JP7321413B2 - ceramic cutting tools - Google Patents

Description

The present invention relates to ceramic cutting tools.

Conventional ceramic cutting tools have been improved in fracture resistance by increasing their strength (see Patent Document 1).

International Publication No. 2014/002743

However, this ceramic cutting tool has insufficient resistance to wear as described below, and has a problem in cutting performance. That is, conventional ceramic cutting tools are required to be improved in terms of crater wear, in which wear progresses due to insufficient hardness, and VB wear, in which wear progresses due to falling off of particles.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic cutting tool with improved wear resistance. The present invention can be implemented as the following modes.

[1] A ceramic cutting tool made of a ceramic sintered body containing at least tungsten carbide and alumina,
Among the XRD peaks of tungsten carbide, the intensity Ia of the peak attributed to the crystal plane (001) and the intensity Ib of the peak attributed to the crystal plane (100) are expressed by the following relational expression when viewed from the rake face: A ceramic cutting tool characterized by satisfying [1] and satisfying the following relational expression [2] when viewed from the flank face.

Relational expression [1]: Ia/Ib≧0.450
Relational expression [2]: Ia/Ib ≤ 0.440

[2] At least one element selected from the group consisting of Group 3 of the periodic table (including lanthanoids), titanium, zirconium, and hafnium is present in the grain boundaries between the tungsten carbide and the alumina. The ceramic cutting tool according to [1], characterized in that

[3] The surface is composed of at least one carbide, nitride, oxide, carbonitride, carbonate, nitroxide, and carbonitride oxide selected from the group consisting of titanium, zirconium, and aluminum. The ceramic cutting tool according to [1] or [2], characterized in that at least one kind of surface coating layer is formed.

By satisfying the relational expression [1]: Ia/Ib≧0.450 when viewed from the rake face, crater wear is suppressed. Further, by satisfying the relational expression [2]: Ia/Ib≦0.440 when viewed from the flank, VB wear is suppressed. Thus, by satisfying the two relational expressions, crater wear and VB wear are suppressed.
When a predetermined element is distributed in the crystal grain boundary between tungsten carbide and alumina, the grain boundary is strengthened and the cutting performance is improved.
Wear resistance is improved when a specific surface coating layer is formed on the surface.

1 is a perspective view of an example of a ceramic cutting tool; FIG. It is a sectional view showing an example of the state of use of a ceramics cutting tool. It is a sectional view showing an example of a ceramics cutting tool. 1 is a schematic perspective view of a tungsten carbide crystal; FIG. It is a sectional view of an example of a ceramics cutting tool. It is a cross-sectional view of an example of a conventional ceramic cutting tool. It is a sectional view of an example of a ceramics cutting tool. 4 is a graph showing changes in temperature and press pressure in the firing process of Examples 1-12. 13 is a graph showing changes in temperature and press pressure in the firing process of Example 13. FIG. 4 is a graph showing changes in temperature and press pressure in the firing process of Comparative Example 1. FIG.

The present invention will be described in detail below. In this specification, the description using "-" for the numerical range includes the lower limit and the upper limit unless otherwise specified. For example, the description “10 to 20” includes both the lower limit “10” and the upper limit “20”. That is, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Ceramic cutting tool 1
The ceramic cutting tool 1 is composed of a sintered body containing at least tungsten carbide and alumina.
A ceramic cutting tool 1 has a rake face 3 and a flank face 5 (see FIGS. 1 and 2). The shape of the ceramic cutting tool 1 is not particularly limited. In addition, in FIG. 2, the code|symbol 4 has shown the to-be-cut object.
Among the XRD (X-ray diffraction) peaks of tungsten carbide, the ceramic cutting tool 1 has a peak intensity Ia attributed to the crystal plane (001) and a peak intensity Ib attributed to the crystal plane (100). satisfies the following relational expression [1] when viewed from the rake face 3 and satisfies the following relational expression [2] when viewed from the flank face 5.

Relational expression [1]: Ia/Ib≧0.450
Relational expression [2]: Ia/Ib ≤ 0.440

In relation to the relational expression [1], the upper limit of Ia/Ib is not particularly limited, but is usually 0.5.
is 0. Also, regarding the relational expression [2], the lower limit of Ia/Ib is not particularly limited, but is usually 0.40, and may be a value close to "0".
(1) Components Contained in Ceramic Cutting Tool 1 and Content of Each Component The ceramic cutting tool 1 contains at least tungsten carbide and alumina.
The content of each component will be explained. The following content is the amount when the entire sintered body (ceramic cutting tool 1) is 100 vol %.
The content of tungsten carbide is not particularly limited. From the viewpoint of hardness and sinterability, the content of tungsten carbide is preferably 20 vol% to 95 vol%, more preferably 23 vol% to 64 vol%, and even more preferably 33 vol% to 64 vol%.
Alumina content is not particularly limited. The content of alumina is preferably 3 vol % to 74 vol %, more preferably 23 vol % to 64 vol %, even more preferably 33 vol % to 64 vol %, from the viewpoint of hardness and sinterability.

The ceramic cutting tool 1 may contain other components than tungsten carbide and alumina. As another component, a component containing at least one element selected from the group consisting of Group 3 of the periodic table (including lanthanoids), titanium, zirconium, and hafnium (hereinafter also referred to as "specific element") is preferably exemplified. be done. Among these components, a component containing at least one element selected from the group consisting of zirconium, yttrium, titanium, hafnium, and ytterbium is preferable from the viewpoint of good tool life.
If these other components are contained, the specific element will be distributed at the grain boundary between tungsten carbide and alumina in the ceramic cutting tool 1 (ceramic sintered body). In this case, the sinterability is improved and the bonding strength of grain boundaries is improved. Although the details of the mechanism by which the bonding strength is improved in this way are not clear, it is presumed that the specific element increases the bonding strength of the grain boundary. More specifically, tungsten carbide, which is a carbide, and alumina, which is an oxide and is chemically stable, are difficult to react with each other, and usually sufficient bonding strength cannot be obtained between them. However, when the specific element intervenes in the grain boundary, the specific element bonds with oxygen of alumina and the specific element bonds with carbon of tungsten carbide, thereby increasing the bonding strength of the grain boundary between tungsten carbide and alumina. It is speculated that As a result of improving the bonding strength of the grain boundaries, the wear resistance of the ceramic cutting tool 1 is improved and the tool life is extended.

In order to distribute the specific element at the grain boundary, each component should be well dispersed by a technique such as bead mill pulverization at the time of manufacturing the ceramic sintered body. For example, when fine zirconia powder or a zirconium salt solution is used as the zirconia raw material, the zirconium element is effectively distributed at the grain boundaries. In addition, it is also effective to perform a dispersion-mixing treatment in which only the zirconia raw material is ground first, or to use grinding media made of zirconia.
In addition, by optimizing the heating rate and holding time during firing, the movement (diffusion) of the specific element can be promoted.

(2) The average particle size of each component is not particularly limited. The average particle size of each component may be 1.0 μm or less, or may be 0.7 μm or less.
The "average particle diameter" in the present specification is a value measured by an intercept method based on an image of a mirror-polished ceramic sintered body etched and observed with an SEM.

(3) Relational Expression of Ia and Ib Here, the relational expression of Ia and Ib will be described.
The peak intensity Ia is the intensity of the peak attributed to the crystal plane (001) among the XRD peaks of tungsten carbide. For example, a peak height near 2θ=31.4° is preferably used.
The peak intensity Ib is the intensity of the peak attributed to the crystal plane (100) among the XRD peaks of tungsten carbide. For example, a peak height near 2θ=35.7° is preferably used.
The peak intensity Ia and the peak intensity Ib satisfy the relational expressions [1] and [2] above, but preferably satisfy the following relational expressions [1′] and [2′].

Relational expression [1′]: Ia/Ib≧0.452
Relational expression [2′]: Ia/Ib≦0.435

More preferably, the peak intensity Ia and the peak intensity Ib satisfy the following relational expressions [1''] [2''].

Relational expression [1″]: Ia/Ib≧0.469
Relational expression [2″]: Ia/Ib≦0.430

(4) Surface coating layer 6
The ceramic cutting tool 1 has at least one carbide, nitride, oxide, carbonitride, carbonate, nitroxide, and carbonitride oxide selected from the group consisting of titanium, zirconium, and aluminum on the surface. At least one surface coating layer 6 may be formed (see FIG. 3). When the surface coating layer 6 is formed, the surface hardness of the ceramic cutting tool 1 is increased, and progress of wear due to reaction and welding with the work material is suppressed. As a result, the wear resistance of the ceramic cutting tool 1 is improved.
At least one carbide, nitride, oxide, carbonitride, carbonate, nitroxide, carbonitride oxide selected from the group consisting of titanium, zirconium, and aluminum includes, but is not limited to, TiN, Suitable examples include TiAlN, TiAlCrN, and AlCrN.
The thickness of the surface coating layer 6 is not particularly limited. The thickness of the surface coating layer 6 is preferably 0.02 μm to 30 μm, more preferably 0.05 μm to 20 μm, even more preferably 0.1 μm to 10 μm, from the viewpoint of wear resistance.

2. Orientation control of tungsten carbide crystal 7 (manufacturing method of ceramic cutting tool 1)
In the ceramic cutting tool 1, the orientation of the tungsten carbide crystal 7 is controlled to satisfy the above relational expressions [1] and [2].
The orientation of the tungsten carbide crystal 7 can be controlled, for example, as follows. That is, the orientation of the tungsten carbide crystals 7 is controlled by controlling the pressure conditions and heating conditions in pressure firing such as hot pressing and spark plasma sintering (SPS: Spark Plasma Sintering).
More specific description will be given. When manufacturing the ceramic cutting tool 1 by sequentially performing the following steps [1] and [2], in the step [2] (firing step), a step of raising the temperature to a predetermined firing temperature and a step of heating from the predetermined firing temperature The orientation of the tungsten carbide crystals 7 is controlled by performing pressurization for a predetermined time while keeping the temperature approximately constant in a specific temperature range in at least one of the temperature lowering step.
[1] A mold is filled with mixed powder containing tungsten carbide powder and alumina powder (filling step).
[2] The mixed powder filled in the mold is fired at a firing temperature for a predetermined time to obtain a fired body (firing step).

In addition, the pressurization in a specific temperature range is appropriately changed according to the size, shape, etc. of the ceramic cutting tool 1 . As conditions for pressurization in a specific temperature range, for example, temperature range: 1500 ° C. to 1600 ° C., pressure: 15 MPa to 45 MPa uniaxial pressurization, treatment time (pressurization time): 1 hour to 4 hours is preferably adopted. be done.

3. Presumed reason why crater wear and VB wear are excellent Here, the presumed reason why the ceramic cutting tool 1 of the present disclosure is excellent in terms of crater wear and VB wear will be described.
Tungsten carbide tends to grow grains along the crystal plane (001) direction, and the crystal plane (001) is said to have the highest hardness. A tungsten carbide crystal 7 is shown in FIG. Reference numeral 9 indicates the crystal plane (001), and reference numeral 11 indicates the crystal plane (100). Moreover, FIG. 5 shows a cross-sectional view of the ceramic cutting tool 1 of the present disclosure, and schematically shows how the tungsten carbide crystals 7 are oriented.
In the ceramic cutting tool 1 of the present disclosure, by satisfying the above relational expression [1], the crystal plane (001) is preferentially oriented (arranged) on the side of the rake face 3 whose hardness is insufficient, and crater wear is suppressed. It is thought that
In addition, in the ceramic cutting tool 1 of the present disclosure, by satisfying the above relational expression [2], it is presumed that particle shedding is less likely to occur, and as a result, VB wear is suppressed. FIG. 6 shows a cross section of a conventional ceramic cutting tool 1. As shown in FIG. This conventional ceramic cutting tool 1 has more tungsten carbide crystals 7 exposing the crystal plane (001) side on the flank face 5 than the ceramic cutting tool 1 of the present disclosure. Such a tungsten carbide crystal 7 is only restrained by peripheral particles 13 (alumina particles, tungsten carbide, etc.) only on the back surface (the right side surface in FIG. 6), so the tungsten carbide crystal 7 easily falls off. . On the other hand, in the ceramic cutting tool 1 of the present disclosure, as shown in FIG. As for the crystal 7, the restrained area restrained from the peripheral particles 13 is increased, and the particles are less likely to fall off. As a result, it is presumed that VB wear is suppressed in the ceramic cutting tool 1 of the present disclosure.
In this way, crater wear and VB wear are suppressed by satisfying relational expressions [1] and [2].
5 shows an example in which the tungsten carbide crystals 7 contained in the ceramic cutting tool 1 all have the same orientation. The tungsten carbide crystals 7 may have different orientations so that the
As described above, in order to control the orientation of the tungsten carbide crystal 7 so as to satisfy the relational expressions [1] and [2], the method described in the above "2. Orientation control of the tungsten carbide crystal" is preferably used. Adopted. According to this method, the orientation of the tungsten carbide crystal 7 in the ceramic cutting tool 1 is controlled by controlling the direction of growth when the tungsten carbide crystal 7 grows into a flat plate in the direction of the (100) plane.

In the following experiments, ceramic sintered bodies of Examples 1 to 13 and Comparative Examples 1 and 2 were produced, and these ceramic sintered bodies were processed to obtain Examples 1 to 13 and Comparative Examples 1 and 2. Each ceramic cutting tool was used.

1. Preparation of Ceramic Sintered Body (1) Composition Table 1 shows the composition of the raw material powders used for the ceramic sintered bodies of Examples and Comparative Examples.
In addition, raw material powder is shown below.
Al ₂ O ₃ powder: average particle size 0.5 μm
WC powder: average particle size 0.7 μm
_ZrO2 powder: average particle size 0.7 _μm , partially stabilized with 3 mol% _{Y2O3 Y2O3} powder _: average particle size 0.7 μm
_TiO2 powder: average particle size 0.5 μm
_HfO2 powder: average particle size 0.9 μm
Yb ₂ O ₃ powder: average particle size 0.8 μm

(2) Mixing Zirconia spherulite and ethanol were put into a resin pot, and then powder other than WC powder was put. At this time, a dispersant was used. Next, after rotating the resin pot for 30 hours, the WC powder was added and further rotated for 30 hours.

(3) Drying and granulation The obtained slurry was passed through a sieve (mesh size: 25 μm) and dried with a vibration dryer. The obtained powder was passed through a sieve (mesh size: 250 μm) to obtain a dry mixed powder.
The steps ((1) to (3)) up to this point are common to all ceramic sintered bodies of Examples and Comparative Examples.

(4) Firing (4-1) Ceramic sintered bodies of Examples 1 to 12 The ceramic sintered bodies of Examples 1 to 12 were hot-press fired by the following method to obtain ceramic sintered bodies.
That is, the dry mixed powder was put into a carbon jig and fired under the conditions shown in Table 1. The mixed powder was held at 1550° C. for 2 hours during heating before reaching the firing temperature.
FIG. 8 shows the temperature and press pressure conditions in this hot press sintering. Before reaching the firing temperature (1700° C. to 1950° C.), a uniaxial pressurization of 1550° C. and 30 MPa is performed. FIG. 8 shows a state in which hot-press firing is performed at a temperature range lower than the firing temperature (here, 1550° C.) for a predetermined time, and then the temperature is raised and hot press firing is performed at the firing temperature. there is
As described above, ceramic sintered bodies of Examples 1 to 12 were obtained.
In Table 1, "Yes" in "Presence or absence of keeping during heating/cooling" means "when heating/cooling, pressure is applied while keeping the temperature approximately constant in a temperature range lower than the firing temperature". Further, "no" means "when raising or lowering the temperature, no pressure is applied while keeping the temperature approximately constant in a temperature range lower than the firing temperature".

(4-2) Ceramic sintered body of Example 13 The ceramic sintered body of Example 13 is the same as the ceramic sintered body of Example 4 up to drying and granulation, but the temperature range lower than the firing temperature ( Here, the timing of pressurization at 1550° C.) is different from that of the ceramic sintered body of Example 4. That is, the temperature was held for 2 hours at 1550° C. when the temperature was lowered from the sintering temperature after sintering, not when the temperature was raised before reaching the sintering temperature.
FIG. 9 shows the temperature and press pressure conditions in this hot press sintering. After sintering, uniaxial pressure is applied at 1550° C. and 800 MPa. FIG. 9 shows that after hot press firing at 1800° C., pressure is applied for a predetermined time at a temperature range lower than the firing temperature (here, 1550° C.).
As described above, a ceramic sintered body of Example 13 was obtained.

(4-3) Ceramic Sintered Body of Comparative Example 1 The ceramic sintered body of Comparative Example 1 is the same as the ceramic sintered body of Example 4 up to drying and granulation, but the ceramic sintered body of Comparative Example 1 For the body, conventional hot press sintering, which does not apply pressure in a temperature range lower than the sintering temperature, was adopted.
FIG. 10 shows the temperature and press pressure conditions in this hot press firing. It shows that pressure is not applied while keeping the temperature approximately constant in the temperature range lower than the firing temperature.
As described above, a ceramic sintered body of Comparative Example 1 was obtained.

(4-4) Ceramic Sintered Body of Comparative Example 2 The ceramic sintered body of Comparative Example 2 is the same as the ceramic sintered body of Example 4 up to drying and granulation, but the subsequent treatment is the same as that of Example 4. It is different from the ceramic sintered body of That is, in the ceramic sintered body of Comparative Example 2, the dry mixed powder was first uniaxially molded at room temperature and 100 MPa. This compact was then fired as follows. The compact was sintered in an argon atmosphere without pressure (primary sintering) and then HIP sintered (sintered by a hot isostatic pressing method). During the primary firing, the compact was held at 1550° C. for 2 hours without pressure. HIP firing was held at 1700° C. for 2 hours under an argon atmosphere of 150 MPa.
As described above, a ceramic sintered body of Comparative Example 2 was obtained.

2. XRD analysis (X-ray diffraction analysis)
(1) Measurement method In order to measure the peak intensity Ia attributed to the crystal plane (001) and the peak intensity Ib attributed to the crystal plane (100), X-ray diffraction was performed on each ceramic sintered body. I made a measurement. The respective peak intensities Ia and Ib were peak heights at the following 2θ values.
Peak intensity Ia: peak height near 2θ = 31.4° Peak intensity Ib: peak height near 2θ = 35.7° Hereafter, peak intensities Ia and Ib were obtained for each of the peak intensities Ia and Ib of the press vertical plane), and the value of Ia/Ib was calculated.
In addition, the peak intensity of each surface was measured under the following conditions.
・X-ray diffractometer RINT-TTR III manufactured by Rigaku Co., Ltd.
・X-ray diffraction conditions Monochromator: Used Target: Cu
Tube current: 300mA
Tube voltage: 50kV
Scan speed 2 degrees/min Sampling width 0.02 degrees

(2) Measurement results XRD analysis of the ceramic sintered bodies showed that the values of Ia/Ib on the press surfaces of the ceramic sintered bodies of Examples 1 to 13 were higher than those on the press vertical surfaces. rice field.
The ceramic sintered body of Comparative Example 1 was not maintained at a specific temperature (1550° C.) lower than the firing temperature, that is, was not maintained at a specific temperature during heating/cooling. In Comparative Example 1, there was no large difference in Ia/Ib on any surface.
The ceramic sintered body of Comparative Example 2 is a ceramic sintered body held without pressure at a specific temperature (1550° C.) lower than the firing temperature. The ceramic sintered body of Comparative Example 2 did not show a large difference in Ia/Ib on any surface.

3. Preparation of ceramic cutting tool Considering the measurement results of XRD analysis, in the ceramic sintered bodies of Examples 1 to 13 and Comparative Example 1, the press surface was the rake surface of the ceramic cutting tool, and the press vertical surface was the flank surface. It was processed into a tool shape (RCGX120700T01020).
The ceramic sintered body of Comparative Example 2 was machined into a tool shape (RCGX120700T01020) so that the uniaxially pressed surface during molding became a rake surface. Table 1 shows the Ia/Ib values for each surface.
Table 1 shows the composition (mixture) of the raw material powder of the ceramic sintered body as described above. Since this composition does not change even after firing, it is the same as the composition of each ceramic sintered body. be. Since each ceramic sintered body after sintering is machined to form a ceramic cutting tool, the composition of the raw material powder is the same as that of the ceramic cutting tool.

4. Cutting test (1) Test method A cutting test was performed using each ceramic cutting tool. The test conditions are as follows.
・Work material: Heat-resistant alloy Inconel 718
・Cutting speed: 240m/min
・Depth of cut: 1.0mm
・Feed rate: 0.2 mm/rotation ・Cutting environment: with cooling water ・Evaluation: Wear amount after 5 passes (200 m/pass) (VB wear amount, crater wear amount)

(2) Test results Table 1 shows the test results. The ceramic cutting tools of Examples 1-13 exhibited good wear resistance. On the other hand, the wear resistance of the ceramic cutting tools of Comparative Examples 1 and 2, in which there was no large difference in Ia/Ib depending on the plane direction, was lower than that of the ceramic cutting tools of Examples 1-13.
From the above results, when viewed from the rake face, the relational expression [1]: Ia / Ib ≥ 0.450 is satisfied, and when viewed from the flank face, the relational expression [2]: Ia / Ib ≤ 0.440 is satisfied. It was confirmed that the crater wear and VB wear were suppressed by filling.

The present invention is not limited to the embodiments detailed above, and various modifications and changes are possible within the scope of the claims of the present invention.

REFERENCE SIGNS LIST 1 ... ceramic cutting tool 3 ... rake face 4 ... workpiece 5 ... flank face 6 ... surface coating layer 7 ... tungsten carbide crystal 13 ... peripheral particles

Claims (3)

A ceramic cutting tool made of a ceramic sintered body containing at least tungsten carbide and alumina,
Among the XRD peaks of tungsten carbide, the intensity Ia of the peak attributed to the crystal plane (001) and the intensity Ib of the peak attributed to the crystal plane (100) are expressed by the following relational expression when viewed from the rake face: A ceramic cutting tool characterized by satisfying [1] and satisfying the following relational expression [2] when viewed from the flank face.

Relational expression [1]: Ia/Ib≧0.450
Relational expression [2]: Ia/Ib ≤ 0.440 At least one element selected from the group consisting of group 3 of the periodic table (including lanthanoids), titanium, zirconium, and hafnium is present at grain boundaries between the tungsten carbide and the alumina. The ceramic cutting tool according to claim 1, wherein At least one of carbides, nitrides, oxides, carbonitrides, carbonates, nitrides, and carbonitrides selected from the group consisting of titanium, zirconium, and aluminum is coated on the surface. 3. The ceramic cutting tool according to claim 1, wherein a surface coating layer of is formed.

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