Surface-coated cutting tool

Abstract

Surface-coated cutting tool having durability even in cutting of Ti-based alloy SOLUTION: A surface skin cutting tool comprising a substrate and a coating layer on the substrate, wherein the coating layer comprises a tungsten carbide layer having an average thickness of 0.1 μm or more and 5.0 μm or less, an average composition of the tungsten carbide layer is WCx (x is 0.8 or more and 1.5 or less), the tungsten carbide layer comprises a cubic crystal structure, and a diffraction peak intensity ratio I (111) / I (002) obtained by X-ray diffraction is 3.0 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool). [Background technology]

[0002] BACKGROUND ART Conventionally, a coated tool has been known in which a coating layer is formed on a substrate such as a tungsten carbide (hereinafter sometimes abbreviated as WC) based cemented carbide. It has been proposed to obtain a coating layer with improved cutting performance, including the ability to cut difficult-to-cut materials such as Ti-based alloys, by adjusting the composition, texture, crystal structure, etc. of this coating layer.

[0003] For example, Patent Document 1 describes a coated tool having a coating of 0.5 to 100 μm in thickness on a substrate, the coating containing 30% or more by volume of cubic tungsten carbide, and is described as a useful coated tool because the coating has excellent surface hardness and durability.

[0004] Patent Document 2 describes a coated tool in which a tungsten carbide film is formed on a WC-based cemented carbide alloy by electron beam physical vapor deposition, and the coated tool is said to be suitable for cutting titanium alloys.

[0005] Patent Document 3 describes a method for depositing WC on a substrate. 1-x (x is 0.54 or more and 0.58 or less), 1-x describes a coated tool containing a hexagonal crystal structure, and the coated tool is said to have excellent chipping resistance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-262405 [Patent Document 2] U.S. Patent No. 5,984,593 [Patent Document 3] International Publication No. 2019 / 181742 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances and proposals, and has an object to provide a surface-coated cutting tool that is durable even when cutting difficult-to-cut materials such as Ti-based alloys.

[0008] The surface-coated cutting tool according to an embodiment of the present invention comprises: a substrate and a coating layer on the substrate; the coating layer has a tungsten carbide layer having an average thickness of 0.1 μm or more and 5.0 μm or less, The tungsten carbide layer has an average composition of WCx (x is 0.8 or more and 1.5 or less), contains crystal grains having a cubic crystal structure, and has a diffraction peak intensity ratio I(111) / I(002) obtained by X-ray diffraction of 3.0 or more.

[0009] The surface-coated cutting tool according to the embodiment may satisfy the following requirement (1). (1) The tungsten carbide layer has a nanoindentation hardness of 30 GPa or more. [Effects of the Invention]

[0010] The surface-coated cutting tool has excellent wear resistance and durability even when cutting difficult-to-cut materials such as Ti-based alloys. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of a longitudinal section (the definition of a longitudinal section will be described later) of a surface-coated cutting tool according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present inventors have conducted research into coatings (sometimes called coating layers, and no distinction is made between the two) for coated tools containing tungsten carbide, and as a result have recognized and discovered the following.

[0013] (1) The coating layer containing tungsten carbide has no affinity for Ti alloys and the like.

[0014] (2) The coating layers containing tungsten carbide described in Patent Documents 1-3 have room for improvement in terms of hardness.

[0015] (3) Therefore, when the composition of the tungsten carbide coating layer is set to a predetermined value and the intensity ratio of specific diffraction lines obtained by X-ray diffraction reaches a predetermined value, the hardness is further improved and excellent wear resistance is exhibited.

[0016] The present invention has been derived based on these recognitions and findings, and a coated tool according to an embodiment of the present invention will be described in detail below. In this specification and claims, when a numerical range is expressed as "L to M" (where L and M are both numerical values), the range includes an upper limit (M) and a lower limit (L). When a unit is specified for only the upper limit without specifying a unit for the lower limit, the units for the upper limit (M) and the lower limit (L) are the same.

[0017] 1.Coating layer FIG. 1 is a schematic diagram showing an example of a longitudinal cross section of a surface-coated cutting tool according to an embodiment of the present invention. As is clear from FIG. 1, the surface-coated cutting tool according to this embodiment has a coating layer (2) on a substrate (1). The coating layer (2) has a tungsten carbide layer (3). In addition to the tungsten carbide layer (3), the coating layer (2) in FIG. 1 also has a base layer (4) and an upper layer (5). However, both the base layer (4) and the upper layer (5) may be provided selectively and are not essential. In the case of an insert, the longitudinal section is a section perpendicular to the base when the surface of the base is considered to be flat and without any irregularities, and in the case of a axial tool, it is a section perpendicular to the axis.

[0018] (1) Tungsten carbide layer (1-1) Composition When the average composition of the tungsten carbide layer is expressed by the formula WCx, x is preferably 0.8 to 1.5. This is because if x is less than 0.8, soft metallic tungsten is likely to precipitate, reducing the wear resistance of the coated tool, while if x exceeds 1.5, brittle amorphous carbon is likely to precipitate in the layer, making cracks more likely to occur during cutting and reducing the wear resistance. More preferably, x is 0.9 to 1.2.

[0019] (1-2) Average thickness The average thickness of the tungsten carbide layer is preferably 0.1 μm or more and 5.0 μm or less. The reason is that if it is less than 0.1 μm, the wear resistance of the coated tool is insufficient, while if it is more than 5.0 μm, chipping and breakage tend to occur during cutting. The average thickness is more preferably 0.3 μm or more and 3.5 μm or less.

[0020] (1-3) X-ray diffraction peak intensity ratio The tungsten carbide layer preferably contains crystal grains having a cubic crystal structure. Here, the term "containing crystal grains having a cubic crystal structure" refers to the detection of a peak I(111) or I(002) when X-ray diffraction is performed on the tungsten carbide layer. When the intensity of the 111 diffraction line (the diffraction line giving the peak of the (111) plane) is I(111) and the intensity of the 002 diffraction line (the diffraction line giving the peak of the (002) plane) is I(002). If the I(111) / I(002) ratio is 3.0 or more, microfracture of the tungsten carbide layer during cutting is suppressed, wear resistance is improved, and durability is ensured even when cutting difficult-to-cut materials such as Ti-based alloys, thereby achieving the aforementioned objectives. More preferably, the I(111) / I(002) ratio is 6.0 or more. In the example of the manufacturing method described below, the upper limit of the I(111) / I(002) ratio is approximately 30.

[0021] (1-4) Nanoindentation hardness The nanoindentation hardness of the tungsten carbide layer is more preferably 30 GPa or more. If the nanoindentation hardness is 30 GPa or more, the tungsten carbide layer is reliably wear-resistant. The nanoindentation hardness of the tungsten carbide layer is even more preferably 33 GPa or more. In an example of the manufacturing method described below, the upper limit of the nanoindentation hardness of the tungsten carbide layer is about 50 GPa.

[0022] (2) Other demographics The above-mentioned object can be achieved by the tungsten carbide layer alone, but in addition, an underlayer may be intentionally provided between the substrate and the tungsten carbide layer, and an upper layer may be intentionally provided on the surface of the tungsten carbide layer.

[0023] (2-1) Base layer An underlayer may be provided, which is made of one or more compound layers selected from the group consisting of Ti and / or TiAl carbide, nitride, and carbonitride layers (the composition of these compound layers is not limited to stoichiometric compositions) and has a total average layer thickness of 0.1 to 10.0 μm. The underlayer improves adhesion between the tungsten carbide layer and the substrate, improving chipping resistance and durability.

[0024] (2-2) Upper layer An upper layer may be provided which is made of one or more compound layers selected from the group consisting of Ti and / or TiAl carbide, nitride, and boride layers (the composition of these compound layers is not limited to a stoichiometric composition) and has a total average layer thickness of 0.1 to 10.0 μm. The upper layer improves heat resistance and further enhances wear resistance.

[0025] (2-3) Unintended demographic In this embodiment, the film is formed so that no layers other than the tungsten carbide layer, the underlayer, and the upper layer are present; however, unintended fluctuations in pressure within the film forming apparatus may occur, resulting in the formation of an unintended layer with a different composition from these layers.

[0026] 2.Base (1)Material The substrate material used in this embodiment can be any known material as long as it does not impede the achievement of the above-mentioned object. Examples include cemented carbide (WC-based cemented carbide, including those containing Co in addition to WC, and those containing carbonitrides of Ti, Ta, Nb, etc.), cermet (mainly composed of TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide), cBN sintered body, and diamond sintered body.

[0027] (2) Shape The shape of the substrate is not particularly limited as long as it is a shape that can be used as a cutting tool, and examples thereof include the shape of an insert and the shape of a drill.

[0028] 3.Measurement method The coating layer is cut at an arbitrary position in the longitudinal section to prepare a specimen for observation. This specimen is prepared using, for example, a focused ion beam (FIB) system. Measurements are then performed on this specimen for observation.

[0029] (1) Average composition The average composition of the tungsten carbide layer is measured by using an energy dispersive X-ray (EDX) analyzer attached to a scanning electron microscope (SEM) or transmission electron microscope (TEM) for measuring the tungsten carbide crystal grains that appear in the cross section. Specifically, three or more square observation areas, each 30 nm long and 30 nm wide, are set on the cross section (preferably with the sides of each observation area spaced at least 100 nm apart), and the x in WCx is measured in each observation area. The arithmetic mean of the measurement results is used as the average composition.

[0030] (2) Average thickness The observation area is, for example, a rectangle with a length in the vertical direction (thickness direction) that includes the entire coating layer and a width in the horizontal direction (direction parallel to the substrate surface) of 5 μm, and five or more of these are set (it is desirable that the sides of each observation area are spaced apart by 20 μm or more). Linear analysis is performed to determine the thickness of each layer, and the average is used to determine the average thickness of each layer.

[0031] Here, the surface of the substrate is determined by observing the longitudinal cross section, determining the interface between the substrate and the coating layer by element mapping, and arithmetically determining the average straight line of the roughness curve of the interface thus obtained, which is defined as the surface of the substrate.The direction perpendicular to the surface of this substrate is then defined as the thickness direction.

[0032] (3) X-ray diffraction X-ray diffraction is measured, for example, under the following measurement conditions. Scan axis: 2θ-θ X-ray source: Cu-Kα ray (1.541862Å) Detector: 0-dimensional detector (scintillation counter) Scan range (2θ): 10°~120°

[0033] (4) Nanoindentation hardness and Young's modulus Based on ISO 14577, the surface of the coating layer is polished to expose the tungsten carbide layer, and then measurements are taken at 10 points using a diamond Berkovich indenter with an indentation load of 100 μN. The nanoindentation hardness is calculated by arithmetically averaging the measurement results.

[0034] 4. Manufacturing method The tungsten carbide layer can be formed, for example, by a film formation method using a high-power pulse sputtering device. As the film formation conditions, for example, WC is used as the target and the target input power is set to 500W to 3000W. Gas conditions: Ar only or Ar and C2H2 mixed gas 0.2 to 1.0 Pa Film forming temperature: 500~600℃ Bias voltage: -100 to 300V Pulse frequency: 500~2000Hz Pulse application time: 50 to 150 μsec Table rotation speed: 1.5 to 3.0 rpm can be given. [Example]

[0035] Next, examples will be described, but the present invention is not limited to these examples.

[0036] The raw material powders were WC powder, Co powder, TaC powder, NbC powder, and Cr3C2 powder. 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 1450°C for 1 hour. After sintering, two types of WC-based cemented carbide substrates 1 and 2 were fabricated: one with an insert shape conforming to ISO standard SEEN1203AFTN1, which had a cutting edge honed to an R of 0.03, and the other with an insert shape conforming to ISO standard CNMG120408, which had a cutting edge honed to an R of 0.03.

[0037] Subsequently, a coating layer was formed on these substrates 1 and 2 according to the following procedures (a) to (d).

[0038] (a) Each of the substrates 1 and 2 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, WC sintered compact targets were placed at four positions on either side of the rotating table in the high-power pulse sputtering apparatus.

[0039] (b) The high-power pulse sputtering apparatus was evacuated and heated to 500°C using a heater while maintaining a vacuum of 0.1 Pa or less. A DC bias voltage of -200 V was then applied to the substrate rotating on the rotating table. Argon (hereinafter referred to as Ar) gas was then 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 substrate was subjected to Ar bombardment for 1 hour.

[0040] (c) Subsequently, the atmosphere inside the apparatus was set to 0.5 Pa, and the atmosphere inside the apparatus was set to Ar gas or Ar gas and C2H2 gas. Thereafter, high-power pulse sputtering was performed on the WC sintered compact target under the predetermined pulse sputtering conditions shown in Table 2, and coated inserts 1 to 13 of the examples shown in Table 3 (hereinafter referred to as Examples 1 to 13) were produced, respectively.

[0041] For comparison purposes, a coating layer was formed on these substrates 1 and 2 using a WC sintered target under the conditions shown in Table 2 according to the procedures (a) to (d), and comparative coated inserts 1 to 13 (hereinafter referred to as Comparative Examples 1 to 13) were produced as comparative coated tools shown in Table 3.

[0042] [Table 1]

[0043] [Table 2]

[0044] In Table 2, the pressures of Ar gas and C2H2 gas are both partial pressures, and 0.0 indicates that they were not used as deposition gases.

[0045] [Table 3]

[0046] In Tables 2 and 3, "-" indicates that there is nothing applicable or that it is not applicable. In Table 3, "○" indicates that it is applicable.

[0047] For Examples 1 to 13 and Comparative Examples 1 to 13, a single-blade wet face milling cutting test, which is a type of high-speed intermittent cutting, was carried out in Cutting Test 1 below using a cutter with the product shape SE445R0506E manufactured by Mitsubishi Materials Corporation.

[0048] Cutting test 1: Milling of Ti-based alloy Workpiece: Ti-6Al-4V block (width 110mm x length 250mm) Tool shape: SE445R0506E (product shape of Mitsubishi Materials Corporation) Cutting speed: 80m / min Cutting depth: 2.0 mm Feed: 0.09mm / tooth Cutting length: 3.0m

[0049] Furthermore, for Examples 1 to 13 and Comparative Examples 1 to 13, a Ti alloy turning test, which is a type of high-speed cutting, was carried out in Cutting Test 2 below.

[0050] Cutting test 2: Turning of Ti-based alloy Work material: Ti-6Al-4V round bar (Φ200mm) Tool shape: CNMG12408 (ISO standard) Cutting speed: 90m / min Cut: 1.5mm Feed: 0.20mm / rev Cutting length: 2.5m

[0051] In Cutting Test 1, the flank wear width was measured after a cutting length of 3.0 m had been completed, and in Cutting Test 2, after a cutting length of 2.5 m had been completed. Tables 4 and 5 show the test results for each. However, if excessive wear or abnormal damage such as chipping occurred before the end of the cutting length, cutting was stopped and the cutting length from the start of cutting (shown as "cutting distance (m) until end of life" in Tables 4 and 5) was measured.

[0052] [Table 4]

[0053] [Table 5]

[0054] As is clear from the results shown in Tables 4 and 5, all of the examples exhibit excellent durability in cutting Ti-based alloys. In contrast, in all of the comparative examples, wear of the cutting edge progressed quickly and chipping occurred, so it is clear that the service life was reached in a short period of time. [Explanation of symbols]

[0055] 1 Base 2 Covering layer 3 Tungsten carbide layer 4 Base layer 5 Upper layer

Claims

1. 1. A surface-coated cutting tool having a substrate and a coating layer on the substrate, the coating layer has a tungsten carbide layer having an average thickness of 0.1 μm or more and 5.0 μm or less, The tungsten carbide layer has an average composition of WCx (x is 0.8 or more and 1.5 or less), contains crystal grains having a cubic crystal structure, and has a diffraction peak intensity ratio I(111) / I(002) obtained by X-ray diffraction of 3.0 or more. A surface-coated cutting tool characterized by:

2. 2. The surface-coated cutting tool according to claim 1, wherein the tungsten carbide layer has a nanoindentation hardness of 30 GPa or more.

Images