Coated tool

Abstract

Provided is a coated tool having excellent durability while having excellent low friction characteristics peculiar to diamond-like carbon.　The present invention provides a coated tool having a hydrogen-containing diamond-like carbon film on a base material, the coated tool including an A layer wherein: the nanoindentation hardness of the diamond-like carbon film is 30 GPa or less; the D / G ratio, which is an intensity ratio of a D band and a G band calculated by means of Raman spectroscopic analysis, is 0.80 or less; and the sp2 / (sp2 + sp3) ratio calculated by means of X-ray photoelectron spectroscopy is 0.35 or more.

Description

Covering tools

[0001] This invention relates to a coating tool.

[0002] Traditionally, press working has mainly used molds made of cold work die steel or hot work die steel, while forging has used molds made of high-speed steel or powder high-speed steel. The materials used for processing are diverse, including high-tensile steel sheets, aluminum-plated steel sheets, stainless steel, and aluminum alloys. In all plastic deformation processes, adhesion of the workpiece material to the mold surface increases frictional resistance and the resulting increase in surface pressure, which easily leads to wear damage and galling on the mold's working surface.

[0003] In recent years, many molds have been fitted with a hard coating made of nitrides or carbonitrides on the mold working surface by physical vapor deposition (PVD) to improve the lifespan of molds used for plastic deformation. Hard coatings made of nitrides or carbonitrides are more than twice as hard as the mold base material such as die steel, and are therefore effective in improving the wear resistance of the mold working surface. However, in environments with high molding loads or when using high-tensile steel sheets, plated steel sheets, stainless steel, or aluminum alloys as workpieces, the sliding motion between the mold working surface and the workpiece during plastic deformation can easily cause the workpiece to adhere or stick to the mold working surface, increasing sliding or frictional resistance and damaging the mold working surface.

[0004] From the perspective of suppressing the adhesion and bonding of the workpiece as described above, diamond-like carbon coatings, which have excellent adhesion resistance and low friction properties, are expected to improve mold life compared to hard coatings of nitrides and carbonitrides. This diamond-like carbon coating is defined as an amorphous coating composed of carbon and hydrogen, but its mechanical properties differ depending on the state of carbon bonding, hydrogen content, and the layered structure of the coating, and the optimal diamond-like carbon coating structure tends to differ under each usage environment. For example, Patent Document 1 discloses a coating structure that uses diamond-like carbon containing N, H, and Si as a base layer for the purpose of self-lubricating properties in sliding. Patent Document 2 discloses a structure in which diamond-like carbon containing at least one of X (B, Cr, Ti), C, and H is laminated on the surface to maintain a stable low coefficient of friction over the long term. Furthermore, Patent Document 3 discloses a structure in which hydrogen-free diamond-like carbon is sandwiched between hydrogen-containing diamond-like carbon for the purpose of reducing internal stress in the coating.

[0005] Japanese Patent Publication No. 2011-001598, International Publication No. 2014 / 196259, Japanese Patent Publication No. Hei 11-100671

[0006] As mentioned above, diamond-like carbon coatings have excellent adhesion resistance and low friction properties. However, because diamond-like carbon coatings are amorphous carbon coatings, they are highly susceptible to crack propagation and have low oxidation resistance. Therefore, especially in fields where temperatures tend to rise easily, such as under no lubrication, boundary lubrication, or high molding surface pressure, diamond-like carbon coatings have a low durability (they are prone to premature wear and fracture), and are not generally actively applied. As described in Patent Documents 1 and 2 above, the hardness of the coating by adding N, Si, Cr, and Ti to the diamond-like carbon coating, and the reduction of internal stress in the coating as described in Patent Document 3, are thought to be related to the friction properties of the coating. However, it cannot be said that there is a sufficient correlation between physical properties such as coating hardness and internal stress and durability, and there is still room for investigation into how to improve durability while retaining the sliding properties represented by the low friction characteristics that are characteristic of diamond-like carbon coatings. Therefore, the object of the present invention is to provide a coated tool that has excellent durability while possessing the excellent low friction characteristics unique to diamond-like carbon coatings.

[0007] The inventors focused on coating properties that exhibit excellent durability, particularly under high-load environments, and investigated diamond-like carbon coatings that combine excellent durability and low friction characteristics. They then diligently studied the influence of the carbon components and coating structure of diamond-like carbon coatings on durability. As a result, they discovered that durability can be dramatically improved by optimizing the various bonding states of carbon, which is a component of diamond, namely the content ratio of the Graphite component related to the sp2 hybrid orbital and the Diamond component related to the sp3 hybrid orbital, the content of the Disordered-Graphite component, and the hardness of the coating, leading to the present invention.

[0008] In other words, the present invention relates to a coated tool having a hydrogen-containing diamond-like carbon film on a substrate, wherein the diamond-like carbon film comprises layer A, the diamond-like carbon film having a nanoindentation hardness of 30 GPa or less, a D / G ratio (intensity ratio of the D band to the G band calculated by Raman spectroscopy) of 0.80 or less, and an sp2 / (sp2+sp3) ratio (calculated by X-ray photoelectron spectroscopy) of 0.35 or more. Furthermore, it is preferable to further provide a layer B, which is a diamond-like carbon film containing hydrogen and argon, on the lower side of the diamond-like carbon film layer A. More preferably, the nanoindentation hardness of layer B is 5 GPa or more higher than that of layer A. Effects of the present invention

[0009] According to the present invention, it is possible to provide a coated tool that has excellent durability while possessing the superior low-friction properties unique to diamond-like carbon.

[0010] This shows the waveform separation graph of the micro-Raman spectroscopy spectrum of the diamond-like carbon film. This shows the waveform separation graph of the X-ray photoelectron spectroscopy spectrum of the diamond-like carbon film. This shows the relationship between film hardness and residual compressive stress in the present invention example and comparative example. This shows the relationship between film hardness and D / G ratio in the present invention example and comparative example. This shows the relationship between film hardness and sp² / (sp²+sp³) ratio in the present invention example and comparative example. This shows the relationship between the time to galling in the pin-on-disk test and the D / G ratio in the present invention example and comparative example. This shows the relationship between the time to galling in the pin-on-disk test and the sp² / (sp²+sp³) ratio in the present invention example and comparative example. This shows the relationship between the time to galling in the pin-on-disk test and film hardness in the present invention example and comparative example. This shows magnified photographs of calotester marks in present invention examples No. 19 to No. 23. This shows a composite EPMA surface analysis map of the calotester mark in present invention example No. 23. The images show the secondary electron image (SEM image) and backscattered electron image (COMP image) of the cross-section of the film at 23, observed with a scanning electron microscope.

[0011] The present invention will now be described in detail. However, the present invention is not limited to the embodiments described herein, and can be appropriately combined and improved without departing from the technical spirit of the invention. The main feature of this embodiment is a coated tool having a hydrogen-containing diamond-like carbon film (hereinafter also simply referred to as a diamond-like carbon film) on a substrate. The diamond-like carbon film is formed in one or more layers. The outermost layer of the diamond-like carbon film has a nanoindentation hardness of 30 GPa or less, a D / G ratio (the ratio of peak intensity of the D band (Disordered-Graphite) and G band (Graphite) as measured by Raman spectroscopy) of the carbon components constituting the film is 0.80 or less, and an sp2 / (sp2+sp3) structural ratio of 0.35 or more as measured by an X-ray photoelectron spectrometer, thereby dramatically improving the durability of the film. Herein, durability refers to abrasion resistance, fracture resistance, or galling resistance. In this invention, the hydrogen-containing diamond-like carbon film refers to a diamond-like carbon film that contains hydrogen by using a hydrogen-containing gas such as a hydrocarbon during film formation, and is typically a diamond-like carbon film containing more than 5 at% hydrogen.

[0012] <Hardness> First, let's explain the reason for limiting the nanoindentation hardness (hereinafter also referred to as "film hardness" or "hardness") of the present invention. Under high-load conditions, diamond-like carbon coated tools undergo localized elastic deformation from the film surface to the interior of the coated substrate at the contact point with the workpiece. Because the elastic limits of the diamond-like carbon film and the substrate are different, as the hardness of the diamond-like carbon film increases, its film properties become brittle, and the film is more prone to fracture or peeling in response to the deformation of the substrate. Therefore, considering the improvement of the film's ability to follow substrate deformation under high surface pressure, the hardness of the diamond-like carbon film is set to 30 GPa or less. Furthermore, there is a strong correlation between the hardness of the diamond-like carbon film and its residual compressive stress. When coating complex shapes such as molds for plastic deformation, applying a thick coating with high residual compressive stress tends to induce poor adhesion accompanied by self-destruction of the film. Therefore, from the viewpoint of suppressing the residual compressive stress of the film, it is important to set the film hardness to 30 GPa or less. The preferred hardness of the coating is 25 GPa or less. There is no particular lower limit, but it can be set to, for example, 10 GPa.

[0013] <D / G Ratio> The diamond-like carbon film of the present invention is also characterized by having a D / G ratio of 0.80 or less, which is the ratio of peak intensities of the D band and the G band, representing the carbon structure that constitutes the film. This D / G ratio is analyzed by Raman spectroscopy. Raman spectroscopy is a method of identifying the state of carbon by waveform separation of the spectrum of Raman scattered light obtained when a laser is shone on the diamond-like carbon film, at 1550 cm⁻¹. －１ The nearby peak is designated as Graphite's G peak, at 1350 cm. －１ It is generally known that the peak obtained in the vicinity is interpreted as the D peak of the Disordered-Graphite. 1330 cm －１ Although there is a peak in the vicinity that is thought to originate from diamond, it is difficult to separate the D peak of Disordered-Graphite from the peak originating from diamond in the measurement results, and in the analysis of the diamond-like carbon film in this invention, 1330 cm⁻¹－１ From 1350cm －１ It is considered appropriate to interpret the peaks in the vicinity as Disordered-Graphite peaks. The D / G ratio represents the content of Disordered-Graphite components in the carbon components constituting the film, that is, the proportion of Graphite components that lack regularity. In terms of the durability of diamond-like carbon, the correlation is more strongly with the D / G ratio than with the film hardness. If the D / G ratio is high, diamond-like carbon has low bonding stability between carbons and is prone to excessive film wear in sliding environments under high surface pressure. Therefore, it is preferable that the D / G ratio of the constituent carbon components of diamond-like carbon, as determined by Raman spectroscopy, be 0.80 or less. More preferably, it is 0.60 or less. Since the effects of the present invention can be achieved within the range of the D / G ratio described above, no lower limit is particularly set, however, for example, a lower limit could be set to 0.30. In this invention, the method for waveform separation of the Raman scattered light spectrum is to first consider the average value from 1800 cm⁻¹ to 1900 cm⁻¹ as the background and subtract it from the total measured spectrum, and then 1330 cm⁻¹ －１ From 1350cm －１ Nearby, or 1550 cm －１ Waveform separation is possible by fitting the waveform using a solver function so that the squared error between the sum of two normal distribution curves derived so that the peaks are in the vicinity of each other and the spectrum obtained from the measurement is minimized.

[0014] <sp2 / (sp2+sp3) ratio> The sp2 / (sp2+sp3) ratio, which is the ratio of sp2 derived from the graphite component to sp3 derived from the diamond component, is also important for identifying the carbon structure of the diamond-like carbon film. The sp2 / (sp2+sp3) ratio is calculated by separating the waveforms of the spectrum obtained from the diamond-like carbon film by X-ray photoelectron spectroscopy (sometimes referred to as XPS analysis) based on the arbitrary bond energy of various carbon bonds. Since the durability of the diamond-like carbon film is closely related to this sp2 / (sp2+sp3) ratio, in this invention the sp2 / (sp2+sp3) ratio is set to 0.35 (35%) or higher. In other words, considering this in conjunction with the aforementioned D / G ratio, it is preferable for diamond-like carbon to have less Disordered Graphite in the carbon components of the film and an increased ratio of sp2 to (sp2 + sp3) in order to improve the durability of the diamond-like carbon film. In addition to the XPS analysis described above, TEM-EELS (electron energy loss spectroscopy in transmission electron microscopy) is also known as a method for identifying the sp2 / (sp2 + sp3) ratio of the carbon structure of the diamond-like carbon film. However, the inventors' studies have shown that TEM-EELS does not show differences in analytical results even among multiple samples with different levels of durability, especially in hydrogen-containing diamond-like carbon films like the present invention, and therefore it is considered unsuitable as a method for measuring the sp2 / (sp2 + sp3) ratio in the diamond-like carbon film of the present invention.

[0015] In this invention, in order to further improve the adhesion and durability against surface pressure of the diamond-like carbon film, it is preferable to create a laminated structure by providing a diamond-like carbon film (layer B) containing hydrogen and argon on the lower layer side (substrate side) of layer A, when layer A is a diamond-like carbon film that satisfies the aforementioned hardness, D / G ratio, and sp2 / (sp2+sp3) ratio. This further improves the adhesion of the diamond-like carbon film. Furthermore, in this invention, it is preferable to make the nanoindentation hardness of layer B 5 GPa or more higher than that of layer A. With this configuration, deformation resistance acting at the interface of the diamond-like carbon film is further suppressed in operating environments with high molding surface pressure, and the durability of the diamond-like carbon film tends to be further improved. On the other hand, since a high proportion of the high-hardness layer in the diamond-like carbon film may induce film fracture, it is preferable that the film thickness ratio of layer A to layer B (film thickness of layer A / film thickness of layer B) be 3 or more.

[0016] In the present invention, it is preferable to provide a mixed film layer made of titanium and carbon between the diamond-like carbon film and the substrate. Since the diamond-like carbon film has low affinity with the substrate, the adhesion of the film can be greatly improved by providing a mixed film layer. At this time, it is preferable to alternately laminate the titanium and graphite metal layers, and at the same time, the mixed film layer does not contain hydrogen, in order to ensure stable adhesion. On the other hand, since the mixed film layer is soft, if it is coated too thickly, it is necessary to suppress peeling from the mixed film layer when a large force is applied to the film interface. Therefore, when the mixed film layer is layer C, it is preferable that the film thickness ratio (film thickness of layer C) / (film thickness of layer A) between layer C and layer A, which is the surface diamond-like carbon film, be 0.3 or less. Here, when layer B, which is a diamond-like carbon film containing hydrogen and argon, is formed as the lower layer of layer A, it is preferable that the film thickness ratio (film thickness of layer C) / (film thickness of layer A + film thickness of layer B) be 0.3 or less.

[0017] In order to further improve the durability of diamond-like carbon under high-load service environments in plastic working, it is effective to set a thicker overall coating film thickness. Therefore, the total film thickness of the layer A, layer B and layer C is preferably 2.5 µm or more. Further, the film thickness of layer A may be set to 2.0 µm or more, and the film thickness of layer B may be set to 0.5 µm or more.

[0018] The diamond-like carbon (layer A) formed on the outermost surface of the coated tool of the present invention can be coated by a film formation method of either sputtering or plasma CVD. For example, when using the sputtering method, a graphite target, a hydrocarbon and argon gas are used as starting materials, and the power density applied to the graphite target serving as a cathode electrode is 0.5 W / cm ２ to 3.5 W / cm ２ , the furnace pressure is in the range of 0.2 Pa to 0.4 Pa, and the bias voltage is in the range of 10 V to 300 V. Conditions may be adjusted so as to obtain the hardness, D / G ratio, and sp2 / (sp2+sp3) ratio of the present invention within the above ranges. When using the plasma CVD method, the power applied to the substrate side is in the range of 200 V to 1000 V, the furnace pressure is in the range of 1.0 Pa to 3.0 Pa, and coating may be performed under plasma discharge while adjusting conditions to obtain the hardness, D / G ratio, and sp2 / (sp2+sp3) ratio of the present invention within the above ranges.

[0019] The diamond-like carbon (layer B) coated on the lower layer side of layer A can be formed mainly by sputtering using a graphite target, a hydrocarbon gas, and an inert gas such as argon gas. The power density applied to the graphite target serving as a cathode electrode is 0.5 W / cm ２ to 3.5 W / cm ２The film should be formed by adjusting the conditions within the range of 0.2 Pa to 0.4 Pa for the furnace pressure and 10 V to 300 V for the bias voltage, so that the hardness of the film is 5 GPa or more harder than that of layer A. Furthermore, it is preferable to form the film while striking the substrate surface with an inert gas. This is because it is possible to apply a peening effect to the film at the same time as film formation, and the adhesion to the substrate can be further improved by applying residual compressive stress. The mixed film layer is preferably formed by sputtering using only a metal target such as titanium, a graphite target, and argon gas.

[0020] In order to prevent deterioration of film properties due to excessive graphitization of the carbon film caused by the heat during film formation, the furnace temperature control for the diamond-like carbon A layer is preferably 200°C or lower, for the diamond-like carbon B layer 270°C or lower, and for the mixed film layer 300°C or lower. Temperature control during film formation is preferably adjusted by controlling the cathode discharge output or bias voltage of the coating apparatus. If the substrate is heated to a high temperature before the film formation process, it may be cooled until the above temperature control for the film formation process becomes possible before proceeding to the film formation process.

[0021] The coating tool of the present invention is preferably applied to sliding parts and molds, for example. Here, sliding parts refer to members whose main purpose is to slide without deforming the mating material, such as bearings, blades, and vanes. Preferably, it is applied to molds, and more preferably to molds used for plastic deformation, such as press working and forging, where the working surface of the mold slides with the workpiece under high load conditions. In this plastic deformation application, the force applied to the surface of the hard coating is large, and as the sliding resistance increases, the stress acting on the surface and inside of the coating increases, making the coating more susceptible to damage. Furthermore, under high load conditions, abrasive wear caused by hard wear particles getting stuck to the mold working surface, adhesive wear caused by the workpiece sticking to the mold working surface, and the destruction or peeling of the coating caused by increased local surface pressure and the resulting elastic deformation of the mold surface are also likely to occur. Each damage mode occurs simultaneously on the mold working surface during plastic deformation, and under high-load conditions, galling easily occurs, leading to the end of the mold's lifespan. Preferably, this invention is applied to molds for press forming of high-tensile steel, press forming and forging of non-ferrous metals such as aluminum, and hot stamping molds for forming steel sheets or plated steel sheets heated to 400°C or higher. The base material for the tool used in this invention is not particularly specified in terms of material, but for example, carbon steel, cold die steel, die steel, high-speed steel, and cemented carbide can be used. Tool steel is particularly preferred.

[0022] [Sample Preparation] As substrates for coating with diamond-like carbon, flat test pieces (20 × 20 × 3 mm) of JIS high-speed steel SKH51 tempered to a hardness of 63 HRC were prepared for coating property analysis, flat test pieces (10 × 24 × 1 mm) of cemented carbide NM15 were prepared for residual compressive stress measurement, and disc-shaped test pieces (60 mm in diameter × 5 mm in thickness) of JIS alloy tool steel SKD11 tempered to a hardness of 59 HRC were prepared for pin-on-disk testing. After the surfaces of these test pieces were mirror-polished mechanically, they were thoroughly degreased, and the films were deposited using a composite PVD coating apparatus capable of multiple film deposition methods. The process within the PVD coating apparatus was 1 × 10 －２After sufficient degassing by heating in a vacuum of 450°C with a pressure of Pa or less, etching was performed using argon gas plasma for 30 minutes with a bias voltage of -200V or higher applied to the substrate and a furnace pressure of 2Pa or less. After the etching process, the furnace temperature was cooled to 300°C or lower. In the film formation process for the mixed film layer (C layer), a power density of 0.5 W / cm² was applied to the cathode electrode, which consisted of a titanium target and a graphite target made from the starting materials, in a furnace into which argon gas had been introduced. ２ From 7.0 W / cm² ２ Power was applied within the specified range, and the substrate was coated by sputtering while applying a bias voltage in the range of 10V to 250V. During this process, the substrate was alternately and continuously brought close to various cathode electrodes to create a nano-order alternating laminated structure of titanium and graphite layers in the mixed film layer (C layer). Subsequently, diamond-like carbon (B layer) and diamond-like carbon (A layer) were fabricated using sputtering, plasma CVD, or a combination thereof to achieve the desired film characteristics. In the sputtering method, a graphite target, hydrocarbons, and argon gas were used as starting materials, and the power density applied to the graphite target (cathode electrode) was 0.5 W / cm². ２ From 3.5 W / cm² ２The experiments were conducted within the following ranges: furnace pressure from 0.2 Pa to 0.4 Pa, and bias voltage from 10 V to 300 V. In the case of plasma CVD, coating was performed under plasma discharge with power applied to the substrate within the range of 200 V to 1000 V and furnace pressure from 1.0 Pa to 3.0 Pa. For samples No. 1 to 23, the total film thickness was adjusted to be within the range of 3.5 μm to 6.5 μm. The film thickness of layer A was set to 2.0 μm or more, and the film thickness of layer B (if layer B was present) was set to 0.5 μm or more. For comparison, sample No. 24 was prepared by coating the same substrate as above with approximately 1.0 μm of hydrogen-free diamond-like carbon (ta-C) film (hereinafter, hydrogen-containing diamond-like carbon film and hydrogen-free diamond-like carbon film may be collectively referred to as "diamond-like carbon film") using the arc ion plating method. And for comparison, there is also a nitride coating (Al ６０ Cr ４０ Sample No. 25, coated with approximately 3.5-4.0 μm of N, and also a nitride film (Ti ５０ Al ５０ Sample No. 26, coated with approximately 3.5 to 4.0 μm of N, was also prepared. Table 1 shows the details and film properties of each sample. The film thickness ratios for samples No. 1 to 23, calculated as (film thickness of layer C) / (film thickness of layer A), or (film thickness of layer C) / (film thickness of layer A + film thickness of layer B), were in the range of 0.10 to 0.25.

[0023] (1) Calculation of D / G ratio by Raman spectroscopy The D / G ratio of the constituent carbon components of the diamond-like carbon film was calculated using a micro-Raman spectrophotometer (JEOL JPS-SYS2000) and the analysis was performed from the surface of the diamond-like carbon A layer. A He-Ne laser was used as the X-ray source, and the measurement width was 1000 cm. －１ From 2000cm －１ The measurement was performed using Microsoft Excel to separate the waveforms from the obtained spectra. The waveform separation method involved first measuring 1800 cm⁻¹. －１ From 1900cm －１ The average value was considered the background and subtracted from the total measured spectrum. Waveform separation was performed at 1330 cm⁻¹, as shown in Figure 1.－１ From 1350cm －１ Nearby, or 1550 cm －１ The positions of the two normal distribution curves were determined by fitting them using a solver function to minimize the squared error between the sum of the two derived normal distribution curves, which were positioned so that the peaks were in the vicinity of each other, and the spectrum obtained from the measurements. Then, at 1350 cm² for each normal distribution curve, －１ The nearby peak is called D Peak (Disordered-Graphite), at 1550 cm. －１ The nearby peak was designated as the G peak (Graphite), and the D / G ratio was calculated.

[0024] (2) Calculation of sp2 / (sp2+sp3) ratio by XPS analysis To calculate the sp2 and sp3 content ratio of the constituent carbon components of the diamond-like carbon film, an X-ray photoelectron analyzer (Kratos AXIS-HSI) was used to analyze the surface of the diamond-like carbon A layer. Monochrome Al-Kα rays were used as the X-ray source, and peaks caused by C1s in the measurement range of 280 eV to 292 eV were analyzed. The spectra obtained from the measurements were analyzed by fitting and separating waveforms using Excel as shown in Figure 2. The peak around 284 eV was defined as the sp2 bond, the peak around 285 eV as the sp3 bond, and the peak around 287 eV as the C=O bond, and the sp2 / (sp2+sp3) ratio was calculated.

[0025] (3) Film Hardness Measurement To measure the film hardness of the diamond-like carbon, a film cross-section was prepared by polishing the film at a 5° angle. Using a nanoindenter (ELIONIX ENT-1100a), measurements were taken on the diamond-like carbon A layer and diamond-like carbon B layer with a measurement load of 20 mN, and the average value of ten points was calculated.

[0026] (4) Residual Compressive Stress Measurement The residual compressive stress of the diamond-like carbon coating was calculated from the amount of warpage of a cemented carbide NM15 flat test piece before and after diamond-like carbon coating using the Stoney equation expressed as σ = Es·D²·η / (3(1−vs)d). In the formula, Es represents the Young's modulus of the substrate, vs represents the Poisson's ratio of the substrate, L represents the length to deflection, d represents the film thickness, D represents the substrate thickness, and η represents the amount of deflection. A stylus surface profilometer (SURFCOM 480A manufactured by Mitutoyo) was used to measure the amount of warpage of the test piece. Table 1 shows the measured D / G ratio, sp2 / (sp2+sp3) ratio, coating hardness, and residual compressive stress. In Table 1, the sp2 / (sp2+sp3) ratio is expressed as a percentage (%). Note that for Sample Nos. 25 and 26, which are nitride coatings, the measurements described in (1) to (4) above have not been performed.

[0027]

[0028] Fig. 3 shows a correlation diagram between coating hardness and residual compressive stress. From Table 1 and Fig. 3, for all diamond-like carbon of Sample Nos. 1 to 24, a strong correlation is observed between coating hardness and residual compressive stress. That is, it can be inferred that residual compressive stress is dominant in the strengthening mechanism of diamond-like carbon films. When the residual compressive stress is high, the coating is prone to self-destruction depending on factors such as the shape factor of the object to be coated, therefore in the present example, those with a residual compressive stress of 2.00 GPa or less are regarded as non-defective products. From Table 1 and Fig. 3, it was confirmed that samples having a diamond-like carbon coating with a hardness of 30 GPa or less have a favorable residual compressive stress value of 2.00 GPa or less.

[0029] For various diamond-like carbon coatings of Sample Nos. 1 to 26, Fig. 4 shows a correlation diagram between coating hardness and D / G ratio, and Fig. 5 shows a correlation diagram between coating hardness and sp2 / (sp2+sp3) ratio. These have a low correlation with coating hardness, and there are types where the D / G ratio or the sp2 / (sp2+sp3) ratio differ even when the coating hardness is equivalent. That is, it suggests that indicators for identifying the carbon structure of diamond-like carbon coatings, such as the D / G ratio or the sp2 / (sp2+sp3) ratio, are not directly related to the strengthening mechanism of the coating.

[0030] Next, for samples No. 1-3, 5-12, 14-20, 22, and 24-26, the sliding characteristics and durability until galling damage occurred under each load were verified using a 3-pin on-disk tester. An Orientec friction and wear tester (FEM-3-1020-ADX) was used for the 3-pin on-disk test. The evaluation specimens were 60 mm x 5 φD11 (59 HRC) base material, with the mirror-finished 60 mm surface coated with the film of each sample. SKD61 (45 HRC) φ5 mm x 8 mm was used as the mating material, and the 5 mm surface, which had been flat-ground, was pressed against the evaluation specimen for the test. The pin on-disk test conditions were air, no lubrication, and sliding at 250 rpm on a sliding diameter of φ33 mm. The measured loads were 10 kgf, 30 kgf, 50 kgf, 70 kgf, 90 kgf, and 120 kgf. Each load test was performed for 300 seconds, and the average friction coefficient and testable time during the sliding test at each load were measured to evaluate durability. An average friction coefficient of less than 0.50 was considered a good result, indicating low sliding resistance. The testable time was defined as the time from the start of the test to the occurrence of galling, which was considered the point at which the friction coefficient rapidly increased or decreased during the sliding test, or when damage to the coating was visually confirmed. For samples where galling occurred, the test load was not increased further, and the test was terminated. Table 2 shows the results of the 3-pin on-disk test for each sample. If no galling occurred, the maximum test time of 300 seconds at each load is recorded in the testable time column of Table 2.

[0031] From Table 2, the diamond-like carbon films of Comparative Samples No. 1 to 3, 5 to 12, 14, and 24 suffered galling under the test load condition of 10 kgf to 50 kgf. In addition, the nitride films of Comparative Samples No. 25 and No. 26 were tested up to a test load of 90 kgf, but the average friction coefficient was 0.50 or more at any test load, indicating high sliding resistance. In contrast, Samples No. 15 to 20 and 22, which are examples of the present invention, had a low average friction coefficient of 0.27 or less at each test load, and the test load at which galling occurred was 70 kgf or more in all cases, confirming excellent durability. In particular, Examples No. 19, 20, and 22 of the present invention provided with a diamond-like carbon B layer enabled the test even at a test load of 90 kgf or more, and showed very good results.

[0032]

[0033] FIG. 6 shows the relationship between the D / G ratio and the time to galling in the pin-on-disk test for each sample, FIG. 7 shows the relationship of sp2 / (sp2+sp3), and FIG. 8 shows the relationship with film hardness. In Samples No. 1 to No. 23, as the D / G ratio decreased and the sp2 / (sp2+sp3) ratio increased, the time to galling became longer, showing a tendency of excellent durability. It was confirmed that when the content of Disordered-Graphite as a carbon constituent of diamond-like carbon increases, the bonding stability of the film is lost, the film is prone to wear under sliding surface pressure, and galling damage is easily caused. Regarding the sp2 / (sp2+sp3) ratio, it was confirmed that as the proportion of sp2 in the film increases, that is, as the Graphite component increases, galling tends to be less likely to occur. Regarding film hardness, it was confirmed that the softer the film hardness is 30 GPa or less, the more excellent the galling resistance is. From the above, it was found that the examples of the present invention that satisfy all the requirements of having a D / G ratio of 0.80 or less, a sp2 / (sp2+sp3) ratio of 35% (0.35) or more, and a film hardness of 30 GPa or less, which are defined as good by having durability against a test load of 70 kgf or more in the pin-on-disk test, are excellent in durability.

[0034] Next, the effect of hardness-based durability improvement on the diamond-like carbon coating of the present invention having a B layer was confirmed. The state of the B layer coating can be determined by polishing the surface of the coating with a φ30 mm steel ball and diamond paste using a calometer (manufactured by Anton Paar), and observing the calometer marks. Figure 9 shows the calometer marks of the present invention examples No. 19, 20, 22, and 23. Of the present invention examples No. 19, 20, 22, and 23, examples No. 22 to No. 23, in which the hardness of the B layer is 5 GPa or more higher than that of the A layer, showed suppressed wear at the interface compared to the present invention examples No. 19 and 20, confirming that the durability of the B layer can be further improved.

[0035] The presence of the aforementioned hydrogen and argon-containing B layer can be easily confirmed by the following method. Figure 10 shows a composite image of the results of surface analysis of C, Ti, and Ar measured using FE-EPMA (JEOL JXA-8500F) on the calo tester trace of Invention No. 22. When Ar is contained only in the B layer, Ti, which is a mixed film layer, is detected directly above the substrate, followed by the diamond-like carbon B layer where C and Ar are detected at the same position, and then the A layer where only C is detected. Furthermore, as shown in Figure 11, the presence or absence of Ar can also be confirmed by scanning electron microscope (SEM) secondary electron images (COMP) or backscattered electron images (COMP) of the film cross-section. In addition, the hardness of the B layer in the example of the present invention can be identified using nanoindenter hardness measurement from the film cross-section.

Claims

1. A coated tool having a hydrogen-containing diamond-like carbon film on a substrate, wherein the diamond-like carbon film has a nanoindentation hardness of 30 GPa or less, a D / G ratio (intensity ratio of the D band to the G band calculated by Raman spectroscopy) of 0.80 or less, and an sp2 / (sp2+sp3) ratio (calculated by X-ray photoelectron spectroscopy) of 0.35 or more, comprising a layer A.

2. The coating tool according to claim 1, further comprising a B layer, which is a diamond-like carbon film containing hydrogen and argon, on the lower side of the diamond-like carbon film A layer.

3. The coating tool according to claim 2, wherein the B layer has a nanoindentation hardness of 5 GPa or more higher than the A layer.

Images