Patent Publication Number: US-2015072135-A1

Title: Hard coating film for cutting tool and cutting tool coated with hard coating film

Description:
TECHNICAL FIELD 
     The present invention relates to a cutting tool hard film disposed as coating on a surface of a cutting tool and a hard film coated cutting tool provided with the hard film and particularly to an improvement for increasing both abrasion resistance and welding resistance. 
     BACKGROUND ART 
     Cutting tools such as drills and taps are provided and coated with a hard film to increase abrasion resistance. TiN-based, TiCN-based, TiAlN-based and AlCrN-based coatings are widely used for this cutting tool hard film and improvements are achieved for further increasing performance thereof. For example, this corresponds to an abrasion resistance member described in Patent Document 1. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-138209 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     However, a cutting tool with a hard film formed by the conventional technique as described above may have insufficient welding resistance at the time of cutting depending on a type of work material and a cutting condition. Therefore, a tool life may be shortened due to welding of work material etc., and room for improvement exists. Therefore, it is requested to develop a cutting tool hard film and a hard film coated cutting tool excellent in both abrasion resistance and welding resistance. 
     The present invention was conceived in view of the situations and it is therefore an object of the present invention to provide a cutting tool hard film and a hard film coated cutting tool excellent in both abrasion resistance and welding resistance. 
     Means for Solving the Problem 
     To achieve the object, the first aspect of the invention provides a cutting tool hard film disposed as coating on a surface of a cutting tool, comprising: a hard phase that is a nitride phase, an oxide phase, a carbide phase, a carbonitride phase, or a boride phase containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si; and a binding phase that is a phase containing at least one element out of Au, Ag, and Cu, wherein the cutting tool hard film has composite structure with the hard phase and the binding phase three-dimensionally arranged. 
     Effects of the Invention 
     As described above, according to the first aspect of the invention, the cutting tool hard film comprises: a hard phase that is a nitride phase, an oxide phase, a carbide phase, a carbonitride phase, or a boride phase containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si; and a binding phase that is a phase containing at least one element out of Au, Ag, and Cu, the cutting tool hard film has composite structure with the hard phase and the binding phase three-dimensionally arranged, and, therefore, since the structure is achieved with the hard phase bound by Au, Ag, and Cu, friction coefficient and cutting resistance can be reduced, and a high hardness film excellent in lubricity and welding resistance is acquired. Thus, the cutting tool hard film excellent in both abrasion resistance and welding resistance can be provided. 
     The second aspect of the invention provides the cutting tool hard film recited in the first aspect of the invention, wherein an average particle diameter of particles making up the hard phase is within a range of 1 nm to 100 nm. Consequently, since so-called nanocomposite structure is achieved with the hard phase bound by Au, Ag, and Cu at the nano-level, friction coefficient and cutting resistance can further be reduced, and the high hardness film excellent in lubricity and welding resistance is acquired. 
     The third aspect of the invention which depends from the first aspect of the invention or the second aspect of the invention provides a hard film coated cutting tool having the cutting tool hard film recited in the first aspect of the invention or the second aspect of the invention disposed as coating on a surface. Consequently, since the structure is achieved with the hard phase bound by Au, Ag, and Cu, friction coefficient and cutting resistance can be reduced, and a high hardness film excellent in lubricity and welding resistance is acquired. Thus, the hard film coated cutting tool excellent in both abrasion resistance and welding resistance can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a drill that is an embodiment of a hard film coated cutting tool of the present invention and is a front view from a direction orthogonal to an axial center. 
         FIG. 2  is an enlarged bottom view of the drill depicted in  FIG. 1  viewed from a tip disposed with a cutting edge. 
         FIG. 3  is an enlarged cross-sectional view around a surface of a body of the drill of  FIG. 1 , exemplarily illustrating a configuration of a hard film that is an embodiment of a cutting tool hard film of the present invention. 
         FIG. 4  is a schematic of structure of the hard film of  FIG. 3 . 
         FIG. 5  is a diagram for explaining an example of a coating method of the hard film of  FIG. 3 . 
         FIG. 6  is a diagram of coating structures of samples used in a drilling test conducted by the present inventors for verifying an effect of the present invention, and also indicates respective test results. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     A cutting tool hard film of the present invention is preferably applied to surface coating of various cutting tools including rotary cutting tools such as end mills, drills, face mills, forming mills, reamers, and taps, as well as non-rotary cutting tools such as tool bits. Although cemented carbide and high speed tool steel are preferably used as tool base material, i.e., material of a member provided with the hard film, other materials are also available and, for example, the cutting tool hard film of the present invention is widely applied to cutting tools made of various materials such as cermet, ceramics, polycrystalline diamond, single-crystal diamond, polycrystalline CBN, and single-crystal CBN. 
     The cutting tool hard film of the present invention is disposed as coating on a portion or the whole of the surface of a cutting tool and is preferably disposed on a cutting portion involved with cutting in the cutting tool. More preferably, the cutting tool hard film is disposed to coat at least a cutting edge or a rake surface in the cutting portion. 
     The hard phase is made of nitride, oxide, carbide, carbonitride, or boride containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si, or mutual solid solution thereof Specifically, the hard phase is a phase comprising TiN, TiAlN, TiAlCrVSiB, ZrVO, HfCrCN, NbN, CrN, MoSiC, AlN, SiN, etc. 
     Although the cutting tool hard film of the present invention is preferably disposed by, for example, a PVD method such as an arc ion plating method, an ion beam deposition method, a sputtering method, a PLD (Pulse Laser Deposition) method, and an IBAD (Ion Beam Assisted Deposition) method, other film formation methods such as a plating method, a liquid quenching method, and a gas aggregation method are also employable. 
     Embodiment 
     A preferred embodiment of the present invention will now be described in detail with reference to the drawings. In the drawings used in the following description, portions are not necessarily precisely depicted in terms of dimension ratio, etc. 
       FIG. 1  is a diagram of a drill  10  that is an embodiment of a hard film coated cutting tool of the present invention and is a front view from a direction orthogonal to an axial center O.  FIG. 2  is an enlarged bottom view of the drill  10  depicted in  FIG. 1  viewed from a tip disposed with a cutting edge  12  (i.e., a direction indicated by an arrow II). The drill  10  of this embodiment depicted in  FIGS. 1 and 2  is a two-flute twist drill and integrally includes a shank  14  and a body  16  in the axial center O direction. The body  16  has a pair of flutes  18  twisted clockwise around the axial center O. The tip of the body  16  is provided with a pair of the cutting edges  12  corresponding to the pair of the flutes  18  and, when the drill  10  is rotationally driven clockwise around the axial center O in a view from the shank  14 , a hole is cut in work material by the cutting edges  12  while chips generated at the time of cutting of the hole are discharged through the flutes  18  toward the shank  14 . 
       FIG. 3  is an enlarged cross-sectional view around a surface of the body  16  of the drill  10 , exemplarily illustrating a configuration of a hard film  22  that is an embodiment of the cutting tool hard film of the present invention.  FIG. 4  is a schematic of structure of the hard film  22  photographed by a TEM (transmission electron microscope). As depicted in  FIG. 3 , the drill  10  is formed by coating a surface of a tool base material (tool parent material)  20  made of high speed tool steel (high-speed steel) with the hard film  22 , for example. Film thickness of the hard film  22  is preferably about 2.5 to 6.0 μm. As depicted in  FIG. 4 , the hard film  22  has structure in which multiple particles (particulate elements) making up a hard phase  24  are bound to each other by a binding phase  26  disposed in gaps thereof. Although a planar microscope photograph is exemplarily illustrated in  FIG. 4 , the hard film  22  has the structure in which the hard phase  24  and the binding phase  26  are bound to each other as depicted in  FIG. 4  in both the planar direction (direction parallel to the surface) and the thickness direction (direction perpendicular to the surface). Therefore, the hard film  22  has composite structure with the hard phase  24  and the binding phase  26  three-dimensionally (sterically) arranged. 
     The binding phase  26  is a phase comprising Au, Ag, or Cu containing unavoidable impurities, or mutual solid solution thereof. The hard phase  24  is made of nitride, oxide, carbide, carbonitride, or boride containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si, or mutual solid solution thereof, and contains unavoidable impurities. Therefore, specifically, the hard phase  24  is a phase (dispersed phase) comprising TiN, TiAlN, TiAlCrVSiB, ZrVO, HfCrCN, NbN, CrN, MoSiC, AlN, SiN, etc. Preferably, an average particle diameter of the particles making up the hard phase  24  is within a range of 1 nm to 100 nm. For example, the average particle diameter of the particles making up the hard phase  24  is calculated for a plurality of particles (particulate elements) making up the hard phase  24  randomly extracted from a microscope photograph as depicted in  FIG. 4 , based on an average value of long diameters, short diameters, or long and short diameters corresponding to diameter dimensions of the particles. For example, an average value of the diameter dimensions in the plurality of the extracted particles is calculated as the average particle diameter. In other words, the hard film  22  has nanocomposite structure in which the hard phase  24  formed into particles having a size within a range of 1 nm to 100 nm is dispersively (diffusively) disposed in the binding phase  26  acting as a matrix. Therefore, the hard film  22  comprises nanostructured metal made up of multiple-phase nanocrystals. 
       FIG. 5  is a diagram for explaining an example of a coating method of the hard film  22 . Coating of the hard film  22  on the drill  10  etc. is performed by using, for example, a sputtering apparatus  30  as depicted in  FIG. 5  under control of a controller  36 . Preferably, first, in an etching process used as pretreatment, a negative bias voltage is applied by a bias power source  34  to the tool base material  20  placed in a chamber  32  of the sputtering apparatus  30 . This causes positive argon ions Ar +  to collide with the tool base material  20  and the surface of the tool base material  20  is roughened. 
     Subsequently, for example, the hard phase  24  in the hard film  22  is formed in a sputtering process. For example, a constant negative bias voltage (e.g., about −50 to −60 V) is applied by a power source  40  to a target  38  such as Si making up the hard phase  24  while a constant negative bias voltage (e.g., about −100 V) is applied by the bias power source  34  to the tool base material  20  so as to cause the argon ions Ar +  to collide with the target  38 , thereby beating out constituent material such as Si. Reactant gas such as nitrogen gas (N 2 ) and hydrocarbon gas (CH 4 , C 2 H 2 ) is introduced into the chamber  32  at predetermined flow rates in addition to argon gas, and nitrogen atoms N and carbon atoms C combine with Si etc. beaten out from the target  38  to form SiN etc., which are attached as the hard phase  24  in the hard film  22  to the surface of the tool base material  20 . This treatment is executed alternately with treatment of the sputtering process using Ag etc. making up the binding phase  26  as the target  38  to form the hard film  22  having the composition as depicted in  FIG. 4  on the surface of the tool base material  20 . Alternatively, targets may be respectively formed for the hard phase  24  and the binding layer  26 , and the sputtering may be performed by using the multiple targets in a synchronized manner to form the hard film  22  on the surface of the tool base material  20 . 
     Other preferably used methods of forming the hard film  22  on the surface of the tool base material  20  include, for example, a well-known plating method (plating technique), a liquid quenching method in which molten alloy acquired by melting the metal making up the hard film  22  is quenched faster than a rate causing crystal nucleation to acquire amorphous alloy, and a gas aggregation method in which nanoparticles acquired by evaporating and aggregating the metal making up the hard film  22  in He gas are deposited on a substrate cooled by liquid nitrogen to solidify and form nano-fine powder scraped off from the substrate. 
     A drilling test conducted by the present inventors for verifying an effect of the present invention will then be described.  FIG. 6  is a diagram of coating structures of inventive products and test products used in this test and respective test results (machined hole numbers and judgments). The present inventors created inventive products 1 to 10 and test products 1 to 9 as samples by coating cemented carbide drills having a tool diameter of 8.3 mmφ with hard films having respective film structures and film thicknesses depicted in  FIG. 6  and conducted a cutting test for each of the test products under the following cutting conditions. Out of the samples depicted in  FIG. 6 , the inventive products 1 to 10 correspond to inventive products to which the hard film  22  of this embodiment is applied and the test products 1 to 9 correspond to non-inventive products to which a hard film not satisfying the requirement of the present invention (out of the requirement of claim  1  or  2 ) is applied. A hard-phase particle diameter in  FIG. 6  is an average value of diameter dimensions of multiple hard-phase constituent particles randomly extracted from a microscope photograph etc. of a film of each sample. The machined hole number depicted in  FIG. 6  is the hole number when a flank wear width is 0.2 mm and an acceptance criterion is the machined hole number equal to or greater than 20 when the flank wear width is 0.2 mm. 
     [Machining Conditions] 
     Tool shape: φ3 cemented carbide drill 
     Work material: Inconel (registered trademark) 718 
     Cutting machine: vertical type M/C 
     Cutting speed: 10 m/min 
     Feed speed: 0.1 mm/rev 
     Machining depth: 33 mm (blind) 
     Step amount: non-step 
     Cutting oil: oil-based 
     As depicted in  FIG. 6 , all the inventive products 1 to 10 include the hard phase  24  that is a nitride phase, an oxide phase, a carbide phase, a carbonitride phase, or a boride phase containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si, and the binding phase  26  that is a phase containing at least one element out of Au, Ag, and Cu, and have composite structure with the hard phase  24  and the binding phase  26  three-dimensionally arranged. An average particle diameter of the particles making up the hard phase  24  is within a range of 1 nm to 100 nm. Therefore, the hard film  22  satisfying the requirements of claims  1  and  2  of the present invention is applied to all the inventive products 1 to 10. As apparent from the test results depicted in  FIG. 6 , the acceptance criterion is satisfied by the inventive products 1 to 10 to which the hard film  22  of the embodiment is applied since all the samples have the machined hole numbers equal to or greater than 20 when the flank wear width is 0.2 mm. 
     Particularly, the inventive product 2 includes the hard phase  24  comprising SiN and the binding phase  26  comprising Ag with the average particle diameter of 22.7 nm for the hard phase  24  and the film thickness of 4.1 μm, and results in the machined hole number of  41 ; the inventive product 9 includes the hard phase  24  comprising MoSiC and the binding phase  26  comprising Ag and Au with the average particle diameter of 94.6 nm for the hard phase  24  and the film thickness of 5.1 μm, and results in the machined hole number of 38; the inventive product 1 includes the hard phase  24  comprising CrN and the binding phase  26  comprising Au with the average particle diameter of 1.0 nm for the hard phase  24  and the film thickness of 2.6 μm, and results in the machined hole number of 36; the inventive product 4 includes the hard phase  24  comprising TiN and the binding phase  26  comprising Au and Cu with the average particle diameter of 100.0 nm for the hard phase  24  and the film thickness of 5.8 μm, and results in the machined hole number of 33; the inventive product 7 includes the hard phase  24  comprising TiAlCrVSiB and the binding phase  26  comprising Ag, Cu, and Au with the average particle diameter of 66.9 nm for the hard phase  24  and the film thickness of 3.5 μm, and results in the machined hole number of 31; and, therefore, it can be seen that these inventive products result in the machined hole numbers equal to or greater than 30 when the flank wear width is 0.2 mm and exhibit particularly favorable cutting performance. 
     Although including the hard phase  24  that is a nitride phase, an oxide phase, a carbide phase, a carbonitride phase, or a boride phase containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si, and the binding phase  26  that is a phase containing at least one element out of Au, Ag, and Cu, all the test products 1 to 7 have an average particle diameter of the particles making up the hard phase  24  deviating from the range of 1 nm to 100 nm and do not satisfy the requirement of claim  2  of the present invention. In particular, the test products 1, 4, 6, and 7 have a smaller average particle diameter of the particles making up the hard phase  24  less than 1 nm and the test products 2, 3, and 5 have an average particle diameter of the particles making up the hard phase  24  larger than 100 nm. If a hard film has an average particle diameter of the particles making up the hard phase  24  deviating from the range of 1 nm to 100 nm as described above, the hard film cannot have preferred nanocomposite structure with the hard phase  24  dispersively (diffusively) disposed in the binding phase  26  or, in other words, does not have composite structure with the hard phase  24  and the binding phase  26  three-dimensionally arranged. Therefore, none of the test products 1 to 7 satisfies the requirement of claim  1  of the present invention. None of the test products 8 and 9 has the binding phase  26  that is a phase containing at least one element out of Au, Ag, and Cu, and satisfies the requirement of claim  1  of the present invention. As apparent from the test results depicted in  FIG. 6 , it can be seen that all the test products 1 to 9 have the machined hole numbers less than 20 when the flank wear width is 0.2 mm and are inferior in cutting performance to the inventive products 1 to 10. 
     It is considered that this is because a hard film not satisfying the requirement of claim  1  or  2  of the present invention has insufficient welding resistance and reaches the end of life earlier due to welding, peeling, etc. 
     As described above, this embodiment includes the hard phase  24  that is a nitride phase, an oxide phase, a carbide phase, a carbonitride phase, or a boride phase containing at least one element out of group IVa elements, group Va elements, group VIa elements, Al, and Si, and the binding phase  26  that is a phase containing at least one element out of Au, Ag, and Cu, and has composite structure with the hard phase  24  and the binding phase  26  three-dimensionally arranged and, therefore, since the structure is achieved with the hard phase  24  bound by Au, Ag, and Cu, friction coefficient and cutting resistance can be reduced, and a high hardness film excellent in lubricity and welding resistance is acquired. Thus, the cutting tool hard film  22  excellent in both abrasion resistance and welding resistance can be provided. 
     An average particle diameter of the particles making up the hard phase  24  is within the range of 1 nm to 100 nm and, therefore, since so-called nanocomposite structure is achieved with the hard phase  24  bound by Au, Ag, and Cu at the nano-level, friction coefficient and cutting resistance can further be reduced, and the high hardness hard film  22  excellent in lubricity and welding resistance is acquired. 
     This embodiment provides the drill  10  as a hard film coated cutting tool having the hard film  22  disposed as coating on a surface and, therefore, since the structure is achieved with the hard phase  24  bound by Au, Ag, and Cu, friction coefficient and cutting resistance can be reduced, and a high hardness film excellent in lubricity and welding resistance is acquired. Thus, the drill  10  excellent in both abrasion resistance and welding resistance can be provided. 
     Although the preferred embodiment of the present invention has been described in detail with reference to the drawings, the present invention is not limited thereto and is implemented with various modifications applied within a range not departing from the spirit thereof. 
     NOMENCLATURE OF ELEMENTS 
       10 : drill (hard film coated cutting tool)  12 : cutting edge  14 : shank  16 : body  18 : flutes  20 : tool base material  22 : hard film (cutting tool hard film)  24 : hard phase  26 : binding phase  30 : sputtering apparatus  32 : chamber  34 : bias power source  36 : controller  38 : target  40 : power source