Covering tools

Abstract

To provide a coating tool that can achieve excellent durability, while reducing droplets.SOLUTION: A coating tool comprises a base material and a hard film on the base material. The hard film has an A layer formed on the base material and a B layer formed on the A layer. The A layer is nitride or carbonitride containing 50 atom% or more and 70 atom% or less of Al and 30 atom% or more and 50 atom% or less of Cr, with respect to total amounts of metal (including semimetal) elements. The B layer is nitride or carbonitride containing 70 atom% or more and 85 atom% or less of Al and a 15 atom% or more and 30 atom% or less of Cr, with respect to the total amounts of the metal (including semimetal) elements. A grain of the B layer is finer than a grain of the A layer. In the B layer, streaky-shaped phases having different brightness are confirmed by observation using a transmission electron microscope. The phases having different brightness have regions where contents of Al are relatively more and regions where contents of Al are relatively less. The A layer and the B layer contain Ar.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a coated tool applied to tools such as dies and cutting tools.

Background Art

[0002] [[ID=eleven]] AlCr nitride is a film type excellent in wear resistance and heat resistance and is widely applied as a coated die or a coated cutting tool. In recent years, coated tools coated with an Al-rich AlCr nitride having an Al content ratio exceeding 70 atomic% by an arc ion plating method have begun to be proposed (Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a small-diameter tool such as a tool having a tool diameter of 2 mm or less, the influence of droplets on the tool performance tends to be large. The present inventor has confirmed that an Al-rich AlCr nitride coated by an arc ion plating method tends to have many droplets and there is room for improvement in the durability of the tool. Droplets can be reduced by using a sputtering method for forming a hard film. However, when a hard film is simply formed using a sputtering method, the wear resistance may be inferior to that of a hard film formed using an arc ion plating method. In view of the above circumstances, the present invention aims to provide a coating tool that reduces droplets by applying a sputtering method to Al-rich AlCr nitride or carbonitride while achieving durability equivalent to or better than that obtained by using an arc ion plating method. [Means for solving the problem]

[0005] A coating tool according to one aspect of the present invention comprises a base material and a hard coating film on the base material, The hard coating comprises a layer A provided on the substrate and a layer B provided on the layer A. The aforementioned layer A is a nitride or carbonitride containing Al in an amount of 50 atomic% to 70 atomic% and Cr in an amount of 30 atomic% to 50 atomic% relative to the total amount of metal elements (including metalloids). The aforementioned B layer is a nitride or carbonitride containing Al in an amount of 70 atomic% to 85 atomic% and Cr in an amount of 15 atomic% to 30 atomic% relative to the total amount of metal elements (including metalloids). The aforementioned layer B is finer than the aforementioned layer A. In the aforementioned layer B, streaky phases with varying brightness were observed using a transmission electron microscope. The aforementioned phases of different brightness levels have regions with relatively high Al content and regions with relatively low Al content. The coated tool is composed of layers A and B, both containing Ar. [Effects of the Invention]

[0006] According to the present invention, a highly durable coated tool can be obtained that has an Al-rich AlCr nitride or carbonitride sputtered coating. [Brief explanation of the drawing]

[0007] [Figure 1] This is a bright-field STEM image (40,000x magnification) of the hard coating according to this embodiment 1. [Figure 2] This is a dark-field STEM image (40,000x magnification) of the hard coating according to this embodiment 1. [Figure 3] This is a cross-sectional TEM image (400,000x magnification) of layer A according to this embodiment 1. [Figure 4] This is a cross-sectional TEM image (400,000x magnification) of layer B according to this embodiment 1. [Modes for carrying out the invention]

[0008] The inventors have confirmed that sputtered coatings of Al-rich AlCr nitrides or carbonitrides having a specific microstructure exhibit excellent durability on coating tools. The embodiments of the present invention will be described in detail below. The coated tool of this embodiment has a layer A consisting of columnar crystals formed on a substrate, and a layer B consisting of columnar crystals and fine crystals formed on layer A. The coated tool of this embodiment can be applied to molds and cutting tools. In particular, it is preferable to apply it to small-diameter end mills with a tool diameter of 5 mm or less, and more preferably 3 mm or less.

[0009] In this embodiment, the base material is not particularly limited. Cold work tool steel, hot work tool steel, high-speed steel, cemented carbide, etc., may be used as appropriate depending on the application. The base material may be pre-treated with nitriding or bombardment.

[0010] First, let me explain Layer A. Layer A is provided on the substrate. Layer A is a nitride or carbonitride containing 50 to 70 atomic percent Al and 30 to 50 atomic percent Cr relative to the total amount of metal elements (including metalloids; the same applies hereinafter). Nitrides or carbonitrides mainly composed of Al and Cr have an excellent balance of wear resistance and heat resistance, and also exhibit excellent adhesion to the substrate. In layer A, the Al content is 50 atomic percent or more, assuming that the total amount of metal elements constituting layer A is 100 atomic percent. Furthermore, it is preferable that the Al content of layer A is 55 atomic percent or more. On the other hand, if the Al content becomes too high, the toughness of the hard coating decreases. Therefore, the Al content of layer A is 70 atomic percent or less. Furthermore, it is preferable that the Al content of layer A is 65 atomic percent or less. The A layer has a Cr content ratio of 30 atomic % or more. This increases the durability of the A layer and also increases the adhesion to the substrate. Furthermore, it is preferable that the A layer has a Cr content ratio of 35 atomic % or more. On the other hand, if the Cr content ratio becomes too large, the amount of Al relatively decreases, and the heat resistance of the A layer deteriorates. Therefore, the A layer has a Cr content ratio of 50 atomic % or less. Furthermore, it is preferable that the Cr content ratio of the A layer is 45 atomic % or less.

[0011] The A layer is composed of columnar crystals. The crystal structure of the A layer is cubic. The columnar crystals of the A layer extend along the film thickness direction of the hard film. The adhesion is increased because the A layer provided on the substrate is composed of columnar crystals. The average crystal grain size of the A layer is preferably 120 nm or more and 300 nm or less. That is, the average width of the columnar crystals of the A layer is preferably 120 nm or more and 300 nm or less. The average crystal grain size of the A layer or the average width of the columnar crystals can be obtained from a cross-sectional observation image using a transmission electron microscope. The width of the columnar crystals of the A layer is the length of the columnar crystals in a direction orthogonal to the direction in which the columnar crystals extend (substantially the film thickness direction). The average width of the columnar crystals is calculated using the width measured at the central portion in the film thickness direction of the hard film. The central portion in the film thickness direction refers to a portion within 10% from the center in the film thickness direction of the hard film to both sides in the film thickness direction. The average width of the columnar crystals is calculated as the average value of the widths of 10 or more columnar crystals confirmed by the cross-sectional observation image. The film thickness of the A layer is preferably 0.3 μm or more and 3 μm or less.

[0012] The A layer may contain metal elements other than Al and Cr. For example, for the purpose of improving wear resistance, heat resistance, etc., the A layer can also contain one or more elements selected from the elements of Group 4a, Group 5a, and Group 6a of the periodic table and Si, B, Y, YB, and Cu. These elements are generally contained to improve the film properties of the coated tool and can be added within a range that does not significantly reduce the durability of the coated tool. However, if the content ratio of metal elements other than Al and Cr becomes too large, the durability of the coated tool may decrease. Therefore, when the A layer contains metal elements other than Al and Cr, the total content ratio is preferably 10 atomic% or less, and more preferably 5 atomic% or less.

[0013] Next, the B layer will be described. The B layer is provided on the A layer. The B layer is a nitride or carbonitride containing 70 atomic% or more and 85 atomic% or less of Al and 15 atomic% or more and 30 atomic% or less of Cr with respect to the total amount of metal elements. The B layer has an Al content ratio of 70 atomic% or more. As the Al content in the B layer increases, it becomes easier to form an oxidation protective film on the tool surface, and the film structure becomes finer, so wear of the hard film due to welding is likely to be suppressed. Furthermore, the Al content ratio of the B layer is preferably 75 atomic% or more. On the other hand, if the Al content ratio becomes too large, the toughness of the hard film will be significantly reduced. Therefore, the B layer has an Al content ratio of 90 atomic% or less. Furthermore, the Al content ratio of the B layer is preferably 85 atomic% or less. The B layer has a Cr content ratio of 10 atomic% or more. This makes it easier to form a uniform and dense oxidation protective film on the tool surface during processing, and tool damage is likely to be suppressed. Furthermore, the B layer preferably has a Cr content ratio of 15 atomic% or more. On the other hand, if the Cr content ratio becomes too large, the relative amount of Al will decrease, and it will be difficult to obtain the effect of increasing the Al content ratio. Therefore, the B layer has a Cr content ratio of 30 atomic% or less. Furthermore, the B layer preferably has a Cr content ratio of 25 atomic% or less.

[0014] The B layer may contain metallic elements other than Al and Cr. For example, the B layer may contain one or more elements selected from groups 4a, 5a, and 6a of the periodic table, as well as Si, B, Y, YB, and Cu, for the purpose of improving wear resistance and heat resistance. These elements are generally included to improve the coating properties of coated tools and can be added in a range that does not significantly reduce the durability of the coated tool. However, if the content ratio of metallic elements other than Al and Cr becomes too high, the durability of the coated tool may decrease. Therefore, when the B layer contains metallic elements other than Al and Cr, it is preferable that the total content ratio is 10 atomic% or less, and more preferably 5 atomic% or less.

[0015] Layer B is finer-grained than layer A. That is, the average grain size of layer B is smaller than the average grain size of layer A. Layer B may also be composed of grains with a grain size smaller than the average grain size of layer A. Layer B may also be composed of grains smaller than the grains of layer A. The fine-grained structure of layer B makes it easier to suppress wear of the hard coating due to welding. In addition, it makes it easier for a uniform oxide protective film to form on the tool surface. In this embodiment, layer B consists of columnar crystals and microcrystals. Preferably, the columnar crystals of layer B have an average grain size of 50 nm or less, and the microcrystals have an average grain size of 10 nm or less. The method for calculating the average grain size of the columnar crystals of layer B is the same as the method for calculating the average grain size of layer A described above. The average grain size of the microcrystals of layer B can be measured from a cross-sectional image obtained using a transmission electron microscope using the section method or the area measurement method.

[0016] In layer B, streaky phases of varying light and dark colors are observed using a transmission electron microscope. These phases have regions with relatively high Al content and regions with relatively low Al content. Each of these streaky phases extends along the thickness direction of layer B. The direction in which these streaky phases extend may be inclined with respect to the thickness direction of layer B. The crystal structure of layer B consists of cubic and hexagonal crystals. The regions with relatively high Al content have a higher proportion of hexagonal AlN compared to the regions with relatively low Al content. The thickness of layer B is preferably 0.5 μm or more and 3 μm or less. It is preferable that layer B is thicker than layer A. The boundary between layer A and layer B is preferably uneven. The boundary between layer A and layer B is preferably more uneven than the upper surface of layer B and the substrate surface. The uneven boundary can be confirmed by cross-sectional observation with a transmission electron microscope. The uneven boundary between layer A and layer B can further improve the adhesion between layer A and layer B, which have different particle sizes. The boundary between layer A and layer B is preferably made up of multiple irregularities with a length of 0.1 μm or more from top to bottom. The length from top to bottom may be 0.3 μm or more.

[0017] Layers A and B are sputtered coatings and contain argon (Ar). Being sputtered coatings reduces the frequency of droplet formation, which are defects in hard coatings. To stabilize the coating properties, it is preferable that layers A and B contain argon at a concentration of 0.01 atomic% or more relative to the total amount of metallic and nonmetallic elements. Furthermore, it is preferable that layers A and B contain argon at a concentration of 0.05 atomic% or more. A high argon content can lead to defects. It is preferable that layers A and B contain argon at a concentration of 0.80 atomic percent or less relative to the total amount of metallic and nonmetallic elements. Furthermore, it is preferable that the argon content ratio be 0.70 atomic percent or less. Layer B, with its finer structure, tends to contain more argon than layer A. The hard coating according to this embodiment may also contain noble gases other than argon if sputtered using a mixed gas containing other noble gases in addition to argon.

[0018] The argon content of the hard coating according to this embodiment can be measured using an electron probe microanalyzer (EPMA) on a mirror-finished hard coating, similar to the measurement of the metal element content described above. Similar to the measurement of the metal element content described above, it can be determined from the average of five analysis points within an analysis range of approximately 1 μm in diameter after mirror finishing. The hard coating according to this embodiment may contain trace amounts of argon, oxygen, and carbon as nonmetallic elements, in addition to nitrogen.

[0019] <Interlayer, upper layer> In this embodiment, to further improve the adhesion of the hard coating, an intermediate coating may be provided between the tool's base material and the hard coating, if necessary. For example, a layer made of metal, nitride, carbonitride, or carbide may be provided between the tool's base material and the hard coating. Furthermore, a hard film having a different component ratio or composition from the hard film according to this embodiment may be formed separately on top of the hard film according to this embodiment. Moreover, the hard film according to this embodiment and a separate hard film having a different composition ratio or composition from the hard film according to this embodiment may be laminated together.

[0020] <Manufacturing method> In the hard coating according to this embodiment, it is preferable to apply a sputtering method using three or more AlCr alloy targets, sequentially applying power to the targets, and providing a period of time during which power is simultaneously applied to both the target to which power application has ended and the target to which power application has started when the target to which power is being applied switches. Such a sputtering method maintains a high ionization rate of the target material during coating, resulting in a dense hard coating at the micro level, and inevitably tends to contain less argon and oxygen. Furthermore, it is preferable to set the furnace temperature of the sputtering apparatus to 350°C to 500°C, the negative pressure bias voltage applied to the substrate to -170V to -40V, and the furnace pressure to 0.1Pa to 0.4Pa by introducing Ar gas and N2 gas. When coating with carbonitride, a small amount of carbon may be added to the target, or part of the reaction gas may be replaced with methane gas.

[0021] The maximum power density of a power pulse is 0.1 kW / cm². 2 It is preferable to keep it above. Furthermore, 0.3 kW / cm² is preferable. 2 The above is preferable. Furthermore, in this composition system, if the energy of the film-forming ions becomes too high, the hexagonal crystals become too numerous. Therefore, the maximum power density of the power pulse is 0.8 kW / cm². 2The following is preferable: The duration of the power pulse applied to each target is preferably 30 milliseconds or less. Furthermore, the time during which power is simultaneously applied to both the alloy target where power application ends and the alloy target where power application begins is preferably 20 microseconds or more and 100 microseconds or less.

[0022] The same AlCr alloy target may be used for coating layers A and B. The film composition can be adjusted by changing the ionization rate of the target material by changing the maximum power density. In sputtering of an AlCr alloy target, Cr is relatively easier to ionize, and Al is relatively more difficult to ionize. Therefore, when the maximum power density of the power pulse is small, the amount of Al in the hard film may be less than that of the target composition. When coating with the hard film according to the present invention, the same AlCr alloy target may be used for coating layers A and B, with a smaller maximum power density of the power pulse for layer A and a larger maximum power density for layer B. Alternatively, layers A and B may be coated using AlCr alloy targets with different compositions. [Examples]

[0023] <Base material> As a base material, a two-flute ball end mill made of cemented carbide with a composition of WC(Bal.)-Co(8.0 mass%)-VC(0.3 mass%)-Cr3C2(0.5 mass%) and a hardness of 94.0 HRA (Rockwell hardness, measured according to JIS G 0202) was prepared.

[0024] This embodiment 1 used a sputtering apparatus capable of mounting six sputter evaporation sources. Of these deposition sources, six Al75Cr25 alloy targets (values ​​are atomic ratios, the same applies below) were installed in the apparatus as deposition sources to coat a hard film. The tool, which served as the substrate, was fixed to a sample holder within 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 on its own axis at 2 revolutions per minute and revolved around the fixed jig and sample holder. The distance between the tool and the target surface was 100 mm. The introduced gases were Ar and N2, and were supplied through a gas supply port provided in the sputtering apparatus.

[0025] <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 400°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 -170 V was applied to the tool, and tool cleaning (bombardment) with Ar ions was performed for more than 20 minutes.

[0026] <Coating with a hard film> In the coating of this embodiment 1, the furnace temperature was set to 400°C, and Ar gas (0.16 Pa) and N2 gas (0.10 Pa) were introduced into the sputtering apparatus furnace to set the furnace pressure to 0.26 Pa. A DC bias voltage was applied to the substrate, and the overlap time of the power applied to the targets was set to 50 microseconds. The discharge time per cycle of the power applied to each target was 0.2 milliseconds, and the maximum power density was 0.4 kW / cm². 2 Then, with a negative pressure bias voltage of -60V applied to the substrate, power was continuously applied to six Al75Cr25 alloy targets to coat the substrate with an A layer of approximately 1.0 μm. Next, the maximum power density applied to each target is set to 0.8 kW / cm². 2 Then, a layer B approximately 2.0 μm thick was coated on top of layer A.

[0027] Comparative Example 1 used an arc ion plating apparatus. An Al60Cr40 alloy target was placed inside the apparatus as the deposition source. First, the tool was cleaned with Ar ions (bombardment treatment). Next, the furnace pressure of the arc ion plating apparatus was set to 5.0 × 10⁻⁶ -3 The furnace was evacuated to below Pa, the internal temperature was set to 500°C, and N2 gas was introduced to achieve an internal pressure of 3.2 Pa. Next, a DC bias voltage of -100V was applied to the tool, and a current of 150A was supplied to the Al60Cr40 alloy target to coat the surface of the tool with a hard film of approximately 3.0 μm. Comparative Example 1 is a composition commonly used in the market.

[0028] The hard coating was analyzed using wavelength-dispersive electron probe microanalysis (WDS-EPMA) attached to an electron probe microanalyzer (JXA-8500F, manufactured by JEOL Ltd). Acceleration voltage: 10kV, irradiation current: 5×10⁻¹⁰ -8 A. With an acquisition time of 10 seconds, five points were measured within an analysis area with a diameter of 1 μm. In this Example 1, the average composition of layer A was Al65Cr35N (atomic ratio), and the average composition of layer B was Al75Cr25N (atomic ratio). Furthermore, in relation to the total amount of metallic and nonmetallic elements, layer A contained 0.36 atomic percent Ar, and layer B contained 0.55 atomic percent Ar.

[0029] Microanalysis was performed on Example 1 using a transmission electron microscope. Figure 1 shows a bright-field STEM image, and Figure 2 shows a dark-field STEM image. Layer A on the substrate side and layer B on top of it are visible. Layer B is confirmed to be finer in grain than layer A. Figure 3 shows a cross-sectional TEM image of layer A. Figure 4 shows a cross-sectional TEM image of layer B. Layer A consists of columnar crystals, while layer B consists of columnar crystals and fine crystals. Streaky phases of different brightness and darkness are visible in layer B. The crystal structure of layer A was cubic. The crystal structure of layer B was cubic and hexagonal. Analysis of the phases of different brightness and darkness revealed that the bright areas in Figure 1 had a relatively high Al content, and the dark areas had a relatively low Al content. The areas with a relatively high Al content had more hexagonal AlN compared to the areas with a relatively low Al content.

[0030] (Condition) Dry processing Tool: 2-flute carbide ball end mill Model number: EPDBE2010-6, ball radius 0.5mm Cutting method: bottom cutting Workpiece material: STAVAX (52HRC) (manufactured by Börer Uddeholm Co., Ltd.) Cutting depth: Axial direction, 0.04 mm; Radial direction, 0.04 mm Cutting speed: 75.4m / min Feed rate per blade: 0.018 mm / blade Cutting distance: 15m Evaluation method: After machining, the workpiece was observed using a scanning electron microscope at a magnification of 1000x. The width of the friction between the tool and the workpiece on the tool flank surface was measured, and the portion with the largest friction width was defined as the maximum wear width of the flank surface.

[0031] [Table 1]

[0032] This embodiment 1, having the microstructure described above, exhibited a smaller maximum flank wear width and superior durability compared to comparative example 1. It is presumed that tool damage was suppressed because this embodiment 1 had a high Al content and a fine coating structure.

Claims

[Claim 1] A coating tool comprising a base material and a hard coating film on the base material, The hard coating has a layer A provided on the substrate and a layer B provided on the layer A. The aforementioned layer A is a nitride or carbonitride containing Al in an amount of 50 atomic% to 70 atomic% and Cr in an amount of 30 atomic% to 50 atomic% based on the total amount of metal (including metalloid) elements. The aforementioned B layer is a nitride or carbonitride containing Al in an amount of 70 atomic% to 85 atomic% and Cr in an amount of 15 atomic% to 30 atomic% relative to the total amount of metal (including metalloid) elements. The aforementioned layer B is finer than the aforementioned layer A. In the aforementioned layer B, streaky phases with varying brightness were observed using a transmission electron microscope. The aforementioned phases of different brightness levels have regions with relatively high Al content and regions with relatively low Al content. A coating tool characterized in that the aforementioned layer A and layer B contain Ar.

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