JP7567611B2 - Ceramic-based surface-coated cutting tools - Google Patents

Description

This invention relates to a ceramic-based surface-coated cutting tool that exhibits excellent chipping resistance, fracture resistance, peeling resistance, and wear resistance over long periods of use in ultra-high speed milling of cast iron.

Conventionally, surface-coated cutting tools have been known in which a hard coating layer made of a Ti compound layer is formed by vapor deposition on the surface of a substrate made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet.

For example, in Patent Document 1, in order to provide a surface-coated cutting tool in which a hard coating layer exhibits excellent chipping resistance and wear resistance in high-speed milling cutting work accompanied by high heat generation and large thermal shock, the following is provided on the surface of a tool substrate made of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet:
(a) a lower layer consisting of a Ti nitride layer having an average layer thickness of 0.1 to 2 μm;
(b) a Ti carbide layer having a fine-grained longitudinally grown crystal structure and an average layer thickness of 0.5 to 3 μm;
a Ti compound layer having a granular crystal structure, which is composed of one or more layers selected from a Ti carbide layer, a Ti nitride layer and a Ti carbonitride layer, and has an average layer thickness of 0.2 to 1 μm;
an intermediate layer having a total average layer thickness of 3 to 10 μm and consisting of an alternating laminate structure;
(c) an aluminum oxide layer having an average layer thickness of 0.5 to 5 μm;
There has been proposed a surface-coated cutting tool characterized in that the hard coating layer composed of the above (a) to (c) is formed to a total average layer thickness of 4 to 15 μm.
In particular, the intermediate layer of this surface-coated cutting tool, which is made of alternating laminations, has the effect of increasing thermal cracking, reducing the stress at which the cracks open, and slowing the progression and propagation of the cracks. Therefore, when used for high-speed milling of steel or cast iron, which generates high heat and is subjected to large impacts, the tool exhibits excellent wear resistance over long periods of use without suffering abnormal damage such as chipping, fracture, or peeling, and thus achieves a long service life for the coated tool.

Furthermore, Patent Document 2 proposes a surface-coated cutting tool made of an aluminum oxide-based ceramic, in which an intermediate coating layer made of at least one compound of Ti, Zr and Hf is formed on the surface of an aluminum oxide-based ceramic base made of silicon carbide, zirconium oxide and aluminum oxide, and a hard coating layer made of an aluminum oxide layer is formed on the surface of this intermediate coating layer, in order to provide a surface-coated cutting tool that exhibits excellent cutting performance over a long period of time without chipping or chipping in the hard coating layer even when subjected to normal continuous cutting, intermittent cutting or heavy cutting.
Furthermore, with this ceramic cutting tool, the intermediate coating layer prevents the diffusion of Si components from the ceramic base to the aluminum oxide layer, thereby suppressing the grain growth of the aluminum oxide and maintaining a fine grain structure, so that no chipping or chipping occurs when cutting cast iron, etc., and excellent cutting performance can be exhibited for a long period of time.

JP 2011-031319 A Japanese Patent Application Publication No. 4-315504

In recent years, the machining speed of cast iron milling has been increasing with the increasing efficiency of cutting processes. However, when the cutting conditions become ultra-high speed conditions such as vc≧500 m/min, the tool life of a conventional surface-coated cutting tool based on a cemented carbide alloy (see, for example, Patent Document 1) is reached in a short time due to wear of the hard coating layer, and a conventional surface-coated cutting tool based on a ceramic (see, for example, Patent Document 2) does not have sufficient adhesion strength between the ceramic substrate and the hard coating layer, causing peeling, etc., and therefore the properties of the hard coating layer cannot be fully exhibited, resulting in a short tool life.

From the above viewpoint, the present inventors have conducted extensive research to extend the service life of surface-coated cutting tools, particularly ceramic-based surface-coated cutting tools having a tool base made of sialon (SiAlON) or silicon _nitride ( _Si3N4 ), and have investigated ceramic-based surface-coated cutting tools that exhibit excellent cutting performance over long periods of use by increasing the adhesion strength between the ceramic tool base and the hard coating layer and thereby suppressing peeling of the hard coating layer even in milling of cast iron under ultra-high speed conditions (e.g., vc≧500 m/min). As a result, the following findings were obtained.

In a ceramic-based surface-coated cutting tool having a tool substrate made of ceramics (e.g., sialon, silicon nitride) containing silicon (hereinafter sometimes referred to as Si), when the Si component from the tool substrate diffuses into a hard _coating layer made of an _Al2O3 layer, _{the Al2O3} particles become coarse, making chipping and breakage more likely to occur, as disclosed in Patent Document 2.

Therefore, when forming a hard coating layer on the surface of a ceramic substrate, the inventors formed a Ti compound (at least one selected from Ti _nitrides , carbides, carbonitrides, carbonates and carbonitrides ₎ layer on the surface of the ceramic substrate as an intermediate layer to suppress the diffusion of Si components into the _Al2O3 layer, and further set the thickness of the Si diffusion region formed in this intermediate layer to a predetermined value or less, and formed an _Al2O3 layer on that surface as an upper layer, thereby improving the chipping resistance and defect resistance of the hard coating layer.

Furthermore, the inventors have conducted research to further improve the adhesive strength between the ceramic base and the intermediate layer, and have found that by blasting the ceramic base surface under specific conditions before forming the hard coating layer and then forming the intermediate layer thereon, the diffusion of the Ti component that constitutes the intermediate layer into the ceramic base is promoted, and a Ti diffusion region with a specified Ti content is formed in a specified depth region, thereby dramatically improving the adhesive strength between the ceramic base and the intermediate layer.
As a result, it has been found that the occurrence of peeling between the ceramic substrate and the hard coating layer is suppressed, excellent cutting performance is exhibited over long periods of use, and the life of the ceramic-based surface-coated cutting tool is extended.

Furthermore, after forming the intermediate layer on the surface of the ceramic base, the ceramic base on which the intermediate layer has been formed is subjected to a heat treatment under specific conditions before the step of forming _{the Al2O3} layer as the upper layer, thereby further promoting the diffusion of the Ti component into the interior of the ceramic base.
When the ceramic base on which the intermediate layer is formed is subjected to a heat treatment under the above-mentioned specific conditions, diffusion of Ti into the ceramic base occurs, and at the same time, diffusion of Si components from the ceramic base toward the intermediate layer also occurs, resulting in the formation of a Si-diffused region in the intermediate layer.
However, as described above, in order to prevent adverse effects on _{the Al2O3} layer, the diffusion of the Si component into _{the Al2O3} layer must be suppressed. Therefore, it is necessary to limit the Si content and the thickness of the Si-diffused region formed in the intermediate layer to a predetermined value or less so as to prevent the diffusion of the Si component into _{the Al2O3} layer.
The heat treatment for forming the Ti diffusion region having the predetermined thickness and the predetermined Ti content, and further the Si diffusion region having the predetermined thickness and the predetermined Si content, can be carried out, for example, within the following heat treatment condition range.
Heating temperature: 1020-1080℃
Holding time: 2 to 10 hours Atmosphere: Hydrogen or argon Pressure: 50 kPa or less

As described above, the present inventors have discovered that, in a ceramic-based surface-coated cutting tool, by forming an intermediate layer made of a Ti compound between a ceramic substrate and an _{upper Al2O3} layer, and by forming a Si-diffused region of a predetermined thickness in the intermediate layer and a Ti-diffused region of a predetermined thickness in the ceramic substrate, it is possible to obtain a ceramic-based surface-coated cutting tool that has excellent chipping resistance, fracture resistance and peeling resistance and exhibits excellent wear resistance over long periods of use, even under ultra-high speed milling cutting conditions for cast iron.

The present invention has been made based on the above findings,
"(1) A ceramic-based surface-coated cutting tool in which a hard coating layer consisting of an intermediate layer and an upper layer is coated on the surface of a sialon or silicon nitride ceramic substrate,
(a) an intermediate layer having a total average layer thickness of 0.3 to 1.5 μm and made of one or more Ti compounds selected from Ti nitrides, carbides, carbonitrides, carbonates and carbonitrides is formed on the surface of the ceramic substrate;
(b) an upper layer made of Al ₂ O ₃ having an average thickness of 2 μm to 10 μm is formed on the surface of the intermediate layer;
(c) a Ti-diffused region having a Ti content of 2 at% or more is formed from the interface between the ceramic base and the intermediate layer toward the inside of the ceramic base, and the Ti-diffused region has an average thickness of 0.10 μm or more and 0.70 μm or less;
(d) A ceramic-based surface-coated cutting tool, characterized in that a Si-diffusion region having a Si content of 2 at% or more is formed from the interface between the ceramic base and the intermediate layer toward the inside of the intermediate layer, and the Si-diffusion region has an average thickness of 0.05 μm or more and 0.30 μm or less.

In the ceramic-based surface-coated cutting tool of this invention, the components of the ceramic base and the intermediate layer are diffused into both, forming a Ti-diffused region on the ceramic base side and a Si-diffused region on the intermediate layer side. This provides sufficient adhesion strength between the ceramic base and the hard coating layer, so that even when used in ultra-high speed milling of cast iron, peeling does not occur, and the tool has excellent chipping resistance and defect resistance, and exhibits excellent wear resistance over long periods of use, achieving a long service life for the ceramic-based surface-coated cutting tool.

1 is a schematic vertical sectional view of a ceramic-based surface-coated cutting tool according to the present invention;

The present invention is described in detail below.

As shown in the schematic vertical cross-sectional view of FIG. 1, the ceramic-based surface-coated cutting tool of the present invention has an intermediate layer made of a Ti compound layer formed on the surface of a ceramic substrate, and further has an upper layer made of an _Al2O3 layer formed on the surface of the _intermediate layer.
A Ti-diffused region is formed from the interface between the ceramic substrate and the intermediate layer toward the inside of the ceramic substrate (the downward direction in FIG. 1), while a Si-diffused region is formed from the interface between the ceramic substrate and the intermediate layer toward the inside of the intermediate layer (the upward direction in FIG. 1).

Ceramic substrate:
In the present invention, the tool substrate of the ceramic-based surface-coated cutting tool is made of a ceramic substrate containing silicon.
Examples of the ceramic substrate containing silicon include sialon (SiAlON) and silicon nitride (Si ₃ N ₄ ). It is preferable to use sialon ceramics, which have excellent hardness and heat resistance.

As the sialon (SiAlON) ceramic substrate, a ceramic substrate having a β-sialon ratio of 75 to 100% and a binder phase of 1 to 15 vol % is particularly preferred.
This is because when Ti, which is a component of the intermediate layer, is diffused into the ceramic base to form a Ti-diffused region, the Ti component easily diffuses into β-sialon having an acicular structure. If the β-sialon ratio is less than 75%, sufficient Ti diffusion cannot be obtained, and the adhesive strength between the ceramic base and the intermediate layer is no longer sufficient.
Regarding the binder phase, if the content of the binder phase in the ceramic base exceeds 15 vol%, the Ti component cannot be sufficiently diffused into the ceramic base, whereas if the content of the binder phase is less than 1 vol%, the toughness of the base itself becomes insufficient. Therefore, the binder phase is preferably 1 to 15 vol%.

Here, the β-sialon ratio is defined as follows.
X-ray diffraction is performed on a ceramic substrate consisting of α-sialon, β-sialon, and a binder phase to measure the diffraction peak intensity β1 of the (101) plane of the β-sialon and the diffraction peak intensity β2 of the (210) plane, and also the diffraction peak intensity α1 of the (102) plane of the α-sialon and the diffraction peak intensity α2 of the (210) plane are measured. The value calculated from {(β1+β2)/(β1+β2+α1+α2)}×100 is the β-sialon ratio.
The X-ray diffraction conditions for determining the β-sialon ratio are as follows: measurement conditions: Cu tube, measurement range (2θ): 20 to 80 degrees, scan step: 0.013 degrees, measurement time per step: 0.48 sec/step.

The method for measuring the content of the binder phase is as follows.
An SEM (scanning transmission electron microscope) image is obtained at a magnification of 5,000 times for any cross section of the ceramic base, and the SEM image is binarized using image processing software (specifically, for example, ImageJ, etc.) to identify the binder phase. The content ratio of the binder phase can be obtained by calculating the ratio of the area occupied by the binder phase to the area of the entire field of view.
The binder phase is an amorphous grain boundary phase formed when sintering aids such as Al ₂ O ₃ , MgO, Y ₂ O ₃ , and Yb ₂ O ₃ and silica components contained in silicon nitride generate a liquid phase during sintering.

Middle layer:
The surface of the ceramic substrate is coated with an intermediate layer having a total average layer thickness of 0.3 to 1.5 μm and made of one or more Ti compounds selected from Ti nitrides, carbides, carbonitrides, carbonates and carbonitrides.
Since the above-mentioned Ti compounds each have excellent high-temperature strength, the hard coating layer is provided with high-temperature strength and has excellent adhesion to the upper layer made of Al ₂ O _3. Furthermore, in the present invention, a Ti-diffused region is formed in the ceramic substrate, and the intermediate layer made of the Ti compound has a function of supplying the Ti component, and also has a function of preventing the Si component diffusing from the ceramic substrate from adversely affecting the upper layer made of Al ₂ O ₃ by forming a Si-diffused region only inside the intermediate layer.
However, if the total average layer thickness of the intermediate layer made of the Ti compound exceeds 1.5 μm, abnormal damage such as chipping and breakage becomes likely to occur, particularly in ultra-high speed milling of cast iron, so the total average layer thickness is set to 1.5 μm or less.
On the other hand, if the total average layer thickness of the intermediate layer is less than 0.3 μm, the diffusion amount and diffusion penetration depth of the Ti component will be insufficient, and it will be impossible to form a Ti diffusion region of a specific depth and with a specific Ti content in the ceramic base as described below. As a result, not only will the adhesion strength between the ceramic base and the intermediate layer be insufficient, making peeling more likely to occur, but the Si component diffusing from the ceramic base will not be able to be contained within the Si diffusion region formed in the intermediate layer, reducing the chipping resistance and defect resistance of the upper layer consisting of an Al ₂ O ₃ layer.
Therefore, the total average thickness of the intermediate layer made of a Ti compound is set to 0.3 to 1.5 μm.

Ti diffusion region:
A Ti-diffusion region having a Ti content of 2 at % or more is formed with an average thickness of 0.10 μm or more and 0.70 μm or less from the interface between the ceramic base and the intermediate layer toward the inside of the ceramic base (in FIG. 1 , the Ti-diffusion region is formed downward from the interface between the ceramic base and the intermediate layer, and the Ti-diffusion region has an average thickness of 0.10 μm or more and 0.70 μm or less). The formation of the Ti-diffusion region significantly improves the adhesion strength between the ceramic base and the intermediate layer, and suppresses the occurrence of peeling between the ceramic base and the hard coating layer.
Here, the Ti-diffused region refers to a region in which the Ti content is 2 at % or more.
Furthermore, the average thickness of the Ti-diffusion region refers to the average thickness from the interface between the ceramic base and the intermediate layer in a region where the Ti content is 2 at% or more. If the average thickness of the Ti-diffusion region is thinner than 0.10 μm, the effect of improving the adhesive strength between the ceramic base and the intermediate layer is small, and the object of the present invention cannot be achieved. On the other hand, if the average thickness of the Ti-diffusion region is excessively thick, exceeding 0.70 μm, the strength of the ceramic base itself will decrease. Therefore, the average thickness of the Ti-diffusion region where the Ti content is 2 at% or more is set to be 0.10 μm or more and 0.70 μm or less.

Blasting:
In the present invention, a Ti-diffusion region of a predetermined average thickness and with a predetermined Ti content is formed from the interface between the ceramic base and the intermediate layer toward the inside of the ceramic base, and the formation of the Ti-diffusion region is promoted by subjecting the surface of the tool base to a blasting treatment.
That is, the tool base of the present invention is composed of _sialon or silicon nitride ceramics and _a binder phase, and the binder phase is an amorphous grain boundary phase formed when sintering aids such as _Al2O3 , MgO, _Y2O3 , _Yb2O3 , and the silica component contained in silicon _nitride generate a liquid phase during sintering. By subjecting the surface of the ceramic base to a blast treatment, the amorphous grain boundary phase with low hardness is selectively removed, thereby promoting the diffusion of the Ti component into the grain boundaries when the hard coating layer is formed, and a Ti-diffused region with a specified Ti content can be formed in a specified depth region.
The preferred range of blasting conditions is as follows:
Blasting fluid: abrasive grains + water,
Abrasive grains: _{Al2O3 powder} grains,
Abrasive grain size: 100-440 (mesh),
Abrasive grain concentration: 15-60% by mass,
Blasting pressure: 0.10-0.35MPa
Projection time: 8-30 seconds

Si diffusion region:
A Si-diffusion region having a Si content of 2 at % or more is formed with an average thickness of 0.05 μm or more and 0.30 μm or less from the interface between the ceramic base and the intermediate layer toward the inside of the intermediate layer (in FIG. 1, the Si-diffusion region is formed in the upward direction from the interface between the ceramic base and the _intermediate layer, and the Si-diffusion region has an average thickness of 0.05 μm or more and 0.30 μm or less). By forming the Si-diffusion region, it is possible to maintain the wear resistance without reducing the chipping resistance and defect resistance of the upper layer consisting of the _Al2O3 layer.
Here, the Si-diffused region refers to a region in the intermediate layer where the Si content is 2 at % or more.
The average thickness of the Si diffusion region refers to the average thickness from the interface between the ceramic base and the intermediate layer in a region where the Si content is 2 at% or more. If the average thickness of the Si diffusion region is thinner than 0.05 μm, the effect of improving the adhesive strength between the ceramic base and the intermediate layer is small, and the object of the present invention cannot be achieved. On the other hand, if the average thickness of the Si diffusion region exceeds 0.30 μm and becomes excessively thick, the Al ₂ O ₃ particles in the upper layer will grow abnormally starting from Si, causing a decrease in the strength of the upper layer. Therefore, the average thickness of the Si diffusion region where the Si content is 2 at% or more is set to 0.05 μm or more and 0.30 μm or less.

Heat treatment:
In the present invention, after an intermediate layer made of a Ti compound layer is formed on a sialon or silicon nitride ceramic substrate by a normal CVD method, a heat treatment can be carried out as necessary to promote the formation of a Ti diffusion region. The specific range of heat treatment conditions is, for example, as follows:
Heating temperature: 1020-1080℃
Holding time: 2 to 10 hours Atmosphere: Hydrogen or argon atmosphere Pressure: 50 kPa or less

Ti content and thickness in the Ti diffusion region, and Si content and thickness in the Si diffusion region:
The method for measuring the Ti content in the Ti diffusion region, the method for measuring (determining) the thickness of the diffusion region based on this measured value (Ti content of 2 at% or more), the method for measuring the Si content in the Si diffusion region, and the method for measuring (determining) the thickness of the diffusion region are as follows.
First, a polished surface of a longitudinal section (a section perpendicular to the surface of the tool substrate) including the hard coating layer and the tool substrate was photographed with a transmission electron microscope (TEM) at a magnification of 30,000 times, and then the transmission electron microscope photograph was binarized using image analysis software to separate it into two phases, the hard coating layer and the tool substrate, and the curve forming the interface between the hard coating layer and the tool substrate was linearly approximated. Next, a straight line was drawn in a direction parallel to the obtained straight line, and the total length of the line segments belonging to the hard coating layer side was l (small el), and the total length of the line segments belonging to the tool substrate side was L, and the straight line at the position where L/(L+l)=0.8 was determined as the interface between the hard coating layer and the tool substrate.
Next, in the field of view of the transmission microscope in which the interface was determined, the Ti content was measured by an energy dispersive X-ray analyzer (EDS) at any five points in the substrate that were equidistant from the interface, and the region in which the average Ti content at the five points was 2 at % or more was defined as a Ti-diffusion region, and the thickness of the Ti-diffusion region, which was the distance from the interface, was measured.
The term "Ti content is 2 at% or more" means that the Ti content is 2 at% relative to the total content of Ti, Si, Al, O, N and binder phase components obtained by quantitative analysis using TEM-EDS.
Furthermore, in the field of view of the transmission microscope where the interface was determined, the Si content was measured by an energy dispersive X-ray analyzer (EDS) at any five points in the hard coating layer that were equidistant from the interface, and the area where the average Si content at the five points was 2 at% or more was defined as a Si diffusion area, and the thickness of the Si diffusion area, which is the distance from the interface, was measured.
The term "Si content is 2 at % or more" means that the Si content is 2 at % relative to the total content of Ti, Si, C, O, and N obtained by quantitative analysis using TEM-EDS.

Top layer consisting of ₃ layers of Al ₂ O:
The upper layer consisting of three Al ₂ O ₃ layers has the effect of maintaining the wear resistance of the hard coating layer. However, if the average layer thickness is less than 2 μm, the wear resistance cannot be ensured over a long period of use, while if the average layer thickness exceeds 10 μm, the chipping resistance, defect resistance, and wear resistance during ultra-high speed milling cutting are reduced. Therefore, the average layer thickness is set to 2 to 10 μm.

For the purpose of identifying tools before and after use, a TiN layer having a golden color tone may be vapor-deposited on the upper surface as necessary. In this case, the average layer thickness may be 0.1 to 1 μm. This is because a sufficient identification effect cannot be obtained with a thickness of less than 0.1 μm, whereas the identification effect of the TiN layer is sufficient with an average layer thickness of up to 1 μm.

Next, the ceramic-based surface-coated cutting tool of this invention will be specifically described using examples.

[Example]
Preparation of ceramic substrate:
As _raw material powders, _Si3N4 powder, AlN powder, _{Y2O3 powder} , _Yb2O3 and _{Al2O3 powder} , all having an average particle size within the range of 0.1 to 1.0 μm, were prepared. These raw material powders were mixed according to the composition shown in Table 1, wet mixed in a ball mill for 96 hours, dried, and then pressed into a _thick powder at a pressure of 100 MPa. This compact was sintered under the conditions of holding at 1800°C for 2 hours in a nitrogen atmosphere of 1 MPa. After sintering, it was processed to a specified size, and the cutting edge was processed into a width of 0.10 mm, an angle of 20 degrees, and R: 0.02 mm to produce ceramic bases A and B for cutting tools having a throw-away tip shape specified in ISO-SDCW120408.
Table 1 shows the composition of the substrates A and B, as well as the β-sialon ratio.

Next, the surfaces of the substrates A and B prepared above were subjected to a blasting treatment under the conditions shown in Table 2, thereby reducing the amount of amorphous grain boundary phase present on the substrate surface and exposing a large amount of sialon (SiAlON) and _{Si3N4 ,} which are the main hard phases, on the substrate surface.
The preferred range of processing conditions for the blasting treatment is as follows.
Blasting fluid: abrasive grains + water,
Abrasive grains: _{Al2O3 powder} grains,
Abrasive grain size: 100-440 (mesh),
Abrasive grain concentration: 15-60% by mass,
Blasting pressure: 0.10-0.35MPa
Projection time: 8-30 seconds

Next, an intermediate layer consisting of a Ti compound layer shown in Table 3 was deposited on the blasted surfaces of the substrates A and B using a conventional chemical vapor deposition apparatus under conventional chemical vapor deposition conditions to a total average layer thickness shown in Table 5, producing substrates 1 to 10 coated with the intermediate layer.

Next, some of the substrates 1 to 10 were subjected to a heat treatment under the conditions shown in Table 4, and a Ti-diffused region having a thickness shown in Table 5 was formed.
The heat treatment is a process carried out on the ceramic base having the intermediate layer formed thereon in order to further promote diffusion of the Ti component into the ceramic base. This process may be carried out as required, and is not necessarily an essential step in the production of the ceramic-based surface-coated cutting tool of the present invention.

Next, on the surfaces of the substrates 1 to 10 that had been subjected to the heat treatment or had not been subjected to the heat treatment, an upper layer consisting of three Al ₂ O ₃ layers shown in Table 3 was deposited by vapor deposition under normal chemical vapor deposition conditions to have an average layer thickness shown in Table 5, thereby producing the ceramic-based surface-coated cutting tools 1 to 10 of the present invention (hereinafter referred to as the "tools of the present invention").

[Comparative Example]
For the purpose of comparison, a surface-coated cutting tool as a comparative example (hereinafter referred to as a "comparative example tool") different from the tool of the present invention was prepared as follows.

Comparative Example Tools 1 to 10 were produced using the tool base shown in Table 1 in the same manner as the tool of the present invention (i.e., the heat treatment, the formation of the intermediate layer, and the formation of the upper layer were almost the same as those of the tool of the present invention), except that the tool base was not subjected to blast treatment or was subjected to blast treatment under conditions outside the range of preferred treatment conditions.
Table 6 shows the base type, blast treatment type, heat treatment type, intermediate layer type and total average layer thickness, and upper layer average layer thickness for comparative example tools 1 to 10.

In addition, for the tool of the present invention and the comparative example tool prepared as described above, cross sections perpendicular to the substrate surface were observed and measured, and the substrate region having a Ti content of 2 at% or more was designated as the Ti-diffusion region, and the intermediate layer region having a Si content of 2 at% or more was designated as the Si-diffusion region, thereby determining the thicknesses of the Ti-diffusion region and the Si-diffusion region.
The values are shown in Tables 5 and 6.

Here, the thickness of the Ti diffusion region and the average thickness of the Si diffusion region were measured by the following method.
First, a polished surface of a longitudinal section (a section perpendicular to the surface of the tool substrate) including the hard coating layer and the tool substrate was photographed with a transmission electron microscope (TEM) at a magnification of 30,000 times, and then the transmission electron microscope photograph was binarized using image analysis software to separate it into two phases, the hard coating layer and the tool substrate, and the curve forming the interface between the hard coating layer and the tool substrate was linearly approximated. Next, a straight line was drawn in a direction parallel to the obtained straight line, and the total length of the line segments belonging to the hard coating layer side was l (small el), and the total length of the line segments belonging to the tool substrate side was L, and the straight line at the position where L/(L+l)=0.8 was determined as the interface between the hard coating layer and the tool substrate.
Next, in the field of view of the transmission microscope in which the interface was determined, the Ti content was measured by an energy dispersive X-ray analyzer (EDS) at any five points in the substrate that were equidistant from the interface, and the region in which the average Ti content at the five points was 2 at % or more was defined as a Ti-diffusion region, and the thickness of the Ti-diffusion region, which was the distance from the interface, was measured.
Furthermore, in the field of view of the transmission microscope where the interface was determined, the Si content was measured by an energy dispersive X-ray analyzer (EDS) at any five points in the hard coating layer that were equidistant from the interface, and the area where the average Si content at the five points was 2 at% or more was defined as a Si diffusion area, and the thickness of the Si diffusion area, which is the distance from the interface, was measured.
The total average thickness of the intermediate layers and the average thickness of the upper layers of the tools of the present invention and the comparative example are shown in Tables 5 and 6, and were obtained by averaging values measured at multiple points using a scanning electron microscope.

Next, for each of the coated tools 1 to 10 of the present invention and the comparative coated tools 1 to 10, an ultra-high speed milling test was carried out under the following cutting conditions while the tools were all clamped to the tip of a tool steel cutter having a cutter diameter of 80 mm using a fixing jig.
<Cutting conditions>
Workpiece: JIS FCD600, block material 100 mm wide, 400 mm long Cutting speed: 1000 m/min
Axial depth: 1.0 mm,
Radial cut: 60 mm
Feed per blade: 0.1 mm/blade
Cutting time: 15 minutes,
Dry ultra-high speed milling cutting test of ductile cast iron under the conditions of (normal cutting speed is 500m/min),
The wear width of the flank of the cutting edge was measured, and the occurrence of abnormal damage was observed.
Table 7 shows the measurement and observation results.

From the results shown in Tables 5 to 7, it can be seen that in a ceramic-based surface-coated cutting tool having an upper layer made of _Al2O3 formed on the surface of a _sialon ceramic base with an intermediate layer made of a Ti compound therebetween, a Ti-diffused region of a predetermined average thickness extending from the interface between the ceramic base and the intermediate layer toward the inside of the ceramic base, and a Si-diffused region of a predetermined average thickness extending from the interface between the ceramic base and the intermediate layer toward the inside of the intermediate layer, when this coated tool is subjected to ultra-high speed milling of cast iron, etc., not only does it not peel off, but it also exhibits excellent chipping resistance and defect resistance and exhibits excellent wear resistance over long periods of use, thereby enabling the ceramic-based surface-coated cutting tool to have a longer life.

On the other hand, in comparative coated tools in which the Ti and Si diffusion regions were not formed, or in which the Ti and Si diffusion regions were formed with thicknesses outside the average thicknesses specified in the present invention, the tool life was short due to the occurrence of abnormal damage such as peeling, chipping, and defects, or a decrease in wear resistance.

As described above, the ceramic-based surface-coated cutting tool of the present invention exhibits excellent chipping resistance, fracture resistance, peeling resistance and wear resistance in ultra-high speed milling cutting of cast iron and the like, which is accompanied by high heat generation and is subjected to large thermal shock, and can fully meet the demands for labor-saving and energy-saving in cutting.

Claims (1)

A ceramic-based surface-coated cutting tool having a sialon or silicon nitride ceramic substrate surface coated with a hard coating layer consisting of an intermediate layer and an upper layer,
(a) an intermediate layer having a total average layer thickness of 0.3 to 1.5 μm and made of one or more Ti compounds selected from Ti nitrides, carbides, carbonitrides, carbonates and carbonitrides is formed on the surface of the ceramic substrate;
(b) an upper layer made of Al ₂ O ₃ having an average thickness of 2 μm to 10 μm is formed on the surface of the intermediate layer;
(c) a Ti-diffused region having a Ti content of 2 at% or more is formed from the interface between the ceramic base and the intermediate layer toward the inside of the ceramic base, and the Ti-diffused region has an average thickness of 0.10 μm or more and 0.70 μm or less;
(d) A ceramic-based surface-coated cutting tool, characterized in that a Si-diffusion region having a Si content of 2 at % or more is formed from the interface between the ceramic base and the intermediate layer toward the inside of the intermediate layer, and the Si-diffusion region has an average thickness of 0.05 μm or more and 0.30 μm or less.

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