US20170173703A1 - Sintered body and cutting tool - Google Patents

Sintered body and cutting tool Download PDF

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Publication number
US20170173703A1
US20170173703A1 US15/300,155 US201615300155A US2017173703A1 US 20170173703 A1 US20170173703 A1 US 20170173703A1 US 201615300155 A US201615300155 A US 201615300155A US 2017173703 A1 US2017173703 A1 US 2017173703A1
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Prior art keywords
sintered body
grains
sialon
cutting
hard phase
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US15/300,155
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Inventor
Kentaro Chihara
Satoru Kukino
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Sumitomo Electric Industries Ltd
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Sumitomo Electric Industries Ltd
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Assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD. reassignment SUMITOMO ELECTRIC INDUSTRIES, LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHIHARA, Kentaro, KUKINO, SATORU
Publication of US20170173703A1 publication Critical patent/US20170173703A1/en
Priority to US15/958,643 priority Critical patent/US10870154B2/en
Abandoned legal-status Critical Current

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    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/583Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on boron nitride
    • C04B35/5831Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on boron nitride based on cubic boron nitrides or Wurtzitic boron nitrides, including crystal structure transformation of powder
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23BTURNING; BORING
    • B23B27/00Tools for turning or boring machines; Tools of a similar kind in general; Accessories therefor
    • B23B27/14Cutting tools of which the bits or tips or cutting inserts are of special material
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C29/00Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
    • C22C29/16Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on nitrides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23BTURNING; BORING
    • B23B27/00Tools for turning or boring machines; Tools of a similar kind in general; Accessories therefor
    • B23B27/14Cutting tools of which the bits or tips or cutting inserts are of special material
    • B23B27/18Cutting tools of which the bits or tips or cutting inserts are of special material with cutting bits or tips or cutting inserts rigidly mounted, e.g. by brazing
    • B23B27/20Cutting tools of which the bits or tips or cutting inserts are of special material with cutting bits or tips or cutting inserts rigidly mounted, e.g. by brazing with diamond bits or cutting inserts
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/583Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on boron nitride
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C19/00Alloys based on nickel or cobalt
    • C22C19/03Alloys based on nickel or cobalt based on nickel
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C29/00Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C29/00Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
    • C22C29/12Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on oxides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23BTURNING; BORING
    • B23B2226/00Materials of tools or workpieces not comprising a metal
    • B23B2226/12Boron nitride
    • B23B2226/125Boron nitride cubic [CBN]
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23CMILLING
    • B23C2226/00Materials of tools or workpieces not comprising a metal
    • B23C2226/12Boron nitride
    • B23C2226/125Boron nitride cubic [CBN]
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30Constituents and secondary phases not being of a fibrous nature
    • C04B2235/38Non-oxide ceramic constituents or additives
    • C04B2235/3852Nitrides, e.g. oxynitrides, carbonitrides, oxycarbonitrides, lithium nitride, magnesium nitride
    • C04B2235/3865Aluminium nitrides
    • C04B2235/3869Aluminium oxynitrides, e.g. AlON, sialon
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/96Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
    • C04B2235/9607Thermal properties, e.g. thermal expansion coefficient

Definitions

  • the present invention relates to a sintered body for cutting a nickel-based heat-resistant alloy and to a cutting tool including this sintered body, and particularly relates to a sintered body for cutting a nickel-based heat-resistant alloy formed of crystal grains with a coarse grain size, and to a cutting tool including this sintered body.
  • a nickel-based heat-resistant alloy is an alloy based on nickel to which chromium, iron, niobium, molybdenum, and the like are added.
  • the nickel-based heat-resistant alloy is excellent in high-temperature characteristics such as thermal resistance, corrosion resistance, oxidation resistance, and creep resistance, and suitable for use in applications requiring thermal resistance, such as aircraft jet engine, automobile engine, and industrial turbine.
  • the nickel-based heat-resistant alloy is a material difficult to cut.
  • a cutting tool for cutting such a nickel-based heat-resistant alloy As a cutting tool for cutting such a nickel-based heat-resistant alloy, a cutting tool has been proposed including a sintered body which contains cubic boron nitride having the second highest strength after diamond and having high wear resistance.
  • WO00/47537 discloses, as a sintered body to be included in the cutting tool as described above, a sintered body with high crater resistance and high strength containing 50 vol % to 78 vol % of high pressure phase boron nitride and a balance of a binder phase.
  • Japanese Patent Laying-Open No. 2000-226262 also discloses a high-hardness high-strength sintered body produced by sintering hard grains which are high-pressure-type boron nitride grains each covered with a coating layer, and a binder phase uniting the hard grains.
  • PTD 3 discloses a sintered body containing cubic boron nitride, a first compound, and a second compound, in which the content of the cubic boron nitride is not less than 35 vol % and not more than 93 vol %.
  • PTD 3 Japanese Patent Laying-Open No. 2011-140415
  • a problem of respective sintered bodies disclosed in WO00/47537 (PTD 1), Japanese Patent Laying-Open No. 2000-226262 (PTD 2), and Japanese Patent Laying-Open No. 2011-140415 (PTD 3) is that the fracture resistance of the sintered bodies is not high while the wear resistance is high when the sintered bodies are used for cutting a workpiece. Fracture of the cutting tool is a critical problem when used for cutting parts of an aircraft jet engine, an automobile engine, and the like for which high dimensional accuracy and high surface quality are required.
  • the cutting tool is used for cutting a nickel-based heat-resistant alloy formed of crystal grains with a coarse grain size, specifically a grain size number of 5 or less defined by American Society for Testing and Materials (hereinafter also referred to as ASTM) standard E112-13, there is a problem that a fracture called boundary damage is likely to occur to a cutting blade of the cutting tool.
  • ASTM American Society for Testing and Materials
  • An object is therefore to solve the above problems and provide a sintered body having high fracture resistance in addition to high wear resistance, as well as a cutting tool including this sintered body.
  • a sintered body in an aspect of the present invention is a sintered body including cubic boron nitride grains as hard phase grains, and having a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , for cutting a nickel-based heat-resistant alloy formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by American Society for Testing and Materials standard E112-13.
  • a cutting tool in another aspect of the present invention is a cutting tool including the sintered body as described above.
  • a sintered body having high fracture resistance in addition to high wear resistance, as well as a cutting tool including this sintered body can be provided.
  • a sintered body in an embodiment of the present invention is a sintered body including cubic boron nitride grains as hard phase grains, and having a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , for cutting a nickel-based heat-resistant alloy formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by American Society for Testing and Materials (hereinafter also referred to as ASTM) standard E112-13.
  • the sintered body in the present embodiment has a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , and therefore exhibits high fracture resistance when used for cutting a nickel-based heat-resistant alloy which is formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13.
  • the sintered body has high fracture resistance in addition to high wear resistance derived from the cubic boron nitride grains.
  • the sintered body in the present embodiment may further include a binder and different-type hard phase grains including at least one selected from the group consisting of silicon nitride, SiAlON, and alumina, as the hard phase grains other than the cubic boron nitride grains.
  • This sintered body thus further includes a binder and different-type hard phase grains including at least one selected from the group consisting of silicon nitride, SiAlON, and alumina, as the hard phase grains other than the cubic boron nitride grains, to thereby exhibit high fracture resistance when used for cutting a nickel-based heat-resistant alloy formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13.
  • the sintered body thus has high fracture resistance in addition to high wear resistance.
  • a ratio V BN /V H of a volume V BN of the cubic boron nitride grains to a volume V H of the different-type hard phase grains may be not less than 0.5 and not more than 1.5.
  • This sintered body thus has a ratio V BN /V H of not less than 0.5 and not more than 1.5, as a ratio of a volume V BN of the cubic boron nitride grains to a volume V H of the different-type hard phase grains, to thereby have high fracture resistance in addition to high wear resistance.
  • the SiAlON may include cubic SiAlON.
  • This sintered body thus includes cubic SiAlON which has low reactivity to the metal and higher hardness than those of ⁇ -SiAlON and ⁇ -SiAlON, to thereby have higher wear resistance.
  • the SiAlON may further include at least one of ⁇ -SiAlON and ⁇ -SiAlON, and a peak intensity ratio Rc of an intensity at an X-ray diffraction main peak of the cubic SiAlON to a sum of respective intensities at respective X-ray diffraction main peaks of the ⁇ -SiAlON, the ⁇ -SiAlON, and the cubic SiAlON may be not less than 20%.
  • This sintered body thus includes the cubic SiAlON, and at least one of ⁇ -SiAlON and ⁇ -SiAlON, and has a ratio of 20% or more of the cubic SiAlON to the sum of the ⁇ -SiAlON, the ⁇ -SiAlON, and the cubic SiAlON, in term of the intensity at a main peak of X-ray diffraction. Accordingly, the sintered body has high fracture resistance as well as high wear resistance.
  • the binder may include at least one kind of binder selected from the group consisting of at least one kind of element out of titanium, zirconium, aluminum, nickel, and cobalt, nitrides, carbides, oxides, carbonitrides, and borides of the elements, and solid solutions thereof.
  • the binder strongly bonds the different-type hard phase grains and the cubic boron nitride grains, and increases the fracture toughness of the sintered body. The sintered body therefore has higher fracture resistance.
  • a content of the hard phase grains in the sintered body may be not less than 60 vol % and not more than 90 vol %. This sintered body has well-balanced high wear resistance and high fracture resistance.
  • the sintered body may have a Vickers hardness of not less than 20 GPa. This sintered body thus has a Vickers hardness of not less than 20 GPa, and therefore has high wear resistance.
  • the nickel-based heat-resistant alloy may be Inconel® 718.
  • This sintered body also exhibits high fracture resistance in addition to high wear resistance when used for cutting Inconel® 718 formed of crystal grains with a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13, which is a typical example of the nickel-based heat-resistant alloy.
  • a cutting tool in another embodiment of the present invention is a cutting tool including the sintered body in the aforementioned embodiment.
  • the cutting tool in the present embodiment includes the sintered body in the aforementioned embodiment, and therefore exhibits high fracture resistance when used for cutting a nickel-based heat-resistant alloy which is formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13.
  • the cutting tool thus has high fracture resistance in addition to high wear resistance.
  • a sintered body in an embodiment of the present invention is a sintered body including cubic boron nitride grains as hard phase grains, and having a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , for cutting a nickel-based heat-resistant alloy formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by American Society for Testing and Materials (ASTM) standard E112-13. Crystal grains having a smaller grain size number are coarser crystal grains.
  • the grain size number of 5 or less corresponds to a crystal grain size of about 50 ⁇ m or more.
  • the sintered body in the present embodiment has a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , and therefore exhibits high fracture resistance when used for cutting a nickel-based heat-resistant alloy which is formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13.
  • the sintered body thus has high fracture resistance in addition to high wear resistance.
  • the cutting resistance is the cutting resistance against the cutting blade of a cutting tool including the sintered body containing cubic boron nitride grains with high wear resistance, when cutting a nickel-based heat-resistant alloy. As a result of this, the following was found.
  • the alloy When a nickel-based heat-resistant alloy was cut, the alloy was cut with a significantly higher cutting resistance as compared with the cutting resistance when cutting a hardened steel which is also a difficult-to-cut material. Therefore, due to contact with swarf with high hardness, a deep boundary damage in a V-shape as seen from the flank face of the tool was generated in the tool. It was also found that the boundary damage extending into the cutting blade caused decrease of the strength of the cutting edge.
  • the inventors of the present invention considered that a cause of such a boundary damage was decrease of the temperature of the cutting edge during cutting, due to the high thermal conductivity of the cubic boron nitride grains forming the cutting blade.
  • the thermal conductivity of the sintered body is further increased by the high thermal conductivity of the metal binder itself, to a thermal conductivity of 70 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 .
  • the inventors of the present invention examined the relation between the cutting resistance and the thermal conductivity of the sintered body including the cubic boron nitride grains forming the cutting blade of the cutting tool. As a result, the inventors found that increase of the thermal conductivity of the sintered body caused increase of the cutting resistance when a Ni-based heat resistant alloy such as Inconel® is cut. When a Ni-based heat-resistant alloy is cut, the temperature at a portion where a workpiece (work) and the cutting edge of the cutting tool contact each other increases to approximately 700° C., and accordingly the workpiece at the contact portion is softened. Then, the deforming stress decreases and accordingly the cutting resistance decreases.
  • a Ni-based heat resistant alloy such as Inconel®
  • the inventors of the present invention examined the relation between the cutting resistance and the thermal conductivity of the sintered body forming the cutting blade of the cutting tool and including cubic boron nitride grains, and consequently found that a higher thermal conductivity of the sintered body forming the cutting blade of the cutting tool caused a higher cutting resistance and a greater damage to the cutting blade.
  • the inventors of the present invention exhaustively performed cutting of workpieces which were a plurality of nickel-based heat-resistant alloys different from each other in grain size of crystal grains, and consequently found that a coarser grain size of the crystal grains of the nickel-based heat-resistant alloy was accompanied by a higher cutting resistance during the cutting.
  • a nickel-based heat-resistant alloy was cut that was formed of crystal grains with a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13
  • the cutting tool reached the end of the life in a considerably short time due to fracture, before wear increased.
  • the nickel-based heat-resistant alloy is a material which does not easily soften when being cut.
  • increase of the thermal conductivity of the sintered body forming the cutting blade of the cutting tool is accompanied by increase of the cutting resistance. It is considered that the cutting edge fractures due to this.
  • the material for the cutting tool is often required to have high thermal conductivity for the purpose of preventing plastic deformation (thermal deformation) or thermal cracks of the cutting tool itself.
  • the inventors of the present invention found that, in the case of cutting a nickel-based heat-resistant alloy formed of crystal grains with a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13, increase of the thermal conductivity of the material for the cutting tool is accompanied by increase of a boundary damage of the cutting edge of the cutting blade and increase of the cutting resistance, and accordingly the cutting edge of the cutting blade is likely to fracture. Therefore, contrary to the conventional approach, the inventors tried decreasing the thermal conductivity of the sintered body including cubic boron nitride grains.
  • the inventors found that the grain size of the cubic boron nitride powder used as a material for the sintered body could be made finer and an inorganic compound such as TiN, TiC, TiAlN, or AlB 2 could be used as a binder to thereby decrease the thermal conductivity of the sintered body.
  • the cubic boron nitride powder has an average grain size of 1.5 ⁇ m or less.
  • crystal grains having lower thermal conductivity than cubic boron nitride grains were added to the sintered body to thereby suppress necking between cubic boron nitride grains in the sintered body and successfully decrease the thermal conductivity of the sintered body Accordingly, the temperature of the cutting edge of the tool when cutting a nickel-based heat-resistant alloy could be kept high, the workpiece was thus softened to exhibit decreased cutting resistance, and the boundary damage of the cutting edge of the cutting blade was reduced. Accordingly, fracture of the cutting edge of the cutting blade of the cutting tool can be suppressed. In this way, the present invention has been completed.
  • the thermal conductivity of the sintered body is less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , preferably less than 15 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 .
  • the thermal conductivity of the sintered body is preferably not less than 5 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 and less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , more preferably not less than 10 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 and less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , and still more preferably not less than 10 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 and less than 15 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 .
  • the thermal conductivity of the sintered body is determined in the following way. From the sintered body, a sample with a diameter of 18 mm and a thickness of 1 mm is cut as a sample to be used for measuring the thermal conductivity, and a laser-flash-method thermal constant measuring apparatus is used to measure the specific heat and the thermal diffusivity. The thermal conductivity is calculated by multiplying the thermal diffusivity by the specific heat and the density of the sintered body.
  • the sintered body in the present embodiment further includes a binder and different-type hard phase grains including at least one selected from the group consisting of silicon nitride, SiAlON, and alumina, as the hard phase grains other than the cubic boron nitride grains.
  • This sintered body thus further includes the different-type hard phase grains which are grains of at least one selected from the group consisting of silicon nitride, SiAlON, and alumina, the cubic boron nitride grains, and the binder, to thereby exhibit high fracture resistance when used for cutting a nickel-based heat-resistant alloy formed of crystal grains having a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13.
  • the sintered body thus has high fracture resistance in addition to high wear resistance. Since the sintered body includes the cubic boron nitride grains and additionally includes different-type hard phase grains which are grains of at least one selected from the group consisting of silicon nitride, SiAlON, and alumina, and which are different-type crystal grains lower in thermal conductivity than the cubic boron nitride grains, necking between cubic boron nitride grains in the sintered body is suppressed and the thermal conductivity of the sintered body is decreased.
  • different-type hard phase grains which are grains of at least one selected from the group consisting of silicon nitride, SiAlON, and alumina, and which are different-type crystal grains lower in thermal conductivity than the cubic boron nitride grains
  • a ratio V BN /V H of a volume V BN of the cubic boron nitride grains to a volume V H of the different-type hard phase grains is preferably not less than 0.5 and not more than 1.5.
  • This sintered body thus has a ratio V BN /V H of not less than 0.5 and not more than 1.5, as a ratio of a volume V BN of the cubic boron nitride grains to a volume V H of the different-type hard phase grains, to thereby have high fracture resistance in addition to high wear resistance.
  • the ratio V BN /V H is less than 0.5, the content of the cubic boron nitride grains having high hardness is relatively low, resulting in decrease of the hardness of the sintered body, which may cause decrease of the wear resistance of a cutting tool for which this sintered body is used.
  • the ratio V BN /V H is more than 1.5, the cubic boron nitride grains having high thermal conductivity are excessively present in the sintered body, which may make it impossible to have a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 .
  • a predetermined amount of the different-type hard phase grains in a powder state and a predetermined amount of the cubic boron nitride grains in a powder state are added and mixed before being sintered. It was confirmed that when X-ray diffraction was performed before and after sintering, there was no significant change in peak intensity ratio between the different-type hard phase grains and the cubic boron nitride grains and the volume ratio between the different-type hard phase grains and the cubic boron nitride grains added in the powder state was substantially maintained as it was in the sintered body.
  • X-ray diffraction of the sintered body is performed and a ratio V BN /V H of a volume V BN of the cubic boron nitride grains to a volume V H of the different-type hard phase grains can be calculated from the X-ray diffraction peak intensity ratio between the different-type hard phase grains and the cubic boron nitride grains.
  • a CP cross section polisher
  • SEM scanning electron microscope
  • EDX energy dispersive X-ray spectrometry
  • the SiAlON includes cubic SiAlON.
  • This sintered body thus includes cubic SiAlON which has low reactivity to the metal and higher hardness than those of ⁇ -SiAlON and ⁇ -SiAlON, to thereby have higher wear resistance.
  • the SiAlON further includes at least one of ⁇ -SiAlON and ⁇ -SiAlON, and a peak intensity ratio Rc of an intensity at an X-ray diffraction main peak of the cubic SiAlON to a sum of respective intensities at respective X-ray diffraction main peaks of the ⁇ -SiAlON, the ⁇ -SiAlON, and the cubic SiAlON is not less than 20% (the peak intensity ratio is hereinafter also referred to as peak intensity ratio Rc of the cubic SiAlON).
  • This sintered body thus includes the cubic SiAlON and at least one of ⁇ -SiAlON and ⁇ -SiAlON, and the ratio, in terms of the intensity at the X-ray diffraction main peak, of the cubic SiAlON to the sum of the -SiAlON, the ⁇ -SiAlON, and the cubic SiAlON is not less than 20%. Accordingly, the sintered body has high fracture resistance as well as high wear resistance.
  • Peak intensity ratio Rc of the cubic SiAlON is an index corresponding to the ratio of the cubic SiAlON to the different-type hard phase grains.
  • the peak intensity ratio Rc of the cubic SiAlON may be determined as follows.
  • the sintered body is surface-ground with a diamond abrasive formed of diamond abrasive grains passing a #400 sieve (a sieve with a mesh size of 38 ⁇ m).
  • a peak intensity Ic (311) of (311) plane which is a main peak of the cubic SiAlON, a peak intensity I ⁇ (201) of (201) plane which is a main peak of the ⁇ -SiAlON, and a peak intensity I ⁇ (200) of (200) plane which is a main peak of ⁇ -SiAlON can be determined.
  • the values of these peak intensities can be used to calculate peak intensity ratio Rc of the cubic SiAlON based on the following formula (I). If peak intensity ratio Rc of the cubic SiAlON is less than 20%, the hardness of the sintered body decreases, and the wear resistance may decrease.
  • the binder includes at least one kind of binder selected from the group consisting of at least one kind of element out of titanium (Ti), zirconium (Zr), aluminum (Al), nickel (Ni), and cobalt (Co), nitrides, carbides, oxides, carbonitrides, and borides of the elements, and solid solutions thereof.
  • the binder strongly bonds the different-type hard phase grains and the cubic boron nitride grains, and increases the fracture toughness of the sintered body.
  • the sintered body therefore has high fracture resistance.
  • a metal element such as Al, Ni, Co, an intermetallic compound such as TiAl, or a compound such as TiN, ZrN, TiCN, TiAlN, Ti 2 AlN, TiB 2 , AlB 2 , for example, is suitably used.
  • the different-type hard phase grains and the cubic boron nitride grains are strongly bonded.
  • the fracture toughness of the binder itself is high, the fracture toughness of the sintered body is accordingly high, and thus the fracture resistance of the sintered body is high.
  • the content of the hard-phase grains in the sintered body is preferably not less than 60 vol % and not more than 90 vol % (the content refers to the content of the cubic boron nitride grains when the cubic boron nitride grains are included as hard-phase grains, and refers to the total content of the different-type hard phase grains and the cubic boron nitride grains when the different-type hard phase grains and the cubic boron nitride grains are included as hard-phase grains; therefore, the content of hard-phase grains may be defined as the total content of the different-type hard phase grains and the cubic boron nitride grains regardless of whether the different-type hard phase grains are present or not, as the content of the different-type hard phase grains may be regarded as 0 vol % when the hard-phase grains do not include the different-type hard phase grains).
  • This sintered body has well-balanced high wear resistance and high fracture resistance. If the content of hard-phase grains (the total content of the different-type hard phase grains and the cubic boron nitride grains) is less than 60 vol %, the sintered body has a lower hardness, which may result in lower wear resistance. If the content of hard-phase grains (the total content of the different-type hard phase grains and the cubic boron nitride grains) is more than 90 vol %, the sintered body has a lower fracture toughness, which may result in lower fracture resistance.
  • a predetermined amount of the different-type hard phase grains in a powder state, a predetermined amount of the cubic boron nitride grains in a powder state, and a predetermined amount of the binder in a powder state are added and mixed before being sintered. It was confirmed that when X-ray diffraction was performed before and after sintering, there was no significant change in peak intensity ratio between the different-type hard phase grains, the cubic boron nitride grains, and the binder, and the volume ratio between the different-type hard phase grains, the cubic boron nitride grains, and the binder added in the powder state was substantially maintained as it was in the sintered body.
  • a CP or the like may be used to mirror polish a sintered-body cross section, observe the cross section with an SEM, examine constituent elements of crystal grains by means of EDX, and identify the different-type hard phase grains, the cubic boron nitride grains, and the binder to thereby determine an area ratio therebetween to be regarded as a volume ratio. In this way as well, the volume ratio between the different-type hard phase grains, the cubic boron nitride grains, and the binder included in the sintered body can be determined.
  • the sintered body has a Vickers hardness of preferably not less than 20 GPa, and more preferably not less than 22 GPa. This sintered body thus has a Vickers hardness of not less than 20 GPa, and therefore has high wear resistance. If the Vickers hardness is less than 20 GPa, the wear resistance may be low.
  • the Vickers hardness of the sintered body in the present embodiment may be measured as follows.
  • the sintered body embedded in a Bakelite resin is polished for 30 minutes with diamond abrasive grains of 9 ⁇ m and for 30 minutes with diamond abrasive grains of 3 ⁇ m.
  • a Vickers hardness tester is used to press a diamond indenter into the polished surface of the sintered body with a load of 10 kgf.
  • the Vickers hardness H VH0 is determined.
  • the length of a crack extending from the indentation is measured.
  • the fracture toughness is determined.
  • the nickel-based heat-resistant alloy is preferably Inconel® 718.
  • This sintered body also exhibits high fracture resistance in addition to high wear resistance when used for cutting Inconel® 718 formed of crystal grains with a coarse grain size represented by a grain size number of 5 or less defined by ASTM standard E112-13, which is a typical example of the nickel-based heat-resistant alloy.
  • Inconel® 718 is an alloy mainly including 50 to 55 mass % of nickel (Ni), 17 to 21 mass % of chromium (Cr), 4.75 to 5.50 mass % of niobium (Nb), 2.80 to 3.30 mass % of molybdenum (Mo), and about 12 to 24 mass % of iron (Fe), for example.
  • Inconel® 718 is excellent in high-temperature strength provided by an Nb compound generated through age-hardening, and used for aircraft jet engine and various high-temperature structural members. Meanwhile, in terms of cutting, Inconel® 718 is a difficult-to-cut material which promotes wear of the cutting tool due to high affinity with the tool material, and which is likely to cause fracture of the tool due to the large high-temperature strength of the workpiece.
  • the method of manufacturing the sintered body in the present embodiment is not particularly limited.
  • the method includes the step of preparing different-type hard phase powder, the step of mixing the different-type hard-phase powder, cubic boron nitride powder, and binder powder, and the sintering step. The method will hereinafter be described in the order of the steps.
  • ⁇ -SiAlON powder and c-SiAlON powder synthesized in the following way may be used, in addition to silicon nitride powder and alumina powder having an average grain size of 5 ⁇ m or less.
  • ⁇ -SiAlON represented by a chemical formula: Si 6-Z Al Z O Z N 8-Z (where z is larger than 0 and not more than 4.2) may be synthesized from silica (SiO 2 ), alumina (Al 2 O 3 ), and carbon (C) as starting materials, using the general carbon reduction nitriding method, in a nitrogen ambient at atmospheric pressure.
  • Powder of ⁇ -SiAlON may also be obtained by using a high-temperature nitriding synthesis method to which applied nitriding reaction of metal silicon in a nitrogen ambient at atmospheric pressure or more, as represented by the following formula (II).
  • Si powder (with an average grain size of 0.5 to 45 ⁇ m and a purity of 96% or more, more preferably 99% or more), SiO 2 powder (with an average grain size of 0.1 to 20 ⁇ m), and Al powder (with an average grain size of 1 to 75 ⁇ m) are weighed in accordance with a desired value of Z, and thereafter mixed with a ball mill or shaker mixer or the like, to thereby prepare material powder for synthesizing ⁇ -SiAlON.
  • AlN aluminum nitride
  • Al 2 O 3 alumina
  • the temperature at which ⁇ -SiAlON powder is synthesized is preferably 2300 to 2700° C.
  • the pressure of nitrogen gas filling a container in which ⁇ -SiAlON powder is synthesized is preferably 1.5 MPa or more.
  • a combustion synthesis apparatus or HIP (hot isostatic pressing) apparatus is suitable.
  • commercially available ⁇ -SiAlON powder and ⁇ -SiAlON may be used.
  • ⁇ -SiAlON powder and/or ⁇ -SiAlON powder may be treated at a temperature of 1800 to 2000° C. and a pressure of 40 to 60 GPa, to thereby cause phase transformation of a part thereof to cubic SiAlON, and accordingly obtain c-SiAlON powder including cubic SiAlON.
  • a shock pressure of approximately 40 GPa and a temperature of 1800 to 2000° C. may be used to obtain different-type hard phase powder in which cubic SiAlON and ⁇ -SiAlON and/or ⁇ -SiAlON are mixed.
  • the shock pressure and the temperature may be changed to control the ratio of the cubic SiAlON to the different-type hard phase grains.
  • powder of a binder which is at least one kind of binder selected from the group consisting of at least one kind of element out of titanium (Ti), zirconium (Zr), aluminum (Al), nickel (Ni), and cobalt (Co), nitrides, carbides, oxides, carbonitrides, and borides of the elements, and solid solutions thereof, is added and mixed.
  • binder powder powder of a metal element such as Al, Ni, Co having an average grain size of 0.01 to 1 ⁇ m, powder of an intermetallic compound such as TiAl having an average grain size of 0.1 to 20 ⁇ m, or powder of a compound such as TiN, ZrN, TiCN, TiAlN, Ti 2 AlN, TiB 2 , AlB 2 having an average grain size of 0.05 to 2 ⁇ m, for example, is preferably used.
  • 10 to 40 vol % of the binder powder is added, relative to the total amount of the different-type hard phase powder, the cubic boron nitride powder, and the binder powder.
  • balls made of silicon nitride or alumina of approximately ⁇ 3 to 10 mm may be used as media to perform ball-mill mixing for a short time of within 12 hours in a solvent such as ethanol, or perform mixing by means of a medialess mixing apparatus such as ultrasonic homogenizer or wet jet mill, to thereby obtain a slurry mixture in which the different-type hard phase powder, the cubic boron nitride powder, and the binder powder are uniformly dispersed.
  • the slurry mixture thus obtained is air-dried, or dried with a spray dryer or slurry dryer, or the like, to thereby obtain a powder mixture.
  • the shaped powder mixture is sintered by means of a high-pressure generator such as belt-type ultrahigh pressure press machine, under a pressure of 3 to 7 GPa and at a temperature of 1200 to 1800° C.
  • a high-pressure generator such as belt-type ultrahigh pressure press machine
  • the shaped powder mixture may undergo preliminary sintering to be compacted to a certain extent, which may then be sintered.
  • an SPS (spark plasma sintering) apparatus may be used to sinter the powder mixture under a pressure of 30 to 200 MPa and at a temperature kept at 1200 to 1600° C.
  • a cutting tool in another embodiment of the present invention is a cutting tool including the sintered body in the above-described first embodiment.
  • the cutting tool in the present embodiment thus includes the sintered body in the first embodiment, and therefore exhibits high fracture resistance when cutting a nickel-based heat-resistant alloy formed of crystal grains with a coarse grain size represented by a grain size number of 5 or less defined under ASTM standard E112-13.
  • the cutting tool has high fracture resistance in addition to high wear resistance.
  • the cutting tool in the present embodiment may suitably be used for cutting a difficult-to-work material such as heat-resistant alloy at a high speed.
  • the nickel-based heat-resistant alloy used for parts of an aircraft or automobile engine is a difficult-to-work material which exhibits a high cutting resistance due to its great high-temperature strength, and which is therefore likely to cause wear and/or fracture of the cutting tool.
  • the cutting tool in the present embodiment exhibits excellent wear resistance and fracture resistance even when cutting the nickel-based heat-resistant alloy.
  • the cutting tool used at a cutting speed of 100 m/min or more exhibits an excellent tool life.
  • ⁇ -silicon nitride powder (SN-F1 manufactured by Denka Company Limited, with an average grain size of 2 ⁇ m)
  • 13-SiAlON powder Z-2 manufactured by Zibo Hengshi Technology Development Co., Ltd., with an average grain size of 2 ⁇ m
  • ⁇ -alumina powder (TM-D manufactured by Taimei Chemicals Co., Ltd., with an average grain size of 0.1 ⁇ m) were used.
  • c-SiAlON powder synthesized in the following way was used as the different-type hard phase grains.
  • a mixture obtained by mixing 500 g of ⁇ -SiAlON powder and 9500 g of copper powder functioning as heat sink was placed in a steel pipe, and thereafter shock-compressed with an explosive of an amount which was set so that the temperature was 1900° C. and the shock pressure was 40 GPa, to thereby synthesize the c-SiAlON powder including cubic SiAlON.
  • the powder mixture in the steel pipe after being shock-compressed was removed, and acid-washed to remove the copper powder. In this way, the synthesized powder was obtained.
  • the peak intensity ratio Rc of the cubic SiAlON calculated from the above-indicated formula (I) was 95%.
  • the amount (vol %) of the added binder powder was equal to the volume ratio (vol %) of the binder to the total amount of the different-type hard phase grains, the cubic boron nitride grains, and the binder in the sintered body shown in Table 1.
  • the different-type hard phase powder and the cubic boron nitride powder were blended so that their volume ratio was equal to the ratio V BN /V H of the volume V BN of the cubic boron nitride grains to the volume V H of the different-type hard phase grains in the sintered body shown in Table 1.
  • Sample No. 1-14 was prepared by mixing only the cubic boron nitride powder and TiN powder as a binder, without adding the different-type hard phase powder.
  • fine cubic boron nitride powder SBN-F G-1 manufactured by Showa Denko KK., with an average grain size of 1 ⁇ m was used as the cubic boron nitride powder.
  • Sample No. 1-15 was prepared by mixing only the cubic boron nitride powder and Co powder (HMP manufactured by Umicore) as a binder, without adding the different-type hard phase powder.
  • HMP manufactured by Umicore the same cubic boron nitride powder as that of No. 1-1 to No. 1-13 was used.
  • the powder to be sintered of each of Samples No. 1-1 to No. 1-15 prepared in the above-described manner was vacuum-packed in a refractory metal capsule with a diameter of ⁇ 20 mm, and thereafter electrically heated to a temperature of 1500° C. while being pressurized to a pressure of 5 GPa by means of a belt-type ultrahigh pressure press, to thereby prepare a sintered body.
  • an FE-SEM field emission scanning electron microscope
  • EDX energy dispersive X-ray spectroscopy
  • the SEM image was image-processed with WinROOF manufactured by Mitani Corporation, to thereby determine the area ratio between the different-type hard phase grains, the cubic boron nitride grains, and the binder, and the area ratio was regarded as the volume ratio. In this way, the volume ratio between the different-type hard phase grains, the cubic boron nitride grains, and the binder included in the sintered body was determined. As a result of this, in any of respective sintered bodies of Samples No. 1-1 to No.
  • the ratio V BN /V H of the volume V BN of the cubic boron nitride grains to the volume V H of the different-type hard phase grains in the sintered body was substantially identical to the ratio of the volume of the cubic boron nitride powder to the volume of the different-type hard phase powder as blended. Moreover, in any of respective sintered bodies of Samples No. 1-1 to No.
  • the content of the hard-phase grains in the sintered body was substantially identical to the ratio of the hard-phase grains as blended (the total ratio of the different-type hard phase powder and the cubic boron nitride powder as blended) (vol %).
  • a sample to be used for measuring the hardness was cut and embedded in a Bakelite resin. After this, the sample was polished for 30 minutes with diamond abrasive grains of 9 ⁇ m and for 30 minutes with diamond abrasive grains of 3 ⁇ m.
  • a Vickers hardness tester HV-112 manufactured by Akashi was used to press a diamond indenter into a polished surface of the sample with a load of 10 kgf From the indentation formed by the pressing of the diamond indenter, the Vickers hardness H V10 was determined. Further, the length of a crack extending from the indentation was measured.
  • the sintered body was processed into the shape of the brazed insert of DNGA150412 (ISO model number), and the tool life of the brazed insert was evaluated by using the insert for turning of Inconel® 718 (manufactured by Daido-Special Metals Ltd.) with crystal grains having a coarse grain size represented by a grain size number of 5 defined by American Society for Testing and Materials (ASTM) standard E112-13.
  • ASTM American Society for Testing and Materials
  • the cutting conditions in the present Example are as follows.
  • the sintered body of Sample No. 1-7 having a thermal conductivity of 22 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 reached the end of the tool life when the cutting length reached 0.2 km
  • the sintered body of Sample No. 1-15 having a thermal conductivity of 35 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 reached the end of the tool life when the cutting length reached 0.1 km.
  • the sintered bodies of Samples No. 1-1 to No. 1-6 and No. 1-8 to No. 1-14 having a thermal conductivity of less than 20 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 reached the end of the tool life when the cutting length reached 0.3 to 1.0 km.
  • the tool life of these sintered bodies was considerably longer, namely 1.5 to 10 times as long as that of the sintered bodies of Sample No. 1-7 or 1-15.
  • the different-type hard phase grains forming the sintered body were ⁇ -silicon nitride grains and the Vickers hardness remained to be 21.0 GPa. As a result of this, this sample reached the end of the tool life due to wear when the cutting length reached 0.4 km.
  • the different-type hard phase grains forming the sintered body were ⁇ -SiAlON grains and the Vickers hardness remained to be 21.2 GPa. As a result of this, this sample reached the end of the tool life due to wear when the cutting length reached 0.4 km.
  • the fracture toughness was 4.8 MPa ⁇ m 1/2 .
  • the cutting edge of the tool fractured and thereby the sample reached the end of the tool life when the cutting length reached 0.3 km.
  • the thermal conductivity was 35 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 .
  • the temperature of the cutting edge of the tool decreased during cutting and thus the cutting resistance increased and a boundary damage of the cutting edge increased. Accordingly, the cutting edge of the tool fractured. Due to this, the sample reached the end of the tool life when the cutting length reached 0.1 km.
  • C-SiAlON powder which was synthesized through shock compression in a similar manner to Example 1 and in which cubic SiAlON had a peak intensity ratio Rc of 95% was used as different-type hard phase powder to be used for preparing respective sintered bodies of Samples No. 2-1 to No. 2-10.
  • the same cubic boron nitride powder (SBN-F G1-3 manufactured by Showa Denko K.K.) as that used for Samples No. 1-1 to No. 1-13 in Example 1 was used as cubic boron nitride powder of Samples No. 2-1 to No. 2-10.
  • the binder powder shown in Table 2 was added to 30 g in total of the different-type hard phase powder and the cubic boron nitride powder, so that the content of the binder powder to the total amount of the different-type hard phase powder and the cubic boron nitride powder was 20 vol %.
  • the different-type hard phase powder and the cubic boron nitride powder were blended so that the volume ratio therebetween was equal to the ratio V BN /V H of 1 of the volume V BN of the cubic boron nitride grains to the volume V H of the different-type hard phase grains in the sintered body.
  • TiCN powder TiN—TiC 50/50 manufactured by Japan New Metals Co., Ltd., with an average grain size of 1 ⁇ m
  • TiN powder TiN-01 manufactured by Japan New Metals Co., Ltd., with an average grain size of 1 ⁇ m
  • TiAl powder TiAl manufactured by KCM Corporation
  • Al powder 300F manufactured by Minalco Ltd.
  • Co powder HMP manufactured by Umicore
  • ZrN powder ZrN-1 manufactured by Japan New Metals Co., Ltd.
  • Ti 2 AlN powder with an average grain size of 1 ⁇ m
  • the ceramic component TiN, TiCN, Ti 2 AlN and the metal component Co or Al were blended at a ratio by mass of 2 (ceramic component) to 1 (metal component).
  • the powder to be sintered of each of Samples No. 2-1 to No. 2-10 prepared in the above-described manner was vacuum-packed in a refractory metal capsule with a diameter of ⁇ 20 mm, and thereafter electrically heated to a temperature of 1500° C. while being pressurized to a pressure of 5 GPa by means of a belt-type ultrahigh pressure press, to thereby prepare a sintered body.
  • the surface of the sintered body was surface-ground by means of a #400 diamond abrasive, and thereafter X-ray diffraction of the ground surface was performed by means of an X-ray diffractometer. From an obtained diffraction pattern, the peak intensity Ic (311) of (311) plane of the cubic SiAlON and the peak intensity I ⁇ (200) of (200) plane of the ⁇ -SiAlON were determined, and the peak intensity ratio Rc (Ic (311) /(Ic (311) +I ⁇ (200) ) ⁇ 100) was calculated. The results are shown in Table 2.
  • the volume ratio between the different-type hard phase grains, the cubic boron nitride grains, and the binder included in the sintered body was determined, in a similar manner to Example 1.
  • the ratio V BN /V H of the volume V BN of the cubic boron nitride grains to the volume V H of the different-type hard phase grains in the sintered body was substantially 1.
  • the content of the hard phase grains in the sintered body was approximately 80 vol %.
  • the sintered body was processed into the shape of the brazed insert of DNGA150412 (ISO model number), and the tool life of the brazed insert was evaluated by using the insert for turning of Inconel® 713C with crystal grains having a coarse grain size represented by a grain size number of 2 defined by ASTM standard E112-13. Under the following conditions, an external cylindrical turning test was conducted. A cutting length at which one of the flank face wear and the flank face fracture of the tool cutting edge reached 0.2 mm before the other was determined, and the determined cutting length was regarded as a tool life (km). The results are shown in Table 2. The life factor indicating whether the factor that caused the tool to reach the end of the tool life was wear or fracture is also shown in Table 2.
  • the cutting conditions in the present Example are as follows.
  • the sintered body had high fracture toughness. However, the sintered body had relatively high thermal conductivity. Therefore, the sintered body had a tool life corresponding to a cutting length of 0.5 km due to fracture.
  • the sintered body including cubic boron nitride grains include both the cubic boron nitride grains having excellent hardness and toughness and the ceramic grains having low thermal conductivity, to thereby provide an advantage that the sintered body is excellent in wear resistance when used for cutting a difficult-to-cut material such as nickel-based heat-resistant alloy which has high cutting resistance and which does not easily soften.
  • the sintered body provides a tool material improving the fracture resistance of the cutting edge of the cutting tool.
  • the sintered body exhibits excellent wear resistance and fracture resistance when used for cutting a difficult-to-cut material such as titanium (Ti) other than the heat-resistant alloy such as Inconel®, and is particularly applicable to high-speed cutting.
  • a difficult-to-cut material such as titanium (Ti) other than the heat-resistant alloy such as Inconel®

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