JP5585929B2 - Surface-coated cutting tool with excellent fracture resistance due to hard coating layer - Google Patents

Description

This invention is formed when the hard coating layer is formed as fine columnar crystals and has a biaxially oriented section with excellent toughness, so when used under severe cutting conditions such as high-speed cutting of steel or cast iron. Further, the present invention relates to a surface-coated cutting tool (hereinafter referred to as a coated tool) that exhibits excellent heat resistance and fracture resistance and can extend the life of the cutting tool.

  In general, for coated tools, inserts that are detachably attached to the tip of a cutting tool for turning of work materials such as various types of steel and cast iron, and the inserts are detachably attached to be used for chamfering and grooving. An insert type end mill that performs cutting processing in the same manner as a solid type end mill used for processing and shoulder processing is known.

Further, a Ti—Si nitride (hereinafter referred to as Ti _1-x Si _x N) is formed on the surface of a tool base composed of a tungsten carbide (hereinafter referred to as WC) based cemented carbide sintered body as a coated tool. A coating tool formed by physically vapor-depositing a hard coating layer is widely known, and is used for continuous cutting and intermittent cutting of various steels and cast iron.
In particular, as a technique paying attention to the crystal structure of nitride or carbonitride such as Ti and Si, in the documents shown in Patent Document 1 and Patent Document 2, titanium carbonitride deposited by chemical vapor deposition is twinned. There has been proposed a technique for increasing the bonding force between grains forming a hard coating layer by having a structure. Further, in the document shown in Patent Document 3, the TiSiN crystal grains forming the hard coating layer are entirely composed of crystal grains having a crystal orientation <111> in the direction of 0 to 15 degrees from the normal direction of the tool base. Titanium carbonitride showing a crystal arrangement in which the proportion of small-angle grain boundaries (0 to 15 degrees) is 50% when the angle between adjacent crystal grains occupying 15% is measured. Thus, techniques for improving the fracture resistance of surface-coated cutting tools have been proposed.

Japanese Patent No. 4004133 Japanese Patent No. 3768136 JP 2009-220239 A

  In recent years, the FA of cutting devices has been remarkable, and in addition, there are strong demands for labor saving, energy saving, cost reduction and efficiency for cutting, and with this, high-efficiency heavy cutting such as high feed and high cutting However, in the above-mentioned conventional coated tools, there are no particular problems when various steels and cast irons are machined under normal conditions, but they are shocking and intermittent to the cutting edge. When it is used for intermittent high-speed cutting such as dry high-speed milling where high load is applied, cracks are likely to develop inside the hard coating layer and the heat resistance of the hard coating layer is low. The cutting edge portion is easily damaged, and this causes the service life to be reached in a relatively short time.

In view of the above, the inventors of the present invention have adopted the crystalline form of the hard coating layer composed of the Ti _1-x Si _x N layer in order to increase the fracture resistance of the coated tool and extend the service life. The following findings were obtained as a result of intensive research.

For example, a hard coating layer made of a Ti _1-x Si _x N layer of a conventional coating tool can be obtained by sintering the above WC-based cemented carbide alloy in a sputtering (SP) apparatus, which is a kind of physical vapor deposition apparatus shown in FIG. Wearing a tool base consisting of a body, for example,
In-apparatus heating temperature: 300-500 ° C
DC bias voltage applied to the tool base: −50 to −100 V,
Cathode electrode: Ti-Si alloy Sputtering power: 3-6 kW,
Gas flow in the apparatus: nitrogen (N ₂ ) gas + argon (Ar) gas,
In-apparatus gas pressure: 0.3 to 1.5 Pa,
Under these conditions, a Ti _1-x Si _x N layer (hereinafter referred to as a conventional Ti _1-x Si _x N layer) is formed.

However, the present inventors have formed a Ti _1-x Si _x N layer by ion plating using, for example, a pressure gradient type Ar plasma gas which is a kind of physical vapor deposition apparatus schematically shown in FIG. Using the device, install the tool base in the device,
Tool substrate temperature: 240-400 ° C.
Evaporation source: Metal Ti, Metal Si
Plasma gun discharge power For metal Ti: 10-12 kW,
Plasma gun discharge power For metal Si: 5 to 8 kW,
Reaction gas flow rate: nitrogen _{(N 2)} gas 80 to 120 sccm,
Discharge gas: Argon (Ar) gas 30-50 sccm,
DC bias voltage applied to the tool base: 0 V,
Deposition rate: When Ti is deposited under the condition of 0.04 to 0.11 nm / second, this Ti _1-x Si _x N layer (hereinafter referred to as a modified Ti _1-x Si _x N layer) It has been found that it has excellent wear resistance and fracture resistance in heavy feed machining with high feed and high depth of cut, which requires a high load on the cutting edge, compared to the Ti _1-x Si _x N layer. .

This invention was made based on the above research results,
“A surface-coated cutting tool obtained by physically vapor-depositing a hard coating layer made of a Ti _1-x Si _x N film having an average layer thickness of 0.2 to 2 μm on the surface of a tool base made of a tungsten carbide-based cemented carbide sintered body X satisfies 0.1 ≦ x ≦ 0.3, and
The Ti _1-x Si _{x N} layer is made of columnar crystal structure having the same height as the average layer thickness, further, when measuring the crystal orientation of the crystal grains of the surface in electron backscatter diffraction apparatus, adjacent A section having a section diameter of 0.2 to 4 μm surrounded by a crystal interface in which the orientation difference of the crystal orientation with respect to the measurement point is 15 degrees or more occupies 20% or more of the total area measured , and When a crystal grain structure in a horizontal cross section having a depth of 100 nm is observed from the surface of the Ti _1-x Si _x N layer, crystal grains having a grain size of 10 to 100 nm occupy 90% or more of the measurement area. A surface-coated cutting tool. "
It has the characteristics.

  The present invention will be described in detail below.

As already described, the present invention comprises, for example, a WC-based cemented carbide sintered body in an apparatus using an ion plating apparatus using a pressure gradient type Ar plasma gas shown schematically in FIG. Install the tool base,
Tool substrate temperature: 240-400 ° C.
Evaporation source: Metal Ti, Metal Si
Plasma gun discharge power For metal Ti: 10-12 kW,
Plasma gun discharge power For metal Si: 5 to 8 kW,
Reaction gas flow rate: nitrogen _{(N 2)} gas 80 to 120 sccm,
Discharge gas: Argon (Ar) gas 30-50 sccm,
DC bias voltage applied to the tool base: 0 V,
Deposition rate: 0.04-0.11 nm / second,
The film is formed under the conditions. It is already well known that the Ti component, which is a conventional component of the Ti _1-x Si _x N layer, improves the high-temperature strength, the Si component improves the heat resistance, and N has the effect of improving the layer strength. In addition to this, the modified Ti _1-x Si _x N layer of the present invention exhibits excellent toughness and fracture resistance even under severe use conditions such as high-speed interrupted cutting conditions.
The reason for this is strongly related to the unique grain morphology of the modified Ti _1-x Si _x N layer, as will be described below.

First, with respect to the modified Ti _1-x Si _x N layer formed by the above vapor deposition, the hard coating layer Ti _1-x Si _x N is formed using an electron beam backscattering diffractometer in a state where the surface is a polished surface. When the crystal orientation of the horizontal cross section of the layer surface is analyzed, the crystal grain boundary where the orientation difference in crystal orientation between adjacent measurement points is 15 degrees or more around a specific axis (hereinafter referred to as the rotation angle). It was found that the area occupied by the section having a section diameter of 0.2 to 4 μm surrounded by occupies 20% or more of the measured area.
Note that the rotation angle in describing the difference in orientation refers to the rotation angle when two crystals have the same orientation in one rotation operation with respect to one of two crystals having different orientations. In addition, the section diameter here is defined to indicate the diameter of a perfect circle having the same area as the section area.

Furthermore, when the crystal structure of a horizontal cross section having a depth of 0.1 μm from the surface of the film was observed using a transmission electron microscope and the individual crystal grain sizes were measured, the crystal grains having a diameter of 10 to 100 nm were found to have a total measurement area. It was found that the area ratio accounted for 90% or more.
The diameter here is defined to indicate the diameter of a perfect circle having the same area as the crystal grain.

  This characteristic will be described in detail below.

Above, is constituted by 90% of the diameter 10~100nm grain in terms of area ratio, and crystal orientation adjacent piecewise internal angular difference is divided diameter 0.2~4μm such that less than 15 degrees In the modified Ti _1-x Si _x N layer in which the section is present in an area ratio of 20% or more, the crystal grains constituting the inside of the section are at least an area ratio of 50% or more of crystal grains having a diameter of 10 to 100 nm. It is configured.
Thus, at least 50% or more of crystal grains present in said section in area ratio is crystal grains existing in the vicinity of the crystal grain and, misorientation of the crystal orientation is less than 15 degrees rotation angle in particular present in the same categories Since the biaxial orientation is such that the interfacial consistency between the crystal grains present in the section is high, it has excellent toughness like a single crystal, and further has a diameter of 10 to 10. Since it has a fine structure of 100 nm and can maintain excellent fracture resistance, the tool life can be extended even in intermittent heavy cutting, in which cracks and fractures tend to occur in the coating.

In the above modified Ti _1-x Si _x N layer, when the value of x is less than 0.05, the proportion of Si is relatively reduced, and the heat resistance characteristic effect of Si cannot be sufficiently obtained. If it exceeds 3, the ratio of Ti becomes relatively small, and the desired high-temperature strength cannot be obtained. Therefore, the value of x was set to 0.05 ≦ x ≦ 0.3.
Also, if the size of the crystal grains is less than 10 nm, the strength of the crystal grains themselves cannot be obtained and the desired strength cannot be obtained, and if it exceeds 100 nm, the crystal grains become coarse and cause chipping. The size of crystal grains occupying 90% or more of the film in terms of area ratio was determined to be 10 nm to 100 nm.
Further, constituting the Ti _1-x Si _{x N} layer, since the area ratio of the segments crystal orientation is enclosed at the interface of 15 degrees or more is less than 20%, which can not be obtained the desired toughness, the area of the segment The ratio was set to 20% or more.

Coated tool of the present invention, among the Ti _1-x Si x N crystal grains constituting the hard coating layer comprising Ti _1-x Si x N layer, a particle size of 10~100nm crystal grains in total area ratio When the crystal orientation of the surface crystal grains occupies 90% or more and is measured with an electron beam backscattering diffractometer, the crystal interface is surrounded by a crystal interface where the crystal orientation difference between adjacent measurement points is 15 degrees or more. Since the section having a section diameter of 0.2 to 4 μm occupies 20% or more of the entire measured area, excellent high-temperature strength can be obtained even in dry intermittent high-speed cutting where a high load is applied to the cutting edge. In addition to heat resistance, it exhibits excellent fracture resistance and toughness, exhibits excellent tool properties, and contributes to prolonging tool life.

FIG. 2 shows a schematic diagram of an ion plating apparatus using a pressure gradient type Ar plasma gun for vapor-depositing a hard coating layer (modified Ti _1-x Si _x N layer) of the surface-coated cutting tool of the present invention, Is a schematic front view, and (b) is a schematic plan view. It shows a schematic diagram of a conventional hard coating layer of the surface-coated cutting tool (conventional Ti _1-x Si _{x N} layer) sputtering (SP) apparatus for depositing form. Shows a schematic diagram of a modified Ti _1-x Si _{x N} composed of layer hard layer of the surface-coated cutting tool of the present invention, (a) represents also a horizontal sectional structure view,, (b) the orientation difference in the crystal orientation The schematic diagram of the distribution of the crystal | crystallization interface which becomes 15 degrees or more is shown.

Next, the coated tool of the present invention will be specifically described with reference to examples.
In addition, although demonstrated centering on a covering insert here, it is applicable not only to a covering insert but to various covering tools, such as a covering end mill and a covering drill.

As raw material powders, WC powder, TiC powder, VC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder all having an average particle diameter of 0.8 to 4 μm are prepared. Blended into the composition shown, wet mixed with a ball mill for 72 hours, dried, and then pressed into a green compact at a pressure of 100 MPa. The green compact was held at a temperature of 1400 ° C. for 1 hour in a vacuum of 6 Pa. After sintering, the surface was polished, and tool bases A1 to A10 for milling made of WC-base cemented carbide having an ISO standard / SEEN1203 insert shape were formed.

Next, the tool bases A1 to A10 and B1 to B10 are ultrasonically cleaned in acetone and dried, and attached to an ion plating apparatus using a pressure gradient type Ar plasma gun shown in FIG. As the evaporation source, metal Ti was attached. First, the inside of the apparatus was evacuated and the inside of the apparatus was heated to 240 to 420 ° C. with a heater while maintaining a vacuum of 1.0 × 10 ⁻³ Pa or less. After being introduced to 2.3 × 10 ⁻² Pa, the discharge power of the pressure gradient plasma gun is set to 2 kW, Ar ions are generated in the apparatus, and a bias voltage of −200 V is applied to the tool base, The tool base was treated with Ar bombardment for 10 minutes, and then the inside of the apparatus was once evacuated to about 1 × 10 ⁻³ Pa,
Under the conditions shown in Table 2, the discharge power of the pressure gradient type Ar plasma gun is 12 kW, the pressure in the furnace is 3 × 10 ^{−2 to} 6 × 10 ⁻² Pa while flowing Ar gas at 60 sccm and nitrogen gas at 100 sccm. A plasma beam is incident on the metal Ti evaporation source and the metal Si evaporation source to generate vapors of metal Ti and metal Si, ionize with the plasma beam, and the modified Ti _1-x Si _x N layer in the chamber The plasma gun is measured so that the growth rate is within a range of ± 0.01 nm / sec from the target rate (0.04 to 0.11 nm / sec) while measuring the growth rate using a crystal oscillation type film thickness controller. The modified Ti _1-x Si _x N layer having a predetermined target layer thickness shown in Table 4 is vapor-deposited on the surface of the tool base while adjusting the output of the tool. Light coated inserts (hereinafter referred to as the present invention inserts) 1 to 14 were produced.
Table 2 shows various conditions for ion plating using a pressure gradient type Ar plasma gun, which are conditions for forming the modified Ti _1-x Si _x N layers of the inserts 1 to 14 of the present invention.

For the purpose of comparison, the above tool bases A1 to A10 are ultrasonically cleaned in acetone and dried, and then mounted on the sputtering (SP) apparatus shown in FIG. 2, and metal Cr is used as a cathode electrode (evaporation source). And the Ti—Si alloy, first, the inside of the apparatus is evacuated and the inside of the apparatus is heated to 400 ° C. with a heater while maintaining a vacuum of 0.01 Pa or less, Ar gas is introduced at 200 sccm, and the metal Cr and the above-mentioned A DC bias voltage of −800 V is applied between the tool substrate and the surface of the tool substrate is subjected to Cr bombardment for 5 minutes, and then nitrogen gas and Ar gas are introduced into the apparatus as atmospheric gases under the conditions shown in Table 3. And an atmosphere of 0.5 Pa, and a DC bias voltage of −50 V is applied as a bias voltage between the metal Ti and the tool base, thereby the tool base. A conventional surface-coated insert (hereinafter referred to as a conventional insert) 1 as a conventional coated tool is formed by vapor-depositing a conventional Ti _1-x Si _x N layer having a target layer thickness shown in Table 6 as a hard coating layer on the surface of ~ 14 were produced.
Table 3 shows sputtering conditions for forming the conventional Ti _1-x Si _x N layers of the conventional inserts 1 to 14.

A conventional Ti _1-x Si x N layer of the reforming Ti _1-x Si x N layer and a conventional insert 10 of the present invention the insert 10, while the surface and the polishing surface, electron backscatter diffraction The crystal orientation of the hard coating layer surface was analyzed using an apparatus (EBSD). That is, the crystal orientation of the modified Ti _1-x Si _x N layer is measured in a 10 μm × 10 μm region at an interval of 0.03 μm / step, measurement noise is removed, and then the crystal between adjacent measurement points is measured. the interface misorientation orientation is 15 degrees or more at a rotation angle displayed on the map of the measurement region as illustrated in FIG. 3 (b), among the realm segments are separated by their interfaces, 0. The area ratio with respect to the total measurement area having a segment diameter of 2 to 4 μm was determined, and this value is shown in Tables 4 and 5 together with the average value of the segment diameters.
Further, after mechanically polishing the hard coating layer from the substrate side to a thickness of about 1 mm, using an Ar ion polishing apparatus, the hard coating layer was polished to a thickness of 100 nm to form a thin piece, and then the layer was formed using a transmission electron microscope. The crystal grain size of the Ti _1-x Si _x N layer in the vicinity of a depth of 100 nm from the surface is observed, and the surface of the tool base surface of the modified Ti _1-x Si _x N layer is exemplified as shown in FIG. among them, measuring the area ratio α the width 10~100nm fine grains occupy, with the area percentage of the total measured area of the segment shown in tables 4 and 5.
From Table 4, the modified Ti _1-x Si _x N layers of the inserts 1 to 14 of the present invention account for 90% of the area ratio of Ti _1-x Si _x N crystal grains having a diameter of 10 to 100 nm, and an electron beam When analyzing the crystal orientation with a backscattering diffractometer, the area ratio of the section having a section diameter of 0.2 to 4 μm surrounded by an interface having a crystal orientation difference of 15 degrees or more at the rotation angle is 20% of the total measurement area. % has a higher, it can be seen that there more than 20% by indicator area ratio is formed by 10~100nm fine crystals having a biaxial orientation.
On the other hand, from Table 5, the conventional Ti _1-x Si x N layer of the conventional insert 1-14, partition segment diameter 0.2~4μm Segmented by interfacial having a difference in crystal orientation of 15 degrees or more at a rotation angle Although the area ratio is 20% or more of the total measurement area, the existence ratio of fine crystals of 10 to 100 nm is 90% or less in area ratio, and the surface structure is constituted by coarse grains having a diameter of 100 nm or more. . That is, it can be seen that there is no section constituted by a fine crystal of 10 to 100 nm having biaxial orientation, and only a coarse single crystal of 100 nm or more.

Next, for the above-mentioned inserts 1 to 10 of the present invention and the conventional inserts 1 to 10, this is screwed to the tip of the tool steel tool with a fixing jig,
Work material: Plane dimension 100 mm x 250 mm Thickness 50 mm JIS standard / SUS316 plate material Cutting speed: 200 m / min. ,
Cutting depth: 3 mm,
Table feed per blade: 0.3 mm / tooth,
Cutting time: 2 minutes,
Stainless steel dry high-speed milling test under the following conditions (referred to as cutting condition 1) (normal cutting speed and table feed are 150 m / min and 0.2 mm / rev., Respectively),
Work material: Plane size 100 mm × 250 mm JIS / SCM440 plate material with a thickness of 50 mm Cutting speed: 250 m / min. ,
Cutting depth: 3 mm,
Table feed per blade: 0.3 mm / tooth,
Cutting time: 2 minutes,
Dry high-speed milling test of alloy steel under the following conditions (referred to as cutting condition 2) (normal cutting speed and table feed are 160 m / min and 0.2 mm / rev., Respectively),
In each cutting test, the flank wear width of the cutting edge was measured.
The measurement results are shown in Table 6.

From Tables 4 and 6, according to the inserts 1 to 14 of the present invention, the crystal grains having a grain size of 10 to 100 nm occupy 90% or more of the measurement area, and the surface grain of the surface is measured by an electron beam backscattering diffractometer. when measuring the crystal orientation, the whole divisions segment surrounded by the crystal interface misorientation crystal orientation of adjacent measurement points is the rotation angle of 15 degrees or more diameter 0.2~4μm is measured area 20% or more of them, that is, the presence of many 0.2 to 4 μm sections composed of strongly oriented 10 to 100 nm crystal grains, exhibiting excellent fracture resistance and toughness, It can be seen that excellent tool life is achieved even under dry intermittent high-speed cutting conditions.
On the other hand, from Tables 5 and 6, in the conventional inserts 1 to 14, the conventional Ti _1-x Si _x N layer has a small area ratio occupied by 10 to 100 nm crystal grains, and only coarse single crystal particles. Therefore, it is clear that the chipping resistance and toughness are inferior, and that the service life can be reached in a relatively short time due to chipping, chipping, etc. under dry intermittent high speed cutting conditions.

As described above, the coated tool according to the present invention has a hard coating layer (modified Ti _1-x Si _x N layer) having excellent fracture resistance and toughness. It can be used as various types of coated tools such as drills, and thereby prevents the occurrence of tool defects due to insufficient toughness, insufficient strength, etc., and exhibits excellent cutting performance over a long period of use. Therefore, it is possible to sufficiently satisfy the cost reduction and prolong the tool life.

Claims (1)

In a surface-coated cutting tool in which a hard coating layer made of a Ti _1-x Si _x N film having an average layer thickness of 0.2 to 2 μm is physically vapor-deposited on the surface of a tool base made of a tungsten carbide-based cemented carbide sintered body , X satisfies 0.05 ≦ x ≦ 0.3, and
The Ti _1-x Si _x N layer has a columnar crystal structure having a height equal to the average layer thickness, and when the crystal orientation of the surface crystal grains is measured with an electron beam backscattering diffractometer, adjacent measurements are performed. A section having a section diameter of 0.2 to 4 μm surrounded by a crystal interface in which the orientation difference of the crystal orientation with respect to a point is 15 degrees or more occupies 20% or more of the total area measured, and the Ti _{When a} crystal grain structure in a horizontal cross section having a depth of 100 nm is observed from the surface of the _1-x Si _x N layer, crystal grains having a grain size of 10 to 100 nm occupy 90% or more of the measurement area. A surface-coated cutting tool.