JP6940815B2 - Surface coating cutting tool with excellent wear resistance and peeling resistance for the hard coating layer - Google Patents

Description

According to the present invention, even when used for high-speed cutting of difficult-to-cut materials such as alloy tool steel and Ti alloy, the hard coating layer has excellent wear resistance and peeling resistance, so that it can be used for a long period of time. It relates to a surface-coated cutting tool (hereinafter, also referred to as “covered tool”) having excellent cutting performance.

Conventionally, from the viewpoint of improving wear characteristics in coated tools, for example, in Patent Document 1, for example, in Patent Document 1, a tungsten carbide-based cemented carbide substrate surface is formed by chemical vapor deposition as a lower layer, particularly titanium or the like. It has been proposed to use a coating tool having a hard coating layer having an element diboride (TiB ₂ ) layer and an α-aluminum oxide layer formed by chemical vapor deposition as an upper layer. Due to the diffusion of boron in the bonding layer in the cemented carbide substrate and the TiB ₂ layer under the conditions of high temperature and high vacuum during film formation, a boron-containing brittle layer is formed, and therefore the life of the abrasion-resistant component material is extended. There was a problem of significant reduction.
On the other hand, in Patent Document 2, for example, tungsten carbide is used as a covering tool that exhibits excellent wear resistance even when used for high-speed cutting of high-hardness steel such as hardened material of alloy tool steel and bearing steel. _{Of Al and Ti satisfying the composition formula: (Al 1-X} Ti _X ) N (where X indicates 0.25 to 0.60 in atomic ratio) as a lower layer on the surface of the base cemented carbide substrate. It has a lower layer made of a composite nitride layer, a close-contact bonding layer made of a ZrBN (zirconium nitride) layer on the lower layer, and ZrB ₂ (on the close-contact bonding layer). It has been proposed to use a coating tool in which a hard coating layer having an upper layer composed of a (zirconium nitride) layer is formed.
Further, in Patent Document 3, in a coating tool in which a coating layer composed of _{at least a Zr boride (ZrB 2} ) layer is formed on the outermost surface of a cemented carbide substrate having a tungsten carbide group _{, the Zr boride (ZrB 2} ) is used. The layer is composed of a composite structure of crystal grain structures having a plurality of average particle sizes, and specifically, a secondary having an average particle size of 50 to 100 nm composed of an aggregate of primary crystal grains having an average particle size of 5 to 30 nm. It is composed of crystal grains and tertiary crystal grains having an average particle size of 200 to 1000 nm composed of aggregates of the secondary crystal grains, and has high film strength (for example, nanoindentation hardness measured at a load of 200 mg is 3600 kgf /). By ^{forming a composite structure having mm 2} or more (= 35.3 GPa or more)), the cutting conditions are more severe than the cutting conditions described in Patent Document 2, that is, various Ti-based alloys and high Si-containing Al-Si. A covering tool that exhibits excellent wear resistance and peeling resistance has been proposed even when cutting a hard difficult-to-cut material such as a cemented carbide is used under high-speed cutting conditions.

Japanese Unexamined Patent Publication No. 51-148713 Japanese Unexamined Patent Publication No. 2006-1004 Japanese Patent No. 5488824

By the way, in recent years, there has been a strong demand for labor saving and energy saving in cutting, and along with this, covering tools have come to be used under more severe conditions. It is required to have excellent wear resistance and peeling resistance even under further high-speed cutting conditions.
_{However, using a coating tool composed of a coating layer having a Zr boride (ZrB 2} ) layer, which is proposed in Patent Document 2 and Patent Document 3, the difficult-to-cut material is subjected to further high-speed cutting conditions. When cutting is performed, these coating layers cannot withstand plastic deformation and particles fall off from the coating layer, resulting in poor wear resistance, resulting in abnormal wear and film peeling. , Had the problem of reaching the end of its life early.

Therefore, from the above-mentioned viewpoint, the present inventors have excellent wear resistance and peeling resistance over a long period of time even when used for high-speed cutting of the difficult-to-cut material, and have a tool life. As a result of diligent research on covering tools that bring about improvement, the following findings were obtained.
That is, the present inventors _{obtain a high-hardness Zr-boride (ZrB 2} ) layer having a vertically elongated columnar crystal structure by forming a _{Zr-boride (ZrB 2) layer under limited conditions.} it can, in such Zr boride (ZrB ₂₎ layer, since the substrate and the parallel direction of the grain boundary is reduced, found to have crystal grain falling hardly occurs properties, further, Zr boride (ZrB ₂ ) Focusing on the orientation of the crystal grains constituting the layer, the diffraction peak intensities from each crystal lattice plane were measured by X-ray diffraction. As a result, the (100) plane had the maximum peak intensity and the orientation index. When Tc (hkl) was determined, it was found that when Tc (100) was 2.0 or more, a hard coating layer having excellent wear resistance and peeling resistance could be obtained.
Since the coated cutting tool having the Zr boro compound (ZrB ₂ ) layer as a hard coating layer has both wear resistance and peeling resistance, high-speed cutting of difficult-to-cut materials such as alloy tool steel and Ti alloy It has been found that when used for machining, it has excellent cutting characteristics and further improves the tool life.

式（Ａ）において、Ｉ（ｈｋｌ）は（ｈｋｌ）面のＸ線回折強度を示し、Ｉ_０（ｈｋｌ）はＩＣＤＤカード００−０３４−０４２３によるＺｒＢ_２の（ｈｋｌ）面のＸ線回折標準強度を示す。
また、（ｈｋｌ）は（００１）、（１００）、（１０１）、（１１０）、（１０２）、（１１１）、（２０１）、（１１２）の８面であり、式（Ａ）の中括弧内は各面におけるＸ線回折強度のＸ線回折標準強度に対する比の平均値を示す。
（２）前記上部層の前記Ｚｒ硼化物層におけるナノインデンテーション押し込み硬さが、押し込み荷重２００ｍｇｆのとき、４５．０ＧＰａ以上であることを特徴とする（１）に記載の表面被覆切削工具。
（３）（１）または（２）に記載の表面被覆切削工具において、前記上部層であるＺｒ硼化物層の上層として、０．３〜２．０μｍの平均層厚を有するα型もしくはκ型のＡｌ_２Ｏ_３層を有することを特徴とする（１）または（２）に記載の表面被覆切削工具。」
を特徴とするものである。 The present invention has been made based on the above findings.
"(1) In a surface-coated cutting tool in which a hard coating layer is formed on the surface of a tool substrate made of a tungsten carbide-based cemented carbide or a titanium nitride-based cermet.
(A) The hard coating layer has a lower layer and an upper layer from the surface side of the tool substrate.
(B) The lower layer is composed of one or more layers of a carbide layer, a nitride layer, a carbonitride layer, a carbonic acid oxide layer and a carbonic acid oxide layer of Ti, and 0.1 to 3 layers. Having a Ti compound layer with a total average layer thickness of .0 μm,
(C) The upper layer has a Zr boride layer having an average layer thickness of 1.0 to 15.0 μm.
(D) In the vertical cross section of the upper layer, the vertically elongated columnar crystal grains having an aspect ratio of 3 or more have a vertically elongated columnar crystal structure having an area ratio of 80% or more.
(E) The upper layer is a Zr-boride layer in which the maximum peak due to X-ray diffraction appears on the (100) plane, and the orientation index Tc (hkl) of the Zr-boride layer represented by the following formula (A). A surface-coated cutting tool, characterized in that Tc (100) ≥ 2.0.

Equation (A)

In formula (A), I (hkl) indicates the X-ray diffraction intensity of the (hkl) plane, and I ₀ (hkl) is the X-ray diffraction standard intensity of the (hkl) plane of _{ZrB 2} according to the ICDD card 00-034-0423. Is shown.
Further, (hkl) is the eight faces of (001), (100), (101), (110), (102), (111), (201), and (112), and the curly braces of the formula (A). The inside shows the average value of the ratio of the X-ray diffraction intensity to the X-ray diffraction standard intensity on each surface.
(2) The surface coating cutting tool according to (1), wherein the nanoindentation indentation hardness of the upper layer in the Zr boride layer is 45.0 GPa or more when the indentation load is 200 mgf.
(3) In the surface coating cutting tool according to (1) or (2), α-type or κ-type having an average layer thickness of 0.3 to 2.0 μm as the upper layer of the Zr boride layer which is the upper layer. The surface coating cutting tool according to (1) or (2), which has the Al ₂ O _{3 layer of the above.} "
It is characterized by.

Next, the covering tool of the present invention will be described in detail.

Hard coating layer;
The hard coating layer according to the present invention has a lower layer composed of one or more Ti compound layers and an upper layer which is a Zr boride layer from the tool substrate side, and further, if necessary, an upper layer. As the upper layer of the layer, it has an α-type or κ-type aluminum oxide layer (Al ₂ O ₃ layer).
If the average thickness of the hard coating layer is less than 1.1 μm, wear resistance cannot be exhibited for a long period of time, while if it exceeds 20.0 μm, defects and chipping are likely to occur as the entire coating layer. It is desirable to set it to 1.1 to 20.0 μm.
The average thickness of the hard coating layer can be measured using, for example, an SEM (scanning electron microscope) or a TEM (transmission electron microscope) in a cross section perpendicular to the tool substrate.

Lower layer;
The lower layer formed on the tool substrate is composed of one or more Ti compound layers of a carbide layer of Ti, a nitride layer, a carbonitride layer, a carbonic acid oxide layer and a carbonic acid oxide layer, and is a tool. Since the adhesion between the substrate and the Zr boronized layer, which is the upper layer, can be enhanced, the occurrence of abnormal damage such as chipping and peeling can be suppressed.
If the total average layer thickness of the lower layer composed of the Ti compound layer is less than 0.1 μm, the effect of the lower layer is not sufficiently exhibited, while if it exceeds 3.0 μm, the crystal grains tend to be coarsened and chipping occurs. It is desirable to set it to 0.1 μm to 3.0 μm because it becomes easy.

Upper layer (Zr boride layer);
(1) Average layer thickness
The upper layer (Zr boride layer) formed on the lower layer has high hardness and excellent wear resistance, and particularly when the average layer thickness is 1.0 to 15.0 μm, the hardness and resistance are high. It exerts an excellent effect from the viewpoint of wear resistance.
For the average layer thickness of the upper layer, a scanning electron microscope (magnification 5000 times) is used to measure the layer thickness of 5 points in the observation field of the cross section in the direction perpendicular to the tool substrate, and the average layer thickness is averaged. Can be sought.
(2) Vertical columnar crystal structure As described above, the Zr-boride (ZrB ₂ ) layer constituting the upper layer according to the present invention has a vertically long columnar crystal structure, so that particles are suppressed from falling off from the coating layer. Demonstrates excellent wear resistance and peel resistance.
The vertically long columnar crystal structure referred to here means _{that when the vertical cross section of the Zr boride (ZrB 2} ) layer is observed, the major axis of the crystal grains is oriented in the vertical direction, and the minor axis with respect to the major axis diameter of the crystal grains. It refers to a structure in which the aspect ratio defined as the ratio of diameters is 3 or more, and the area ratio of the vertically elongated crystal grains in the structure is 80% or more.
If the aspect ratio is less than 3, the shape approaches equiaxed crystals, which may cause dropping, and even if the aspect ratio is 3 or more, if the area ratio occupied by these crystal grains is less than 80%, Since it is not possible to exert a sufficient effect, the aspect ratio of the vertically elongated columnar crystal grains is defined as 3 or more, and the area ratio occupied by the vertically elongated columnar crystal grains is defined as 80% or more. It has excellent peel resistance.
The aspect ratio and the area ratio of the vertically elongated crystal grains are measured by, for example, electron backscatter diffraction (EBSD) on a longitudinal cross-sectional image obtained by cross-sectional observation at a magnification of 5000 using a scanning electron microscope (SEM). , Measure the major axis diameter, minor axis diameter, and vertical cross-sectional area of each crystal grain, determine the aspect ratio from the major axis diameter and minor axis diameter, and then determine the aspect ratio of the crystal grains having an aspect ratio of 3 or more. The ratio of the area of the vertical section to be measured to the total area of the vertical section was calculated as the area ratio.

上記式（Ａ）において、Ｉ（ｈｋｌ）は測定された（ｈｋｌ）面のＸ線回折強度を示し、Ｉ_０（ｈｋｌ）はＩＣＤＤカード００−０３４−０４２３によるＺｒＢ_２の（ｈｋｌ）面のＸ線回折標準強度を示す。
また、（ｈｋｌ）は（００１）、（１００）、（１０１）、（１１０）、（１０２）、（１１１）、（２０１）、（１１２）の８面であり、式（Ａ）の中括弧内は各面におけるＸ線回折強度のＸ線回折標準強度に対する比の平均値を示す。
本発明被覆工具においては、少なくとも前記Ｚｒ硼化物層は、（１００）面にＸ線回折による最大ピーク強度を有し、かつ、配向性指数Ｔｃ（１００）≧２．０という高い配向性を有することにより、切削加工時にＺｒ硼化物層に大きなせん断力が働いた場合においても、耐塑性変形性を有するため、Ｚｒ硼化物層からの結晶粒の脱落の発生や、これに伴うチッピング、欠損、剥離の発生、さらには、偏摩耗等の異常損傷の発生を抑制することができるため、耐摩耗性の向上が図られる。 (3) Maximum Peak Intensity, Orientation Index As described above, the present invention has a maximum peak on the (100) plane when X-ray diffraction is performed on the upper layer (Zr boride layer). It has been found that when Tc (100), which is an orientation index on the (100) plane, is 2.0 or more, excellent wear resistance and chipping resistance are exhibited.
FIG. 1 shows an example of a chart of diffraction peak intensities from each crystal lattice plane measured by X-ray diffraction for the Zr boride layer of the coating tool of the present invention.
As is clear from FIG. 1, it can be seen that the Zr-boride layer of the coating tool of the present invention has the maximum diffraction peak intensity for the (100) plane as compared with the peak strength of the other crystal lattice planes.
The X-ray diffraction was measured by the 2θ-θ method using CuKα rays using PANalytical Empyrene of Spectris as an X-ray diffractometer, and the measurement conditions were a measurement range (2θ): 15 to 130 degrees, X-ray output: The measurement was performed under the conditions of 45 kV, 40 mA, divergence slit: 0.5 degrees, scan step: 0.013 degrees, and measurement time per step: 0.48 sec / step.
Further, when the orientation index Tc (hkl) was determined for the Zr boride layer, the value of Tc (100) was 2.0 or more, and the (100) plane had a high orientation.
The orientation index Tc (hkl) is defined by the following formula.


Equation (A)

In the above formula (A), I (hkl) indicates the X-ray diffraction intensity of the measured (hkl) plane, and I ₀ (hkl) is the X of the (hkl) plane of _{ZrB 2} by the ICDD card 00-034-0423. Indicates the standard intensity of line diffraction.
Further, (hkl) is the eight faces of (001), (100), (101), (110), (102), (111), (201), and (112), and the curly braces of the formula (A). The inside shows the average value of the ratio of the X-ray diffraction intensity to the X-ray diffraction standard intensity on each surface.
In the coating tool of the present invention, at least the Zr boride layer has a maximum peak intensity due to X-ray diffraction on the (100) plane and has a high orientation index Tc (100) ≥ 2.0. As a result, even when a large shearing force acts on the Zr boride layer during cutting, it has plastic deformation resistance, so that crystal grains fall off from the Zr boride layer, and chipping and chipping due to this, Since it is possible to suppress the occurrence of peeling and the occurrence of abnormal damage such as uneven wear, wear resistance can be improved.

(4) Hardness As described above, the upper layer (Zr boride layer) has high hardness and excellent wear resistance, but further, nanoindentation indentation hardness (indentation load 200 mgf). When is 45.0 GPa or more, a better effect can be exhibited.
The nanoindentation hardness was measured by polishing the surface of the Zrboride layer based on the nanoindentation test method (ISO 14577) and using a diamond Berkovich indenter with a pushing load of 200 mgf.

Method of forming the upper layer (Zr boride (ZrB _{2) layer):}
The Zr-boride layer having a vertically long columnar crystal structure, a maximum peak on the (100) plane, and a high orientation index with respect to the (100) plane according to the present invention is, for example, after forming the lower layer on a tool substrate. It can be formed by sequentially performing the treatment under the conditions shown in each of the following steps using the following chemical vapor deposition method.
That is, in the method for forming the Zr boride (ZrB _{2 ) layer, in the ZrB 2} initial nucleation step which is the first step, the reaction atmosphere temperature is relatively low as compared _{with the ZrB 2} crystal growth step which is the second step. In addition, by lowering the raw material gas concentration ratio, a reaction atmosphere having high (100) orientation and easy formation of a vertically long columnar structure as an initial nucleus is created, and in the ZrB2 crystal growth step, which is the _{second step,} By raising the reaction atmosphere temperature and increasing the raw material gas concentration ratio to create a reaction atmosphere in which the vertically elongated columnar structure is easy to grow, (100) the vertically elongated columnar structure having high orientation and a desired high aspect ratio. Can be obtained.

[Film formation conditions]
1) First step (ZrB ₂ initial nucleation step)
Treatment method: Film formation using CVD method Reaction gas composition (volume%):
Gas group A: BCl ₃ : 0.25 to 1.00%, ZrCl ₄ : 0.10 to 1.00%,
H ₂ : The rest
Reaction atmosphere temperature: 900 ° C to 950 ° C
Reaction atmospheric pressure: 3 kPa to 10 kPa
Reaction time: 20-90 minutes

2) Second step (ZrB ₂ crystal growth step)
Treatment method: Film formation using CVD method Reaction gas composition (volume%):
Gas group B: BCl ₃ : 0.25 to 3.00%, ZrCl ₄ : 0.25 to 2.00%,
H ₂ : The rest
Reaction atmosphere temperature: 900 ° C to 1050 ° C
Reaction atmospheric pressure: 3 kPa to 10 kPa
Reaction time: Until the target film thickness is reached

Aluminum oxide layer (upper layer);
The coating tool of the present invention can form an aluminum oxide layer as an upper layer of a Zr boride layer which is an upper layer.
_{The aluminum oxide layer was determined to form an α-type Al 2} O ₃ layer or a κ-type Al ₂ O ₃ layer having an average layer thickness of 0.3 to 2.0 μm by a usual chemical vapor deposition method.
_{By forming an α-type Al 2} O ₃ layer or a κ type Al ₂ O ₃ layer as an upper layer with respect to the upper layer, it is possible to further improve the high-temperature hardness and heat resistance of the hard coating layer.
When the average layer thickness of the aluminum oxide layer is less than 0.3 μm, the effect of extending the life due to the improvement of wear resistance is small, and when the average layer thickness exceeds 2.0 μm, the crystal grains of aluminum oxide become coarse. As described above, it is desirable that the average layer thickness is 0.3 to 2.0 μm, because it becomes easy to reduce high temperature hardness and high temperature strength, and welding chipping, peeling, etc. may occur.

The surface-coated cutting tool according to the present invention has a high-hardness Zr boro compound (ZrB ₂ ) layer having a vertically long columnar crystal structure as a hard coating layer formed on the surface of a tool substrate. _{The crystal grains forming the Zr-borrated (ZrB 2} ) layer have the property of being less likely to fall off, and have the maximum peak intensity on the (100) plane, and the orientation index Tc on the (100) plane. When (100) is 2.0 or more, a hard coating layer having excellent wear resistance and peel resistance is formed, so that it is used for high-speed cutting of difficult-to-cut materials such as alloy tool steel and Ti alloy. If so, it has excellent cutting characteristics and further improves the tool life.

An example (orientation index) of the diffraction peak intensity obtained from each crystal lattice plane measured by X-ray diffraction is shown for the upper layer (Zr boride layer) of the hard coating layer in the coating tool 1 of the present invention. The whole schematic view of the cross-sectional structure SEM photograph of the surface coating layer of the coating tool of this invention is shown.

Next, the covering tool of the present invention will be specifically described with reference to Examples.

As raw material powders, both WC powder having an average particle size of 1 to 3 [mu] m, TiC powder, ZrC powder, TaC powder, NbC powder, _Cr 3 _{C 2} powder, TiN powder, and Co powder was prepared, these raw powders , Add wax to the compounding composition shown in Table 1, ball-mill mix in acetone for 24 hours, dry under reduced pressure, press-mold into a green compact of a predetermined shape at a pressure of 98 MPa, and press-mold this green compact. Is vacuum sintered in a vacuum of 5 Pa at a predetermined temperature in the range of 1370 to 1470 ° C. for 1 hour, and after sintering, a tool made of WC-based superhard alloy having an insert shape of ISO standard CNMG120408. The substrates A to C were produced, respectively.

Further, as raw material powders, WC powder, TiC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder having an average particle size of 1 to 3 μm are prepared, and these raw material powders are blended as shown in Table 1. It was blended into the composition, further added with wax, mixed in a ball mill in acetone for 24 hours, dried under reduced pressure, press-molded into a green compact having a predetermined shape at a pressure of 98 MPa, and the green powder was press-molded into a green compact of a predetermined shape in a vacuum of 5 Pa, 1370. Vacuum-sintered at a predetermined temperature within the range of ~ 1470 ° C. under the condition of holding for 1 hour, and after sintering, a tool base D made of WC-based superhard alloy having an ISO standard SEMT13T3AGSN insert shape was produced.

Further, as the raw material powder, both the average (TiC / TiN = 50/50 in mass ratio) TiCN having a particle size of 0.5~2μm powder, ZrC powder, TaC powder, NbC powder, Mo ₂ C powder, WC powder , Co powder and Ni powder are prepared, these raw material powders are blended into the compounding composition shown in Table 2, wet-mixed with a ball mill for 24 hours, dried, and then press-molded into a green compact at a pressure of 98 MPa. This green compact was sintered in a nitrogen atmosphere of 1.3 kPa at a temperature of 1500 ° C. for 1 hour, and after sintering, a tool base E made of TiCN-based cermet having an ISO standard CNMG120408 insert shape was prepared. bottom.

Further, as raw material powders, TiCN (TiC / TiN = 50/50 by mass ratio) powder, ZrC powder, TaC powder, NbC powder, WC powder, Co powder and Ni, each having an average particle size of 0.5 to 2 μm. Powders are prepared, these raw material powders are blended into the compounding composition shown in Table 2, wet-mixed with a ball mill for 24 hours, dried, and then press-molded into a green compact at a pressure of 98 MPa to obtain the green compact. It was sintered in a nitrogen atmosphere of 1.3 kPa at a temperature of 1500 ° C. for 1 hour, and after sintering, a tool substrate F made of TiCN-based cermet having an ISO standard SEMT13T3AGSN insert shape was prepared.

Then, each of these tool bases A to F was charged into a normal chemical vapor deposition apparatus, and the covering tools 1 to 14 of the present invention were manufactured by the following procedure.
(A) First, with respect to the tool substrate of Table 1 or Table 2 indicated by the tool substrate symbol of Table 6, the Ti compound layer having the target layer thickness shown in Table 6 is shown in Table 3 as a lower layer. Deposition formation was performed under the formation conditions.
(B) Next, based on the formation symbols in Table 6, an upper layer (Zr boride layer) having a target layer thickness is vapor-deposited under the formation conditions shown in Table 4, and for those having an aluminum oxide layer, further , The covering tools 1 to 14 of the present invention were produced by vapor-depositing an aluminum oxide layer having a target layer thickness under the formation conditions shown in Table 5.

Further, for the purpose of comparison, each of the tool substrates A to F is charged into a normal chemical vapor deposition apparatus by the same procedure as that of the covering tools 1 to 14 of the present invention, and the comparative example covering tool 1 is carried out by the following procedure. ~ 14 was manufactured. That is,
(A) For the tool substrate of Table 1 or 2 indicated by the tool substrate symbol of Table 7, a Ti compound layer having a target layer thickness shown in Table 7 is formed as a lower layer as shown in Table 3. The vapor deposition was formed at.
(B) Next, based on the formation symbols in Table 7, an upper layer (Zr boride layer) having a target layer thickness is vapor-deposited under the formation conditions shown in Table 4, and for those having an aluminum oxide layer, further , Comparative Example Covering Tools 1 to 14 were manufactured by vapor-depositing an aluminum oxide layer having a target layer thickness under the formation conditions shown in Table 5.

The diffraction peak intensities from each lattice surface were measured by X-ray diffraction for the upper layers (Zr boride layer) of the covering tools 1 to 14 of the present invention and the covering tools 1 to 14 of the comparative example.
FIG. 1 shows a chart obtained for the covering tool 1 of the present invention.
The X-ray diffraction was measured by the 2θ-θ method using CuKα rays using PANalytical Empyrean manufactured by Spectris as an apparatus.
The measurement conditions are measurement range (2θ): 15 to 130 degrees, X-ray output: 45 kV, 40 mA, divergence slit: 0.5 degrees, scan step: 0.013 degrees, measurement time per step: 0.48 sec / step. Is.
From the chart obtained above, it was determined whether or not the diffraction peak intensity from the (100) plane was the maximum by showing the lattice plane having the maximum diffraction peak intensity. (See Tables 6 and 7)

上記式（Ａ）において、Ｉ（ｈｋｌ）は測定された（ｈｋｌ）面のＸ線回折強度を示し、Ｉ_０（ｈｋｌ）はＩＣＤＤカード００−０３４−０４２３によるＺｒＢ_２の（ｈｋｌ）面のＸ線回折標準強度を示す。
また、（ｈｋｌ）は（００１）、（１００）、（１０１）、（１１０）、（１０２）、（１１１）、（２０１）、（１１２）の８面であり、式（Ａ）の中括弧内は８面の各面におけるＸ線回折強度のＸ線回折標準強度に対する比の平均値を示す。 Further, the orientation index Tc (100) was determined based on the measurement result of the diffraction peak intensity.
The orientation index Tc (100) is calculated by the following formula (A) and is shown in Tables 6 and 7.

Equation (A)

In the above formula (A), I (hkl) indicates the X-ray diffraction intensity of the measured (hkl) plane, and I ₀ (hkl) is the X of the (hkl) plane of _{ZrB 2} by the ICDD card 00-034-0423. Indicates the standard intensity of line diffraction.
Further, (hkl) is the eight faces of (001), (100), (101), (110), (102), (111), (201), and (112), and the curly braces of the formula (A). The inside shows the average value of the ratio of the X-ray diffraction intensity to the X-ray diffraction standard intensity on each of the eight surfaces.

Further, the vertical cross sections of the upper layers (Zr boronized layer) of the covering tools 1 to 14 of the present invention and the covering tools 1 to 14 of the comparative examples were obtained by cross-section observation at a magnification of 5000 using a scanning electron microscope (SEM). For the vertical cross-sectional image, the major axis diameter, minor axis diameter, and vertical cross-sectional area were measured for each crystal grain by electron backscatter diffraction (EBSD), and the aspect was measured from the major axis diameter and minor axis diameter. The ratio was obtained, and then the ratio of the area of the vertical cross section to be measured to the total area of the vertical cross section of the crystal grains having an aspect ratio of 3 or more was obtained as the area ratio, and is shown in Tables 6 and 7.

Further, the thickness of each constituent layer of the hard coating layer of the covering tools 1 to 14 of the present invention and the covering tools 1 to 14 of the comparative example was measured in a vertical cross section using a scanning electron microscope (SEM), and the average of five points was measured. When calculated from the values, all showed an average layer thickness substantially the same as the target layer thickness.

Further, with respect to the upper layers (Zr boride layer) of the coating tools 1 to 14 of the present invention and the coating tools 1 to 14 of the comparative examples, the surface of the Zr boride layer was polished based on the nanoindentation test method (ISO 14577). Measurements were made using a diamond Berkovich indenter at a indentation load of 200 mgf. The number of measurement points was 20 for each sample, and the average values are shown in Tables 6 and 7.

Next, with the various covering tools clamped to the tip of the tool steel cutting tool with a fixing jig, the covering tools 1 to 10 of the present invention and the covering tools 1 to 10 of the comparative example are shown below in Inconel 718. A dry continuous cutting test was carried out, the flank wear width of the cutting edge was measured, and the presence or absence of welding was observed, and the results are shown in Table 8.

≪Cutting condition A≫
Cutting test: Inconel 718 dry continuous cutting test Work material: Inconel 718 round bar
Cutting speed: 60m / min,
Notch: 1.0 mm,
Feed amount: 0.2 mm / rev.
Cutting time: 5 minutes,

Further, with the various covering tools clamped to the tip of the tool steel cutter with a fixing jig, the covering tools 11 to 14 of the present invention and the covering tools 11 to 14 of the comparative example are subjected to high-speed intermittent heavy cutting as shown below. A dry high-speed face milling cutter and a center-cut cutting process test were carried out, and the flank wear width of the cutting edge was measured. The results are shown in Table 9.

≪Cutting condition B≫
Cutting test: Dry high-speed face milling test for structural steel SKD61 Work material: JIS / SKD61 Block material with width 60 mm and length 400 mm Rotation speed: 1200 min ^-1 ,
Cutting speed: 300m / min,
Notch: 1.5 mm,
Single blade feed amount: 0.2 mm / blade,
Cutting time: 5 minutes,

From the results shown in Tables 8 and 9, the surface-coated cutting tool of the present invention is an alloy that is a difficult-to-cut material by containing a Zr boride layer having a vertically elongated columnar crystal structure showing high orientation as a hard coating layer. It exhibits excellent chipping resistance and abrasion resistance in high-speed cutting of tool steel and Ti alloys.
On the other hand, none of the comparative example covering tools has a desired structure such as having no columnar crystal structure, and therefore, due to the progress of wear, the occurrence of welding, the occurrence of chipping, etc., in a short time. It reached the end of its life.

As described above, the surface-coated cutting tool of the present invention exhibits excellent welding resistance, chipping resistance, and abrasion resistance even in high-speed cutting of difficult-to-cut materials such as alloy tool steel and Ti alloy. Therefore, it is fully satisfied with the high performance of the cutting device, the labor saving and energy saving of the cutting process, and the cost reduction.

Claims (3)

In a surface-coated cutting tool in which a hard coating layer is formed on the surface of a tool substrate made of a tungsten carbide-based cemented carbide or a titanium nitride-based cermet.
(A) The hard coating layer has a lower layer and an upper layer from the surface side of the tool substrate.
(B) The lower layer is composed of one or more layers of a carbide layer, a nitride layer, a carbonitride layer, a carbonic acid oxide layer and a carbonic acid oxide layer of Ti, and 0.1 to 3 layers. Having a Ti compound layer with a total average layer thickness of .0 μm,
(C) The upper layer has a Zr boride layer having an average layer thickness of 1.0 to 15.0 μm.
(D) In the vertical cross section of the upper layer, the vertically elongated columnar crystal grains having an aspect ratio of 3 or more have a vertically elongated columnar crystal structure having an area ratio of 80% or more.
(E) The upper layer is a Zr-boride layer in which the maximum peak due to X-ray diffraction appears on the (100) plane, and the orientation index Tc (hkl) of the Zr-boride layer represented by the following formula (A). A surface-coated cutting tool, characterized in that Tc (100) ≥ 2.0.

Equation (A)

In formula (A), I (hkl) indicates the X-ray diffraction intensity of the (hkl) plane, and I ₀ (hkl) is the X-ray diffraction standard intensity of the (hkl) plane of _{ZrB 2} according to the ICDD card 00-034-0423. Is shown.
Further, (hkl) is the eight faces of (001), (100), (101), (110), (102), (111), (201), and (112), and the curly braces of the formula (1). The inside shows the average value of the ratio of the X-ray diffraction intensity to the X-ray diffraction standard intensity on each surface. The surface coating cutting tool according to claim 1, wherein the nanoindentation indentation hardness of the upper layer in the Zr boride layer is 45.0 GPa or more when the indentation load is 200 mgf. _{In the surface coating cutting tool according to claim 1 or 2, the α-type or κ-type Al 2} having an average layer thickness of 0.3 to 2.0 μm as the upper layer of the Zr boride layer which is the upper layer. the surface-coated cutting tool according to claim 1 or claim 2 characterized by having a O ₃ layer.

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