JP2006307242A - Hard film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To particularly improve toughness even in a hard film having high hardness and excellent high temperature oxidation resistance without sacrificing its adhesion, and further, to provide a hard film having improved welding resistance and lubrication properties in a high temperature state, and adaptable to an advanced cutting process such as a dry process, a high-speed process and a high-feeding process. <P>SOLUTION: The hard film is formed on the surface of a substrate by a physical vapor deposition process. The hard film has a composition comprising one or more kinds of metallic elements selected from the group 4a, 5a, 6a metals, Al and B, and Si, and one or more kinds of nonmetallic elements selected from C, N and O. The hard film has a columnar structure. Each crystal grain in the columnar structure has a multilayer structure composed of a plurality of layers having a different in the Si content, a region in which at least crystal lattice streaks are continued is present in the boundary region between the layers, and the thickness T (nm) of each layer satisfies 0.1≤T≤100. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a hard coating that imparts extremely excellent toughness to the mechanical properties of hard coatings such as wear resistance, adhesion and high temperature oxidation resistance coated on cemented carbide, cermet, high speed steel, die steel, etc. About.

With a tool coated with a conventional hard coating, the cutting speed is increased for the purpose of improving the efficiency of metal processing, and the high feed cutting process in which the feed amount per blade exceeds 0.3 mm under cutting conditions. However, satisfactory performance has not been obtained in terms of adhesion and mechanical properties of the hard film, such as oxidation resistance and wear resistance. From such a background, a technique for the purpose of further improving the oxidation resistance and wear resistance of a hard coating has been disclosed. The following patent documents disclose Si-containing hard coatings and techniques related to increasing the hardness of the coating.
Patent Documents 1 to 4 and Patent Document 6 describe a compound film, a crystal form, and the like relating to a hard film containing Si, and Patent Document 5 describes that a compound layer and a composition modulation layer are periodically stacked and crystallized between layers. A wear-resistant laminated hard film in which the lattice is continuous for one period or more is described. Patent Document 6 describes, for example, a hard film having high lubricity composed of molybdenum disulfide and TiN, and Patent Documents 7 and 8 describe superlattices. (Artificial lattice) It is described that the hardness of a hard coating is increased by lamination.

JP-A-8-170167 JP 2000-326108 A Japanese Patent Application Laid-Open No. 7-328812 Japanese Patent No. 3460288 JP-A-8-127863 Japanese National Patent Publication No. 11-509580 Japanese Patent No. 3416938 JP 2001-293601 A

However, the above Patent Documents 1 to 4 are attempts using only the arc discharge ion plating method in the physical vapor deposition method, and in the processing of steel types that are likely to be welded to the cutting edge or the like, from the large and small discussion of wear generation However, stable processing cannot be expected without first improving the welding characteristics. In Patent Documents 5 and 6, the adhesion and hardness of the hard coating are not sufficient, and the wear resistance of the cutting tool is not sufficiently improved. Patent Documents 7 and 8 do not satisfy the requirement of having sufficient lubricity to withstand dry cutting conditions while maintaining oxidation resistance and wear resistance.
Therefore, none of the hard coatings described in the above documents satisfy the requirements for toughness that can cope with dryness, high speed, and high feed while maintaining wear resistance and oxidation resistance. An object of the present invention is to improve particularly toughness without sacrificing adhesion even in a hard film having high hardness and excellent high-temperature oxidation resistance. At the same time, it is intended to provide a hard coating that can improve welding resistance and lubrication characteristics at high temperatures, and can cope with, for example, dry processing, high speed, and high feed in cutting and the like.

  The hard film of the present invention is a hard film formed on a substrate surface by physical vapor deposition, and the hard film contains one or more metal elements selected from 4a, 5a, 6a group, Al, and B and Si. The hard coating has a columnar structure, and the crystal grains in the columnar structure are composed of a plurality of layers having different Si contents. In the boundary region between the layers, there is at least a region where crystal lattice stripes are continuous, and the thickness T (nm) of each layer is 0.1 ≦ T ≦ 100. By adopting this configuration, since the hard coating of the present invention contains Si, it is excellent in oxidation resistance, wear resistance and lubricity, and also has excellent adhesion to the substrate, toughness and welding resistance. Can be provided.

In the hard coating of the present invention, Si is present as a crystalline phase, and the crystalline phase preferably has α-type Si ₃ N ₄ and β-type Si ₃ N ₄ . The hard coating preferably has a bond between Si and O (hereinafter referred to as Si—O bond). The surface of the hard coating is preferably smoothed by machining.

  The present invention is to improve toughness without sacrificing adhesion even in a hard film having high hardness and high-temperature oxidation resistance. At the same time, it was possible to provide a hard coating with improved welding resistance and lubrication characteristics at high temperatures. When the hard coating of the present invention is applied to, for example, a cutting tool or the like, stability and a long tool life can be obtained even in a severe interrupted cutting environment at the time of mold processing, including dry high-efficiency cutting. It is extremely effective in improving productivity.

(1) Composition of coating The composition of the hard coating of the present invention comprises one or more metal elements selected from the groups 4a, 5a, 6a, Al, and B of the periodic table and Si, and from C, N, and O. Having one or more non-metallic elements selected. When the hard coating of the present invention contains Si, a dense Si oxide is formed in the vicinity of the coating surface layer in a high temperature environment. For example, when this is applied to a cutting tool, the Si oxide formed by the heat generated during cutting suppresses diffusion of the Fe element contained in the work material into the hard coating. As a result, welding at the cutting edge of the tool is suppressed. The Si content is preferably from 0.1 to 30% in atomic percent of only the metal element. When the Si content exceeds 30%, the hardness and heat resistance of the hard coating are improved, but the fracture surface structure changes from a columnar structure to a fine granular structure. When the microstructure is fine, the crystal grain boundaries of the hard coating increase, and oxygen in the atmosphere and Fe element of the work material are likely to diffuse due to heat generated during cutting. As a result, for example, when applied as a hard coating of a coated cutting tool, welding occurs on the cutting edge, and the lubricity is impaired. Therefore, the structure of the fracture surface of the hard coating is also important, and it is important to have a columnar structure especially in high feed processing. On the other hand, if the Si content exceeds 30%, the residual stress in the hard coating increases, and peeling easily occurs from the interface between the substrate and the hard coating. Since welding occurs at the peeling portion, it is important to prevent the occurrence of peeling. On the other hand, 0.1% of the lower limit of the Si content is a limit at which Si can be easily detected.
When the hard film of the present invention contains B, there is an effect of increasing the hardness and lubricity of the hard film. For example, when a hard film containing B is coated on a cutting tool, the tool life is extended. The improvement in hardness is due to the c-BN phase, and the improvement in lubricity is due to the h-BN phase. By optimizing the ratio of B and N, hardness and lubricity can be improved at the same time. The ratio between the c-BN phase and the h-BN phase can be controlled by a bias voltage applied during film formation.
When Al is contained in the metal composition of the hard coating of the present invention, Al ₂ O ₃ is formed on the surface layer, and the static heat resistance of the hard coating is improved, but in actual cutting, Fe in the work material, etc. Diffuses into the hard coating. Therefore, the Al content is preferably 50% or less in terms of atomic% of only the metal element. A more preferable Al content is 70% to 20%. If it is less than 20%, the wear resistance and oxidation resistance of the hard coating may be inferior.
In the C, N, and O components of the non-metallic component, the O content is more preferably 0.3% or more and 5% or less in terms of atomic% of only the non-metallic element in order to improve lubricity. When the O content exceeds 5%, the lubricity of the hard coating is improved, but the hardness is lowered, and the crystal structure of the fracture surface is refined, and scraping wear tends to occur. In the composition of the hard coating, when the total amount of metal elements is m and the total amount of nonmetallic elements is n, the atomic ratio (n / m) is preferably more than 1.0, and is 1.02 or more. Is more preferable. The upper limit of n / m is preferably 1.7.

(2) Structure and characteristics of film When the cross section of the hard film is observed with a transmission electron microscope (hereinafter referred to as TEM), it is found that the cross-sectional structure of the hard film of the present invention has a plurality of layers showing light and dark. These layers are composed of a layer having a relatively high Si content (referred to as layer A) and a layer having a relatively low Si content (referred to as layer B), and the A layer and the B layer are alternately interfaced. Laminate without. As a result of composition analysis by energy dispersive X-ray spectroscopy (hereinafter referred to as EDX) attached to the TEM, the difference between the average value of Si content in the A layer and the average value of Si content in the B layer is 10 % Or less, more preferably in the range of 0.2 to 5%. When the difference in content is in the range of 0.2 to 5%, the hard coating has high toughness. By providing a difference in Si content between the A layer and the B layer, it is possible to obtain a hard coating that improves toughness and suppresses residual compressive stress while maintaining excellent lubricity.
The hard coating of the present invention has a columnar structure, the columnar crystal grains have a plurality of layers having a difference in Si content without a clear interface, and at least a region where crystal lattice fringes are continuous in the boundary region between the layers. Exists. The columnar structure is a crystal structure that grows vertically in the film thickness direction. The hard coating is polycrystalline, but each crystal grain has a form similar to a single crystal. In addition, the columnar crystal grains have a multilayer structure having a plurality of layers having different Si contents in the growth direction, and crystal lattice fringes are continuous in the boundary region between the layers. Here, the continuity of the crystal lattice stripes does not have to be in all the interlayer boundary regions, and it is sufficient if there is an interlayer boundary region in which the crystal lattice stripes are substantially continuous when observed with a TEM. Since the columnar crystal grains have a multilayer structure composed of a plurality of layers having different Si contents, the hard coating as a whole has toughness.
The thickness T of each layer of the hard coating is 0.1 to 100 nm. When T exceeds 100 nm, distortion occurs in the boundary region between the layers, the lattice stripes in the crystal grains become discontinuous, and the mechanical strength of the hard coating is lowered. For example, when a hard film is formed on a cutting tool, laminar fracture occurs in the hard film due to a cutting impact in the initial stage of cutting. Avoiding the occurrence of strain in the boundary region between layers is effective in improving the adhesion between the hard film and the substrate. On the other hand, the lower limit of T was set to 0.1 nm, which is the minimum thickness at which the layer structure can be confirmed with an X-ray diffractometer or a transmission electron microscope. Moreover, when a multilayer hard film is formed with a lamination period of less than 0.1 nm, the film characteristics vary.
The hard coating of the present invention preferably has a portion in which the presence of Si is Si ₃ N ₄ in the coating cross-sectional portion selected from the portion distinguished from the region forming the columnar crystal grains. The presence of Si ₃ N ₄ is confirmed by Raman spectroscopy. The _{Si 3 N 4, Si 3 N} 4 of α-type crystal structure and a β-type crystal structure is present. Therefore, the α-type Si ₃ N ₄ peak is obtained in the wave number range of 830 to 850 cm ⁻¹ , and the β-type Si ₃ N ₄ peak is obtained in the wave number range of 1020 to 1070 cm ⁻¹ . Here, α-type Si ₃ N ₄ is a relatively soft crystalline phase, and β-type Si ₃ N ₄ is a relatively hard crystalline phase. Hardness and toughness can both be improved. This phenomenon is due to the following reasons. That is, since a hard crystalline phase and a soft crystalline phase are deposited together in the hard coating, distortion occurs, and an increase in the internal stress of the hard coating increases the hardness. On the other hand, although a hard film has a strain but a soft crystalline phase, there is a cushioning effect between relatively hard crystalline phases. As a result, it is rich in toughness.
The hard coating of the present invention preferably has a Si—O bond. In particular, the hard film exhibits excellent lubricity due to the presence of Si—O bonds on the surface. For example, when applied to a coated cutting tool, intense welding at the initial stage of cutting can be suppressed. The Si—O bond can be confirmed by the presence of a peak in the range of 100 to 105 eV by X-ray photoelectron spectroscopy (hereinafter referred to as XPS). XPS was performed using an electron neutralization gun with an AlKα X-ray source and an analysis area of 100 μm in diameter.

(3) Manufacturing method of film | membrane The physical vapor deposition method from which plasma density differs is used in order to manufacture the multilayer hard film of this invention. Specifically, in order to continuously grow crystal grains having no interface, an arc discharge ion plating (hereinafter referred to as AIP) method having a high plasma density in a plasma reaction gas and a low plasma density are used. Magnetron sputtering (hereinafter referred to as MS) is performed simultaneously. Thereby, the crystal grains themselves in the hard coating have a large mechanical strength. On the other hand, when the AIP method and the MS method are performed sequentially or intermittently, a clear interface is formed between the layers of the hard coating, and the strength of the hard coating is reduced there.
Since the plasma density generated by the AIP method is very high, energy generated when ions generated in the plasma are incident on the substrate is large, and although a good hard film is formed, it is difficult to suppress the residual compressive stress. In addition, it is difficult to give a difference in the content of the specific element between the layers of the hard film having a multilayer structure. Therefore, it is preferable to combine the AIP method and the MS method to impart excellent lubricity, adhesion and wear resistance to the hard film having high hardness.
Specifically, it is preferable to use a vacuum apparatus having an AIP target and an MS target and a reactive gas suitable for both the AIP method and the MS method. In the vacuum processing chamber, at least a pair of evaporation sources capable of at least the AIP method and the MS method are installed, and are designed so that they can be discharged simultaneously. However, the evaporation source of the AIP method and the evaporation source of the MS method are not necessarily paired, and one or more evaporation sources of both types are installed in the same vacuum processing chamber as long as simultaneous discharge is possible. . The composition of each target is not limited. However, it is desirable to use a system containing Si as a target material for the MS method. Accordingly, Si can be contained in the hard coating without any safety problem in the environment of the plasma-assisted chemical vapor deposition method in which the reaction containing Si uses sulfur.
The reaction gas used for film formation is not limited to nitrogen or argon, and any gas species can be used as long as the AIP evaporation source and the MS evaporation source can be discharged simultaneously to form plasma. There are no restrictions. However, in order to make the lubricating properties of the hard coating of the present invention excellent, it is preferable to contain oxygen in the reaction gas used during film formation. As a result, the hard coating has Si—O bonds. This is because this Si—O bond contributes to the lubricating properties of the hard coating.
The AIP target may be a single alloy target or a target of a plurality of metals or alloys having different compositions. When the AIP method and the MS method are simultaneously performed while the substrate is alternately approaching both targets in a state where the reaction gas is turned into plasma, ions having different valences reach the substrate at the same time. When the substrate approaches an AIP evaporation source with a high plasma density, a hard layer is formed, and then when a substrate approaches an MS evaporation source with a low plasma density, a soft layer is formed. As a result, distortion occurs in the entire film, and the film is hardened by internal stress. At this time, there is no clear interface between the hard layer and the soft layer. Further, the composition in the interface region gradually changes with a slope. As described above, since the soft layer is sandwiched between the hard layers through the region where the composition gradually changes, the entire hard film has toughness and impact resistance while maintaining high hardness due to the cushion effect. The hard film has a columnar structure and has columnar crystal grains having a soft layer and a hard layer.
By simultaneously discharging the AIP method and the MS method, the crystal grain structure in the hard film having a multilayer structure is allowed to grow continuously without being divided and the multilayer structure exists in the same crystal grain. Is possible. As a result, it is possible to improve mechanical strength such as toughness of the hard coating. The reason for this is that even when films having different compositions are laminated, there is no clear lamination interface, and therefore peeling and destruction from the lamination interface are difficult to occur. Furthermore, by simultaneously discharging the AIP method and the MS method, it is possible to add a high melting point material or a highly lubricating material, which was difficult to generate plasma by the AIP method, to the hard coating film. When performing the AIP method and the MS method at the same time, the arrangement of each deposition source comprising an AIP deposition source that generates a high-density plasma and an MS deposition source that generates a low-density plasma and the coated substrate is as follows. It is preferable to arrange them so that the films are laminated alternately.
By simultaneously discharging the AIP method and the MS method with different plasma densities, Si ₃ N ₄ can be present in the hard coating containing Si. For example, consider the case of adding Si by the MS method. There are α-type crystals and β-type crystals having different crystal forms in Si ₃ N ₄ , and the existence ratio of both can be controlled by film forming conditions in the MS method. The α-type crystal is relatively soft and the β-type crystal is relatively hard, but both exist in the coating at an appropriate ratio, so that in addition to increasing the hardness and toughness of the Si-containing hard coating, further lubrication The characteristics can also be improved. When the AIP method and the MS method are used simultaneously, Si ₃ N ₄ is in the form of α-type crystals and β-type crystals by setting the discharge output of the MS evaporation source to 6.5 kW or less. Furthermore, if it is set to 3.5 kW or less, the plasma density becomes smaller, so more α-type Si ₃ N ₄ is contained than β-type Si ₃ N ₄ , which is a preferred embodiment in the present invention. This is because when the soft layer is formed by the evaporation source of the MS method having a low plasma density, the soft layer contains a large amount of α-type Si ₃ N _4. This is because the difference is effective for the cushion effect. In the above, the case where Si is added by the MS method has been described. However, when the coating substrate is passed through the plasma of the AIP method and the coating is laminated, the Si element is deposited on the coating by wraparound. As a result, when viewed from the cross section of the film, the Si element is present in the entire stacking direction, although the content difference occurs.
When simultaneously discharging the AIP method and the MS method with different plasma densities, it is desirable to optimize the setting of the necessary reaction gas pressure. In the AIP method, a relatively high reaction gas pressure is used, and a range of about 1 Pa to about 8 Pa can be stably coated. On the other hand, since the plasma density is low, the MS method is performed at a reaction gas pressure of less than 0.5 Pa in order to increase the deposition rate. Then, the conditions of the reactive gas pressure that can form plasma at the same time by the AIP method and the MS method and can improve the high hardness and toughness, which are physical properties of the formed hard film, were examined. As a result, when the reaction gas pressure P1 (Pa) was 0.5 ≦ P1 ≦ 8.0, a hard coating satisfying the characteristics was obtained. If it is less than 0.5 Pa, it is difficult to discharge by the AIP method. In the AIP method, it is important to suppress the generation of macro particles. As a suppression measure, a magnetic field region is applied around the target, but many macro particles are generated even under a condition of less than 0.5 Pa. This macro particle is not preferable because it increases the number of defects inside the hard film. On the other hand, if it exceeds 8.0 Pa, it is difficult to discharge in the MS method, and it is difficult to generate uniform plasma. As a result, the toughness of the hard coating is inferior, which is not preferable.
Regarding the film forming conditions, the current value of the AIP method is preferably set in the range of 100 to 150A. The discharge output of the MS method is preferably set to 6.5 kW or less. This is preferred to make Si ₃ N ₄ crystalline. Furthermore, it is suitable for controlling the thickness T of each layer of the multilayer hard coating having a columnar structure to 100 nm or less and making the lattice fringes of the columnar crystal grains continuous. Thereby, it is possible to secure a strong adhesion and to form a hard film having high hardness and high toughness.

When the hard film of the present invention is formed on the cutting tool, the work material is prevented from being welded because of excellent lubricity, adhesion and wear resistance. The hard film has lubricity and can suppress welding and diffusion of the work material element in dry cutting where the cutting edge portion is at a high temperature. The cutting tool coated with the hard coating corresponds to dry, high speed, and high feed cutting. High feed cutting means, for example, cutting in which the feed amount per blade exceeds 0.3 mm / tooth. By smoothing the surface of the hard coating of the present invention by machining, the friction resistance is stabilized, and the variation in the cutting life of the tool is reduced. When an intermediate layer made of Ti nitride, carbonitride or boronitride, TiAl alloy, Cr, W, or the like is provided on the surface of the substrate, the adhesion between the substrate and the hard coating increases, and the peel resistance of the hard coating and Improved fracture resistance. The cutting tool coated with the hard coating of the present invention is suitable for dry cutting, but can also be used for wet cutting. In either case, the presence of the intermediate layer can prevent the hard film from being broken due to repeated fatigue.
The material of the cutting tool that forms the hard coating of the present invention is not limited. Any of cemented carbide, high speed steel, die steel, etc. may be used. The hard coating of the present invention can be formed not only on cutting tools but also on heat resistant members such as dies, bearings, rolls, piston rings, sliding members, wear resistant members and internal combustion engine parts that require high hardness. . The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

For the coating of the hard coating of the present invention, a cemented carbide insert serving as a substrate was coated using a device in which an AIP evaporation source and an MS evaporation source were provided in a small vacuum apparatus. Each evaporation source uses various alloy targets, and the reaction gas is selected from N ₂ gas, CH ₄ gas, and Ar / O ₂ mixed gas so that the desired film can be obtained. A reaction pressure capable of generating plasma was selected. As other coating conditions, a substrate temperature of 450 ° C. and a bias voltage of −40V to −150V were applied. In the coating step, it is desirable to perform film formation by the AIP method before performing simultaneous discharge, and to perform simultaneous discharge by the AIP method and the MS method after ensuring adhesion. Using the obtained hard coating-coated insert, a cutting test was performed under the following cutting conditions. The work material used in the cutting test was prepared by drilling holes on the surface in advance at equal intervals. By cutting the surface of the work material under high-efficiency machining conditions, intermittent cutting was assumed, and the possible cutting length until the insert was impacted and damaged was evaluated.
(Cutting conditions)
Tool: Face mill Insert shape: SDE53 type special shape Cutting method: Center cut method Workpiece shape: width 100mm x length 250mm
Work material: SCM440, Hardness HB280, There are many Φ10 drill holes on the surface. Cutting depth: 2.0mm
Cutting speed: 180 m / min
1 blade feed amount: 1.5 mm / blade Cutting oil: None, dry cutting The evaluation method evaluates in an intermittent environment where a strong impact can be applied to the insert blade edge, and whether the insert blade edge part is damaged, Alternatively, machining was performed until the tool became uncuttable due to wear of the hard coating or the like, and the cuttable distance at that time was defined as the tool life. Tables 1 and 2 show the details of the hard coating and the results of the cutting test for the invention examples, comparative examples, and conventional examples.

Table 2 shows the evaluation results of Invention Examples 1 to 14, Comparative Examples 15 to 28, and Conventional Examples 29 to 33. As shown in Examples 1 to 14 of the present invention, high-efficiency processing can be performed by applying the hard coating of the present invention. That is, there is a clear difference in cutting performance depending on the presence of Si-O bonds near the hard coating surface and the amount of Si content when Si is added to the hard coating using two or more physical evaporation sources. As a result, it appeared. In particular, the hard film to which Si was added by NbSi ₂ shown in Invention Example 9 showed the best result in this evaluation. Therefore, the hard coating was examined in detail for Example 9 of the present invention. The result is shown in FIG. In the XPS analysis, Si—O bonds were confirmed in the range of 100 to 105 eV. Due to the presence of this Si—O bond, intense welding at the initial stage of cutting was suppressed. Thus, in the vicinity of the hard coating surface of Example 9 of the present invention, a dense oxide having excellent lubricating properties is present, and a remarkable effect was exhibited in the processing of a metal in which welding is intensely generated. The added Si was NbSi ₂ installed in the MS vapor deposition source, and the discharge output was set to 6.5 kW. As a result, the amount of added Si was 14.8 atomic%, which was in the range of an appropriate Si addition amount. Furthermore, the fracture surface structure of the hard film was observed with a scanning electron microscope (hereinafter referred to as SEM) at a magnification of 15000 times. The result is shown in FIG. As shown in FIG. 2, the fracture surface structure of the hard coating was a columnar structure. The hard film-coated insert having such a composition and structure has also obtained mechanical strength in the shearing direction in cutting with high impact such as high feed processing. Furthermore, FIG. 3 is a result of observing the fractured surface structure with a TEM at a magnification of 20,000 times. Each crystal grain having the columnar structure of the hard film had a multilayer structure. FIG. 4 shows the result of magnifying and observing the crystal grains of FIG. The crystal grains had a multi-layered structure in which a plurality of black layers and gray layers having different brightnesses were alternately laminated. This observation confirmed that each crystal grain was grown in almost the same direction so as to be perpendicular to the substrate surface. From the striped pattern shown in FIG. 4, it can be seen that the thickness of each layer is about 3 to 4 nm. Since the magnification is different between FIG. 3 and FIG. 4, the number of striped patterns in both does not match. FIG. 5 shows the result of further observing the portion in the field of view of FIG. 4 and confirming the continuity of the lattice fringes of each layer in the multilayer portion at a magnification of 2 million times. The observation region in FIG. 5 is enlarged while confirming the positions of the black layer and the gray layer seen in FIG. 4, and the black layer and the gray layer in FIG. 5 correspond to those in FIG. The two lines drawn in FIG. 5 separate the areas corresponding to the black layer and the gray layer, respectively.
FIG. 6 is a schematic diagram corresponding to the photograph of FIG. However, the spacing of the checkered pattern is enlarged for clarity of explanation. FIG. 5 shows that crystal lattice fringes are continuous in the boundary region between layers in the multilayer structure. The continuity of the crystal fringes need not be established in all the boundary regions, and it is sufficient if there is a region in the TEM photograph where the continuity of the lattice fringes is recognized. Although there is a black region on the left side of FIG. 5, this is not related to the black layer shown in FIG. FIG. 7 shows an electron diffraction image of a region surrounded by a circle in FIG. 6, and FIG. 8 shows a schematic diagram of FIG. As apparent from FIGS. 7 and 8, the electron diffraction image of the black layer indicated by the star mark and the electron diffraction image of the gray layer indicated by the circle mark substantially coincide with each other, so that the epitaxial region is epitaxial in the boundary region between the black layer and the gray layer. The checkered pattern is continuous due to the relationship Thus, it can be seen that the columnar crystal grains having a multi-layer structure are in the form of a single crystal. As the composition of the black layer and the gray layer in the multilayer columnar crystal grain of Example 9 of the present invention, the composition of point P (black layer) and point Q (gray layer) in FIG. 5 was analyzed by EDX attached to the TEM. Table 3 shows the composition of the black and gray layers.

From Table 3, the difference of the content of added Si was confirmed. When the Si content exceeds 30 atomic%, the crystal structure becomes finer, so the difference in content must be controlled within 30 atomic%. In Invention Example 9, since the discharge output of NbSi 2 was set to 6.5 kW, the difference in content was 12.4 atomic%.
For Inventive Example 9 The chemical state of Si was investigated by Raman spectroscopy, _Si 3 _{N 4} peak of the α-type crystal structure ranges from wave number 800 of 850 cm ^-1 as shown in FIG. 9, and from the wave number 1020 1170Cm A Si ₃ N ₄ peak having a β-type crystal structure was obtained in the range of ⁻¹ . FIG. 10 shows the measurement results of the friction coefficients of Invention Examples 8 and 9 and Conventional Examples 30 and 32. For the measurement, a friction and wear tester using a ball-on-disk system was used, and the measurement was performed in an atmosphere at a high temperature of 600 ° C. From the measurement results, it was confirmed that the lubrication characteristics were significantly improved by adding Si to the hard coating. Invention Example 6 containing Si obtained cutting performance three times that of Comparative Example 20. By applying the Si addition of the present invention, the friction coefficient of the coating having (TiAl) N as a basic composition was also greatly reduced. Further, in Example 9 of the present invention, in addition to the above-described cutting conditions, intermittent parts such as a fixing hole as seen in mold processing were also processed. Here too, due to the improvement in the toughness of the hard coating, stable cutting could be performed without loss even under severe impact.
From the above evaluation results, in order to improve the lubrication characteristics of the hard coating and to obtain stable cutting performance, the Si addition source was a target material made of an intermetallic compound such as NbSi ₂ , CrSi ₂ , WSi ₂ , or TiSi ₂ . . Also preferred are alloy targets such as WSi, CrSi, NbSi, TiSi. The hard coating of the present invention was applied to drills, end mills, punches, dies, etc., and was effective for application in an intermittent environment.

  Except for Comparative Examples 17, 21, 22, 23, and 27, the Si content was large and was 30 atomic% or more. In particular, Comparative Example 20 had a Si—O bond and the thickness of one layer in the multilayer structure was within an appropriate range, but the Si content was added in a large amount of 34 atomic%. As a result of confirming the structure of the film fracture surface, an amorphous microstructure as shown in FIG. 11 was obtained. The hardness of the hard film was 26 GPa and was in a softening tendency. The softening of the film is due to the fact that the Si content was not an appropriate value. In Comparative Example 17, Si—O bonds were confirmed, and the Si content was within an appropriate range of 9.1 atomic%. However, the thickness of one layer in the multilayer laminated structure of the hard coating obtained by discharging the AIP method and the MS method simultaneously was 134.5 nm. Therefore, the cutting test result was short life due to early wear. This is because the discharge output of the CrSi target by the MS method, which is the condition at the time of film formation, was 6.6 kW, so that the thickness of one layer in the layer stack structure exceeded 100 nm, and the lattice of each layer in the multilayer structure was distorted. This is because the crystal lattice fringes become discontinuous due to the occurrence of, and the crystal structure of the hard coating is refined. In Comparative Example 23, no Si—O bond was confirmed, and the Si content was an appropriate range of 7 atomic%. The thickness of one layer of the multilayer structure was 30.6 nm. For this reason, the cutting test result was an effect of increasing the hardness by adding Si, and it was possible to process a certain distance, but it was insufficient for suppressing welding that occurred at the initial stage of cutting. This is because the Si—O bond was not formed because oxygen was not added to the reaction gas used during film formation. In Comparative Examples 21 and 22, the Si—O bond was not confirmed, and the Si content was not detectable even when using an analyzer such as XPS. The thickness of one layer of the multilayer structure was 0.2 and 0.8 nm, which are close to the confirmation limit. Therefore, in the cutting test result, welding at the initial stage of cutting was intense. In particular, in Comparative Example 22, sparks were generated and the evaluation was stopped. This is because the discharge output of the target material of WSi and NbSi by the MS method used at the time of film formation was 0.5 kW, so that the Si content, the chemical bonding state, and the thickness of one layer of the stack were small.

  Conventional examples 29 to 33 are examples in which coating is performed only by the AIP method. Hard film coated only by the AIP method has very high hardness and residual compressive stress, and lacks the toughness of the hard film, making it difficult to improve the toughness of the hard film because it easily breaks inside the hard film. Met. It is possible to some extent if the temperature, bias voltage, reaction pressure, arc current, and composition of the target that is the starting source of the hard film are studied in the AIP method. However, the hard coating containing Si formed by the film formation of only the AIP evaporation source, when toughness was improved, the hardness was lowered and the wear resistance was significantly lowered. For this reason, although the impact resistance of the covering member is improved, it is difficult to ensure wear resistance and a satisfactory life cannot be obtained. On the other hand, although it is not described in the conventional example, in the case of a hard film formed only by the MS method, since the plasma density is low, metal ions or gas ions ionized in the plasma are incident on the workpiece. Energy was low and adhesion was low. In addition, it is possible to obtain a hard film with high toughness for a hard film formed by the AIP method, but it is difficult to obtain a hard film with high hardness. It was difficult to get.

FIG. 1 shows the XPS analysis result of Example 9 of the present invention. FIG. 2 shows a cross-sectional structure of the hard film of Example 9 of the present invention. FIG. 3 shows the result of observation with a transmission electron microscope of the hard film of Example 9 of the present invention. FIG. 4 shows an enlarged observation result of FIG. FIG. 5 shows an enlarged observation result of FIG. FIG. 6 shows a schematic diagram of FIG. FIG. 7 shows the electron diffraction results of Example 9 of the present invention. FIG. 8 shows a schematic diagram of FIG. FIG. 9 shows the Raman analysis result of Example 9 of the present invention. FIG. 10 shows the measurement result of the coefficient of friction. FIG. 11 shows a cross-sectional structure of the hard film of Comparative Example 20.

Claims (4)

A hard film coated by physical vapor deposition, wherein the hard film contains one or more metal elements selected from the group 4a, 5a, 6a, Al, B and Si, and is selected from C, N, O The hard coating has a columnar structure, and the crystal grains in the columnar structure have a multilayer structure including a plurality of layers having different Si contents, A hard film characterized in that at least a region where crystal lattice stripes are continuous exists in the boundary region, and the thickness T (nm) of each layer is 0.1 ≦ T ≦ 100. 2. The hard coating according to claim 1, wherein Si is present as a crystalline phase in the hard coating, and the crystalline phase has α-type Si ₃ N ₄ and β-type Si ₃ N _4. Hard film to do. 3. The hard film according to claim 1, wherein the hard film has a bond of Si and O. The hard film according to any one of claims 1 to 3, wherein the surface of the hard film is smoothed by machining.