JP2011067883A - Surface coated cutting tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface coated cutting tool with a coating compatibly satisfying wear resistance and rigidity, and having excellent adhesion to a substrate. <P>SOLUTION: The surface coated cutting tool includes the substrate; and the coating formed on the substrate. The coating includes a first coating layer. The first coating layer includes a fine structure region and a coarse structure region. A compound constituting the fine structure region has a mean crystal grain size of 10-200 nm. The fine structure region exists occupying a range from the surface side of the first coating layer to a thickness of 50% or more with respect to the entire thickness of the first coating layer, and has an average compressive stress that is stress in the range of &ge;-4 GPa and &le;-2 GPa. The first coating layer has a stress distribution in the thickness direction thereof, and has two or more maximum or minimum values in the stress distribution. These maximum or minimum values located closer to the surface side in the thickness direction have higher compressive stress. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a surface-coated cutting tool, and more particularly to a surface-coated cutting tool having a coating film that improves properties such as wear resistance.

  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). A tool in which a coating made of carbide, nitride, carbonitride, boronitride, oxide such as IVa group, Va group, VIa group metal or Al (aluminum) of the periodic table is coated to a thickness of 3 to 20 μm. The usage rate 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 a drill, end mill, milling or turning cutting edge replaceable type (throw away) tip can be increased. It is often used for required cutting tools.

  In recent years, in order to improve the cutting efficiency, the cutting speed is becoming faster, and accordingly, tools are required to further improve various characteristics such as wear resistance, toughness, and adhesion. As an attempt to meet this requirement, for example, in Patent Document 1, as an attempt to improve wear resistance, toughness, and adhesion, adhesiveness is increased by increasing compressive stress in a continuous or stepwise manner from the substrate side to the coating surface side. Attempts have been made to achieve both wear resistance and wear resistance. However, in the proposed cutting tool as described above, the compressive stress of the coating increases or decreases uniformly from the coating surface side to the substrate surface side, and the compressive stress is applied to the substrate to remarkably improve toughness. It was necessary to increase from the side to the coating surface side, and in order to improve the wear resistance, it was necessary to increase the compressive stress from the coating surface side to the substrate side. Therefore, wear resistance is insufficient when attempting to improve toughness, and conversely, when attempting to improve wear resistance, the toughness is reduced and it is difficult to achieve both wear resistance and toughness.

  In Patent Document 2, an attempt is made to generate both high wear resistance and toughness by generating a high compressive residual stress inside the coating by changing the substrate bias voltage continuously or stepwise. In Patent Document 3, the maximum and minimum points are given to the compressive stress in the film, and the compressive stress on the surface side of the film is lowered, so that both wear resistance and toughness are improved, and the film is slightly peeled off. Attempts have been made to control. However, in Patent Documents 2 and 3, since the compressive stress on the outermost surface of the coating is set low, there is a problem of lack of wear resistance.

JP 2003-094208 A JP 2001-315006 A JP 2006-055938 A

  The present invention has been made in view of the current situation as described above. The object of the present invention is to provide a coating that has both wear resistance and toughness and excellent adhesion to the substrate. Another object is to provide a surface-coated cutting tool.

  The present inventor has made extensive studies to solve the above-mentioned problems, and by controlling the crystal grain size of the film, the coarse film region and the fine structure region of the crystal are formed in the film, so that the entire film is formed. Rather than having a uniform structure over the entire area, the propagation of cracks is suppressed to improve toughness, wear resistance is improved by the fine structure area, and the coating structure on the substrate side is made a coarse structure area. The knowledge that the adhesiveness with a material can be improved was acquired. The present invention has been completed as a result of further various studies based on these findings.

  That is, the surface-coated cutting tool of the present invention includes a base material and a coating formed on the base material, the coating includes a first coating layer, and the first coating layer is a compound constituting the first coating layer. A fine texture region having a fine average crystal grain size and a coarse texture region having a coarse average crystal grain size, wherein the fine texture region has an average crystal grain size of the compound of 10 to 200 nm, and An average compression that occupies a range of 50% or more of the total thickness of the first coating layer from the surface side of the first coating layer and is a stress in a range of −4 GPa to −2 GPa. The first coating layer has a stress distribution in its thickness direction, and has two or more maximum values or minimum values in the stress distribution, and these maximum values or minimum values are in the thickness direction. It is characterized by having higher compressive stress at the surface side It is.

  Here, it is preferable that the first coating layer has the highest compressive stress on the outermost surface, and the microstructure region is from the surface side of the first coating layer to the entire thickness of the first coating layer. It is preferable to occupy a range where the thickness is 50% or more and 80% or less.

  The coarse tissue region preferably has an average crystal grain size of 300 to 1500 nm of the compound, and the compound constituting the first coating layer is composed of an IVa group element, a Va group element of the periodic table, It is a compound composed of at least one element selected from the group consisting of Group VIa elements, aluminum, boron, silicon and germanium, and at least one element selected from the group consisting of boron, carbon, nitrogen and oxygen It is preferable.

  In addition to the first coating layer, the coating may include one layer or two or more layers.

  The surface-coated cutting tool of the present invention has a coating having excellent wear resistance and toughness as well as excellent adhesion to the substrate by having the above-described configuration.

It is the graph which represented notionally the stress distribution of the thickness direction of the 1st coating layer of this invention. It is a graph different from FIG. 1 which represented notionally the stress distribution of the thickness direction of the 1st coating layer of this invention.

Hereinafter, the present invention will be described in more detail.
<Surface coated cutting tool>
The surface-coated cutting tool of the present invention has a configuration including a base material and a coating film formed on the base material. Since such a film exhibits an effect of improving wear resistance or toughness with respect to the base material, it is preferable to cover the entire surface of the base material. However, it is not deviated from the scope of the present invention even if it is not covered with this film or the structure of the film is partially different.

  Such a surface-coated cutting tool of the present invention includes a drill, an end mill, a cutting edge replacement cutting tip for a drill, a cutting edge replacement cutting tip for an end mill, a cutting edge replacement cutting tip for milling, a cutting edge replacement cutting tip for turning, It can be suitably used as a cutting tool such as a metal saw, gear cutting tool, reamer, and tap. In particular, it is particularly suitable for milling applications where impacts are intermittently applied, and in these applications it is particularly excellent in toughness and wear resistance.

<Base material>
Any substrate can be used as the substrate used in the surface-coated cutting tool of the present invention as long as it is conventionally known as this type of substrate. For example, cemented carbide (for example, WC-based cemented carbide, including WC, including Co or containing carbonitride such as Ti, Ta, Nb, etc.), cermet (TiC, TiN, TiCN, etc.) 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 preferable.

  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 hardness and strength at high temperatures, and have excellent characteristics as substrates for surface-coated cutting tools for the above applications.

<Coating>
In the surface-coated cutting tool of the present invention, the coating formed on the substrate includes at least a first coating layer. That is, the coating of the present invention may be constituted only by the first coating layer (in this case, the first coating layer is formed in contact with the substrate), or such a first coating layer. In addition, one or two or more other layers may be included. Such layers other than the first coating layer may be formed between the base material and the first coating layer as described later, or may be formed on the first coating layer. However, even when such a layer is formed on the first coating layer, the first coating layer may be the outermost layer (a layer constituting the coating surface) in the cutting edge portion involved in the cutting process. preferable.

  In the present invention, the cutting edge part involved in cutting includes a part that is in direct contact with the work material, and a peripheral part thereof (a part that is not in direct contact with the work material but increases in temperature during cutting, etc.) ).

  Such a coating film of the present invention has an effect of improving various characteristics such as wear resistance, oxidation resistance, toughness, and coloring property for identifying a used blade edge, and its chemical composition. Is not particularly limited, and any conventionally known one can be adopted.

<First coating layer and its structure>
The 1st coating layer of this invention says the layer containing the fine structure area | region where the average crystal grain diameter of the compound which comprises it is minute, and the coarse structure area | region where this average crystal grain diameter is coarse. Such a first coating layer is formed by aggregating crystal particles of a compound, and a region where the crystal particles having an average crystal grain size of 10 to 200 nm are aggregated is defined as a microstructure region. A region where crystal grains having an average crystal grain size exceeding 200 nm are aggregated is defined as a coarse tissue region.

  And this fine structure area | region is this 1st coating film from the surface side (The surface on the opposite side to the surface which opposes a base material (surface which is far from a base material.) Is called a surface.) It is characterized by occupying a range of 50% or more of the total thickness of the layer. That is, the first coating layer is composed of two regions in the thickness direction, a coarse tissue region is present on the substrate side, and a fine tissue region is present on the surface side. The thickness of the region occupies 50% or more with respect to the entire first coating layer.

  The present invention succeeds in achieving both high wear resistance and high toughness by adopting such a configuration for the first coating layer. That is, by forming the fine structure region, the unit that the coating breaks down, and thus the wear resistance is improved. In addition, the crystal grain boundaries increase as the crystal grains are miniaturized, and as a result, the cracks generated on the coating surface side do not easily progress toward the substrate side, and the toughness is improved. Furthermore, by providing an interface having a different crystal grain size in the coating, the progress of cracks is suppressed at the interface between the fine structure region and the coarse structure region, and further improvement in toughness can be expected. On the other hand, the coarse crystal particles are gathered on the base material side because the hard particles constituting the base material and the first coating layer grow in accordance with this, thereby the adhesion between the coating film and the base material. It is for improving. Thus, the 1st coating layer of this invention has the effect | action which improves toughness and abrasion resistance highly, and also improves adhesiveness with a base material.

  In order to achieve the above effect, it is necessary to set the average crystal grain size of the crystal grains in the fine structure region to 10 to 200 nm. If the average crystal grain size is less than 10 nm, it cannot be distinguished from amorphous, and the above effect obtained by reducing the crystal grain size cannot be obtained, and the average crystal grain size exceeds 200 nm. And toughness decreases.

  On the other hand, the optimum range of the average crystal grain size of the crystal grains in the coarse tissue region varies depending on the size of the hard particles constituting the base material, but is preferably 300 to 1500 nm. If the average crystal grain size is less than 300 nm, the difference in grain size from the microstructure region becomes small, and therefore, the effect of suppressing crack propagation at the interface with the microstructure region is reduced, and the adhesion to the substrate is reduced. The toughness tends to be remarkably lowered when the average crystal grain size exceeds 1500 nm.

  Further, the thickness of the fine structure region needs to occupy 50% or more of the total thickness of the first coating layer as described above, and more preferably 50% or more and 80% or less. When the thickness of the microstructure region is less than 50%, improvement in wear resistance and toughness cannot be achieved. On the other hand, if the thickness exceeds 80%, the adhesion to the substrate may be reduced. For example, even if the fine structure region occupies 55% or more in the state of film formation, if the surface side 15% of the fine structure region is removed by post-processing, the fine structure in the post-processed state Since the proportion of the area is out of the above range, it is not preferable because sufficient wear resistance and toughness cannot be obtained.

  In the present invention, the average crystal grain size of the compound (crystal particles) can be determined as follows. That is, the base material and the coating film (first coating layer) formed on the base material are integrally cut, the cross section is embedded in resin, and mirror-polished by a lapping process. And the cross section is observed by FE-SEM (electrolytic emission type scanning electron microscope). At that time, by observing as a reflected electron image, portions having the same crystal orientation are observed with the same contrast, and the same contrast portion is regarded as one crystal particle.

  Next, a straight line having an arbitrary length (preferably corresponding to 400 μm) parallel to the substrate surface is drawn at an arbitrary position of the first coating layer with respect to the image thus obtained. Then, the number of crystal grains included in the straight line is measured, and the length obtained by dividing the length of the straight line by the number of crystal grains is defined as the average crystal grain diameter in that portion of the first coating layer.

  In addition, the interface between the fine structure region and the coarse structure region is observed in a direction perpendicular to the substrate surface by observing a cross section of the coating (first coating layer) using, for example, a transmission electron microscope (TEM). The point where the crystal orientation changes. Alternatively, if there is no clear change at the point where such crystal orientation is present, and if it changes with a certain width (the length in the direction perpendicular to the substrate surface), the intermediate point of the width An interface between the fine tissue region and the coarse tissue region.

<Thickness of the first coating layer>
Although the thickness of the 1st coating layer of this invention is not specifically limited, It is preferable that they are 0.1 micrometer or more and 20 micrometers or less. If the thickness of the first coating layer is less than 0.1 μm, the above effects may not be sufficiently exhibited, and if it exceeds 20 μm, the coating itself may be easily peeled off.

<Stress distribution of the first coating layer>
In the first coating layer of the present invention, the microstructure region needs to have an average compressive stress that is a stress in a range of −4 GPa to −2 GPa. When the stress exceeds −4 GPa, the coating peels off at the edge of the cutting edge depending on the shape of the cutting tool, which is not preferable. Further, if the stress is a compressive stress smaller than −2 GPa, sufficient toughness cannot be obtained.

  Moreover, it is preferable that the stress of the whole 1st coating layer is -0.5--4GPa by an average stress. This is because sufficient toughness may not be obtained if the compressive stress is less than -0.5 GPa, and peeling (breakage) may occur from the inside of the coating if it exceeds -4 GPa.

  On the other hand, the first coating layer of the present invention has a stress distribution in the thickness direction, and has two or more maximum values or minimum values in the stress distribution, and these maximum values or minimum values are the surface in the thickness direction. The one located on the side needs to have a higher compressive stress. Hereinafter, description will be given with reference to FIG.

  FIG. 1 is a graph conceptually showing the stress distribution in the thickness direction of the first coating layer. That is, the first coating layer of the present invention has a stress distribution such as the stress distribution curve shown in FIG. In FIG. 1, point A and point B indicate maximum values, and point D and point E indicate minimum values. In FIG. 1, two maximum values and two minimum values are shown, but the maximum value and the minimum value in the present invention are not limited to two each, and the maximum value or the minimum value is not limited. As long as there are two or more, the number is not particularly limited (and therefore includes the case where there is only one local maximum or local minimum).

  Further, the maximum value or the minimum value needs to have a higher compressive stress as it is located on the surface side in the thickness direction. That is, as shown in FIG. 1, the local maximum value at point B has a higher compressive stress than the local maximum value at point A, and the local compressive stress at point E is higher than the local minimum value at point D. Will have. Thus, when there are two or more maximum values and minimum values, it is preferable that both of them have higher compressive stress as they are located on the surface side in the thickness direction. And as shown by the point C of FIG. 1, it is preferable that the highest compressive stress is shown in the outermost surface of a 1st coating layer.

In addition, the stress distribution of the 1st coating layer in this invention is not restricted only to such an aspect shown by FIG. 1, For example, an aspect like FIG. 2 is also included. That is, the “maximum value” and “minimum value” of the present invention not only indicate a maximum value and a minimum value in a mathematical sense, but also a range where stress is present as shown in FIG. This is a concept including a case where a certain numerical value is indicated by a certain thickness in a layer. That is, the range indicated by the range and b ₁ ~b ₂ represented by a ₁ ~a ₂ in FIG. 2 are included in the "maximum value" in the present invention, the scope and e ₁ ~ represented by d ₁ to d ₂ The range indicated by e ₂ is included in the “minimum value”. Moreover, the highest compressive stresses indicated in the outermost surface is a concept including a case to continue in the range (i.e., a range of thickness from the outermost surface) in as indicated by the scope of c ₁ to c ₂ in FIG. 2 Show.

Incidentally, each range shown by the above-described _{a 1 ~a 2, b 1 ~b} 2, c 1 ~c 2, d 1 ~d 2, e 1 ~e 2 is not particularly limited first The thickness is preferably 10 to 30% with respect to the thickness of the entire coating layer. This is because as long as the thickness is in such a range, the same effect as when the “maximum value” and the “minimum value” are expressed as “points” as shown in FIG. 1 can be exhibited.

  In this case, the stress in the portion closest to the base material side of the first coating layer is preferably in the range of −2 GPa or more and −0.5 GPa or less, and the outermost surface of the first coating layer is −5 GPa or more and −4 GPa or less. It is preferable to have a compressive stress that is a stress in the range of. In the present invention, the “outermost surface of the first coating layer” conceptually indicates the outermost surface as the word indicates, but as an actual measurement condition, an average compression from the surface to a thickness of 0.5 μm is used. It shall mean stress.

  When the first coating layer of the present invention has such a stress distribution, the wear resistance and toughness are highly compatible with the structure of the first coating layer described above, and the substrate The adhesion between the film and the coating is further improved. This is because by reducing the compressive stress on the base material side, while ensuring the adhesion between the base material and the first coating layer (coating film), gradually increasing the compressive stress toward the outermost surface, the coating itself Propagation of cracks that occur on the surface of the coating during cutting, etc. by preventing internal fracture of the coating due to stress, and having two or more maximum or minimum values and by refining the crystal structure toward the outermost surface It is thought that this is because

  Here, the compressive stress referred to in the present invention is one type of internal stress (intrinsic strain) present in the film, and is represented by a numerical value (unit: GPa) of “−” (minus). For this reason, the expression that the compressive stress (internal stress) is high indicates that the absolute value of the numerical value is large, and the expression that the compressive stress (internal stress) is low indicates that the absolute value of the numerical value is small. I mean. Incidentally, what the above numerical value is represented by “+” (plus) is tensile stress.

The average compressive stress and stress distribution of the present invention are measured by the following 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 tilt method, and the diffraction angle 2θ with respect to various ψ directions is measured in a plane including the stress direction to be measured and the sample surface normal set at the measurement position, and 2θ− A sin ² ψ diagram can be created, and the average compressive stress from the gradient to the depth (distance from the coating surface side) can be determined. In the case of the present invention, the thickness from the coating surface side of the fine structure region is obtained by observing the cross section of the coating, and the average compressive stress up to the thickness (depth) is measured to obtain the average compressive stress of the fine structure region. it can. Further, the stress distribution can be measured by sequentially obtaining an average compressive stress in the thickness direction (more accurately, it is an average stress because it can include a tensile stress). That is, the stress distribution of the present invention can be understood as a set of average stresses from the coating surface side to its thickness. In this respect, the average stress at a certain point in the film indicates the average stress from the surface of the film to that point.

  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 incident point on the sample, and the ω axis is perpendicular to the incident X-ray on the sample surface. When the sample is rotated around the χ axis that coincides with the incident X-ray when the ω axis is rotated in parallel with the data base, the sample is adjusted 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 formed by the normal line of the diffraction surface and the normal line of the sample surface while rotating.

  As an X-ray source for measuring the average stress in the thickness direction of such a film, synchrotron radiation (in terms of the quality of the X-ray source (high brightness, high parallelism, wavelength variability, etc.)) SR) is preferably used.

Further, 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 necessary. The Young's modulus can be measured using a dynamic hardness meter, and since the Poisson's ratio does not vary greatly depending on the material, a value of around 0.2 may be used.

<Composition of the first coating layer>
As the above-mentioned compound constituting the first coating layer of the present invention, conventionally known compounds used for this kind of application can be used without particular limitation. For example, group IVa elements (Ti, Zr) of the periodic table of elements , Hf, etc.), group Va elements (V, Nb, Ta, etc.), group VIa elements (Cr, Mo, W, etc.), aluminum (Al), boron (B), silicon (Si), and germanium (Ge). At least one element selected from the group (hereinafter also referred to as “first element”) and at least one element selected from the group consisting of boron, carbon, nitrogen and oxygen (hereinafter also referred to as “second element”). It is preferable that it is a compound comprised by these. The compound is derived from, for example, the second element, and includes carbides, nitrides, oxides, borides, carbonitrides, carbonates, nitrides, carbonitrides, etc., and solid solutions thereof. Is also included. However, the case where both the first element and the second element are boron is excluded.

Examples of such compounds include Ti, Al, (Ti _1-x Al _x ), (Ti _1-x Si _x ), (Al _1-x Cr _x ), (Ti _1-xy Si _x Al _y ). Or (Al _1-xy Cr _x V _y ) nitrides, carbonitrides, nitrogen oxides or carbonitride oxides (including those containing B, Cr, etc.) as suitable compositions thereof (In the formula, x and y represent any number of 1 or less).

  More preferably, TiCN, TiN, TiSiN, TiSiCN, TiAlN, TiAlCrN, TiAlSiN, TiAlSiCrN, AlCrN, AlCrCN, AlCrVN, TiBN, TiAlBN, TiBCN, TiAlBCN, TiSiBCN, AlN, AlCN and the like can be mentioned. In these compositions, each atomic ratio follows the above general formula. Further, the composition ratio of the first element and the second element includes 1: 1 and is not limited to this, and any conventionally known composition ratio is included.

  In the first coating layer of the present invention, it is desirable that the kind of constituent elements does not change throughout the layer, and the atomic ratio is also constant. This is because when the type and atomic ratio of the constituent elements are not constant and change, an unnecessary stress strain or structural change is caused in the first coating layer, and the strength at the interface where the strain or change occurs decreases. .

<Layers other than the first coating layer>
The film of the present invention can contain one layer or two or more layers in addition to the first film layer. Examples of such a layer include an intermediate layer formed between the base material and the first coating layer and an outermost surface layer formed on the first coating layer. These layers can be formed to provide other effects such as oxidation resistance and lubricity, while the first coating layer exhibits the effects as described above.

  The intermediate layer is formed for the purpose of improving wear resistance or improving adhesion to the substrate, and can be formed in one layer or two or more layers. Such an intermediate layer can be made of, for example, TiN, TiCN, TiSiN, TiAlN, AlCrN, TiAlCrN, TiAlSiN, TiAlCrSiN, or the like. In these compositions, conventionally known atomic ratios can be adopted without any particular limitation. Such an intermediate layer is preferably formed with a thickness of 0.2 μm or more and 1 μm or less, and preferably has an average stress of −1 GPa or more and −0.1 GPa or less.

  The outermost surface layer is formed for the purpose of coloring or the like for identifying used blade edges, and can be formed as one layer or two or more layers. Such an outermost surface layer can be made of, for example, Cr, CrN, TiN, TiCN, or the like. In these compositions, conventionally known atomic ratios can be adopted without any particular limitation. Such an outermost surface layer is preferably formed with a thickness of 0.1 μm or more and 0.3 μm or less.

<Method for producing film>
The method for producing the coating film of the present invention can be employed without any particular limitation on a conventionally known method, but it is particularly preferable to form by a physical vapor deposition method (PVD method). This is because the structure of the first coating layer can be easily controlled.

  That is, according to the study of the present inventor, it has been found that the control of the structure of the first coating layer is affected by the substrate bias voltage when the coating is formed by physical vapor deposition. For example, a cubic film is formed by changing the surface energy of the substrate when a substrate bias voltage (in the present invention, the voltage applied to the substrate is referred to as a substrate bias voltage for convenience) is applied to the substrate, and the surface energy of the substrate changes. ) Changes in orientation. Specifically, for example, in the case of known TiAlN, when the substrate bias voltage is high, the orientation of the formed film in the growth direction shows (111), and conversely, when the substrate bias voltage is low, it becomes (200). .

  In general, the oriented plane of the film grows preferentially. However, when the orientation changes during the growth, the crystal plane on which the film grows changes, so that the crystal plane on which the film grows changes. And if the crystal plane to grow changes, the disorder | damage | failure will arise by it and it will be thought that the crystal | crystallization formed becomes fine.

  It was found that when the substrate bias voltage is actually controlled to change from the (200) orientation to the (111) orientation, the coating structure becomes finer. Furthermore, since the growth crystal plane of the film gradually changes when the substrate bias voltage continuously changes as in Patent Document 1, even if the substrate bias voltage changes the orientation of the film, The film grows following the crystal structure (orientation) that has continued to grow. For this reason, the crystal structure produced | generated will coarsen and the ratio of the fine structure area | region which occupies for the whole film thickness will fall. On the other hand, if film formation is started at a low substrate bias voltage and is changed to a high substrate bias voltage at the beginning of film formation, the compressive stress in the film becomes too high, resulting in film peeling and chipping, resulting in reduced toughness and adhesion. Will do.

  Therefore, in order to relieve the compressive stress in the film, a high (absolute value) substrate bias in which the orientation of the film changes after film formation for a certain time at a low (absolute value) substrate bias voltage (for example, 0 to −50 V). A voltage (for example, −90 to −150 V) is suddenly applied and the high substrate bias voltage is held for a certain time, and then a low substrate bias voltage whose orientation changes again is applied (at this time, the low substrate to be applied again) It is preferable to set the bias voltage higher than the first low substrate bias voltage and then set the bias voltage higher than the first high substrate bias voltage when a high substrate bias voltage is applied again thereafter. As described above, by repeating the operation of rapidly changing the substrate bias voltage, it is possible to form the microstructure region in the first coating layer of the present invention. In addition, a local maximum value or a local minimum value can be formed in the stress distribution by rapidly changing the substrate bias voltage. In general, when a film is formed with a high substrate bias voltage, the film has a high compressive stress. Therefore, a local maximum value is formed when the film is rapidly changed from a high substrate bias voltage to a low substrate bias voltage. Note that, by forming a film at a low substrate bias voltage for a predetermined time in the initial stage of film formation, the film can be formed while relaxing the stress in the film. By controlling the substrate bias voltage in this way, it is possible to form the first coating layer of the present invention in which the fine texture region is formed in a wide range on the coating surface side while suppressing film peeling and chipping.

  In the present invention, a low substrate bias voltage means that the absolute value of the voltage is small, and a high substrate bias voltage means that the absolute value of the voltage is large.

  In the present invention, by forming the layers other than the first coating layer by physical vapor deposition, it is possible to improve the adhesion between the layers and improve the production efficiency.

  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, it is preferable to use an ion plating method or a magnetron sputtering method among these various methods.

  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 attract 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 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 ionization rate 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 base material before forming the coating film, so that the effect of further improving the adhesion of the coating film can be obtained. . 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, argon gas is introduced and a high voltage is applied to the target to generate glow discharge, and argon ionized by this glow discharge is accelerated toward the target. A target atom formed by irradiating and sputtering a target to be ejected and ionized is accelerated by a substrate bias voltage between the target and the substrate and deposited on a substrate. Examples of such a magnetron sputtering method include a balanced magnetron sputtering method and an unbalanced magnetron sputtering method.

  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 and a comparative example was confirmed by XPS (X-ray photoelectron spectroscopy analyzer). The average compressive stress was measured by the sin ² ψ method described above. Further, the average crystal grain size of the coating was carried out by observing the cross section of the coating by the method described above.

In the measurement by the sin ² ψ method, the energy of the X-ray used was 10 keV, and the peak of the diffraction line was a (200) plane of Ti _0.5 Al _0.5 N. 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 (MST nanoindenter) is adopted as the Young's modulus. The value of TiN (0.19) was used as the Poisson's ratio.

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

  The film of the present invention preferably has a cubic crystal structure because the crystallinity is stable and the effects of the present invention can be easily obtained. However, whether the crystal structure is a cubic crystal or not is preferable. This can be confirmed by using an X-ray diffractometer (XRD). That is, CuKα ray is used as an X-ray source, acceleration voltage is 40 kV, current is 50 mA, measurement range is 2θ = 20 ° -80 ° and step width is 0.02 ° by θ-2θ method. can do. From the XRD pattern thus obtained, it was confirmed that the crystal structure of the film of the example of the present invention was a cubic crystal.

<Production of surface-coated cutting tool>
First, as a base material for the surface-coated cutting tool, a blade tip replaceable cutting tip made of PK cemented carbide (ISO standard) in the shape of SDKN42 (ISO standard) was prepared and mounted on a cathode arc ion plating apparatus.

Subsequently, while the pressure of the chamber of the apparatus is reduced by a vacuum pump, the temperature of the base material is heated to 450 ° C. by a heater installed in the apparatus, and 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, while setting an alloy target as a metal evaporation source so that Ti _0.5 Al _0.5 N is formed with a thickness of 5 μm as a coating (first coating layer) formed so as to be in direct contact with the substrate, While introducing nitrogen gas as the reaction gas, the base material (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 1 below. Surface-coated cutting tools of Examples 1 to 4 and Comparative Examples 1 to 4 in which a film was formed on a substrate were prepared by supplying an arc current and generating metal ions from an arc evaporation source.

  For example, in Example 1, the substrate bias voltage is held at −30 V for 40 minutes at the initial stage of film formation, then the substrate bias voltage is rapidly changed to −110 V and held at −110 V for 10 minutes, and then the substrate bias voltage is continued. Was abruptly changed to −50V and held at −50V for 10 minutes. Subsequently, the substrate bias voltage was rapidly changed to −130 V and held at −130 V for 10 minutes, and then the substrate bias voltage was rapidly changed to −70 V and held at −70 V for 10 minutes. Thereafter, the substrate bias voltage was suddenly changed again to -150 V and held at -150 V for 10 minutes to form the first coating layer of the present invention. In Table 1, Examples 2 to 4 also adopt the same notation as Example 1 for the change in the substrate bias voltage. However, in Example 3, a TiN layer having a thickness of 0.3 μm was formed as an intermediate layer. Unlike the first coating layer, the intermediate layer was formed with a substrate bias voltage of −30 V and constant for 5 minutes.

  On the other hand, in Comparative Example 1, the substrate bias voltage was kept constant at −30 V, and the film was formed on the substrate by holding for 90 minutes. In Comparative Example 2, the substrate was formed by forming a film at a constant low substrate bias voltage (−30 V) for 30 minutes at the initial stage of film formation and then forming a film at a constant high substrate bias voltage (−150 V) for 60 minutes. A film is formed thereon. Further, in Comparative Example 3, the substrate bias voltage was continuously changed from −30 V to −150 V over 90 minutes (represented as “inclined” in Table 1. The same applies hereinafter), whereby a film was formed on the substrate. Is formed. On the other hand, Comparative Example 4 relates to the film forming method of Patent Document 3, in which the substrate bias voltage is continuously changed from −50 V to −150 V over 30 minutes at the initial stage of film formation, and then the substrate is applied over 20 minutes. The bias voltage was continuously changed from −150 V to −50 V, the substrate bias voltage was continuously changed from −50 V to −150 V over 20 minutes, and finally the substrate bias voltage was changed from −150 V to −− over 20 minutes. A film is formed on the substrate by continuously changing the voltage to 50V.

  Tables 2 and 3 show the structures of the coatings (first coating layer in the examples) of each surface-coated cutting tool thus obtained.

  In Table 2, in the comparative example, for the sake of convenience, the “fine structure region” indicates the region on the coating surface side, and the “coarse structure region” indicates the region on the substrate side of the coating. In addition, the “ratio occupied by the fine structure region” means what percentage of the fine structure region occupies the entire thickness of the first coating layer from the surface side of the first coating layer (the coating in the comparative example). Indicates. In Table 3, “first maximum value”, “first minimum value”, “second maximum value”, and “second minimum value” are point A, point D, point B, Corresponding to the point E, the “position” is present at a position where each point has a thickness of what percentage with respect to the total thickness of the first coating layer from the surface side of the first coating layer (the coating in the comparative example). “Stress” indicates the average stress at that position. Note that “third maximum value” and “third minimum value” in Example 4 are not described in FIG. 1, but the above-mentioned “first maximum value”, “first minimum value”, and the like It means the same notation. The “outermost surface” corresponds to the point C in FIG. 1, and the “position” refers to the total thickness of the first coating layer from the surface side of the first coating layer (the coating in the comparative example). % Of the thickness of the average stress in the portion, and “stress” indicates the average stress.

<Evaluation>
Each surface-coated cutting tool obtained as described above was subjected to wear resistance evaluation and toughness evaluation under the following conditions, and the results are shown in Table 4.

<Abrasion resistance evaluation>
Work material: SCM435 (Hardness HB280)
Cutting speed: 230 m / min.
Feed: 0.3 mm / blade Cutting depth: 2 mm
Cutting form: Dry Cutting length: 2m
Cutting method: Milling Evaluation: The amount of flank wear was measured, and the smaller the wear amount, the better the wear resistance.

<Toughness evaluation>
Work material: S50C hole material Cutting speed: 150 m / min.
Feed: Increase from 0.10 mm / blade to 0.05 mm / blade spacing Cutting: 2 mm
Cutting type: Dry Cutting length: Increase feed every 0.3 m Cutting method: Milling cutting Evaluation: Cutting until chipping is performed, and by finding the feed at the time of chipping, the larger the feed value, the better the toughness It was evaluated.

  As is clear from Table 4, the surface-coated cutting tools of Examples 1 to 4 of the present invention are superior in both wear resistance and toughness compared to the surface-coated cutting tools of Comparative Examples 1 to 4. It was confirmed. In particular, it can be seen that the surface-coated cutting tools of Examples 1 to 4 of the present invention achieve both wear resistance and toughness as compared with Comparative Example 2 and Comparative Example 4 having similar microstructure regions. And the surface-coated cutting tool of Examples 1-4 of this invention was excellent in the adhesiveness of a base material and a film, without a base material and a film peeling.

  Therefore, it is clear that the surface-coated cutting tool of the present invention is provided with a film having both wear resistance and toughness and excellent adhesion to the substrate.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  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.

Claims (6)

A surface-coated cutting tool comprising a substrate and a coating formed on the substrate,
The coating includes a first coating layer;
The first coating layer includes a fine structure region in which an average crystal grain size of a compound constituting the first coating layer is minute and a coarse structure region in which the average crystal grain size is coarse,
The fine texture region is a range in which the average crystal grain size of the compound is 10 to 200 nm and the thickness is 50% or more with respect to the total thickness of the first coating layer from the surface side of the first coating layer. And has an average compressive stress that is a stress in the range of −4 GPa or more and −2 GPa or less,
The first coating layer has a stress distribution in its thickness direction, and has two or more maximum values or minimum values in the stress distribution, and these maximum values or minimum values are located on the surface side in the thickness direction. Surface-coated cutting tool with higher compressive stress.   The surface-coated cutting tool according to claim 1, wherein the first coating layer has the highest compressive stress on the outermost surface.   3. The microstructural region occupies a range of 50% to 80% of the total thickness of the first coating layer from the surface side of the first coating layer, according to claim 1 or 2. The surface-coated cutting tool described.   The surface-coated cutting tool according to any one of claims 1 to 3, wherein the coarse structure region has an average crystal grain size of 300 to 1500 nm of the compound.   The compound constituting the first coating layer includes at least one element selected from the group consisting of group IVa element, group Va element, group VIa element, aluminum, boron, silicon and germanium in the periodic table, boron The surface-coated cutting tool according to any one of claims 1 to 4, which is a compound composed of at least one element selected from the group consisting of carbon, nitrogen and oxygen.   The surface-coated cutting tool according to claim 1, wherein the coating includes one layer or two or more layers in addition to the first coating layer.

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