Coated cutting tools

Abstract

To improve the durability of a coated cutting tool provided with a layer of nitride of TiSi on a layer of nitride of AlCrSi coated by sputtering.SOLUTION: A coated cutting tool includes a base material and a hard film formed on the base material. The hard film has a layer of nitride of AlCrSi provided on the base material and a layer of nitride of TiSi provided on the layer of the nitride of AlCrSi. The hard film exhibits a face-centered cubic lattice structure in an X-ray diffraction, and 2θ determined by X-ray diffraction has a peak of (111) surface in a range of 37°-38°, and a half value width of the X-ray diffraction peak of the (111) surface is 0.50°- 0.60°. The hard film contains less than 0.2 atomic % of Ar when assuming that the total of a metallic element including a semimetal and a non-metallic element is 100 atomic %.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a coated cutting tool. [Background technology]

[0002] Coated cutting tools with a TiSi nitride layer on top of an AlCrSi nitride layer have excellent durability and have been studied extensively. For example, Patent Document 1 discloses a coated cutting tool in which a Ti bombardment layer is formed on the surface of a substrate by arc ion plating, followed by a layer of AlCrSi nitride and then a layer of TiSi nitride. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2014 / 156699 [Overview of the project] [Problems that the invention aims to solve]

[0004] In recent years, high-power sputtering has begun to be applied to coated cutting tools. According to the inventors' research, it has been confirmed that there is room for improvement in the durability of coated cutting tools in which a layer of TiSi nitride is provided on top of a layer of AlCrSi nitride coated by sputtering. [Means for solving the problem]

[0005] One aspect of the present invention is a coated cutting tool comprising a substrate and a hard coating formed on the substrate, wherein the hard coating has a layer of AlCrSi nitride provided on the substrate and a layer of TiSi nitride provided on the AlCrSi nitride layer, exhibits a face-centered cubic lattice structure in X-ray diffraction, has a (111) plane peak in the range of 37° to 38° for 2θ determined by X-ray diffraction, has a full width at half maximum of 0.50° or more and 0.60° or less for the X-ray diffraction peak of the (111) plane, and contains 0.2 atomic percent or less of Ar when the total of metallic elements including metalloids and nonmetallic elements is 100 atomic percent. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a coated cutting tool with excellent durability. [Brief explanation of the drawing]

[0007] [Figure 1] This is an example of a cross-sectional view (30,000x magnification) of the hard coating according to this Example 1. [Figure 2] This is an example of a cross-sectional view (30,000x magnification) of the hard coating related to Comparative Example 1. [Figure 3] This figure shows the X-ray diffraction measurement results of the hard coating according to this embodiment 1. [Modes for carrying out the invention]

[0008] The inventors of the present invention have arrived at this invention after confirming that a coated cutting tool, which has layers of AlCrSi nitride and TiSi nitride formed by sputtering, exhibits excellent durability when the full width at half maximum of the peak intensity of the (111) plane in X-ray diffraction is within a certain range. The details are described below.

[0009] In the coated cutting tool of this embodiment, the base material is not particularly limited, but it is preferable to use a WC-Co-based cemented carbide, which has excellent strength and toughness, as the base material.

[0010] In the coated cutting tool of this embodiment, a layer of AlCrSi nitride is provided on the substrate. The AlCrSi nitride layer is a film type with excellent heat resistance and wear resistance, and by providing it as a lower layer under the TiSi nitride layer, the durability of the coated cutting tool can be increased. In this embodiment, the AlCrSi nitride layer preferably contains 50 to 70 atomic percent of Al, 30 to 45 atomic percent of Cr, and 1 to 10 atomic percent of Si, with a further preference of 1 to 3 atomic percent of Si. Reducing the amount of Si added is preferable as it reduces the amount of AlN in the hcp structure. In this embodiment, the AlCrSi nitride layer preferably has a nanoindentation hardness of 30 GPa or more and 35 GPa or less, and an elastic modulus of 520 GPa or more and 620 GPa or less.

[0011] In the coated cutting tool of this embodiment, a layer of TiSi nitride is provided on top of the AlCrSi nitride layer described above. TiSi nitride is a type of film with a fine structure and high hardness, and by providing it as an upper layer on top of the AlCrSi nitride, the durability of the coated cutting tool can be increased. The TiSi nitride layer in this embodiment preferably has a nanoindentation hardness of 40 GPa or more. Ti is preferably 60 atomic% to 90 atomic%. Si is preferably 10 atomic% to 40 atomic%.

[0012] The hard coating according to this embodiment exhibits a face-centered cubic lattice structure in X-ray diffraction, and has a peak in the (111) plane in the range of 2θ of 37° to 38° as determined by X-ray diffraction. This peak originates from CrN and is suitable for evaluating AlCrSi nitrides. In this embodiment, the hard coating has a full width at half maximum of 0.50° to 0.60° of the X-ray diffraction peak of the (111) plane where 2θ is 37° to 38°. This allows the AlCrSi nitride layer to have a finer structure without reducing hardness, elastic modulus, or compressive residual stress, thereby improving the durability of the coated cutting tool. X-ray diffraction can be performed using a commercially available X-ray diffractometer under the following measurement conditions: tube voltage 45kV, tube current 40mA, X-ray source Cukα (λ=0.15405nm), and 2θ between 20 and 80 degrees.

[0013] In this embodiment, it is preferable that the AlCrSi nitride layer does not have a peak due to the hcp structure of AlN in the intensity profile determined from the brightness of the limited-field diffraction pattern. A low amount of hcp structure of AlN at the micro level can improve the durability of the coated cutting tool. In this embodiment, the intensity profile determined from the brightness of the limited-field diffraction pattern is evaluated after removing the background.

[0014] In this embodiment, the hard coating contains argon (Ar) at an amount of 0.2 atomic percent or less, when the total amount of metallic elements including metalloids and nonmetallic elements is set to 100 atomic percent. In the sputtering method, argon ions are used to sputter the target component. To coat the hard film, it is easy to incorporate argon into the hard film. While the hardness increases when the grain size of the hard film is finer, the number of grain boundaries increases, and the argon contained in the hard film becomes concentrated at the grain boundaries. If the argon content ratio of the hard film is too high, the toughness of the hard film decreases, and it becomes difficult to achieve sufficient tool performance. Therefore, in this embodiment, in order to reduce the argon concentration at the grain boundaries of the hard film, the argon content is set to 0.2 atomic% or less, when the total amount of metallic elements including metalloids and nonmetallic elements is set to 100 atomic%. In this embodiment, there is no particular limit to the lower limit of the argon (Ar) content ratio. Since the hard film according to this embodiment is coated by the sputtering method, it can contain argon (Ar) at a concentration of 0.01 atomic% or more.

[0015] For the hard coating according to the present embodiment, when the film thickness of the AlCrSi nitride layer is t1 and the film thickness of the TiSi nitride layer is t2, t1 / t2 is preferably 0.7 or more and 1.3 or less. When the film thicknesses of the AlCrSi nitride layer and the TiSi nitride layer are approximately equal, the coated cutting tool exhibits excellent durability. t1 is preferably 0.5 µm or more and 3 µm or less. t2 is preferably 0.5 µm or more and 3 µm or less.

[0016] The coated cutting tool of the present embodiment may be provided with an intermediate coating between the base material and the AlCrSi nitride layer. Between the AlCrSi nitride layer and the TiSi nitride layer, a laminated coating in which the AlCrSi nitride layer and the TiSi nitride layer are alternately laminated may be provided. The total film thickness of the laminated coating is preferably smaller than the film thickness of the AlCrSi nitride layer located below the laminated coating. The total film thickness of the laminated coating is preferably smaller than the film thickness of the TiSi nitride layer located above the laminated coating. The film thickness of each constituent layer of the laminated coating is preferably in the range of 1 nm or more and 10 nm or less. In the laminated coating alternately laminated at the nano level, the compositions of the respective layers intermix. Therefore, for the AlCrSi nitride layer and TiSi nitride layer alternately laminated at the nano level, the AlCrSi nitride layer contains Ti, and the TiSi nitride layer in the laminated coating contains Al and Cr. When the total film thickness of the laminated coating is t3, t3 / (t1+t2+t3) is preferably 0.05 or more and 0.3 or less. Further, it is more preferable that t3 / (t1+t2+t3) is 0.07 or more and 0.2 or less. Another separate hard coating may be provided on the upper TiSi nitride layer.

[0017] The hard coating according to the present embodiment is a sputtered coating applied by a sputtering method. Among sputtering methods, it is preferable to apply a sputtering method in which power is sequentially applied to targets, and when switching the target to which power is applied, the sputtering method provides a period in which power is simultaneously applied to both the target whose power application is ending and the target whose power application is starting. The maximum power density of the electric power pulse is 0.5kW / cm 2 or higher, which is preferable. It is preferable that the period during which electric power is simultaneously applied to both the alloy target that finishes the application of electric power and the alloy target that starts the application of electric power is 5 microseconds or more and 20 microseconds or less. In order to increase the ionization rate of target components, it is preferable to use three or more AlCrSi-based alloy targets and three or more TiSi-based alloy targets. It is preferable that pre-discharge is performed with the furnace temperature of the sputtering apparatus set to 430°C or higher, the flow rate of nitrogen gas introduced into the furnace is 350 sccm or more, and the flow rate of argon gas is 300 sccm or more and 450 sccm or less. It is preferable that the pressure in the furnace is 0.6 Pa to 0.8 Pa. It is preferable that the negative bias voltage applied to the cutting tool serving as a substrate is controlled within the range of -80V to -40V. It is preferable that the hard coating is formed at a furnace temperature of 500°C or higher and 550°C or lower.

[0018] The hard coating of the present embodiment may contain unavoidable impurities included in the sputtering target. Inevitable impurities in the hard coating are allowed to be contained as long as they do not affect the performance of the hard coating. In the hard coating of the present embodiment, it is preferable that the content of impurities other than metal elements including semimetals and nitrogen is 1 atomic% or less for each element as measured by quantitative analysis using EPMA (Electron Probe Micro Analyzer).

[0019] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. [Examples]

[0020] <Tool> As a tool, a two-flute ball end mill (tool diameter: 0.8 mm, manufactured by MOLDINO Co., Ltd.) made of cemented carbide with a composition of WC(bal.)-Co(8.0 mass%)-Cr(0.5 mass%)-Ta(0.3 mass%), an average WC particle size of 0.5 µm, and a hardness of 93.6 HRA (Rockwell hardness, a value measured in accordance with JIS G 0202) was prepared.

[0021] A sputtering apparatus capable of accommodating 12 sputter evaporation sources was used. Of these deposition sources, six AlCrSi alloy targets (Al 58%, Cr 40%, Si 2%, the numbers represent atomic ratios, the same applies below) and six TiSi alloy targets (Ti 80%, Si 20%) were installed in the apparatus as deposition sources. The targets used had dimensions of 16 cm in diameter and 12 mm in thickness. The tool was fixed to the sample holder inside the sputtering apparatus, and a bias power supply was connected to the tool. The bias power supply was designed to apply a negative bias voltage to the tool independently of the target. The tool rotated at 3 revolutions per minute and revolved around the fixed jig and sample holder. The nearest-nearest distance between the tool and the target surface was set to 100 mm. The introduced gases were Ar and N2, and were supplied through a gas supply port provided in the sputtering apparatus.

[0022] <Bombard treatment> First, before applying a hard coating to the tool, the tool underwent bombardment using the following procedure: The furnace temperature was raised to 430°C by the heater in the sputtering apparatus and heated for 30 minutes. Afterward, the furnace of the sputtering apparatus was evacuated, and the furnace pressure was set to 5.0 × 10⁻⁶. -3 The pressure was kept below Pa. Then, Ar gas was introduced into the furnace of the sputtering apparatus, and the furnace pressure was adjusted to 0.8 Pa. A DC bias voltage of -200V was applied to the tool to perform tool cleaning (bombardment) with Ar ions.

[0023] In this embodiment 1, after bombardment, while maintaining the furnace temperature at 510°C, Ar gas was introduced into the sputtering apparatus at 400 sccm, and then N2 gas was introduced at 470 sccm to set the furnace pressure to 0.72 Pa. Next, a DC bias voltage of -50V was applied to the tool, and a pressure of 1.5 kW / cm was applied to the AlCrSi alloy target. 2The maximum power density was applied, the discharge time per power cycle was set to 3.6 milliseconds, and the time during which power was simultaneously applied to the AlCrSi alloy target was 10 microseconds, resulting in a coating of AlCrSi nitride with a film thickness of approximately 0.6 μm.

[0024] Next, while maintaining the furnace temperature at 510°C, Ar gas was introduced into the sputtering apparatus at a rate of 400 sccm, followed by N2 gas at a rate of 410 sccm to bring the furnace pressure to 0.7 Pa. Then, a DC bias voltage of -50 V was applied to the tool, and a sputtering rate of 1.5 kW / cm² was applied to the AlCrSi alloy target. 2 The maximum power density was applied, the discharge time per power cycle was set to 3.6 milliseconds, and the time during which power was simultaneously applied to the AlCrSi alloy target was set to 10 microseconds. Additionally, 1.5 kW / cm² was applied to the TiSi alloy target. 2 The maximum power density was applied, with a discharge time of 3.6 milliseconds per power cycle, and the total time that power was simultaneously applied to the TiSi alloy target was 10 microseconds. Then, power was continuously applied to each alloy target to coat it with a laminated film with individual layer thicknesses of approximately 4 nm and a total film thickness of approximately 0.1 μm. This laminated film is a hard film in which layers of AlCrSi nitride and TiSi nitride are alternately stacked. In the laminated film, the AlCrSi nitride layer contains Ti, and the TiSi nitride layer contains Al and Cr.

[0025] Next, while maintaining the furnace temperature at 510°C, Ar gas was introduced into the sputtering apparatus at a rate of 400 sccm, followed by N2 gas at a rate of 270 sccm to bring the furnace pressure to 0.54 Pa. A DC bias voltage of -50V was applied to the tool, and a sputtering rate of 1.5 kW / cm² was applied to the TiSi alloy target. 2 By applying the maximum power density, with a discharge time of 3.6 milliseconds per cycle of applied power, and assuming a total power application time of 10 microseconds, a TiSi nitride layer with a thickness of approximately 0.4 μm was coated onto the TiSi alloy target.

[0026] This second embodiment is the same as this first embodiment, except that the furnace temperature was set to 540°C when coating each layer of the hard coating. Comparative Example 1 was the same as Example 1 except that the furnace temperature was set to 430°C when coating each layer of the hard coating. Comparative Example 2 was the same as Example 1 except that the furnace temperature was set to 450°C when coating each layer of the hard coating. Comparative Example 3 was the same as Example 1 except that the furnace temperature was set to 480°C when coating each layer of the hard coating. Comparative Example 4 was the same as Example 1 except that the furnace temperature was set to 570°C when coating each layer of the hard coating.

[0027] The hard coating composition was measured using wavelength-dispersive electron probe microanalysis (WDS-EPMA) attached to an electron probe microanalyzer (JXA-8500F, manufactured by JEOL Ltd). A ball end mill used for physical property evaluation was mirror-finished, and the irradiation current was set to an acceleration voltage of 10kV and an irradiation current of 5×10⁻¹⁰ -8 A. With an acquisition time of 10 seconds, five measurements were taken within a 1 μm diameter area, and the Ar content ratio was determined from the average value.

[0028] Using an X-ray diffractometer (EMPYREA, manufactured by PaNalytical Co., Ltd.), the crystal structure was confirmed and the full width at half maximum (FWHM) was measured under the following conditions: tube voltage 45kV, tube current 40mA, X-ray source Cukα (λ=0.15405nm), and 2θ 20-80 degrees.

[0029] The hardness and elastic modulus of an AlCrSi nitride layer were analyzed using a nanoindentation tester (ENT-2100, Elionix Co., Ltd.). For the analysis, the cross-section of the film, with the test piece tilted 5 degrees relative to the outermost surface of the film, was mirror-polished. A region was selected within the polished surface of the film where the maximum indentation depth was less than approximately 1 / 10 of the film thickness. Fifteen measurements were taken under an indentation load of 9.807 mN, and the hardness and elastic modulus were calculated from the average of the five points obtained by excluding the five points with the highest values ​​and the five points with the lowest values.

[0030] The residual compressive stress of the hard coating was calculated by measuring the deflection of a sample using a roughness tester (surface roughness tester DX-23 manufactured by Tokyo Seimitsu Co., Ltd.) under the measurement conditions of a measurement length of 22 mm and a measurement speed of 1.5 mm / s, and using the following formula. Here, Es is the Young's modulus of the base material, D is the thickness of the test piece, δ is the deflection of the test piece occurring before and after coating, L is the length from the end face in the length direction of the test piece deflected by the coating to the maximum deflection portion, vs is the Poisson's ratio of the base material used for the test piece, and d is the film thickness of the hard coating coated on the surface of the test piece.

[0031] (Formula) σ=Es*D 2 *δ / 3*I 2 *(1-νs)*d

[0032] (Condition) Dry machining Tool: 2-flute cemented carbide ball end mill Model number: EPDBE2010-6, ball radius 0.5 mm Cutting method: Bottom surface cutting Work material: STAVAX (52HRC) (manufactured by Bohler Uddeholm K.K.) Depth of cut: Axial direction, 0.03 mm; radial direction, 0.03 mm Cutting speed: 67.8 m / min Feed per flute: 0.0135 mm / flute Cutting distance: 15 m Evaluation method: After cutting, observation was performed at a magnification of 1000× using a scanning electron microscope, the width of abrasion between the tool and the workpiece on the tool flank was measured, and the portion with the largest abrasion width was defined as the maximum flank wear width.

[0033] [Table 1]

[0034] All of the hard coatings have a face-centered cubic crystal structure, and contained argon in the range of 0.01 to 0.03 atomic%. As representative examples of microstructure observation images, Figure 1 shows a fracture surface observation image of Example 1, and Figure 2 shows a fracture surface observation image of Comparative Example 1. In Examples 1 and 2 and Comparative Example 4, where the coating temperature was high, the AlCrSi nitride layer was refined. On the other hand, no significant microstructure change due to coating temperature was observed in the upper TiSi nitride layer. As a representative example of X-ray diffraction, Figure 3 shows the X-ray diffraction results for Example 1. The full width at half maximum (FWHM) of the (111) plane in Examples 1 and 2 was 0.56° to 0.57°, which was smaller than the others. In Comparative Example 4, the AlCrSi nitride layer was refined, but because the coating temperature was too high, the FWHM value of the (111) plane was large, and the hardness, elastic modulus, and residual stress were lower compared to these examples. Examples 1 and 2 showed superior coating properties and durability of coated cutting tools compared to the comparative example. It is presumed that Examples 1 and 2, with a half-width of 0.56° to 0.57° on the (111) plane of the hard coating, exhibited high hardness, elastic modulus, and compressive residual stress while maintaining a refined coating structure, resulting in superior durability of the coated cutting tools.

Claims

[Claim 1] The invention comprises a substrate and a hard coating formed on the substrate, wherein the hard coating has a layer of AlCrSi nitride provided on the substrate and a layer of TiSi nitride provided on the AlCrSi nitride layer. A coated cutting tool characterized in that the entire hard coating exhibits a face-centered cubic lattice structure in X-ray diffraction, has a peak in the (111) plane in the range of 37° to 38° for 2θ determined by X-ray diffraction, the full width at half maximum of the (111) plane X-ray diffraction peak is 0.50° or more and 0.60° or less, and contains 0.2 atomic percent or less of Ar when the total of metallic elements including semimetals and nonmetallic elements is taken as 100 atomic percent.

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