Surface-coated cutting tool

Abstract

To provide a surface-coated cutting tool having durability also in low speed cutting of a hard-to-cut material such as a Ti base alloy.SOLUTION: A surface-coated cutting tool has a base and a coating layer on the base, wherein the coating layer contains an Al boride layer having an average thickness of 0.5 to 10.0 μm and an average composition of AlBx(2.2≤x≤4.5).SELECTED DRAWING: None

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 referred to 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 boride coating layer of at least one of Al, Si, Cr, W, Ti, Nb, and Zr on a substrate, the boride coating layer having a cubic crystal structure, the strongest diffraction ray intensity on the (001) plane, and a residual compressive stress of 0.1 GPa or more, and is said to be able to release heat generated during cutting, thereby preventing welding and deformation of the cutting edge. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-238281 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances and proposals, and aims to provide a surface-coated cutting tool that is durable even when cutting difficult-to-cut materials such as Ti-based alloys at low speeds (cutting speeds of 30 to 50 m / min).

[0006] 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 an average thickness of 0.5 to 10.0 μm and an average composition of AlB x The Al boride layer has a structure where x is 2.2≦x≦4.5.

[0007] The surface-coated cutting tool according to the embodiment may satisfy the following requirement (1).

[0008] (1) The coating layer has a nanoindentation hardness of 5 to 25 GPa. [Effects of the Invention]

[0009] The surface-coated cutting tool has excellent durability even when used in low-speed cutting of difficult-to-cut materials such as Ti-based alloys. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors have conducted research into coating layers for coated tools containing metal borides, and as a result have recognized and discovered the following points (1) to (3).

[0011] (1) The AlB2 layer has excellent heat resistance and wear resistance when cutting Ti alloys.

[0012] (2) However, in the low-speed cutting of Ti alloys, which are prone to adhesion, the AlB2 layer lacks lubricity, resulting in poor adhesion resistance and insufficient durability due to chipping.

[0013] (3) As a result of further investigation, it was found that lubricity can be improved by increasing the amount of B in the Al boride, that is, by increasing the atomic ratio of B to Al more than AlB2.

[0014] 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.

[0015] 1.Coating layer (1)Al boride layer The coating layer has an average thickness of 0.5 to 10.0 μm and an average composition of AlB x It is preferable to include an Al boride layer where (2.2≦x≦4.5).

[0016] The reason for specifying the average thickness of the Al boride layer within the above range is that a thickness smaller than 0.5 μm results in a decrease in abrasion resistance, and a thickness greater than 10.0 μm results in a decrease in chipping resistance. The average thickness is more preferably 1.0 to 4.0 μm.

[0017] The average composition of the Al boride layer is AlB x It is preferable that x satisfies (2.2≦x≦4.5). The reason is that if x is smaller than 2.2, the lubricity of the Al boride layer decreases, resulting in insufficient welding resistance, while if x is larger than 4.5, the heat resistance decreases, resulting in insufficient wear resistance.

[0018] The nanoindentation hardness of the Al boride layer is more preferably 5 to 25 GPa. The reason why a nanoindentation hardness in this range is more preferable is that if it is less than 5 GPa, the wear resistance may be insufficient, while if it exceeds 25 GPa, chipping is likely to occur.

[0019] (2) Other demographics The above-mentioned object can be achieved by the Al boride layer alone, but an underlayer may be provided between the substrate and the Al boride layer, and a surface layer may be provided on the surface of the Al boride layer.

[0020] (2-1) Base layer An underlayer having a total average thickness of 0.1 to 5.0 μm and consisting of one or more Ti compound layers selected from Ti boride, carbide, nitride, carbonate, and carbonitride oxylayers (the composition of these Ti compound layers is not limited to a stoichiometric composition) may be provided. The underlayer further improves adhesion between the coating layer including the laminated structure and the substrate.

[0021] (2-2) Surface layer A surface layer may be selectively provided on the alternating lamination. A TiN layer (the atomic ratio of Ti to N in the TiN layer is not limited to the stoichiometric ratio) may be provided as the surface layer. When this TiN layer is provided, the TiN layer itself has a golden color tone, and therefore, for example, it can be used as an identification layer to distinguish whether the coated tool is unused or used based on a change in color tone. The average thickness of this TiN layer as an identification layer may be, for example, 0.1 to 1.0 μm. The surface layer may also be an Al2O3 layer, the average thickness of which may be 0.1 to 15.0 μm.

[0022] (2-3) Unintended demographic In this embodiment, the film is formed so that no layers other than the Al boride layer, the underlayer, and the surface layer are present. However, unintended fluctuations in pressure within the film forming apparatus may occur, resulting in the formation of a layer with an unintended composition different from the Al boride layer, the underlayer, and the surface layer.

[0023] 2.Base (1)Material Any known material can be used for the substrate in this embodiment 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, and cBN sintered body.

[0024] (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.

[0025] 3.Measurement method The average composition of the Al boride layer constituting the coating layer and the average thicknesses of the Al boride layer, the lower layer, and the surface layer are measured as follows.

[0026] (1) Average composition The coating layer is cut at a longitudinal section at an arbitrary position (a section perpendicular to the horizontal plane when the tool substrate surface is considered to be a horizontal plane assuming that there are no minute irregularities on the surface of the tool substrate) to prepare a specimen for observation. This specimen is prepared using, for example, a focused ion beam (FIB) system or a cross section polisher (CP). Measurements are then performed on this specimen for observation.

[0027] The average composition of the Al boride layer is determined by averaging the results of line analysis performed at five or more points in the thickness direction of the Al boride layer using an energy dispersive X-ray spectrometer (EDS) attached to a transmission electron microscope (TEM).

[0028] (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 the number of such rectangles is set to be at least 5. Using the results of defining the interfaces with the Al boride layer, lower layer, and surface layer described above, line analysis is performed to determine the thickness of each layer, and the average of these is used to determine the average thickness of the Al boride structure layer, lower layer, and surface layer.

[0029] 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.

[0030] (3) Hardness The nanoindentation hardness is determined based on the nanoindentation test method (ISO 14577) by polishing the surface of the coating layer, measuring at 10 points using a diamond Berkovich indenter under an indentation load of 2 mN, and averaging the measurements.

[0031] 4. Manufacturing method The metal boride layer can be formed, for example, by a film formation method using a magnetron sputtering device or a high-power pulse sputtering device. As the film formation conditions, for example, AlB2 was used as the target, Target input power: 500W~5000W Pulse frequency: 500~1500Hz Pulse application time: 50 to 150 μsec Gas conditions: Ar 0.2 to 1.0 Pa Film forming temperature: 350~750℃ Table rotation speed: 1.5 to 3.0 rpm Bias voltage: 50 to 300 V can be given. The underlayer and the surface layer may be formed by a known method. [Example]

[0032] Next, examples will be described, but the present invention is not limited to these examples.

[0033] 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, the cutting edge was honed to an R of 0.03 to produce WC-based cemented carbide substrates 1 and 2 with the insert shape specified in ISO standard SEEN1203AFTN1.

[0034] Subsequently, a coating layer was formed on these substrates 1 and 2 according to the following procedures (a) to (d).

[0035] (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, AlB2-based sintered compact targets were placed on either side of the rotating table in the high-power pulse sputtering apparatus.

[0036] (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.

[0037] (c) Subsequently, the atmosphere inside the apparatus was set to 0.5 Pa, and the atmosphere inside the apparatus was filled only with Ar gas. Thereafter, high-power pulse sputtering was performed on the AlB2-based sintered compact target by controlling the Ar gas pressure 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.

[0038] For comparison purposes, a lower layer and a coating layer were formed on these substrates 1 and 2 using an AlB2-based sintered compact 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.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

[0042] 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 using a cutter with the product shape SE445R0506E manufactured by Mitsubishi Materials Corporation. The following cutting tests were carried out.

[0043] Cutting test Workpiece: Ti-6Al-4V block (width 110mm x length 250mm) Cutting speed: 40m / min Cutting depth: 1.0 mm Feed: 0.15mm / tooth Cutting length: 4.0m

[0044] After the cutting test was completed (after a cutting length of 4.0 m was completed), the flank wear width was measured. Tables 4 and 5 show the test results. However, if excessive wear or abnormal damage such as chipping occurred before the cutting length reached 4.0 m, cutting was stopped and the cutting length from the start of cutting (shown in Table 4 as "cutting distance (m) until end of life") was measured.

[0045] [Table 4]

[0046] As is clear from the results shown in Table 4, all of the Examples exhibit excellent durability in low-speed cutting of materials that have high adhesion to coated tools, such as Ti-based alloys. In contrast, in all of the comparative examples, wear of the cutting edge progresses quickly during low-speed cutting of the highly weldable materials, and chipping due to welding also occurs, so it is clear that the usable life is reached in a short period of time.

Claims

1. 1. A surface-coated cutting tool having a substrate and a coating layer on the substrate, The coating layer has an average thickness of 0.5 to 10.0 μm and an average composition of AlB ｘ (2.2≦x≦4.5) A surface-coated cutting tool characterized by:

2. 2. The surface-coated cutting tool according to claim 1, wherein the coating layer has a nanoindentation hardness of 5 to 25 GPa.

Images