# Patent

## Title
Surface-coated cutting tool and method of manufacturing the same

## Abstract

A surface-coated cutting tool of the present invention includes a base material and a coating film formed on the base material. The coating film includes at least one TiB2 layer. The TiB2 layer includes Cl together with TiB2. This surface-coated cutting tool is characterized in that assuming that in the TiB2 layer, a first region represents a region having a thickness of 0.5 μm from an interface on the base material side, and a second region represents a region having a thickness of 0.5 μm from an interface on the coating film surface side, an atomic ratio Cl/(Ti+Cl) between Ti and Cl is higher in the first region than in the second region.

## Background
TECHNICAL FIELD
The present invention relates to a surface-coated cutting tool including a base material and a coating film formed on the base material, and a method of manufacturing the surface-coated cutting tool.
BACKGROUND ART
Conventionally, there is a known surface-coated cutting tool including a base material and a coating film formed on the base material, in which a TiB2 layer is included as the coating film.
For example, Japanese Patent Laying-Open No. 51-148713 (PTD 1) discloses a wear-resistant molding member comprising a cemented carbide base body and a surface layer that is formed of two laminated partial layers including an outer partial layer made of aluminum oxide and/or zirconium oxide, and an inner partial layer made of one or more types of borides, particularly, diboride that is an element of titanium, zirconium, hafnium or the like (that is, a TiB2 layer).
The inner partial layer of the above-described surface layer forms a TiB2 layer of 3 μm that is obtained under high-temperature and high-vacuum conditions of 1000° C. and 50 torr by introducing hydrogen at 1900 l/hour, TiCl4 at 20 ml/hour and BCl3 at 4 g/hour each as reactive raw material gas, and forming a film for one hour. Also, the outer partial layer forms an aluminum oxide layer of 5 μm.
However, under the high-temperature and high-vacuum conditions during the film formation as mentioned above, diffusion of boron in a junction layer and a TiB2 layer into the cemented carbide base body causes production of a strong η layer and/or a boron-containing brittle layer, thereby significantly reducing the lifetime of this wear-resistant molding member.
For the purpose of solving the above-described problems, a coated product is proposed that is improved in wear resistance by suppressing diffusion of boron and finely granulating TiB2 in the TiB2 layer (Japanese Patent National Publication No. 2011-505261 (PTD 2)). This coated product is formed by coating the surface of the cemented carbide base material with a layer of 0.1 μm to 3 μm made of a group of titanium nitride, titanium carbonitride and titanium boron carbonitride, and then, forming a TiB2 layer of 1 μm to 5 μm. The conditions of forming the TiB2 layer of various layers mentioned above are as follows. Specifically, a TiB2 layer having a thickness of 2.5 μm is formed by the thermal CVD method for 1 hour at a standard pressure and at a temperature of 800° C., using a raw material gas composition including 10% by volume of hydrogen, 0.4% by volume of TiCl4, 0.7% by volume of BCl3, and 88.9% by volume of argon gas. In this coated product, a boron-containing brittle layer caused by diffusion of boron into the cemented carbide base material is not formed, and the particle size of TiB2 in the TiB2 layer is also controlled to be 50 nm or lower, so that the lifetime of the tool is improved to some extent.
CITATION LIST
Patent Document
PTD 1: Japanese Patent Laying-Open No. 51-148713
PTD 2: Japanese Patent National Publication No. 2011-505261
SUMMARY OF INVENTION
Technical Problem
As described above, the coated product in PTD 2 is improved in lifetime of the tool to some extent. However, attention is paid only on suppression of formation of a strong η layer and/or a boron-containing brittle layer, or on control of the particle size of TiB2 in the TiB2 layer. Accordingly, there are limitations in further improving the performance of the TiB2 layer, so that consideration from another point of view has been required.
Furthermore, as in the case where such a coated product is used to process a Ti-based alloy that is a difficult-to-cut material, particularly in the process in which the temperature of the cutting edge tends to rise, and in the process in which the cutting edge of the tool tends to undergo stress concentration and vibration due to the specific shape of scraps (saw-blade shape), chipping of the cutting edge of the tool caused by breaking of a hard coating film due to various types of impacts may significantly reduce the lifetime of the tool, and thus, improvement in strength of the coating film has been required.
The present invention has been made in light of the above-described circumstances. An object of the present invention is to provide a surface-coated cutting tool including a TiB2 layer as a coating film and highly improved in wear resistance and impact resistance.
Solution to Problem
As a result of concentrated studies for solving the above-described problems, the inventors of the present invention have found that it is important for improvement in impact resistance to control the concentration of chlorine included in the TiB2 layer. Then, upon conducting further studies based on this knowledge, they completed the present invention.
Specifically, a surface-coated cutting tool according to the present invention includes a base material and a coating film formed on the base material. The coating film includes at least one TiB2 layer. This TiB2 layer includes Cl together with TiB2. Assuming that in the TiB2 layer, a first region represents a region having a thickness of 0.5 μm from an interface on the base material side, and a second region represents a region having a thickness of 0.5 μm from an interface on the coating film surface side, an atomic ratio Cl/(Ti+Cl) between Ti and Cl is higher in the first region than in the second region.
In this case, it is preferable that the atomic ratio Cl/(Ti+Cl) is 0.0001 to 0.01 in the first region, and is 0.00001 to 0.001 in the second region. It is preferable that the TiB2 layer has a thickness of 1 to 10 μm.
Furthermore, the present invention also relates to a method of manufacturing a surface-coated cutting tool including a base material and a coating film formed on the base material, in which the coating film includes at least one TiB2 layer. The method includes the step of forming the TiB2 layer. The step is a step of forming the TiB2 layer with a chemical vapor deposition method by using a raw material gas including at least TiCl4 and BCl3, and is characterized in that a molar ratio TiCl4/BCl3 between the TiCl4 and the BCl3 in the raw material gas is equal to or higher than 0.6 at the start of the step, and is lower than 0.6 at the end.
Advantageous Effects of Invention
The surface-coated cutting tool according to the present invention achieves an excellent effect of greatly improving wear resistance and impact resistance.


DESCRIPTION OF EMBODIMENTS
The present invention will be hereinafter described in greater detail.
<Surface-Coated Cutting Tool>
The surface-coated cutting tool according to the present invention has a configuration including a base material and a coating film formed on the base material. It is preferable that such a coating film covers the entire surface of the base material. However, even if a part of the base material is not covered by this coating film or the configuration of the coating film is partially different, such a structure does not deviate from the scope of the present invention.
The above-described surface-coated cutting tool according to the present invention can be suitably used as a cutting tool such as a drill, an end mill, a cutting edge replaceable-type cutting tip for a drill, a cutting edge replaceable-type cutting tip for an end mill, a cutting edge replaceable-type cutting tip for milling, a cutting edge replaceable-type cutting tip for turning, a metal saw, a gear cutting tool, a reamer, and a tap.
<Base Material>
As the base material used for the surface-coated cutting tool according to the present invention, any material can be used as long as it is conventionally known as the above-described type of base material. For example, the base material is preferably any one of cemented carbide (for example, WC-based cemented carbide or a material containing WC and Co or carbonitride of Ti, Ta, Nb or the like), cermet (mainly composed of TiC, TiN, TiCN, or the like), high-speed steel, ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, and the like), a cubic boron nitride sintered body, a diamond sintered body, and the like.
Among these various base materials, particularly, it is preferable to select WC-based cemented carbide and cermet (particularly, TiCN-based cermet). This is because these base materials are excellent in balance between the hardness and the strength particularly at a high temperature, and have excellent characteristics as a base material of the surface-coated cutting tool for the above-described use.
In the case where the surface-coated cutting tool is a cutting edge replaceable-type cutting tip or the like, the base material in this case may be those having a chip breaker or not having a chip breaker, and a cutting-edge ridgeline portion may be shaped in any of a sharp edge (a ridge in which a rake face and a flank face cross each other), honing (obtained by processing a sharp edge so as to have curve (R)), a negative land (obtained by beveling), and a combination of honing and a negative land.
<Coating Film>
The coating film of the present invention may include other layers as long as it includes at least one TiB2 layer. Examples of other layers may include an Al2O3 layer, a TiN layer, a TiCN layer, a TiBNO layer, a TiCNO layer, a TiAlN layer, a TiAlCN layer, a TiAlON layer, a TiAlONC layer, and the like. In the present invention, in the case where the compositions of layers other than the TiB2 layer are expressed by chemical formulae such as “TiN” and “TiCN” and in the case where the atomic ratio is not particularly specified in the chemical formulae, it is not assumed that the atomic ratio of each element is only “1”, but assumed that all of conventionally-known atomic ratios are included.
Such a coating film according to the present invention serves to cover the base material to achieve an effect of improving several characteristics such as wear resistance and impact resistance.
It is suitable that such a coating film of the present invention has a thickness of 2 μm to 20 μm, more preferably, 5 μm to 15 μm. When the thickness is less than 2 μm, the wear resistance may be insufficient. When the thickness exceeds 20 μm, the coating film may be peeled off or broken with great frequency when relatively strong stress is applied between the coating film and the base material during the intermittent process.
<TiB2 Layer>
The TiB2 layer included in the coating film of the present invention is characterized in that the TiB2 layer includes Cl (chlorine) together with TiB2, and assuming that in the TiB2 layer, a first region represents a region having a thickness of 0.5 μm from an interface on the base material side, and a second region represents a region having a thickness of 0.5 μm from an interface on the coating film surface side, an atomic ratio Cl/(Ti+Cl) between Ti and Cl is higher in the first region than in the second region. Due to controlling the concentration of chlorine in the thickness direction as described above, the TiB2 layer of the present invention shows an excellent effect of significantly improving wear resistance and impact resistance. This is because setting an amount of Cl to be relatively small in the second region results in higher hardness and strength as well as improved wear resistance. On the other hand, setting an amount of Cl to be relatively large in the first region results in lower hardness and improved followability. Namely, it is estimated that due to lower hardness in the first region, the buffering effect is achieved, and thus, even if a crack occurs in the second region, the crack is mitigated in this first region, which results in improvement in impact resistance, and in combination with the wear resistance improving effect of the second region itself, the wear resistance and the impact resistance are significantly improved.
In contrast, when the amount of Cl is small throughout the TiB2 layer, the hardness becomes high and thus the wear resistance is excellent, while the impact resistance is reduced. On the other hand, when the amount of Cl is large throughout the TiB2 layer, the adhesion and the wear resistance are both reduced.
A reason why the thickness of each of the first region and the second region is defined as 0.5 μm is that when the thickness is less than 0.5 μm, the atomic ratio Cl(Ti+Cl) cannot be sufficiently specified in some cases, from the perspective of analytical accuracy. Therefore, from the perspective of analytical accuracy and from the perspective that the first region represents a region which most reflects the characteristics in the vicinity of the interface on the base material side and the second region represents a region which most reflects the characteristics in the vicinity of the interface on the coating film surface side, the thickness of each region is defined as 0.5 μm. When specifying the atomic ratio Cl/(Ti+Cl) in the first region and the second region, it is preferable to prevent a measurement error by obtaining an average value of numerical values (ratios) at different three or more points for each region.
As described above, the TiB2 layer of the present invention is mainly composed of TiB2 (titanium diboride) and also includes Cl, and by actively controlling the concentration of Cl which has been conventionally known as being present as a residue of the raw materials at the time of manufacturing, the aforementioned excellent effect has been successfully obtained. The manner of presence of such Cl included in the TiB2 layer is not particularly limited. Cl and TiB2 may be made into a solid solution, or may be present as a free atom or ion. Furthermore, even if the TiB2 layer of the present invention contains inevitable impurities other than TiB2 and Cl, the TiB2 layer does not deviate the scope of the present invention.
In this case, it is preferable that the atomic ratio Cl/(Ti+Cl) is 0.0001 to 0.01 in the first region, and is 0.00001 to 0.001 in the second region. More preferably, the atomic ratio Cl/(Ti+Cl) is 0.0001 to 0.005 in the first region, and is 0.00001 to 0.0008 in the second region.
The atomic ratio Cl/(Ti+Cl) is set to be 0.0001 to 0.01 in the first region, and thereby, thermal impacts and vibrations occurring during formation of the coating film or during cutting process are mitigated, which allows improvement in impact resistance.
On the other hand, the atomic ratio Cl/(Ti+Cl) is set to be 0.00001 to 0.001 in the second region, and thereby, the hardness is improved, which allows improvement in wear resistance.
Furthermore, it is suitable that the TiB2 layer of the present invention has a thickness of 1 μm to 10 μm, and more preferably, 1.5 μm to 8 μm. When the thickness is less than 1 μm, the TiB2 layer may not be able to sufficiently exert wear resistance in the continuous process. When the thickness exceeds 10 μm, impact resistance may not be stabilized in intermittent cutting.
When the thickness of the TiB2 layer exceeds 1 μm, an intermediate region is present between the aforementioned first and second regions. However, a composition (i.e., the atomic ratio Cl/(Ti+Cl)) of this intermediate region is not particularly limited. Such a composition of the intermediate region may be the same as the composition of the aforementioned first region, or may be the same as the composition of the aforementioned second region. Alternatively, the intermediate region may have an intermediate composition between those of the aforementioned first and second regions. Furthermore, the composition of the intermediate region may be higher than the atomic ratio Cl/(Ti+Cl) in the aforementioned first region, or may be lower than the atomic ratio Cl/(Ti+Cl) in the aforementioned second region. Such a composition of the intermediate region may vary in the thickness direction.
In the aforementioned TiB2 layer of the present invention, impacts are mitigated that occur when various types of workpieces including a difficult-to-cut material such as a Ti alloy are cut, and the wear resistance is improved. Therefore, the wear resistance and the impact resistance are highly improved, and thus, the breakage resistance and the lifetime of the tool itself are improved.
<Other Layers>
The coating film of the present invention can include other layers as well as the TiB2 layer described above. Examples of such other layers may include, but are not limited to, an underlying layer made of TiN, TiC, TiBN and the like and formed directly above the base material for further enhancing adhesion between the base material and the coating film, a TiCN layer formed between such an underlying layer and the TiB2 layer for enhancing adhesion therebetween, an Al2O3 layer formed on the TiB2 layer for enhancing oxidation resistance, an intermediate layer made of TiCNO, TiBNO and the like and formed between the Al2O3 layer and the TiB2 layer for enhancing adhesion therebetween, an outermost layer made of TiN, TiCN, TiC and the like and formed on the outermost surface of the coating film for indicating as to whether the cutting edge has been used or not, and the like.
The above-described other layers can generally be formed to have a thickness of 0.1 μm to 10 μm.
<Manufacturing Method>
The present invention also relates to a method of manufacturing a surface-coated cutting tool including a base material and a coating film that is formed on the base material and includes at least one TiB2 layer. The manufacturing method includes the step of forming the TiB2 layer. This step is a step of forming the TiB2 layer with a chemical vapor deposition method by using a raw material gas including at least TiCl4 (titanium tetrachloride) and BCl3 (boron trichloride), and is characterized in that a molar ratio TiCl4/BCl3 between the TiCl4 and the BCl3 in the raw material gas is equal to or higher than 0.6 at the start of the step, and is lower than 0.6 at the end. In other words, the TiB2 layer of the present invention described above can be formed by this manufacturing method.
In this way, according to the manufacturing method of the present invention, in the step of forming the TiB2 layer, the molar ratio TiCl4/BCl3 between TiCl4 and BCl3 in the raw material gas is different between at the start of the step and at the end of the step, thereby allowing formation of the structure of the characteristic TiB2 layer as described above. The detailed mechanism is not yet solved as to why the TiB2 layer is configured to have a characteristic structure as described above by employing the above-described conditions. It is, however, conceivable that this is because when the crystals of the TiB2 layer grow, the breakup state, the evaporation state and the desorption state of Cl of TiCl4 and BCl3 in the raw material gas change depending on the molar ratio between TiCl4 and BCl3, and as a result, a content ratio of Cl in the TiB2 layer changes.
In this regard, as long as the molar ratio TiCl4/BCl3, is equal to or higher than 0.6 at the start of the step and is lower than 0.6 at the end, the TiB2 layer having the configuration of the present invention can be obtained. However, the molar ratio may gradually change from the start to the end, or may be switched at any point in the step.
Furthermore, it is preferable that the molar ratio TiCl4/BCl3 shows a maximum numerical value at the start and shows a minimum numerical value at the end. However, the molar ratio TiCl4/BCl3 may show the minimum value and the maximum value at any point of the step.
Furthermore, when the TiB2 layer of the present invention has the intermediate region between the first region and the second region as described above, the composition (i.e., the atomic ratio Cl/(Ti+Cl)) of this intermediate region shows a tendency to change depending on the aforementioned change in molar ratio TiCl4/BCl3 of the raw material gas.
When more specifically explaining the above-described manufacturing method, the raw material gas (which is also referred to as reaction gas) to be used in the step of forming the TiB2 layer can be TiCl4, BCl3, H2, and Ar. The molar ratio TiCl4/BCl3 between TiCl4 and BCl3 at the start of the step needs to be equal to or higher than 0.6, and further, is preferably equal to or higher than 1.0. This is because when the molar ratio is lower than 0.6, the atomic ratio Cl/(Ti+Cl) in the first region becomes lower and it becomes difficult to make the atomic ratio in the first region higher than the atomic ratio in the second region. It is preferable that the molar ratio TiCl4/BCl3 at the start of the step is equal to or lower than 10. This is because when the molar ratio exceeds 10, the atomic ratio Cl/(Ti+Cl) in the first region exceeds 0.01 and a tendency not to obtain the intended strength is shown. Furthermore, the reaction efficiency is extremely reduced and a large amount of unreacted substances are deposited, and the reaction operation itself may not be able to continue.
On the other hand, the molar ratio TiCl4/BCl3 at the end of the step needs to be lower than 0.6, and further, is preferably lower than 0.5. This is because when the molar ratio is equal to or higher than 0.6, the atomic ratio Cl/(Ti+Cl) in the second region becomes higher than 0.001 and the impact resistance becomes insufficient. It is preferable that the molar ratio TiCl4/BCl3 at the end of the step is equal to or higher than 0.1. This is because when the molar ratio is lower than 0.1, the deposition rate of TiB2 is significantly reduced and it may become difficult to generate the intended TiB2 film.
As described above, the molar ratio TiCl4/BCl3 of the raw material gas is set to be lower at the end of the step of forming the TiB2 layer than at the start, thereby allowing formation of the TiB2 layer having the aforementioned structure.
It is preferable that H2 in the aforementioned raw material gas is set at about 70 mol % to 99 mol %, and Ar is set at about 0 mol % to 20 mol % (i.e., Ar may not be included in some cases). As described above, H2 and Ar occupy a major part of the raw material gas in terms of volume ratio.
Furthermore, the reaction temperature in this step is set at 800° C. to 950° C., and more preferably, at 850° C. to 900° C. When the reaction temperature is less than 800° C., it becomes difficult to form the TiB2 layer having the characteristics of the present invention. When the reaction temperature exceeds 950° C., TiB2 is coarsely granulated or a strong η layer (WCoB layer) and a boron-containing brittle layer (CoB layer) may be generated if the base material is made of cemented carbide. In this regard, the manufacturing method of the present invention provides an excellent effect that generation of a strong η layer and a boron-containing brittle layer can be prevented.
With regard to the TiB2 layer according to the present invention, as long as the above-described conditions are employed, other conditions such as a pressure can be employed without particularly limiting the conventionally known conditions. In addition, when the coating film of the present invention includes layers other than the TiB2 layer, these layers can be formed by the conventionally known chemical vapor deposition method and physical vapor deposition method. Although the formation method thereof is not particularly limited, it is preferable to form these layers by the chemical vapor deposition method in terms of the fact that these layers can be formed consecutive with the TiB2 layer within one chemical vapor deposition apparatus.
Examples
Although the present invention will be hereinafter described in greater detail with reference to Examples, the present invention is not limited thereto.
<Preparation of Base Material>
Base materials A and B shown in the following Table 1 were prepared. Specifically, the raw material powder having a blending composition shown in Table 1 was uniformly mixed, and pressurized and molded in a predetermined shape, which was then sintered at 1300° C. to 1500° C. for 1 to 2 hours, thereby achieving a base material made of cemented carbide formed in two types of shapes including CNMG120408NUX and SEET13T3AGSN-G. In other words, two types of different shapes were prepared for each base material.
The above-described two types of shapes each are manufactured by Sumitomo Electric Hardmetal Corp. CNMG120408NUX has a shape of a cutting edge replaceable-type cutting tip for turning while SEET13T3 AGSN-G has a shape of a cutting edge replaceable-type cutting tip for rotary cutting (milling).









TABLE 1









Blending Composition (% by Mass)













Co
Ni
Cr3C2
TaC
WC


















A
5.0
0.3
0.5
—
Remainder



B
9.0
—
—
3.0
Remainder










<Formation of Coating Film>
The coating film was formed on the surface of the base material prepared as described above. Specifically, the base material was placed within the chemical vapor deposition apparatus to thereby form the coating film on the base material by the chemical vapor deposition method. The formation conditions of the coating film are as described in the following Tables 2 and 3, and the film formation time was adjusted to achieve each thickness described in Table 4. Table 2 shows the formation conditions of each layer other than the TiB2 layer, and Table 3 shows the formation conditions of the TiB2 layer. In addition, TiBNO and TiCNO in Table 2 each are an intermediate layer in Table 4 described later, and other compounds also correspond to layers, respectively, in Table 4 other than the TiB2 layer (the formation conditions of the TiCN layer and the formation conditions of TiCN as the outermost layer are the same).
Also as shown in Table 3, there are 7 types of formation conditions “a” to “e” and “x” to “y” for the TiB2 layer, in which conditions “a” to “e” are the conditions in accordance with the method of the present invention while conditions “x” to “y” are the conditions in accordance with Comparative Examples (the conventional technique). Furthermore, the raw material gas composition described in the section of “At the Start” was used in the first half of the entire film formation time for forming the TiB2 layer, and the raw material gas composition described in the section of “At the End” was used in the latter half.
For example, the formation condition “a” shows that the raw material gas (reaction gas) having a composition including 2.5 mol % of TiCl4, 3.7 mol % of BCl3 and 93.8 mol % of H2 was used in the first half and the raw material gas (reaction gas) having a composition including 2.0 mol % of TiCl4, 3.7 mol % of BCl3 and 94.3 mol % of H2 was used in the latter half, to form the TiB2 layer by the chemical vapor deposition method under the conditions of a pressure of 80.0 kPa and a temperature of 850° C. The molar ratio TiCl4/BCl3 in each raw material gas composition is as shown in Table 3. The composition at the start of the step of forming the TiB2 layer is the composition described in “At the Start” in Table 3, and the composition at the end is the composition described in “At the End” in Table 3.
In addition, each layer other than the TiB2 layer shown in Table 2 was also similarly formed except that the raw material gas composition was not changed during film formation. It is to be noted that the “remainder” in Table 2 shows that H2 occupies the remainder of the raw material gas (reaction gas). Furthermore, “total gas amount” indicates the total volume flow rate at which gas is introduced into a CVD oven per unit time, assuming that the gas in the standard condition (0° C., 1 atmosphere) is ideal gas.
Furthermore, the composition (including the atomic ratio Cl/(Cl+Ti) in the TiB2 layer) of each coating film was checked by SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy). As the atomic ratio Cl/(Cl+Ti) in each of the first region and the second region, an average value of values obtained by measuring the atomic ratio at three points for each region was used. The results thereof are shown in Table 3.
<Peel Occurrence Time of TiB2 Layer>
The peel occurrence time of the TiB2 layer was measured as follows.
First, round-honed CNMA12008 (manufactured by Sumitomo Electric Hardmetal Corp.) was used as the base material and the surface thereof was polished (Ra≦0.5 μm), and thereafter, the TiB2 layer having a thickness of 5 μm was directly formed on the base material under the conditions described in Table 3. Then, a 20% aqueous dispersion including spherical alumina having an average particle size of 100 μm was injected onto the aforementioned TiB2 layer at compressed air of 0.3 MPa (a distance between the base material (cutting-edge ridgeline) and an injection port was set at 30 mm), and a breaking state of the TiB2 layer (in the cutting-edge ridgeline portion) was observed by using a microscope.
Then, the time (second) until the TiB2 layer was peeled off or broken was measured. The longer the time is, the more excellent the adhesion to the base material and the impact resistance are. The results thereof are shown in Table 3.









TABLE 2









Film Formation Conditions












Raw Material Gas Composition
Pressure
Temperature
Total Gas Amount



(% by Volume)
(kPa)
(° C.)
(L/min)















TiN
TiCl4 = 1.8%, N2 = 30.5%, H2 = Remainder
7.8
900
50


(Underlying


Layer)


TiN
TiCl4 = 1.0%, N2 = 50.5%, H2 = Remainder
80.2
1000
78


(Outermost


Layer)


TiCN
TiCl4 = 2.3%, CH3CN = 1.0%, H2 = Remainder
11.0
850
55


TiBNO
TiCl4 = 30.7%, BCl3 = 0.3%, CO = 1.2%, CO2 = 1.2%,
6.5
960
80



N2 = 50.7%, H2 = Remainder


TiCNO
TiCl4 = 2.7%, CO = 3.0%, CH4 = 2.0%, N2 = 30.7%,
15.8
1020
70



H2 = Remainder


Al2O3
AlCl3 = 2.6%, CO2 = 3.75%, H2S = 0.1%, HCl = 2.0%,
10.0
1030
65



H2 = Remainder



















TABLE 3









Film Formation













At the Start
At the End
Conditions
Properties















Molar

Molar

Tem-
Atomic Ratio
Peel



Ratio

Ratio
Pres-
pera-
Cl/(Ti + Cl)
Occurance

















Raw Material Gas
(TiCl4/
Raw Material Gas
(TiCl4/
sure
ture
First
Second
Time



Compostition (mol %)
BCl3)
Composition (mol %)
BCl3)
(kPa)
(° C.)
Region
Region
(second)





















The
a
TiCl4 = 2.5%, BCl3 = 3.7%,
0.68
TiCl4 = 2.0%, BCl3 = 3.7%,
0.54
80.0
850
0.0013
0.0008
100


Present

H2 = 93.8%

H2 = 94.3%


Inven-
b
TiCl4 = 1.0%, BCl3 = 0.4%,
2.50
TiCl4 = 1.0%, BCl3 = 3.7%,
0.27
97.0
900
0.0016
0.0006
115


tion

H2 = 98.6%

H2 = 95.3%



c
TiCl4 = 5.1%, BCl3 = 1.0%,
3.10
TiCl4 = 1.0%, BCl3 = 5.1%,
0.20
90.0
830
0.0020
0.0005
95




Ar = 17%, H2 = 76.9%

Ar = 17%, H2 = 77.9%



d
TiCl4 = 2.9%, BCl3 = 0.7%,
4.14
TiCl4 = 0.4%, BCl3 = 4.0%,
0.10
85.0
880
0.0018
0.0003
120




Ar = 17%, H2 = 79.4%

Ar = 17%, H2 = 78.6%



e
TiCl4 = 1.9%, BCl3 = 0.2%,
9.50
TiCl4 = 3.0%, BCl3 = 5.1%,
0.59
87.0
800
0.0025
0.0008
100




Ar = 46.3%, H2 = 51.6%

Ar = 46.3%, H2 = 45.6%


Compar-
x
TiCl4 = 0.4%, BCl3 = 0.7%,
0.57
TiCl4 = 0.4%, BCl3 = 0.7%,
0.57
101.3
800
0.0007
0.0007
30


ative

Ar = 88.9%, H2 = 10%

Ar = 88.9%, H2 = 10%


Example
y
TiCl4 = 0.22%, BCl3 = 0.04%,
5.50
TiCl4 = 0.22%, BCl3 = 0.04%,
5.50
101.3
1000
0.0004
0.0004
35




H2 = 99.74%

H2 = 99.74%









<Production of Surface-Coated Cutting Tool>
A coating film was formed on a base material by the conditions in Tables 2 and 3 shown above, thereby producing surface-coated cutting tools (two types (the shape of the base material is different) of cutting edge replaceable-type cutting tips for each coating film) of Examples 1 to 20 and Comparative Examples 1 to 7 shown in the following Table 4.
For example, the table shows that the surface-coated cutting tool of Example 4 has a configuration, in which base material A shown in Table 1 was employed as a base material, to form a TiN layer having a thickness of 0.5 μm as an underlying layer on the surface of base material A under the conditions shown in Table 2, on which a TiCN layer having a thickness of 2.0 μm was formed under the conditions shown in Table 2, on which a TiB2 layer having a thickness of 2.5 μm was formed under the formation condition “c” in Table 3, on which a TiBNO layer having a thickness of 0.5 μm as an intermediate layer, an Al2O3 layer having a thickness of 1.5 μm and a TiN layer having a thickness of 0.8 μm as an outermost layer were formed in this order under the conditions shown in Table 2, to thereby form a coating film having a total thickness of 7.8 μm on the base material.
In addition, since all of the TiB2 layers of Comparative Examples 1 to 7 are formed under the conditions of the conventional technique that is not based on the method of the present invention, these TiB2 layers do not show the configuration similar to that of the present invention (i.e., the atomic ratio Cl/(Ti+Cl) does not change and is fixed in the thickness direction. See Table 3).
It is to be noted that each of blank columns in Table 4 shows that the relevant layer is not formed.










TABLE 4









Configuration of Coating Film


















Underlying









Type of
Layer
TiCN
TiB2
Intermediate
Al2O3
Outermost
Total Thickness



Base
(TiN layer)
Layer
Layer
Layer
Layer
Layer
of Coating Film



Material
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)



















Example 1
A
1.5
—
a(4.5)
—
—
—
6.0


Example 2
A
0.8
—
e(5.0)
—
—
—
5.8


Example 3
A
1.0
3.2
b(3.0)
—
—
TiCN(0.5)
7.7


Example 4
A
0 5
2.0
c(2.5)
TiBNO(0.5)
1.5
TiN (0.8)
7.8


Example 5
B
0.5
1.7
a(3.0)
TiBNO(0.5)
1.0
—
6.7


Example 6
A
1.0
3.6
d(2.2)
TiBNO(0.3)
1.5
—
8.6


Example 7
A
0.6
2.4
d(6.0)
TiBNO(0.5)
2.2
—
11.7


Example 8
B
1.5
2.0
b(2.7)
TiBNO(0.5)
1.0
—
7.7


Example 9
B
1.0
1.8
e(4.5)
TiBNO(0.5)
0.5
—
8.3


Example 10
A
1.1
3.6
a(3.7)
TiBNO(0.3)
2.0
—
10.7


Example 11
B
1.0
—
e(5.5)
TiCNO(0.4)
1.2
—
8.1


Example 12
B
1.0
3.4
b(2.4)
TiBNO(0.8)
1.0
—
8.6


Example 13
A
0.8
—
a(6.2)
TiBNO(0.4)
0.8
—
8.2


Example 14
B
1.0
1.2
c(3.2)
TiBNO(0.5)
1.0
—
6.9


Example 15
B
1.1
—
c(3.0)
TiBNO(0.5)
1.6
—
6.2


Example 16
A
1.5
—
e(4.0)
TiBNO(0.4)
2.0
—
7.9


Example 17
A
0.9
2.3
e(3.0)
TiBNO(0.5)
2.0
—
8.7


Example 18
B
1.5
—
a(4.2)
—
—
—
5.7


Example 19
B
1.0
1.5
d(1.9)
TiBNO(0.5)
2.3
TiN(1.0)
8.2


Example 20
B
1.7
—
e(5.3)
—
—
—
7.0


Comparative
A
1.5
—
x(5.0)
—
—
—
6.5


Example 1


Comparative
A
1.5
2.3
y(3.0)
TiBNO(0.5)
2.5
TiN(1.0)
10.8


Example 2


Comparative
A
1.3
—
x(6.0)
TiBNO(0.4)
1.5
TiCN(1.0)
9.9


Example 3


Comparative
B
1.9
2.7
y(2.0)
TiCNO(0.7)
2.2
—
9.5


Example 4


Comparative
B
0.8
2.0
y(3.8)
TiBNO(0.5)
1.5
—
8.6


Example 5


Comparative
B
1.4
2.5
x(2.8)
TiBNO(0.4)
1.8
—
8.9


Example 6


Comparative
B
1.5
—
x(6.0)
TiCNO(0.6)
1.3
—
9.4


Example 7









<Cutting Test>
The surface-coated cutting tools obtained as described above were used to perform four types of cutting tests as described below.
<Cutting Test 1>
With regard to each of the surface-coated cutting tools (those having a shape of CNMG120408NUX were used) of Examples and Comparative Examples shown in the following Table 5, the cutting time until the wear amount of the flank face (Vb) reached 0.25 mm under the following cutting conditions was measured, and the final damage state of the cutting edge was observed. The results thereof are shown in Table 5. The results show that the longer the cutting time is, the more excellent the wear resistance is. Furthermore, the results also show that the more the final damage state is close to the state of normal wear, the more excellent the impact resistance is.
<Cutting Conditions>
Workpiece: cutting outer periphery of Ti6Al4V round bar
Circumferential speed: 70 m/min
Feeding speed: 0.15 mm/rev
Cutting amount: 1.5 mm
Cutting fluid: existing










TABLE 5







Cutting Time




(Minute)
Final Damage State




















Example 1
20.0
Normal Wear



Example 2
17.0
Normal Wear



Example 3
21.0
Normal Wear



Example 7
25.0
Normal Wear



Example 16
20.0
Normal Wear



Comparative
8.0
Normal Wear



Example 1



Comparative
5.0
Chipping



Example 3










As can be seen from Table 5, it is apparent that the surface-coated cutting tools of Examples of the present invention are excellent both in wear resistance and impact resistance as compared to the surface-coated cutting tools of Comparative Examples.
Furthermore, in the final damage state in Table 5, “normal wear” means a damage state caused only by wearing without occurrence of chipping, breakage and the like (having a smooth wearing surface), and “chipping” means an extremely small chipped portion occurring in the cutting edge portion.
<Cutting Test 2>
With regard to each of the surface-coated cutting tools (those having a shape of CNMG120408NUX were used) of Examples and Comparative Examples shown in the following Table 6, the cutting time until the wear amount of the flank face (Vb) reached 0.25 mm under the following cutting conditions was measured, and the final damage state of the cutting edge was observed. The results thereof are shown in Table 6. The results show that the longer the cutting time is, the more excellent the wear resistance is. The results also show that the more the final damage state is close to the state of normal wear, the more excellent the impact resistance is.
<Cutting Conditions>
Workpiece: cutting outer periphery of INCONEL 718 round bar
Circumferential speed: 50 m/min
Feeding speed: 0.15 mm/rev
Cutting amount: 1.5 mm
Cutting fluid: existing










TABLE 6







Cutting Time




(Minute)
Final Damage State




















Example 4
35.0
Normal Wear



Example 6
29.0
Normal Wear



Example 10
24.0
Micro-Breakage of





Front Boundary



Example 13
28.0
Normal Wear



Example 17
26.0
Normal Wear



Comparative
17.0
Micro-Breakage of



Example 2

Front Boundary










As can be seen from Table 6, it is apparent that the surface-coated cutting tools of Examples of the present invention are excellent both in wear resistance and impact resistance as compared to the surface-coated cutting tools of Comparative Examples.
In the final damage state in Table 6, “normal wear” means a damage state caused only by wearing without occurrence of chipping, breakage and the like (having a smooth wearing surface), and “micro-breakage of front boundary” means an extremely small chipped portion occurring in the cutting edge portion forming a finished surface in which the base material is recognized as being exposed.
<Cutting Test 3>
With regard to each of the surface-coated cutting tools (those having a shape of SEET13T3AGSN-G were used) of Examples and Comparative Examples shown in the following Table 7, the pass frequency and the cutting distance until the breakage occurred or the wear amount of the flank face (Vb) reached 0.25 mm under the following cutting conditions were measured, and the final damage state of the cutting edge was observed. The results thereof are shown in Table 7.
In addition, the pass frequency is the repeated number of times of the operation repeatedly performed, in which one side surface (a surface of 300 mm×80 mm) of the workpiece described below (shape: a block of 300 mm), 100 mm×80 mm) is rotary cut from its one end to the other end by a cutter attached with one surface-coated cutting tool (cutting edge replaceable-type cutting tip) (it is to be noted that the pass frequency having a number with a decimal point indicates that the above-mentioned conditions are satisfied in the middle of the course from one end to the other end). In addition, the cutting distance means the total distance of the workpiece that has been cut until the above-described conditions were satisfied, and corresponds to the product of the pass frequency and the length of the side surface mentioned above (300 mm).
The results show that the greater the pass frequency is (that is, the longer the cutting distance is), the more excellent the wear resistance is. Furthermore, the results also show that the more the final damage state is close to the state of normal wear, the more excellent the impact resistance is.
<Cutting Conditions>
Workpiece: Ti6Al4V block material
Circumferential speed: 80 m/min
Feeding speed: 0.25 mm/s
Cutting amount: 1.0 mm
Cutting fluid: existing
Cutter: WGC4160R (manufactured by Sumitomo Electric Hardmetal Corp.)
Number of attached tips: 1











TABLE 7








Cutting Distance




Pass Frequency
(m)
Final Damage State



















Example 5
23.0
6.9
Normal Wear


Example 12
19.5
5.9
Normal Wear


Example 14
25.0
7.5
Normal Wear


Example 15
21.0
6.3
Normal Wear


Example 20
20.0
6.0
Normal Wear


Comparative
15.0
4.5
Normal Wear


Example 4


Comparative
6.0
1.8
Breakage


Example 6









As can be seen from Table 7, it is apparent that the surface-coated cutting tools of Examples of the present invention are excellent both in wear resistance and impact resistance as compared to the surface-coated cutting tools of Comparative Examples.
In addition, in the final damage state in Table 7, “normal wear” means a damage state caused only by wearing without occurrence of chipping, breakage and the like (having a smooth wearing surface), and “breakage” means a large chipped portion occurring in the cutting edge portion.
<Cutting Test 4>
With regard to each of the surface-coated cutting tools (those having a shape of SEET13T3AGSN-G were used) of Examples and Comparative Examples shown in the following Table 8, the pass frequency and the cutting distance until the breakage occurred or the wear amount of the flank face (Vb) reached 0.25 mm under the following cutting conditions were measured, and the final damage state of the cutting edge was observed. The results thereof are shown in Table 8.
In addition, as in Cutting Test 3, the pass frequency is the repeated number of times of the operation repeatedly performed, in which one side surface (a surface of 300 mm×80 mm) of the workpiece described below (shape: a block of 300 mm×100 mm×80 mm) is rotary cut from its one end to the other end by a cutter attached with one surface-coated cutting tool (cutting edge replaceable-type cutting tip) (it is to be noted that the pass frequency having a number with a decimal point indicates that the above-mentioned conditions are satisfied in the middle of the course from one end to the other end). As in Cutting Test 3, the cutting distance also means the total distance of the workpiece that has been cut until the above-described conditions were satisfied, and corresponds to the product of the pass frequency and the length of the side surface mentioned above (300 mm).
The results show that the greater the pass frequency is (that is, the longer the cutting distance is), the more excellent the wear resistance is. Furthermore, the results also show that the more the final damage state is close to the state of normal wear, the more excellent the impact resistance is.
<Cutting Conditions>
Workpiece: SUS304 block material
Circumferential speed: 150 m/min
Feeding speed: 0.2 mm/s
Cutting amount: 1.0 mm
Cutting fluid: existing
Cutter: WGC4160R (manufactured by Sumitomo Electric Hardmetal Corp.)
Number of attached tips: 1











TABLE 8








Cutting Distance




Pass Frequency
(m)
Final Damage State



















Example 8
21.7
6.5
Normal Wear


Example 9
19.5
5.9
Normal Wear


Example 11
18.0
5.4
Normal Wear


Example 18
20.0
6.0
Normal Wear


Example 19
17.8
5.3
Normal Wear


Comparative
15.0
4.5
Normal Wear


Example 5


Comparative
7.0
2.1
Breakage


Example 7









As can be seen from Table 8, it is apparent that the surface-coated cutting tools of Examples of the present invention are excellent both in wear resistance and impact resistance as compared to the surface-coated cutting tools of Comparative Examples.
In addition, in the final damage state in Table 8, “normal wear” means a damage state caused only by wearing without occurrence of chipping, breakage and the like (having a smooth wearing surface), and “breakage” means a large chipped portion occurring in the cutting edge portion.
Although the embodiments and examples of the present invention have been explained as described above, it is also intended from the beginning to combine the configurations of the above-described embodiments and examples as appropriate.
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.

## Claims

1. A surface-coated cutting tool comprising:
a base material; and
a coating film formed on said base material,
said coating film including at least one TiB2 layer,
said TiB2 layer including Cl together with TiB2, and
assuming that in said TiB2 layer, a first region represents a region having a thickness of 0.5 μm from an interface on said base material side, and a second region represents a region having a thickness of 0.5 μm from an interface on said coating film surface side, an atomic ratio Cl/(Ti+Cl) between Ti and Cl being higher in said first region than in said second region.

2. The surface-coated cutting tool according to claim 1, wherein
said atomic ratio Cl/(Ti+Cl) is 0.0001 to 0.01 in said first region, and is 0.00001 to 0.001 in said second region.

3. The surface-coated cutting tool according to claim 1, wherein
said TiB2 layer has a thickness of 1 to 10 μm.

4. A method of manufacturing a surface-coated cutting tool including a base material and a coating film formed on said base material, said coating film including at least one TiB2 layer, said method comprising the step of:
forming said TiB2 layer,
said step being a step of forming said TiB2 layer with a chemical vapor deposition method by using a raw material gas including at least TiCl4 and BCl3, and
a molar ratio TiCl4/BCl3 between said TiCl4 and said BCl3 in said raw material gas being equal to or higher than 0.6 at the start of said step, and being lower than 0.6 at the end.