JP2018161736A - Surface-coated cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-coated cutting tool exerting excellent defect resistance and wear resistance in a high-speed intermittent cutting work.SOLUTION: There is provided a surface-coated cutting tool in which a hard coating layer including at least a TiAlN layer having an average thickness of 0.5-10.0 μm is provided on the surface of a tool base substance. The cutting tool has the following characteristics (a) to (d): (a) the TiAlN layer has an average composition satisfying 0.10≤x≤0.35 (x is an atomic ratio) when representing the compositional formula thereof by (TiAl)N; (b) in the longitudinal section of the TiAlN layer, the layer includes the fine crystal grain whose crystal grain width measured in a direction parallel to the surface of the tool base substance is 30 to 100 nm, and does not include the coarse crystal grains having the grain width wider than 100 nm; (c) in the longitudinal section of the layer, the area ratio occupied by the fine crystal grain is 10 to 70 area%; and (d) in the longitudinal section of the layer, the area ratio occupied by the fine crystal grain in which the angle made by a normal line of the surface of the tool base substance and a normal line of (001) of the fine crystal grain having the cubic structure is 20 degrees or less, is 10 area% or more.SELECTED DRAWING: Figure 3

Description

  The present invention provides a surface-coated cutting tool (hereinafter referred to as a coated coating tool) that exhibits excellent chipping resistance and wear resistance in a high-speed intermittent cutting process such as alloy steel, and exhibits excellent cutting performance over a long period of use. Tool).

In general, as a coated tool, for throwing inserts that can be used detachably attached to the tip of a cutting tool for turning and planing of various materials such as steel and cast iron, and for drilling and cutting the work material Known drills and miniature drills, end mills used for chamfering and grooving, shoulder processing, etc. of the work material, solid hob, pinion cutter used for gear cutting of the tooth profile of the work material, etc. Yes.
Many proposals have been made for the purpose of improving the cutting performance of the coated tool.

For example, as shown in Patent Document 1, a coated tool including a coating including a refractory layer deposited by physical vapor deposition on the surface of a tool base, wherein the refractory layer is M _1-x Al _x N (wherein X ≧ 0.68, and M is Ti, Cr or Zr), and the refractory layer contains a cubic crystal phase and has a hardness of at least 25 GPa, high hardness and low residual stress Abrasion-resistant coated tools have been proposed.

Further, in Patent Document 2, in a coated tool in which a hard coating layer composed of a TiAlN layer is coated on the surface of a tool base, the hard coating layer has an Al maximum content point (Ti minimum content point) along the layer thickness direction. Al lowest content points (Ti highest content points) are alternately present at predetermined intervals, and the Al highest content point to the Al lowest content point, the Al lowest content point to the Al highest content point Al ( Ti) It has a component concentration distribution structure in which the content changes continuously, and the Al highest content point is the composition formula: (Ti _1-X Al _X ) N (wherein the atomic ratio, X is 0. 70 to 0.95), and the above-mentioned lowest Al content point is a composition formula: (Ti _1-Y Al _Y ) N (wherein Y represents 0.40 to 0.65 in atomic ratio), respectively. Satisfied and adjacent Al highest content point and Al lowest Distance Yu points, coated tool having excellent wear resistance is 0.01~0.1μm have been proposed.

Japanese Patent Laying-Open No. 2015-36189 JP 2003-211304 A

  In recent years, the performance of cutting machines has been dramatically improved, while there is a strong demand for labor saving, energy saving, and cost reduction for cutting, and as a result, cutting has become a trend toward higher speed and higher efficiency. However, in the above-mentioned conventional coated tool, when this is used for cutting under normal cutting conditions such as steel and cast iron, no particular problem occurs. Crack generation / propagation cannot be suppressed when used for cutting that involves high heat generation, such as high-speed interrupted cutting, and that imposes an impact and intermittent high load on the cutting edge. Therefore, defects are likely to occur and the progress of wear is promoted, so that the service life is reached in a relatively short time.

For example, in the conventional coated tool shown in Patent Document 1, a TiAlN layer which is one form of M _1-x Al _x N is a layer having high hardness and excellent wear resistance, and the higher the Al content, the more resistant it is. Although it is excellent in wearability, on the other hand, there is a problem in that fracture resistance is lowered because lattice strain increases.
Moreover, in the conventional coated tool shown by patent document 2, although high temperature hardness, heat resistance, and toughness can be made compatible by forming a composition change in the layer thickness direction, in the layer formed in the layer thickness direction There is a problem that the generation and propagation of cracks in the direction perpendicular to the layer thickness cannot be sufficiently prevented due to the anisotropy.

  In view of the above, the present inventors, from the above-mentioned viewpoint, are accompanied by high heat generation such as high-speed intermittent cutting of alloy steel and the like, and a cutting operation in which a shocking and intermittent high load acts on the cutting blade. As a result of conducting research focusing on the component composition, crystal structure and layer structure of the hard coating layer in order to develop a coated tool that can achieve both fracture resistance and wear resistance with excellent hard coating layer under the conditions, The following findings were obtained.

  That is, the inventor of the present invention provides a coated tool in which a hard coating layer including at least a composite nitride of Ti and Al (hereinafter sometimes referred to as “TiAlN”) layer is provided on the surface of the tool base. The composition ratio of the total amount of Ti and Al is relatively high, thereby ensuring the wear resistance of the hard coating layer as a whole, and the TiAlN layer is composed of ultrafine crystal grains and fine crystal grains. The area ratio of the fine crystal grains is 10 to 70 area%, the crystal grain width does not include coarse crystal grains larger than 100 nm, and the normal line of the (001) plane of the fine crystal grains and the tool base surface While improving the wear resistance of the fine crystal grains, the ratio of the area occupied by the fine crystal grains whose angle to the normal line is 20 degrees or less is 10 area% or more of the total area of the fine crystal grains. , Ultrafine grain Since the impact at the time of cutting can be mitigated with crystal grains, the coated tool of the present invention is accompanied by high heat generation, and high-speed interrupted cutting in which impact and intermittent high loads act on the cutting blade. Under the conditions, it is possible to achieve both excellent fracture resistance and wear resistance.

This invention has been made based on the above findings,
“At least a composite nitride layer of Ti and Al having an average layer thickness of 0.5 to 10.0 μm is formed on the surface of a tool base made of any one of a WC-based cemented carbide, a TiCN-based cermet, and a cubic boron nitride sintered body. In a surface-coated cutting tool provided with a hard coating layer containing,
(A) The composite nitride layer of Ti and Al has the composition
Composition formula: (Ti _x Al _1-x ) N
Represented by 0.10 ≦ x ≦ 0.35 (where x is an atomic ratio),
(B) In the longitudinal section of the composite nitride layer of Ti and Al, fine grain having a crystal grain width measured in a direction parallel to the surface of the tool base is 30 to 100 nm, and the crystal grain width is larger than 100 nm Does not contain coarse grains
(C) In the longitudinal section of the composite nitride layer of Ti and Al, the area ratio of the fine crystal grains in the longitudinal section is 10 to 70 area%,
(D) In the longitudinal section of the composite nitride layer of Ti and Al, the angle formed by the normal of the tool base surface and the (001) normal of the fine crystal grains having a cubic structure is 20 degrees or less. The surface-coated cutting tool characterized in that the area ratio of the fine crystal grains having a crystal structure to the total area of the fine crystal grains in the longitudinal section is 10 area% or more. "
It is characterized by.

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

Average thickness of the TiAlN layer:
The hard coating layer includes at least a TiAlN layer, but if the average layer thickness of the TiAlN layer is less than 0.5 μm, the effect of improving wear resistance imparted by the TiAlN layer cannot be sufficiently obtained, while the average layer thickness is If the thickness exceeds 10.0 μm, the strain in the TiAlN layer increases and the layer itself tends to break. Therefore, the average thickness of the TiAlN layer is set to 0.5 to 10.0 μm.

Average composition of TiAlN layer:
TiAlN layer,
Composition formula: (Ti _x Al _1-x ) N
It is necessary to have an average composition that satisfies 0.10 ≦ x ≦ 0.35 (where x is an atomic ratio).
When x representing the average composition of the Ti component is less than 0.10, TiAlN crystal grains having a hexagonal structure are easily formed, the hardness of the TiAlN layer is lowered, and sufficient wear resistance cannot be obtained.
On the other hand, when x representing the average composition of the Ti component exceeds 0.35, the composition ratio of the Al component decreases, so that the high-temperature hardness and high-temperature oxidation resistance of the TiAlN layer decrease.
Accordingly, the average composition x of the Ti component is 0.10 ≦ x ≦ 0.35.
In the above composition formula, the value of N / (Ti + Al + N) does not necessarily need to be a stoichiometric ratio of 0.5. Carbon or carbon that is inevitably detected due to the influence of contamination on the surface of the tool base or the like. Excluding elements such as oxygen, the atomic ratio of the content ratio of Ti, Al, and N is quantified, and the atomic ratio of the content ratio of N to the total atomic ratio of the content ratios of Ti, Al, and N is 0.45 or more. In the range of 65 or less, the same effect can be obtained in the TiAlN layer of the present invention, and there is no particular problem.

Fine crystal grains in the TiAlN layer:
In the TiAlN layer of the present invention, the TiAlN crystal grains measured in a direction parallel to the tool substrate surface include fine crystal grains having a width of 30 to 100 nm and no coarse crystal grains having a crystal grain width of more than 100 nm, The area ratio of the fine crystal grains in the vertical section of the TiAlN layer is 10 to 70 area%.
Here, the reason why the crystal grain width of the fine crystal grain is set to 30 to 100 nm and the coarse crystal grain having a crystal grain width larger than 100 nm is not included is as follows.
When excessively coarse TiAlN crystal grains with a grain width exceeding 100 nm are present, the grain boundary length in the entire TiAlN layer is shortened, so that it is difficult to disperse the impact applied during cutting, resulting in a reduction in fracture resistance. To do.
On the other hand, since the grain boundaries increase when the crystal grain width of the fine crystal grains is less than 30 nm, the probability of contact between the work material and the grain boundary portion at the time of the cutting process is increased, so that the grains are likely to fall apart. This is because the wear resistance cannot be ensured by the fine crystal grains.
The reason why the area ratio of the fine crystal grains is set to 10 to 70 area% is as follows.
When the area ratio of the fine crystal grains is less than 10 area%, the ratio of the ultrafine crystal grains in the TiAlN layer increases and the grain boundaries increase. Breaking easily occurs and wear resistance decreases.
On the other hand, when the area ratio of the fine crystal grains exceeds 70 area%, the fracture resistance decreases due to the reduction of the ultrafine crystal grains that play a role of dispersing the impact during the cutting process.

Further, in the present invention, when measured in the longitudinal section of the TiAlN layer, a cube whose angle formed by the normal line of the tool base surface and the (001) normal line of the fine crystal grains having a cubic structure is 20 degrees or less. The area ratio of the fine crystal grains having a crystal structure to the total area of the fine crystal grains in the longitudinal section is 10 area% or more (including the case of 100 area%).
This is because, among the fine crystal grains having a (001) orientation having excellent wear resistance, a cubic crystal having a (001) orientation such that the angle formed with the normal to the tool substrate surface is 20 degrees or less. Since there are many fine crystal grains with a structure (10 area% or more), when the surface of the TiAlN crystal grains comes into contact with the work material during cutting, any TiAlN crystal grains are uniformly cut in the same direction. This is because the occurrence of uneven wear is suppressed, and as a result, the effect of wear resistance of the fine crystal grains having a cubic structure having the (001) orientation can be improved.
Temporarily, the longitudinal cross section of the fine crystal grains having a cubic structure in which the angle formed by the normal line of the tool base surface and the normal line of (001) of the fine crystal grains having a cubic structure is 20 degrees or less. When the area ratio of the total area of the fine crystal grains is less than 10 area%, since each crystal grain is cut in a different direction at the time of cutting, uneven wear occurs as the cutting progresses, This leads to a decrease in wear resistance.

The hard coating layer of the present invention can be configured as a single layer structure of the TiAlN layer described above,
In the hard coating layer configured as a laminated structure of two or more layers, the TiAlN layer can be formed as at least one of the layers constituting the laminated structure.

Calculation method of crystal grain width, fine crystal grain area ratio, fine crystal grain (001) normal and tool substrate surface normal, and frequency distribution:
The crystal grain width, crystal structure, area ratio, and crystal orientation of the TiAlN layer of the present invention are measured with respect to the tool substrate surface using, for example, a crystal orientation analyzer attached to a transmission electron microscope. It can obtain | require by observing and measuring the longitudinal cross-section of the hard coating layer to contain.
In the present invention, the “longitudinal section of the hard coating layer” refers to a cross section perpendicular to the interface between the hard coating layer and the tool base (tool base surface).
The method of observing the longitudinal section of the hard coating layer including the TiAlN layer with a transmission electron microscope is as follows. First, a longitudinal section of a hard coating layer including a TiAlN layer is cut out, and then a section polished to a thickness (30 nm) or less comparable to the crystal grain size is set, and an electron beam accelerated to 200 kV is applied to the surface of the section. Observation is performed by irradiating the surface (that is, the surface corresponding to the hard coating layer including the TiAlN layer).
Next, the method for determining the analysis range of the crystal grain width, crystal structure, area ratio, and crystal orientation with respect to the tool base surface from the observation result of the longitudinal section of the hard coating layer including the TiAlN layer is as follows.
First, two points on the interface between the hard coating layer and the tool base in the observation image of the longitudinal section of the hard coating layer are arbitrarily selected. At that time, the length connecting the two points with a line segment is selected to be 1000 nm. The analysis range of the crystal orientation is 1000 nm in a direction parallel to the line segment (this direction is hereinafter defined as “the lateral direction of the analysis range”), and 400 nm in the vertical direction (hereinafter, this direction is defined as “the longitudinal direction of the analysis range”). )) Rectangle range. At that time, all the above ranges include only the longitudinal section of the TiAlN layer (not including the tool base and the hard coating layer other than the TiAlN layer).
An analysis method for obtaining crystal orientation map data in the measurement range is as follows. While irradiating the surface of the slice with an electron beam inclined at 0.5 to 1.0 degree with respect to the normal direction of the surface of the slice, the electron beam is irradiated at an arbitrary beam diameter and interval. Scan and continuously capture the electron diffraction pattern and analyze the crystal orientation of each measurement point. The acquisition conditions of the diffraction pattern used in this measurement are a camera length of 20 cm, a beam size of 2.2 nm, and a measurement step of 2.0 nm.
An analysis method for discriminating individual crystal grains from the obtained electron beam diffraction pattern is as follows. First, when the crystal orientations of the adjacent points of the measurement point are separated by 5 degrees or more, it is determined that the measurement point belongs to the grain boundary. Next, the measurement points belonging to the grain boundary are connected by a line segment, thereby defining a portion surrounded by the line segment as a crystal grain. However, when this line segment is in contact with the TiAlN layer surface, the surface where the TiAlN layer and the hard coating layer are in contact, or the surface of the tool substrate, it is regarded as the grain boundary of each surface or interface. Then, the crystal grain width is measured from the distance between the grain boundary in the direction parallel to the lateral direction of the analysis range, and the crystal grain having a crystal grain width of 30 nm or more and 100 nm or less is defined as a fine grain part. Further, the area ratio of the fine crystal grains is calculated by dividing the total number of measurement points included in the fine grain part by the total number of measurement points of the crystal grains. Since the area occupied by one measurement point is constant, the area ratio is obtained from the ratio of the number of measurement points.
A method of calculating the angle formed by the normal of the tool base surface and the (001) normal of the fine crystal grains having a cubic structure and the calculation of the angular number distribution will be described. First, using the crystal orientation analyzer, the (001) plane is a crystal plane at a measurement point included in the fine grain part with respect to the normal L1 of the tool base surface 1a (direction perpendicular to the tool base surface 1a). An inclination angle (see FIGS. 1A and 1B) formed by the normal L2 is measured. Among the inclination angles, the inclination angles within the range of 0 to 20 degrees (within the range from 0 degrees in FIG. 1A to 20 degrees in FIG. 1B) with respect to the normal direction L1 are divided every 5 degrees pitch. The percentages present in each category. In addition, about 20 degree | times or more, it does not classify | categorize for every pitch of 5 degree | times, but totals the thing of 20 degree | times or more as one division. The result is represented by a tilt angle number distribution graph (FIG. 2) in which the horizontal axis is the tilt angle section and the vertical axis is the ratio.
The calculation method of the calculation method of the crystal grain width, the area ratio of the fine crystal grains, the angle formed with the (001) normal of the fine crystal grains, and the angular number distribution has been described in one analysis range. When performing analysis, five analysis ranges are set, and an average value is calculated.
Note that the area ratio of the ultrafine crystal grains (the crystal grain width is less than 30 nm) and the coarse crystal grains (the crystal grain width is larger than 100 nm) is also calculated by the same method as the area ratio of the fine crystal grains.

Method for forming TiAlN layer:
The TiAlN layer of the present invention is formed, for example, by simultaneous discharge of sputtering and arc ion plating using a physical vapor deposition apparatus (hereinafter referred to as “SP / AIP apparatus”) provided with a sputtering apparatus and an arc ion plating apparatus. be able to.
3A and 3B are schematic views of an SP / AIP apparatus for forming a TiAlN layer of the present invention.
A Ti-Al alloy cathode electrode (target) having a predetermined composition for arc ion plating is disposed opposite to the opposing wall surfaces of the SP / AIP apparatus shown in FIGS. 3 (a) and 3 (b). A metal Ti cathode electrode (target) for sputtering is disposed opposite to the opposite wall surfaces of the AIP apparatus, and a Ti-Al alloy cathode electrode (target) and a metal Ti are placed on a table provided in the center of the apparatus. The tool base is placed at positions (for example, four places as shown in FIG. 3A) that are substantially equidistant from the cathode electrode (target).
Next, while rotating the tool base on the table, the tool base is heated to a predetermined temperature range, a reaction gas is introduced into the apparatus, and sputtering and arc ion plating are performed simultaneously, thereby forming the TiAlN layer of the present invention. A film can be formed.
In this case, sputtering conditions and arc ion plating conditions are generally as follows.
Sputtering conditions Sputtering target (cathode electrode): metal Ti
Sputtering current (A): 6-7
Arc ion plating conditions Ti composition (atomic%) of TiAl alloy target (cathode electrode): 5 to 30
Arc current (A): 100-110
Common conditions N ₂ gas pressure (Pa): 2 to 2.5
Tool substrate temperature (° C.): 450 to 500
Bias voltage (-V): 300-320

  In the coated tool of the present invention, the hard coating layer includes at least a TiAlN layer, the TiAlN layer includes fine crystal grains having a crystal grain width of 30 to 100 nm, and includes coarse crystal grains having a crystal grain width of greater than 100 nm. The area ratio of the fine crystal grains in the longitudinal section of the TiAlN layer is 10 to 70 area%. Further, (001) normal line of the fine crystal grains having a cubic structure and the normal line of the tool base surface Since the fine crystal grains having a cubic structure with an angle of 20 degrees or less occupy 10% by area or more of the total area of the fine crystal grains in the longitudinal section, wear resistance is achieved by the presence of the fine crystal grains. On the other hand, since the ultrafine crystal grains can alleviate the impact during cutting, the coated tool of the present invention is accompanied by high heat generation, and also has an impact and intermittent high on the cutting edge. Load acts Fast intermittent cutting processing conditions, it is possible to achieve both excellent chipping resistance and wear resistance.

Schematic diagram showing a case where the inclination angle formed by the normal of the (001) plane, which is the crystal plane of the fine crystal grains, with respect to the normal of the tool base surface (direction perpendicular to the tool base surface in the cross-section polished surface) is 0 degree. is there. FIG. 6 is a schematic diagram showing a case where the inclination angle formed by the normal line of the (001) plane, which is the crystal plane of the fine crystal grains, with respect to the normal line of the tool base surface (direction perpendicular to the tool base surface in the cross-section polished surface) is 20 degrees. is there. It is a graph which shows an example of inclination-angle number distribution which the normal line of a tool base | substrate surface and the normal line of (001) of the fine crystal grain which has a cubic crystal structure make. The schematic diagram of the physical vapor deposition apparatus (SP / AIP apparatus) which used together the sputtering apparatus used for film-forming the TiAlN layer of this invention coated tool and an arc ion plating apparatus is shown, (a) is a schematic plan view, (b) ) Is a schematic front view.

Next, the coated tool of the present invention will be specifically described with reference to examples.
As a specific description, a coated tool using a WC-based cemented carbide as a tool base will be described, but the same applies to a coated tool using a TiCN-based cermet or a cubic boron nitride sintered body as a tool base.

As raw material powders, Co powder, TiC powder, VC powder, TaC powder, NbC powder, Cr ₂ C ₃ powder, and WC powder, all having an average particle diameter of 1 to 3 μm, were prepared. After adding the wax, mixing in a ball mill in acetone for 24 hours, drying under reduced pressure, press molding at a pressure of 100 MPa, and these compacts are in the range of 1370 to 1470 ° C. WC-based cemented carbide tool bases 1 to 3 having an ISO standard SEEN1203AFEN insert shape were manufactured by vacuum sintering under conditions of holding at a predetermined temperature for 1 hour and processing to a predetermined size.

After the tool bases 1 to 3 are ultrasonically cleaned in acetone and dried, a metal Ti cathode electrode (target) for sputtering and a Ti—Al alloy cathode electrode (target) having a predetermined composition for arc ion plating are obtained. Arranged in the arranged SP / AIP apparatus, and the arrangement position is a position away from the central axis of the table for mounting the tool base provided in the SP / AIP apparatus, and is a Ti-Al alloy cathode. The electrode (target) and the metal Ti cathode electrode (target) were arranged at substantially equal distances (for example, four places shown in FIG. 3A).
In the SP / AIP apparatus, the tool base is heated to 400 ° C. with a heater while the inside of the apparatus is evacuated and kept in vacuum, and then a DC bias voltage of −1000 V is applied to the tool base that rotates on the table. In addition, an arc current of 100 A was passed through the Ti—Al alloy cathode electrode (target) to generate an arc discharge, and the tool base surface was bombarded.
Next, nitrogen gas is introduced as a reaction gas into the apparatus to obtain the nitrogen pressure shown in Table 2, and the temperature of the tool base rotating on the table is maintained at the temperature shown in Table 2, and the bias shown in Table 2 is used. A voltage was applied to the tool base, and an arc discharge was generated by applying an arc current shown in Table 2 to a Ti—Al alloy cathode electrode (target) having a predetermined composition shown in Table 2 to perform arc ion plating.
Furthermore, simultaneously with the arc ion plating, applying the bias shown in Table 2 to the tool base and the metal Ti cathode electrode (target), and applying the current shown in Table 2 to the metal Ti cathode electrode (target), Sputtering was performed.
By carrying out sputtering and arc ion plating at the same time in the above steps, the present coated tools 1 to 10 (hereinafter referred to as the present tools 1 to 10) shown in Table 4 on which the TiAlN layer of the present invention is formed are manufactured. did.

For comparison purposes, the SP / AIP apparatus shown in FIG. 3 is used to perform bombard cleaning on each of the tool bases 1 and 2 under the same conditions as in the case of the tools 1 to 10 of the present invention. By forming the TiAlN layer only under the arc ion plating conditions, comparative example coated tools 1 to 10 (hereinafter referred to as comparative example tools 1 to 10) shown in Table 5 were produced.
For reference, a reference coated tool 1 (hereinafter referred to as Reference Example Tool 1) shown in Table 5 was manufactured by forming a TiN layer only under the sputtering conditions shown in Table 3.

For the TiAlN layers of the inventive tools 1 to 10 and the comparative example tools 1 to 10 and the TiN layer of the reference example tool 1 produced as described above, the cross section perpendicular to the tool base is observed with a plurality of fields of view using a scanning electron microscope. The average layer thickness was calculated from the average value of the point layer thicknesses.
Moreover, the average composition (atomic ratio) of Ti with respect to the total amount of Al and Ti in the TiAlN layers of the inventive tools 1 to 10 and comparative tools 1 to 10 was measured using an electron beam microprobe analyzer (EPMA). An electron beam was irradiated to the surface of the sample whose longitudinal section of the TiAlN layer was polished, and the average composition of Ti was calculated from the analysis result of the generated characteristic X-ray, and the average value of 10 points was obtained.
Tables 4 and 5 show the respective values.

Moreover, about the TiAlN layer of this invention tools 1-10 and comparative example tools 1-10, using a transmission electron microscope, the crystal grain width in a TiAlN layer, a fine crystal grain (crystal grain width: 30-100 nm), super Area ratio of fine crystal grains (grain width less than 30 nm), coarse crystal grains (greater than grain width 100 nm), crystal structure of fine crystal grains, fine crystal grains having normal line and cubic structure of tool base surface The angle formed with the normal line of (001) was calculated.
Specifically, it is as follows.
The crystal grain width is calculated as follows. First, when the crystal orientations of the adjacent points of the measurement point are separated by 5 degrees or more, it is determined that the measurement point belongs to the grain boundary. Next, the measurement points belonging to the grain boundaries were connected by line segments, and the portion surrounded by the line segments was defined as crystal grains. However, when this line segment is in contact with the surface or the interface with the substrate, it is regarded as the grain boundary of this surface or interface. And the crystal grain width was measured from the distance between the grain boundaries in the direction parallel to the lateral direction of the analysis range.
The area ratio of the fine crystal grains is a crystal grain having a crystal grain width of 30 nm or more and 100 nm or less as a fine grain part, and the total number of measurement points included in the fine grain part is divided by the total number of measurement points of the crystal grains. The area ratio of fine crystal grains was calculated. Since the area occupied by one measurement point is constant, the area ratio is obtained from the ratio of the number of measurement points. The ultrafine crystal grains have crystal grain widths of less than 30 nm, and the coarse crystal grains have crystal grains larger than 100 nm, and the area ratio was determined in the same manner as the fine crystal grains.
The crystal structure of the fine grain part was judged as cubic or hexagonal from the electron diffraction image of the fine grain part.
The angle formed between the normal of the tool base surface and the normal of (001) of the fine crystal grains having a cubic structure is relative to the normal L1 of the tool base surface 1a (direction perpendicular to the tool base surface 1a). The inclination angle (see FIGS. 1A and 1B) formed by the normal line L2 of the (001) plane, which is the crystal plane at the measurement point included in the fine grain part, was measured.
Tables 4 and 5 show the respective values.

Next, the inventive tools 1 to 10, the comparative tools 1 to 10 and the reference tool 1 were subjected to a dry high-speed face milling, which is a kind of high-speed interrupted cutting, and a center cut cutting test under the following conditions. The flank wear width was measured.
Cutting test: Dry high-speed face mill, center cut cutter diameter: 125 mm,
Work material: JIS / SCM445 Block material with a width of 100 mm and a length of 380 mm,
Cutting speed: 355 m / min,
Cutting depth: 2.0 mm,
Single blade feed amount: 0.21 mm / tooth,
Cutting time: 8 minutes,
Table 6 shows the test results.

  From the results shown in Table 6, in the coated tool of the present invention, the TiAlN layer contains fine crystal grains of 10 to 70 area%, and the (001) normal line of the fine crystal grain and the normal line of the tool base surface. Since the fine crystal grains having an angle of 20 degrees or less occupy 10% by area or more of the total area of the fine crystal grains, the presence of the fine crystal grains in the TiAlN layer increases the wear resistance, The fine crystal grains relieve the impact during cutting, and thus exhibit excellent fracture resistance and wear resistance in high-speed intermittent cutting of alloy steel.

  On the other hand, the comparative tool 2, 4, 6, 7, 8 and the reference tool 1 or (001) of the fine crystal grains in which 10 to 70 area% of fine crystal grains are not present in the TiAlN layer. Comparative tool 1, 3, 5, 9, in which the fine crystal grains whose angle formed between the normal line of (1) and the normal line of the tool substrate surface is 20 degrees or less do not exist in an area of 10 area% or more of the total area of the fine crystal grains 10 and the reference example tool 1, and the comparative example tool 2 and the reference example tool 1 in which coarse crystal grains are present, it is apparent that the service life is reached in a relatively short time due to the occurrence of defects or a decrease in wear resistance. It is.

The coated tool according to the present invention has excellent fracture resistance when it is subjected to high-speed intermittent cutting such as alloy steel that is accompanied by high heat generation and impact and intermittent high load acts on the cutting edge. Since it exhibits excellent wear resistance over a long period of use, it can satisfactorily respond to the FA of the cutting device, the labor saving and energy saving of the cutting, and the cost reduction.

Claims (1)

At least a composite nitride layer of Ti and Al having an average layer thickness of 0.5 to 10.0 μm is included on the surface of a tool base made of any one of a WC-based cemented carbide, a TiCN-based cermet, and a cubic boron nitride sintered body. In surface-coated cutting tools provided with a hard coating layer,
(A) The composite nitride layer of Ti and Al has the composition
Composition formula: (Ti _x Al _1-x ) N
Represented by 0.10 ≦ x ≦ 0.35 (where x is an atomic ratio),
(B) In the longitudinal section of the composite nitride layer of Ti and Al, fine grain having a crystal grain width measured in a direction parallel to the surface of the tool base is 30 to 100 nm, and the crystal grain width is larger than 100 nm Does not contain coarse grains
(C) In the longitudinal section of the composite nitride layer of Ti and Al, the area ratio of the fine crystal grains in the longitudinal section is 10 to 70 area%,
(D) In the longitudinal section of the composite nitride layer of Ti and Al, the angle formed by the normal of the tool base surface and the (001) normal of the fine crystal grains having a cubic structure is 20 degrees or less. The surface-coated cutting tool characterized in that the area ratio of the fine crystal grains having a crystal structure to the total area of the fine crystal grains in the longitudinal section is 10 area% or more.