JP4593996B2 - Surface coated cutting tool - Google Patents

Description

  The present invention relates to drills, end mills, drill tip replacement tips, end mill tip replacement tips, milling tip replacement tips, turning tip replacement tips, metal saws, gear cutting tools, reamers, taps, etc. More particularly, the present invention relates to a surface-coated cutting tool in which a coating for improving characteristics such as wear resistance is formed on the surface (outermost layer).

  Conventionally, cemented carbides (WC-Co alloys or alloys obtained by adding carbonitrides such as Ti (titanium), Ta (tantalum), Nb (niobium), etc.) have been used as cutting tools. However, with the recent increase in cutting speed, cemented carbide, cermet, or alumina-based or silicon nitride-based ceramics is used as a base material, and the surface is subjected to CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition). Hard alloy tool with a coating of carbide, nitride, carbonitride, boronitride, oxide such as IVa, Va, VIa group metals and Al (aluminum) of the periodic table of elements coated to a thickness of 3-20 μm The usage rate of is increasing.

  In particular, the coating by the PVD method can increase the wear resistance without causing deterioration of the base material strength, so that the strength of drills, end mills, milling cutters or turning edge insert type (throw away) inserts for turning is required. It is often used for cutting tools.

  In recent years, in order to further improve the cutting efficiency, the cutting speed has been increased, and accordingly, the tool is required to have higher wear resistance. However, when high wear resistance is required, the toughness is lowered, so that it is required to achieve both high wear resistance and high toughness.

  As an attempt to meet this requirement, a technique has been proposed in which internal stress such as compressive stress is changed continuously or stepwise in the coating formed on the surface of the base material of such a cutting tool (Patent Document 1). With such a proposal, a certain degree of effect is being given to the requirement of achieving both wear resistance and toughness.

  However, the cutting tool according to the above proposal has a mode in which the compressive stress of the coating uniformly increases or decreases from the coating surface side to the base material surface side. It was necessary to increase the stress from the substrate surface side to the coating surface side, and to significantly improve the wear resistance, it was necessary to increase the compressive stress from the coating surface side to the substrate surface side.

  That is, in the aspect having the maximum compressive stress on the surface of the coating, the toughness is excellent, but the compressive stress decreases uniformly or stepwise toward the substrate surface side, so that the wear resistance is inferior. On the contrary, in the aspect having the maximum compressive stress on the substrate surface side, although it is excellent in abrasion resistance, the compressive stress is uniformly reduced stepwise toward the coating surface side, so that the toughness is inferior. .

  In particular, the cutting tool having the maximum compressive stress on the surface of the coating film has a large compressive stress, so that the coating film self-destructs after film formation (after coating is completed) or when impact stress is applied, and minute film peeling (hereinafter referred to as “film peeling”). , Which is referred to as film chipping), which adversely affects the appearance quality as a cutting tool and the cutting performance during high-precision machining.

In this type of cutting tool, the balance between toughness and wear resistance is one of the most basic characteristics, and therefore, it has been desired to provide a cutting tool that achieves a high degree of compatibility between the two.
JP 2001-315006 A

  The present invention has been made in view of the above-described situation, and the object of the present invention is to provide a surface-coated cutting tool in which the toughness and wear resistance of the cutting tool are both highly compatible and in particular, film chipping is suppressed. Is to provide.

  The present inventor has made extensive studies to solve the above problems, and as a result, the compressive stress in the surface portion of the coating formed as the outermost layer on the substrate is reduced and the compressive stress is increased in the coating. If the maximum point is formed in the strength distribution, the development of cracks on the surface of the coating near the maximum point can be suppressed while maintaining high wear resistance and resistance to film chipping. The knowledge that it might improve is obtained. In addition, further research has led to the knowledge that further improvement in wear resistance can be achieved by continuously reducing the compressive stress from the maximum point to the bottom of the coating. . The present invention has been completed by further research based on these findings.

  That is, the surface-coated cutting tool of the present invention is a surface-coated cutting tool comprising a substrate and a coating formed on the substrate, and the coating is an outermost layer on the substrate. And has a compressive stress, and the compressive stress is changed so as to have a strength distribution in the thickness direction of the coating, and the strength distribution indicates that the compressive stress on the surface of the coating is the surface of the coating. To the intermediate point located between the surface of the film and the bottom surface of the film, and has a maximum point at the intermediate point, and the compressive stress continues from the intermediate point to the bottom surface of the film. It is characterized by decreasing.

  Here, the said compressive stress can be made into the stress of the range of -15GPa or more and 0GPa or less. The intermediate point may be located at a distance of 0.1% to 50% of the thickness of the coating from the surface of the coating.

  The compressive stress can be minimized on the surface of the coating, and the compressive stress has a value of 25 to 95% of the compressive stress at the midpoint of the coating on the surface of the coating. it can.

  Moreover, the said compressive stress shall have a value of 35-85% of the compressive stress of the intermediate point of the said film in the surface of the said film.

  In addition, the compressive stress continuously increases to the intermediate point after the compressive stress on the surface of the coating is maintained for a certain distance from the surface of the coating toward the intermediate point. Can do.

  The surface-coated cutting tool of the present invention has the above-described configuration, so that it has a characteristic that the toughness and the wear resistance are both highly compatible and particularly the resistance to film chipping is improved.

  In particular, by having a compressive stress smaller than the inside of the coating on the surface of the coating, wear resistance and resistance to chipping are improved, and a maximum point of the strength distribution of the compressive stress is formed in a portion close to the surface inside the coating. As a result, the progress of cracks generated on the surface of the coating can be suppressed, and the toughness can be remarkably improved. Further, by further reducing the compressive stress from the maximum point to the bottom surface of the coating, it is possible to achieve a higher degree of wear resistance.

  As described above, the present invention succeeds in achieving both high toughness and wear resistance and improving particularly the resistance to film chipping by synergistic action of these effects.

  Hereinafter, the present invention will be described in more detail. In the following description of the embodiments, the description is made with reference to the drawings. In the drawings of the present application, the same reference numerals denote the same or corresponding parts.

<Surface coated cutting tool>
As shown in FIG. 1, the surface-coated cutting tool 1 of the present invention has a configuration including a base material 2 and a coating 3 formed on the base material. In FIG. 1, the coating 3 is formed so as to be in direct contact with the surface of the substrate 2. However, as long as the coating 3 is the outermost layer, an arbitrary intermediate is provided between the coating 3 and the substrate 2 as described later. A layer may be formed. In the present application, the term “film formed on a substrate” includes the case where an arbitrary intermediate layer is formed in this way.

  Such a surface-coated cutting tool according to the present invention includes a drill, an end mill, a drill tip replacement tip, an end mill tip replacement tip, a milling tip replacement tip, a turning tip replacement tip, a metal saw, and a gear cutter. It can be suitably used as a cutting tool for tools, reamers, taps, etc., and is particularly suitable for finish cutting or precision cutting applications, and particularly suitable for turning applications. Excellent toughness and wear resistance depending on the application. In particular, the finish surface roughness of the work material is improved due to its excellent resistance to film chipping, and the rough finish simultaneous processing is possible because it is also excellent in the finish surface gloss of the work material.

<Base material>
As the base material used in the surface-coated cutting tool of the present invention, any base material can be used as long as it is a conventionally known base material for this type of application. For example, cemented carbide (for example, WC-based cemented carbide, including WC, including Co, or further including carbonitride such as Ti, Ta, Nb), cermet (TiC, TiN, TiCN, etc.) Main component), high speed steel, ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cubic boron nitride sintered body, or diamond sintered body Is preferred.

  Among these various substrates, it is particularly preferable to select a WC-based cemented carbide, cermet, and cubic boron nitride sintered body. This is because these substrates are particularly excellent in the balance between high-temperature hardness and strength, and have excellent characteristics as a substrate for a surface-coated cutting tool for the above applications.

<Coating>
The coating film of the present invention is formed on the above-mentioned base material and is the outermost layer. As long as it is formed in this way, it is not always necessary to cover the entire surface of the base material, and the surface of the base material may include a portion where the coating film is not formed. In addition, when a part of the surface of the film is removed by arbitrary post-processing after the film is once formed, a layer newly exposed on the outermost surface after the removal is also included in the object of the present invention. It becomes a film. Further, when an intermediate layer is formed between the base material and the coating as will be described later, if the intermediate layer is exposed as an outermost layer by removing the coating by any post-processing, the exposed portion In this case, the intermediate layer is the coating of the present invention (in this case, when the intermediate layer is formed of a plurality of layers, the outermost layer (the layer that is the outermost surface) of the plurality of layers is the present invention). It becomes a film of).

  Such a coating is formed in order to impart an effect of improving various properties such as wear resistance, oxidation resistance, toughness of the tool, and coloring property for identifying the used blade edge part, The composition is not particularly limited, and a conventionally known one can be adopted. For example, at least one element selected from the group consisting of group IVa element, group Va element, group VIa element, Al (aluminum), B (boron), Si (silicon) and Ge (germanium) in the periodic table Examples of the composition include carbides, nitrides, oxides, carbonitrides, carbonates, nitrides, carbonitrides, or solid solutions thereof.

In particular, Ti, Al, (Ti _1-x Al _x ), (Al _1-x V _x ), (Ti _1-x Si _x ), (Al _1-x Cr _x ), (Ti _1-xy Al _x Si) _y ) or (Al _1-xy Cr _x V _y ) nitride, carbonitride, nitrogen oxide or carbonitride oxide (wherein x and y are any number of 1 or less), etc. Examples of suitable compositions thereof include those containing Cr and the like.

  More preferably, TiCN, TiN, TiSiN, TiSiCN, TiAlN, TiAlCrN, TiAlSiN, TiAlSiCrN, AlCrN, AlCrCN, AlCrVN, TiBN, TiAlBN, TiSiBN, TiBCN, TiAlBCN, TiSiBCN, AlN, AlCN, AlVN, etc. it can. In these compositions, each atomic ratio follows the example of the above general formula.

  Moreover, such a film shall be formed as a single layer. Here, the single layer may be a single layer or a plurality of layers, but it means a structure in which the types of constituent elements constituting each layer are the same. For this reason, as long as the types of constituent elements are the same, even if a plurality of elements having different atomic ratios are stacked, they are included in the single layer here.

  The film of the present invention is preferably composed of the same constituent elements throughout the film, and the same atomic ratio.

<Thickness of coating>
The thickness of the coating of the present invention is not particularly limited, but is preferably 0.1 μm or more and 10 μm or less. If the thickness is less than 0.1 μm, the effect of improving various properties due to the formation of the film may not be sufficiently obtained, and if it exceeds 10 μm, the film itself may be easily peeled off.

<Method for forming film>
Although the formation method of the film of this invention is not specifically limited, It is preferable to form by the physical vapor deposition method (PVD method). This is because by adopting the physical vapor deposition method in this way, the compressive stress of the coating can be easily changed so as to form an intensity distribution.

  That is, according to the present inventors' research, it has been found that the compressive stress of the film is affected by the temperature, reaction gas pressure, substrate bias voltage, etc. when the film is formed by physical vapor deposition. In particular, it has been found that the influence of the substrate bias voltage when forming a film is the largest.

  This is because, for example, when a large substrate bias voltage is applied to the base material, the elements constituting the coating are supplied in high energy to the base material in an ionic state, so that the impact when both of these collide increases. As a result, it is considered that the compressive stress of the film formed is increased. On the other hand, when the substrate bias voltage is small, it is presumed that the impact due to the collision between the base material and the ion element is small, and the compressive stress is also small.

  Therefore, in order for the compressive stress of the coating to have a strength distribution with respect to the thickness direction of the coating, a physical vapor deposition method is adopted when the coating is formed on the substrate, and the substrate bias voltage is set. It can be done by adjusting.

  As described above, it is preferable to employ a physical vapor deposition method as a method for forming a film of the present invention, but this does not exclude chemical vapor deposition methods known as other formation methods.

  Examples of such physical vapor deposition include conventionally known methods such as sputtering and ion plating that can adjust the substrate bias voltage. In particular, among these various methods, it is preferable to employ an ion plating method or a magnetron sputtering method.

  Here, the ion plating method uses a metal as a cathode and a vacuum chamber as an anode, evaporates and ionizes the metal, and at the same time applies a negative voltage (substrate bias voltage) to the substrate to extract ions. A method of depositing metal ions on the surface. In this method, if nitrogen is put in a vacuum and reacted with a metal, a nitride compound of the metal is formed. For example, if titanium is used as a metal and reacted with nitrogen, titanium nitride (TiN) is formed.

  There are various types of such ion plating methods, and it is particularly preferable to employ the cathode arc ion plating method in which the ion ratio of the raw material elements is high.

  When this cathode arc ion plating method is used, it is possible to perform metal ion bombardment treatment on the surface of the substrate before forming the coating, so that the adhesion of the coating is remarkably improved. You can also. For this reason, the cathode arc ion plating method is a preferable process from the viewpoint of adhesion.

  On the other hand, in the magnetron sputtering method, after making the inside of a vacuum chamber high vacuum, Ar gas is introduced and a high voltage is applied to the target to generate glow discharge, and Ar ionized by this glow discharge is accelerated toward the target. By irradiating and sputtering the target, the target atoms that jump out and are ionized are accelerated by a substrate bias voltage between the target and the substrate and deposited on a substrate to form a film. Such a magnetron sputtering method includes a balanced magnetron sputtering method, an unbalanced magnetron sputtering method, and the like.

  In the above, a method for controlling the substrate bias voltage by a physical vapor deposition method is mentioned as a method for forming the strength distribution of the compressive stress of the film. However, the present invention is not limited to such a method. Absent. For example, a method of applying a compressive stress by mechanical impact such as blasting after forming a film, a method of relaxing the compressive stress using a heat source such as a heater or a laser, a method of combining these methods, and the like can be mentioned.

<Compressive stress of coating>
The coating of the present invention has a compressive stress. The compressive stress is preferably a stress in the range of −15 GPa to 0 GPa. More preferably, the lower limit is −10 GPa, more preferably −8 GPa. Further, the upper limit is more preferably -0.5 GPa, still more preferably -1 GPa.

  When the compressive stress of the coating is less than −15 GPa, the coating may be peeled off particularly at the edge portion of the cutting edge depending on the shape of the cutting tool (the cutting edge has an extremely small acute angle or a complicated shape). Further, when the compressive stress of the coating exceeds 0 GPa, the coating stress becomes a tensile state, so that the coating is cracked, which may cause the tool itself to be lost.

  Here, the compression stress referred to in the present invention is a kind of internal stress (intrinsic strain) existing in the film, and is represented by a numerical value (unit: GPa) of “−” (minus). Therefore, the expression that the compressive stress (internal stress) is large indicates that the absolute value of the numerical value is large, and the expression that the compressive stress (internal stress) is small is that the absolute value of the numerical value is small. Indicates.

Moreover, such a compressive stress of the present invention is measured by a method called the sin ² ψ method. X-ray sin ² [psi method using is widely used as a method of measuring residual stress in a polycrystalline material. This measurement method is described in detail on pages 54 to 66 of "X-ray stress measurement method" (Japan Society for Materials Science, published by Yokendo Co., Ltd. in 1981). The X-ray penetration depth is fixed in combination with the method, and the diffraction angle 2θ with respect to various ψ directions is measured in the plane including the stress direction to be measured and the sample surface normal set at the measurement position to obtain 2θ−sin ^2. A ψ diagram can be created, and the average compressive stress from the gradient to the depth (distance from the surface of the coating) can be determined. Similarly, by sequentially measuring the average compressive stress to different depths, the strength distribution of the compressive stress in the thickness direction of the coating can be obtained.

  More specifically, X-rays that cause X-rays from an X-ray source to enter a sample at a predetermined angle, detect X-rays diffracted by the sample with an X-ray detector, and measure internal stress based on the detected values. In the stress measurement method, an X-ray is incident from an X-ray source at an arbitrary setting angle on the sample surface at an arbitrary position of the sample, passes through the X-ray irradiation point on the sample, and the ω axis is perpendicular to the incident X-ray When rotating the sample around the χ axis that coincides with the incident X-ray when the ω axis is rotated in parallel with the sample stage, the sample is placed so that the angle formed by the sample surface and the incident X-ray is constant. The compressive stress inside the sample can be obtained by measuring the diffraction line while changing the angle ψ between the normal line of the diffraction surface and the normal line of the sample surface while rotating.

  As an X-ray source for obtaining the intensity distribution in the thickness direction of such a film, synchrotron radiation (SR) is used in terms of the quality of the X-ray source (high brightness, high parallelism, wavelength variability, etc.). It is preferable to use it.

In addition, in order to obtain the compressive stress from the 2θ-sin ² ψ diagram as described above, the Young's modulus and Poisson's ratio of the coating are required. However, the Young's modulus can be measured using a dynamic hardness meter or the like, and since the Poisson's ratio does not vary greatly depending on the material, a value of around 0.2 may be used. In the present invention, the accurate compressive stress value is not particularly important, and the strength distribution of the compressive stress is important. For this reason, when the compressive stress is obtained from the 2θ-sin ² ψ diagram, the strength distribution of the compressive stress can be substituted by obtaining the lattice constant and the lattice spacing without using the Young's modulus.

<Intensity distribution>
The compressive stress of the coating of the present invention changes so as to have a strength distribution in the thickness direction of the coating. Here, the thickness direction of the coating is a direction from the surface of the coating toward the bottom surface of the coating (the coating is the outermost layer on the base material, and therefore the outermost layer on the outermost layer side). Is perpendicular to the direction. More specifically, referring to FIG. 2 which is an enlarged cross-sectional view of the portion of the film 3 in FIG. 1, the thickness direction of the film is the direction indicated by the arrow 7 from the surface 4 of the film toward the bottom surface 6 of the film. It is. The arrow 7 is shown in a direction from the surface 4 of the coating toward the bottom surface 6 of the coating for convenience, but it is not necessary to limit the vertical direction as long as the direction is perpendicular to the surface of the coating. It may be directed from the bottom surface 6 of the coating toward the surface 4 of the coating.

  The strength distribution indicates that the magnitude of the compressive stress changes by forming a distribution in the thickness direction of the coating. Therefore, the compressive stress has a strength distribution in the thickness direction of the film, in other words, the magnitude of the compressive stress changes not in the direction parallel to the surface of the film but in the direction perpendicular to the surface of the film. To do.

  The strength distribution is such that the compressive stress on the surface of the coating continuously increases from the surface of the coating to an intermediate point located between the surface of the coating and the bottom surface of the coating, and a maximum point at the intermediate point. And the compressive stress continuously decreases from the intermediate point to the bottom surface of the coating.

  This feature will be described in more detail with reference to FIG. 2 and FIG. 3 showing an example of the intensity distribution of the present invention. FIG. 3 is a graph showing the strength distribution in the thickness direction of the film, with the distance from the surface of the film as the horizontal axis and the compressive stress as the vertical axis.

  First, as shown in FIG. 2, the intermediate point 5 is located between the surface 4 of the coating and the bottom surface 6 of the coating, but is perpendicular to the surface 4 of the coating. In terms of distance, it is not necessarily required to be 1/2 of the thickness of the coating (the vertical distance from the coating surface 4 to the coating bottom surface 6). Usually, such an intermediate point 5 is located closer to the surface 4 of the film than to the bottom surface 6 of the film.

  Preferably, the intermediate point 5 is a distance of 0.1% or more and 50% or less of the thickness of the coating (the distance in the vertical direction from the coating surface 4 to the bottom surface 6 of the coating) from the surface of the coating. More preferably, the lower limit is 0.3%, more preferably 0.5%, and the upper limit is 40%, more preferably 35%. If it is less than 0.1%, when used for finishing cutting or precision cutting, the reduction of compressive stress is incomplete, the effect of suppressing film chipping is reduced, and the effect of improving the finished surface roughness may not be seen. is there. On the other hand, if it exceeds 50%, the effect of increasing the compressive stress inside the coating is reduced, and the effect of improving toughness may not be exhibited.

  In such a strength distribution, the compressive stress can be minimized on the surface 4 of the coating (in other words, the absolute value thereof is minimized). Thereby, particularly excellent wear resistance and resistance to film chipping can be obtained. On the other hand, the compressive stress may be minimized at the bottom surface 6 of the coating (in other words, the absolute value thereof is minimized). Thereby, particularly excellent wear resistance can be obtained.

  In addition, it is preferable that the said compressive stress has a value of 25-95% of the compressive stress in the intermediate point of the said film in the surface of the said film. More preferably, the upper limit is 90%, more preferably 85%, and the lower limit is 30%, more preferably 35%.

  When this value is less than 25%, sufficient toughness may not be obtained, and when it exceeds 95%, the effect of reducing the compressive stress on the coating surface is reduced, and the effect of suppressing film chipping is not seen. There is.

  On the other hand, the maximum point is a position observed at the intermediate point (a point at which the distance from the surface of the coating is about 0.1 μm in FIG. 3), and is a compression of the surface of the coating. The stress (compressive stress having a value of about −1.8 GPa in FIG. 3) continuously increases toward the bottom surface 6 of the coating, and the degree of increase changes at this maximum point. It is. Here, the change in the degree of increase indicates that the compressive stress continuously decreases in the direction of the bottom surface of the film at the maximum point as shown in FIG.

  In FIG. 3, the maximum point is an aspect that exists only at one point of the intermediate point. However, the aspect of the present invention is not limited to such an aspect, and is in the thickness direction of the film. The case where the maximum point exists with a certain thickness is also included. Here, the existence of a maximum point with a certain thickness means that the compressive stress at the maximum point has a substantially constant value from the intermediate point to the thickness (preferably 1/2 or less of the thickness of the coating). Say. Thus, the toughness can be further improved by the presence of the maximum point with a certain thickness from the intermediate point.

  Therefore, the maximum point in the present application has the same meaning as the maximum point which is a mathematical function term, or has a broader meaning.

  In FIG. 3, the compressive stress continuously increases from the surface of the film (that is, the point where the distance from the surface of the film is 0 μm), but this is the only aspect of the present invention. For example, as shown in FIG. 4, the case where the compressive stress on the surface of the coating is maintained within a certain distance (preferably 0.5 μm or less) toward the bottom of the coating is included. That is, the compressive stress has a compressive stress smaller than the inside (in other words, a compressive stress whose absolute value is smaller than the absolute value thereof) on the surface of the coating, and the compressive stress is from the surface of the coating. A mode in which the compressive stress continuously increases to the intermediate point after being maintained for a certain distance (preferably 0.5 μm or less) toward the intermediate point is included.

  Thus, when the compressive stress on the surface of the film is maintained within a certain distance from the surface of the film toward the bottom surface of the film, it has a particularly excellent film chipping suppressing effect and wear resistance. Therefore, it is preferable.

  In addition, when the compressive stress continuously increases from the surface of the coating to the intermediate point, it does not only increase in a convex state as shown in FIG. 3, but also increases in a convex state. It also includes the case of increasing linearly. Furthermore, even when the amount of decrease (inclination) is partially changed or when the degree of increase (inclination) is changed in the middle or when it is stepwise (increases stepwise), the entire surface of the coating film If it increases toward the intermediate point, it is included in the case of increasing continuously here.

  In addition, when the compressive stress continuously decreases from the intermediate point to the bottom surface of the coating, it does not only decrease in a convex state as shown in FIG. 3 but also decreases in a convex state. It also includes the case of decreasing linearly. Furthermore, even if the increase (inclination) is partially changed or the degree of decrease (inclination) is changed in the middle or stepwise (decrease stepwise) as a whole, If it decreases toward the bottom surface of the coating, it is included in the case of continuous decrease here.

  Thus, in the present invention, the strength distribution of the compressive stress on the surface of the coating continuously increases from the surface of the coating to an intermediate point located between the surface of the coating and the bottom of the coating, The intermediate point has a maximum point. Thus, by having a compressive stress smaller than the inside at the surface of the coating, the wear resistance of the coating surface is improved as much as possible and the resistance to membrane chipping is improved, and by the large compressive stress near the maximum point, Extremely good toughness is provided.

  Furthermore, in the present invention, extremely excellent wear resistance is provided by the continuous reduction of the compressive stress from the intermediate point to the bottom surface of the coating. In this way, the surface-coated cutting tool of the present invention exhibits an extremely excellent effect of successfully achieving both toughness, wear resistance, and resistance to film chipping.

  Such an excellent effect does not have the maximum point as described above, and the compressive stress is reduced or increased continuously or stepwise from the surface of the coating toward the bottom of the coating. This is a special effect that cannot be shown in the surface-coated cutting tool (Patent Document 1).

<Others>
In the surface-coated cutting tool of the present invention, an arbitrary intermediate layer 8 can be formed between the substrate 2 and the coating 3 as shown in FIG. Such an intermediate layer 8 usually has a characteristic of improving the wear resistance and improving the adhesion between the substrate and the coating, and can be formed as one layer or a plurality of layers. In this case, the bottom surface 6 of the coating is a surface where the coating 3 and the intermediate layer 8 are in contact.

  Such an intermediate layer can be made of, for example, TiN, TiCN, TiSiN, TiAlN, AlCrN, AlVN, TiAlCrN, TiAlSiN, TiAlSiCrN, AlCrVN, or the like. In these compositions, each atomic ratio follows the example of the general formula exemplified as the composition of the film.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. In addition, the compound composition of the film in an Example was confirmed by XPS (X-ray photoelectron spectroscopy analyzer). The compressive stress and thickness (or distance from the coating surface) were measured by the above-described sin ² ψ method.

In the measurement by the sin ² ψ method, the energy of the X-ray used was 10 keV, and the diffraction peaks of Ti _0.5 Al _0.5 N (Examples 1 to 6) and Al _0.7 Cr _0.25 V _0.05 N (Examples 7 to 10). (200) plane. Then, the measured diffraction peak position is determined by fitting a Gaussian function, the slope of the 2θ-sin ² ψ diagram is obtained, and the value obtained using a dynamic hardness meter (a nano indenter manufactured by MTS) is used as the Young's modulus. The stress value was determined using the value of TiN (0.19) for the Poisson's ratio.

  In the following, the film is formed by the cathode arc ion plating method, but it can also be formed by, for example, a balanced or unbalanced sputtering method. Moreover, although the thing of a specific film composition is formed below, the thing of a composition other than this can acquire the same effect.

<Examples 1-6>
<Production of surface-coated cutting tool>
First, as a base material for a surface-coated cutting tool, a cutting edge replaceable tip having a material and a tool shape shown in Table 1 below (depending on the evaluation method of each characteristic described later) is prepared, and this is used as a cathode arc ion plate. It was attached to the ting device.

Subsequently, the inside of the chamber of the apparatus is depressurized by a vacuum pump, and the temperature of the base material is heated to 450 ° C. by a heater installed in the apparatus, so that the pressure in the chamber is 1.0 × 10 ⁻⁴ Pa. A vacuum was drawn until

  Next, argon gas was introduced to maintain the pressure in the chamber at 3.0 Pa, the substrate bias power supply voltage of the substrate was gradually increased to −1500 V, and the surface of the substrate was cleaned for 15 minutes. . Thereafter, argon gas was exhausted.

Next, an alloy target, which is a metal evaporation source, is set so that Ti _0.5 Al _0.5 N is formed with a thickness of 3 μm as a film formed to be in direct contact with the substrate, and nitrogen gas is used as a reaction gas. The substrate current (substrate) temperature was 450 ° C., the reaction gas pressure was 4.0 Pa, and the substrate bias voltage was changed as shown in Table 2 below to supply an arc current of 100 A to the cathode electrode. The surface-coated cutting tools of Examples 1 to 6 having the intensity distribution of compressive stress shown in Table 3 below were produced by generating metal ions from an evaporation source.

  In addition, the time described in said table | surface has shown the elapsed time after starting evaporation of metal ion with an alloy target. Moreover, the numerical value of the voltage shown in each column shows the bias voltage of the substrate corresponding to the above-mentioned elapsed time. For example, when it is described with a range such as “−70 V to −150 V”, This shows that the substrate bias voltage was gradually increased from −70 V to −150 V at a constant rate during the elapsed time, and in this case, the compressive stress of the coating gradually increases. On the other hand, when it is described with a range such as “−150 V to −50 V”, it indicates that the substrate bias voltage was gradually decreased from −150 V to −50 V at a constant rate during the elapsed time. In this case, the compressive stress of the coating gradually decreases, but the maximum point of the compressive stress is formed when the voltage starts to decrease.

  As described above, by changing the substrate bias voltage in relation to the elapsed time, it is possible to form a state where the intensity distribution of the compressive stress in the coating increases or decreases continuously.

  In the table above, the numerical values described in the column of the compressive stress on the surface and the compressive stress on the bottom surface indicate the compressive stress indicated on the surface of the coating film and the bottom surface of the coating film, respectively. In addition, the numerical value described in the middle point column indicates the distance from the surface of the coating to the intermediate point as the distance in the thickness direction of the coating (the numerical value of “%” is relative to the thickness of the coating, It is indicated by both “μm” display). The numerical value described in the maximum point column indicates the compressive stress at the maximum point.

  Thus, the surface-coated cutting tool of the present invention of Examples 1 to 6 includes the base material and the coating film formed on the base material, and the coating film becomes the outermost layer on the base material. And has a compressive stress, and the compressive stress changes so as to have a strength distribution in the thickness direction of the coating, and the strength distribution is determined by the compressive stress on the surface of the coating. Continuously increasing from the surface of the coating to the midpoint located between the surface of the coating and the bottom of the coating, having a local maximum at the midpoint and the compressive stress from the midpoint to the bottom of the coating Continuously decreases.

  For comparison, a surface-coated cutting tool was prepared in the same manner as described above except that the substrate bias voltage was maintained at −150 V for 60 minutes after the start of evaporation of metal ions by the alloy target (Comparative Example 1). ).

  The surface-coated cutting tool of Comparative Example 1 had no strength distribution of the compressive stress of the coating, and the compressive stress was constant from the bottom of the coating to the surface of the coating.

<Examples 7 to 10>
<Production of surface-coated cutting tool>
First, as the base material of the surface-coated cutting tool, the same one as used in Examples 1 to 6 was used. And this base material was mounted | worn with the cathode arc ion plating apparatus.

Subsequently, the inside of the chamber of the apparatus is depressurized by a vacuum pump, and the temperature of the base material is heated to 450 ° C. by a heater installed in the apparatus, so that the pressure in the chamber is 1.0 × 10 ⁻⁴ Pa. A vacuum was drawn until

  Next, argon gas was introduced to maintain the pressure in the chamber at 3.0 Pa, the substrate bias power supply voltage of the substrate was gradually increased to −1500 V, and the surface of the substrate was cleaned for 15 minutes. . Thereafter, argon gas was exhausted.

Next, an alloy target, which is a metal evaporation source, is set so that Al _0.7 Cr _0.25 V _0.05 N is formed with a thickness of 3 μm as a film formed so as to be in direct contact with the substrate, and as a reaction gas While introducing nitrogen, the substrate (substrate) temperature was 450 ° C., the reaction gas pressure was 4.0 Pa, and the substrate bias voltage was changed as shown in Table 4 below to supply an arc current of 100 A to the cathode electrode, By generating metal ions from an arc evaporation source, the surface-coated cutting tools of Examples 7 to 10 having the compressive stress intensity distribution shown in Table 5 below were produced.

  In addition, the time described in said table | surface has shown the elapsed time after starting evaporation of metal ion with an alloy target similarly to the case of Table 2. FIG. Similarly to the case of Table 2, the numerical value of the voltage shown in each column also indicates the substrate bias voltage corresponding to the elapsed time.

  In the above table, the numerical values described in the column of the compressive stress on the surface and the compressive stress on the bottom surface indicate the compressive stress shown on the surface of the coating and the bottom surface of the coating, respectively, as in Table 3. Also, the numerical value described in the middle point column also shows the distance from the surface of the coating to the middle point as the distance in the thickness direction of the coating as in Table 3 (the numerical value indicated by “%” indicates the coating). And is indicated by both “μm” indications). The numerical value described in the maximum point column also indicates the compressive stress at that point, as in Table 3.

  Thus, the surface-coated cutting tool of Examples 7 to 10 of the present invention includes the base material and the coating film formed on the base material, and the coating film becomes the outermost layer on the base material. And has a compressive stress, and the compressive stress changes so as to have a strength distribution in the thickness direction of the coating, and the strength distribution is determined by the compressive stress on the surface of the coating. Continuously increasing from the surface of the coating to the midpoint located between the surface of the coating and the bottom of the coating, having a local maximum at the midpoint and the compressive stress from the midpoint to the bottom of the coating Continuously decreases.

  For comparison, the surface-coated cutting tool is the same as described above except that the substrate bias voltage is uniformly reduced from −200 V to −20 V over 60 minutes after the evaporation of metal ions is started by the alloy target. (Comparative Example 2).

  In the surface-coated cutting tool of Comparative Example 2, the strength distribution of the compressive stress of the coating did not have a local maximum point, and decreased uniformly from the bottom of the coating to the surface of the coating.

<Evaluation of wear resistance of surface coated cutting tools>
For each of the surface-coated cutting tools of Examples 1 to 10 and Comparative Examples 1 and 2 prepared above, a continuous cutting test and an intermittent cutting test were performed according to the conditions shown in Table 1 above. The time when the flank wear width of the blade edge exceeded 0.15 mm was measured as the cutting time.

  Tables 6 and 7 below show the cutting times measured above as the evaluation results of the wear resistance of the surface-coated cutting tool. The longer the cutting time, the better the wear resistance. In the continuous cutting test, the presence or absence of gloss on the finished surface of the work material was also observed, and the observation results are also shown in Tables 6 and 7. In this case, “glossy” means that the finished surface of the work material is glossy, and “white turbidity” means that the finished surface of the work material is not glossy and becomes cloudy.

  As is clear from Tables 6 and 7, the surface-coated cutting tool according to the present invention of Examples 1 to 10 in both the continuous cutting test and the intermittent cutting test is compared with the surface-coated cutting tool of Comparative Examples 1 and 2. In addition, the wear resistance (see continuous cutting test) and toughness (see intermittent cutting test) are improved, and the finished surface can be glossed, so it has excellent resistance to film chipping and the life of the surface-coated cutting tool is further increased. Confirmed that it has improved.

<Evaluation of surface gloss of surface coated cutting tools>
Each of the surface-coated cutting tools of Examples 1 to 10 and Comparative Examples 1 and 2 prepared above was subjected to a finish surface gloss evaluation test under the following conditions.

  That is, as shown in Table 1 above, the cutting conditions were as follows. S45C was used as a work material, the cutting speed was 200 m / min, the feed rate was 0.2 mm / rev, and the cutting was 0.5 mm. I did it.

  The evaluation results of the finished surface gloss of each surface-coated cutting tool are shown in Tables 6 and 7 below. As is apparent from Tables 6 and 7, the surface-coated cutting tools according to the present invention of Examples 1 to 10 have improved finished surface gloss as compared with the surface-coated cutting tools of Comparative Examples 1 and 2. It was confirmed that the film was excellent in resistance to chipping.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic sectional drawing of the surface covering cutting tool of this invention. It is the schematic sectional drawing which expanded the part of the film of the surface coating cutting tool of this invention. It is a graph which shows one aspect | mode of the intensity distribution of the compressive stress of a film. It is a graph which shows the one aspect | mode of the strength distribution of the compressive stress of a film when the compressive stress of the film surface is maintained for a fixed distance. It is a schematic sectional drawing of the surface coating cutting tool of this invention which formed the intermediate | middle layer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Surface coating cutting tool, 2 base material, 3 coating, 4 coating surface, 5 middle point, 6 coating bottom surface, 7 arrow, 8 intermediate layer.

Claims (5)

A surface-coated cutting tool comprising a substrate and a coating formed on the substrate,
The coating is the outermost layer on the substrate and has a compressive stress,
The compressive stress has changed to have a strength distribution in the thickness direction of the coating,
The strength distribution is such that the compressive stress on the surface of the coating continuously increases from the surface of the coating to an intermediate point located between the surface of the coating and the bottom surface of the coating, and a maximum point is reached at the intermediate point. And the compressive stress continuously decreases from the midpoint to the bottom surface of the coating ,
The intermediate point is located at a distance of 0.1% to 50% of the thickness of the coating from the surface of the coating,
The surface-coated cutting tool characterized in that the compressive stress has a value of 25 to 95% of the compressive stress at the midpoint of the coating on the surface of the coating.   The surface-coated cutting tool according to claim 1, wherein the compressive stress is a stress in a range of −15 GPa to 0 GPa. The surface-coated cutting tool according to claim 1 , wherein the compressive stress is minimized on the surface of the coating. The surface-coated cutting tool according to any one of claims 1 to 3, wherein the compressive stress has a value of 35 to 85% of a compressive stress at an intermediate point of the coating on the surface of the coating. The compressive stress is continuously increased to the intermediate point after the compressive stress on the surface of the coating is maintained for a distance of 0.5 μm or less from the surface of the coating toward the intermediate point. The surface-coated cutting tool according to any one of claims 1 to 4 , wherein the surface-coated cutting tool is characterized.

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