JP7016866B2 - Surface-coated cubic boron nitride sintered body and cutting tool equipped with this - Google Patents

Description

The present invention relates to a surface-coated cubic boron nitride sintered body and a cutting tool comprising the same. This application claims priority based on Japanese Patent Application No. 2017-105583 filed on May 29, 2017. All the contents of the Japanese patent application are incorporated herein by reference.

Conventionally, a cutting tool using a cubic boron nitride (hereinafter, also referred to as "cBN") sintered body is known. For example, Japanese Patent Application Laid-Open No. 2015-209354 (Patent Document 1) applies a bias voltage to a cBN sintered body, etches the surface of the cBN sintered body with Ar ions, and then coats the surface. A technique for manufacturing a cutting tool by forming a cutting tool is disclosed.

JP 2015-209354A

The surface-coated cubic boron nitride sintered body according to one aspect of the present disclosure includes a base material which is a cubic boron nitride sintered body and a coating film which is in contact with the base material and covers the base material. At the interface between the cubic boron nitride in the substrate and the coating film, the Fe content is 1 at% or less, the W content is 1 at% or less, and the O content is 2 at% or less.

FIG. 1 is a partial cross-sectional view showing an example of the configuration of a cutting tool according to the present embodiment. FIG. 2 shows the sample No. It is a 2 million times TEM image (bright-field image) showing the interface between the cubic boron nitride and the coating film in 2. FIG. 3 shows the sample No. It is a 2 million times TEM image (HAADF image (high-angle annular dark field image)) showing the interface between the cubic boron nitride and the film in 2.

[Issues to be resolved by this disclosure]
By the way, in recent years, there has been an increasing demand for higher cutting speeds and improved cutting performance for difficult-to-cut materials. However, with a conventional cutting tool, the coating film tends to peel off when the cutting speed is increased or when cutting a difficult-to-cut material, and the above requirements cannot be sufficiently satisfied.

In view of the above points, the present disclosure provides a surface-coated cubic boron nitride sintered body having excellent peeling resistance of a coating film and a cutting tool provided with the same.

[Effect of this disclosure]
According to the above, it is possible to provide a surface-coated cubic boron nitride sintered body and a cutting tool having excellent peeling resistance of the coating film.

[Explanation of Embodiments of the present invention]
First, embodiments of the present disclosure will be listed and described. In this specification, the notation in the form of "M to N" means the upper and lower limits of the range (that is, M or more and N or less), and there is no description of the unit in M and the unit is described only in N. , The unit of M and the unit of N are the same.

[1] The surface-coated cubic boron nitride sintered body according to the present disclosure includes a base material which is a cubic boron nitride sintered body and a coating film which is in contact with the base material and covers the base material. At the interface between the cubic boron nitride in the substrate and the coating film, the Fe content is 1 at% or less, the W content is 1 at% or less, and the O content is 2 at% or less.

The cubic boron nitride sintered body, which is a base material, is composed of cubic boron nitride and a binder. The adhesion between the substrate and the coating is affected by the difference in lattice constant between the crystals of cubic boron nitride and the crystals of the coating in the substrate. In general, the lattice constant of the crystal of the coating is larger than the lattice constant of the crystal of cubic boron nitride. Here, when at least one of Fe and W is present at the interface, it penetrates into the crystal of the coating film and increases the lattice constant of the crystal. As a result, the difference in lattice constant between the cubic boron nitride crystal and the film crystal becomes larger, and the adhesion between the substrate and the film decreases. However, according to the above configuration, it is possible to suppress a decrease in adhesion due to a difference in lattice constant between the crystal of cubic boron nitride and the crystal of the coating film.

Fe is often contained in a jig used when forming a film, and easily adheres to the surface of the base material. Further, the base material is often used by being brazed to a cemented carbide obtained by sintering WC powder. Therefore, when a film is formed on the surface of the base material after being brazed to the cemented carbide, W contained in the cemented carbide tends to adhere to the surface of the base material. When Fe or W is present at the interface between the base material and the coating film, Fe or W penetrates into the crystal of the coating film, so that the lattice constant of the crystal becomes large and the adhesion between the base material and the coating film tends to decrease. However, according to the above configuration, it is possible to suppress a decrease in adhesion due to a difference in lattice constant between the crystals of cubic boron nitride in the substrate and the crystals of the coating.

Further, if an oxide is present at the interface between the cubic boron nitride and the coating film, the adhesion between the cubic boron nitride and the coating film tends to decrease. However, according to the above configuration, it is possible to suppress the deterioration of the adhesion between the cubic boron nitride and the coating film due to the oxide.

As a result, it is possible to realize a surface-coated cubic boron nitride sintered body in which the adhesion between the cubic boron nitride and the coating film is improved and the peeling resistance of the coating film is improved.

[2] The thickness of the layer in which the total content of the Fe content and the W content is 0.05 at% or more is 5 nm or less. As a result, it is possible to suppress a decrease in adhesion caused by at least one of Fe and W, and the adhesion between the base material and the coating film is further improved.

[3] In the surface-coated cubic boron nitride sintered body, the coating is a polycrystal. The region within 10 nm from the interface in the film is composed of crystal grains having an average particle size of 10 nm or less. As a result, the grain boundaries in the region near the interface in the coating film are increased, the stress generated at the interface can be relaxed, and the peeling resistance of the coating film is further improved. Further, by increasing the grain boundaries, the action of preventing plastic deformation and crack growth at the grain boundaries is enhanced. Further, even when an impact is applied, the coating film is less likely to peel off, and the impact resistance of the surface-coated cubic boron nitride sintered body is improved.

[4] The Ar content at the interface is 1 at% or less. Generally, the surface of the base material is irradiated with Ar ions to perform a cleaning process. At this time, Ar may adhere to the surface of the base material and remain at the interface between the base material and the coating film. When a large amount of Ar is present at the interface, the crystallinity of the coating film deteriorates and the stress at the interface increases, so that the adhesion between the base material and the coating film decreases. However, according to the above configuration, since the Ar content at the interface is 1 at% or less, the adhesion between the base material and the coating film is improved.

[5] In the surface-coated cubic boron nitride sintered body, the thickness of the coating film is 0.3 μm or more and 10 μm or less. As a result, the effect of improving the wear resistance of the coating can be more remarkable.

[6] In the surface-coated cubic boron nitride sintered body, the coating film is at least one element selected from the group consisting of Al, Ti, Cr and Si, and at least selected from the group consisting of C and N. Contains at least one compound consisting of one element. This improves the hardness, wear resistance, and oxidation resistance of the coating film.

[7] The cutting tool according to the present disclosure includes the surface-coated cubic boron nitride sintered body. According to the above-mentioned cutting tool, the peeling resistance of the coating film is improved. As a result, the life of the cutting tool can be extended.

[Details of Embodiments of the present invention]
Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described. However, this embodiment is not limited to these. In the drawings used in the following embodiments, the same reference numerals represent the same parts or equivalent parts. Further, when a compound or the like is represented by a chemical formula in the present specification, it is intended to include all conventionally known atomic ratios when the atomic ratio is not particularly limited, and is not necessarily limited to those in the stoichiometric range. For example, when described as "AlCrN", the ratio of the number of atoms constituting AlCrN is not limited to Al: Cr: N = 0.5: 0.5: 1, and includes all conventionally known atomic ratios.

<Cutting tools>
FIG. 1 is a partial cross-sectional view showing an example of the configuration of a cutting tool according to the present embodiment. As shown in FIG. 1, the cutting tool 100 includes a base metal 101 and a surface-coated cBN sintered body 10 fixed to a predetermined region of the base metal 101 via a brazing layer 102.

The shape and use of the cutting tool 100 are not particularly limited. For example, drills, end mills, replaceable cutting tips for drills, replaceable cutting tips for end mills, replaceable cutting tips for milling, replaceable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, cranks. Examples include shaft pin milling chips.

The shape and material of the base metal 101 are not particularly limited, and conventionally known ones can be used. For example, the base metal 101 is a cemented carbide obtained by mixing and sintering WC (tungsten carbide) and a binder (for example, Co).

The surface-coated cBN sintered body 10 includes a base material 11 and a coating film 12 that is in contact with the base material 11 and covers the base material 11. The base material 11 is fixed to the base metal 101 via the brazing layer 102. The material (brazing material) of the brazing layer may be appropriately selected in consideration of the bonding strength and the melting point, and a material having a melting point of 800 ° C. or higher (for example, a material containing Ag as a main component) is preferable.

The coating film 12 covers the surface of the base material 11 and extends to the surface of the base metal 101 to form the rake face 100a and the flank surface 100b of the cutting tool 100. It is preferable that the coating film 12 covers the entire surface of the base material 11, but even if a part of the base material 11 is not covered with the coating film 12, or the composition of the coating film 12 is partially different. It does not deviate from the scope of the present invention.

"Base material"
The base material 11 is a cBN sintered body containing cBN and a binder. The cBN sintered body may contain other components as long as it contains cBN and a binder, and may also contain unavoidable impurities due to the raw materials used, production conditions, and the like. cBN is contained in the cBN sintered body, for example, in an amount of 40 to 75% by volume.

The binder is not particularly limited as long as it exhibits an action of binding cBNs to each other, and any conventionally known binder can be used. The binder is, for example, a group 4 element (Ti, Zr or Hf, etc.), a group 5 element (V, Nb or Ta, etc.) and a group 6 element (Cr, Mo, W, etc.) in the periodic table of elements. It is preferably a compound containing at least one of these elements and at least one of C, N, B and O, a solid solution of such a compound, or an aluminum compound. The binder may contain two or more of the above compound, the solid solution of the above compound, and the aluminum compound.

《Capsule》
The coating film 12 is a polycrystal. The coating film 12 is formed directly above the base material 11 by a physical vapor deposition method, and is in contact with the base material 11 to cover the base material 11. The coating film 12 is, for example, at least one compound composed of at least one element selected from the group consisting of Al, Ti, Cr and Si and at least one element selected from the group consisting of C and N. including. Examples of the compound include TiAlN, AlCrN, TiAlSiN, TiSiN, TiCN and the like. By selecting such a compound as the coating film 12, the hardness of the coating film 12 is improved, and the wear resistance and oxidation resistance are improved. As the wear resistance of the coating film 12 is improved, the cutting resistance is less likely to increase and the wear is less likely to develop.

The thickness of the coating film 12 is preferably 0.3 to 10 μm. As a result, the effect of the coating film can be remarkably exhibited. The effects include improvements in hardness, wear resistance, oxidation resistance, reactivity resistance, and chipping resistance. If the thickness of the coating film 12 is less than 0.3 μm, these effects may not be sufficiently exhibited, and if it exceeds 10 μm, chipping is likely to occur due to the residual stress in the coating film 12. The lower limit of the thickness of the coating film 12 is more preferably 0.5 μm, still more preferably 1 μm. The upper limit of the thickness of the coating film 12 is more preferably 8 μm, further preferably 6 μm, and particularly preferably 4 μm.

A thin film having one layer or two or more layers may be formed as the second coating on the surface of the coating 12. Examples of such a thin film include a film having any material of a nitride, a carbide, a carbonitride, and an oxide of a group 4 element.

<< Interface between cubic boron nitride and coating >>
Of the interface between the substrate 11 and the coating 12, the Fe content is 1 at% or less, the W content is 1 at% or less, and the O content is 2 at% at the interface between the cubic boron nitride and the coating 12. It is as follows.

For the Fe content and W content, the microstructure and elemental analysis of the fracture surface of the surface-coated cBN sintered body 10 are performed using an energy dispersive X-ray analyzer (EDS) attached to a transmission electron microscope (TEM). It is measured by. Specifically, a line crossing the interface along the normal direction of the interface between the cubic boron nitride in the substrate 11 and the coating film 12 is specified in the TEM image, and along the line using EDS. A line scan measurement is performed to measure the change in the concentration distribution of the element. Here, the interface between the cubic boron nitride and the coating film 12 is a position where the concentration of B contained in the cubic boron nitride is 1/2 of the average value of the concentration in the base material 11.

Fe and W are metallic elements (foreign metal elements) that are not contained in the elements constituting the cubic boron nitride and the coating film 12, and when detected at the interface, they are concentrated in the vicinity of the interface. Fe is abundantly contained in the jig used when forming the film 12. W is included in the base metal 101 when the base metal 101 is made of a cemented carbide containing WC. Therefore, Fe released from the jig and W released from the base metal 101 easily adhere to the surface of the base material 11 and easily remain at the interface between the base material 11 and the coating film 12.

When Fe is concentrated near the interface, a peak occurs in the concentration distribution of Fe obtained by the line scan measurement. The peak includes points corresponding to the interface on the line. Here, the maximum concentration (at%) of the peak is defined as the Fe content at the interface. The W content at the interface is determined by the same method.

When at least one of Fe and W is present near the interface, it penetrates into the crystals of the coating 12 and increases the lattice constant of the crystals constituting the coating 12. As a result, the difference between the lattice constant of the crystals of cubic boron nitride constituting the base material 11 and the lattice constant of the crystals constituting the coating 12 becomes large, and the adhesion between the cubic boron nitride and the coating 12 is lowered. However, by defining the contents of Fe and W at the interface as described above, the deterioration of the adhesion between the cubic boron nitride and the coating film 12 caused by Fe or W is suppressed, and the peeling resistance of the coating film 12 is improved. Can be improved.

The Fe content at the interface is more preferably 0.5 at% or less, still more preferably 0.3 at% or less. The W content at the interface is more preferably 0.5 at% or less, still more preferably 0.3 at% or less. The lower limit of the contents of Fe and W at the interface is not particularly limited, and is ideally 0 at%.

The oxygen (O) content (at%) at the interface between the cubic boron nitride in the base material 11 and the coating film 12 is 2 at% or less. The O content at the interface is measured by the same method as for Fe and W. However, when O is not concentrated near the interface, no peak occurs in the O concentration distribution obtained by the line scan measurement of EDS. In this case, the average value of the O content (at%) in the section of 2 nm on the film 12 side and 2 nm on the cubic boron nitride side from the interface, for a total of 4 nm, is obtained as the O content of the interface.

Most of O at the interface between cubic boron nitride and the film 12 exists as an oxide. Such an oxide reduces the adhesion between the cubic boron nitride and the coating film 12. However, by defining the O content (at%) at the interface between the cubic boron nitride and the coating 12 as described above, the adhesion between the cubic boron nitride and the coating 12 due to the oxide at the interface is lowered. Can be suppressed and the peeling resistance of the coating film 12 can be improved.

The O content at the interface is more preferably 1 at% or less, further preferably 0.5 at% or less, and particularly preferably 0.3 at% or less. The lower limit of the O content (at%) at the interface is not particularly limited, but is preferably below the detection limit of EDS, ideally 0 at%.

The thickness of the layer in which the total content of the Fe content and the W content is 0.05 at% or more (hereinafter, also referred to as “different metal element layer”) is preferably 5 nm or less. The thickness of the dissimilar metal element layer is determined based on the analysis result using the EDS incidental to the TEM described above. Specifically, in the synthetic data of the concentration distribution of Fe and W obtained by the line scan measurement of EDS, the line length at which the total content is 0.05 at% or more is determined as the thickness of the dissimilar metal element layer. .. When the thickness of the dissimilar metal element layer is 5 nm or less, the decrease in adhesion caused by at least one of Fe and W can be suppressed, and the adhesion between the cubic boron nitride and the coating film 12 is further improved. The thickness of the dissimilar metal element layer is more preferably 3 nm or less, further preferably 2 nm or less, and particularly preferably 1 nm or less. The lower limit of the thickness of the dissimilar metal element layer is not particularly limited, and is ideally 0 nm.

The Ar content at the interface between the cubic boron nitride and the coating film 12 is preferably 1 at% or less, more preferably 0.5 at% or less, still more preferably 0.3 at% or less. Before forming the coating film 12 on the base material 11, a process of irradiating the surface of the base material 11 with Ar ions to clean the base material 11 is usually performed. Therefore, Ar ions adhere to the surface of the base material 11 and tend to remain at the interface between the cubic boron nitride and the coating film 12. Ar ions remaining at the interface also deteriorate the crystallinity of the interface in the film and increase the stress, so that the adhesion between the cubic boron nitride and the film 12 tends to decrease. Therefore, by defining the Ar content at the interface as described above, the adhesion between the cubic boron nitride and the coating film 12 can be further improved. The Ar content (at%) at the interface is determined by analysis using EDS incidental to TEM as in Fe and W. The lower limit of the Ar content at the interface is not particularly limited, and is ideally 0 at%.

The region within 10 nm from the interface in the film 12 is preferably composed of crystal grains having an average particle size of 10 nm or less. As a result, grain boundaries increase in the vicinity of the interface in the coating film 12. As a result, the stress generated by the difference in the lattice constants between the crystals of cubic boron nitride constituting the base material 11 and the crystals constituting the coating 12 is easily relaxed by the grain boundaries, and the peeling resistance of the coating 12 is further improved. can. Further, by increasing the grain boundaries, the action of preventing plastic deformation and crack growth at the grain boundaries is enhanced. Further, even when an impact is applied, the coating film is less likely to peel off, so that the impact resistance of the surface-coated cBN sintered body 10 is improved. The average particle size of the crystal grains in the region within 10 nm from the interface in the film 12 is more preferably 5 nm or less, and further preferably 3 nm or less. The average particle size is preferably 1 nm or more in consideration of crystallinity.

<Manufacturing method of cutting tools>
The method for manufacturing a cutting tool of the present embodiment includes, for example, a step of preparing a base material (hereinafter referred to as "base material preparation step"), a step of cleaning the surface of the base material (hereinafter referred to as "bomberd process"), and a step of cleaning the base material surface. It is provided with a step of forming a film on the surface of the base material (hereinafter referred to as “deposition step”). Further, the method for manufacturing a cutting tool includes a first pretreatment step carried out before the bombard step and a second pretreatment step carried out before the film forming step. Hereinafter, each step will be described in detail.

<< Substrate preparation process >>
First, a base material which is a cBN sintered body is produced by using a known method. For example, a substrate is produced by sintering a mixture of cBN particles and a raw material powder of a binder under high temperature and high pressure.

Next, the obtained base material is processed into a predetermined shape and then brazed to the base metal. As a result, a cutting tool whose cutting edge portion is made of a base material (however, it does not have a coating film) can be obtained.

<< First pretreatment process >>
The joint body of the base metal and the base material obtained in the base material preparation step is installed in the chamber of the PVD (Physical Vapor Deposition) device, and the inside of the chamber is evacuated to vacuum by a vacuum pump. At this time, in order to reduce the influence of outgas (outgas) in the chamber, it is preferable to heat the base material to, for example, 650 ° C.

Using a vacuum pump connected to the chamber, the pressure in the chamber is reduced to 1 × 10 ^-3 Pa or less, preferably 5 × 10 ^-4 Pa or less. Moisture pressure in the chamber is measured while depressurizing the chamber. The water pressure in the chamber is more preferably 1 × 10 ^-4 Pa or less, still more preferably 5 × 10 ^-5 Pa or less. The lower limit of the water pressure in the chamber is not particularly limited, but it can be easily lowered to about 1 × 10 ^-5 Pa by using a vacuum pump.

A gas purification device may be connected to the chamber and used in combination with a vacuum pump to control the water pressure in the chamber. A gas purification device is a device that removes water using a catalyst or an adsorbent. By using the gas purification device, the water pressure in the chamber can be easily reduced to about 1 × 10 ^-6 Pa.

《Bomberd process》
An inert gas is introduced into the chamber where the water pressure is limited to 1 × 10 ^-3 Pa or less, and a bias voltage is applied to the substrate to irradiate the surface of the substrate with inert gas ions. As a result, impurities such as oxides are removed from the surface of the base material, and the surface of the base material is cleaned. As the inert gas ion, for example, Ar ion can be used.

At this time, the substrate is irradiated with the inert gas ion until the water pressure in the chamber becomes 5 × 10 ^-3 Pa or less (preferably 3 × 10 ^-3 Pa or less). Moisture pressure in the chamber is measured with the chamber containing an inert gas. By bombarding until the water pressure in the chamber becomes low, the oxide film on the surface of the cubic boron nitride can be removed, and the oxidation of the surface of the cubic boron nitride during and after the bombard can be suppressed. .. The water pressure in the chamber is more preferably 5 × 10 ^-4 Pa or less, still more preferably 2 × 10 ^-4 Pa or less.

The bias voltage applied to the substrate is -100 to -300 V. Under high bias voltage conditions (for example, -500V) as described in JP-A-2015-209354, inert gas ions collide with the base metal and various jigs in the chamber, resulting in the base metal and curing. Metal particles (for example, Fe, W) are released from the jig and are likely to be deposited on the surface of the substrate (respatter). However, by setting the absolute value of the bias voltage to 300 V or less as described above, it is possible to prevent the metal particles discharged from the base metal and the jig from adhering to the surface of the base material. Further, it is possible to prevent the inert gas ion from remaining on the surface of the substrate.

By setting the absolute value of the bias voltage to 300 V or less, the irradiation energy of the inert gas ion to the substrate is reduced, but the water pressure in the chamber is maintained at a low state as described above. Oxidation of the surface of cubic boron nitride can be sufficiently suppressed.

If the absolute value of the bias voltage is less than 100 V, the irradiation energy of the inert gas ion to the substrate becomes too low, and the surface of the substrate cannot be sufficiently cleaned. Therefore, the absolute value of the bias voltage is set to 100 V or more.

The inert gas in the chamber is 0.6 to 1 Pa. This makes it possible to prevent the inert gas ions from remaining on the surface of the substrate.

By performing the bombarding step as described above, it is possible to prevent metal atoms, O, and inert gas ions contained in the jig and the base metal from adhering to the surface of the substrate.

<< Second pretreatment process >>
Next, the vacuum pump is operated to exhaust the inert gas from the chamber. Then, wait until the water pressure in the chamber becomes 2 × 10 ^-4 Pa or less, preferably 1 × 10 ^-4 Pa. At this time, the base material is heated to 500 ° C. or higher. The water pressure in the chamber is more preferably 3 × 10 ^-5 or less, still more preferably 2 × 10 ^-5 or less.

<< Film formation process >>
After the water pressure in the chamber becomes 2 × 10 ^-4 Pa or less, a film is formed on the surface of the base material by a physical vapor deposition method. As the physical vapor deposition method, any conventionally known method (arc ion plating method, sputtering method, etc.) can be adopted.

In the arc ion plating method, a film can be formed by using a target (metal evaporation source) containing a metal species that constitutes the film and a reaction gas such as CH ₄ or N ₂ . As a condition for forming a film by the arc ion plating method, a known condition for forming a film of a surface-coated cBN sintered body by the arc ion plating method can be adopted.

In the sputtering method, a film can be formed by using a target containing a metal species that constitutes the film, a reaction gas such as CH ₄ or N ₂ , and a subatter gas such as Ar, Kr or Xe. As a condition for forming the coating layer by the sputtering method, a known condition for forming a coating film of the surface-coated cBN sintered body by the sputtering method can be adopted.

Among the sputtering methods, it is possible to use the High Power Impulse Magnetron Sputtering (HiPIMS method), which can instantaneously input the electric power charged by the capacitor to efficiently ionize the target material. preferable. This makes it possible to form a dense film.

In the above bombarding process, since metal atoms, O, and inert gas ions contained in the jig and the base metal on the surface of the base material are suppressed from adhering to the surface of the base material, the cubic boron nitride and the coating film are used. The content of these atoms at the interface can be reduced. In addition, since nucleation and grain growth occur uniformly during film formation, the grain boundaries near the interface in the coating film increase, and the stress generated at the interface can be relieved. As a result, the adhesion between the cubic boron nitride and the coating film is improved, and the peeling resistance of the coating film is improved.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Sample No. The cutting tools 1 to 9, 12 to 15 include the above-mentioned surface-coated cBN sintered body. Sample No. The cutting tools 10 and 11 are comparative examples.

<Sample No. Cutting tool of 1>
A mixture of 70% by volume of cBN and the remaining binder (TiN, Ti, Al) was sintered at 1400 ° C. and 5 Pa to prepare a base material as a cBN sintered body. This sintered body was joined to a base metal made of WC-based cemented carbide and molded into an ISO standard DNGA150408 shape. For joining, a brazing material containing Ag as a main component was used.

Next, a bonded body of the base material and the base metal was installed in the chamber of the PVD device using the HiPIMS method.

Here, the PVD apparatus will be described. A vacuum pump is connected to the chamber of the PVD device, and the inside of the chamber can be evacuated. A rotary table is installed in the chamber, and the rotary table is configured so that a bonded body including a base material can be set via a jig. The base material set in the chamber can be heated by the heater installed in the chamber. Further, a gas pipe for introducing gas used in the bombarding process and the film forming process is connected to the chamber via a mass flow controller (MFC) for flow rate control. Further, in the chamber, a tungsten filament for generating Ar ions for the bombard process and a sputtering source for the film forming process to which the necessary power supply is connected are arranged. The evaporation source raw material (target) required for film formation can be set in the spatter source.

The substrate was heated at 650 ° C. for 2 hours by a heater installed in the chamber while evacuating the inside of the chamber with a vacuum pump. After that, heating and evacuation were continued until the water pressure in the chamber became 1 × 10 ^-3 Pa or less. The water pressure in the chamber was measured using a gas analyzer "Qulee CGM-052" manufactured by ULVAC, Inc.

Then, when the water pressure in the chamber became 1 × 10 ^-3 Pa or less, the bombard step was started and the surface of the substrate was cleaned with Ar ions for 60 minutes. The water pressure before the start of bombard was 0.921 × 10 ^-3 Pa. In the bombard process, Ar gas was introduced into the chamber to maintain the pressure in the chamber at 0.8 Pa. At this time, a bias voltage of −150 V was applied to the substrate and a current was passed through the tungsten filament to generate a glow discharge in Ar gas.

The water pressure in the chamber was measured during the bombard, and the bombard was continued until the water pressure became 5 × 10 ^-3 Pa or less. The water pressure at the end of the bombard was 4.92 × 10 ^-3 Pa. Moisture pressure in the bombard was measured with Ar gas in the chamber.

After that, Ar gas was exhausted from the chamber, and the mixture was waited until the water pressure in the chamber became 2 × 10 ^-4 Pa or less. At this time, the temperature was controlled so that the temperature of the base material was 500 ° C.

Then, when the water pressure in the chamber became 2 × 10 ^-4 Pa or less, the film forming step of forming a film on the surface of the substrate was started according to the following film forming conditions to form the film. The water pressure at the start of the film forming process (hereinafter referred to as “moisture pressure at the start of film formation”) was 1.94 × 10 ^-4 Pa.

<< Film formation conditions >>
Target: Ti _0.5 Al _0.5 (powder metallurgy)
Pulse power: 45kW
Pulse width: 0.2ms
Average power: 7.0kW
Bias voltage: -40V
Base material temperature: 430 ° C
Ar partial pressure: 0.45Pa
Reaction gas: N ₂ (the partial pressure of the reaction gas was adjusted so as to form a film in the transition mode).

<Sample No. 2,3,10,12,13 cutting tools>
The point where the bombard process is started when the moisture pressure in the chamber is less than 5 × 10 ^-4 Pa, and the point where the film formation process is started when the moisture pressure in the chamber is less than 1 × 10 ^-4 Pa. Except for the sample No. Sample No. 1 under the same conditions as 1. 2 cutting tools were manufactured.

The point at which the bombard process is started when the moisture pressure in the chamber is below 3 × 10 ^-4 Pa, and the point at which the film formation process is started when the moisture pressure in the chamber is below 5 × 10 ^-5 Pa. Except for the sample No. Sample No. 1 under the same conditions as 1. 3 cutting tools were produced.

The point where the bombard process is started when the moisture pressure in the chamber is less than 2 × 10 ^-3 Pa, and the point where the film formation process is started when the moisture pressure in the chamber is less than 5 × 10 ^-4 Pa. Except for the sample No. Sample No. 1 under the same conditions as 1. 10 cutting tools were made.

The point where the bombard process is started when the moisture pressure in the chamber is less than 1 × 10 ^-4 Pa, and the point where the film formation process is started when the moisture pressure in the chamber is less than 3 × 10 ^-5 Pa. Except for the sample No. Sample No. 1 under the same conditions as 1. Twelve cutting tools were made.

The point at which the bombard process is started when the moisture pressure in the chamber is below 5 × 10 ^-5 Pa, and the point at which the film formation process is started when the moisture pressure in the chamber is below 2 × 10 ^-5 Pa. Except for the sample No. Sample No. 1 under the same conditions as 1. Thirteen cutting tools were made.

Sample No. The water pressure at the start of the bombard, the water pressure at the end of the bombard, and the water pressure at the start of film formation in each of 2, 3 and 10 are as shown in Table 1 described later.

<Sample No. 4, 5, 11 cutting tools>
Except for the fact that the bias voltage applied to the substrate in the bombard step was -100 V, the sample No. Sample No. 1 under the same conditions as 1. 4 cutting tools were produced. Except for the fact that the bias voltage applied to the substrate in the bombard step was -250V, the sample No. Sample No. 1 under the same conditions as 1. 5 cutting tools were produced. Except for the fact that the bias voltage applied to the substrate in the bombard step was −500 V, the sample No. Sample No. 1 under the same conditions as 1. Eleven cutting tools were made.

<Sample No. 6 cutting tools>
Except for the fact that the film forming step was performed according to the following film forming conditions, the sample No. Sample No. 1 under the same conditions as 1. 6 cutting tools were produced.

<< Film formation conditions >>
Target: Al _0.6 Cr _0.4 (powder metallurgy)
Pulse power: 30kW
Pulse width: 2.0 ms
Average power: 6.0kW
Bias voltage: -45V
Base material temperature: 430 ° C
Ar partial pressure: 0.45Pa
Reaction gas: N ₂ (the partial pressure of the reaction gas was adjusted so as to form a film in the transition mode).

<Sample No. 7 cutting tools>
Except for the fact that the film forming step was performed according to the following film forming conditions, the sample No. Sample No. 1 under the same conditions as 1. 7 cutting tools were produced.

<< Film formation conditions >>
Target: Ti _0.45 Al _0.45 Si _0.1 (powder metallurgy)
Pulse power: 45kW
Pulse width: 0.2ms
Average power: 7.0kW
Bias voltage: -40V
Base material temperature: 430 ° C
Ar partial pressure: 0.45Pa
Reaction gas: N ₂ (the partial pressure of the reaction gas was adjusted so as to form a film in the transition mode).

<Sample No. 8 cutting tools>
Except for the fact that the film forming step was performed according to the following film forming conditions, the sample No. Sample No. 1 under the same conditions as 1. 8 cutting tools were produced.

<< Film formation conditions >>
Target: Ti _0.8 Si _0.2 (powder metallurgy)
Pulse power: 45kW
Pulse width: 0.1 ms
Average power: 6.0kW
Bias voltage: -30V
Base material temperature: 430 ° C
Ar partial pressure: 0.50 Pa
Reaction gas: N ₂ (the partial pressure of the reaction gas was adjusted so as to form a film in the transition mode).

<Sample No. 9 cutting tools>
Except for the fact that the film forming step was performed according to the following film forming conditions, the sample No. Sample No. 1 under the same conditions as 1. 9 cutting tools were manufactured.

<< Film formation conditions >>
Target: Ti (powder metallurgy)
Pulse power: 60kW
Pulse width: 10.0ms
Average power: 8.0kW
Bias voltage: -40V
Base material temperature: 550 ° C
Ar partial pressure: 0.50 Pa
Reaction gas: N ₂ , CH ₄ (the partial pressure of each reaction gas was adjusted so as to form a film in the transition mode).

<Sample No. 14 cutting tools>
Except for the fact that the arc ion plating method was used to form the film and the film formation step was performed according to the following film formation conditions, the sample No. Sample No. 1 under the same conditions as 1. 14 cutting tools were made.

<< Film formation conditions >>
Target: Ti _0.5 Al _0.5 (powder metallurgy)
Arc current: 80A
Bias voltage: -100V
Base material temperature: 430 ° C
N ₂ voltage divider: 3.0 Pa
<Sample No. 15 cutting tools>
The arc ion plating method was used to form the film, and the sample No. Except for the fact that the film forming step was performed under the same film forming conditions as in No. 14. Sample No. 13 under the same conditions as No. 13. Fifteen cutting tools were made.

<Bomberd treatment conditions and target material>
Table 1 shows the sample No. The conditions of the bombard process and the target used at the time of film formation in each of 1 to 15 are shown.

<Analysis method of the interface between cubic boron nitride and the coating>
Sample No. For each of the cutting tools 1 to 15, analytical samples were prepared which were broken in the direction perpendicular to the interface between the base material and the coating film. The fracture surface is smoothed by irradiating it with a focused ion beam, and then analyzed by an ion milling device using an Ar ion beam so that the thickness along the normal direction of the fracture surface is 100 nm. The fracture surface of the sample was polished. This is to suppress the variation in the measured value of the O content depending on the thickness of the sample for analysis.

Immediately after polishing the fracture surface of the analytical sample (within 5 minutes after polishing is completed), the sample is introduced into the TEM device to acquire a TEM image near the interface between the cubic boron nitride and the coating, and the cubic boron nitride. A line scan measurement by EDS was performed so as to cross the interface with the coating film. The following was used as an analyzer.

"Analysis equipment"
・ TEM: "JEM-2100F / Cs" manufactured by JEOL Ltd.
(Cs collector: CEOS "CESCOR")
(TEM observation conditions: acceleration voltage 200 kV, probe size 0.13 nm)
・ EDS: "JED2300 Series Dry SD60GV Detector" manufactured by JEOL Ltd.
(Line scan conditions: Acceleration voltage 200 kV, measurement point interval 0.25 nm (however, it will be 0.5 nm due to binning at the time of result output)).

First, in the TEM image, a line having a length of 200 nm that crosses the interface along the normal direction of the interface between the cubic boron nitride and the coating is specified, and the concentration distribution of the elements along the line is specified using EDS. A line scan measurement was performed to measure the change. The measurement elements were Fe, W, O and Ar in addition to B and N, which are calibration elements of cubic boron nitride, and the constituent elements of the film. Then, a point where the concentration of B is 1/2 of the average value of the concentration in the substrate was specified as a point on the interface.

Next, assuming that the concentration of the elements other than B and N detected in the cubic boron nitride is the background level (detection limit) in the measurement, the concentration of each of these elements in the cubic boron nitride is assumed. The average values of were calculated, these values were excluded from the measurement results of the line scan, and the measured elemental concentrations were recalculated. The maximum concentration of the peak (peak including points on the interface) of the concentration distribution of Fe and W near the interface in the recalculated line scan measurement result was defined as the content (at%) of Fe and W at the interface.

Sample No. For cutting tools 1-15, at least one of Fe and W was detected at the interface.

Furthermore, the O content (at%) at the interface was evaluated from the line scan measurement results using EDS. When the peak of the O concentration distribution was observed at the interface in the line scan measurement, the maximum concentration of the peak was defined as the O content (at%) at the interface, as in Fe and W. On the other hand, when the peak of the O concentration distribution is not seen at the interface in the line scan measurement, the average O content (at%) in the section of 2 nm from the interface to the coating side and 2 nm to the cubic boron nitride side for a total of 4 nm. The value was taken as the O content (at%) at the interface.

Furthermore, the Ar content (at%) at the interface was evaluated from the line scan measurement results using EDS.

<Thickness of dissimilar elemental layer>
In the above line scan measurement result, the line length in which the total content of Fe and W is 0.05 at% or more was measured as the thickness of the layer (different metal element layer) containing Fe and W.

<Average particle size of the film near the interface>
In a 5 million times TEM image, the average grain size of the crystal grains at a position 10 nm from the interface in the coating film was measured. Specifically, a lattice image is taken in a high-resolution TEM image, crystal grains are distinguished by the difference in crystal orientation and the presence of grain boundaries, the widths of 30 crystal grains are measured for one sample, and the average value is calculated. The average grain size was used.

<Thickness of coating>
The cutting edge part was cut out by wire electric discharge machining, and the cut out part was embedded in resin. Then, the cross section of the coating film was exposed by CP (cross section polisher) processing based on the ion milling method, and an SEM image at a magnification of 15,000 times was observed. The thickness of the coating film was measured at 5 points in the region within 1 mm from the tip of the cutting edge, and the average value was taken.

<Cutting test>
Sample No. Using each of the cutting tools 1 to 15, a cutting test of intermittent cutting was carried out under the following conditions, and the cutting time until chipping occurred was determined as the tool life. The tool life correlates with the peelability of the coating, and the better the peelability, the longer the tool life. Therefore, the peelability of the coating film can be evaluated by checking the tool life.

《Cutting conditions》
Work material: Carved and hardened steel SCM415H-5V, HRC62 (diameter 100 mm x length 300 mm, with 5 V-grooves in the axial direction of the work material)
Cutting speed: V = 130 m / min.
Feed: f = 0.1 mm / rev.
Notch: ap = 0.2 mm
Wet / Dry: Dry.

<result>
Table 2 shows the sample No. For each of the cutting tools 1 to 15, the content at the interface between Fe and W, the content of O and Ar at the interface, the thickness of the dissimilar metal element layer, and the average particle size at a position 10 nm from the interface in the coating. , The measurement result of the thickness of the coating and the tool life is shown.

Sample No. It was confirmed that the cutting tools of 1 to 9, 12 to 15 had a tool life of 20 minutes or more and were excellent in peeling resistance of the coating film.

Sample No. In 1 to 9, 12 to 15, the absolute value of the bias voltage applied to the base material in the bombard treatment is limited to 300 V or less, so that the amount of Fe released from the jig in the chamber is reduced and the amount of Fe is reduced. The amount of W emitted from the cemented carbide connected to the substrate is reduced. As a result, it was confirmed that the Fe content was 1 at% or less and the W content was 1 at% or less at the interface between the cubic boron nitride and the coating film.

FIG. 2 shows the sample No. It is a 2 million times TEM image (bright-field image) showing the interface between the cubic boron nitride and the coating film in 2. FIG. 3 shows the sample No. It is a 2 million times TEM image (HAADF image (high-angle annular dark field image)) showing the interface between the cubic boron nitride and the film in 2. As shown in FIGS. 2 and 3, almost no layers of Fe, W and oxides are seen at the interface, and it can be seen that the crystal grains near the interface in the film are small. This is because the amount of Fe, W, O, and Ar present on the surface of cubic boron nitride is small, so that nucleation and grain growth occur uniformly during the film formation process. That is, the concentration in the place where the nucleus is generated is suppressed, and the coexistence of the place where the grain grows easily and the place where the grain grows hard is also suppressed.

When the Fe content at the interface is 1 at% or less and the W content is 1 at% or less, it is possible to suppress an increase in the lattice constant of the crystals in the film due to Fe and W entering the crystals of the film. As a result, it is possible to suppress an increase in the lattice constant difference between the crystals of cubic boron nitride in the substrate and the crystals of the coating, and the adhesion between the cubic boron nitride and the coating is improved.

Furthermore, the sample No. In 1 to 9, 12 to 15, the water pressure before the start of the bombard is limited to 1 × 10 ^-3 Pa or less, and the water pressure at the end of the bombard is limited to 5 × 10 ^-3 Pa or less. As a result, the O content at the interface between the cubic boron nitride and the coating film is suppressed to 2 at% or less, and the deterioration of the adhesion between the cubic boron nitride and the coating film due to O can be suppressed.

As described above, by lowering the contents of Fe, W and O at the interface, the adhesion between the cubic boron nitride and the coating film is improved, and the sample No. It is considered that the peeling resistance of the coating film in the cutting tools 1 to 9, 12 to 15 was improved.

On the other hand, the sample No. It was confirmed that the tool life of 10 cutting tools was as short as 2 minutes. Sample No. At No. 10, the water pressure before the start of the bombard is 1.98 × 10 ^-3 Pa, and the water pressure at the end of the bombard is 7.93 × 10 ^-3 Pa. Therefore, at the interface between the cubic boron nitride and the coating film. The O content (at%) is higher than 2 at%. As a result, it is considered that the adhesion between the cubic boron nitride and the coating film is lowered and the tool life is shortened.

Sample No. It was confirmed that even with 11 cutting tools, the tool life was as short as 14 minutes. Sample No. In No. 11, since the bias voltage applied to the base material in the bombard process is as high as 500 V, the amount of Fe discharged from the jig in the chamber and the amount of W discharged from the cemented carbide bonded to the base material are Increase. Therefore, the total content of Fe and W at the interface between the cubic boron nitride and the coating film was as high as 4.4 at%. As a result, it is considered that Fe and W widen the lattice constant difference between the cubic boron nitride crystal and the coating crystal, reduce the adhesion between the cubic boron nitride crystal and the coating, and shorten the tool life.

Furthermore, the sample No. It was confirmed that the tool life was 30 minutes or more in 1 to 3, 6 to 9, 12 to 15. It is considered that this is because the thickness of the dissimilar metal element layer is 3 nm or less and the average particle size of the coating film near the interface is 5 nm or less, so that the adhesion between the cubic boron nitride and the coating film is further improved. Therefore, it was confirmed that it is preferable that the thickness of the dissimilar metal element layer is 3 nm or less and the average particle size of the coating film near the interface is 5 nm or less.

Furthermore, the sample No. In 2, 3, 12, 13, and 15, it was confirmed that the tool life was 40 minutes or more. It is considered that this is because the average particle size of the coating film near the interface is 3 nm or less, so that the stress at the interface between the cubic boron nitride and the coating film can be easily relaxed. Therefore, it was confirmed that it is preferable to set the average particle size of the coating film near the interface to 3 nm or less.

Although the embodiments and examples of the present invention have been described as described above, it is planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

The embodiments and examples disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the embodiments and examples described above, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

10 Surface coated cBN sintered body, 11 base material, 12 coating, 100 cutting tool, 100a rake surface, 100b flank surface, 101 base metal, 102 brazing layer.

Claims (6)

A base material that is a cubic boron nitride sintered body,
A coating that is in contact with the substrate and covers the substrate is provided.
At the interface between the cubic boron nitride in the substrate and the coating film, the Fe content is 1 at% or less, the W content is 1 at% or less, and the O content is 2 at% or less .
The thickness of the layer in which the total content of the Fe content and the W content is 0.05 at% or more is 5 nm or less.
A surface-coated cubic boron nitride sintered body having a coating thickness of 0.3 μm or more and 10 μm or less . The surface-coated cubic boron nitride sintered body according to claim 1, wherein the surface-coated cubic boron nitride sintered body is fixed to a base metal composed of a cemented carbide containing WC . The coating is polycrystalline and is
The surface-coated cubic boron nitride sintered body according to claim 1 or 2, wherein the region within 10 nm from the interface in the coating is composed of crystal grains having an average particle size of 10 nm or less. The surface-coated cubic boron nitride sintered body according to any one of claims 1 to 3, wherein the Ar content at the interface is 1 at% or less. The coating comprises at least one compound consisting of at least one element selected from the group consisting of Al, Ti, Cr and Si and at least one element selected from the group consisting of C and N. , The surface-coated cubic boron nitride sintered body according to any one of claims 1 to 4 . A cutting tool comprising the surface-coated cubic boron nitride sintered body according to any one of claims 1 to 5 .

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