Surface-coated cutting tools

Abstract

A surface-coated cutting tool comprising a tool body and a coating layer on the tool body, wherein: the average thickness of the coating layer is 0.5-5.0 µm; the coating layer has a Ti-Zr-boride composite layer; and the Ti-Zr-boride composite layer has a crystalline phase and an amorphous phase, and has an average composition such that when expressed by the compositional formula TixZr(1-x)By, the atomic ratios x and y satisfy 0.3≤x≤0.7 and 1.5≤y≤3.0.

Description

[Technical Field]

[0001] The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool). This application claims priority to Japanese Patent Application No. 2020-55011, filed on March 25, 2020. The entire contents of said Japanese patent application are incorporated herein by reference. [Background technology]

[0002] Conventionally, coated tools have been known in which a tool substrate is made of cemented carbide or the like and a coating layer is formed on the surface of the tool substrate by a vapor deposition method. These coated tools have wear resistance, but various proposals have been made to further improve this wear resistance, including a proposal for a coating layer containing boron.

[0003] For example, Patent Document 1 discloses a method for forming a titanium nitride film on the surface of a tool substrate, the method comprising: forming a titanium nitride film on the surface of the tool substrate; 1-(X+Z) Al X B Z A coated tool has been proposed that has a lower layer made of a composite nitride layer of Ti, Al, and B satisfying the atomic ratios X, Z, and N (where X is 0.25 to 0.65 and Z is 0.01 to 0.10), an adhesive bonding layer made of a zirconium boronide layer with an average thickness of 0.1 to 0.5 μm, and an upper layer made of a zirconium boride layer with an average thickness of 0.8 to 5 μm. This coated tool is said to have excellent wear resistance even when cutting high-hardness steel and other materials at high speeds.

[0004] Furthermore, for example, Patent Document 2 proposes a coated tool having a Ti-boride layer with an average thickness of 0.5 to 5 μm on the surface of a tool substrate, the layer being configured as a composite structure of crystal grains with multiple average grain sizes, the composite structure being composed of secondary crystal grains with an average grain size of 20 to 70 nm, which are made up of aggregates of primary crystal grains with an average grain size of 10 to 15 nm, and tertiary crystal grains with an average grain size of 300 to 600 nm, which are made up of aggregates of the secondary crystal grains. This coated tool is said to be able to suppress peeling of the soft coating layer due to welding during high-speed cutting of soft, difficult-to-cut materials.

[0005] Furthermore, for example, Patent Document 3 discloses a tool having a Zr boride layer with an average thickness of 0.5 to 5 μm on the surface of a tool substrate, the layer being configured as a composite structure of crystal grains having a plurality of average grain sizes, The composite structure has an average grain size of 5 to 30 nm and is composed of an aggregate of primary crystal grains. Secondary crystal grains of 0 to 100 nm and aggregates of the secondary crystal grains with an average grain size of 200 to 100 A coated tool consisting of 0 nm tertiary crystal grains has been proposed. It is said that adhesion is suppressed during high-speed cutting of this hard, difficult-to-cut material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-1006 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-139795 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-40615 Summary of the Invention [Problem to be solved by the invention]

[0007] While cutting equipment has become increasingly sophisticated and automated, there is a growing demand for cutting difficult-to-cut materials, including titanium-based alloys and austenitic stainless steels, which are prone to welding during cutting.

[0008] The present invention has been made in view of the above circumstances and proposals, and an object of the present invention is to provide a coated tool that exhibits excellent crack resistance and wear resistance over long periods of use, particularly when used in high-speed intermittent cutting of Ti-based alloys and austenitic stainless steels.

[0009] Here, high-speed intermittent cutting of Ti-based alloys refers to cutting at a cutting speed of 70 m / min or faster, in which the cutting edge of a cutting tool alternates between cutting and idling, and high-speed intermittent cutting of austenitic stainless steel refers to cutting at a cutting speed of 100 m / min or faster, in which the cutting edge of a cutting tool alternates between cutting and idling. [Means for solving the problem]

[0010] A surface-coated cutting tool according to an embodiment of the present invention includes a tool substrate and a coating layer on the tool substrate, The coating layer is the average layer thickness 0.5 to 5.0 μm R Ti and Zr composite boride layer It consists of The Ti and Zr composite boride layer has a composition represented by the formula: Ti x Zr (1-x) B y When expressed as above, the average composition satisfies the atomic ratios x and y of 0.3≦x≦0.7 and 1.5≦y≦3.0, and further has a crystalline phase composed of crystal grains with a hexagonal crystal structure and an amorphous phase. death , The crystalline phase has hexagonal crystal grains with an average grain size of 2 to 30 nm, and the area ratio of the Ti and Zr composite boride phase to the crystalline phase is 50 to 95 area %. .

[0011] Furthermore, the surface-coated cutting tool according to the embodiment has the following features (1) to ( 2 ) may satisfy one or more of the following items.

[0013] ( 1 ) The nanoindentation hardness of the Ti and Zr boride layer is 25 to 40 GPa.

[0014] ( 2 ) Regarding the hexagonal crystal grains constituting the crystalline phase of the Ti and Zr boride layer, when the peak intensities of the 001 diffraction line, 100 diffraction line, and 101 diffraction line in X-ray diffraction are Ih(001), Ih(100), and Ih(101), respectively, the following relationship must be satisfied: 0.01≦Ih(001) / {Ih(001)+Ih(100)+Ih(101)}≦0.50. [Effects of the Invention]

[0015] According to the above, even when materials with high adhesion to coated tools, such as Ti-based alloys and austenitic stainless steels, are subjected to high-speed intermittent cutting, excellent crack resistance and wear resistance are exhibited over long periods of use. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present inventors have recognized the following points regarding the coated tools described in the above Patent Documents 1 to 3.

[0017] (1) The coated tool described in Patent Document 1 contains boron in the coating layer, enabling high-speed cutting of high-hardness steels such as alloy steels and quenched bearing steels. However, it cannot be said that the tool has sufficient cutting properties for high-speed intermittent cutting of materials that are prone to welding during cutting, such as the aforementioned Ti-based alloys and austenitic stainless steels.

[0018] (2) The coated tool described in Patent Document 2 enables high-speed cutting of soft, difficult-to-cut materials such as Al-based alloys. However, sufficient consideration is not given to high-speed, interrupted cutting of materials that are prone to welding during cutting, such as the aforementioned Ti-based alloys and austenitic stainless steels.

[0019] (3) The coated tool described in Patent Document 3 has a coating layer made of a Zr boride layer, and even when cutting hard, difficult-to-cut materials such as Ti-based alloys and high-Si-content Al-Si alloys under high-speed cutting conditions, the occurrence of welding is suppressed, and peeling resistance and wear resistance are improved. However, in consideration of recent cutting conditions, further improvement in wear resistance is required.

[0020] Based on this understanding, the present inventors have conducted extensive research into Ti-boride layers and Zr-boride layers as coating layers, and have made the novel discovery that wear resistance is improved when the Ti-Zr composite boride coating layer has a crystalline phase and an amorphous phase.

[0021] Hereinafter, a surface-coated cutting tool according to an embodiment of the present invention will be described in detail. In this specification and claims, when a numerical range is expressed as "A to B" (where A and B are both numerical values), the range includes an upper limit (B) and a lower limit (A), and the upper limit (B) and the lower limit (A) have the same unit. The numerical values ​​also include tolerances.

[0022] Average coating thickness: The coating layer has a composite boride layer of Ti and Zr, and its average layer thickness is preferably 0.5 to 5.0 μm. This is because if the average layer thickness is less than 0.5 μm, it is difficult to maintain wear resistance over a long period of time, while if it exceeds 5.0 μm, chipping is likely to occur. A more preferred range of the average layer thickness is 1.0 to 2.5 μm.

[0023] Here, the average thickness of the coating layer is measured as follows: For example, a focused ion beam (FIB) system, a cross-section polisher (CP) or the like is used to cut the coating layer at a longitudinal cross section (a cross section perpendicular to the surface of the tool substrate when the surface is treated as a flat surface, ignoring minute irregularities on the surface of the tool substrate) at an arbitrary position to prepare a sample for observation, and the longitudinal cross section is observed at multiple positions (for example, five positions) using a scanning electron microscope (SEM) to obtain the arithmetic average of the layer thicknesses obtained.

[0024] Average composition of Ti and Zr complex boride layer: The Ti and Zr composite boride layer has the composition formula: Ti x Zr (1-x) B yWhen expressed as above, it is preferable that the average composition satisfy the atomic ratios x and y be 0.3≦x≦0.7 and 1.5≦y≦3.0. The reason for this is as follows: When x is less than 0.3, the crystal structure is disrupted, resulting in the formation of metallic Ti in the composite boride layer, and adhesive wear is likely to occur at the contact area between the Ti-Zr composite boride layer and a workpiece such as a Ti-based alloy. On the other hand, when x exceeds 0.7, the crystal structure is disrupted, resulting in the formation of metallic Zr in the composite boride layer, and the hardness of the composite boride layer is reduced. Furthermore, when y is less than 1.5, adhesive wear is likely to occur at the contact area between the Ti-Zr composite boride layer and a workpiece such as a Ti-based alloy. On the other hand, when y exceeds 3.0, the crystal structure is disrupted, resulting in a decrease in hardness. It is more preferable that x be in the range of 0.4 to 0.6, and more preferably that y be in the range of 1.8 to 2.2.

[0025] The average composition of the Ti and Zr composite boride layer is measured as follows. The Ti content (x) and boron content (y) are both measured using an electron probe microanalyzer (EPMA), which irradiates the surface of the coating layer or five locations on a longitudinal cross section of the coating layer at any position with an electron beam. The characteristic X-rays obtained from each location are analyzed to quantify the content of each element, and the results are then arithmetically averaged.

[0026] Here, it is not clear why a Ti-Zr composite boride layer is an excellent coating layer for coated tools used when cutting highly adhesive materials such as Ti-based alloys and austenitic stainless steel. However, it is presumed that this is because Ti-Zr composite borides have low solid solubility in Ti-based alloys and other materials, and are highly unreactive, thereby suppressing adhesive wear between the coating layer and Ti-based alloys on the abrading surface, and also mitigating the thermal effects on the tool substrate caused by the low thermal conductivity of Ti-based alloys.

[0027] Crystalline and amorphous phases in Ti and Zr composite boride layers: It is preferable that the Ti-Zr composite boride layer have a crystalline phase and an amorphous phase. The reason for this preference is unclear, but is thought to be as follows: The presence of the amorphous phase produces boron oxide on the abrasion surface between the Ti-Zr composite boride layer and the Ti-based alloy workpiece during cutting, which imparts solid lubricity to the Ti-Zr composite nitride layer and improves the wear resistance of the Ti-Zr composite boride layer.

[0028] Furthermore, the crystal grains (hexagonal crystals) of the hexagonal structure that make up the crystalline phase are preferably fine crystal grains, and more preferably have an average grain size in the range of 2 to 30 nm. The reason for this is that the fracture unit of the Ti and Zr composite boride layer caused by welding is the crystal unit, so if the crystal grains are fine crystals, that is, if the crystal grains are small, the fracture unit will be small, and wear of the layer accompanied by fracture will be suppressed, improving wear resistance.

[0029] The average grain size of the crystal grains that make up the crystalline phase is determined as follows: Analysis is performed using an automated crystal orientation mapping (ACOM)-TEM with a transmission electron microscope (TEM) to define the grain boundaries. The area enclosed by the grain boundaries is then defined as a crystal grain, and the maximum length of that area is defined as the grain size. The grain size is determined for each of any five crystal grains, and the arithmetic average is taken as the average grain size.

[0030] Here, the differentiation between crystalline and amorphous phases is performed as follows. Specifically, a longitudinal section is observed using a TEM, and an image is obtained at a magnification sufficient to distinguish, for example, a few nanometers on the observation surface. This image is then subjected to FFT image transformation processing to select bright spots corresponding to the lattice constant (e.g., bright spots (including circular) corresponding to the (001) plane of a hexagonal crystal structure). Further, an inverse FFT transformation processing is performed, followed by binarization processing. This processing enables the enhancement of the crystalline structure of the lattice fringes and angles having the lattice constant selected as each bright spot. Similar processing is performed for each lattice constant to create an enhanced image corresponding to each lattice constant, such as a (001) plane enhanced image or a (100) plane enhanced image. The enhanced images are then combined by ORing the aforementioned enhanced images.

[0031] Then, the binarized image is expanded so that the lattice spacing with the largest lattice constant is filled, resulting in an image in which the lattice spacing of at least the largest lattice width is densely filled. In this case, the filled-in portions represent the crystalline phase, and the unfilled portions represent the amorphous phase. The magnification is not particularly limited as long as it allows the above-mentioned lattice constant to be observed.

[0032] Unlike ORing, this is a process in which the logical sum of pixels in the same position in two or more images is calculated for each pixel in the image to obtain the resulting image. Specifically, if a specific pixel is a bright point in one image, it is considered a bright point, and if it is a dark point in all images, it is considered a dark point.

[0033] Using the above-mentioned method for distinguishing between crystalline and amorphous phases, the crystalline phase and amorphous phase are distinguished for each of five arbitrary visual fields. The area percentage of the crystalline phase in each visual field is calculated, and the arithmetic average of the calculated area percentages is taken as the area percentage of the crystalline phase. The area percentage of the crystalline phase is more preferably 50 to 95% by area. The reason for this is as follows.

[0034] If the area ratio of the crystalline phase is less than 50% by area, the hardness decreases due to the small amount of crystalline phase in the Ti and Zr composite boride layer, and the coating layer may not perform as well as it should. On the other hand, if the area ratio of the crystalline phase exceeds 95% by area, the wear resistance decreases and grain boundary fracture becomes dominant, causing entire crystal grains to fall off at the grain boundaries, resulting in poor cutting performance. Here, the reason for the decrease in wear resistance is thought to be that the Ti and Zr composite boride layer becomes less likely to form boron oxide during cutting.

[0035] Nanoindentation hardness of Ti and Zr composite boride layer: The Ti and Zr composite boride layer more preferably has a nanoindentation hardness of 25 to 40 GPa. When the nanoindentation hardness is in this range, chipping resistance and wear resistance are further improved. This is presumably because, when the nanoindentation hardness is in this range, the Ti and Zr composite boride layer has a crystalline phase and an amorphous phase, which more reliably exhibits improved wear resistance.

[0036] Here, the nanoindentation hardness was measured based on the nanoindentation test method (ISO14577), by polishing the surface of the Ti and Zr composite boride layer and indenting it with a Berkovich indenter made of diamond at a load of 1.96 × 10 -3 The test is carried out at a pressure of 200 mgf. At least 10 random points are measured, and the arithmetic average of the measurements is taken as the hardness measurement value. In this measurement, the distance between each measurement point is set to at least 20 times the indentation depth during the test.

[0037] Crystal orientation of the crystalline phase in the Ti and Zr composite boride layer: The hexagonal 001 diffraction line, 100 diffraction line, and 101 diffraction line measured by X-ray diffraction are diffraction peaks due to the (001), (100), and (101) planes, respectively. When these peak intensities are designated as Ih(001), Ih(100), and Ih(101), respectively, it is more preferable to satisfy the relationship 0.01≦Ih(001) / {Ih(001)+Ih(100)+Ih(101)}≦0.50. Satisfying this relationship further improves wear resistance.

[0038] Here, the diffraction peak intensities of the (001), (100), and (101) planes of the hexagonal crystal can be measured using X-ray diffraction with a 2θ / θ focusing optical system using Cu-Kα radiation (wavelength λ: 0.15405 nm).

[0039] The (001) plane of a hexagonal crystal is sometimes expressed as the (0001) plane. Similarly, the (100) plane is sometimes expressed as the (10-10) plane, (1-100) plane, (01-10) plane, (-1100) plane, (-1010) plane, or (0-110) plane. Similarly, the (101) plane is sometimes expressed as the (10-11) plane, (1-101) plane, (01-11) plane, (-1101) plane, (-1011) plane, or (0-111) plane. These are equivalent plane indices.

[0040] Other layers (bottom layer): The coating layer containing the Ti and Zr composite boride layer of this embodiment exhibits sufficiently excellent crack resistance and wear resistance over long periods of use, even when materials that have high adhesion to cutting tools, such as Ti-based alloys and austenitic stainless steels, are machined by high-speed intermittent cutting. However, when a lower layer containing a Ti compound (not limited to a stoichiometric compound) layer having a total average layer thickness of 0.1 to 2.0 μm and consisting of one or more layers selected from the group consisting of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, and a carbonitride oxide layer is provided adjacent to the tool substrate in addition to the coating layer, the effect of this layer, combined with that of the lower layer, can provide even better chipping resistance and thermal crack resistance.

[0041] If the total average thickness of the lower layers is less than 0.1 μm, the effect of the lower layers is not fully exhibited, whereas if it exceeds 2.0 μm, the crystal grains in the lower layers tend to become coarse, making chipping more likely to occur.

[0042] Tool base: (1)Material Any conventionally known substrate for this type of tool substrate can be used as the tool substrate, as long as it does not impede the achievement of the above-mentioned object. Examples include cemented carbide (WC-based cemented carbide, WC, and those containing Co and carbonitrides of Ti, Ta, Nb, etc.), cermets (those containing TiC, TiN, TiCN, etc. as their main components), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), and cBN sintered compacts, and any of these is preferred.

[0043] (2) Shape There are no particular restrictions on the shape of the tool substrate as long as it is a shape that can be used as a cutting tool, and examples thereof include an insert shape and an end mill shape. [Example]

[0044] Next, examples will be described, but the present invention is not limited to these examples.

[0045] The raw material powders were WC powder, VC powder, TaC powder, NbC powder, Cr3C2 powder, and Co powder, all with average particle sizes of 1 to 3 μm. These raw material powders were blended according to the composition shown in Table 1, wet mixed in a ball mill for 72 hours, and dried. They were then pressed into a green compact at a pressure of 100 MPa. This green compact was sintered in a vacuum of 6 Pa at a temperature of 1400°C for 1 hour. After sintering, the cutting edge was honed to an R of 0.03 to produce tool substrates 1 and 2 made of WC-based cemented carbide with insert shapes conforming to ISO standard CNMG120408.

[0046] Furthermore, the same raw material powders as above were compounded according to the composition shown in Table 1. The mixture was wet mixed in a ball mill for 72 hours, dried, and then pressed into a green compact at a pressure of 100 MPa. This green compact was sintered in a vacuum of 6 Pa at a temperature of 1400°C for 1 hour to produce a 4 mm diameter sintered round bar for forming a cemented carbide substrate. Furthermore, the sintered round bar was ground to produce tool substrates (end mill shape) 3 and 4 made of WC-based cemented carbide, each with a cutting edge diameter and length of 2 mm x 4 mm and a four-flute square shape with a 40 degree helix angle.

[0047] Subsequently, a lower layer (provided only on some of the tool substrates) and a coating layer were formed on these tool substrates 1 to 4 according to the following procedures (a) to (d).

[0048] (a) Each of the tool substrates 1 to 4 was ultrasonically cleaned in acetone and, in a dried state, mounted along its outer periphery at a predetermined radial distance from the central axis on a rotating table in a high-power pulse sputtering apparatus. Meanwhile, a Ti target and sintered targets of Ti, Zr, and boron were placed in four positions facing each other across the rotating table in the high-power pulse sputtering apparatus.

[0049] (b) The inside of the apparatus was evacuated and heated to 500°C using a heater while maintaining a vacuum of 0.1 Pa or less. Then, a DC bias voltage of -200 V was applied to the tool substrate, which was rotating and revolving on the rotary table. Then, argon (hereinafter referred to as Ar) gas was introduced into the apparatus as a reactive gas, creating an atmosphere of 2.0 Pa. Furthermore, a current of 40 A was passed through a tungsten filament provided in the apparatus to excite Ar ions, and the tool substrate was subjected to Ar bombardment for 1 hour.

[0050] (c) Ar gas and nitrogen gas were introduced into the apparatus as reactive gases to create a reactive atmosphere of 0.6 Pa, and high-power pulse sputtering was performed on the Ti target under the specified pulse sputtering conditions shown in Table 2. As a result, a TiN layer having an average thickness shown in Table 3 was formed on the surface of the tool substrate as the lower layer of the coating layer. However, the lower layer was not formed on all of the tool substrates.

[0051] (d) Subsequently, the nitrogen gas among the gases introduced into the apparatus was turned off and switched to Ar gas, and the atmosphere inside the apparatus was set to 0.5 Pa. The nitrogen gas was sufficiently discharged, and the atmosphere inside the apparatus was filled with only Ar gas. Thereafter, high-power pulse sputtering was performed on a sintered compact target consisting of Ti, Zr, and boron under the predetermined pulse sputtering conditions shown in Table 2 for a time corresponding to the layer thickness, and Example Coated Inserts 1 to 15 and Example Coated End Mills 16 to 30 shown in Table 3 (hereinafter, these are collectively referred to as Examples 1 to 30) were obtained. However, Examples 6 and 9, and 21 and 24 are reference examples. ) were produced, respectively.

[0052] For comparison purposes, lower layers and coating layers were formed on these tool substrates 1 to 4 under the conditions shown in Table 4 according to the procedures (a) to (d) above, and comparative coated inserts 1 to 9 and comparative coated end mills 11 to 19 (10 is a missing number, hereinafter referred to as Comparative Examples 1 to 9 and 11 to 19) were manufactured as comparative coated tools shown in Table 5. However, lower layers were not formed on all tool substrates.

[0053] [Table 1]

[0054] In Table 1, "-" indicates that it is not contained.

[0055] [Table 2]

[0056] In Table 2, the examples are a and b and the tool base symbol is *When a and b are α and β, Example a uses tool base α, and Example b uses tool base β (a, b, α, and β are numbers), and "-" indicates that the corresponding processing was not performed.

[0057] [Table 3]

[0058] In Table 3, the examples are a and b and the tool base symbol is * When α and β are used, Example a uses tool substrate α, and Example b uses tool substrate β (a, b, α, and β are numbers). Also, the strength ratio ** is the value of Ih{001} / {Ih{001}+Ih{100}+Ih{101}}, and "-" indicates that it does not exist.

[0059] [Table 4]

[0060] In Table 4, the comparative examples are a and b, and the tool base symbol is * When a and b are α and β, comparative example a indicates that tool base α was used, and comparative example b indicates that tool base β was used (a, b, α, and β are numbers), and "-" indicates that the corresponding treatment was not performed.

[0061] [Table 5]

[0062] In Table 5, the comparative examples are a and b, and the tool base symbol is * When α and β are used, Comparative Example a uses tool base α, and Comparative Example b uses tool base β (a, b, α, and β are numbers). Also, the strength ratio ** is the value of Ih{001} / {Ih{001}+Ih{100}+Ih{101}}, and "-" indicates that it does not exist.

[0063] Next, the following cutting tests 1 and 2 were carried out on Examples 1 to 30 and Comparative Examples 1 to 19, and the results are shown in Tables 6 and 7.

[0064] For Examples 1 to 15 and Comparative Examples 1 to 9, a dry high-speed intermittent cutting test (cutting test 1) was carried out under the following conditions, with each being screwed to a fixing jig at the tip of a tool steel bit.

[0065] Cutting test 1 Work material: JIS SUS316L round bar with four longitudinal grooves evenly spaced along the length, Cutting speed: 160m / min, Cut: 2mm, Feed: 0.3mm / rev, Cutting time: 10 minutes

[0066] After the cutting test, the flank wear width was measured and the presence or absence of chipping was observed. However, if chipping occurred before the end of the cutting time, cutting was stopped and the time from the start of cutting was measured. Table 6 shows the test results.

[0067] [Table 6]

[0068] In Table 6, the cutting time (minutes) until the end of life in the comparative example refers to the cutting time (minutes) until the end of life is reached due to chipping.

[0069] Next, for Examples 16 to 30 and Comparative Examples 11 to 19, a wet high-speed intermittent cutting test (cutting test 2) was carried out in side machining using an end mill under the following conditions.

[0070] Cutting test 2 Workpiece: Block of Ti-based alloy (Ti-6%Al-4%V alloy by mass%) (width 100mm x length 250mm) Cutting speed: 110m / min Rotation speed: 17508 min -1 Cutting depth: 2.0 mm Feed: 0.07mm / rev End mill blade outer diameter: 2mm

[0071] The cutting length was 150 m (cutting time: approximately 123 minutes), the flank wear width was measured, and the occurrence of chipping was observed. However, if chipping occurred before the cutting length reached 150 m, cutting was stopped and the time from the start of cutting was measured. Table 7 shows the test results.

[0072] [Table 7]

[0073] In Table 7, the cutting time (minutes) until the end of life in the comparative example indicates the cutting time (minutes) until the end of life is reached due to chipping.

[0074] From the results shown in Tables 6 and 7, the examples in which the coating layer using the Ti and Zr composite boride layer has a crystalline phase and an amorphous phase exhibit excellent adhesion resistance and wear resistance in high-speed intermittent cutting of materials that have high adhesion to coated tools, such as various Ti-based alloys and austenitic stainless steel. In contrast, in the comparative example, the cutting edge wear progresses quickly during high-speed intermittent cutting of the material with high weldability, and it is clear that the cutting edge reaches the end of its useful life in a relatively short period of time.

[0075] The above-disclosed embodiments are merely illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, not by the above-disclosed embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

Claims

1. 1. A surface-coated cutting tool having a tool substrate and a coating layer on the tool substrate, the coating layer is a composite boride layer of Ti and Zr having an average layer thickness of 0.5 to 5.0 μm, The Ti and Zr composite boride layer has a composition represented by the formula: Ti ｘ Zr （１－ｘ） B ｙ wherein the average composition satisfies the atomic ratios x and y of 0.3≦x≦0.7 and 1.5≦y≦3.0, and further comprises a crystalline phase constituted by crystal grains of a hexagonal crystal structure and an amorphous phase, the hexagonal crystal grains constituting the crystalline phase having an average grain size of 2 to 30 nm, and the crystalline phase occupies an area ratio of 50 to 95 area % of the Ti and Zr composite boride phase. A surface-coated cutting tool characterized by:

2. A surface-coated cutting tool as described in claim 1, characterized in that the nanoindentation hardness of the Ti and Zr composite boride layer is 25 to 40 GPa.

3. A surface-coated cutting tool as described in claim 1 or 2, characterized in that when the peak intensities of the 001 diffraction line, 100 diffraction line and 101 diffraction line in X-ray diffraction for the hexagonal crystal grains of the Ti and Zr composite boride layer are Ih(001), Ih(100) and Ih(101), respectively, the relationship 0.01≦Ih(001) / {Ih(001)+Ih(100)+Ih(101)}≦0.50 is satisfied.

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