JP4634241B2 - 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 an object of the present invention is to provide a surface-coated cutting tool that achieves both high toughness and wear resistance of the cutting tool and suppresses film chipping. It 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 increased and the strength distribution of the compressive stress in the coating is increased. It was found that if a minimum point is formed, stress such as impact can be relaxed in the vicinity of the minimum point while maintaining high toughness, and resistance to film chipping can be improved at the same time. Furthermore, further research has led to the knowledge that the wear resistance can be improved at the same time by maintaining a certain compressive stress from the minimum 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 changes so as to have a strength distribution in the thickness direction of the coating, and the strength distribution has a maximum compressive stress on the surface of the coating. The compressive stress continuously decreases 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 has a minimum point at the intermediate point. Here, since the intermediate point has a minimum point in this way, it is intended to suppress the development of cracks toward the bottom surface of the coating by relaxing stress such as self-destruction and impact of the coating at this point. This intermediate point is not located (overlapped) at the interface with the base material, and thus is located between the surface of the coating and the base material as described above. That is, when an intermediate layer as described below is not formed as a lower layer of the coating between the coating and the substrate, this intermediate point is included when located at the bottom of the coating (that is, at the interface with the substrate). Absent. However, when the intermediate layer is formed as the lower layer of the film, the case where the intermediate point is located on the bottom surface of the film is included.

  In particular, the surface-coated cutting tool of the present invention is a surface-coated cutting tool comprising a base material and a coating film formed on the base material, and the coating film is an 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 has a maximum compressive stress on the surface of the coating. And the compressive stress continuously decreases 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 has a minimum point at the intermediate point. The compressive stress is preferably a constant value up to the bottom surface of the coating. Thus, wear resistance can be remarkably improved by setting the compressive stress to a constant value from the intermediate point to the bottom surface of the coating.

  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 may have a value of 20 to 90% of the compressive stress on the surface of the coating at the intermediate point.

  Moreover, the said compressive stress shall have a value of 40 to 80% of the compressive stress of the surface of the said film in the said intermediate point.

  The compressive stress has the maximum compressive stress on the surface of the coating, and after the maximum compressive stress is maintained for a certain distance from the surface of the coating toward the intermediate point, the compressive stress is The stress can be continuously reduced to the midpoint.

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

  In particular, by having the maximum compressive stress on the surface of the coating, it is possible to effectively prevent the chipping of the tool that occurs at the beginning of cutting, improve toughness as a cutting tool, and compressive stress is applied to the portion near the surface inside the coating. By forming the minimum point of the intensity distribution, the portion exerts an effect of relaxing stress such as self-destruction or impact of the film, and thus the resistance to film chipping is drastically improved.

  Further, by having a certain compressive stress from the minimum point to the bottom surface of the coating, the wear resistance is drastically improved.

  As described above, the present invention succeeds in improving the resistance against film chipping as well as making the toughness and the wear resistance highly compatible by synergistically acting 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. Even when an arbitrary intermediate layer is formed in this way, the expression “film formed on a substrate” is used.

  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 heavy cutting or intermittent cutting applications, and particularly suitable for milling applications. Excellent toughness and wear resistance depending on the application. Furthermore, since it has excellent resistance to film chipping, the finish surface roughness of the work material is improved, and since the finish surface gloss of the work material is also excellent, simultaneous rough finishing is possible.

<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 kind of use. 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 substrate, and the portion where the coating is not formed on the surface of the substrate or the strength distribution of the compressive stress described later is satisfied. It does not matter even if there is no part. In addition, when a part of the surface of the film is removed by arbitrary post-processing after the film is once formed, the compressive stress of the present invention is also applied to a layer newly exposed on the outermost surface after the film is removed. In the case of a film satisfying the intensity distribution, it is included in the present invention. Further, when an intermediate layer is formed between the base material and the coating as will be described later, the exposed portion is also removed when the coating is removed by any post-processing and the intermediate layer is exposed as the outermost layer. Of the present invention is included in the present invention (in this case, when the intermediate layer is formed of a plurality of layers, the plurality of layers Among these, the outermost layer (the layer that is the outermost surface) is the coating film of the present invention).

  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, group IVa elements (Ti, Zr, Hf, etc.), group Va elements (V, Nb, Ta, etc.), group VIa elements (Cr, Mo, W, etc.), Al (aluminum), B ( Boron), Si (silicon) and Ge (germanium) at least one element selected from the group consisting of carbides, nitrides, oxides, carbonitrides, carbonates, nitrogen oxides, carbonitride oxides or these What is comprised with a solid solution can be illustrated as the composition.

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. Therefore, 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 referred to here.

  The coating of the present invention is preferably composed of the same constituent elements throughout the coating, and the same atomic ratio, but the thickness of each layer is less than 0.1 μm, A single layer of the present invention also includes a case of a super multi-layer film structure in which the types of constituent elements are not the same (for example, when two layers of A and B are repeatedly laminated). Shall.

<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. Further, as will be described later, it is also possible to adjust by using a mechanical shock, a thermal shock, or an annealing phenomenon due to heat.

  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. The sin ² ψ method using X-rays is widely used as a method for measuring the residual stress of 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 and performing a mathematical method, 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 set 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 on the sample surface. 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 has the maximum compressive stress (in other words, the compressive stress having the maximum absolute value) on the surface of the coating, and from the surface of the coating to the surface of the coating and the bottom of the coating. It is preferable that the compressive stress continuously decreases to an intermediate point located at, has a minimum point at the intermediate point, and has a constant value 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 severe heavy cutting such as intermittent cutting with high impact force, the application of compressive stress may be incomplete, and the effect of suppressing defects may not be seen. On the other hand, if it exceeds 50%, the effect of reducing the compressive stress inside the coating is lowered, and the effect of improving the resistance to film chipping may not be shown.

  At such an intermediate point, the compressive stress preferably has a value of 20 to 90% of the compressive stress on the surface of the coating. More preferably, the upper limit is 85%, more preferably 80%, and the lower limit is 30%, more preferably 40%.

  If this value is less than 20%, sufficient toughness may not be obtained, and if it exceeds 90%, impact absorption (relaxation of stress) may be incomplete and the effect of suppressing film chipping may not be seen. .

  On the other hand, the above-mentioned minimum point is a position observed at the above-mentioned intermediate point (point where the distance from the surface of the coating is about 0.1 μm in FIG. 3), and is the maximum on the surface of the coating. The compressive stress (compressive stress having a value of about −5 GPa in FIG. 3) continuously decreases toward the bottom surface 6 of the coating, and the degree of the decrease changes at this minimum point. Is. Here, the change in the degree of decrease indicates that the compressive stress becomes a constant value in the direction of the bottom surface of the film with this minimum point as a boundary as shown in FIG. Therefore, this minimum point has a meaning that is in agreement with or broader than the minimum point that is a mathematical function term.

  There is only one such minimum point in the intensity distribution, which is fundamentally different from the step change (step change) in Patent Document 1.

  In FIG. 3, the compressive stress is maximized only on the surface of the film (that is, the point where the distance from the surface of the film is 0 μm). Not only in the case where the maximum compressive stress is present only at the point where the distance is 0 μm, but as shown in FIG. 4, the maximum compressive stress is constant from the surface of the coating toward the bottom of the coating (preferably 0). .5 μm or less). That is, the compressive stress has a maximum compressive stress on the surface of the coating, and the maximum compressive stress is a certain distance (preferably 0.5 μm or less) from the surface of the coating toward the intermediate point. In the embodiment, the compression stress is continuously reduced to the intermediate point after being maintained for a while.

  Thus, it is preferable that the maximum 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, since particularly excellent toughness is obtained.

  In addition, when the compressive stress continuously decreases from the surface of the coating to the intermediate point, 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 when the increase (inclination) is partially changed or when the decrease (gradient) is changed in the middle, or even when it is stepwise (decrease stepwise), the entire surface of the coating film If it decreases toward the intermediate point, it is included in the case of decreasing continuously here.

  In addition, the case where the compressive stress has a constant value from the intermediate point to the bottom surface of the coating includes not only the case where the compressive stress has a completely constant numerical value but also the case where the compressive stress is considered to be substantially constant.

  As described above, in the present invention, the intensity distribution has the maximum compressive stress on the surface of the coating, and continues from the surface of the coating to an intermediate point located between the surface of the coating and the bottom of the coating. And the minimum point at the midpoint. By having the maximum compressive stress on the surface of the film in this way, the generation of cracks occurring on the surface of the film is suppressed as much as possible, and self-destruction of the film due to the large compressive stress on the surface of the film near its minimum point By preventing and relieving stress such as impact applied to the coating surface, an excellent effect of excellent toughness and resistance to film chipping is shown.

  Furthermore, in the present invention, since the compressive stress becomes a constant value from the intermediate point to the bottom surface of the coating, self-destruction of the coating can be suppressed and extremely excellent wear resistance is provided. 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 is characterized in that the compressive stress is reduced or increased continuously or stepwise uniformly from the surface of the coating to the bottom of the coating without having the above-mentioned minimum point. 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 X-ray used was 10 keV, and the diffraction peaks were (200) of Ti _0.5 Al _0.5 N (Examples 1 to 6) and Al _0.7 Cr _0.3 N (Examples 7 to 10). ) Surface. 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 indicates the bias voltage of the substrate corresponding to the elapsed time described above. For example, when a single numerical value such as “−50 V” is described, It shows that the substrate bias voltage was constant throughout the elapsed time. In this case, the compressive stress in the coating also has a constant value. On the other hand, when it is described with a range such as “−50V to −150V”, it indicates that the substrate bias voltage is gradually increased from −50V to −150V at a constant speed during the elapsed time. In this case, the compressive stress of the film gradually increases, but a minimum point of the compressive stress is formed at the point where the increase in voltage is started.

  In this way, by changing the substrate bias voltage in relation to the elapsed time or making it a constant numerical value, it is possible to form a minimum point or a portion where the compressive stress has a constant value in the strength distribution of the compressive stress in the film. it can.

  In addition, the numerical value described in the column of the surface compressive stress in the said table | surface has shown the maximum compressive stress shown in the surface of a film. 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). Moreover, the numerical value described in the column of the minimum point has shown the compressive stress in the minimum point, and this compressive stress becomes a constant value to the bottom face of a film.

  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 has a maximum compressive stress on the surface of the coating. And the compressive stress continuously decreases 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 has a minimum point at the intermediate point. To a bottom surface of the coating film, the compressive stress becomes a constant value.

  For comparison, the surface-coated cutting tool is similar to the above except that the substrate bias voltage is uniformly increased from −20 V to −150 V over 60 minutes after the start of evaporation of metal ions by the alloy target. (Comparative Example 1).

  In the surface-coated cutting tool of Comparative Example 1, the strength distribution of the compressive stress of the coating did not have a minimum point, and increased uniformly 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 _0.3 N is formed with a thickness of 3 μm as a film formed so as to be in direct contact with the substrate, and nitrogen is used as a reaction gas. While introducing the substrate, the substrate (substrate) temperature was set to 450 ° C., the reaction gas pressure was set to 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 the evaporation source, the surface-coated cutting tools of the present invention 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 addition, the numerical value described in the column of the surface compressive stress in the said table | surface has shown the maximum compressive stress shown on the surface of a film similarly to the case of Table 3. FIG. 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). Similarly to the case of Table 3, the numerical value described in the minimum point column also indicates the compressive stress at that point, and this compressive stress is a constant value up to the bottom surface of the coating.

  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 has a maximum compressive stress on the surface of the coating. And the compressive stress continuously decreases 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 has a minimum point at the intermediate point. To a bottom surface of the coating film, the compressive stress becomes a constant value.

  For comparison, the surface-coated cutting tool is the same as described above except that the substrate bias voltage is uniformly increased from −20 V to −200 V over 60 minutes after the start of evaporation of metal ions 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 minimum point, and increased uniformly from the bottom surface of the coating to the surface of the coating.

<Evaluation of wear resistance 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 wet (water-soluble emulsion) continuous cutting test and an intermittent cutting test under the following conditions. Then, the time when the flank wear width of the blade edge exceeded 0.2 mm was measured as the cutting time.

The cutting conditions are as shown in Table 1 above.
Tables 6 and 7 below show the cutting times measured above as evaluation results of the wear resistance of the surface-coated cutting tool. The longer the cutting time, the better the wear resistance. Further, 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. Further, it was confirmed that the wear resistance was further improved and the finished surface was glossy, and the life of the surface-coated cutting tool was further improved.

<Evaluation of toughness of surface-coated cutting tools>
For each of the surface-coated cutting tools of Examples 1 to 10 and Comparative Examples 1 and 2 produced above, a toughness evaluation test was performed under the following conditions.

  That is, as shown in Table 1 above, the cutting conditions were as follows: a block (length 300 mm × width 150 mm) provided with 50 through holes in the S50C material was used as the work material, cutting speed 180 m / min, feed amount The feed rate was increased from 0.10 mm / blade to 0.05 mm / blade, the infeed was 2.0 mm, and the cutting length was 300 mm, and dry milling was performed.

  Tables 6 and 7 below show the maximum feed measured above as the toughness evaluation result of the surface-coated cutting tool. The larger the maximum feed amount, the better the toughness.

  As is apparent from Tables 6 and 7, the surface-coated cutting tool according to the present invention of Examples 1 to 10 has improved toughness as compared with the surface-coated cutting tool of Comparative Examples 1 and 2. confirmed.

  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 one aspect | mode of the strength distribution of the compressive stress of a film when the maximum 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 has a maximum compressive stress on the surface of the coating, and the compressive stress continuously decreases from the surface of the coating to an intermediate point located between the surface of the coating and the bottom of the coating. and, have a minimum point at the intermediate point,
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 according to claim 1, wherein the compressive stress has a value of 20 to 90% of the compressive stress of the surface of the coating at the intermediate point . 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 has a maximum compressive stress on the surface of the coating, and the compressive stress continuously decreases from the surface of the coating to an intermediate point located between the surface of the coating and the bottom of the coating. and, which has a minimum point at the intermediate point, Ri Do and the constant value compressive stress from the midpoint to the bottom surface of said 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 according to claim 1, wherein the compressive stress has a value of 20 to 90% of the compressive stress of the surface of the coating at the intermediate point .   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 any one of claims 1 to 3, wherein the compressive stress has a value of 40 to 80% of a compressive stress of the surface of the coating at the intermediate point. The compressive stress has a maximum compressive stress on the surface of the coating, and the maximum compressive stress 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 claim 1 , wherein the compressive stress continuously decreases to the intermediate point.

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