JP2022150860A - Surface-coated cutting tool - Google Patents

Abstract

To provide a surface-coated cutting tool which exhibits excellent crack resistance and wear resistance over a long-term use even if the surface-coated cutting tool is used for material such as a Ti-based alloy having high adhesibility to a surface coated cutting tool.SOLUTION: A surface-coated cutting tool is provided which has a tool substrate and a coating layer on a surface of the tool substrate, the coating layer has an average layer thickness of 0.5 to 5.0 μm, and when an average composition thereof is represented by the following composition formula: Ti1-xCrxBy, x satisfies 0.05 to 0.50, y satisfies 1.5 to 3.0. A columnar crystal grain of hexagonal crystal structure has an area ratio of 40% or more in a longitudinal section of the coating layer, and the columnar crystal grain of the hexagonal crystal structure has an average width W of 0.02 to 0.10 μm, and an average aspect ratio A of 2.0 to 5.0, and an average value θ of an angle between the columnar crystal grain and a perpendicular line of a surface of the tool substrate is 5 to 30 degrees.SELECTED DRAWING: Figure 1

Description

The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool).

Conventionally, there has been known a coated tool having a tool substrate made of cemented carbide or the like and having a coating layer formed on the surface of the tool substrate by a vapor deposition method. Although this coated tool has wear resistance, various proposals have been made in order to further improve this wear resistance, and proposals have also been made regarding coating layers containing metal borides.

For example, in Patent Document 1, the coating on the surface of the tool substrate via an intermediate coating is a boride of one or more elements selected from Al, Si, Cr, W, Ti, Nb, and Zr, and has a hexagonal The intermediate film is a nitride or carbonitride made of AlxMy (x + y = 100, 40 ≤ x ≤ 95, 5 ≤ y ≤ 60, M is selected from Ti, Cr, V, Nb and one or more of them), a coated tool having a cubic crystal structure on the tool substrate side and a hexagonal crystal structure on the coating side is described, and the coated tool is said to be excellent in wear resistance.

Also, for example, Patent Document 2 describes a tool having a coating layer having a TiB ₂ layer with a hardness of at least 50 GPa, said coating layer being said to have a high hardness.

JP 2012-228735 A Japanese Patent No. 6561048

The present invention has been made in view of the above circumstances and proposals. It is an object of the present invention to provide a surface-coated cutting tool that exhibits crack resistance and wear resistance over a long period of use.

A surface-coated cutting tool according to an embodiment of the present invention is
(a) having a tool substrate and a coating layer on the surface of the tool substrate;
(b) The coating layer has an average layer thickness of 0.5 to 5.0 μm, and the average composition is represented by the composition formula: Ti _1-x Cr _x B _y , where x is 0.05 to 0. .50, y satisfies 1.5 to 3.0,
(c) columnar crystal grains having a hexagonal crystal structure occupy an area ratio of 40% or more in the vertical cross section of the coating layer;
(d) The columnar crystal grains of the hexagonal crystal structure have an average width W of 0.02 to 0.10 μm and an average aspect ratio A of 2.0 to 5.0, and The average value θ of the angles formed with the perpendicular is 5 to 30 degrees.

According to the above, even when a material with high adhesion to a surface-coated cutting tool such as a Ti-based alloy is used for cutting, excellent crack resistance and wear resistance are exhibited over a long period of use. do.

Fig. 3 is an explanatory diagram of the maximum projected length (Ti) parallel to the surface of the tool base and the maximum projected length (Vi) parallel to the normal to the surface of the tool base in columnar crystal grains (i) having a hexagonal structure. FIG. 4 is an explanatory diagram of the angle (θi) formed by a columnar crystal grain (i) having a hexagonal crystal structure and the normal to the surface of the tool base, and the length (Hi) of the crystal grain. FIG. 4 is an explanatory diagram of the grain width (Wi) in columnar grains (i) having a hexagonal crystal structure.

The inventor of the present invention has extensively studied a composite boride of Ti and Cr (hereinafter sometimes referred to as "TiCrB"). As a result, TiCrB, which is Ti boride (TiB ₂ ) with the addition of Cr, which has relatively low reactivity to Ti-based alloys, maintains the hexagonal crystal structure of TiB ₂ and does not impair its wear resistance. The inventors have found that the welding resistance can be improved. In addition, since TiCrB has a hexagonal columnar crystal structure, it is possible to reduce the size of the fracture when the coating layer breaks, so large-scale fracture is suppressed and excellent performance is achieved in cutting Ti-based alloys. It was also found to be expressed.

A surface-coated cutting tool according to an embodiment of the present invention will be described below. In the present specification and claims, when a numerical range is expressed as "A to B" (both A and B are numerical values), the range includes the numerical values of the upper limit (B) and the lower limit (A). , and the units of the upper limit (B) and the lower limit (A) are the same. Also, the numerical values include tolerances.

In addition, in the present specification and claims, the surface of the tool base refers to the following.
That is, when the tool base has a flat surface like an insert, the longitudinal section (in the case of an insert, a cross section perpendicular to the tool base when the surface of the tool base is considered to be a plane while ignoring the unevenness of the surface of the tool base) Elemental mapping using energy dispersive X-ray spectroscopy (EDS) is performed in a cross section perpendicular to the shaft for a shaft tool), and a known image for the obtained elemental map The treatment defines the interface between the coating layer (if there is a lower layer described below, the lower layer is used in place of the coating layer) and the tool substrate, and the roughness of the interface between the coating layer and the tool substrate thus obtained is determined. Arithmetically determine the mean line for the curve and use this as the surface of the tool base. The direction perpendicular to the average line is defined as the direction perpendicular to the tool substrate (layer thickness direction).

Also, even if the tool base has a curved surface such as a drill or an end mill, if the tool diameter is sufficiently large relative to the thickness of the coating layer, the distance between the coating layer and the tool base in the measurement area will increase. Since the interface is substantially planar, the surface of the tool substrate can be determined in a similar manner.

That is, for example, in the case of drills and end mills, elemental mapping is performed using EDS in a longitudinal section of the coating layer perpendicular to the axial direction, and the obtained elemental map is subjected to known image processing. The interface between the layer and the tool substrate is defined, and the mean line is arithmetically obtained for the roughness curve of the interface between the coating layer and the tool substrate thus obtained, and this is used as the surface of the tool substrate. The direction perpendicular to the average line is defined as the direction perpendicular to the tool substrate (layer thickness direction).

1. Coating Layer (1) Average Layer Thickness The average layer thickness of the coating layer is preferably 0.5 to 5.0 μm. The reason for this is that if the average layer thickness is less than 0.5 μm, it is difficult to exhibit wear resistance and chipping resistance over a long period of time. This is because the layer tends to peel off from the tool substrate, and chipping tends to occur.
More preferably, the average layer thickness of the coating layer is 0.5 to 3.0 μm.

In addition, the average layer thickness of the coating layer can be obtained by, for example, using a focused ion beam system (FIB), a cross section polisher (CP), or the like, for the hard coating layer at any position. A sample for observation was prepared by cutting along the plane, and the longitudinal section was observed using a scanning electron microscope (SEM), and the layer thickness measurement results at multiple locations (e.g., 5 locations) were averaged. It is a thing.

(2) Average composition The average composition of the coating layer is represented by the composition formula: Ti _1-x Cr _x B _y , where x is 0.05 to 0.50 and y is 1.5 to 3.0. preferably.
The reason is as follows.

When x is less than 0.05, the coating layer cannot exhibit sufficient adhesion resistance, while when it exceeds 0.50, the hardness of the coating layer becomes insufficient.
If y is less than 1.5, the coating layer cannot exhibit sufficient adhesion resistance, while if it exceeds 3.0, the hexagonal crystal structure will not be formed, and the hardness of the coating layer will be insufficient, resulting in poor resistance. Chipping resistance is reduced.
More preferably, x is 0.10 to 0.35 and y is 1.7 to 2.5.

The average composition is obtained by irradiating the surface of the coating layer with an electron probe microanalyzer (EPMA) or 5 points in the longitudinal section of the coating layer at any position, and obtaining from each point. The content of each element is quantified by analyzing characteristic X-rays corresponding to the elements forming the coated layer, and the result is calculated by arithmetic mean.

(3) Hexagonal columnar crystal grains (3-1) Area ratio Columnar crystal grains with a hexagonal crystal structure (sometimes referred to as hexagonal columnar crystal grains) have an area ratio of 40% or more in the longitudinal section of the coating layer. is preferred. If the area ratio is less than 40%, the coating layer does not have the wear resistance and chipping resistance necessary to achieve the aforementioned objectives. A higher area ratio is preferable, and the upper limit is not limited and may be 100%, that is, all crystal grains may be columnar crystal grains having a hexagonal crystal structure.
Here, the columnar crystal grains having a hexagonal crystal structure refer to those having an aspect ratio exceeding 1, which will be described later.

(3-2) Crystal Width and Aspect Ratio The average crystal width of hexagonal columnar crystal grains is preferably 0.02 to 0.10 μm. The reason for this is that if the grain size is less than 0.02 μm, the grain size is small, the grain tends to come off during cutting, and wear resistance is poor. This is because the fracture size becomes large when it occurs, resulting in poor wear resistance.

Also, the average aspect ratio is preferably 2.0 to 5.0. The reason for this is that if it is less than 2.0, the number of granular crystal grains is larger than that of columnar crystal grains, resulting in poor wear resistance. This is because the size of the fracture becomes large when the fracture occurs, resulting in poor wear resistance.

(3-3) Angle Formed with Normal to Surface of Tool Substrate It is preferable that the average angle θ formed by the columnar crystal grains of the hexagonal crystal structure and the normal to the surface of the tool substrate is 5 to 30 degrees. The reason for this is that when the average value θ of the angles is within this range, crystal grains are less likely to drop off during cutting, wear is suppressed, and excellent wear resistance is exhibited.

(3-4) Measurement method The area ratio, crystal width and aspect ratio, and the angle formed with the normal to the surface of the tool substrate are measured as follows after defining the grain boundaries.

[1] Defining grain boundaries Automatic crystal orientation mapping (ACOM) using a transmission electron microscope (TEM)-Analysis using TEM was performed to determine the crystal grains of the hexagonal columnar grains i. define boundaries.
Here, i is a number for distinguishing hexagonal columnar crystal grains, i = 1 to n, n is the total number of hexagonal columnar crystal grains to be measured, and the value is 20 or more. Choose.

[2] Measurement of Size of Hexagonal Columnar Grain i After defining the grain boundary and identifying the hexagonal columnar grain i, the size of the hexagonal columnar grain is measured.
That is, as shown in FIG. 1, for hexagonal columnar grains i,
1) maximum vertical projection length Vi
2) maximum horizontal projection length Li
3) Maximum horizontal transverse length Ti
to measure.

here,
The maximum vertical projection length Vi in 1) above is the length projected in the direction parallel to the surface of the tool base when a parallel light beam is applied to the hexagonal columnar grains i from a direction parallel to the surface of the tool substrate. Then, when a plurality of straight lines perpendicular to the surface of the tool substrate intersect the hexagonal columnar grains i at two points, one close to the tool substrate and one far from the tool substrate, The length in the direction perpendicular to the surface of the tool base between the point closest to the tool base and the point furthest from the tool base among the points farthest from the tool base,
The maximum horizontal projection length Li in 2) above is the length projected in the direction perpendicular to the hexagonal columnar grains i when parallel rays are applied from the direction perpendicular to the surface of the tool substrate. Then, when a plurality of straight lines parallel to the surface of the tool base intersect the hexagonal columnar grains i at two points on the left side and right side of the tool base, the most is the length in the direction parallel to the surface of the tool base between the point on the left and the point on the rightmost of the points on the right,
The maximum horizontal transverse length Ti in 3) above is the maximum length of a straight line parallel to the surface of the tool substrate that traverses the hexagonal columnar grains i.

[3] Conversion of measured length From 1) maximum vertical projection length Vi, 2) maximum horizontal projection length Li, and 3) maximum horizontal transverse length Ti measured in "2" above,
4) Length Hi of hexagonal columnar grains i
5) Width Wi of hexagonal columnar grain i
Convert to

That is, as shown in FIG. 2, a quadrangle whose side lengths are the maximum vertical projection length Vi and the maximum horizontal projection length Li is drawn, and the angle θi between the diagonal and the side giving the maximum vertical projection length is seeking
4) The length Hi of the hexagonal columnar grains is
Hexagonal columnar grain length Hi = Vi/cos θi
Calculated by

Also, as shown in FIG. 3, the length of the hypotenuse is the maximum horizontal transverse length Ti, and a right-angled triangle having the angle θi is drawn,
5) The width Wi of the hexagonal columnar grains i is
Width Wi of hexagonal columnar grain i = Ti x cos θi
, respectively.

[4] Average crystal width and average aspect ratio

Then, the aspect ratio (Ai) of the hexagonal columnar crystal grain i is defined as Ai=Hi/Wi, and the average crystal width (W), Calculate the average aspect ratio (A) and the θi average value (θ).

The average crystal width (W) is obtained by [Equation 1].

Also, the average aspect ratio A is obtained by [Equation 2] from the aspect ratio (Ai=Hi/Wi) and the area (Si=Hi×Wi).

Furthermore, the average value (θ) of the angle θi formed with the normal to the surface of the tool base is obtained from [Equation 3].

2. Other layer (lower layer)
As a hard coating layer, the hard coating layer containing the composite boride layer of Ti and Cr of the present embodiment is sufficiently excellent even when cutting a material having high adhesion to a cutting tool such as a Ti-based alloy. In addition to the hard coating layer, Ti carbide layer, nitride layer, carbonitride layer, carbonate layer and carbonitride oxide layer are provided. Adjacent to the tool substrate, a lower layer consisting of one or more layers of which contains a Ti compound (not limited to a stoichiometric compound) layer having a total average layer thickness of 0.1 to 2.0 μm When provided, this layer enhances the adhesion between the coating layer and the tool substrate, and can exhibit even better chipping resistance and thermal crack resistance.

3. Tool Substrate (1) Material Any material can be used as long as it is a conventionally known material for a tool substrate, as long as it does not interfere with the achievement of the above-mentioned object. For example, cemented carbide (WC-based cemented carbide, containing Co in addition to WC, and further containing carbonitrides such as Ti, Ta, Nb, etc.), cermet (TiC, TiN, TiCN, etc. as a main component, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cBN sintered body, or diamond sintered body. .

(2) Shape The shape of the tool base is not particularly limited as long as it is a shape used as a cutting tool, examples of which include the shape of an insert, the shape of a drill, and the shape of an end mill.

4. Manufacturing Method A sputtering method or a High Power Impulse Magnetron Sputtering (HiPIMS) method, which facilitates suppression of mixed droplets, can be used.

EXAMPLES Next, examples will be described, but the present invention is not limited to these examples.

As raw material powders, WC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder, all having an average particle size of 1 to 3 μm, were prepared. After blending in the formulation composition, wet-mixing in a ball mill for 72 hours, drying, press molding into a compact at a pressure of 100 MPa, and holding the compact at a temperature of 1400 ° C. in a vacuum of 6 Pa for 1 hour. to prepare a round bar sintered body for forming a carbide substrate with a diameter of 4 mm, and further from the round bar sintered body, by grinding, the diameter of the cutting edge × length is 2 mm × Tool substrates (end mills) 1 and 2 made of WC-based cemented carbide and having a 4-flute square shape with a helix angle of 40 degrees and 4 mm were manufactured.

(a) Each of the tool substrates 1 and 2 is ultrasonically cleaned in acetone, dried, and placed radially at a predetermined distance from the central axis on a rotary table in a high-power pulse sputtering apparatus. On the other hand, in the high-power pulse sputtering apparatus, plate-shaped targets were installed at four locations facing each other across the rotary table. That is, two sintered targets of Ti, Cr, and boron facing each other and two Ti metal targets facing each other were arranged.

(b) While the inside of the device is evacuated and maintained at a vacuum of 0.1 Pa or less, the inside of the device is heated with a heater to 500 ° C., and then a direct current of −200 V is applied to the tool base that revolves while rotating on the rotary table. After applying a bias voltage, an argon (hereinafter referred to as Ar) gas is introduced into the apparatus as a discharge/sputtering gas to create an atmosphere of 2.0 Pa. Furthermore, Ar ions were excited by passing a current of 40 A through a tungsten filament provided in the apparatus, and the tool substrate was subjected to Ar bombardment treatment for 1 hour.

(c) Ar gas as a sputtering gas and nitrogen gas as a reaction gas are introduced into the apparatus to create a reaction atmosphere of 0.6 Pa, and a high power is applied to the Ti target under predetermined pulse sputtering conditions shown in Table 2. Pulse sputtering was performed to form a TiN layer having an average layer thickness shown in Table 2 on the surface of the tool base as a lower layer of the hard coating layer. However, not all tool substrates were formed with a bottom layer.

(d) Subsequently, nitrogen gas among the gases to be introduced into the device is closed, the atmosphere in the device is set to 0.5 Pa, nitrogen gas is sufficiently discharged, and after the atmosphere in the device becomes Ar gas only, Ti A sintered body target composed of , Cr, and boron is subjected to high-power pulse sputtering under the predetermined pulse sputtering conditions shown in Table 2 for a time corresponding to the layer thickness, and the coated end mill of the present invention shown in Table 3 (hereinafter referred to as an example ) 1 to 10 were manufactured.

For the purpose of comparison, a lower layer and a hard coating layer were formed on these tool substrates 1 and 2 under the conditions shown in Table 4 by the procedures (a) to (d) above, and the comparative coating shown in Table 5 was obtained. End mills (hereinafter referred to as comparative examples) 1 to 6 were manufactured. However, not all tool substrates were formed with a bottom layer.

Next, the following cutting tests were performed on Examples 1 to 10 and Comparative Examples 1 to 6, and the results are shown in Table 6.

Work material: Ti-based alloy (mass%, Ti-6%Al-4%V alloy) block material (width 190mm x 250mm)
Cutting speed: 80m/min
Rotation speed: 12732min ^-1
Feeding speed: 1019mm/min
Axial depth of cut (ap): 2.0mm
Radial depth of cut (ae): 0.2mm
End mill blade outer diameter: 2mm

After cutting to a cutting length of 150 m (corresponding to a cutting time of 147 minutes), the flank wear width was measured and the presence or absence of chipping was observed.

As is clear from the results shown in Table 6, Examples 1 to 10 have excellent wear resistance and adhesion resistance even in the wet cutting test of the Ti-based alloy.
On the other hand, in Comparative Examples 1 to 6, chipping occurred and the tool life was short.

Claims (1)

A surface-coated cutting tool having a tool substrate and a coating layer on the surface of the tool substrate,
The coating layer has an average layer thickness of 0.5 to 5.0 μm, and its average composition is represented by the composition formula: Ti _1-x Cr _x B _y , where x is 0.05 to 0.50, y satisfies 1.5 to 3.0,
Columnar crystal grains with a hexagonal crystal structure have an area ratio of 40% or more in the longitudinal section of the coating layer,
The columnar crystal grains of the hexagonal crystal structure have an average width W of 0.02 to 0.10 μm and an average aspect ratio A of 2.0 to 5.0. The average value θ of the angles formed is 5 to 30 degrees,
A surface-coated cutting tool characterized by:

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