JP7775560B2 - Hard coating and cutting tool using same - Google Patents

Description

The present invention relates to a hard coating and a cutting tool using the same.

Cutting tools used to process metal materials such as steel are subject to high impacts and may be exposed to temperatures of over 800°C during cutting because the objects they cut are extremely hard. For this reason, the surface of cutting tools is usually coated to improve their wear resistance, heat resistance, etc.

The coating is achieved by depositing nitrides such as titanium and chromium onto a substrate such as high-speed steel or cemented carbide to form a thin film. Various methods have been proposed to improve wear resistance, etc.

For example, Patent Document 1 proposes a hard material layer having at least one layer package in which the hard material layer has at least one (Al _y Cr _1-y )X layer (0.2≦y≦0.7) and/or one (Ti _z Si _{1- z} )X layer (0.01≦z≦0.3), further includes one (AlCrTiSi)X mixed layer, then another ( _Ti z Si 1-z )X layer, then another (AlCrTiSi)X mixed layer, then another (Al _y Cr _1-y )X layer, where X is, for example, N.

JP 2013-176837 A

Patent Document 1 describes that optimal thicknesses of the Al _y Cr _1-y N layer and Ti _z Si _1-z N layer in the hard material layer are necessary to improve the life (paragraph [0016] of Patent Document 1). The optimal thicknesses are 75 to 200 nm, preferably 120 to 170 nm, for the Al _y Cr _1-y N layer, and 50 to 150 nm, preferably 70 to 120 nm, for the Ti _z Si _1-z N layer.

AlCrN and TiSiN are materials commonly used to coat cutting tools. AlCrN has the advantage of excellent chipping resistance at low temperatures, but the disadvantage of reduced hardness and strength at high temperatures due to the loss of N. TiSiN also has the advantage of excellent wear resistance and being suitable for high-speed cutting operations, but the disadvantage of being hard and brittle. Therefore, hard coatings containing AlCrN and TiSiN are required to possess both of these advantages while avoiding the above disadvantages.

The hard material layer described in Patent Document 1 includes the mixed layer and has thick Al _y Cr _1-y N and Ti _z Si _1-z N layers, so there is a high probability that it will exhibit average properties of AlCrN and TiSiN or that any of the above-mentioned drawbacks will become apparent. Therefore, there is room for improvement in terms of the hard material layer exhibiting stable high performance under a wide range of processing conditions.

Furthermore, other conventional hard coatings have not been able to avoid the problem of the defects of either AlCrN or TiSiN being exposed. As a result, cutting tools coated with these hard coatings have insufficient properties such as hardness, heat resistance, wear resistance, and chipping resistance, and have a short lifespan, especially under severe cutting conditions.

Therefore, one aspect of the present invention aims to realize a hard coating that combines the advantages of AlCrN and TiSiN and exhibits stable, high performance under a wide range of processing conditions, as well as a cutting tool that uses the same.

The inventors investigated the composition and structure of a hard coating that combines the advantages of AlCrN and TiSiN. As a result, they discovered that by using specific compositions of AlCrN and TiSiN and forming specific layered structures of AlCrN and TiSiN layers, it is possible to create a hard coating that exhibits stable, high performance under a wide range of processing conditions, leading to the invention.

In order to solve the above problems, a hard coating according to one embodiment of the present invention has a structure in which A layers made of Al _x Cr _1-x N and B layers made of Ti _1-y Si _y N are alternately laminated, and when a combination of the alternately laminated A layers and B layers is called C layer, the thickness of C layer is 7 nm or more and 18 nm or less, the total thickness of C layer is 1 μm or more and 6 μm or less, and the thicknesses of A layer and B layer are each less than 10 nm (where x is 0.6 or more and 0.7 or less, and y is more than 0.05 and less than 0.08).

One aspect of the present invention makes it possible to realize a hard coating that combines the advantages of AlCrN and TiSiN and exhibits stable, high performance under a wide range of machining conditions, as well as a cutting tool using the same. In other words, it is possible to provide a hard coating that has excellent wear resistance, heat resistance, and chipping resistance, as well as excellent film strength.

1 is a longitudinal sectional view schematically showing the structure of the surface of a cutting tool provided with a hard coating according to an embodiment of the present invention. 1 is a vertical cross-sectional view schematically showing an example of the structure of an arc evaporation device. 3 is a top view of the arc evaporation device shown in FIG. 2 when viewed vertically from above. FIG. 1 shows X-ray diffraction patterns obtained by subjecting two types of cutting tools (sample 1 and sample 2) provided with hard coatings in which AlCrN and TiSiN are laminated together to X-ray diffraction. FIG. 5 is an enlarged view of the vicinity of 2θ=34 to 40° in FIG. 4. The X-ray diffraction patterns are shown when three types of cutting tools (samples 3 to 5) provided with hard coatings in which AlCrN and TiSiN are laminated are subjected to X-ray diffraction. FIG. 7 is an enlarged view of the vicinity of 2θ=34 to 40° in FIG. 6. The hard coating of one of the cutting tools obtained in the examples was observed with a scanning transmission electron microscope (STEM), and the results are shown below. This is the result of observing the hard coating shown in the left diagram of FIG. 8 at a magnification of 1,000,000 times.

One embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of the present invention. Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[Embodiment 1: Hard Coating]
A hard coating according to one embodiment of the present invention has a structure in which A layers made of Al _x Cr _1-x N and B layers made of Ti _1-y Si _y N are alternately laminated, and when a combination of the alternately laminated A layers and B layers is called C layer, the thickness of C layer is 7 nm or more and 18 nm or less, the total thickness of C layer is 1 μm or more and 6 μm or less, and the thicknesses of A layer and B layer are each less than 10 nm (where x is 0.6 or more and 0.7 or less, and y is more than 0.05 and less than 0.08).
FIG. 1 is a longitudinal cross-sectional view schematically illustrating the surface structure of a cutting tool provided with a hard coating according to one embodiment of the present invention. In the figure, 11 is a substrate, 12 is a hard coating, and 10 is a cutting tool. FIG. 1 illustrates a case in which n A layers and n B layers are laminated, with the A layers represented as A ₁ to A _n and the B layers represented as B ₁ to B _n . In the figure, "..." indicates that the descriptions for A ₃ to B _n-1 are omitted. While FIG. 1 illustrates an embodiment in which the surface of substrate 1 is coated with A layer and B layer is laminated on the A layer, the present invention is not limited to this. Alternatively, the surface of substrate 1 may be coated with B layer and A layer may be laminated on the B layer.

1, layers A and layers B are alternately stacked. A layer C (e.g., C 1 , C ₂ , and C _n in the figure), which is a combination of the alternately stacked layers A and _B , has a thickness of 7 nm or more and 18 nm or less.

The "structure in which layers A and B are alternately laminated" refers to a structure in which, for example, the surface of layer A is in contact with the surface of layer B, and the surface of layer B opposite the surface in contact with layer A is in contact with the surface of another layer A, and this structure is repeated. In other words, it refers to a laminate structure in which a combination of a pair of layers A and B is a repeating unit. For example, the surface of layer _A1 in the figure is in contact with the surface of layer _B1 in the figure, and the surface of layer _B1 that is not in contact with layer _A1 is in contact with layer _A2 .

As mentioned above, Al _x Cr _1-x N constituting the A layer has the advantage of excellent chipping resistance at low temperatures, but has the disadvantage of reduced hardness and strength at high temperatures due to the loss of N. Also, Ti _1-y Si _y N constituting the B layer has the advantage of excellent wear resistance and being suitable for high-speed cutting work, but has the disadvantage of being hard and brittle.

By making Layer C a thin layer with a thickness of 7 nm to 18 nm, it is possible to achieve a hard coating that brings out only the advantages mentioned above and does not reveal the disadvantages mentioned above. This point will be explained below.

By setting the thickness of the C layer to 7 nm or more and 18 nm or less, in the hard coating, one A layer is sandwiched between two B layers with the thin C layer stacked. Because one A layer is sandwiched between two B layers, the only exposed surface of the A layer is the side. Because the C layer is thin, the thickness of the side is very thin. Therefore, the N contained in the Al _x Cr _1-x N of the A layer is prevented from falling off by Ti _1-y Si _y N, even at high temperatures.

Furthermore, by setting the thickness of the C layer to 7 nm or more and 18 nm or less, in the hard coating, one B layer is sandwiched between two A layers with the thin C layer stacked. Because the C layer is thin and one B layer is sandwiched between two A layers, the growth of defects or cracks due to the drawbacks of Ti _1-y Si _y N is prevented by Al _x Cr _1-x N.

In this way, the C layers are prevented from revealing the defects of Al _x Cr _1-x N and Ti _1-y Si _y N. The hard coating according to one embodiment of the present invention has a structure in which C layers in which the above-mentioned defects are prevented from appearing are stacked, and therefore the above-mentioned defects are not revealed in the hard coating as a whole, and only the above-mentioned advantages can be revealed.

On the other hand, in the package structure described in Patent Document 1, for example, as mentioned above, the optimum layer thickness is 75 to 200 nm, preferably 120 to 170 nm, for the Al _y Cr _1-y N layer, and 50 to 150 nm, preferably 70 to 120 nm, for the Ti _z Si _1-z N layer.

In such a configuration, due to the large layer thickness, it is not possible to sufficiently prevent the detachment of N from the Al _y Cr _1-y N layer, or to sufficiently prevent the development of defects or cracks due to defects in the Ti _z Si _1-z N layer. Furthermore, the hard substance layer described in Patent Document 1 has a plurality of mixed layers, but the mixed layers are layers that exhibit the average properties of AlCrN and TiSiN, or layers that expose defects that either AlCrN or TiSiN have.

In one embodiment of the present invention, the thickness of the C layer is more preferably 9 nm to 17 nm, and even more preferably 11 nm to 15 nm, which makes it possible to more efficiently prevent the development of defects or cracks caused by the loss of N in Al _x Cr _1-x N and the defects of Ti _1-y Si _y N.

In one embodiment of the hard coating, the thickness of each of the A layer and the B layer is less than 10 nm.

In order for the hard coating to exhibit excellent wear resistance, heat resistance, chipping resistance, and high film strength, it is preferable that the A layer and the B layer are contained in the C layer in a balanced manner. Therefore, the ratio of the thickness of the A layer to the thickness of the B layer within the C layer is preferably 2:3 to 3:2, more preferably 4:5 to 5:4, and most preferably 6:7.

The total thickness of the C layers is 1 μm or more and 6 μm or less. In other words, the hard coating has a structure in which a large number of C layers are stacked, i.e., an ultra-multilayer structure.

The hard coating has a structure in which a structure capable of bringing out only the advantages of Al _x Cr _1-x N and Ti _1-y Si _y N is repeatedly laminated in an ultra-multilayer structure. Therefore, the hard coating has excellent wear resistance, heat resistance, and chipping resistance, as well as excellent film strength. Because the hard coating has these excellent properties, it can be used to process a variety of materials, from soft to hard (for example, hardness of 20 to 60 HRC), and can be adapted to a variety of processing conditions.

As a result, it can deliver stable, high performance under a wide range of processing conditions. The various processing conditions mentioned above include conditions for processing temperatures ranging from low to high, and conditions for processing methods such as wet processing, dry processing, and high-speed cutting.

These hard coatings are particularly suitable for use in gear cutting. Gear cutting is the process of cutting steel or other materials into complex gear shapes. Machining the large cuts in the gear shape places a heavy load on the cutting tool blade. Machining the small cuts in the gear shape places a heavy load only on the cutting edge of the cutting tool. Therefore, hard coatings used in gear cutting are particularly required to have high wear resistance, heat resistance, chipping resistance, and strength.

A hard coating that is weak in any of the following: wear resistance, heat resistance, chipping resistance, and strength cannot withstand harsh cutting conditions at the weak points, resulting in a shortened cutting tool life and reduced processing efficiency. As described above, the hard coating according to one embodiment of the present invention has excellent wear resistance, heat resistance, and chipping resistance, as well as excellent film strength. Therefore, it can be suitably used for gear cutting. Of course, this is not a limitation, and the hard coating can also be suitably used for other processing applications. For example, it can be suitably used as a hard coating for cemented carbide blades, drills, end mills, etc., as described below.

It is more preferable that the total thickness of the C layer is 2 μm or more and 4.5 μm or less.

The hard coating may have an embodiment in which an A layer that does not form the C layer is laminated subsequent to a B layer that forms the C layer at an end of the laminate structure. For example, the hard coating may have an embodiment in which an A layer is laminated subsequent to a _Bn layer as shown in Figure 1. Similarly, the hard coating may have an embodiment in which a B layer that does not form the C layer is laminated subsequent to an A layer that forms the C layer at an end of the laminate structure.

In this case, the structure is one in which the A layer is sandwiched between two B layers, or one in which the B layer is sandwiched between two A layers, so that only the advantages of Al _x Cr _1-x N and Ti _1-y Si _y N can be exhibited, just like when an integer number of C layers are stacked.

The x in the Al _x Cr _1-x N is 0.6 or more and 0.7 or less, and the y in the Ti _1-y Si _y N is more than 0.05 and less than 0.08. A hard coating according to one embodiment of the present invention comprises an A layer made of Al _x Cr _1-x N of the above composition, a B layer made of Ti _1-y Si _y N, and a C layer having a thickness of 7 nm or more and 18 nm or less, and a total thickness of the C layers being 1 μm or more and 6 μm or less. This allows the hard coating to exhibit the excellent wear resistance and the like described above.

Al _x Cr _1-x N in which x is 0.6 or more and 0.7 or less can be prepared by controlling the composition of the AlCr target as a raw material, the N ₂ pressure during C layer formation, the bias voltage, etc. Similarly, Ti _1-y Si _y N in which y is more than 0.05 and less than 0.08 can be prepared by controlling the composition of the TiSi target as a raw material, the N ₂ pressure during C layer formation, the bias voltage, etc.

Furthermore, it can be confirmed by an EDX analyzer attached to the SEM and/or TEM that x in the prepared Al _x Cr _1-x N is 0.6 or more and 0.7 or less, and y in Ti _1-y Si _y N is more than 0.05 and less than 0.08.

The hard coating according to one embodiment of the present invention can be produced, for example, by arc ion plating a substrate. An example of an apparatus that can be used for this method is a vacuum deposition apparatus such as an arc evaporation apparatus (manufactured by Nippon ITF Corporation) equipped with a Stir-One evaporation source.

Fig. 2 is a longitudinal cross-sectional view showing a schematic example of the structure of the arc evaporation device. Fig. 3 is a top view of the arc evaporation device shown in Fig. 2 when viewed vertically from above. In the figure, 20 denotes the arc evaporation device, 21 denotes a Cr evaporation source, 22 denotes an Al _x Cr _1-x arc evaporation source, 23 denotes a Ti _1-y Si _y arc evaporation source, 24 denotes a rotary table, 25 denotes a small table, 26 denotes an arc power supply, and 27 denotes a bias power supply. The small table 25 is connected to the rotary table 24 by gears, and therefore rotates on its own axis as the rotary table 24 rotates. The gear ratio between the rotary table 24 and the small table 25, where the number of gears on the small table 25 is 1, is preferably a value greater than 6 and not an integer.

The interior of the arc evaporation apparatus 20 is a vacuum chamber. Below, we will explain one example of a method for manufacturing a cutting tool by using the arc evaporation apparatus 20 to coat a substrate with a hard coating according to one embodiment of the present invention. This method is also used in the examples described below.

First, the rotating table 24 with the substrate 11 placed on the small table 25 is placed inside (inside the furnace of) the arc evaporation device 20.

Next, the interior of the arc evaporation device 20 is evacuated to a specified degree of vacuum, and the substrate 11 is heated by a heater (not shown) until it reaches 400°C. Subsequently, as shown in FIG. 3, argon gas is introduced into the furnace, and the pressure inside the furnace is set to 1 Pa. After that, a bias voltage of -900 V is applied to the substrate 11 by the bias power supply 27, and the substrate 11 is etched by argon ions. After the argon gas is evacuated, nitrogen gas is introduced into the furnace, and the internal pressure is set to 4 Pa, as shown in FIG. 3.

Next, the arc power supply 26 is operated to cause an arc discharge of Al _x Cr _1-x from the arc evaporation source 22 at 150 A, and an arc discharge of Ti _1-y Si _y from the arc evaporation source 23 at 140 A. As a result, Al _x Cr _1-x and Ti _1-y Si _y are evaporated into the nitrogen gas atmosphere.

Since the turntable 24 is rotating and the substrate 11 is rotating on its axis, when the substrate 11 faces the arc evaporation source 22, Al _x Cr _1-x is evaporated onto the substrate 11 and simultaneously combines with the nitrogen gas, forming a film of Al _x Cr _1-x N on the surface of the substrate 11.

On the other hand, when the substrate 11 faces the arc evaporation source 23, Ti _1-y Si _y is evaporated onto the substrate 11 and simultaneously combines with the nitrogen gas, forming a film of Ti _1-y Si _y N on the surface of the substrate 11.

By repeating the above steps, a hard coating according to one embodiment of the present invention can be formed on the surface of the substrate 11. At this time, a bias voltage is applied to the substrate 11, which strongly attracts ions of the evaporated metal elements (Ti, Si, Al, Cr) into the substrate 11, densifying the film and adjusting the strength and residual stress of the hard coating.

The thickness of the C layer and the total thickness of the C layer can be controlled to between 7 nm and 18 nm and between 1 μm and 6 μm, respectively, by adjusting the arc current and the rotation speed of the turntable 24.

After forming a hard coating having the specified C layer thickness and the total thickness of the C layers, the temperature inside the furnace is cooled to 200°C or below, the furnace is opened to the atmosphere, and the manufactured cutting tool is removed.

The fact that the produced hard coating has a predetermined structure can be confirmed, for example, by observing the longitudinal cross section of the hard coating using a scanning transmission electron microscope. The predetermined structure is a structure in which layers A and B are alternately laminated, with the thickness of layer C being 7 nm to 18 nm, and the total thickness of layers C being 1 μm to 6 μm. For example, based on the observation results shown in Figure 9 (described below), the thickness of layer C can be calculated by measuring the total thickness of 10 to 20 consecutive layers and dividing by the number of combinations of layers A and B. The thicknesses of layers A and B can be determined by measuring the thickness of each of approximately 5 to 10 layers and calculating the average value.

In a hard coating according to one embodiment of the present invention, the ratio (A/B) of the sub-peak intensity (A) to the main peak intensity (B) in the X-ray diffraction pattern of the hard coating is preferably 0.4 or more and 0.75 or less.

The main peak is a peak of the crystals of Layer A and Layer B. Subpeaks are peaks that appear near the main peak (near the low-angle and high-angle sides of the main peak in the X-ray diffraction pattern) and are peaks attributable to the super multi-layer structure. The ratio is an indicator of whether the hard coating has the super multi-layer structure.

The X-ray diffraction pattern can be obtained by performing X-ray diffraction measurement of the hard coating using the θ-2θ method under the following conditions, for example. The conditions are: Measurement device: Bruker AXS X-ray diffractometer D8 DISCOVER, X-ray source: Cu-Kα, tube voltage: 40 kV, tube current: 40 mA, slit width: 0.5°, one-dimensional detector, step: 0.02°, accumulation time: 0.6 seconds, scan range 2θ = 30 to 50°. The method for determining the ratio (A/B) is described below.

Figure 4 shows the X-ray diffraction patterns obtained by subjecting two types of cutting tools (sample 1 and sample 2) equipped with hard coatings made of laminated AlCrN and TiSiN to X-ray diffraction. Figure 5 is an enlarged view of Figure 4 near 2θ = 34 to 40°.

First, as shown in Figure 5, a line was drawn connecting the intensity at 2θ = 34° and the intensity at 2θ = 39° for each of Sample 1 and Sample 2. Next, the differences between the line and each of the following peaks (subpeak 1 near 36°, the peak of the TiSiN(111) plane near 36.5°, the peak of the AlCrN(111) plane near 37.3°, and subpeak 2 near 37.8°) (the length of the vertical line shown in the figure) are defined as the intensities I1, I2, I3, and I4 of each peak. The ratio (A/B) is then defined as (I1 + I4)/(I2 + I3). The results of calculating these ratios for Sample 1 and Sample 2 shown in Figure 4 are shown in Table 1.

Figure 6 shows the X-ray diffraction patterns obtained by subjecting three types of cutting tools (samples 3 to 5) equipped with hard coatings formed by laminating AlCrN and TiSiN to X-ray diffraction. Figure 7 is an enlarged view of the area of 2θ = 34 to 40° in Figure 6. The straight line shown in Figure 7 was drawn, and the ratio (A/B) was determined using the same method as described for samples 1 and 2. The results are shown in Table 2.

The ratio is more preferably 0.45 or greater and 0.72 or less, and even more preferably 0.5 or greater and 0.55 or less. This provides a more useful indicator that the hard coating has the ultra-multilayer structure.

The hard coating according to one embodiment of the present invention preferably has a compressive stress of -0.5 GPa or more and -4.0 GPa or less. According to this configuration, the hard coating has high resistance to impact and is less likely to break. From this viewpoint, the compressive stress is more preferably -1 GPa or more and -3 GPa or less, and even more preferably -1.5 GPa or more and -2.5 GPa or less. The compressive stress can be measured, for example, by the sin ² φ method using X-ray diffraction or a measurement method based on the Stoney equation using a test piece.

The hard coating according to one embodiment of the present invention preferably has a surface roughness Ra of 0.03 μm or more and 0.18 μm or less. If the surface roughness Ra exceeds 0.18 μm, irregularities will occur not only on the surface of the hard coating but also inside, making it difficult to form the ultra-multilayer structure. Furthermore, it will be difficult to find the subpeaks in the X-ray diffraction pattern. The lower the lower limit of the surface roughness Ra, the better, but the practical lower limit is 0.03 μm.

Therefore, a surface roughness Ra of the hard coating of 0.03 μm or more and 0.18 μm or less is an indicator that the hard coating according to one embodiment of the present invention has the ultra-multilayer structure. Furthermore, with this configuration, it can be said that the surface smoothness of the hard coating is extremely high.

As a result, the hard coating can consistently demonstrate high performance under a wide range of processing conditions, and its high smoothness can improve the quality of the processed object.

From this perspective, the surface roughness Ra of the hard coating is more preferably 0.06 μm or more and 0.15 μm or less, and even more preferably 0.08 μm or more and 0.14 μm or less.

The surface roughness Ra can be measured, for example, by the following method. That is, the surface of a test piece with a sufficiently small surface roughness Ra is coated with the hard coating using an ion plating method or the like, and the surface roughness Ra of the coated test piece is then measured.

An example of the test piece is a test piece with a surface roughness Ra of 0.01 μm or less. Because the surface roughness Ra of this test piece is sufficiently small, the surface roughness Ra of the test piece coated with the hard coating can be considered to be the surface roughness Ra of the hard coating.

Another method for measuring the surface roughness Ra is, for example, the following method. That is, a longitudinal section is prepared for a cutting tool whose substrate surface has been coated by ion plating or the like. Next, the shape of the interface between the hard coating and the substrate is extracted as a profile of the substrate surface using a scanning electron microscope, and Ra is calculated according to the Ra calculation method. Similarly, the shape of the hard coating surface is extracted as a film surface profile, and Ra is calculated according to the Ra calculation method. The Ra of the hard coating is determined by subtracting the Ra of the substrate surface from the Ra of the film surface.

Ra can be measured using, for example, a surface roughness measuring instrument manufactured by DEKTAK.

The hard coating according to one embodiment of the present invention preferably has a nanoindentation hardness of 35 GPa or more and 40 GPa or less.

With this configuration, the hard coating has sufficient strength. Therefore, it has sufficient resistance to machining high-hardness materials, which can contribute to improving the sharpness of cutting tools and the ability to remove chips.

The nanoindentation hardness can be measured, for example, using an Elionix Nanoindenter ENT-1100 as the measuring device and a Berkovich indenter to apply a load of 2 g to the hard coating on the surface of the cutting tool.

[Embodiment 2: Cutting Tool]
A cutting tool according to one embodiment of the present invention comprises a substrate and a hard coating covering the surface of the substrate, the hard coating being the hard coating according to one embodiment of the present invention.

Examples of cutting tools include gear cutting tools such as hobs, cemented carbide blades, broaches, rolling flat dies, shaving cutters, and pinion cutters; drills; end mills; thread cutting tools such as taps, thread cutting dies, chasers, thread milling cutters, and thread rolling dies; indexable tools such as inserts; and wear-resistant tools such as drawing tools, rolling tools, shearing tools, forging tools, molds, tools for electronic-related components, and machine attachment parts.

The hard coating according to one embodiment of the present invention does not simply have wear resistance, heat resistance, chipping resistance, or high hardness, but rather has a good balance of all of these properties. Therefore, the cutting tool can be used with a wide range of workpiece materials, for example, with hardnesses ranging from 20 to 60 HRC.

In recent years, the operating conditions for gear cutting tools have become increasingly high-speed and dry, increasing the impact on the cutting edges and causing the cutting edge temperatures to rise. Furthermore, gear cutting tools, like hobs, have multiple cutting edges, and due to the nature of gear cutting, the load on each cutting edge varies.

As a result, cutting tools equipped with hard coatings that are weak in any of the above characteristics cannot be used stably under the above conditions. Furthermore, such cutting tools cannot cope with loads that vary from cutting edge to cutting edge, and therefore cannot be used as gear cutting tools. The cutting tool according to one embodiment of the present invention possesses all of the above characteristics in a balanced manner, allowing for stable operation even under the above conditions. Furthermore, it can be suitably used as a gear cutting tool.

The cutting tool can be obtained by forming the hard coating on a substrate using a method such as arc ion plating. Other methods that can be used include sputtering methods such as HiPIMS (high power pulse sputtering), and vapor deposition.

The substrate can be made of high-speed steel, cemented carbide, etc. Examples of cemented carbide include WC-Co alloys, WC-TiC-Co alloys, WC-TaC-Co alloys, WC-TiC-TaC-Co alloys, WC-Ni alloys, and WC-Ni-Cr alloys.

〔summary〕
The present invention includes the following aspects.
<1>
The substrate has a structure in which an A layer made of Al _x Cr _1-x N and a B layer made of Ti _1-y Si _y N are alternately laminated,
When a combination of the A layer and the B layer alternately stacked is referred to as a C layer, the thickness of the C layer is 7 nm or more and 18 nm or less,
the total thickness of the C layer is 1 μm or more and 6 μm or less,
The hard coating, wherein the thickness of each of the A layer and the B layer is less than 10 nm.

(wherein, x is 0.6 or more and 0.7 or less, and y is more than 0.05 and less than 0.08.)
<2>
<1> The hard coating according to <1>, wherein in an X-ray diffraction pattern of the hard coating, a ratio (A/B) of a sub-peak intensity (A) to a main peak intensity (B) is 0.4 or more and 0.75 or less.
<3>
<1> or <2>. The hard coating according to <1> or <2>, wherein the compressive stress is −0.5 GPa or more and −4.0 GPa or less.
＜4＞
<4> The hard coating according to any one of <1> to <3>, having a surface roughness Ra of 0.03 μm or more and 0.18 μm or less.
<5>
A cutting tool comprising: a substrate; and a hard coating covering a surface of the substrate, wherein the hard coating is the hard coating according to any one of <1> to <4>.
<6>
The cutting tool according to <5>, wherein the cutting tool is a gear cutting tool.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 13
(1) Manufacturing of a Cutting Tool with a Hard Coating According to an Embodiment of the Present Invention Using the arc evaporation apparatus 20 shown in Figures 2 and 3, a cutting tool with a hard coating according to an embodiment of the present invention was manufactured based on the method described above with reference to Figures 2 and 3. The substrates used were a high-speed steel hob; a 20 mm square, 2 mm thick high-speed steel test piece with a mirror-lapped surface (surface roughness Ra = 0.01 μm or less); and a cemented carbide test piece with a width of 10 mm, a length of 20 mm, and a thickness of 1 mm. In this example, a total of 13 hobs, each 80 mm in diameter and 150 mm in length, were manufactured. These were designated as cutting tools according to Examples 1 to 13.

When the cutting tools according to Examples 1 to 13 were prepared, x in Al _x Cr _1-x arc-discharged from the arc evaporation source 22 was 0.6 or more and 0.7 or less (see the "Al composition" column in Table 3). Furthermore, y in Ti _1-y Si _y arc-discharged from the arc evaporation source 23 was greater than 0.05 and less than 0.08 (see the "Si composition" column in Table 3). The composition ratios (atm %) of Al and Cr in the A layer (a layer made of Al _x Cr _1-x N) and the composition ratios (atm %) of Ti and Si in the B layer (a layer made of Ti _1-y Si _y N) of the hard coatings thus obtained are shown in Table 3. The thickness of the C layer, the film thickness (total thickness of the C layers), and the number of layers (the sum of the number of A layers and the number of B layers) of the hard coatings are also shown in Table 3.

For each example, the high-speed steel test pieces and cemented carbide test pieces were also subjected to the above method at the same time as the example. The atm %, C layer thickness, total C layer thickness, and number of layers of the hard coatings formed on these test pieces were the same as those of the hard coatings obtained in the corresponding examples.

Figure 8 shows the results of observing the longitudinal cross section of the hard coating of one of the cutting tools obtained in the examples using a scanning transmission electron microscope (STEM) (bright-field image, magnification: 50,000 times).

Figure 9 shows the results of observing the hard coating shown in Figure 8 at 1,000,000 magnification. As can be seen from Figure 9, a regular layered structure is well formed. Based on the observation results shown in Figure 9, the thickness of layer C can be calculated by measuring the total thickness of 10 to 20 consecutive layers and dividing this by the number of combinations of layers A and B. For the hard coatings obtained in Examples 1 to 13 and Comparative Examples 1 to 4, the thickness of layer C was calculated based on the results of STEM observation. The total thickness of layer C was determined by measuring the total thickness of the layers C observed by STEM.

(2) X-ray Diffraction The hobs obtained in Examples 1 to 13 were subjected to X-ray diffraction and measured using the θ-2θ method under the following conditions. The conditions were: Measurement apparatus: Bruker AXS X-ray diffractometer D8 DISCOVER, X-ray source: Cu-Kα, tube voltage: 40 kV, tube current: 40 mA, slit width: 0.5°, step: 0.02°, accumulation time: 0.6 seconds, scan range 2θ = 30 to 50°. Next, from the X-ray diffraction pattern obtained for each hob, the ratio (A/B) of the subpeak intensity (A) to the main peak intensity (B) was calculated based on the method described above with reference to Figures 3 to 6. The results are shown in Table 3.

(3) Measurement of surface roughness Ra of hard coating The surface roughness Ra of the surface-coated test pieces made of high-speed steel obtained at the same time as Examples 1 to 13 was measured using a surface roughness measuring instrument manufactured by DEKTAK, and this was taken as the surface roughness Ra of the hard coating. The results are shown in Table 3.

(4) Measurement of nanoindentation hardness of hard coating For the hobs obtained in Examples 1 to 13, a nanoindenter ENT-1100 manufactured by Elionix was used, and a Berkovich indenter was used to apply a load of 2 g to the hard coating on the surface of each cutting tool to measure the nanoindentation hardness of the hard coating. The results are shown in Table 3.

(5) Measurement of compressive stress The warpage of the surface-coated test pieces made of cemented carbide obtained in Examples 1 to 13 was measured using a surface roughness measuring instrument manufactured by DEKTAK, and the compressive stress was measured based on the Stoney equation. The results are shown in Table 3.

(6) Cutting test 1
The hobs obtained in Examples 1 to 7 were subjected to dry machining of SCM415 gears at a cutting speed (V) of 180 m/min, a feed rate of 2.5 mm/rev., and climb cut. The wear width of the cutting edge was checked under a microscope every 100 pieces machined. The results were evaluated based on the number of machining runs until the wear width exceeded 0.2 mm or the cutting edge was chipped. The results are shown in Table 3.

(7) Cutting test 2
The hobs obtained in Examples 8 to 13 were subjected to dry machining of SCR420H gears at a cutting speed (V) of 160 m/min, a feed rate of 1.5 mm/rev., and climb cut. The wear width of the cutting edge was checked under a microscope every 100 pieces machined. The results were evaluated based on the number of machining runs until the wear width exceeded 0.2 mm or the cutting edge was chipped. The results are shown in Table 3.

Comparative Examples 1 to 4
Layers A and B having the compositions shown in Table 3 were formed on a high-speed steel hob, a 20 mm square, 2 mm thick high-speed steel test piece with a mirror-lapped surface, and a cemented carbide test piece having a width of 10 mm, a length of 20 mm, and a thickness of 1 mm, by the same methods as in Examples 1 to 13. As a result, hobs and test pieces having the thickness of layer C, the total thickness of layer C, and the number of layers shown in Table 3 were obtained.

When the cutting tools according to Comparative Examples 1 to 4 were prepared, x in Al _x Cr _1-x arc-discharged from the arc evaporation source 22 was the value shown in the "Al composition" column of Table 3. Furthermore, y in Ti _1-y Si _y arc-discharged from the arc evaporation source 23 was the value shown in the "Si composition" column of Table 3. In Comparative Examples 3 and 4, the arc current and the rotation speed of the turntable 25 were changed from those in Examples 1 to 13 and Comparative Examples 1 and 2, and the C layer thickness was set to less than 7 nm or more than 18 nm.

The hob was subjected to X-ray diffraction, nanoindentation hardness measurement of the hard coating, and cutting test 1, as in Examples 1 to 13. Furthermore, the surface roughness Ra was measured using the surface-coated test piece made of high-speed steel, and the compressive stress was measured using the surface-coated test piece made of cemented carbide. The results are shown in Table 3.

The "subpeak intensity ratio" is the ratio (A/B) of the subpeak intensity (A) to the main peak intensity (B) in the X-ray diffraction pattern of the hard coating, and the "film hardness" is the nanoindentation hardness of the hard coating.

In Comparative Example 1, the Si composition is 5.0 atm%, which does not exceed 5 atm%. In Comparative Example 2, the Si composition is 8.0 atm%, which does not exceed 8 atm%. In Comparative Example 3, the C layer thickness is 5 nm, which does not meet the requirement of 7 nm to 18 nm. In Comparative Example 4, the C layer thickness is 20 nm, which does not meet the requirement of 7 nm to 18 nm.

The hobs described in Comparative Examples 1 to 4 have sub-peak intensity ratios and surface roughness Ra comparable to those of the Examples, but the results of Cutting Test 1 are clearly inferior to those of the Examples. This is thought to be because they do not satisfy the requirements that a hard coating according to one embodiment of the present invention should have.

On the other hand, the hobs described in Examples 1 to 13 satisfy all of the Al composition, Cr composition, Ti composition, Si composition, C layer thickness, and total C layer thickness required for a hard coating according to one embodiment of the present invention. As a result, the results of the cutting test were very good.

As described above, the hard coating according to one embodiment of the present invention has a structure in which A layers made of Al _x Cr _1-x N and B layers made of Ti _1-y Si _y N are alternately laminated, and when a combination of the A layers and the B layers is called C layer, the thickness of C layer is 7 nm or more and 18 nm or less, the total thickness of C layer is 1 μm or more and 6 μm or less, and the thicknesses of A layer and B layer are each less than 10 nm (where x is 0.6 or more and 0.7 or less, and y is more than 0.05 and less than 0.08) and thereby satisfies the requirements, thereby providing a hard coating having excellent wear resistance, heat resistance, and chipping resistance, as well as excellent film strength.

The present invention can be suitably used in cutting tools used under a wide range of machining conditions.

REFERENCE SIGNS LIST 10: Cutting tool 11: Substrate 12: Hard coating A ₁ to A _n : A layer B ₁ to B _n : B layer C ₁ to C _n : C layer 20: Arc evaporation device 21: Cr evaporation source 22: Arc evaporation source of Al _x Cr _1-x 23: Arc evaporation source of Ti _1-y Si _y 24: Rotary table 25: Small table 26: Arc power supply 27: Bias power supply

Claims (5)

The substrate has a structure in which an A layer made of Al _x Cr _1-x N and a B layer made of Ti _1-y Si _y N are alternately laminated,
When a combination of the A layer and the B layer alternately stacked is referred to as a C layer, the thickness of the C layer is 7 nm or more and 18 nm or less,
the total thickness of the C layer is 1 μm or more and 6 μm or less,
the thickness of each of the A layer and the B layer is less than 10 nm;
In an X-ray diffraction pattern, the ratio (A/B) of the sub-peak intensity (A) to the main peak intensity (B) is 0.4 or more and 0.75 or less.
Hard coating.
(wherein, x is 0.6 or more and 0.7 or less, and y is more than 0.05 and less than 0.08.) The hard coating according to claim 1, having a compressive stress of -0.5 GPa or more and -4.0 GPa or less. The hard coating according to claim 1, having a surface roughness Ra of 0.03 μm or more and 0.18 μm or less. A cutting tool comprising a substrate and a hard coating covering a surface of the substrate, the hard coating being the hard coating according to any one of claims 1 to 3 . The cutting tool according to claim 4 , wherein the cutting tool is a gear cutting tool.