consisting of fine primary particles of 1 μm or less is prepared by uniformly mixing.

Then, the powder was heated to 0. It is molded into a predetermined shape under pressure of 5 ton/cm2 or more, and fired at about 1300 to 1800°C under normal pressure or pressure to close to the theoretical density.

In this way, a tetragonal phase that does not transform to a monoclinic phase even at room temperature remains in the sintered body.

Although the firing atmosphere is not particularly limited, firing in the atmosphere is economically most advantageous.

It goes without saying that the higher the molding pressure, the more advantageous it is, and the firing temperature is more preferably about 1350 to 1650°C.

When the firing temperature is outside the range of 1300 to 1800°C, the strength of the sintered body decreases.

In the material of the present invention in which the tetragonal phase remains in the zirconia solid solution sintered body, energy that generates cracks due to external thermal stress and mechanical stress or energy that causes fine cracks to progress further remains inside. It is presumed that the tetragonal phase absorbs these stresses, thereby exhibiting high durability against these stresses.

Therefore, the material of the present invention exhibits excellent heat resistance, thermal shock resistance, high strength, and high hardness even under extremely harsh metal cutting conditions, and furthermore, it has little affinity with metals and is chemically stable. It also has excellent machinability on difficult-to-cut materials such as aluminum alloys and copper alloys.

The sintered body of the tetragonal phase-containing zirconia solid solution of the present invention has properties such as excellent heat resistance, thermal shock resistance, high strength, and high hardness, so it can be used not only as a cutting tool material but also as a variety of cutting tool materials. It is also useful as a wear-resistant material, high-strength material, etc.

Example 1 Yttrium chloride with a purity of 99.9% was added to a 1 mol% solution of zirconium oxychloride with a purity of 99.9% so that Y2O3 was 3.5 mol% with respect to ZrO2, and after uniformly mixing, A mixed hydroxide is obtained by coprecipitation, which is dehydrated and dried, and calcined at 800° C. to obtain a primary particle powder having an average particle size of about 150 holes.

The powder is pressure-molded at 2 tons/cm 2 , fired in an open atmosphere electric furnace at 1480° C. for 2 hours, and then gradually cooled to room temperature.

This fired body contains three phases: a monoclinic phase, a tetragonal phase, and an equiaxed phase, and the total amount of the tetragonal phase and the equiaxed phase is 90%.
Weight%, hardness HRA92.6, bending strength 92kg/mm
It was 2.

The obtained sintered body is ground and polished to a size of 13 mm square, a thickness of 5.0 mm, and a nose radius of 0.5 mm.

This sample was mounted on a lathe and the cutting speed was 500 m/min.
, depth of cut 1.0mm, feed 0.15mm/rev. An aluminum alloy containing 13% Si was turned under the following conditions.

The flank wear of the sample cutting tool after a total of 10 minutes and 33 seconds was 0.
．． It was 24 mm.

In addition, the smooth surface of the turned surface was almost the same as when a diamond tool was used.

The crystal phase in the zirconia solid solution sintered body was measured using the following procedure.

(i) The surface of the sintered compact sample is ground with a diamond grindstone #100 and the flat surface is irradiated with X-rays, and each crystal structure is confirmed by the diffraction line profile.Monoclinic crystals are tetragonal and equiaxed crystals. Since the lattice spacing of the diffraction lines is greatly different from that of
Quantification can be performed from the diffraction X-ray intensity ratio (area ratio). (ii) Tetragonal and equiaxed crystals have similar lattice spacing values, and their separation and quantification can be performed directly and accurately. I can't.

Therefore, the diffraction X-ray image of equiaxed crystal (c): c<111>, c
<200>, c<202>, c<311>, c<222
> and c<400> and diffraction X-ray image of tetragonal crystal (t): t
<111>, t<002>, t<200>, t<202
>, t<220>, t<113>, t<311>, t<
113>, t<311>, t<222>, t<004>
and t<400> to confirm whether or not tetragonal crystals exist in the sample.

(iii) A mixture of equiaxed crystals and tetragonal crystals <111> (the two cannot be distinguished) for samples in which the presence of tetragonal crystals was confirmed in (ii) above, and equiaxed crystals for samples without tetragonal crystals. <111> was taken, and the value of tetragonal + equiaxed crystal was determined from the ratio of the intensity (■) of monoclinic <111> and monoclinic <111> according to the formula below.

The bending strength was determined by polishing the surface of a 25 mm long, 3 mm square test piece smooth in the longitudinal direction, and performing a three-point bending test with a span distance of 20 mm.

Example 2 A zirconium oxychloride solution and a yttrium chloride solution were mixed so that Y2O3 was 2.3 mol% with respect to ZrO2, and the mixed hydroxide obtained by coprecipitation was dehydrated and dried, and temporarily heated at 900°C. A primary particle powder having a particle size of about 230λ is obtained by firing.

The powder is pressure-molded at 2 ton/cm 2 and fired at 1500° C. for 2 hours in an open atmosphere electric furnace.

The content of tetragonal phase and equiaxed phase in the sintered body is 85% by weight, hardness HRA 92.5, bending strength 110 kg/mm2
Met.

When the obtained sintered body was used as a cutting tool material in the same manner as in Example 1, the flank wear of the sample cutting tool after a total of 12 minutes and 6 seconds was 0.22 mm, which was equivalent to or higher than that in Example 1. Excellent results were obtained.

Example 3 Calcium carbonate (special grade reagent) was added to a 1 mol % zirconium oxychloride (purity 999%) solution, stirred thoroughly to dissolve it, and then aqueous ammonia was added dropwise to dissolve 4 mol % calcium based on ZrO2. A zirconium hydroxide adsorbed is obtained, which is dehydrated and dried, and calcined at 900° C. to obtain a primary particle powder having an average particle size of about 280 Å.

After dispersing the secondary particles of this powder to an average particle size of 0.3 μ or less, they were pressure-molded at 2.5 ton/cm2, fired at 1500°C for 2 hours in an open atmosphere electric furnace, and then slowly heated to room temperature. It got cold.

This fired body contains three phases: a monoclinic phase, a tetragonal phase, and an equiaxed phase, and the content of the two phases of the tetragonal phase and the equiaxed phase is 78% by weight. Strength 70kg/mm2
Met.

This sintered body was used for turning under the same conditions as in Example 1.

The flank wear of the sample cutting tool after a total of 4 minutes and 21 seconds was 0.
It was 23 mm.

Example 4 1 mol% zirconium oxychloride (99.9% purity)
Magnesium chloride (special grade reagent) was added to the solution, stirred thoroughly, and then co-precipitated with aqueous ammonia to obtain a mixed hydroxide containing 5 mol% of magnesium based on ZrO2, which was dehydrated and dried at 950°C. The average particle size is approximately 32.
A powder with primary particles of 0 Å is obtained.

This powder was dispersed to have a secondary particle average particle diameter of 0.3 μm or less, then pressure molded at 2.5 ton/cm 2 , fired in an electric furnace at 1530° C. for 2 hours, and then slowly cooled to room temperature.

This fired body contains a triad of monoclinic phase, tetragonal phase and equiaxed phase, the total amount of the two phases of tetragonal phase and equiaxed phase is 70% by weight, hardness HRA92.3, Bending strength 85kg/mm2
Met.

This sintered body was used for turning under the same conditions as in Example 1.

The flank wear of the sample cutting tool after a total of 6 minutes and 27 seconds was 0.
It was 24 mm.

Comparative Examples 1 to 6 (i) Comparative Example 1: In Example 4, the amount of magnesium as a stabilizer for ZrO2 was 8.5 mol%,
Except for dispersing the powder with a calcination temperature of 1400°C and an average primary particle size of about 2 μm into an average secondary particle size of 2.5 μm or less,
A sintered body was obtained in the same manner as in Example 4.

The amount of tetragonal crystals + equiaxed crystals, bending strength hardness, etc. are those of Comparative Examples 2 to 6.
The results are shown in Table 1.

(ii) Comparative example: Y for ZrO2 in Example 2
A sintered body was obtained in the same manner as in Example 2, except that the amount of 2O3 was 2.0 mol %, the calcination temperature was 1200°C, and the primary particle powder had a particle size of 1.5 μm.

(iii) Comparative Example 3: In Example 2, the amount of Y2O3 relative to ZrO2 was 4.8 mol%, and the firing temperature was 185%.
A sintered body was obtained in the same manner as in Example 2 except that the temperature was 0°C.

(iv) Comparative Example 4: A sintered body was obtained in the same manner as in Example 3, except that the amount of CaO relative to ZrO2 in Example 3 was changed to 9 mol%.

(v) Comparative Example 5: Ca for ZrO2 in Example 3
Containing 2.0 mol% O and 3.0 mol% Y2O,
A sintered body was obtained in the same manner as in Example 3 except that the firing temperature was 1650°C.

(vi) Comparative Example 6: Example 4 except that the amount of magnesium relative to ZrO2 in Example 4 was 15 mol%.
A sintered body was obtained in the same manner as above.

From the results shown in Table 1, when the total amount of the tetragonal phase and the equiaxed phase is less than 60% by weight (Comparative Examples 1 and 2), the bending strength is extremely low and cannot be put to practical use at all. is clear.

Even if the total amount of the tetragonal phase and the equiaxed phase is within the range of 60% and 95% by weight, if there is no tetragonal phase (
Comparative Example 3) also had low bending strength.

Moreover, when the content of the tetragonal phase and the equiaxed phase exceeds 95% by weight, the bending strength becomes significantly lower in the absence of the tetragonal phase (Comparative Example 6); Even if a system phase exists, the hardness (HRA) may not reach 90 (
Comparative example 4).

Regarding Comparative Example 5, in which the total amount of the tetragonal phase and the equiaxed phase is 98%, the presence of the tetragonal phase is also recognized, and the bending strength and hardness (HRA) have reached the practical range. Therefore, it was finished into a cutting tool in the same manner as in Example 1, and then used in the same manner as in Example 1 for turning an aluminum alloy containing 13% Si.

However, it was found that defects occurred after 10 seconds and that it could not be put to practical use.

Claims (1)

[Claims] 1 Consists of a sintered body of a zirconia solid solution containing one or more oxides of yttrium, calcium, and magnesium, and the crystals of the sintered body have three phases: monoclinic, tetragonal, and equiaxed. A zirconia cutting tool material characterized in that the total amount of two phases of tetragonal system and equiaxed system is 60 to 95% by weight.