JP2007056324A - Hard film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To particularly improve wear resistance and adhesion of a hard film by the increase of its hardness without sacrificing the characteristics of high temperature oxidation resistance and toughness therein. <P>SOLUTION: The hard film has a composition comprising Si and one or more metallic elements selected from the group 4a, 5a, 6a metals, Al and B, and one or more 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 difference in the Si content, a region in which at least crystal lattice streaks are continued is present in the boundary region between the layers, provided that the peak intensity of α type Si<SB>3</SB>N<SB>4</SB>by Raman spectroscopic analysis is defined as Iα and the peak intensity of β type Si<SB>3</SB>N<SB>4</SB>as Iβ, 1.0≤Iβ/Iα≤20.0 is satisfied, and, provided that the peak intensity of the (200) plane by X-ray diffraction is defined as Ib and the peak intensity of the (111) plane as Ia, Ib/Ia>1.0 is satisfied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hard film having excellent wear resistance and adhesion due to high hardness, and also having high-temperature oxidation resistance and toughness characteristics.

  The following patent document discloses a technique related to a Si-containing hard coating.

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

The above Patent Documents 1 to 4 are attempts to improve the wear resistance characteristics of a hard coating using only an arc discharge ion plating (hereinafter referred to as AIP) method in a physical vapor deposition method, and welding occurs on a blade edge or the like. In the processing of steel types that are easily deformed, stable processing cannot be expected unless the welding characteristics, that is, the lubrication characteristics are improved, rather than the discussion of the occurrence of wear. 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, any of the hard coatings described in the above documents can be applied to dry, high speed, high feed while maintaining wear resistance and oxidation resistance. It does not meet the toughness requirements that have a major impact on
The object of the present invention is not to sacrifice the high-temperature oxidation resistance and toughness properties of the hard coating, and in particular to improve the excellent wear resistance and adhesion by increasing the hardness of the hard coating. For example, it is to provide a hard coating that can cope with dry processing, high speed, and high feed in cutting and the like.

The hard coating of the present invention comprises one or more metal elements selected from the group 4a, 5a, 6a, Al and B and Si, and comprises one or more non-metal elements selected from C, N and O. The hard coating has a columnar structure, and the crystal grains in the columnar structure have a multilayer structure composed of a plurality of layers having different Si contents, and at least crystal lattice fringes are continuous in the boundary region between the layers. The thickness T (nm) of each layer is 0.1 ≦ T ≦ 100, and Si present in the hard film is crystalline of α-type Si ₃ N ₄ and β-type Si ₃ N ₄ . When the peak intensity of the α-type Si ₃ N ₄ by Raman spectroscopy is Iα and the peak intensity of the β-type Si ₃ N ₄ is Iβ, 1.0 ≦ Iβ / Iα ≦ 20.0 The peak intensity of (200) plane by X-ray diffraction is Ib, and the peak intensity of (111) plane is A hard film characterized by Ib / Ia> 1.0 when Ia is given. By adopting this configuration, the hard coating containing Si of the present invention has excellent wear resistance and adhesion due to the increased hardness of the hard coating. At this time, it is possible to provide a hard film with improved characteristics without sacrificing the high temperature oxidation resistance and toughness characteristics of the hard film.
The hard coating of the present invention preferably has a bond between Si and O (hereinafter referred to as Si—O bond). Furthermore, the surface of the hard coating is preferably smoothed by machining.

  The present invention is not to sacrifice the high-temperature oxidation resistance and toughness properties of the hard coating, and particularly to improve the excellent wear resistance and adhesion by increasing the hardness of the hard coating. 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 die 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%, β-type Si ₃ N ₄ formed in the hard film increases, and Iβ / Iα in the peak intensity ratio in Raman spectroscopic analysis with α-type Si ₃ N ₄ formed simultaneously. Becomes larger than 20.0. In this case, although the hardness and heat resistance of the hard coating are improved, the residual compressive stress of the hard coating is increased and the adhesion is significantly impaired. Moreover, when Iβ / Iα exceeds 20.0, 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 a sudden defect occurs. 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. For this purpose, the Si content is adjusted to 30% or less, and the Iβ / Iα value is controlled to 20.0 or less. 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 coating of the present invention contains B, the hardness of the hard coating can be further increased. For example, when a hard film containing B is coated on a cutting tool, the tool life is extended. Hardness can be improved by interposing a c-BN phase. In addition, the lubrication characteristics can be improved by interposing the h-BN phase. 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. However, in cutting, Fe or the like in the work material diffuses into the hard film. The Al content is preferably at most 50% in terms of atomic% of only metal elements. A more preferable Al content is 20% to 50%. 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. However, the hardness decreases, the crystal structure of the fracture surface becomes finer, 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 20 % 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, a hard coating that improves toughness and suppresses residual compressive stress can be obtained.
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 by 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 by an X-ray diffractometer or TEM. 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 has a portion where the presence of Si is Si ₃ N ₄ in the coating cross-section selected from the portion distinguished from the region forming the columnar crystal grains. The presence of Si ₃ N ₄ can be 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. The hard coating of the present invention satisfies 1.0 ≦ Iβ / Iα ≦ 20.0, and is effective in improving wear resistance by increasing the hardness by controlling within this range, and the fracture surface structure becomes a columnar structure. And toughness. In particular, a columnar structure is important in high feed processing. By allowing both α-type Si ₃ N ₄ and β-type Si ₃ N ₄ to coexist, it is possible to simultaneously improve the hardness and toughness of the Si-containing hard coating. 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.
Further, the hard coating of the present invention has an effective peak intensity ratio Ib / Ia value in X-ray diffraction of Ib / Ia> 1.0, preferably 1.0 <Ib / Ia <35.0. . In the hard coating of the present invention, it is important to reduce the residual compressive stress that greatly affects the adhesion. A hard coating strongly oriented in the (111) plane has a large residual compressive stress that hinders adhesion. In a hard film having an fcc structure obtained by a physical vapor deposition (hereinafter referred to as PVD) method, strong peaks appear on the (111) plane, the (200) plane, and the (220) plane. In the case of the hard coating of the present invention, control is performed so that crystals are strongly oriented in the (200) plane. 200) A hard coating strongly oriented in the plane can reduce stress and is effective in improving adhesion. In order to control the orientation plane, there is optimization of the temperature during film formation. This is because the orientation strength changes depending on the incident energy of ions reaching the substrate. Therefore, first, the correlation between the temperature during film formation and the peak obtained by X-ray diffraction of the hard film was examined. In the present invention, when the temperature of the substrate is 700 ° C. or lower, the Ib / Ia value is Ib / Ia> 1.0. In the case of film formation at 400 ° C. or lower, the orientation strength to the (200) plane was further increased, and the Ib / Ia value was 36.0. Further, when the film was formed at 350 ° C., the Ib / Ia value was 40.0. However, the temperature at the time of film formation affects the relaxation of the residual stress and the magnitude of the kinetic energy of the generated ions. From such points, film formation at 400 ° C. or lower is not preferable because it adversely affects adhesion. On the other hand, when the film is formed at a higher temperature, the residual compressive stress generated in the hard film works in a direction to be relaxed. Therefore, the case where the film was formed under conditions exceeding 700 ° C. was also examined. At this time, it was confirmed that an element present on the surface of the substrate in contact with the hard film diffuses into the hard film and the interface becomes brittle. Next, the correlation between the bias voltage during film formation and the peak obtained by X-ray diffraction of the hard coating was examined. In order to control the orientation plane, it is also effective to optimize the bias voltage when attracting ions during film formation to the substrate. In order to strongly orient in the (200) plane, it is preferable to set a relatively low bias voltage of 40 to 150V. When a bias voltage exceeding 150 V is applied, the temperature at the time of film formation is affected, but the orientation to the (111) plane tends to become strong. In this case, the residual compressive stress easily exceeds 8 GPa, which is inconvenient for the adhesion of the hard coating. For these reasons, the Ib / Ia value is defined as Ib / Ia> 1.0.

(3) Method for producing film It is effective to use PVD methods having different plasma densities to produce the multilayer hard film of the present invention. Specifically, in order to continuously grow crystal grains without an interface, an AIP method having a high plasma density and a magnetron sputtering (hereinafter referred to as MS) method having a low plasma density in a plasma reaction gas are simultaneously performed. Do. The magnitude of the plasma density can be determined by the film formation speed (μm / hour) in each film formation method. In a hard coating containing Si, one method is to control the presence state of crystalline Si ₃ N ₄ by the Si content. In order to control the abundance ratio of the α-type and β-type of the crystalline Si ₃ N ₄ of the present invention, the film-forming speed obtained by the AIP system (μm / hour: AIP) ), And when the film formation rate obtained by the MS method is (μm / hour: MS), control is performed so that (μm / hour: AIP) / (μm / hour: MS) is 2.0 or more. . As a result, the Iβ / Iα value in the Raman spectroscopic analysis becomes Iβ / Iα ≧ 1.0. Further, when the deposition rate ratio is 100.0 or less, the Iβ / Iα value in the Raman spectroscopic analysis is Iβ / Iα ≦ 20.0. When coating is performed in a state where the deposition rate ratio exceeds 100.0, the Iβ / Iα value exceeds 20.0, and β-type Si ₃ N ₄ which is a hard crystal existing in the hard film. Will increase. Increasing the β type improves the hardness and heat resistance of the hard coating. However, the impact resistance and toughness of the hard coating are impaired. For example, when coating is performed under the conditions that the film formation speed by the AIP method is 1.5 μm / hour and the film formation speed by the MS method is 0.01 μm / hour, the film formation speed ratio is 150.0. is there. The hardness of the hard film obtained here reaches 36 GPa and exhibits high hardness. However, the residual compressive stress becomes 7.2 GPa, which causes a decrease in adhesion. On the other hand, when coating is performed under the conditions that the film formation speed by the AIP method is 1.5 μm / hour and the film formation speed by the MS method is 0.1 μm / hour, the film formation speed ratio is 15.0. 0.0 ≦ Iβ / Iα ≦ 20.0 is satisfied. From this, the crystal grain of a hard film | membrane has a big 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 AIP method generates very high plasma density and film formation speed, the energy generated when ions generated in the plasma are incident on the substrate is large, and although a high-quality hard film is formed, the residual compressive stress is suppressed. Have difficulty. 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, by combining the AIP method and the MS method and controlling the Iβ / Iα value of the hard coating to 1.0 ≦ Iβ / Iα ≦ 20.0, it has excellent wear resistance and adhesion due to high hardness. In addition, it is possible to obtain a hard film having both high-temperature oxidation resistance and toughness characteristics.
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. Further, there is no safety problem in the environment of the plasma-assisted chemical vapor deposition method using a reaction gas containing Si, and Si can be contained in the hard coating.
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 are present in the film at an appropriate ratio, that is, 1.0 ≦ Iβ / Iα ≦ 20.0. It is possible to increase the hardness of the hard film containing Si and improve the high temperature oxidation resistance. 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. However, if it is set to 0.3 kW or less, the plasma density becomes smaller, so that Iβ / Iα <1.0, so that α-type Si ₃ N ₄ is included more than β-type Si ₃ N ₄ . Under these conditions, a hard film having excellent wear resistance due to high hardness cannot be obtained. The reason why the hard film has toughness is that when the soft layer is formed by the evaporation source of the MS method having a low plasma density, the soft layer mainly contains a large amount of α-type Si ₃ N _4. This is because a significant difference between the hard layer and the hard layer is effective for the cushion effect. However, if the α type is increased, the entire hard coating tends to be softened, and it is difficult to achieve both wear resistance characteristics. 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 that is widely less than 0.5 Pa in order to increase the film formation 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 acts on the periphery of the target. However, many macro particles are generated under the 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. As a result, it is possible to ensure a strong adhesion and to form a hard film having high hardness and toughness.

When the hard coating of the present invention is formed on the cutting tool, it has excellent wear resistance and adhesion due to the high hardness of the hard coating, so it is possible to prevent sudden breakage due to a large impact with the work material It becomes. As a result, the cutting tool coated with the hard coating can cope with dry cutting, high speed, and high feed of cutting. 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, a hard film mainly composed of TiAl, a hard film mainly composed of Cr, CrAl, or W is provided on the surface of the substrate, the substrate and the hard film The adhesion is increased, and the peel resistance and fracture resistance of the hard coating are improved. 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 is an evaluation in an intermittent environment in which 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, 2 and 3 show the details of the hard coating and the results of the cutting test for the inventive examples, comparative examples and conventional examples.

Tables 2 and 3 show the evaluation results of Invention Examples 1 to 15, Comparative Examples 16 to 31, and Conventional Examples 32 to 47. As shown in Examples 1 to 15 of the present invention, high-efficiency processing can be performed by applying the hard coating of the present invention. That is, with respect to the hard film of the present invention, both α-type and β-type peaks of crystalline Si ₃ N ₄ obtained by performing Raman spectroscopic analysis were detected, and the Iβ / Iα value was 1.0 ≦ The Ib / Ia value obtained by X-ray diffraction satisfies Iβ / Iα ≦ 20.0, and Ib / Ia> 1.0, preferably 1.0 <Ib / Ia <35.0. It is necessary to be. Furthermore, there is a clear difference in cutting performance due to the presence of Si-O bonds near the hard coating surface and the Si content and structure 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 added with Si by TiSi ₂ shown in Invention Example 6 showed the best result in this evaluation. Therefore, the hard coating was examined in detail for Inventive Example 6. The result is shown in FIG. In the XPS analysis, Si—O bonds were obtained 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 6 of the present invention, a dense oxide having excellent lubrication characteristics is present, and a remarkable effect was exerted in the processing of a metal in which welding is severely generated. For Si addition, TiSi ₂ was installed in the MS evaporation source, and the discharge output was set to 6.5 kW. As a result, the amount of Si added was 14.4 atomic%, which was within the appropriate range of Si addition. 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. 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 in FIG. 3 at a magnification of 200,000 with a TEM. 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. As a result, the checkered pattern is continuous. 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 grains of Example 6 of the present invention, the composition of the point P (black layer) and the point Q (gray layer) in FIG. 5 was analyzed by EDX attached to the TEM. Table 4 shows the composition of the black and gray layers.

From Table 4, the difference of Si content 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 6, since the discharge output of TiSi ₂ was set to 6.5 kW, the difference in Si content was 12.4 atomic%.
FIG. 9 shows the results of investigation of the chemical state of Si by Raman spectroscopic analysis for Example 6 of the present invention. _Si 3 _{N 4} peak of the β-type crystal structure _Si 3 _{N 4} peak of the α-type crystal structure from the wavenumber 800 in the range of 850 cm ^-1, and from the wave number 1020 to a range of 1170cm ^-1 was obtained. The peak intensity ratio Iβ / Iα of the α type and β type was calculated to be 1.95. The hardness of the hard film was 35 GPa and was high. By applying the coating method of the present invention, there was a relatively hard β type than the relatively soft α type Si ₃ N ₄ present in the hard film, so there was a tendency to increase the hardness, At the same time, it showed improved performance in cutting that required impact resistance due to the presence of a relatively soft α-type in the hard coating. FIG. 10 shows the measurement results of the friction coefficients of Examples 13 and 14 of the present invention and Comparative Examples 28 and 29. For the measurement, a friction and wear tester using a ball-on-disk system was used, and the measurement was performed in a high temperature environment of 600 ° C. in the atmosphere. From the measurement results, it was confirmed that the lubrication characteristics were significantly improved by having the Si—O bond in the hard coating. For example, the present invention example 6 containing Si has a numerical value of the friction coefficient of less than half that of the comparative example 21, and a cutting performance of about 15 times is obtained. By applying the Si—O formation of the present invention, the coefficient of friction of the coating having (TiAl) N as a basic composition was also greatly reduced. Further, in Example 7 of the present invention, in addition to the cutting conditions described above, machining of intermittent parts such as fixing hole machining as seen in die machining was also performed. 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 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.

As shown in Comparative Examples 17, 19, 21, 24, 25, and 29, satisfactory cutting performance could not be obtained when conditions necessary for the hard coating of the present invention were not satisfied. It is necessary to adjust the physical properties of the hard coating as in the present invention example. Comparative Example 30 has a large Si content and 30 atomic% or more, the peak in Raman spectroscopic analysis is strongly oriented to β-type Si ₃ N ₄ , and the peak intensity ratio with α-type Si ₃ N ₄ exceeds 20. It was. As a result, defects were reached in the early stage of cutting. 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 the comparative example, Si—O bond was not confirmed. Therefore, the improvement of the lubrication characteristics, which is the object of the present invention, cannot be achieved. This is because the Si—O bond was not formed because oxygen was not added to the reaction gas used during film formation.

Conventional examples 32 to 47 are examples in which coating is performed by using the AIP method or the MS method alone. The hard film coated by the AIP method has very high hardness and residual compressive stress, and the toughness of the hard film is insufficient, so that the hard film tends to break. It was difficult to improve the toughness of the hard coating, and it was often lost in the early stage of cutting. It is possible to some extent if the temperature, bias voltage, reaction pressure, arc current, and target composition of the hard coating are examined 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 characteristics of the covering member are improved, it is difficult to ensure wear resistance, and a satisfactory life cannot be obtained. On the other hand, in the case of a hard film formed by the MS method, since the plasma density is low, energy when metal ions or gas ions ionized in the plasma are incident on the object to be processed is low, and adhesion is 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, so that it has a long life as a hard film coating member. It was difficult to get.

FIG. 1 shows the XPS analysis result of Example 6 of the present invention. FIG. 2 shows a cross-sectional structure of the hard film of Example 6 of the present invention. FIG. 3 shows the result of observation with a transmission electron microscope of the hard film of Example 6 of the 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 6 of the present invention. FIG. 8 shows a schematic diagram of FIG. FIG. 9 shows the Raman analysis result of Example 6 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 30.

Claims (3)

The hard coating contains one or more metal elements selected from the group 4a, 5a, 6a, Al, and B and Si, and consists of one or more non-metal elements selected from C, N, and O. The film has a columnar structure, and the crystal grains in the columnar structure have a multilayer structure composed of a plurality of layers having different Si contents, and at least a region where crystal lattice fringes are continuous in the boundary region between the layers. And the thickness T (nm) of each layer is 0.1 ≦ T ≦ 100, and Si present in the hard coating exists as a crystalline phase of α-type Si ₃ N ₄ and β-type Si ₃ N _4. When the peak intensity of the α-type Si3N4 by Raman spectroscopy is Iα and the peak intensity of the β-type Si ₃ N ₄ is Iβ, 1.0 ≦ Iβ / Iα ≦ 20.0, and X-ray diffraction When the peak intensity of the (200) plane is Ib and the peak intensity of the (111) plane is Ia A hard film characterized by Ib / Ia> 1.0. 2. The hard film according to claim 1, wherein the hard film has a bond of Si and O. The hard film according to claim 1, wherein the surface of the hard film is smoothed by machining.