JP7507582B2 - Ceramic sintered body and cutting tool - Google Patents

Description

This disclosure relates to a ceramic sintered body and a cutting tool.

In recent years, there has been a demand for faster and more efficient material processing in various manufacturing sites, and even faster cutting is expected. For this reason, ceramic tools with excellent heat resistance are used when performing cutting. One example is a cutting tool made of an Al ₂ O ₃ -WC sintered body, which has high hardness and high thermal conductivity.

Conventional _sintered bodies containing _Al2O3 and WC do not have sufficient bonding at the WC/WC interface, and may not be able to withstand high loads as material processing speeds and efficiency increases. Therefore, the performance of cutting tools made of such sintered bodies is not necessarily satisfactory.

International Publication No. 2018/198719

However, in the sintered body disclosed in Patent Document 1, the brittle metal layer condenses, and tungsten added to increase the melting point of the metal layer reacts with WC in the structure to produce coarse particles of brittle W ₂ C. Therefore, the sintered body does not have sufficient chipping resistance.
The present disclosure has been made in view of the above-mentioned circumstances, and has an object to provide a ceramic sintered body and a cutting tool capable of improving fracture resistance. The present disclosure can be realized in the following aspects.

[1] A ceramic sintered body containing alumina (Al ₂ O ₃ ) and tungsten carbide (WC),
Nickel (Ni) is contained in the grain boundaries between adjacent tungsten carbide (WC) crystal grains,
The mass of the ceramic sintered body is taken as 100 mass%,
The content of tungsten carbide (WC) is 48.0 mass% or more,
The content of alumina (Al ₂ O ₃ ) is 3.5 mass% or more,
The content of nickel (Ni) contained in the crystal grain boundaries is 0.5 mass % or more and 3 mass % or less .

[ 2 ] At least one element selected from the group consisting of chromium (Cr), molybdenum (Mo), niobium (Nb), tantalum (W), and hafnium (Hf) is present in the crystal grain boundaries . The ceramic sintered body according to [1 ] .

[ 3 ] The ceramic sintered body according to _{any one of [1] and [2 ]} , wherein at least one selected from the group consisting of scandium (Sc), yttrium (Y), lanthanoids, titanium (Ti), zirconium (Zr), and hafnium (Hf) is contained in the grain boundaries between adjacent alumina (Al 2 O 3 ) crystal grains and tungsten carbide (WC) crystal grains.

[ 4 ] A cutting tool comprising the ceramic sintered body according to any one of [1] to [ 3 ].

[ 5 ] A cutting tool using the ceramic sintered body according to any one of [1] to [ 3 ] as a substrate, and having a coating layer formed on the surface of the substrate.

The ceramic sintered body of the present disclosure contains at least one element selected from the group consisting of iron (Fe), cobalt (Co), and nickel (Ni) in the grain boundaries between adjacent tungsten carbide (WC) crystal grains, which strengthens the bond at the grain boundaries between the tungsten carbide crystal grains, thereby improving the chipping resistance of the ceramic sintered body .
When the total content of iron (Fe), cobalt (Co), and nickel (Ni) contained in the grain boundaries between tungsten carbide (WC) crystal grains is 0.5% by mass or more and 4.5% by mass or less, assuming the mass of the ceramic sintered body to be 100% by mass, the bond in the grain boundaries between the tungsten carbide crystal grains can be further strengthened, and therefore the chipping resistance of the ceramic sintered body can be further improved.
When at least one element selected from the group consisting of chromium (Cr), molybdenum (Mo), niobium (Nb), tantalum (W), and hafnium (Hf) is present at the grain boundaries between tungsten carbide (WC) crystal grains , the softening temperature of the metal layer increases, making it able to withstand higher speed cutting.
When the grain boundaries between adjacent alumina (Al ₂ O ₃ ) and tungsten carbide (WC) crystal grains contain at least one element selected from the group consisting of scandium (Sc), yttrium (Y), lanthanoids, titanium (Ti), zirconium (Zr), and hafnium (Hf), the bonds at the grain boundaries between the alumina and tungsten carbide crystal grains can be strengthened, and the chipping resistance of the ceramic sintered body can be further improved.
By using the ceramic sintered body of the present invention for a cutting tool, it is possible to achieve both wear resistance and chipping resistance during high-speed machining of steel materials.
When a coating layer is formed on the ceramic sintered body of the present invention as a substrate, the surface can be hardened and oxidation of the substrate on the surface can be suppressed, thereby improving the wear resistance of the cutting tool.

FIG. 2 is a diagram showing a schematic SEM image of a ceramic sintered body. FIG. 2 is an enlarged view showing a part of FIG. 1 . 1 is a graph showing the concentration of cobalt element in the vicinity of grain boundaries between tungsten carbide crystal grains, measured by EDS.

The following provides a more detailed explanation. In this specification, when a numerical range is described using "to" it is intended to include both the lower limit and the upper limit unless otherwise specified. For example, "10 to 20" is intended to include both the lower limit of "10" and the upper limit of "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Sintered ceramics 1
(1) Structure of the ceramic sintered body 1 As shown in Fig. 1, the ceramic sintered body 1 includes alumina (Al ₂ O ₃ ) crystal grains 11 and tungsten carbide (WC) crystal grains 12. Fig. 1 is a schematic diagram of an SEM image of the ceramic sintered body 1 obtained by a SEM (Scanning Electron Microscope). However, Fig. 1 is a conceptual diagram of the SEM image of the ceramic sintered body 1, and does not accurately show an actual SEM image. Fig. 2 is an enlarged view of the part surrounded by the dashed line on the inside of Fig. 1, and shows a part of the interface between the tungsten carbide crystal grains 12.

The grain boundaries G between adjacent tungsten carbide crystal grains 12 contain at least one element selected from the group consisting of iron (Fe), cobalt (Co), and nickel (Ni).

For example, the graph in Fig. 3 is a graph in which the concentration of cobalt element in the vicinity of the grain boundary G between adjacent tungsten carbide crystal grains 12 is measured by EDS. The horizontal axis of the graph in Fig. 3 indicates each position on a line crossing the grain boundary G, from position A1 in one tungsten carbide crystal grain 12, through position A2 on the grain boundary G, to position A3 in the other tungsten carbide crystal grain 12. The vertical axis of the graph in Fig. 3 indicates the concentration of cobalt (C0) element. Cobalt is distributed in the grain boundary G where the tungsten carbide crystal grains 12 are adjacent to each other. Here , no matter which position of the grain boundary G is subjected to line analysis using EDS, at least one element selected from the group consisting of iron, cobalt, and nickel is detected .

In this way, by including at least one element selected from the group consisting of iron, cobalt, and nickel in the grain boundaries G between adjacent tungsten carbide crystal grains 12, it is possible to strengthen the bonds at the grain boundaries G between the tungsten carbide crystal grains 12. As a result, it is possible to improve the chipping resistance of the ceramic sintered body 1.

The mass of the ceramic sintered body 1 is taken as 100 mass%, and the total content of iron (Fe), cobalt (Co), and nickel (Ni) contained in the grain boundaries between tungsten carbide (WC) crystal particles is preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 1.5 mass% or more. This total content is preferably 4.5 mass% or less, more preferably 3 mass% or less, and even more preferably 2 mass% or less. This total content is preferably 0.5 mass% or more and 4.5 mass% or less, more preferably 1 mass% or more and 3 mass% or less, and even more preferably 1.5 mass% or more and 2 mass% or less. With this configuration, the bond at the grain boundaries G between the tungsten carbide crystal particles 12 can be further strengthened. Therefore, the chipping resistance of the ceramic sintered body 1 can be further improved.

It is preferable that at least one element selected from the group consisting of chromium (Cr), molybdenum (Mo), niobium (Nb), tantalum (W) and hafnium (Hf) is present at the grain boundaries between tungsten carbide (WC) crystal grains. With this configuration, the softening temperature of the metal layer is increased, and the metal layer can withstand higher speed cutting.

It is preferable that the ceramic sintered body 1 contains at least one element selected from the group consisting of scandium (Sc), yttrium (Y), lanthanides, titanium (Ti), zirconium (Zr), and hafnium (Hf) in the grain boundaries between adjacent alumina crystal grains 11 and tungsten carbide crystal grains 12. This configuration can strengthen the bond in the grain boundaries between the alumina crystal grains 11 and tungsten carbide crystal grains 12. This can further increase the chipping resistance of the ceramic sintered body 1.

(2) Manufacturing method of ceramic sintered body 1 (manufacturing method A)
There is no particular limitation on the method for producing the ceramic sintered body 1. An example of the method for producing the ceramic sintered body 1 will be described below.

(2.1) Raw Materials The following raw material powders are used as raw materials.
・Tungsten carbide powder (WC powder)
Alumina powder ( _{Al2O3 powder} )
・Zirconia powder ( _ZrO2 powder)
・Cobalt powder (Co powder)
Nickel powder (Ni powder)
・Molybdenum powder (Mo powder)
・Tantalum powder (Ta powder)
・Hafnium powder (Hf powder)

(2.2) Preparation of Mixed Dry Powder (Raw Material Powder X) (2.2.1) Tungsten carbide powder, alumina powder, zirconia powder, cobalt powder, nickel powder, molybdenum powder, tantalum powder, and hafnium powder are prepared.
(2.2.2) Tungsten carbide powder and metal powder (cobalt powder, nickel powder, molybdenum powder, tantalum powder, and hafnium powder listed in Table 1) are pre-pulverized. The resulting slurry is passed through a sieve with a mesh size of 25 μm and dried by a vibrating dryer. The resulting powder is passed through a sieve with a mesh size of 125 μm to obtain raw material powder X in which tungsten carbide powder is coated with metal powder.
(2.3) Blending Raw material powder X and alumina powder are charged into a Karman agitator equipped with a cooling jacket together with ion-exchanged water cooled to 5° C. or less, and stirred while cooling to obtain a slurry.
(2.4) Drying and granulation The obtained slurry is passed through a sieve with an opening of 25 μm and dried under reduced pressure using a rotary evaporator. The obtained powder is passed through a sieve with an opening of 250 μm to obtain a dry powder.
(2.5) Firing The obtained mixed dry powder is put into a carbon jig and sintered at a predetermined temperature under vacuum conditions, and then hot press sintered at a predetermined temperature. In this manner, the ceramic sintered body 1 is produced. The ceramic sintered body 1 may be subjected to shape and surface finishing by at least one of cutting, grinding, and polishing.

(3) Use of cutting tool The cutting tool is composed of the ceramic sintered body 1. The cutting tool can be applied to various cutting tools known in the art. Suitable examples of the cutting tool include indexable inserts for turning or milling (cutting inserts, throw-away inserts), drills, and end mills. The cutting tool is a cutting tool in a broad sense, and refers to all tools that perform turning, milling, etc.

(4) Surface Coating Layer The cutting tool may have a coating layer formed on the surface of the substrate, the substrate being the ceramic sintered body 1. When the coating layer is formed, the surface hardness of the cutting tool increases and the progress of wear caused by reaction and adhesion with the workpiece is suppressed. As a result, the wear resistance of the cutting tool is improved.
The components of the coating layer are not particularly limited. The coating layer is preferably formed of at least one compound selected from carbides, nitrides, oxides, carbonitrides, carbonates, oxynitrides, and carbonitrides of titanium, zirconium, and aluminum. The at least one compound selected from carbides, nitrides, oxides, carbonitrides, carbonates, oxynitrides, and carbonitrides of titanium, zirconium, and aluminum is not particularly limited, and suitable examples include TiN, TiCN, TiAlN, TiAlVN, Al ₂ O ₃ , and CrAlN.
The thickness of the coating layer is not particularly limited, but is preferably 0.02 μm or more and 30 μm or less from the viewpoint of abrasion resistance.

1. Preparation of ceramic sintered bodies 1.1 Ceramic sintered bodies of Examples 1 to 22 (sintered bodies prepared by manufacturing method A)
(1) Raw Materials The following raw material powders were used as raw materials.
Tungsten carbide powder (WC powder): average particle size 0.7 μm
Alumina powder (Al ₂ O ₃ powder): average particle size 0.5 μm
Zirconia powder ( _ZrO2 powder): average particle size 0.3 μm
Cobalt powder (Co powder): average particle size 0.1 μm
Nickel powder (Ni powder): average particle size 0.1 μm
Molybdenum powder (Mo powder): average particle size 0.1 μm
Tantalum powder (Ta powder): average particle size 0.1 μm
Hafnium powder (Hf powder): average particle size 0.1 μm

(2) Preparation of Mixed Dry Powder (Raw Material Powder X) (2.1) Tungsten carbide powder, alumina powder, zirconia powder, cobalt powder, nickel powder, molybdenum powder, tantalum powder, and hafnium powder were prepared.
(2.2) Tungsten carbide powder and metal powder (cobalt powder, nickel powder, molybdenum powder, tantalum powder, and hafnium powder as listed in Table 1) were pre-pulverized. The tungsten carbide powder and metal powder were put into a resin pot together with cemented carbide balls, binder powder (polyvinyl alcohol), and acetone and pulverized. The pulverization time was 55 hours. The obtained slurry was passed through a sieve with a mesh size of 25 μm and dried by a vibrating dryer. The obtained powder was passed through a sieve with a mesh size of 125 μm to obtain raw material powder X in which tungsten carbide powder was coated with metal powder.
(3) Preparation Raw material powder X and alumina powder were charged into a Karman agitator equipped with a cooling jacket together with ion-exchanged water cooled to 5°C or less, and stirred while cooling to obtain a slurry. Stirring was carried out for 6 hours while keeping the water temperature at 5°C or less. In addition, for Examples 17 to 22, zirconia powder was also charged into the Karman agitator and stirred.
(4) Drying and granulation The obtained slurry was passed through a sieve with 25 μm openings and dried under reduced pressure using a rotary evaporator. The obtained powder was passed through a sieve with 250 μm openings to obtain a dry powder.
(5) Firing The obtained mixed dry powder was weighed in the composition (mass%) ratio shown in Table 1, then put into a carbon jig, sintered at a predetermined temperature under vacuum conditions, and then hot press sintered at a predetermined temperature. Specifically, it was sintered at 800°C for 2 hours under vacuum conditions, and then hot press sintered at the sintering temperature shown in Table 1. In the hot press sintering, the sintering time is 2 hours, the pressure is 30 MPa, and the atmospheric gas is argon (Ar). In this way, the ceramic sintered body 1 is produced. The ceramic sintered body 1 may be finished in shape or on the surface by at least one of cutting, grinding, and polishing. The composition (mass%) shown in Table 1 is rounded off to the nearest tenth.

1.2 Ceramic sintered bodies of Comparative Examples 1 to 5 (sintered bodies prepared by Experimental Method B)
In the ceramic sintered bodies of Comparative Examples 1 to 5, the tungsten carbide powder and the metal powder were not pre-pulverized.
(1) Raw Materials The following raw material powders were used as raw materials.
Tungsten carbide powder (WC powder): average particle size 0.7 μm
Alumina powder (Al ₂ O ₃ powder): average particle size 0.5 μm

(2) Preparation of mixed dry powder (mixture)
(2.1) Tungsten carbide powder and alumina powder were prepared.
(2.2) Tungsten carbide powder and alumina powder were placed in a resin pot together with acetone and stirred for 60 hours.
(3) Drying and granulation The obtained slurry was passed through a sieve with a mesh size of 25 μm and dried using a vibration dryer. The obtained powder was passed through a sieve with a mesh size of 250 μm to obtain a dry powder.
(4) Firing The obtained dried powder was put into a carbon jig and hot-pressed and sintered at the sintering temperature shown in Table 1. The sintering time was 2 hours, the pressure was 30 MPa, and the atmospheric gas was argon (Ar). In this manner, the ceramic sintered bodies of Comparative Examples 1 to 5 were produced. The shape and surface of the ceramic sintered body may be finished by at least one of cutting, grinding, and polishing.

2. Cutting Test (1) Test Method Cutting tests were carried out using cutting tools made of each of the ceramic sintered bodies to evaluate chipping resistance.
The test conditions are as follows.
・Tool shape:DNGA150412BQT00520
・Cutting material: Titanium alloy (Ti-6Al-4V)
Cutting speed: 500 m/min
・Cutting depth: 0.5mm and up
・Feed rate: 0.1 mm/rev.
・Cutting environment: Wet
The cutting depth is increased by 0.1 mm for each pass from 0.5 mm.
The depth of cut when chipping occurred in the cutting tool was evaluated.

(2) Test Results The test results are shown in Table 1 and will be discussed.
The cutting tools of Examples 1 to 22 satisfy the following first requirement. In contrast, the cutting tools of Comparative Examples 1 to 5 do not satisfy the first requirement. The cutting tools of Examples 1 to 22 had a depth of cut at the time of fracture of 1.0 to 1.8 mm, while the cutting tools of Comparative Examples 1 to 5 had a depth of cut at the time of fracture of 0.5 to 0.6 mm. Therefore, the cutting tools of Examples 1 to 22 had higher fracture resistance than the cutting tools of Comparative Examples 1 to 5. It was therefore confirmed that fracture resistance was improved by satisfying the first requirement.
[First requirement]: Contains at least one element of cobalt and nickel.

Next, the cutting tools of Examples 1 to 16 are compared. All of the cutting tools of Examples 14 to 16 satisfied the second requirement below in addition to the first requirement. On the other hand, none of the cutting tools of Examples 1 to 10 satisfied the second requirement below . The cutting tools of Examples 14 to 16 had a depth of cut at the time of chipping of 1.5 mm. The cutting tools of Examples 1 to 13 had a depth of cut at the time of chipping of 1.0 to 1.2 mm. The cutting tools of Examples 14 to 16 had higher chipping resistance than the cutting tools of Examples 1 to 13. It was therefore confirmed that chipping resistance is further improved by satisfying the second requirement in addition to the first requirement.
[Second requirement] : At least one element selected from the group consisting of molybdenum, tantalum, and hafnium is present in the grain boundaries between tungsten carbide (WC) crystal grains .

Next, the cutting tools of Examples 1 to 22 are compared. All of the cutting tools of Examples 20 to 22 satisfied the third requirement below in addition to the first requirement. On the other hand, none of the cutting tools of Examples 1 to 16 satisfied the third requirement below . The cutting tools of Examples 20 to 22 had a depth of cut at the time of chipping of 1.7 to 1.8 mm. The cutting tools of Examples 1 to 19 had a depth of cut at the time of chipping of 1.0 to 1.5 mm. The cutting tools of Examples 20 to 22 had higher chipping resistance than the cutting tools of Examples 1 to 19. It was therefore confirmed that chipping resistance was further improved by satisfying the third requirement in addition to the first requirement .
[ Third requirement]: The cutting tool contains zirconium.

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

1 ... ceramic sintered body 11 ... alumina crystal grain 12 ... tungsten carbide crystal grain G ... grain boundary between tungsten carbide crystal grains

Claims (5)

A ceramic sintered body containing alumina (Al ₂ O ₃ ) and tungsten carbide (WC),
Nickel (Ni) is contained in the grain boundaries between adjacent tungsten carbide (WC) crystal grains,
The mass of the ceramic sintered body is taken as 100 mass%,
The content of tungsten carbide (WC) is 48.0 mass% or more,
The content of alumina (Al ₂ O ₃ ) is 3.5 mass% or more,
The content of nickel (Ni) contained in the crystal grain boundaries is 0.5 mass % or more and 3 mass % or less. 2. The ceramic sintered body according to claim 1, wherein at least one element selected from the group consisting of chromium (Cr), molybdenum (Mo), niobium (Nb), tantalum (Ta), and hafnium (Hf) is present in the crystal grain boundaries. _3. The ceramic sintered body according to claim ₁ , wherein at least one element selected from the group consisting of scandium (Sc), yttrium (Y), lanthanides, titanium (Ti), zirconium (Zr), and hafnium (Hf) is contained in a grain boundary between adjacent alumina (Al2O3) crystal grains and tungsten carbide (WC ) crystal grains. A cutting tool comprising the ceramic sintered body according to any one of claims 1 to 3 . A cutting tool comprising the ceramic sintered body according to any one of claims 1 to 3 as a substrate, and a coating layer formed on a surface of the substrate.

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