JP2005262389A - Surface-coated cutting tool for processing titanium alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-coated cutting tool particularly suitable for cutting work of a titanium alloy particularly occupying an important position in a hard-to-cut material by improving abrasion resistance. <P>SOLUTION: This surface-coated cutting tool for processing the titanium alloy forms a coating film so as to directly contact with a base material surface. The surface-coated cutting tool for processing the titanium alloy is characterized in that the coating film is composed of a compound composed of any one or both elements of Al and Cr or V and any one or more elements of nitrogen, carbon or oxygen. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cutting tool such as a drill, an end mill, a cutting tip, a cutting edge replacement type tip for milling, a cutting edge replacement type tip for turning, a metal saw, a gear cutting tool, a reamer, a tap, and the like. The present invention relates to a surface-coated cutting tool particularly suitable for machining a formed titanium alloy.

  In recent cutting, in addition to the pursuit of high-speed, high-precision and high-efficiency machining, dry machining is also aimed at as zero emission machining as an environmental measure. In addition, with the advancement of industrial technology, industrial activities that use a lot of difficult-to-cut materials and new materials used in aircraft, space development, nuclear power generation, etc. are becoming more and more active, qualitative diversification and quantitative It is expected that the expansion will be further advanced, and it is naturally required to cope with these cutting processes.

In the past, various surface-coated cutting tools have been proposed and put to practical use for such problems. For example, in order to improve wear resistance and surface protection function, as a hard coating layer (Al _x Ti) on the surface of a hard base material such as a cutting tool such as WC base cemented carbide, cermet, high speed steel or wear resistant tool _1-xy Si _y ) (N _z C _1-z ), except that Al ≦ Si ≦ 0.05 ≦ x ≦ 0.75, 0.01 ≦ y ≦ 0.1, 0.6 ≦ z ≦ 1 The thing with which the film | membrane was coat | covered is known (patent document 1).

  In addition, a nitride, carbonitride, oxynitride, oxycarbonitride containing Ti as a main component containing an appropriate amount of Si, and a nitride, carbonitride, oxynitride, acid containing Ti and Al as main components Carbonitride is one layer each so that Si3N4 and Si exist as independent phases in nitride, carbonitride, oxynitride and oxycarbonitride in which the former microstructure is the main component of Ti. It has been proposed that the performance of the cutting tool is extremely good in the dry high-speed cutting when the coating is performed alternately (Patent Document 2).

  According to this proposal, in the conventional TiAlN film, the alumina layer formed by the surface oxidation that occurs in the cutting process functions as an oxidation protective film against the inward diffusion of oxygen. The layer easily peels off from the porous Ti oxide layer directly below it and is not sufficient for the progress of oxidation. On the other hand, the proposed TiSi-based film has extremely high oxidation resistance of the film itself. In addition, a very dense Ti and Si complex oxide containing Si is formed on the outermost surface, so that the porous Ti oxide layer, which has been a problem in the past, is not formed, thereby improving performance. It is said that.

  On the other hand, hard coatings for cutting tools having Al, Cr, V as main constituent elements have been proposed as hard coatings for cutting tools having higher hardness and superior wear resistance than conventional TiAlN films (Patent Literature). 3).

  However, cutting of a titanium alloy, which occupies a particularly important position among materials called difficult-to-cut materials, is compared with the following (1) to (1) to steel processing performed using a coating as disclosed above. It is very difficult as shown in (3), and is considered to be completely different from such conventional steel processing.

  (1) Since the thermal conductivity of the titanium alloy is small, the cutting heat concentrates on the edge part and the rake face of the cutting edge of the heat generating part, and the cutting temperature rises locally.

  (2) Titanium alloys are chemically active and thus react with the cutting tool material (especially Co in the binder phase) to promote chemical diffusion wear.

(3) Chips of the titanium alloy have a saw-tooth shape, and the cutting resistance changes with time.
Japanese Patent No. 2793773 Japanese Patent No. 3347687 JP 2003-34859 A

  The present invention has been made in view of the current situation as described above, and the object of the present invention is that of a titanium alloy that occupies an especially important position among difficult-to-cut materials because the surface coating is excellent in wear resistance. An object of the present invention is to provide a surface-coated cutting tool specialized for cutting.

  The inventors of the present invention have made various studies on the surface coating film formed on the substrate to solve the above problems, and it is important for the titanium alloy cutting process not to contain Ti in the coating film. As a result of further earnest research based on this knowledge, the present invention was finally completed.

  That is, the present invention provides a surface-coated cutting tool for processing a titanium alloy in which a coating is formed so as to be in direct contact with the surface of the base material, wherein the coating is composed of Al, one of or both of Cr and V, The present invention relates to a surface-coated cutting tool for machining a titanium alloy, comprising a compound composed of one or more elements of nitrogen, carbon, and oxygen.

In addition, the above-mentioned film is composed of (Al _1-ab Cr _a V _b ) (where 0 ≦ a ≦ 0.4, 0 ≦ b ≦ 0.4, 0 ≠ a + b ≦ 0.4), nitrogen, carbon, or oxygen It can consist of a compound comprised with any one or more elements of these.

In addition, the above-mentioned coating is composed of (Al _{1 -ab} Cr _a V _b ) (where 0 ≦ a ≦ 0.4, 0 <b ≦ 0.4, 0 ≠ a + b ≦ 0.4), nitrogen, carbon, or oxygen It can consist of a compound comprised with any one or more elements of these.

  The coating may further contain 20% or less of Si in atomic percent, and may further contain less than 10% in atomic percent of B.

  In addition, in the hardness test by the nanoindentation method that is performed by applying an indentation load controlled so that the indentation depth is 1/10 or less of the film thickness of the film, the maximum indentation depth is obtained. Is hmax and the indentation depth after unloading is hf, (hmax−hf) / hmax can be a numerical value of 0.2 or more and 0.7 or less.

  Moreover, in the hardness test by the nanoindentation method performed by applying the indentation load controlled so that the indentation depth is 1/10 or less of the film thickness of the film, the film is 20 GPa or more and 50 GPa or less. The hardness can be shown.

  The film thickness of the coating film can be 0.5 μm or more and 15 μm or less, the compressive residual stress can be −6 GPa or more and 0 GPa or less, and the crystal structure thereof can be a cubic crystal. .

  The base material is composed of WC-based cemented carbide, cermet, high speed steel, ceramics, cubic boron nitride sintered body, diamond sintered body, silicon nitride sintered body, or aluminum oxide and titanium carbide. It can be any of the mixtures.

  Moreover, the said film can be formed on the said base material by a physical vapor deposition method, and also can be formed by the arc type ion plating method or the magnetron sputtering method.

  According to the surface-coated cutting tool having the above-described configuration of the present invention, a cutting tool such as a drill, an end mill, a cutting tip, a cutting edge exchangeable tip for milling, a cutting edge exchangeable tip for turning, a metal saw, a gear cutting tool, a reamer, a tap, etc. Therefore, it is possible to provide a surface-coated cutting tool having a long life, and in particular, a surface-coated cutting tool excellent for cutting a titanium alloy.

<Surface coated cutting tool for titanium alloy processing>
The surface-coated cutting tool for processing a titanium alloy according to the present invention has a coating formed so as to be in direct contact with the substrate surface.

  Such a surface-coated cutting tool for machining titanium alloys according to the present invention includes cutting tools such as drills, end mills, cutting tips, milling-blade replacement tips, turning-tip replacement tips, metal saws, gear cutting tools, reamers, taps, etc. It can be suitably used as a tool, and is specialized for cutting a titanium alloy.

  The titanium alloy referred to in the present invention is a kind of difficult-to-cut material, and refers to a conventionally known alloy containing titanium, particularly for a material having a hardness of 110 to 450 HB (Brinell hardness). .

  Examples of such a titanium alloy include Ti-6Al-4V (HB = 310), Ti-5Al-2.5Sn, Ti-6Al-2Sn-4Zr-2Mo, Ti-3Al-8V-6Cr-4Mo-4Zr. Ti-10V-2Fe-3Al, Ti-13V-11Cr-3Al, and the like.

  Hereinafter, the description will be made separately for each component.

<Base material>
As the base material used in the surface-coated cutting tool for processing a titanium alloy according to the present invention, any material can be used as long as it is conventionally known as a base material for this type of application. For example, WC-based cemented carbide, cermet, high speed steel, ceramics (silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cubic boron nitride sintered body, diamond sintered body, silicon nitride sintered body, Or it is preferable that it is either the mixture which consists of aluminum oxide and titanium carbide.

<Coating>
The coating film of the present invention is formed so as to be in direct contact with the surface of the substrate. As long as it is formed in this way, it is not always necessary to cover the entire surface of the base material, and the surface of the base material may include a portion where the coating film is not formed.

  Such a film is characterized by comprising a compound composed of Al, one or both of Cr and V, and one or more elements of nitrogen, carbon, and oxygen.

More preferably, the film is made of (Al _1-ab Cr _a V _b ) (where 0 ≦ a ≦ 0.4, 0 ≦ b ≦ 0.4, 0 ≠ a + b ≦ 0.4), nitrogen, carbon Or it can consist of a compound comprised with any one or more elements of oxygen.

  Thus, the compound used as the film is characterized by not containing Ti (titanium) as a metal component but mainly containing Al (aluminum). It is preferable to contain Al as a main component instead of Ti because the oxidation resistance is improved, the thermal conductivity is increased, and heat generated during cutting can be released from the tool surface. Moreover, although it is thought that it originates in the lubrication performance on the surface, since the welding resistance performance of the titanium alloy as the work material is improved, the cutting resistance is reduced, and the chip discharge property can be improved. Therefore, these characteristics act comprehensively, so that the wear resistance of the surface-coated cutting tool is drastically improved, and it is particularly suitable for processing titanium alloys.

Here, the amount of Cr and V, excluding Al, is (Al _1-ab Cr _a V _b ) (where 0 ≦ a ≦ 0.4, 0 ≦ b ≦ 0.4, 0 ≠ a + b ≦ 0.4) Stipulated. Thus, a and b representing the content ratio of Cr and V are respectively defined as 0 ≦ a ≦ 0.4 and 0 ≦ b ≦ 0.4 (where 0 ≠ a + b ≦ 0.4), This is because when a and b exceed 0.4, the hardness of the coating film is lowered and a problem occurs in wear resistance.

  More preferably, a and b are 0 ≦ a ≦ 0.4, 0 <b ≦ 0.4, more preferably 0 ≦ a ≦ 0.35, 0 <b ≦ 0.35 (where 0 ≠ a + b ≦ 0.4). When V is present in the coating (compound), when the coating surface is oxidized in a high temperature environment during cutting, the oxide of V has a low melting point, and therefore acts as a lubricant during cutting and adheres to the work material. Since the effect which suppresses can be anticipated, it is preferable to contain V. In this regard, Cr is contained to show a function of excellent oxidation resistance because it produces a stable and dense oxide, but unlike V, it does not contain this to constitute a compound. You can also.

  On the other hand, the addition of Cr and V to the compound makes it possible to form a cubic Al compound (that is, a coating film) that is a metastable phase at room temperature and normal pressure. For example, in the case of AlN that is a nitride, the estimated lattice constant in the case of a cubic crystal that is usually a hexagonal crystal but a metastable phase is 4.12%, whereas The lattice constant of CrN and VN, in which cubic crystals are stable phases, is 4.14 、, which is very close to cubic AlN, so that AlN becomes cubic and high hardness due to the pulling effect. Therefore, the crystal structure (crystal system) of the coating is preferably cubic, and therefore it is preferable to contain Cr and V as the compound.

  Further, the coating film (the above compound) can further improve the coating film hardness by containing 20% or less of Si in atomic%. The presence of Si in the film is preferable because the structure of the film is refined from a columnar shape to a needle shape and the hardness of the film is improved.

  However, if the Si content exceeds 20%, the coating becomes brittle and conversely, wear is promoted. Moreover, when producing the alloy target used for film formation by hot isostatic pressing, if the Si content exceeds 20%, the target is cracked during firing, and the material strength that can be used for coating is increased. It will not be obtained.

  Therefore, the Si content in the coating (in the above compound) is preferably 20% or less in atomic%, more preferably 5% or more and 15% or less.

  In addition, the coating (the above compound) may contain B in atomic percent of less than 10%. Although the detailed mechanism is unknown, it is preferable that B is contained in the coating because a coating with higher hardness can be obtained. Further, the oxide of B formed by surface oxidation during cutting is particularly preferable because it densifies the oxide of Al. Furthermore, since the oxide of B has a low melting point, it acts as a lubricant during cutting, and can exhibit an effect of suppressing adhesion to a titanium alloy as a work material.

  However, if B exceeds 10%, it is not preferable because it breaks during target firing. Therefore, the B content in the film (in the above compound) is preferably less than 10% in atomic%, and more preferably 0.1% or more and 5% or less.

<Numerical limitation using nanoindentation method>
In the hardness test by the nanoindentation method performed by applying a controlled indentation load so that the indentation depth is 1/10 or less of the film thickness of the film, the maximum indentation depth is hmax. When the indentation depth (indentation depth) after unloading is hf, it is preferable that (hmax−hf) / hmax represents a numerical value of 0.2 to 0.7.

  Here, the nanoindentation method is a kind of hardness test as described in detail in, for example, the document “Tribologist, Vol. 47, No. 3, (2002) p177-183”. Unlike the method of obtaining hardness from the indentation shape after indentation, such as Knoop hardness measurement (micro Knoop method) and Vickers hardness measurement (micro Vickers method), the hardness and Young's modulus are calculated from the relationship between the load and depth when the indenter is indented. It is a method to seek. The comparison between these conventional test methods and the nanoindentation method is shown in Table 1 below.

  As is clear from Table 1, in the conventional Knoop method or Micro Vickers method, which is a hardness test method, the indentation load (F) is as large as 50 mN to 10 N, and therefore the indentation depth (h) is 100 nm or more. It was not only the physical property evaluation of the film but was affected by the base material. As shown in Table 1, the indentation depth (h) referred to in the present application is the surface of the coating (the load is applied by the indenter) from the tip of the indenter when the indenter is pushed under a load. The height (distance) up to (not surface part).

  As pointed out in the above-mentioned document, in order to evaluate the hardness of only the film, it is necessary to measure at an indentation depth (h) of about 1/10 or less of the film thickness. When a 1 μm film is targeted, the indentation depth must be 100 nm or less. Therefore, in the hardness test of the present invention, a nanoindentation method that is executed by applying a controlled indentation load so that the indentation depth is 1/10 or less of the film thickness of the coating film is employed. .

  On the other hand, the method in which the measurer observes the size of the indentation with an optical microscope as in the conventional method is also difficult in terms of measurement accuracy for determining the indentation shape. In this respect, the nanoindentation method is advantageous because it is a method for obtaining the depth mechanically.

  FIG. 1 conceptually shows the relationship between the load and the indentation depth when the indenter is indented into the coating surface in the hardness test by the nanoindentation method executed under the above conditions. In this test, a displacement meter is installed in the indenter drive section, and while continuously measuring the indentation depth (h), the load is gradually increased to the maximum indentation load (Pmax), and the maximum indentation load (Pmax). Then, the indentation depth (h) is measured as the maximum indentation depth hmax. Thereafter, the indentation depth (h) when the load is unloaded to zero (the state where no load is applied) is measured as the indentation depth hf after the unloading.

  In the conventional method such as the micro Knoop method and the micro Vickers method, hf in FIG. 1, that is, the shape of the indentation after unloading the load was measured. However, this method has a problem in measurement accuracy as described above. On the other hand, in the nanoindentation method, when the maximum indentation depth hmax and the indentation depth hf after unloading are measured, the elastic recovery amount of the coating can be obtained from (hmax−hf). If this value is large, it is easy to elastically deform, and if it is small, it is difficult to elastically deform.

  In the present invention, attention is paid to the elastic recovery rate, that is, (hmax−hf) / hmax as an index representing the elastic recovery amount. In order to extend the tool life in the cutting of a titanium alloy, it is important to improve the chipping property and chipability of the cutting edge, particularly the film. In this regard, if a material having a large elastic recovery amount (hmax−hf) can be found, the deformation of the coating material follows the load applied to the blade edge during cutting, and therefore chipping and chipping that occurs particularly at the beginning of cutting are avoided. It becomes possible to suppress.

  As a specific measurement method, the maximum indentation in the hardness test by the nano-indentation method executed by applying an indentation load controlled so that the indentation depth (h) is 1/10 or less of the film thickness. When the depth is hmax and the indentation depth (indentation depth) after unloading is hf, (hmax−hf) / hmax is obtained by measuring these.

  And as a film of this invention, (hmax-hf) / hmax shows what shows the numerical value of 0.2-0.7. This indicates that when (hmax−hf) / hmax is less than 0.2, chipping of the cutting edge tends to occur due to impact during cutting, and (hmax−hf) / hmax exceeds 0.7. This is because the hardness of the film decreases in some cases.

  On the other hand, the hardness of the coating film is 20 GPa or more and 50 GPa or less in a hardness test by a nanoindentation method performed by applying an indentation load controlled so as to have an indentation depth of 1/10 or less of the film thickness of the film. It is preferable that the hardness is shown. This is because if the hardness is less than 20 GPa, the hardness is low and there is a problem in wear resistance. From this point, it is preferable that the hardness is higher, but if it exceeds 50 GPa, the residual compressive stress accumulated in the coating increases, and the cutting edge ridge line before cutting This is because peeling of the film may occur at the portion.

<Film thickness>
The film thickness is preferably 0.5 μm or more and 15 μm or less. If the film thickness is less than 0.5 μm, improvement in wear resistance is not observed. Conversely, if the film thickness exceeds 15 μm, the residual stress in the coating increases and the adhesion strength with the substrate decreases, which is not preferable. As a method for measuring the film thickness, it can be obtained by cutting a surface-coated cutting tool and observing the cross section with an SEM (scanning electron microscope).

<Compressive residual stress of coating>
The compressive residual stress of the coating is preferably -6 GPa or more and 0 GPa or less. If it exceeds 0 GPa, a tensile stress remains in the coating, and the film tends to crack and chipping properties and chipping properties are reduced. Moreover, when it becomes less than -6 GPa, since the residual stress in a film becomes large and the adhesive strength with a base material falls, it is unpreferable.

<Method for forming film>
In order to coat the above-mentioned coating film of the present invention on the substrate surface, it is preferably produced by a film forming process capable of forming a compound having high crystallinity. Therefore, as a result of examining various film forming methods, it is preferable to use a physical vapor deposition method.

  Various physical vapor deposition methods are known, but it is particularly preferable to employ an arc ion plating method or a magnetron sputtering method.

  Examples of the magnetron sputtering method include a balanced magnetron sputtering method and an unbalanced magnetron sputtering method. There are various arc type ion plating methods, and it is particularly preferable to adopt the cathode arc ion plating method in which the ion ratio of the raw material elements is high.

  When this cathodic arc ion plating method is used, metal ion bombardment treatment can be performed on the surface of the substrate before the coating is formed, so that the adhesion of the coating is dramatically improved. For this reason, the cathode arc ion plating method is a preferable process from the viewpoint of adhesion.

<Others>
The surface-coated cutting tool for processing a titanium alloy according to the present invention is mainly composed of Al having a low hardness but a crystal structure of hexagonal system as the outermost surface layer on the coating, and any one or more of nitrogen, carbon and oxygen The compound by these elements may be coat | covered. This is because the chipping property and the chipping property are further improved by having the low hardness coating on the high hardness coating.

  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 is confirmed by XPS (X-ray photoelectron spectroscopy analyzer), hardness and elastic recovery rate ((hmax-hf) / hmax) are nanoindenters (Nano Indenter XP by MTS). Confirmed by 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.

<Production of surface-coated cutting tool for titanium alloy processing>
First, as a base material for a surface-coated cutting tool for machining a titanium alloy, a grade of WC standard cemented carbide of JIS standard S20 and a shape as a cutting tip of CNMG120408 of JIS standard is used as a cathode. Attached to the 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 650 ° 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 was gradually increased to −1500 V, and the substrate surface was cleaned for 15 minutes. Thereafter, argon gas was exhausted.

  Next, as a compound composition of the film formed so as to be in direct contact with the substrate surface, an alloy target as a metal evaporation source is set so as to have a compound composition described in Table 2 below, and nitrogen is used as a reaction gas. The substrate (substrate) temperature was 650 ° C., the reaction gas pressure was 2.0 Pa, and the substrate bias voltage was maintained at −200 V while introducing at least one of methane (as a carbon source), oxygen, or carbon monoxide. The film was formed so as to be in direct contact with the substrate surface by supplying an arc current of 100 A to the cathode electrode and generating metal ions from the arc evaporation source.

  Then, the current supplied to the evaporation source was stopped when the predetermined film thickness described in Table 2 was reached. Normally, this is gradually cooled, but in this example, the substrate was rapidly cooled by introducing He gas and filling the chamber at the same time as the end of coating. In this way, as shown in Table 2, surface-coated cutting tools for machining titanium alloys according to the present invention of Examples 1 to 15 were obtained.

  Although the detailed mechanism has not been elucidated, it is presumed that the crystal grains in the film are refined by the rapid cooling treatment as described above, and the elastic recovery amount is increased. Further, the surface-coated cutting tools of Comparative Examples 1 and 2 corresponding to the conventional products listed in Table 2 were produced in the same manner except that they were not quenched in the above.

  The crystal structure (crystal system) and compressive residual stress of these surface-coated cutting tools are also described in Table 2, and the hardness and elastic recovery rate ((hmax−hf) / hmax) are described in Table 3 below. To do.

<Life evaluation of surface-coated cutting tools>
Each of the surface-coated cutting tools of Examples 1 to 15 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 were a titanium alloy Ti-6Al-4V (HB = 310) as a work material, a cutting speed of 80 m / min, a feed amount of 0.2 mm / rev, and a cutting depth of 1 mm.

  Table 3 shows the cutting times measured above as the results of the life evaluation of the surface-coated cutting tool. As apparent from Table 3, the surface-coated cutting tool for machining titanium alloy according to the present invention in Examples 1 to 15 in both the continuous cutting test and the intermittent cutting test is compared with the surface-coated cutting tool in Comparative Examples 1 and 2. As a result, it was confirmed that the cutting time was extremely long, the life of the surface-coated cutting tool was greatly improved, and it was suitable as a surface-coated cutting tool for machining titanium alloys.

  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 the figure which showed notionally the relationship between the load and indentation depth at the time of pushing the indenter into the film surface in the hardness test by a nanoindentation method.

Claims (13)

In the surface-coated cutting tool for titanium alloy processing in which a film is formed so as to be in direct contact with the substrate surface,
The coating film is made of a compound composed of Al, one or both of Cr and V, and one or more elements of nitrogen, carbon, or oxygen, and a titanium alloy processing surface, Coated cutting tool. The film is made of (Al _1-ab Cr _a V _b ) (where 0 ≦ a ≦ 0.4, 0 ≦ b ≦ 0.4, 0 ≠ a + b ≦ 0.4), and any of nitrogen, carbon, or oxygen 2. The surface-coated cutting tool for machining a titanium alloy according to claim 1, wherein the surface-coated cutting tool is made of a compound composed of at least one element. The film is made of (Al _1-ab Cr _a V _b ) (where 0 ≦ a ≦ 0.4, 0 <b ≦ 0.4, 0 ≠ a + b ≦ 0.4), and any of nitrogen, carbon, or oxygen 2. The surface-coated cutting tool for machining a titanium alloy according to claim 1, wherein the surface-coated cutting tool is made of a compound composed of at least one element.   The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 3, wherein the coating further contains 20% or less of Si in atomic percent.   The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 4, wherein the coating further contains B in an atomic percent of less than 10%.   The maximum indentation depth is hmax in a hardness test by a nanoindentation method performed by applying an indentation load controlled so that the indentation depth is 1/10 or less of the film thickness of the film. 6. When the indentation depth after unloading is hf, (hmax−hf) / hmax shows a numerical value of 0.2 or more and 0.7 or less. Surface coated cutting tool for machining titanium alloys.   The coating film has a hardness test of 20 GPa or more and 50 GPa or less in a hardness test by a nanoindentation method performed by applying an indentation load controlled so as to have an indentation depth of 1/10 or less of the film thickness of the film. The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 6, wherein   The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 7, wherein the film thickness of the coating is 0.5 µm or more and 15 µm or less.   The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 8, wherein the compressive residual stress of the coating is -6 GPa or more and 0 GPa or less.   The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 9, wherein the crystal structure of the coating is cubic.   The base material is a WC-based cemented carbide, cermet, high-speed steel, ceramics, cubic boron nitride sintered body, diamond sintered body, silicon nitride sintered body, or a mixture of aluminum oxide and titanium carbide. The surface-coated cutting tool for processing a titanium alloy according to any one of claims 1 to 10, wherein the tool is any one of the following.   The surface-coated cutting tool for machining a titanium alloy according to any one of claims 1 to 11, wherein the coating is formed on the substrate by a physical vapor deposition method.   The surface-coated cutting tool for machining a titanium alloy according to any one of claims 1 to 12, wherein the coating is formed on the substrate by an arc ion plating method or a magnetron sputtering method.

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