U.S. patent application number 15/300115 was filed with the patent office on 2017-06-22 for sintered body and cutting tool.
The applicant listed for this patent is Sumitomo Electric Industries, Ltd.. Invention is credited to Kentaro Chihara, Satoru Kukino.
Application Number | 20170173702 15/300115 |
Document ID | / |
Family ID | 56788557 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170173702 |
Kind Code |
A1 |
Chihara; Kentaro ; et
al. |
June 22, 2017 |
SINTERED BODY AND CUTTING TOOL
Abstract
A sintered body includes cubic boron nitride grains as hard
phase grains, and has a thermal conductivity of not less than 15
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1, for
cutting a nickel-based heat-resistant alloy formed of crystal
grains having a fine grain size represented by a grain size number
of more than 5 defined by ASTM standard E112-13. A cutting tool
includes this sintered body. Accordingly, the sintered body having
both high wear resistance and high fracture resistance, as well as
the cutting tool including the sintered body are provided.
Inventors: |
Chihara; Kentaro;
(Itami-shi, JP) ; Kukino; Satoru; (Itami-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Electric Industries, Ltd. |
Osaka-shi |
|
JP |
|
|
Family ID: |
56788557 |
Appl. No.: |
15/300115 |
Filed: |
February 16, 2016 |
PCT Filed: |
February 16, 2016 |
PCT NO: |
PCT/JP2016/054394 |
371 Date: |
September 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23B 27/20 20130101;
C22C 29/16 20130101; C04B 35/583 20130101; B23B 27/14 20130101 |
International
Class: |
B23B 27/14 20060101
B23B027/14; C04B 35/583 20060101 C04B035/583; C22C 29/16 20060101
C22C029/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2015 |
JP |
2015-037062 |
Claims
1. A sintered body comprising cubic boron nitride grains as hard
phase grains, and having a thermal conductivity of not less than 15
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1, for
cutting a nickel-based heat-resistant alloy formed of crystal
grains having a fine grain size represented by a grain size number
of more than 5 defined by American Society for Testing and
Materials standard E112-13.
2. The sintered body according to claim 1, wherein the sintered
body further comprises: 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.
3. The sintered body according to claim 2, wherein a ratio
V.sub.BN/V.sub.H of a volume V.sub.BN of the cubic boron nitride
grains to a volume V.sub.H of the different-type hard phase grains
is not less than 1 and not more than 6.
4. The sintered body according to claim 2 or 3, wherein the SiAlON
includes cubic SiAlON.
5. The sintered body according to claim 4, wherein the SiAlON
further includes at least one of .alpha.-SiAlON and .beta.-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
.alpha.-SiAlON, the .beta.-SiAlON, and the cubic SiAlON is not less
than 20%.
6. The sintered body according to claim 2, wherein the binder
includes 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.
7. The sintered body according to claim 1, wherein a content of the
hard phase grains in the sintered body is not less than 60 vol %
and not more than 90 vol %.
8. The sintered body according to claim 1, wherein the sintered
body has a Vickers hardness of not less than 22 GPa.
9. The sintered body according to claim 1, wherein the nickel-based
heat-resistant alloy is Inconel.RTM. 718.
10. A cutting tool comprising the sintered body as recited in claim
1.
Description
TECHNICAL FIELD
[0001] 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 fine grain size, and to a cutting tool including this
sintered body.
BACKGROUND ART
[0002] 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. However, the nickel-based heat-resistant alloy is a
material difficult to cut.
[0003] 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.
[0004] WO00/47537 (PTD 1) for example 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 (PTD 2) 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. Moreover,
Japanese Patent Laying-Open No. 2011-140415 (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 %.
CITATION LIST
Patent Document
[0005] PTD 1: WO00/47537
[0006] PTD 2: Japanese Patent Laying-Open No. 2000-226262
[0007] PTD 3: Japanese Patent Laying-Open No. 2011-140415
SUMMARY OF INVENTION
Technical Problem
[0008] 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. Particularly when the
cutting tool is used for cutting a nickel-based heat-resistant
alloy formed of crystal grains with a fine grain size, specifically
a grain size number of more than 5 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, in addition to normal wear of the flank face of the
cutting tool. Therefore, a sintered body exhibiting both high wear
resistance and high fracture resistance when used for cutting a
workpiece is required.
[0009] An object is therefore to provide a sintered body having
both high wear resistance and high fracture resistance, as well as
a cutting tool including this sintered body.
Solution to Problem
[0010] 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 not less than 15
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1, for
cutting a nickel-based heat-resistant alloy formed of crystal
grains having a fine grain size represented by a grain size number
of more than 5 defined by American Society for Testing and
Materials standard E112-13.
[0011] A cutting tool in another aspect of the present invention is
a cutting tool including the sintered body as described above.
Advantageous Effects of Invention
[0012] According to the foregoing, a sintered body having both high
wear resistance and high fracture resistance, as well as a cutting
tool including this sintered body can be provided.
DESCRIPTION OF EMBODIMENTS
Description of Embodiments of the Invention
[0013] 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 not less than 15
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1, for
cutting a nickel-based heat-resistant alloy formed of crystal
grains having a fine grain size represented by a grain size number
of more than 5 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 not less than 15 Wm.sup.-1K.sup.-1 and not more
than 40 Wm.sup.-1K.sup.-1, and therefore exhibits both high wear
resistance derived from the cubic boron nitride grains and high
fracture resistance when used for cutting a nickel-based
heat-resistant alloy which is formed of crystal grains having a
fine grain size represented by a grain size number of more than 5
defined by ASTM standard E112-13.
[0014] 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 both high wear resistance and
high fracture resistance when used for cutting a nickel-based
heat-resistant alloy formed of crystal grains having a fine grain
size represented by a grain size number of more than 5 defined by
ASTM standard E112-13.
[0015] Regarding the sintered body in the present embodiment, a
ratio V.sub.BN/V.sub.H of a volume V.sub.BN of the cubic boron
nitride grains to a volume V.sub.H of the different-type hard phase
grains may be not less than 1 and not more than 6. This sintered
body thus has a ratio V.sub.BN/V.sub.H of not less than 1 and not
more than 6, as a ratio of a volume V.sub.BN of the cubic boron
nitride grains to a volume V.sub.H of the different-type hard phase
grains, to thereby have both high wear resistance and high fracture
resistance.
[0016] Regarding the sintered body in the present embodiment, 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 .alpha.-SiAlON and .beta.-SiAlON, to thereby
have higher wear resistance.
[0017] The SiAlON may further include at least one of
.alpha.-SiAlON and .beta.-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 .alpha.-SiAlON, the .beta.-SiAlON, and the cubic
SiAlON may be not less than 20%. This sintered body thus includes
the cubic SiAlON, and at least one of .alpha.-SiAlON and
.beta.-SiAlON, and has a ratio of 20% or more of the cubic SiAlON
to the sum of the .alpha.-SiAlON, the .beta.-SiAlON, and the cubic
SiAlON, in term of the intensity at a main peak of X-ray
diffraction. Accordingly, the sintered body has both high wear
resistance and high fracture resistance.
[0018] Regarding the sintered body in the present embodiment, 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. In this sintered body, 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.
[0019] Regarding the sintered body in the present embodiment, 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.
[0020] Regarding the sintered body in the present embodiment, the
sintered body may have a Vickers hardness of not less than 22 GPa.
This sintered body thus has a Vickers hardness of not less than 22
GPa, and therefore has high wear resistance.
[0021] Regarding the sintered body in the present embodiment, the
nickel-based heat-resistant alloy may be Inconel.RTM. 718. This
sintered body also exhibits both high wear resistance and high
fracture resistance when used for cutting Inconel.RTM. 718 formed
of crystal grains with a fine grain size represented by a grain
size number of more than 5 defined by ASTM standard E112-13, which
is a typical example of the nickel-based heat-resistant alloy.
[0022] 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 both high wear resistance and
high fracture resistance when used for cutting a nickel-based
heat-resistant alloy which is formed of crystal grains having a
fine grain size represented by a grain size number of more than 5
defined by ASTM standard E112-13.
DETAILS OF EMBODIMENTS OF THE INVENTION
First Embodiment: Sintered Body
[0023] {Sintered Body}
[0024] 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 not less than 15
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1, for
cutting a nickel-based heat-resistant alloy formed of crystal
grains having a fine grain size represented by a grain size number
of more than 5 defined by American Society for Testing and
Materials (ASTM) standard E112-13. Crystal grains having a smaller
grain size number are coarser crystal grains. Regarding the
nickel-based heat-resistant alloy to be cut by means of the
sintered body in the present embodiment, the grain size number of 5
or less corresponds to a crystal grain size of about 50 .mu.m or
more. The sintered body in the present embodiment has a thermal
conductivity of not less than 15 Wm.sup.-1K.sup.-1 and not more
than 40 Wm.sup.-1K.sup.-1, and therefore exhibits both high wear
resistance and high fracture resistance when used for cutting a
nickel-based heat-resistant alloy which is formed of crystal grains
having a fine grain size represented by a grain size number of more
than 5 defined by ASTM standard E112-13.
[0025] In order to develop a sintered body exhibiting both high
wear resistance and high fracture resistance when used for cutting
a nickel-based heat-resistant alloy which is formed of crystal
grains having a fine grain size represented by a grain size number
of more than 5 defined by ASTM standard E112-13, the inventors of
the present invention initially examined the relation between
cutting resistance and damage to a cutting blade. 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. 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.
[0026] 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.
[0027] In the sintered body with a high content of cubic boron
nitride grains having the second highest thermal conductivity after
diamond grains, necking between the cubic boron nitride grains
occurs in the sintered body to form a three-dimensional mesh
structure. Therefore, the thermal conductivity increases through
this three-dimensional mesh structure. Particularly in the case
where the sintered body includes a metal binder such as cobalt (Co)
or aluminum (Al), as a binder of the cubic boron nitride grains,
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 Wm.sup.-1K.sup.-1.
[0028] 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.RTM. 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.degree. C., and
accordingly the workpiece at the contact portion is softened. Then,
the deforming stress decreases and accordingly the cutting
resistance decreases. However, when cutting is performed with a
cutting tool which is formed of a sintered body having a high
content of cubic boron nitride grains and having a
three-dimensional mesh structure of the grains, and which has high
cooling ability, it is considered that the temperature of the
cutting edge during cutting is kept at a low temperature, and
therefore, the workpiece is not softened and the cutting resistance
increases.
[0029] As set forth above, 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.
[0030] Further, 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. In particular, it was found that, when 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. In contrast, it was found that, when a nickel-based
heat-resistant alloy was cut which was formed of crystal grains
with a fine grain size represented by a grain size number of more
than 5 defined by ASTM standard E112-13, and which may be used for
heat resistant parts of a turbine disk of an aircraft engine or the
like required to have creep resistance, the depth of a damage to
the cutting blade of the cutting tool was smaller as compared with
the case where 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.
However, it was found that the aforementioned boundary damage
occurred and normal wear occurred to the tool flank face.
[0031] Generally, 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. However, 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 fine grain
size represented by a grain size number of more than 5 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.
[0032] As a result of this trial, 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.sub.2 could be used as a binder to
thereby decrease the thermal conductivity of the sintered body.
Preferably, the cubic boron nitride powder has an average grain
size of 1.5 .mu.m less.
[0033] Alternatively, silicon nitride, SiAlON, alumina, or the like
with crystal grains having lower thermal conductivity than cubic
boron nitride grains was added to the sintered body to thereby
obtain a thermal conductivity of the sintered body which was an
intermediate thermal conductivity between that of the conventional
ceramic tool and that of a cubic boron nitride tool, specifically a
thermal conductivity of not less than 15 Wm.sup.-1K.sup.-1 and not
more than 40 Wm.sup.-1K.sup.-1. It was found that a sintered body
could thus be obtained which exhibited both high wear resistance
and high fracture resistance when used for cutting a nickel-based
heat-resistant alloy formed of crystal grains with a fine grain
size represented by a grain size number or more than 5 defined by
ASTM standard E112-13, and accordingly the present invention was
completed.
[0034] In order for the sintered body in the present embodiment to
have both high wear resistance and high fracture resistance, the
sintered body includes cubic boron nitride grains and still has a
thermal conductivity of not less than 15 Wm.sup.-1K.sup.-1 and not
more than 40 Wm.sup.-1K.sup.-1, preferably not less than 20
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1, and more
preferably not less than 20 Wm.sup.-1K.sup.-1 and not more than 35
Wm.sup.-1K.sup.-1. If the thermal conductivity of the sintered body
is more than 40 Wm.sup.-1K.sup.-1, the temperature of the cutting
edge of the cutting tool formed of this sintered body may decrease
to become less than the softening temperature of the workpiece,
resulting in insufficient suppression of boundary damage to the
cutting edge of the cutting blade. If the thermal conductivity of
the sintered body is less than 15 Wm.sup.-1K.sup.-1, the cutting
temperature may become excessively high, resulting in promotion of
wear of the cutting tool formed of this sintered body.
[0035] 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.
[0036] Preferably, 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 both high wear
resistance and high fracture resistance when used for cutting a
nickel-based heat-resistant alloy formed of crystal grains having a
fine grain size represented by a grain size number of more than 5
defined by ASTM standard E112-13.
[0037] Regarding the sintered body in the present embodiment, a
ratio V.sub.BN/V.sub.H of a volume V.sub.BN of the cubic boron
nitride grains to a volume V.sub.H of the different-type hard phase
grains is preferably not less than 1 and not more than 6. This
sintered body thus has a ratio V.sub.BN/V.sub.H of not less than 1
and not more than 6, as a ratio of the volume of the cubic boron
nitride grains to the volume of the different-type hard phase
grains, to thereby have both high wear resistance and high fracture
resistance. If the ratio V.sub.BN/V.sub.H is less than 1, 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 formed of this sintered body. In contrast, if the
ratio V.sub.BN/V.sub.H is more than 6, 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 40 Wm.sup.-1K.sup.-1 or less.
[0038] Regarding the sintered body in the present embodiment, 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.
Therefore, X-ray diffraction of the sintered body is performed and
a ratio V.sub.BN/V.sub.H of a volume V.sub.BN of the cubic boron
nitride grains to a volume V.sub.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. Other than the above-described X-ray
diffraction, a CP (cross section polisher) (manufactured by JEOL
Ltd.) or the like may be used to mirror polish a sintered-body
cross section, observe the cross section with an SEM (scanning
electron microscope), examine constituent elements of crystal
grains by means of EDX (energy dispersive X-ray spectrometry), and
identify the different-type hard phase grains and the cubic boron
nitride grains, to thereby determine an area ratio therebetween to
be regarded as a volume ratio. In this way, the ratio
V.sub.BN/V.sub.H of a volume V.sub.BN of the cubic boron nitride
grains to a volume V.sub.H of the different-type hard phase grains
can also be calculated.
[0039] Regarding the sintered body in the present embodiment,
preferably 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 .alpha.-SiAlON and .beta.-SiAlON,
to thereby have higher wear resistance.
[0040] Preferably, the SiAlON further includes at least one of
.alpha.-SiAlON and .beta.-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 .alpha.-SiAlON, the .beta.-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 .alpha.-SiAlON and .beta.-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 .alpha.-SiAlON, the
.beta.-SiAlON, and the cubic SiAlON is not less than 20%.
Accordingly, the sintered body has both high wear resistance and
high fracture resistance.
[0041] 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 (hereinafter referred to as
#400 diamond abrasive) formed of diamond abrasive grains passing a
#400 sieve (a sieve with a mesh size of 38 .mu.m). From an X-ray
diffraction pattern obtained by measuring the ground surface by
means of characteristic X-ray of Cu-K.alpha., a peak intensity
Ic.sub.(311) of (311) plane which is a main peak of the cubic
SiAlON, a peak intensity I.alpha..sub.(201) of (201) plane which is
a main peak of the .alpha.-SiAlON, and a peak intensity
I.beta..sub.(200) of (200) plane which is a main peak of
.beta.-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.
Rc=Ic.sub.(311)/(Ic.sub.(311)+I.alpha..sub.(201)+I.beta..sub.(200)).time-
s.100 (I)
[0042] Regarding the sintered body in the present embodiment,
preferably 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. In this sintered
body, 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.
[0043] As this binder, a metal element such as Al, Ni, Co, an
intermetallic compound such as TiAl, or a compound such as TiN,
ZrN, TiCN, TiAlN, Ti.sub.2AlN, TiB.sub.2, AlB.sub.2, for example,
is suitably used. In the sintered body including this binder, the
different-type hard phase grains and the cubic boron nitride grains
are strongly bonded. In addition, in the case where 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.
[0044] Regarding the sintered body in the present embodiment, 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.
[0045] Regarding the sintered body in the present embodiment, 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. Other than the
above-described X-ray diffraction, 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.
[0046] Regarding the sintered body in the present embodiment, the
sintered body has a Vickers hardness of preferably not less than 22
GPa, and more preferably not less than 28 GPa. This sintered body
thus has a Vickers hardness of not less than 22 GPa, and therefore
has high wear resistance. If the Vickers hardness is less than 22
GPa, the wear resistance may be low.
[0047] 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 .mu.m and for 30 minutes with diamond abrasive
grains of 3 .mu.m. After this, 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. From the indentation formed by the
pressing of the diamond indenter, the Vickers hardness H.sub.V10 is
determined. Further, the length of a crack extending from the
indentation is measured. Based on the IF (Indentation-Fracture)
method under JIS R 1607: 2010 (Testing methods for fracture
toughness of fine ceramics at room temperature), the fracture
toughness is determined.
[0048] Regarding the sintered body in the present embodiment, the
nickel-based heat-resistant alloy is preferably Inconel.RTM. 718.
This sintered body also exhibits high fracture resistance in
addition to high wear resistance when used for cutting Inconel.RTM.
718 formed of crystal grains with a fine grain size represented by
a grain size number of more than 5 defined by ASTM standard
E112-13, which is a typical example of the nickel-based
heat-resistant alloy.
[0049] Inconel.RTM. 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.RTM. 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.RTM. 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.
[0050] {Method of Manufacturing Sintered Body}
[0051] The method of manufacturing the sintered body in the present
embodiment is not particularly limited. In order to efficiently
manufacture the sintered body having both high wear resistance and
high fracture resistance, 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.
[0052] The method will hereinafter be described in the order of the
steps.
[0053] Step of Preparing Different-Type Hard Phase Powder
[0054] As the different-type hard phase powder, .beta.-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 .mu.m or less.
[0055] .beta.-SiAlON represented by a chemical formula:
Si.sub.6-ZAl.sub.ZO.sub.ZN.sub.8-Z (where z is larger than 0 and
not more than 4.2) may be synthesized from silica (SiO.sub.2),
alumina (Al.sub.2O.sub.3), and carbon (C) as starting materials,
using the general carbon reduction nitriding method, in a nitrogen
ambient at atmospheric pressure.
[0056] Powder of .beta.-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).
3(2-0.5Z)Si+ZAl+0.5ZSiO.sub.2+(4-0.5Z)N.sub.2.fwdarw.Si.sub.6-ZAl.sub.ZO-
.sub.ZN.sub.8-Z (II)
[0057] Si powder (with an average grain size of 0.5 to 45 .mu.m and
a purity of 96% or more, more preferably 99% or more), SiO.sub.2
powder (with an average grain size of 0.1 to 20 .mu.m), and Al
powder (with an average grain size of 1 to 75 .mu.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 .beta.-SiAlON. At this time, other than the
above formula (II), aluminum nitride (AlN) and/or alumina
(Al.sub.2O.sub.3) may be combined appropriately as Al components.
The temperature at which .beta.-SiAlON powder is synthesized is
preferably 2300 to 2700.degree. C. Moreover, the pressure of
nitrogen gas filling a container in which .beta.-SiAlON powder is
synthesized is preferably 1.5 MPa or more. As a synthesis apparatus
which can endure such a gas pressure, a combustion synthesis
apparatus or HIP (hot isostatic pressing) apparatus is suitable.
Moreover, commercially available .alpha.-SiAlON powder and
.beta.-SiAlON may be used.
[0058] Subsequently, .alpha.-SiAlON powder and/or .beta.-SiAlON
powder may be treated at a temperature of 1800 to 2000.degree. 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. For example, in the
case where a shock compression process is used for the treatment
for causing the phase transformation, a shock pressure of
approximately 40 GPa and a temperature of 1800 to 2000.degree. C.
may be used to obtain different-type hard phase powder in which
cubic SiAlON and .alpha.-SiAlON and/or .beta.-SiAlON are mixed. At
this time, the shock pressure and the temperature may be changed to
control the ratio of the cubic SiAlON to the different-type hard
phase grains.
[0059] Step of Mixing Different-Type Hard Phase Powder, Cubic Boron
Nitride Powder, and Binder Powder
[0060] To the different-type hard phase powder prepared in the
above-described way and the cubic boron nitride powder with an
average grain size of 0.1 to 3 .mu.m, 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. As this binder powder,
powder of a metal element such as Al, Ni, Co having an average
grain size of 0.01 to 1 .mu.m, powder of an intermetallic compound
such as TiAl having an average grain size of 0.1 to 20 .mu.m, or
powder of a compound such as TiN, ZrN, TiCN, TiAlN, Ti.sub.2AlN,
TiB.sub.2, AlB.sub.2 having an average grain size of 0.05 to 2
.mu.m, for example, is preferably used. Preferably, 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. If the amount of the added binder powder is
less than 10 vol %, the fracture toughness of the sintered body is
lower, which may result in lower fracture resistance. If the amount
of the added binder powder is more than 40 vol %, the hardness of
the sintered body is lower, which may result in lower wear
resistance.
[0061] For mixing the powder, balls made of silicon nitride or
alumina of approximately .phi.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.
[0062] 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.
[0063] Sintering Step
[0064] After the powder mixture is shaped by means of a hydraulic
press or the like, 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.degree. C. Prior to sintering, the shaped powder
mixture may undergo preliminary sintering to be compacted to a
certain extent, which may then be sintered. Moreover, 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.degree. C.
Second Embodiment: Cutting Tool
[0065] 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 both high wear resistance and high fracture
resistance when cutting a nickel-based heat-resistant alloy formed
of crystal grains with a fine grain size represented by a grain
size number of more than 5 defined under ASTM standard E112-13. 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. However, the cutting tool
in the present embodiment exhibits excellent wear resistance and
fracture resistance even when cutting the nickel-based
heat-resistant alloy. In particular, when cutting Inconel.RTM. 718
which is used for parts of an aircraft engine, the cutting tool
used at a cutting speed of 100 m/min or more exhibits an excellent
tool life.
EXAMPLES
Example 1
[0066] As the different-type hard phase grains, .beta.-silicon
nitride powder (SN--F1 manufactured by Denka Company Limited, with
an average grain size of 2 .mu.m), .beta.-SiAlON powder (Z-2
manufactured by Zibo Hengshi Technology Development Co., Ltd., with
an average grain size of 2 .mu.m), and .alpha.-alumina powder (TM-D
manufactured by Taimei Chemicals Co., Ltd., with an average grain
size of 0.1 .mu.m) were used. Additionally c-SiAlON powder
synthesized in the following way was used as the different-type
hard phase grains.
[0067] As to preparation of the c-SiAlON powder, a mixture obtained
by mixing 500 g of .beta.-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.degree. 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. An X-ray
diffractometer (X' pert Powder manufactured by PANalytical,
Cu-K.alpha. ray, 2.theta.-.theta. method, voltage.times.current: 45
kV.times.40 A, range of measurement: 2.theta.=10 to 80.degree.,
scan step: 0.03.degree., scan rate: one step/sec) was used to
analyze the synthesized powder. Then, cubic SiAlON (JCPDS card:
01-074-3494) and .beta.-SiAlON (JCPDS card: 01-077-0755) were
identified. From an X-ray diffraction pattern of the synthesized
powder, the peak intensity Ic.sub.(311) of (311) plane which was a
main peak of the cubic SiAlON, and the peak intensity
I.beta..sub.(200) of (200) plane which was a main peak of
.beta.-SiAlON, were determined. The peak intensity ratio Rc of the
cubic SiAlON calculated from the above-indicated formula (I) was
95%.
[0068] For each of Samples No. 1-1 to No. 1-14, TiN powder (TiN-01
manufactured by Japan New Metals Co., Ltd., with an average grain
size of 1 .mu.m) was added as a binder at the ratio indicated in
Table 1, to a total amount of 30 g of the different-type hard phase
powder and the cubic boron nitride powder (SBN--F G1-3 manufactured
by Showa Denko K.K., with an average grain size of 2 .mu.m). For
Samples No. 1-3 and No. 1-4, both the .beta.-SiAlON powder and the
c-SiAlON powder were added at different ratios of the c-SiAlON
grains in the SiAlON included in the sintered body. For each of
Samples No. 1-1 to No. 1-16, 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. Moreover, for each of Samples No. 1-1 to No. 1-14, 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.sub.BN/V.sub.H of the volume V.sub.BN of the cubic boron nitride
grains to the volume V.sub.H of the different-type hard phase
grains in the sintered body shown in Table 1. The powder, after the
blending, of each of Samples No. 1-1 to No. 1-14 was placed in a
pot made of polystyrene with a capacity of 150 ml, together with 60
ml of ethanol and 200 g of silicon nitride balls of .phi.6 mm, and
subjected to ball mill mixing for 12 hours. A slurry mixture was
thus prepared. The slurry mixture removed from the pot was
air-dried, and thereafter passed through a sieve with a mesh
opening of 45 .mu.m. Powder to be sintered was thus prepared.
[0069] Moreover, Sample No. 1-15 was prepared by mixing only the
cubic boron nitride powder and TiN powder as a binder, without
adding the different-type hard phase powder. For Sample No. 1-15,
fine cubic boron nitride powder (SBN--F G-1 manufactured by Showa
Denko KK., with an average grain size of 1 .mu.m) was used as the
cubic boron nitride powder.
[0070] Moreover, Sample No. 1-16 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. For Sample No. 1-16, the same cubic boron nitride powder as
that of No. 1-1 to No. 1-14 was used.
[0071] The powder to be sintered of each of Samples No. 1-1 to No.
1-16 prepared in the above-described manner was vacuum-packed in a
refractory metal capsule with a diameter of .phi.20 mm, and
thereafter electrically heated to a temperature of 1500.degree. 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.
[0072] 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 the aforementioned X-ray
diffractometer. From an obtained diffraction pattern, the peak
intensity Ic.sub.(311) of (311) plane of the cubic SiAlON and the
peak intensity I.beta..sub.(200) of (200) plane of the
.beta.-SiAlON were determined, and the peak intensity ratio Rc of
the cubic SiAlON
(Rc=Ic.sub.(311)/(Ic.sub.(311)+I.beta..sub.(200)).times.100) was
calculated. As a result of this, there was substantially no change
from the value of the peak intensity ratio Rc of the cubic SiAlON
before sintering, to the value thereof after sintering, for any of
the sintered bodies of Samples No. 1-3 to No. 1-9 in which the
cubic SiAlON was added.
[0073] After a cross section of the sintered body was
mirror-polished with a CP, an FE-SEM (field emission scanning
electron microscope) was used to observe the structure of the
sintered body, and an EDX (energy dispersive X-ray spectroscopy)
system integrated with the FE-SEM was used to examine constituent
elements of the crystal grains in the structure of the sintered
body and thereby identify the different-type hard phase grains, the
cubic boron nitride grains, and the binder in an image of the SEM.
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.
1-14, the ratio V.sub.BN/V.sub.H of the volume V.sub.BN of the
cubic boron nitride grains to the volume V.sub.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. 1-16, the content of the hard-phase
grains in the sintered body (the total content of the
different-type hard phase grains and the cubic boron nitride
grains) (vol %) 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 %).
[0074] From the sintered body, a sample with a diameter of 18 mm
and a thickness of 1 mm was cut as a sample to be used for
measuring the thermal conductivity, and a laser-flash-method
thermal constant measuring apparatus (LFA447 manufactured by
NETZSCH) was used to measure the specific heat and the thermal
diffusivity. The thermal conductivity was calculated by multiplying
the thermal diffusivity by the specific heat and the density of the
sintered body. The results are shown in Table 1.
[0075] From the sintered body, 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 .mu.m and for 30 minutes with diamond abrasive grains of 3
.mu.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.
[0076] From the indentation formed by the pressing of the diamond
indenter, the Vickers hardness H.sub.V10 was determined. Further,
the length of a crack extending from the indentation was measured.
Further, the length of a crack extending from the indentation was
measured and, based on the IF method under JIS R 1607: 2010
(Testing methods for fracture toughness of fine ceramics at room
temperature), the fracture toughness value was determined. The
results are shown in Table 1.
[0077] Next, 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.RTM. 718 (manufactured by Daido-Special Metals Ltd.)
with crystal grains having a fine grain size represented by a grain
size number of 9 defined by American Society for Testing and
Materials (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 1. 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 1.
[0078] <Cutting Conditions>
[0079] The cutting conditions in the present Example are as
follows. [0080] workpiece: Inconel.RTM. 718 (manufactured by
Daido-Special Metals Ltd., solution heat-treated and age-hardened
material, with a Rockwell hardness HRC (a diamond cone with a tip
radius of 0.2 mm and a tip angle of 120.degree. was used to apply a
load of 150 kgf) corresponding to 44, and with a grain size
represented by a grain size number of 9 defined by ASTM standard
E112-13) [0081] tool shape: DNGA150412 (ISO model number) [0082]
cutting edge shape: chamfer angle--20.degree..times.width 0.1 mm
[0083] cutting speed: 200 m/min [0084] depth of cut: 0.3 mm [0085]
feed rate: 0.2 mm/rev [0086] wet condition (water soluble oil)
TABLE-US-00001 [0086] TABLE 1 Sample No. 1-1 1-2 1-3 1-4 1-5 1-6
1-7 1-8 1-9 different-type hard .beta.- .beta.- .beta.- .beta.- c-
c- c- c- c- phase grains silicon SiAlON SiAlON, SiAlON, SiAlON
SiAlON SiAlON SiAlON SiAlON nitride c-SiAlON c-SiAlON content of
hard 80 80 80 80 80 80 80 80 80 phase grains (vol %) content of 20
20 20 20 20 20 20 20 20 binder (vol %) ratio V.sub.BN/V.sub.H 3 3 3
3 0.8 1 3 6 6.5 peak intensity -- 0 15 20 90 90 90 90 90 ratio Rc
(%) of cubic SiAlON thermal conductivity 35 32 31 30 12 15 25 38 43
(W m.sup.-1 K.sup.-1) physical Vickers 23.7 24.1 24.5 25.2 22.3
22.9 31.2 35.3 33.0 properties hardness of (GPa) sintered fracture
5.7 5.8 6.0 6.2 5.5 5.7 7.5 7.8 6.4 body toughness (MPa m.sup.1/2)
cutting cutting 0.6 0.6 0.7 1.5 0.2 0.8 2.4 1.0 0.2 perfor- length
(km) mance life factor wear wear wear wear wear wear wear fracture
fracture notes EX EX EX EX CE EX EX EX CE Sample No. 1-10 1-11 1-12
1-13 1-14 1-15 1-16 different-type hard .alpha.- .alpha.- .alpha.-
.alpha.- .alpha.- none none phase grains alumina alumina alumina
alumina alumina content of hard 95 90 60 55 80 70 80 phase grains
(vol %) content of 5 10 40 45 20 30 20 binder (vol %) ratio
V.sub.BN/V.sub.H 3 3 3 3 3 -- -- peak intensity -- -- -- -- -- --
-- ratio Rc (%) of cubic SiAlON thermal conductivity 35 30 18 16 20
25 50 (W m.sup.-1 K.sup.-1) physical Vickers 32.5 30.3 22.3 21.5
24.8 29.5 38.0 properties hardness of (GPa) sintered fracture 4.7
5.3 5.8 6.5 5.5 5.2 7.3 body toughness (MPa m.sup.1/2) cutting
cutting 0.3 0.6 0.8 0.4 0.8 0.4 0.2 perfor- length (km) mance life
factor fracture fracture wear wear wear fracture fracture notes EX
EX EX EX EX EX CE EX: Example CE: Comparative Example
[0087] Referring to Table 1, the sintered bodies of Samples No.
1-5, No. 1-9, and No. 1-16 having a thermal conductivity of less
than 15 Wm.sup.-1K.sup.-1 or more than 40 Wm.sup.-1K.sup.-1 reached
the end of the tool life when the cutting length reached 0.2 km.
The sintered bodies of Samples No. 1-1 to No. 1-4, No. 1-6 to No.
1-8, and No. 1-10 to No. 1-15 having a thermal conductivity of not
less than 15 Wm.sup.-1K.sup.-1 and not more than 40
Wm.sup.-1K.sup.-1 reached the end of the tool life when the cutting
length reached 0.3 to 2.4 km, and the tool life of these sintered
bodies was considerably longer, namely 1.5 to 12 times as long as
that of the sintered bodies of Sample No. 1-5, 1-9, or 1-16.
[0088] As to Sample No. 1-1, the different-type hard phase grains
forming the sintered body were .beta.-silicon nitride grains and
the Vickers hardness remained to be 23.7 GPa. As a result of this,
this sample reached the end of the tool life due to wear when the
cutting length reached 0.6 km. Sample No. 1-1 had a shorter life
than Sample No. 1-4.
[0089] As to Sample No. 1-2, the different-type hard phase grains
forming the sintered body were .beta.-SiAlON grains and the Vickers
hardness remained to be 24.1 GPa. As a result of this, this sample
reached the end of the tool life due to wear when the cutting
length reached 0.6 km. Sample No. 1-2 had a shorter life than
Sample No. 1-4.
[0090] As to Sample No. 1-3, while the different-type hard phase
grains forming the sintered body included cubic SiAlON grains, the
peak intensity ratio Rc of the cubic SiAlON was an insufficient
ratio of 15% and the Vickers hardness remained to be 24.5 GPa. As a
result of this, this sample reached the end of the tool life due to
wear when the cutting length reached 0.7 km. Sample No. 1-3 had a
shorter life than Sample No. 1-4.
[0091] As to Sample No. 1-5, because of a low ratio
V.sub.BN/V.sub.H of 0.8 of the volume V.sub.BN of the cubic boron
nitride grains to the volume V.sub.H of the different-type hard
phase grains forming the sintered body, the thermal conductivity
was a low thermal conductivity of 12 Wm.sup.-1K.sup.-1. This sample
reached the end of the tool life due to wear when the cutting
length reached 0.2 km.
[0092] As to Sample No. 1-9, because of a high ratio
V.sub.BN/V.sub.H of 6.5 of the volume V.sub.BN of the cubic boron
nitride grains to the volume V.sub.H of the different-type hard
phase grains forming the sintered body, the thermal conductivity
was a high thermal conductivity of 43 Wm.sup.-1K.sup.-1. As a
result of this, 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
0.2 km.
[0093] As to Sample No. 1-10, because of a high content of 95 vol %
of the hard phase grains in the sintered body (the total content of
the different-type hard phase grains and the cubic boron nitride
grains), the fracture toughness was 4.7 MPam.sup.1/2. As a result
of this, 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. Sample No. 1-10 had a shorter life than Sample No.
1-11.
[0094] As to Sample No. 1-13, because of a low content of 55 vol %
of the hard phase grains in the sintered body (the total content of
the different-type hard phase grains and the cubic boron nitride
grains), the Vickers hardness remained to be 21.5 GPa. As a result
of this, the sample reached the end of the tool life due to wear
when the cutting length reached 0.4 km. Sample No. 1-13 had a
shorter life than Sample No. 1-12.
[0095] As to Sample No. 1-15, since fine cubic boron nitride grains
were used and TiN powder was used as a binder, the thermal
conductivity was 25 Wm.sup.-1K.sup.-1 and the tool life was longer
than that of Sample No. 1-16. However, since the sintered body did
not include different-type hard phase grains, the toughness was low
and this sample reached the end of the tool life due to fracture
when the cutting length reached 0.4 km.
[0096] In contrast, as to Samples No. 1-4, No. 1-6 to No. 1-8, No.
1-12, and No. 1-14 for which the peak intensity ratio Rc of cubic
SiAlON in the different-type hard phase grains forming the sintered
body, the ratio V.sub.BN/V.sub.H of the volume V.sub.BN of the
cubic boron nitride grains to the volume V.sub.H of the
different-type hard phase grains forming the sintered body, and/or
the content of the hard phase grains in the sintered body (the
total content of the different-type hard phase grains and the cubic
boron nitride grains) were controlled so that they were in
respective appropriate ranges, the well-balanced Vickers hardness
and fracture toughness were obtained. As a result of this, the
cutting length at which the sample reached the end of the tool life
due to wear or fracture could be extended to 0.8 km or more.
[0097] In particular, as to Sample No. 1-7 including cubic boron
nitride grains, it was found that this sample having excellent
Vickers hardness and fracture toughness accordingly had a longer
tool life than Samples No. 1-1 including silicon nitride grains and
Sample No. 1-14 including alumina grains.
[0098] As for Sample No. 1-16 including no different-type hard
phase grains, the thermal conductivity was 50 Wm.sup.-1K.sup.-1. As
a result of this, 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
0.2 km.
Example 2
[0099] 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. 1-14 in Example 1 was
used as cubic boron nitride powder of Samples No. 2-1 to No.
2-10.
[0100] For each 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, the cubic boron nitride powder
and the binder powder was 20 vol %. At this time, for each of
Samples No. 2-1 to No. 2-10, 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.sub.BN/V.sub.H of 3 of
the volume V.sub.BN of the cubic boron nitride grains to the volume
V.sub.H of the different-type hard phase grains in the sintered
body. Moreover, as the binder powder, TiCN powder (TiN--TiC 50/50
manufactured by Japan New Metals Co., Ltd., with an average grain
size of 1 .mu.m), TiN powder (TiN-01 manufactured by Japan New
Metals Co., Ltd., with an average grain size of 1 .mu.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.), and Ti.sub.2AlN powder (with an average grain size of 1
.mu.m) were used. For Samples No. 2-8 to No. 2-10, the ceramic
component TiN, TiCN, Ti.sub.2AlN and the metal component Co or Al
were blended at a ratio by mass of 2 (ceramic component) to 1
(metal component).
[0101] For each of Samples No. 2-1 to No. 2-10, the powder obtained
after the blending was placed in a pot made of polystyrene with a
capacity of 150 ml, together with 60 ml of ethanol and 200 g of
silicon nitride balls of .phi.6 mm, and subjected to ball mill
mixing for 12 hours. A slurry was thus prepared. The slurry removed
from the pot was air-dried, and thereafter passed through a sieve
with a mesh opening of 45 .mu.m Powder to be sintered was thus
prepared.
[0102] 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 .phi.20 mm, and
thereafter electrically heated to a temperature of 1500.degree. 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.
[0103] 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.sub.(311) of (311) plane of the cubic SiAlON and the peak
intensity I.beta..sub.(200) of (200) plane of the .beta.-SiAlON
were determined, and the peak intensity ratio Rc
(Ic.sub.(311)/(Ic.sub.(311)+I.beta..sub.(200)).times.100) was
calculated. The results are shown in Table 2.
[0104] After a cross section of the sintered body was
mirror-polished with a CP, 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. As a result of this, in any of the
sintered bodies of Samples No. 2-1 to No. 2-10, the ratio
V.sub.BN/V.sub.H of the volume V.sub.BN of the cubic boron nitride
grains to the volume V.sub.H of the different-type hard phase
grains in the sintered body was substantially 3. Moreover, the
content of the hard phase grains in the sintered body (the total
content of the different-type hard phase grains and the cubic boron
nitride grains) was approximately 80 vol %.
[0105] From the sintered body, a sample with a diameter of 18 mm
and a thickness of 1 mm was cut as a sample to be used for
measuring the thermal conductivity, and the thermal conductivity of
respective sintered bodies of Samples No. 2-1 to No. 2-10 was
calculated in a similar manner to Example 1. The results are shown
in Table 2.
[0106] From the sintered body, a sample to be used for measuring
the hardness was cut, and the Vickers hardness H.sub.V10 and the
fracture toughness value of respective sintered bodies of Samples
No. 2-1 to No. 2-10 were determined in a similar manner to Example
1. The results are shown in Table 2.
[0107] Next, 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 Hastelloy.RTM. X with crystal grains having a fine grain size
represented by a grain size number of 6 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.
[0108] <Cutting Conditions>
[0109] The cutting conditions in the present Example are as
follows. [0110] workpiece: Hastelloy.RTM. X (manufactured by Haynes
International, Inc., solid solution heat-treated material, with a
Brinell hardness HB corresponding to 170, and with a grain size
represented by a grain size number of 6 defined by ASTM standard
E112-13) [0111] tool shape: DNGA150412 (ISO model number) [0112]
cutting edge shape: chamfer angle--20.degree..times.width 0.1 mm
[0113] cutting speed: 200 m/min [0114] depth of cut: 0.2 mm [0115]
feed rate: 0.1 mm/rev [0116] wet condition (water soluble oil)
TABLE-US-00002 [0116] TABLE 2 Sample No. 2-1 2-2 2-3 2-4 2-5 2-6
2-7 2-8 2-9 2-10 binder TiN TiCN TiAl Al Co ZrN Ti.sub.2AlN TiN,
TiCN, TiN, Co Al Al peak intensity 90 84 73 52 61 80 74 71 70 66
ratio Rc (%) of cubic SiAlON thermal conductivity 25 27 22 38 36 18
30 28 32 30 (W m.sup.-1 K.sup.-1) physical Vickers 31.2 32.3 30.5
28.5 27.5 30.8 30.3 29.8 31.1 30.2 properties hardness (GPa) of
sintered fracture 7.5 7.0 7.9 8.3 8.4 6.7 8.0 7.8 8.0 8.3 body
toughness (MPa m.sup.1/2) cutting cutting length 0.7 0.7 0.8 0.6
0.6 0.7 0.9 1.0 1.5 1.5 performance (km) life factor fracture
fracture wear wear wear fracture wear fracture wear wear notes EX
EX EX EX EX EX EX EX EX EX EX: Example
[0117] Referring to Table 2, the sintered bodies of Samples No. 2-1
to No. 2-10 with a thermal conductivity of not less than 15
Wm.sup.-1K.sup.-1 and not more than 40 Wm.sup.-1K.sup.-1 had a long
tool life corresponding to a cutting length of 0.6 to 1.5 km.
[0118] As to Samples No. 2-4 and No. 2-5 in which the metal
component was used as the binder, 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 0.6 km due to fracture.
[0119] In contrast, as to Samples No. 2-1 to No. 2-3, No. 2-6, and
No. 2-7 in which the binder was the ceramic or intermetallic
binder, the well-balanced thermal conductivity and Vickers hardness
could be obtained. As a result, the cutting length at which the end
of the tool life was reached due to wear or fracture could be
extended to 0.7 km or more.
[0120] As for Samples No. 2-8 to No. 2-10 in which both the ceramic
component and the metal component were used as the binder, the
sintered bodies exhibited excellent Vickers hardness and fracture
toughness. Therefore, the cutting length at which the end of the
tool life was reached was 1.0 km or more.
[0121] It should be construed that the embodiments and examples
disclosed herein are given by way of illustration in all respects,
not by way of limitation. It is intended that the scope of the
present invention is defined by claims, not by the description
above, and encompasses all modifications and variations equivalent
in meaning and scope to the claims.
INDUSTRIAL APPLICABILITY
[0122] As seen from the foregoing, 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. In addition, the sintered body
provides a tool material improving the fracture resistance of the
cutting edge of the cutting tool. While the effects produced when
cutting Inconel.RTM. are disclosed herein in connection with the
Examples, 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.RTM., and is particularly applicable to high-speed
cutting.
* * * * *