U.S. patent application number 13/634209 was filed with the patent office on 2013-10-24 for surface-coated cutting tool.
This patent application is currently assigned to SUMITOMO ELECTRIC HARDMETAL CORP.. The applicant listed for this patent is Erika Iwai, Hideaki Kanaoka, Chikako Kojima, Hiroyuki Morimoto, Yoshio Okada, Anongsack Paseuth. Invention is credited to Erika Iwai, Hideaki Kanaoka, Chikako Kojima, Hiroyuki Morimoto, Yoshio Okada, Anongsack Paseuth.
Application Number | 20130279998 13/634209 |
Document ID | / |
Family ID | 47138932 |
Filed Date | 2013-10-24 |
United States Patent
Application |
20130279998 |
Kind Code |
A9 |
Kojima; Chikako ; et
al. |
October 24, 2013 |
SURFACE-COATED CUTTING TOOL
Abstract
A surface-coated cutting tool excellent in wear resistance is
provided. The surface-coated cutting tool of the present invention
includes a base material and a coating formed on the base material.
The coating includes an inner layer and an outer layer. The inner
layer is a single layer or a multilayer stack constituted of two or
more layers made of at least one element selected from the group
consisting of group IVa elements, group Va elements, group VIa
elements in the periodic table, Al, and Si, or a compound of at
least one element selected from this group and at least one element
selected from the group consisting of carbon, nitrogen, oxygen, and
boron. The outer layer includes .alpha.-aluminum oxide as a main
component and exhibits an equivalent peak intensity PR(024) of a
(024) plane of x-ray diffraction of larger than 1.3.
Inventors: |
Kojima; Chikako; (Itami-shi,
JP) ; Okada; Yoshio; (Itami-shi, JP) ;
Kanaoka; Hideaki; (Itami-shi, JP) ; Morimoto;
Hiroyuki; (Itami-shi, JP) ; Paseuth; Anongsack;
(Itami-shi, JP) ; Iwai; Erika; (Itami-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kojima; Chikako
Okada; Yoshio
Kanaoka; Hideaki
Morimoto; Hiroyuki
Paseuth; Anongsack
Iwai; Erika |
Itami-shi
Itami-shi
Itami-shi
Itami-shi
Itami-shi
Itami-shi |
|
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
SUMITOMO ELECTRIC HARDMETAL
CORP.
Itami-shi
JP
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130045057 A1 |
February 21, 2013 |
|
|
Family ID: |
47138932 |
Appl. No.: |
13/634209 |
Filed: |
December 5, 2011 |
PCT Filed: |
December 5, 2011 |
PCT NO: |
PCT/JP2011/078087 PCKC 00 |
371 Date: |
September 11, 2012 |
Current U.S.
Class: |
407/119 |
Current CPC
Class: |
Y10T 428/252 20150115;
C23C 16/34 20130101; C23C 16/403 20130101; Y10T 407/27 20150115;
C23C 16/45523 20130101; C23C 30/005 20130101; C23C 28/044
20130101 |
Class at
Publication: |
407/119 |
International
Class: |
B23B 27/14 20060101
B23B027/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2011 |
JP |
2011-105061 |
May 10, 2011 |
JP |
2011-105062 |
May 10, 2011 |
JP |
2011-105063 |
Claims
1. A surface-coated cutting tool comprising a base material and a
coating formed on the base material, said coating including at
least an inner layer and an outer layer, said inner layer being a
single layer or a multilayer stack constituted of two or more
layers made of at least one element selected from the group
consisting of group IVa elements, group Va elements, group VIa
elements in the periodic table, Al, and Si, or a compound of at
least one element selected from the group consisting of group IVa
elements, group Va elements, group VIa elements in the periodic
table, Al, and Si and at least one element selected from the group
consisting of carbon, nitrogen, oxygen, and boron, and said outer
layer including .alpha.-aluminum oxide as a main component and
exhibiting an equivalent peak intensity PR(024) of a (024) plane of
x-ray diffraction of larger than 1.3.
2. The surface-coated cutting tool according to claim 1, wherein
said equivalent peak intensity PR(024) is larger than 2.0.
3. The surface-coated cutting tool according to claim 1, wherein
the (024) plane of said alumina layer exhibits a maximum peak of
x-ray diffraction.
4. The surface-coated cutting tool according to claim 1, wherein a
(012) plane of said outer layer exhibits a maximum peak intensity
of x-ray diffraction.
5. The surface-coated cutting tool according to claim 1, wherein
said outer layer includes .alpha.-aluminum oxide crystal grains, at
least 50% of .alpha.-aluminum oxide crystal grains located in a
surface of said outer layer in a cross section of said
surface-coated cutting tool cut along a plane including a normal to
a surface of said coating satisfies a condition that a tangent
intersection angle between intersecting tangents is not less than
100.degree. and not more than 170.degree., where one of the
intersecting tangents extends from a deepest point of a depression
formed by one combination of two said .alpha.-aluminum oxide
crystal grains adjacent to each other among three said
.alpha.-aluminum oxide crystal grains adjacent to each other and
located in the surface of said outer layer, and the other of the
intersecting tangents extends from a deepest point of a depression
formed by the other combination of two said .alpha. aluminum oxide
crystal grains adjacent to each other among said three
.alpha.-aluminum oxide crystal grains.
6. The surface-coated cutting tool according to claim 1, wherein
said outer layer includes .alpha.-aluminum oxide crystal grains, at
least 65% of .alpha.-aluminum oxide crystal grains located in a
surface of said outer layer in a cross section of said
surface-coated cutting tool cut along a plane including a normal to
a surface of said coating satisfies a condition that a tangent
intersection angle between intersecting tangents is not less than
100.degree. and not more than 170.degree., where one of the
intersecting tangents extends from a deepest point of a depression
formed by one combination of two said .alpha.-aluminum oxide
crystal grains adjacent to each other among three said
.alpha.-aluminum oxide crystal grains adjacent to each other and
located in the surface of said outer layer, and the other of the
intersecting tangents extends from a deepest point of a depression
formed by the other combination of two said .alpha. aluminum oxide
crystal grains adjacent to each other among said three
.alpha.-aluminum oxide crystal grains.
7. The surface-coated cutting tool according to claim 1, wherein
said outer layer includes .alpha.-aluminum oxide crystal grains, at
least 80% of .alpha.-aluminum oxide crystal grains located in a
surface of said outer layer in a cross section of said
surface-coated cutting tool cut along a plane including a normal to
a surface of said coating satisfies a condition that a tangent
intersection angle between intersecting tangents is not less than
100.degree. and not more than 170.degree., where one of the
intersecting tangents extends from a deepest point of a depression
formed by one combination of two said .alpha.-aluminum oxide
crystal grains adjacent to each other among three said
.alpha.-aluminum oxide crystal grains adjacent to each other and
located in the surface of said outer layer, and the other of the
intersecting tangents extends from a deepest point of a depression
formed by the other combination of two said .alpha. aluminum oxide
crystal grains adjacent to each other among said three
.alpha.-aluminum oxide crystal grains.
8. The surface-coated cutting tool according to claim 1, wherein
said outer layer exhibits an equivalent peak intensity PR(110) of a
(110) plane of x-ray diffraction and an equivalent peak intensity
PR(012) of a (012) plane of x-ray diffraction that are both larger
than 1.
9. The surface-coated cutting tool according to claim 1, wherein
said outer layer includes .alpha.-aluminum oxide crystal grains,
and at least 30% of .alpha.-aluminum oxide crystal grains that are
located in a surface of said outer layer in a cross section of said
surface-coated cutting tool cut along a plane including a normal to
a surface of said coating and are observed at a magnification of
10000 satisfies a condition that a radius of an inscribed circle
abutting on a surface protrusion of one said .alpha.-aluminum oxide
crystal grain is not less than 3 mm.
10. The surface-coated cutting tool according to claim 1, wherein
said outer layer includes .alpha.-aluminum oxide crystal grains,
and at least 50% of .alpha.-aluminum oxide crystal grains that are
located in a surface of said outer layer in a cross section of said
surface-coated cutting tool cut along a plane including a normal to
a surface of said coating and are observed at a magnification of
10000 satisfies a condition that a radius of an inscribed circle
abutting on a surface protrusion of one said .alpha.-aluminum oxide
crystal grain is not less than 3 mm.
11. The surface-coated cutting tool according to claim 1, wherein
said outer layer includes .alpha.-aluminum oxide crystal grains,
and at least 70% of .alpha.-aluminum oxide crystal grains that are
located in a surface of said outer layer in a cross section of said
surface-coated cutting tool cut along a plane including a normal to
a surface of said coating and are observed at a magnification of
10000 satisfies a condition that a radius of an inscribed circle
abutting on a surface protrusion of one said .alpha.-aluminum oxide
crystal grain is not less than 3 mm.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface-coated cutting
tool including a base material and a coating formed on the base
material.
BACKGROUND ART
[0002] A surface-coated cutting tool used for cutting steel, cast
iron and the like generally includes a base material made of a
tungsten-carbide-based cemented carbide and a coating covering the
surface of the base material. The coating is a stack of two or more
layers such as Ti compound layer and alumina layer. Here, the
alumina layer which forms the coating has advantages of excellent
oxidation resistance and heat-resistant stability as well as high
hardness. Meanwhile, the alumina layer has a disadvantage that it
has a relatively lower strength and is brittle than the Ti compound
layer. Due to this disadvantage, chipping may occur to the cutting
edge or wear of the cutting edge may increase, for example, when
the cutting tool cuts a steel or cast iron under severe conditions
such as high-speed cutting or high-speed and high-feed-rate
cutting.
[0003] Trying to overcome this disadvantage of the alumina layer,
Japanese Patent Laying-Open No. 11-138308 (PTL 1) for example
provides different crystal structures formed respectively in the
upper portion and the lower portion of the alumina layer.
Specifically, the lower portion of the alumina layer is formed of a
longitudinal diversified crystal structure and the upper portion of
the alumina layer is formed of a longitudinal uniform crystal
structure.
[0004] Further, according to Japanese Patent Laying-Open No.
2002-120105 (PTL 2), when an alumina layer is to be formed, a gas
to which H.sub.2S gas and SO.sub.2 gas are added is introduced and
further an increased amount of CO.sub.2 is introduced to form the
alumina layer. Accordingly, the alumina layer is formed that has a
crystal structure mainly constituted of .alpha.-crystal and
satisfies the following relations. Namely, the ratio between x-ray
diffraction peak intensity I(030) of the (030) plane that is a main
peak and x-ray diffraction peak intensity I(104) of the (104) plane
satisfies I(030)/I(104)>1, and x-ray diffraction peak intensity
I(012) of the (012) plane satisfies I(012)/I(030)>1.
[0005] Here, the .alpha.-alumina with its orientation in the (030)
plane has a higher crystallographic density than the
.alpha.-alumina with its orientation in the (104) plane. Therefore,
the x-ray diffraction peak intensity of the (104) plane can be
increased to thereby form the .alpha.-alumina crystal formed of
high-density crystal, as described above.
[0006] Japanese Patent Laying-Open No. 07-216549 (PTL 3) discloses
an alumina layer having a single-phase .alpha.-structure textured
in the (110) direction of x-ray diffraction so that texture
coefficient TC (hkl) has a value larger than 1.5. This alumina
layer has good adherence to the underlying base material and
therefore has an advantage that the wear resistance is
excellent.
[0007] European Patent Publication No. 1655387A1 (PTL 4) discloses
an alumina layer having a texture coefficient TC (110) of the (110)
plane of more than 2 and a texture coefficient of a crystal plane
other than the (110) plane of less than 1.5. Further, according to
PTL 4, an alumina contact layer which is a lower layer of the
alumina layer also contains Al so that the bonding strength between
the alumina contact layer and the alumina layer is increased.
[0008] Japanese National Patent Publication No. 09-507528 (PTL 5)
discloses an alumina layer having a thickness of 2.5 to 25 .mu.m
and a crystal grain size of 0.5 to 4 .mu.m. This alumina layer has
a texture coefficient TC of larger than 2.5 and has a single-phase
.alpha.-structure textured in the (104) direction. The alumina
layer having such a crystal structure exhibits a property that it
is excellent in wear resistance and toughness.
[0009] Japanese Patent Laying-Open No. 10-156606 (PTL 6) discloses
a surface-coated cutting tool including a base material with its
surface coated with an inner layer which is further covered with an
alumina layer. According to PTL 6, in addition to a non-oxidizing
gas component which is a main component, an oxidizing gas is
further introduced to form the inner layer. Accordingly, the (110)
plane of the alumina layer exhibits a maximum x-ray diffraction
peak intensity, and lattice stripes of the alumina layer and the
inner layer continue at the interface therebetween.
[0010] As an approach for improving the strength of the alumina
layer other than those explained above in connection with PTLs 1 to
6, there is also a technique of adjusting the thickness and the
surface roughness of the alumina layer as well as the average grain
size of grains constituting the alumina layer. For example,
according to Japanese Patent Laying-Open No. 62-228305 (PTL 7), the
alumina layer has a thickness of 0.5 to 5 .mu.m and a surface
roughness of not more than 1 .mu.m so that the strength and the
adherence of the alumina layer are increased.
[0011] Further, WO1995/019457 (PTL 8) discloses an alumina layer
having a thickness of 2.5 to 25 .mu.m and a grain size of its
constituent grains of 0.5 to 4 .mu.m. This alumina layer has a
single-phase .alpha.-structure textured in the direction of the
(104) plane. Japanese Patent Laying-Open No. 2002-205205 (PTL 9)
also discloses an alumina layer with its thickness adjusted to 2.5
.mu.m or less by using alumina grains having an average grain size
of 2 .mu.m or less. An alumina layer having such a thickness and
such a grain size can be formed to thereby enhance the toughness of
the surface-coated cutting tool.
CITATION LIST
Patent Literature
[0012] PTL 1: Japanese Patent Laying-Open No. 11-138308 [0013] PTL
2: Japanese Patent Laying-Open No. 2002-120105 [0014] PTL 3:
Japanese Patent Laying-Open No. 07-216549 [0015] PTL 4: European
Patent Publication No. 1655387A1 [0016] PTL 5: Japanese National
Patent Publication No. 09-507528 [0017] PTL 6: Japanese Patent
Laying-Open No. 10-156606 [0018] PTL 7: Japanese Patent Laying-Open
No. 62-228305 [0019] PTL 8: WO1995/019457 [0020] PTL 9: Japanese
Patent Laying-Open No. 2002-205205
SUMMARY OF INVENTION
Technical Problem
[0021] The alumina layers formed by the above-described methods of
PTLs 1 to 9, however, do not have a sufficient strength and the
coating is likely to wear when used for cutting. Further, the
conventional technique varies the conditions under which the
alumina layer is formed, machines the alumina layer, or forms a
stack of multiple alumina layers to thereby reduce the roughness
and the size of the grains constituting the alumina layer. However,
the alumina layer has an insufficient strength and is likely to
wear.
[0022] The present invention has been made in view of the present
circumstances as described above, and an object of the invention is
to provide a surface-coated cutting tool excellent in wear
resistance.
Solution to Problem
[0023] The inventors of the present invention have conducted
thorough studies of the crystal orientation of .alpha.-alumina
which forms the alumina layer to find that the equivalent peak
intensity of the (024) plane, which is perpendicular to the crystal
plane of the material forming the base material for the alumina
layer, can be increased to thereby improve the strength of the
alumina layer, and completed the present invention. Further, the
surface of the alumina layer has depressions/protrusions formed due
to .alpha.-aluminum oxide crystal grains. It has been found that
the angle between intersecting tangents drawn respectively from the
deepest points of depressions (the angle is hereinafter also
referred to as "tangent intersection angle") of the
depressions/protrusions can be increased to thereby allow the
alumina layer (hereinafter also referred to as "outer layer") to
horizontally grow relative to the base material, allow the outer
layer to have a dense structure, and improve the strength.
[0024] Further, it has been found that the balance of the
equivalent peak intensity of the (012) plane which is a crystal
plane parallel to the (024) plane of the outer layer and the
equivalent peak intensity of the (110) plane which is a crystal
plane perpendicular to the (024) plane can be made larger than one,
to thereby enhance the strength and the adherence of the alumina
layer.
[0025] The inventors of the present invention have also focused on
the smoothness of the surface of the .alpha.-aluminum oxide crystal
grains and found that a higher smoothness (namely a larger surface
R) of the surface of the .alpha.-aluminum oxide crystal grains can
provide a higher adhesion resistance of the coating.
[0026] Specifically, a surface-coated cutting tool of the present
invention includes a base material and a coating formed on the base
material. The coating includes at least an inner layer and an outer
layer. The inner layer is a single layer or a multilayer stack
constituted of two or more layers made of at least one element
selected from the group consisting of group IVa elements, group Va
elements, group VIa elements in the periodic table, Al, and Si, or
a compound of at least one element selected from the group
consisting of group IVa elements, group Va elements, group VIa
elements in the periodic table, Al, and Si and at least one element
selected from the group consisting of carbon, nitrogen, oxygen, and
boron. The outer layer includes .alpha.-aluminum oxide as a main
component and exhibits an equivalent peak intensity PR(024) of a
(024) plane of x-ray diffraction of larger than 1.3.
[0027] Preferably, the equivalent peak intensity PR(024) is larger
than 2.0. Preferably, the alumina layer has the (024) plane
exhibiting a maximum peak of x-ray diffraction.
[0028] Preferably, the outer layer has a (012) plane exhibiting a
maximum peak intensity of x-ray diffraction.
[0029] Preferably, the outer layer includes .alpha.-aluminum oxide
crystal grains, and at least 50% of .alpha.-aluminum oxide crystal
grains located in a surface of the outer layer in a cross section
of the surface-coated cutting tool cut along a plane including a
normal to a surface of the coating satisfies a condition that a
tangent intersection angle between intersecting tangents is not
less than 100.degree. and not more than 170.degree., where one of
the intersecting tangents extends from a deepest point of a
depression formed by one combination of two .alpha.-aluminum oxide
crystal grains adjacent to each other among three .alpha.-aluminum
oxide crystal grains adjacent to each other and located in the
surface of the outer layer, and the other of the intersecting
tangents extends from a deepest point of a depression formed by the
other combination of two .alpha.-aluminum oxide crystal grains
adjacent to each other among the three .alpha.-aluminum oxide
crystal grains.
[0030] Preferably, the outer layer exhibits an equivalent peak
intensity PR(110) of a (110) plane of x-ray diffraction and an
equivalent peak intensity PR(012) of a (012) plane of x-ray
diffraction that are both larger than 1.
[0031] Preferably, the outer layer includes .alpha.-aluminum oxide
crystal grains, and at least 30% of .alpha.-aluminum oxide crystal
grains that are located in a surface of the outer layer in a cross
section of the surface-coated cutting tool cut along a plane
including a normal to a surface of the coating and are observed at
a magnification of 10000 satisfies a condition that a radius
(surface R) of an inscribed circle abutting on a surface protrusion
of one .alpha.-aluminum oxide crystal grain is not less than 3
mm.
Advantageous Effects of Invention
[0032] The surface-coated cutting tool of the present invention is
configured in the above-described manner to thereby enable the wear
resistance to be increased.
BRIEF DESCRIPTION OF DRAWINGS
[0033] FIG. 1 shows an image, observed with a field emission
scanning electron microscope, of a surface and its vicinity of an
outer layer in a cross section cut along a plane including a normal
to the surface of a coating of a surface-coated cutting tool.
[0034] FIG. 2 shows an image, observed with a field emission
scanning electron microscope, of a surface and its vicinity of an
outer layer in a cross section cut along a plane including a normal
to the surface of a coating of a surface-coated cutting tool.
DESCRIPTION OF EMBODIMENTS
[0035] In the following, the present invention will be described in
detail. It is noted that the thickness of a layer or the thickness
of a coating of the present invention is measured with an optical
microscope or scanning electron microscope (SEM), and the
composition of each layer forming the coating is measured with an
energy dispersive x-ray spectroscopy (EDS) apparatus or the
like.
[0036] <Surface-Coated Cutting Tool>
[0037] A surface-coated cutting tool of the present invention
includes a base material and a coating formed on the base material.
The surface-coated cutting tool of the present invention having
such a basic structure can be used highly advantageously as, for
example, a drill, an end-mill, an indexable insert for milling, or
machining, a metal-slitting saw, a gear cutting tool, a reamer, a
tap, a cutting insert for pin-milling of a crankshaft, or the
like.
[0038] A rake face which is a constituent part of the surface of
the surface-coated cutting tool of the present invention refers to
a face that contacts swarf of a workpiece when cutting work is
being done. Such a rake face preferably has a chip breaker in a
protruded or uneven shape. The chip breaker is provided to thereby
curl and break the swarf into fine fragments of an appropriate
size. Therefore, the swarf can be prevented from being caught and
interfering the cutting work. It is noted that the chip breaker may
not necessarily be formed, and the effects of the present invention
are not lost even if the chip breaker is not provided.
[0039] <Base Material>
[0040] As the base material of the surface-coated cutting tool of
the present invention, any conventionally known base material which
is known as a base material of such a cutting tool may be used
without being particularly limited. For example, cemented carbide
(including, for example, WC-based cemented carbide, the one
containing WC and Co, and the one containing WC and Co and
additionally a carbonitride of Ti, Ta, Nb or the like), cermet
(having TiC, TiN, TiCN or the like as a main component), high-speed
steel, ceramic (such as titanium carbide, silicon carbide, silicon
nitride, aluminum nitride, aluminum oxide, and a mixture thereof),
cubic boron nitride sintered body, diamond sintered body, and the
like, may be examples of such a base material. In the case where a
cemented carbide is used as such a base material, the cemented
carbide may include free carbon or abnormal phase called .eta.
phase in its structure to still provide the effects of the present
invention.
[0041] It is noted that these base materials may have respective
surfaces reformed. For example, in the case of cemented carbide, a
.beta.-free layer may be formed in its surface. In the case of
cermet, a surface-hardened layer may be formed. Even in such a case
where the surface is reformed, the effects of the present invention
are still exhibited.
[0042] <Coating>
[0043] The coating of the present invention includes at least an
inner layer and an outer layer. The inner layer is a single layer
or a multilayer stack constituted of two or more layers and the
single layer or the multilayer stack is made of at least one
element selected from the group consisting of group IVa elements,
group Va elements, group VIa elements in the periodic table, Al,
and Si, or a compound of at least one element selected from the
group consisting of group IVa elements, group Va elements, group
VIa elements in the periodic table, Al, and Si and at least one
element selected from the group consisting of carbon, nitrogen,
oxygen, and boron. The outer layer includes .alpha.-aluminum oxide
as a main component and exhibits an equivalent peak intensity PR of
a (024) plane of x-ray diffraction of larger than 1.3.
[0044] The plane index of the (024) plane and that of the (012)
plane represent the same direction, and the arrangement of atoms of
the (024) plane corresponds to a half of the (012) plane.
Therefore, the equivalent peak intensity of the (024) plane can be
increased so that it is larger than 1.3, to allow a greater number
of atoms to be aligned in the direction perpendicular to the base
material. Thus, the strength of the alumina layer can be increased.
A coating having such an alumina layer is excellent in wear
resistance and exhibits excellent performance that fracture is less
likely to occur.
[0045] Regarding the outer layer, preferably the (012) plane
exhibits a maximum peak intensity of x-ray diffraction.
[0046] The plane index of the (024) plane represents the same
direction as the (012) plane, and the arrangement of atoms of the
(024) plane corresponds to a half of the (012) plane. Therefore,
the equivalent peak intensity of the (024) plane can be increased
so that it is larger than 1.3, to allow a greater number of atoms
to be aligned in the direction perpendicular to the base material.
Thus, the strength of the outer layer can be increased. Moreover,
in the outer layer, the (012) plane exhibits a maximum peak
intensity of x-ray diffraction, and therefore, the arrangement of
atoms in the direction perpendicular to the base material is
strongest and the strength of the alumina layer can be enhanced. A
coating having such an outer layer is excellent in wear resistance
and exhibits excellent performance that fracture is less likely to
occur.
[0047] Regarding the outer layer, preferably both the equivalent
peak intensity PR(110) of the (110) plane of the x-ray diffraction
and the equivalent peak intensity PR(012) of the (012) plane of
x-ray diffraction are larger than 1. Accordingly, atoms are
arranged in the direction in which .alpha.-aluminum oxide grows and
the direction perpendicular thereto, and thus the strength and the
adherence of the outer layer can be increased. The coating having
such an outer layer is excellent in wear resistance and exhibits
excellent performance that fracture is less likely to occur.
[0048] Such a coating of the present invention includes an
embodiment in which the coating covers the whole surface of the
base material, includes an embodiment in which the coating
partially fails to be formed, and further includes an embodiment in
which the manner of stacking layers of the coating is different in
a part of the coating. Further, the coating of the present
invention preferably has a thickness of the whole coating of not
less than 2 .mu.m and not more than 25 .mu.m. If the thickness is
less than 2 .mu.m, the wear resistance may be deteriorated. If the
thickness is larger than 25 .mu.m, the adherence to the base
material and the fracture resistance may be deteriorated. A
particularly preferred thickness of such a coating is not less than
3 .mu.m and not more than 20 .mu.m. In the following, each of the
constituent layers of such a coating will be described.
[0049] Regarding the present invention, the coating preferably
includes a binder layer, an inner layer, an alumina binder layer,
an outer layer, and a state indication layer in this order from the
base-material side. In the following, each of the layers
constituting the coating will be described in the order from the
one on the base-material side.
[0050] <Binder Layer>
[0051] The coating of the present invention preferably includes a
binder layer (a layer abutting on the base material) between the
base material and the inner layer, and the binder layer is
preferably made of a nitride of Ti. The binder layer with such a
composition has high adherence to the base material and can prevent
the coating from entirely peeling off even under harsh cutting
conditions. Such a binder layer can be formed to obtain adherence
which is sufficient for enduring cutting even when a compressive
residual stress is exerted on at least one layer of the coating.
The thickness of the binder layer is preferably not less than 0.05
.mu.m and not more than 1 .mu.m.
[0052] <Inner Layer>
[0053] The coating of the present invention preferably includes at
least one inner layer. The inner layer is a single layer or a
multilayer stack constituted of two or more layers made of at least
one element selected from the group consisting of group IVa
elements, group Va elements, group VIa elements in the periodic
table, Al, and Si, or a compound of at least one element selected
from the group consisting of group IVa elements, group Va elements,
group VIa elements in the periodic table, Al, and Si and at least
one element selected from the group consisting of carbon, nitrogen,
oxygen, and boron. The inner layer containing nitrogen and the
former group of elements is excellent in toughness and has an
advantage that the coating is less likely to be broken even if the
thickness is increased. In contrast, the inner layer containing
carbon and nitrogen and the former group of elements can improve
the crater wear resistance. Further, the inner layer containing
oxygen is excellent in anti oxidation and adhesion resistance and
is therefore preferred. It is noted that the inner layer is not
limited to an inner layer made of a compound, and includes an inner
layer made of a single one of group IVa elements, group Va
elements, group VIa elements in the periodic table, Al, and Si.
[0054] The inner layer is preferably made of at least one element
selected from the group consisting of Cr, Al, Ti, and Si or a
compound of at least one element selected from this group and at
least one element selected from the group consisting of carbon,
nitrogen, oxygen, and boron. The inner layer is more preferably a
layer including TiCN as a main component. "Including TiCN as a main
component" here means that 90% by mass or more of TiCN is included,
and preferably means that the inner layer is made of TiCN only
except for inevitable impurities. The atomic ratio between the
elements included in such a TiCN (carbonitride of Ti) includes
various conventionally known atomic ratios and the atomic ratio
here is not particularly limited.
[0055] In the case where the compound of the present invention is
expressed by a chemical formula such as TiN, the atomic ratio
includes various conventionally known atomic ratios if the atomic
ratio is not particularly limited, and is not necessarily limited
to those in the stoichiometric range only. For example, in the case
where the compound is simply expressed as "TiCN", the atomic ratio
between "Ti" and "C" and "N" is not limited to 50:25:25 only.
Further, in the case where the compound is expressed as "TiN" as
well, the atomic ratio between "Ti" and "N" is not limited to 50:50
only. These atomic ratios include various conventionally known
atomic ratios.
[0056] The inner layer preferably has an average thickness of not
less than 2 .mu.m and not more than 20 .mu.m. The inner layer
satisfying this condition can appropriately keep the balance
between the wear resistance and the fracture resistance. If the
thickness of the inner layer is larger than 20 .mu.m, the fracture
resistance deteriorates, which may not be preferred in some cases.
If the thickness of the inner layer is less than 2 .mu.m, wear of
the coating increases in a high-speed cutting process, which is not
preferred.
[0057] <Alumina Binder Layer>
[0058] The coating of the present invention preferably includes an
alumina binder layer between the inner layer and the outer layer
which is described below. The alumina binder layer is provided to
thereby increase the adherence force between the inner layer and
the outer layer and make it less likely that the outer layer peels
off.
[0059] Regarding the alumina binder layer, in order to increase the
adherence force between the inner layer and the outer layer, the
alumina binder layer preferably has a considerably fine acicular
structure in its surface. An example of the alumina binder layer
may be a TiB.sub.xN.sub.y (where x and y represent an atomic ratio
and satisfy 0.001.ltoreq.x/(x+y).ltoreq.0.2) layer located directly
on the inner layer.
[0060] Further, such an alumina binder layer may also include an
element included in other constituent layers of the coating of the
present invention (particularly an element included in the layers
abutting on the alumina binder layer). Such an alumina binder layer
preferably has a thickness of not less than 0.05 .mu.m and not more
than 1 .mu.m. If the thickness is larger than 1 .mu.m, the wear
resistance deteriorates, which may not be preferred in some cases.
If the thickness is less than 0.05 .mu.m, sufficient adherence
between the alumina binder layer and the outer layer may not be
exhibited in some cases.
[0061] <Outer Layer>
[0062] The coating of the present invention is characterized in
that it includes at least an outer layer, and preferably includes
the outer layer between a state indication layer, which is
described later herein, and the alumina binder layer. Such an outer
layer includes .alpha.-aluminum oxide having an .alpha.-crystal
structure as a main component, and therefore exhibits good
performance against oxidative wear in a high-speed cutting process
and contributes to improvement of the wear resistance. Here,
"including .alpha.-aluminum oxide as a main component" means that
the outer layer includes 50% by mass or more of .alpha.-aluminum
oxide, and preferably the outer layer is made of .alpha.-aluminum
oxide only except for inevitable impurities. Such an outer layer
may also include zirconium, chromium, or the like in addition to
.alpha.-aluminum oxide. .alpha.-aluminum oxide is advantageous in
that it is generally excellent in wear resistance in a high-speed
cutting process. It is noted that the crystal structure of the
outer layer can be identified by means of x-ray diffraction.
[0063] The above-described outer layer is characterized in that the
equivalent peak intensity PR(024) of the (024) plane of x-ray
diffraction is larger than 1.3. Conventionally, in some cases, the
(012) plane perpendicular to the plane direction of the base
material has been focused on as an index defining the crystal
structure forming the alumina layer. Unlike the present invention,
however, the (024) plane has not been focused on in an attempt to
study its optimum equivalent peak intensity.
[0064] According to the present invention, the (024) plane of x-ray
diffraction has been focused on and it has been found that an
equivalent peak intensity PR(024) of the (024) plane of x-ray
diffraction that is larger than 1.3 allows the outer layer
including alumina as a main component to have excellent strength.
The plane index of the (024) plane and that of the (012) plane
represent the same direction, and the arrangement of atoms of the
(024) plane corresponds to a half of the (012) plane. Therefore,
the equivalent peak intensity of the (024) plane can be increased
to thereby increase the number of atoms aligned perpendicularly to
the base material. Thus, the atomic density of the outer layer is
increased and the strength of the outer layer is enhanced. The
equivalent peak intensity PR(024) is preferably larger than 2. In
contrast, if the equivalent peak intensity PR(024) is 1.3 or less,
the strength of the outer layer cannot be enhanced. While the
reason for this has not been clarified, it may be due to the fact
that the atomic density is not necessarily made high.
[0065] In the outer layer of the present invention, the (012) plane
exhibits a maximum peak intensity of x-ray diffraction and
accordingly the outer layer has excellent strength. Further, the
outer layer of the present invention provides an equivalent peak
intensity PR(110) and an equivalent peak intensity PR(012) of
larger than 1 and accordingly the outer layer has excellent
strength and adhesion resistance.
[0066] The (104) plane is also a crystal plane perpendicular to the
base material. According to ASTM File No. 10-173 (Powder
Diffraction File Published by JCPDS International Center for
Diffraction Data), the standard diffraction intensity ratio of the
(024) plane is lower than the standard diffraction intensity ratio
of the (012) plane and the (104) plane that are perpendicular to
the base material. Therefore, it would be more effective, for
enhancement of the strength of the outer layer, to increase the
diffraction intensity of the (024) plane, rather than increasing
the diffraction intensity of the (104) plane.
[0067] Here, PR(024) represents a relative intensity of the x-ray
diffraction peak intensity from the (024) plane of the coating
actually measured by means of x-ray diffraction, with respect to
the isotropic grain x-ray peak intensity indicated in the ASTM
data. Namely, a greater width of PR(024) means that the x-ray peak
intensity from the (024) plane is stronger than other peak
intensities and the orientation is in the direction of (024).
[0068] The above-described PR(024), PR(110), and PR(012) are
calculated in the following manner. For the outer layer of the
surface-coated cutting tool, a Cu K.alpha..sub.1 (wavelength
.lamda.=1.5405 A) x-ray source is used. By the 2.theta.-.theta.
scan x-ray diffraction method, respective x-ray diffraction
intensities of the eight planes, namely the (012), (104), (110),
(113), (024), (116), (124), and (030) planes are measured. Based on
the (hkl) planes defined by the following formulas, the intensities
are calculated. As these eight crystal planes, reflection planes
providing main peaks with a peak intensity of 30 or more indicated
in ASTM File No. 10-173 are employed.
PR(024)={I(024)/I.sub.0(024)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
PR(110)={I(110)/I.sub.0(110)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
PR(012)={I(012)/I.sub.0(012)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
[0069] In the formulas above, I(hkl) represents the actually
measured x-ray diffraction intensity of the (hkl) plane.
I.sub.0(hkl) is the x-ray diffraction intensity indicated in ASTM
File No. 10-173, and represents the x-ray diffraction intensity
from the (hkl) plane of isotropically oriented powder grains.
[0070] In the outer layer of the present invention, preferably the
(024) plane exhibits a maximum peak of x-ray diffraction. Thus, the
ratio of (024) crystal planes is high in the outer layer, and
accordingly, the outer layer represented by the plane index of the
same direction as the (012) plane and having a high atomic density
can be formed.
[0071] Such an outer layer preferably has a thickness of not less
than 0.5 .mu.m and not more than 15 .mu.m, and more preferably the
lower limit of the thickness is 2 .mu.m and the upper limit of the
thickness is 8 .mu.m. If the thickness is larger than 15 .mu.m,
peeling from the tip of the cutting edge or the boundary of the
cutting edge is likely to occur and the fracture resistance may be
deteriorated in some cases. If the thickness is less than 0.5
.mu.m, the resistance against crater wear of the rake face is
excellent and the biting resistance in repetitive cutting such as
threading or grooving may be deteriorated in some cases.
[0072] <Tangent Intersection Angle>
[0073] FIG. 1 shows an image, observed with a field emission
scanning electron microscope (FE-SEM), of a surface of the outer
layer in a cross section cut along a plane including a normal to
the surface of the coating of the surface-coated cutting tool of
the present invention. According to the present invention, the
outer layer preferably includes .alpha.-aluminum oxide crystal
grains. As shown in FIG. 1, in the cross section cut along a plane
including a normal to the coating surface of the surface-coated
cutting tool, at least 50% of the .alpha.-aluminum oxide crystal
grains located in the surface of the outer layer preferably
satisfies the condition that a tangent intersection angle is not
less than 100.degree. and not more than 170.degree.. Here, the
tangent intersection angle is defined as follows. Of three
.alpha.-aluminum oxide crystal grains adjacent to each other
located in the surface of the outer layer, one combination of two
.alpha.-aluminum oxide crystal grains adjacent to each other forms
one depression, and the other combination of two .alpha.-aluminum
oxide crystal grains adjacent to each other forms another
depression. The angle between a tangent extending from the deepest
point of the one depression and a tangent extending from the
deepest point of the other depression is the tangent intersection
angle.
[0074] Here, the tangent intersection angle means an angle (see
FIG. 1) defined in the following manner. Three .alpha.-aluminum
oxide crystal grains adjacent to each other form two depressions.
From respective deepest points of the two depressions, two
half-lines abutting on the .alpha.-aluminum oxide crystal grains
are drawn so that the half-lines intersect toward the surface side
of the outer layer (toward the side opposite to the base material).
Of the intersection angles formed between the intersecting
half-lines, the angle protruding toward the outer layer is the
tangent intersection angle (see FIG. 1). The fact that such a
tangent intersection angle is an obtuse angle provides a smooth
surface of the outer layer formed by the .alpha.-aluminum oxide
crystal grains. In contrast, the fact that the tangent intersection
angle is an acute angle provides a rough surface of the outer layer
formed by the .alpha.-aluminum oxide crystal grains. The outer
layer of the present invention has a smooth surface and accordingly
the outer layer grows horizontally relative to the base material.
Therefore, the crystal structure of the outer layer is a dense
structure and the strength can be increased. The coating having
such an outer layer has an obtuse tangent intersection angle, and
therefore, a workpiece being cut is less likely to adhere to the
coating, and the coating exhibits a property that it is excellent
in wear resistance and chipping resistance.
[0075] Here, the percentage in "at least 50% of the
.alpha.-aluminum oxide crystal grains" described above means the
ratio of the number of .alpha.-aluminum oxide crystal grains each
located between the two half-lines forming a tangent intersection
angle satisfying a condition of not less than 100.degree. and not
more than 170.degree., to the number of .alpha.-aluminum oxide
crystal grains that are present in the surface of the outer layer.
Specifically, it is supposed that 10 .alpha.-aluminum oxide crystal
grains are present in the surface of the outer layer, for example.
When all of the tangent intersection angles formed by five of the
10 .alpha.-aluminum oxide crystal grains satisfy the condition of
not less than 100.degree. and not more than 170.degree. while the
tangent intersection angles formed by the residual .alpha.-aluminum
oxide crystal grains do not satisfy this condition of not less than
100.degree. and not more than 170.degree., 50% of the
.alpha.-aluminum oxide crystal grains located in the surface of the
outer layer has a desired tangent intersection angle.
[0076] The above-defined tangent intersection angle is found by
focusing on the shape of the groove formed between .alpha.-aluminum
oxide crystal grains that are present in the surface of the outer
layer. Therefore, the tangent intersection angle is technically
irrelevant to parameters found by focusing on only the maximum or
the average of the surface roughness in a certain section such as
conventionally known surface roughness parameters (Rz, Ra, Sm for
example). It is impossible to define the surface shape of the outer
layer of the present invention by parameters such as Rz, Ra, Sm.
Namely, it is impossible for the present invention to define the
shape of the groove formed between .alpha.-aluminum oxide crystal
grains by conventionally known parameters (such as Rz, Ra, Sm). The
present invention therefore uses a new parameter (tangent
intersection angle) which replaces the conventionally known
parameters to define the surface shape of the outer layer to which
a workpiece is less likely to adhere. Since such a tangent
intersection angle represents the shape of the groove formed
between .alpha.-aluminum oxide crystal grains, apparently the value
of the tangent intersection angle does not depend on the size of
the .alpha.-aluminum oxide crystal grains. This idea that such a
groove shape influences the adhesion resistance is original in
itself, and in this respect, the present invention is an innovative
invention that has not been present in the past.
[0077] More preferably, at least 65% of the .alpha.-aluminum oxide
crystal grains located in the surface of the outer layer in the
cross section of the surface-coated cutting tool cut along a plane
including a normal to the coating surface satisfies the
above-defined tangent intersection angle. Still more preferably, at
least 80% of the .alpha.-aluminum oxide crystal grains located in
the surface of the outer layer satisfies it.
[0078] <Surface R of .alpha.-Aluminum Oxide Crystal
Grain>
[0079] FIG. 2 shows an image, which is observed with an FE-SEM, of
a surface of the outer layer in a cross section cut along a plane
including a normal to the surface of the coating of the
surface-coated cutting tool of the present invention. As shown in
FIG. 2, preferably at least 30% of the .alpha.-aluminum oxide
crystal grains located in the surface of the outer layer when
observed at a magnification of 10000 in a cross section cut along a
plane including a normal to the coating surface satisfies the
condition that the radius (surface R) of an inscribed circle
abutting on a surface protrusion formed by one .alpha.-aluminum
oxide crystal grain is 3 mm or more.
[0080] Here, the above-mentioned "surface R" is a numerical value
to serve as an index representing the smoothness of the surface of
the .alpha.-aluminum oxide crystal grains. As shown in FIG. 2,
"surface R" means the radius of an inscribed circle abutting on the
outermost portion of a protrusion of the depressions and
protrusions representing a cross section of the .alpha.-aluminum
oxide crystal grains. A greater value of the surface R means that
the surface of the .alpha.-aluminum oxide crystal grains is
smoother, and a smaller value of the surface R means that the
surface of the .alpha.-aluminum oxide crystal grains has sharply
pointed portions. When the surface R of .alpha.-aluminum oxide
crystal grain is 3 mm or more, the surface of the outer layer has
desired smoothness and a workpiece is less likely to adhere in a
cutting process. The coating having such an outer layer has
excellent adhesion resistance and chipping resistance in
combination with the effect obtained from the orientation of the
crystal plane of the outer layer as described above. Since a
greater number of .alpha.-aluminum oxide crystal grains having a
surface R of 3 mm or more in the surface of the outer layer makes
the surface of the outer layer smoother, preferably a largest
possible number of .alpha.-aluminum oxide crystal grains has a
surface R of 3 mm or more.
[0081] The surface R is measured in the following way. The
surface-coated cutting tool is cut along a plane including a normal
to the coating surface. In a cross section thus obtained,
.alpha.-aluminum oxide crystal grains located in the surface of the
outer layer are observed with an FE-SEM at a magnification of
10000.
[0082] The percentage in "at least 30% of the .alpha.-aluminum
oxide crystal grains" described above means the ratio of the number
of .alpha.-aluminum oxide crystal grains having a surface R of 3 mm
or more, to the number of .alpha.-aluminum oxide crystal grains
that are present in a region of 20 .mu.m in the surface of the
outer layer. For example, it is supposed that there are 10
.alpha.-aluminum oxide crystal grains in a region of 20 .mu.m in
the surface of the outer layer. When any three of the
.alpha.-aluminum oxide crystal grains have a surface R of 3 mm or
more and the residual seven .alpha.-aluminum oxide crystal grains
have a surface R of less than 3 mm, 30% of the .alpha.-aluminum
oxide crystal grains located in the surface of the outer layer has
a surface R of 3 mm or more.
[0083] The surface R of crystal grains defined for the present
invention is found by focusing on the shape of the outermost layer
of .alpha.-aluminum oxide crystal grains that are present in the
surface of the outer layer. Therefore, the surface R is technically
irrelevant to parameters found by focusing on only the maximum or
the average of the surface roughness in a certain section such as
conventionally known surface roughness parameters (Rz, Ra, Sm for
example). It is impossible to define the surface shape of the outer
layer of the present invention by parameters such as Rz, Ra, Sm.
Namely, it is impossible for the present invention to define the
shape of the outermost layer of .alpha.-aluminumoxide crystal
grains by conventionally known parameters (such as Rz, Ra, Sm). The
present invention therefore uses a new parameter (surface R of
crystal grain) which replaces the conventionally known parameters
to define the surface shape of the outer layer to which a workpiece
is less likely to adhere. Since such a surface R of crystal grain
thus defined represents the shape of the outermost layer of
.alpha.-aluminum oxide crystal grains, apparently the value of the
surface R does not depend on the size of the .alpha.-aluminum oxide
crystal grains. This idea that such a shape of the outermost layer
of crystal grains influences the adhesion resistance is original in
itself, and in this respect, the present invention is an innovative
invention that has not been present in the past.
[0084] More preferably, at least 50% of the .alpha.-aluminum oxide
crystal grains located in the surface of the outer layer in the
cross section of the surface-coated cutting tool cut along a plane
including a normal to the coating surface satisfies the condition
that the radius (surface R) of an inscribed circle abutting on a
surface protrusion is at least 3 mm. Still more preferably, at
least 70% of the .alpha.-aluminum oxide crystal grains located in
the surface of the outer layer satisfies the condition that the
surface R is at least 3 mm.
[0085] <State Indication Layer>
[0086] The coating of the present invention preferably includes a
state indication layer forming the outermost coating surface. Here,
the state indication layer preferably includes one of a Ti carbide,
a Ti nitride, a Ti carbonitride, and a Ti boride as a main
component. "Including one of a Ti carbide, a Ti nitride, a Ti
carbonitride, and a Ti boride as a main component" means including
at least 90% by mass of one of a Ti carbide, a Ti nitride, and a Ti
carbonitride. Preferably, it means that the state indication layer
is made of only one of a Ti carbide, a Ti nitride, and a Ti
carbonitride except for inevitable impurities. Further, for each of
the Ti carbide, the Ti nitride, and the Ti carbonitride, the ratio
by mass between Ti and elements other than Ti (namely C, N, and CN)
is preferably that the ratio of Ti is 50% by mass or more.
[0087] Among a Ti carbide, a Ti nitride, and a Ti carbonitride, the
nitride of Ti (namely a compound expressed as TiN) is particularly
preferred. Since TiN has a brightest color (gold) among these
compounds, it has an advantage that the corner of the cutting
insert after being used for cutting is easily identified.
[0088] The above-described state indication layer preferably has a
thickness of not less than 0.05 .mu.m and not more than 2 .mu.m. If
the thickness is less than 0.05 .mu.m, it does not provide
sufficient effects in the case where compressive residual stress is
applied, and is not so effective for improving the fracture
resistance. If the thickness is larger than 2 .mu.m, the adherence
to the layer located inside the state indication layer may be
deteriorated in some cases.
[0089] <Method for Manufacture>
[0090] The coating of the present invention is formed by means of
chemical vapor deposition (CVD).
[0091] For each of the layers constituting the coating except for
the outer layer, the conventionally known chemical vapor deposition
may be used without being particularly limited, and conditions and
the like are not limited. For example, as a deposition temperature,
a temperature of approximately 800 to 1050.degree. C. may be used.
As a gas to be used as well, a conventionally known gas such as
nitrile-based gas like acetonitrile may be used without being
particularly limited. As for the outer layer, the outer layer is
formed in the following way so that the equivalent peak intensity
PR(024) of x-ray diffraction is larger than 1.3.
[0092] Specifically, the outer layer may be produced by forming an
alumina binder layer and thereafter oxidizing the surface of the
alumina binder layer to thereby form nucleus of .alpha.-alumina, or
forming .alpha.-alumina nucleus on the alumina binder layer which
is in itself made of an oxide. As the temperature at which the
outer layer is formed, a temperature of 850 to 1050.degree. C. may
be used. The pressure at which the outer layer is formed may be not
less than 40 hPa and not more than 150 hPa. The outer layer is
formed by feeding AlCl.sub.3 gas at a relatively low flow rate of
2% by volume or less and successively increasing/decreasing the
flow rate of H.sub.2S gas serving as a catalyst in 10 seconds to 5
minutes. The outer layer can thus be formed so that the outer layer
has a crystal structure with its orientation in the (024) plane.
Further, the flow rate of H.sub.2S gas can be set to a considerably
low flow rate of 0.15% by volume or less to thereby form the outer
layer with a maximum peak of the (012) plane. Further, the flow
rate of CO.sub.2 can be set to a relatively high flow rate of 4.5%
by volume or more to thereby increase the orientation index of the
(110) plane.
EXAMPLES
[0093] In the following, the present invention will be described in
more detail in connection with Examples. The present invention,
however, is not limited to them.
Examples 1-15, Comparative Examples 1-5
[0094] Examples and Comparative Examples were prepared by similar
manufacturing methods to each other except that respective outer
layers were formed under different conditions from each other.
First, for the base material, raw material powders of a cemented
carbide were mixed so that the contents of the composition were:
83.1 mass % of WC, 5.7 mass % of TiC, 1.3 mass % of TaC, 1.5 mass %
of NbC, 0.4 mass % of ZrC, 0.2 mass % of Cr.sub.3C.sub.2, and 7.8
mass % of Co.
[0095] Next, the raw material powders were press-formed and held in
a vacuum atmosphere at 1400.degree. C. for one hour to thereby
sinter the raw material powders of the cemented carbide. After
this, the press-formed body was removed from the furnace, and the
surface of the body was smooth-polished. Then, on the ridgeline of
the cutting edge, edge treatment was performed with an SiC brush so
that the amount of honing from the rake face side was 0.05 mm in
width. In this way, the base material in the shape of
CNMG120408N-GE (manufactured by Sumitomo Electric Hardmetal) was
prepared. Thus, in the surface of the base material, a p-free layer
of 20 .mu.m in thickness was formed.
[0096] Next, the base material was set in a CVD furnace, and the
known thermal CVD was used to form, from the base-material side, a
binder layer (TiN layer), an inner layer (MT-TiCN layer), an
alumina binder layer (TiCNO layer), an outer layer
(.alpha.-Al.sub.2O.sub.3), and a state indication layer (TiN layer)
in this order.
[0097] Specifically, the temperature in the furnace was first set
at 900.degree. C. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 1 .mu.m in thickness. Then, the
temperature in the furnace was set at 860.degree. C. As
raw-material gases, 2.3 vol % of TiCl.sub.4, 0.5 vol % of
CH.sub.3CN, and 25 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 70 hPa. Accordingly, an MT-TiCN layer of 10
.mu.m in thickness was formed.
[0098] Then, the temperature in the furnace was set at 980.degree.
C. As raw-material gases, 2 vol % of TiCl.sub.4, 0.1 vol % Of
CH.sub.4, and 10 vol % of N.sub.2 were used. A residual content of
H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 67 hPa. Accordingly, a TiCN binder layer was
formed. After this, as raw-material gases, 2 vol % of TiCl.sub.4,
0.1 vol % of CH.sub.4, 10 vol % of N.sub.2, 1 vol % of CO, and 2
vol % of CO.sub.2 were used. A residual content of H.sub.2 gas was
introduced as a carrier gas. The pressure in the furnace was set at
67 hPa. Accordingly, a TiCNO layer with a total thickness of 1
.mu.m or less was formed.
[0099] Subsequently, an outer layer with a thickness of 4 .mu.m was
formed under the conditions of the temperature in the furnace, the
pressure, and the composition of the raw-material gases shown in
Table 1 below. Here, as to the volume ratio of the raw-material gas
"H.sub.2S" in Table 1, "0.30.+-.0.05 variation/30 s" means that the
volume ratio of the introduced H.sub.2S is successively increased
from 0.30 vol % to 0.35 vol %, then successively decreased to 0.25
vol %, and thereafter further increased successively to 0.30 vol %,
this variation of the volume ratio of H.sub.2S is made in one cycle
of 30 seconds, and the cycle is repeated to form the outer
layer.
TABLE-US-00001 TABLE 1 temperature in furnace pressure AlCl.sub.3
CO.sub.2 HCl H.sub.2 (.degree. C.) (hPa) (vol %) H.sub.2S (vol %)
(vol %) (vol %) (vol %) Example 1 1000 70 1.6 0.30 .+-. 0.05
variation/30 s 3.1 1.8 residual 2 980 80 1.5 0.11 .+-. 0.04
variation/15 s 3.0 2.1 residual 3 960 50 1.4 0.27 .+-. 0.08
variation/30 s 2.9 1.5 residual 4 975 80 1.2 0.15 .+-. 0.03
variation/40 s 4.3 3.2 residual 5 1010 100 1.4 0.22 .+-. 0.07
variation/50 s 4.8 1.7 residual 6 950 30 1.0 0.25 .+-. 0.05
variation/40 s 2.2 4.8 residual 7 965 75 1.4 0.20 .+-. 0.05
variation/1.5 min 3.3 3.3 residual 8 1005 60 1.5 0.25 .+-. 0.10
variation/4 min 4.5 4.2 residual 9 980 70 0.9 0.17 .+-. 0.04
variation/35 s 4.5 3.6 residual 10 1000 80 1.2 0.15 .+-. 0.07
variation/3 min 3.9 4.9 residual 11 975 65 1.2 0.01 .+-. 0.05
variation/20 s 4.9 3.0 residual 12 960 70 0.6 0.14 .+-. 0.06
variation/2 min 3.2 4.8 residual 13 1010 85 2.0 0.23 .+-. 0.09
variation/3.5 min 4.6 1.1 residual 14 1005 100 1.9 0.33 .+-. 0.07
variation/20 s 2.1 2.3 residual 15 1020 40 0.8 0.30 .+-. 0.08
variation/1 min 3.5 2.2 residual Comparative 1 1010 9 1.5 0.30 4.0
2.0 residual Example 2 980 90 2.0 0.28 3.7 2.5 residual 3 1020 100
4.0 0.23 2.0 1.0 residual 4 1000 350 8.0 0.15 2.3 3.0 residual 5
1005 70 10.0 0.05 3.5 4.0 residual
[0100] Finally, at the same temperature as the temperature in the
furnace when the outer layer was formed, TiCl.sub.4 gas and N.sub.2
gas were used as raw-material gases and H.sub.2 gas was used as a
carrier gas to form a TiN layer of approximately 1.5 .mu.m in
thickness. In this way, respective surface-coated cutting tools of
the Examples and Comparative Examples were prepared.
[0101] <Evaluation of Equivalent Peak Intensity of Outer
Layer>
[0102] For respective outer layers of the surface-coated cutting
tools of the Examples and Comparative Examples prepared in the
above-described manner, a Cu K.alpha..sub.1 (wavelength
.lamda.=1.5405 A) x-ray source was used, and based on the 20-0 scan
x-ray diffraction method, the x-ray diffraction intensity was
measured. The results are shown in the column "x-ray intensity" in
Table 2. The reflection plane providing a maximum x-ray diffraction
intensity is shown in the column "maximum peak" in Table 2.
TABLE-US-00002 TABLE 2 x-ray intensity maximum I(012) I(104) I(110)
I(113) I(024) I(116) I(124) I(030) PR(024) peak Example 1 2177 98
1260 589 2323 223 255 58 3.14 024 2 1811 98 2019 194 2393 110 164
107 3.04 024 3 2005 756 1136 725 2039 116 248 73 2.85 024 4 1350
2375 300 541 2453 340 785 1003 2.69 024 5 1348 785 1650 453 2200
337 700 650 2.42 024 6 750 669 798 361 987 696 109 500 2.06 024 7
436 934 711 401 987 792 675 206 1.82 024 8 652 750 687 643 757 695
598 650 1.36 024 9 2405 98 1609 991 2236 211 261 1003 2.42 012 10
1334 98 1147 528 682 88 117 373 1.51 012 11 324 1095 2358 996 1720
781 381 299 2.01 110 12 357 1722 2778 449 1264 76 107 115 1.69 110
13 390 99 3004 225 874 68 171 197 1.37 110 14 573 3660 215 761 1850
336 221 451 2.67 104 15 623 2680 1250 761 958 336 221 154 1.51 104
Comparative 1 421 1722 650 449 731 2778 107 115 1.27 116 Example 2
568 3660 210 671 273 264 253 573 0.54 104 3 209 871 1260 184 230
590 98 2 0.66 110 4 324 1152 735 890 296 781 381 299 0.66 104 5 4
1935 2600 23 5 520 12 220 0.01 110
[0103] Equivalent peak intensity PR(hkl) of a (hkl) plane defined
by the following formula was calculated. Based on this PR(hkl), the
x-ray peak intensity from the (024) plane of the outer layer was
quantitatively evaluated.
PR(024)={I(024)/I.sub.0(024)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
[0104] It is noted that (hkl) refers to reflection planes providing
main peaks with a peak intensity of 30 or more indicated in ASTM
File No. 10-173 (Powder Diffraction File Published by JCPDS
International Center for Diffraction Data). Specifically, (hkl)
refers to eight planes: (012), (104), (110), (113), (024), (116),
(124), (030). PR(hkl) represents a relative intensity of the x-ray
diffraction peak intensity from a (hkl) plane of the coating
actually measured by means of x-ray diffraction, with respect to
the isotropic grain x-ray diffraction peak intensity indicated in
the ASTM data. A greater width of PR(hkl) means that the x-ray peak
intensity from the (hkl) plane is stronger than other peak
intensities and the orientation is in the (hkl) direction. In the
column "PR(024)" in Table 2, the equivalent peak intensity PR(hkl)
of the (024) plane is shown.
[0105] In the formula above, I(hkl) represents the actually
measured x-ray diffraction intensity of the (hkl) plane.
I.sub.0(hkl) is the x-ray diffraction intensity indicated in ASTM
File No. 10-173, and represents the x-ray diffraction intensity
from the (hkl) plane of isotropically oriented powder grains.
[0106] <Cutting Test>
[0107] Respective surface-coated cutting tools of the Examples and
Comparative Examples were used to perform a steel machining test
under the following cutting conditions A and thereby evaluate the
rake face wear amount (mm) of the surface-coated cutting tool.
Further, a cast-iron machining test was performed under cutting
conditions B to thereby evaluate the flank face wear amount (mm) of
the surface-coated cutting tool.
[0108] Cutting Test A [0109] Workpiece: S55C round bar [0110]
Cutting Speed: 300 m/min [0111] Feed Rate: 0.30 mm/rev (wet
cutting) [0112] Cut: 2.0 mm [0113] Cutting Time: 23 minutes
[0114] Cutting Test B [0115] Workpiece: FCD700 round bar [0116]
Cutting Speed: 150 m/min [0117] Feed Rate: 0.30 mm/rev (wet
cutting) [0118] Cut: 1.5 mm [0119] Cutting Time: 15 minutes
[0120] Here, the rake face wear amount and the flank face wear
amount were obtained by measuring the width of wear of the
surface-coated cutting tool before and after the cutting test. The
results are shown in the columns "rake face wear amount" and "flank
face wear amount" in Table 3. It is noted that a surface-coated
cutting tool with a smaller rake face wear amount and a smaller
flank face wear amount is superior in wear resistance of the
surface-coated cutting tool.
TABLE-US-00003 TABLE 3 life rake face flank face wear amount wear
amount (mm) (mm) Example 1 0.39 0.041 2 0.48 0.046 3 0.50 0.049 4
0.41 0.054 5 0.49 0.076 6 0.49 0.078 7 0.50 0.09 8 0.65 0.096 9
0.48 0.074 10 0.52 0.091 11 0.50 0.079 12 0.61 0.09 13 0.52 0.094
14 0.42 0.066 15 0.51 0.092 Comparative 1 0.87 0.168 Example 2 0.97
0.189 3 0.91 0.178 4 0.88 0.187 5 1.01 0.211
[0121] It is apparent from the results shown in Table 3 that
respective surface-coated cutting tools of the Examples have
smaller rake face wear amounts and smaller flank face wear amounts
relative to those of the Comparative Examples. It is seen from this
result that respective surface-coated cutting tools of the Examples
are excellent in wear resistance relative to those of the
Comparative Examples. The reason for the enhanced wear resistance
is considered as the enhanced strength of the outer layer. In
contrast, respective surface-coated cutting tools of the
Comparative Examples are insufficient in terms of the strength of
the outer layer and therefore have larger wear amounts of the rake
face and the flank face.
Examples 16-21, Comparative Examples 6-9
[0122] Examples and Comparative Examples were prepared by similar
manufacturing methods to each other except that respective outer
layers were formed under different conditions from each other.
First, for the base material, raw material powders of a cemented
carbide were mixed so that the contents of the composition were:
73.5 mass % of WC, 9.0 mass % of TaC, 6.7 mass % of TiC, 0.3 mass %
of Cr.sub.3C.sub.2, and 10.5 mass % of Co.
[0123] Next, the raw material powders were press-formed and held in
a vacuum atmosphere at 1400.degree. C. for one hour to thereby
sinter the raw material powders of the cemented carbide. After
this, the press-formed body was removed from the furnace, and the
surface of the body was smooth-polished. Then, on the ridgeline of
the cutting edge, edge treatment was performed with an SiC brush so
that the amount of honing from the rake face side was 0.04 mm in
width. In this way, the base material in the shape of SPGN120412
was prepared. In the surface of the base material thus prepared, no
.beta.-free layer was formed.
[0124] Next, the base material was set in a CVD furnace, and the
known thermal CVD was used to form, from the base-material side, a
binder layer (TiN layer), an inner layer (MT-TiCN layer), an
alumina binder layer (TiBN layer), an outer layer
(.alpha.-Al.sub.2O.sub.3), and a state indication layer
(alternating TiN layer/Al.sub.2O.sub.3 layer) in this order.
[0125] Specifically, the temperature in the furnace was first set
at 870.degree. C. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 0.5 .mu.m in thickness. Then, the
temperature in the furnace was kept at 870.degree. C. As
raw-material gases, 2.0 vol % of TiCl.sub.4, 0.4 vol % of
CH.sub.3CN, and 15 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 65 hPa. Accordingly, an MT-TiCN layer of 3 .mu.m
in thickness was formed.
[0126] Then, the temperature in the furnace was set at 950.degree.
C. As raw-material gases, 2 vol % of TiCl.sub.4, 0.01 vol % of
BCl.sub.3, and 13 vol % of N.sub.2 were used. A residual content of
H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 50 hPA. Accordingly, a TiBN layer with a
thickness of approximately 0.5 .mu.m was formed. After this, CO gas
was introduced into the furnace to thereby oxidize the surface of
the TiBN layer.
[0127] Subsequently, an outer layer of 2.5 .mu.m in thickness was
formed under the conditions of the temperature in the furnace, the
pressure, and the contents of the composition of the raw-material
gases shown in Table 4 below.
TABLE-US-00004 TABLE 4 temperature in furnace pressure AlCl.sub.3
ZrC1.sub.4 CO.sub.2 HCl H.sub.2 (.degree. C.) (hPa) (vol %) (vol %)
H.sub.2S (vol %) (vol %) (vol %) (vol %) Example 16 980 65 1.6 0.3
0.30 .+-. 0.05 variation/10 s 3.1 1.8 residual 17 1005 80 1.4 0.5
0.20 .+-. 0.06 variation/2 min 3.1 1.8 residual 18 970 55 0.8 0.4
0.18 .+-. 0.04 variation/25 s 4.4 2.6 residual 19 980 65 1.1 0.2
0.10 .+-. 0.07 variation/50 s 4.9 3.0 residual 20 1005 100 1.9 0.3
0.33 .+-. 0.08 variation/15 s 2.1 2.3 residual 21 960 75 1.8 0.4
0.36 .+-. 0.03 variation/5 min 3.5 2.4 residual Comparative 6 1000
40 2.5 0.3 0.4 2.3 3.3 residual Example 7 980 55 4.8 0.5 0.5 2.2
2.5 residual 8 960 80 6.5 0.2 0.3 4.5 1.8 residual 9 1010 65 5.7
0.4 0.8 3.4 4.6 residual
[0128] Next, the temperature in the furnace was set at 900.degree.
C. TiCl.sub.4 gas and N.sub.2 gas were used as raw-material gases
and H.sub.2 gas was used as a carrier gas to form a TiN layer of
0.5 .mu.m or less in thickness. Again, an outer layer with a
thickness of 0.5 .mu.m or less was formed. The TiN layer with a
thickness of 0.5 .mu.m and the outer layer with a thickness of 0.5
.mu.m were alternately laid on each other so that three TiN layers
and three outer layers alternated with each other. Finally, a state
indication layer of TiN with a thickness of approximately 0.5 .mu.m
was formed. In this way, respective surface-coated cutting tools of
the Examples and Comparative Examples were prepared.
[0129] <Evaluation of Equivalent Peak Intensity of Outer
Layer>
[0130] For respective outer layers of the surface-coated cutting
tools of the Examples and Comparative Examples prepared in the
above-described manner, the same method as the x-ray diffraction
method used for Examples 1 to 15 was used to measure the x-ray
diffraction intensity. The results are shown in the column "x-ray
intensity" in Table 5. The reflection plane providing a maximum
x-ray diffraction intensity is shown in the column "maximum peak"
in Table 5.
TABLE-US-00005 TABLE 5 x-ray intensity maximum I(012) I(104) I(110)
I(113) I(024) I(116) I(124) I(030) PR(024) peak Example 16 2176 99
1259 591 2313 221 245 53 3.14 024 17 443 925 721 431 996 891 676
202 1.80 024 18 2399 96 1621 994 2147 209 193 1021 2.38 012 19 321
1096 2357 995 1719 779 365 321 2.01 110 20 572 3654 223 754 1848
335 219 466 2.67 104 21 621 2679 1257 763 962 332 223 155 1.51 104
Comparative 6 420 1721 649 448 732 2776 105 117 1.27 116 Example 7
565 2679 1248 670 438 263 185 575 0.74 104 8 323 1153 734 889 297
780 382 300 0.67 104 9 12 1946 2634 15 6 527 7 221 0.01 110
[0131] <Cutting Test>
[0132] Respective surface-coated cutting tools of the Examples and
Comparative Examples were used to perform a steel machining test
under the following cutting conditions C and thereby evaluate the
flank face wear amount (mm) of the surface-coated cutting tool.
Further, a cast-iron machining test was performed under cutting
conditions D to thereby evaluate the rake face wear amount (mm) of
the surface-coated cutting tool.
[0133] Cutting Test C [0134] Workpiece: SCM435 block material
[0135] Cutting Speed: 330 m/min [0136] Feed Rate: 0.25 mm/rev (wet
cutting) [0137] Cut: 2.0 mm [0138] Cut Length: 10 m
[0139] Cutting Test D [0140] Workpiece: FC250 block material [0141]
Cutting Speed: 250 m/min [0142] Feed Rate: 0.3 mm/rev (dry cutting)
[0143] Cut: 1.5 min [0144] Cut Length: 12 m
[0145] Here, the rake face wear amount and the flank face wear
amount were obtained by measuring the width of wear of the
surface-coated cutting tool before and after the cutting test. The
results are shown in the columns "rake face wear amount" and "flank
face wear amount" in Table 6. It is noted that a surface-coated
cutting tool with a smaller rake face wear amount and a smaller
flank face wear amount is superior in wear resistance of the
surface-coated cutting tool.
TABLE-US-00006 TABLE 6 life rake face flank face wear amount wear
amount (mm) (mm) Example 16 0.101 0.111 17 0.113 0.122 18 0.114
0.118 19 0.097 0.102 20 0.112 0.116 21 0.122 0.118 Comparative 6
0.199 0.214 Example 7 0.187 0.203 8 0.125 0.134 9 0.203 0.223
[0146] It is apparent from the results shown in Table 6 that
respective surface-coated cutting tools of the Examples have
smaller rake face wear amounts and smaller flank face wear amounts
than those of the Comparative Examples. It is seen from this result
that respective surface-coated cutting tools of the Examples are
excellent in wear resistance relative to those of the Comparative
Examples. The reason for the enhanced wear resistance is considered
as the enhanced strength of the outer layer. In contrast,
respective surface-coated cutting tools of the Comparative Examples
are insufficient in terms of the strength of the outer layer and
therefore have larger wear amounts of the rake face and the flank
face.
[0147] It has been proved from the results above that the
surface-coated cutting tools of the Examples are superior in wear
resistance and fracture resistance relative to the surface-coated
cutting tools of the Comparative Examples.
Examples 22-36, Comparative Examples 10-14
[0148] Examples and Comparative Examples were prepared by similar
manufacturing methods to each other except that respective outer
layers were formed under different conditions from each other.
First, for the base material, raw material powders of a cemented
carbide were mixed so that the contents of the composition were:
82.1 mass % of WC, 7.7 mass % of TiC, 1.2 mass % of TaC, 1.4 mass %
of NbC, 0.2 mass % of Cr.sub.3C.sub.2, and 7.4 mass % of Co.
[0149] Next, the raw material powders were press-formed and held in
a vacuum atmosphere at 1410.degree. C. for one hour to thereby
sinter the raw material powders of the cemented carbide. After
this, the press-formed body was removed from the furnace, and the
surface of the body was smooth-polished. Then, on the ridgeline of
the cutting edge, edge treatment was performed with an SiC brush so
that the amount of honing from the rake face side was 0.05 mm in
width. In this way, the base material in the shape of
CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal) was
prepared. In the surface of the base material thus prepared, no
.beta.-free layer was formed.
[0150] Next, the base material was set in a CVD furnace, and the
known thermal CVD was used to form, from the base-material side, a
binder layer (TiN layer), an inner layer (MT-TiCN layer), an
alumina binder layer (TiCNO layer), an outer layer
(.alpha.-Al.sub.2O.sub.3), and a state indication layer (TiN layer)
in this order.
[0151] Specifically, the temperature in the furnace was first set
at 890.degree. C. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 1 .mu.m in thickness. Then, the
temperature in the furnace was set at 870.degree. C. As
raw-material gases, 2.1 vol % of TiCl.sub.4, 0.45 vol % of
CH.sub.3CN, and 26 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 68 hPa. Accordingly, an MT-TiCN layer of 8 .mu.m
in thickness was formed.
[0152] Then, the temperature in the furnace was set at 980.degree.
C. As raw-material gases, 2.1 vol % of TiCl.sub.4, 0.1 vol % of
CH.sub.4, and 10 vol % of N.sub.2 were used. A residual content of
H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 67 hPA. Accordingly, a TiCN binder layer was
formed. After this, the temperature in the furnace was set at
1010.degree. C. As raw-material gases, 2.3 vol % of TiCl.sub.4, 0.1
vol % of CH.sub.4, 10 vol % of N.sub.2, 1.1 vol % of CO, and 1.1
vol % of CO.sub.2 were used. A residual content of H.sub.2 gas was
introduced as a carrier gas. The pressure in the furnace was set at
67 hPa. Accordingly, a TiCNO layer with a thickness of
approximately 1 .mu.m was formed.
[0153] Subsequently, an outer layer with a thickness of 4 .mu.m was
formed under the conditions of the temperature in the furnace, the
pressure, and the composition of the raw-material gases shown in
Table 7 below. Here, as to the volume ratio of the raw-material gas
"H.sub.2S" in Table 7, "0.13.+-.0.01 variation/35S" means that the
volume ratio of the introduced H.sub.2S is successively increased
from 0.13 vol % to 0.14 vol %, then successively decreased to 0.12
vol %, and thereafter further increased successively to 0.13 vol %,
this variation of the volume ratio of H.sub.2S is made in one cycle
of 35 seconds, and the cycle is repeated to form the outer
layer.
TABLE-US-00007 TABLE 7 temperature in furnace pressure AlCl.sub.3
CO.sub.2 HCl H.sub.2 (.degree. C.) (hPa) (vol %) H.sub.2S (vol %)
(vol %) (vol %) (vol %) Example 22 1005 68 1.49 0.13 .+-. 0.01
variation/35 s 2.9 1.8 residual 23 986 77 1.40 0.11 .+-. 0.04
variation/15 s 2.8 2.0 residual 24 967 50 1.30 0.07 .+-. 0.07
variation/25 s 2.7 1.5 residual 25 981 77 1.12 0.14 .+-. 0.01
variation/40 s 4.0 3.0 residual 26 1015 95 1.30 0.12 .+-. 0.03
variation/55 s 4.5 1.7 residual 27 958 32 0.93 0.05 .+-. 0.05
variation/45 s 2.0 4.5 residual 28 972 73 1.30 0.11 .+-. 0.03
variation/1.5 min 3.1 3.1 residual 29 1010 59 1.40 0.10 .+-. 0.04
variation/4 min 4.2 3.9 residual 30 986 68 0.84 0.08 .+-. 0.04
variation/30 s 4.2 3.4 residual 31 1005 77 1.12 0.01 .+-. 0.07
variation/3 min 3.6 4.6 residual 32 981 64 1.12 0.03 .+-. 0.10
variation/25 a 4.6 2.9 residual 33 967 68 0.56 0.14 .+-. 0.01
variation/2 min 3.0 4.5 residual 34 1015 82 1.86 0.09 .+-. 0.03
variation/2.5 min 4.3 1.1 residual 35 1010 95 1.77 0.06 .+-. 0.07
variation/25 s 2.0 2.2 residual 36 1024 41 0.74 0.11 .+-. 0.04
variation/1 min 3.3 2.1 residual Comparative 10 1005 70 1.3 0.17
.+-. 0.10 variation/20 s 3.9 2.1 residual Example 11 980 88 1.9
0.14 .+-. 0.05 variation/20 s 2.7 2.6 residual 12 1011 100 4.0 0.23
3.0 1.2 residual 13 990 350 8.0 0.15 3.3 3.3 residual 14 968 70
10.0 0.05 2.5 3.5 residual
[0154] Finally, at the same temperature as the temperature in the
furnace when the outer layer was formed, TiCl.sub.4 gas and N.sub.2
gas were used as raw-material gases and H.sub.2 gas was used as a
carrier gas to form a TiN layer of approximately 1.0 .mu.m in
thickness. In this way, respective surface-coated cutting tools of
the Examples and Comparative Examples were prepared.
[0155] <Evaluation of Equivalent Peak Intensity of Outer
Layer>
[0156] For respective outer layers of the surface-coated cutting
tools of the Examples and Comparative Examples prepared in the
above-described manner, a Cu K.alpha..sub.1 (wavelength
.lamda.=1.5405 A) x-ray source was used, and based on the
2.theta.-.theta. scan x-ray diffraction method, the x-ray
diffraction intensity was measured. The results are shown in the
column "x-ray intensity" in Table 8. The reflection plane providing
a maximum x-ray diffraction intensity is shown in the column
"maximum peak" in Table 8.
TABLE-US-00008 TABLE 8 ratio of x-ray intensity maximum
100.degree.-170.degree. I(012) I(104) I(110) I(113) I(024) I(116)
I(124) I(030) PR(024) peak (%) Example 22 1112 119 728 384 573 152
133 214 1.66 012 95 23 843 102 770 388 479 89 112 343 1.47 012 86
24 1310 97 820 461 614 123 131 211 1.62 012 72 25 1377 112 341 297
816 247 57 22 2.69 012 93 26 2368 114 804 567 876 191 129 92 1.80
012 79 27 1764 49 1137 493 646 79 97 392 1.37 012 75 28 2407 51
1327 573 861 109 132 328 1.49 012 65 29 1526 38 532 310 964 98 84
12 2.73 012 50 30 1356 33 629 78 1110 59 43 0 3.19 012 82 31 1068
95 602 0 945 144 46 23 3.05 012 55 32 1855 12 817 454 1198 55 95
490 2.37 012 64 33 1793 56 985 235 1200 65 99 580 2.27 012 51 34
1755 0 534 456 1257 102 83 325 2.80 012 53 35 1691 7 601 370 914 51
74 354 2.26 012 87 36 1673 758 633 123 985 123 57 9 2.39 012 58
Comparative 10 2114 142 1758 440 674 47 137 236 1.16 012 24 Example
11 3556 3485 209 450 765 351 453 50 1.02 012 49 12 878 75 897 325
470 78 136 196 1.44 110 30 13 853 2598 1150 761 863 257 212 144
2.26 104 47 14 780 77 694 349 863 100 134 595 2.23 024 16
[0157] Then, equivalent peak intensity PR(hkl) of a (hkl) plane
defined by the following formula was calculated. Based on this
PR(hkl), the x-ray peak intensity from the (024) plane of the outer
layer was evaluated. In the column "PR(024)" in Table 8, equivalent
peak intensity PR(hkl) of the (024) plane is shown.
[0158] <Evaluation of Tangent Intersection Angle of Outer
Layer>
[0159] Respective surface-coated cutting tools of the Examples and
Comparative Examples were each cut along a plane including a normal
to the coating surface, and the resultant cross section was
mechanically polished and thereafter further ion-polished. For a
region of 20 .mu.m in length in the polished surface, an FE-SEM was
used to perform three-field measurement at a magnification of 5000
to 20000 on .alpha.-aluminum oxide crystal grains located in the
surface of the outer layer to thereby observe the .alpha.-aluminum
oxide crystal grains located in the surface of the outer layer.
Then, from respective deepest points of depressions formed by
.alpha.-aluminum oxide crystal grains adjacent to each other,
half-lines abutting on the .alpha.-aluminum oxide crystal grains
were drawn toward the outside of the outer layer. Of the
intersection angles formed between the intersecting half-lines, the
angle protruding toward the outer layer (tangent intersection
angle) was determined. Then, the ratio of .alpha.-aluminum oxide
crystal grains providing a tangent intersection angle of
100.degree. to 170.degree. to .alpha.-aluminum oxide crystal grains
located in the region of 20 .mu.m in length was determined. The
results are shown in the column "ratio of 100.degree.-170.degree."
in Table 8.
[0160] <Cutting Test>
[0161] Respective surface-coated cutting tools of the Examples and
Comparative Examples were used to perform a steel machining test
under the following cutting conditions A and thereby evaluate the
flank face wear amount (mm) of the surface-coated cutting tool.
Further, a stainless-steel machining test was performed under
cutting conditions B to thereby evaluate the wear amount (mm) of
the boundary region of the surface-coated cutting tool.
[0162] Cutting Test A [0163] Workpiece: S45C round bar [0164]
Cutting Speed: 280 m/min [0165] Feed Rate: 0.25 mm/rev (wet
cutting) [0166] Cut: 1.7 mm [0167] Cutting Time: 15 minutes
[0168] Cutting Test B [0169] Workpiece: SUS316 round bar [0170]
Cutting Speed: 180 m/min [0171] Feed Rate: 0.4 mm/rev (wet cutting)
[0172] Cut: 1.5 mm [0173] Cutting Time: 15 minutes
[0174] Here, the value representing "flank face wear amount" was
obtained by measuring the width of wear of the flank face of the
surface-coated cutting tool before and after the cutting test, and
shown in the column "flank face wear amount" in Table 9. It is
noted that a surface-coated cutting tool with a smaller flank face
wear amount is superior in wear resistance of the surface-coated
cutting tool.
[0175] Further, the value representing "boundary wear amount" was
obtained by measuring wear of the lateral flank face boundary of
the surface-coated cutting tool before and after the cutting test,
and shown in the column "boundary wear amount" in Table 9. It is
noted that a surface-coated cutting tool with a smaller boundary
wear amount is superior in adhesion resistance and oxidation
resistance of the surface-coated cutting tool.
TABLE-US-00009 TABLE 9 life flank face boundary wear amount wear
amount (mm) (mm) Example 22 0.032 0.45 23 0.036 0.53 24 0.039 0.55
25 0.044 0.47 26 0.063 0.54 27 0.065 0.54 28 0.076 0.55 29 0.081
0.69 30 0.062 0.53 31 0.077 0.57 32 0.066 0.55 33 0.076 0.65 34
0.080 0.57 35 0.054 0.48 36 0.078 0.56 Comparative 10 0.165 0.97
Example 11 0.146 0.88 12 0.155 0.92 13 0.163 0.89 14 0.185 1.01
[0176] It is apparent from the results shown in Table 9 that
respective surface-coated cutting tools of the Examples have
smaller flank face wear amounts and smaller boundary wear amounts
than those of the Comparative Examples. It is seen from this result
that respective surface-coated cutting tools of the Examples are
excellent in wear resistance relative to those of the Comparative
Examples. The reason for the enhanced wear resistance of the
surface-coated cutting tool of each Example is considered as the
enhanced strength of the outer layer. In contrast, respective
surface-coated cutting tools of the Comparative Examples are
insufficient in terms of the strength of the outer layer, and
therefore, the outer layer peels off in the initial stage of the
cutting process and the flank face wear and the boundary wear
increase.
Examples 37-42, Comparative Examples 15-18
[0177] Examples and Comparative Examples were prepared by similar
manufacturing methods to each other except that respective outer
layers were formed under different conditions from each other.
First, for the base material, raw material powders of a cemented
carbide were mixed so that the contents of the composition were:
72.5 mass % of WC, 8.5 mass % of TaC, 6.7 mass % of TiC, 0.5 mass %
of Cr.sub.3C.sub.2, and 11.8 mass % of Co.
[0178] Next, the raw material powders were press-formed and held in
a vacuum atmosphere at 1395.degree. C. for one and a half hours to
thereby sinter the raw material powders of the cemented carbide.
After this, the press-formed body was removed from the furnace, and
the surface of the body was smooth-polished. Then, on the ridgeline
of the cutting edge, edge treatment was performed with an SiC brush
so that the amount of honing from the rake face side was 0.04 mm in
width. In this way, the base material in the shape of SPGN120412
was prepared. In the surface of the base material thus prepared, no
.beta.-free layer was formed.
[0179] Next, the base material was set in a CVD furnace, and the
known thermal CVD was used to form, from the base-material side, a
binder layer (TiN layer), an inner layer (MT-TiCN layer), an
alumina binder layer (TiBN layer), an outer layer
(.alpha.-Al.sub.2O.sub.3), and a state indication layer
(alternating TiN layer/Al.sub.2O.sub.3 layer) in this order.
[0180] Specifically, the temperature in the furnace was first set
at 880.degree. C. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 0.5 .mu.m in thickness. Then, the
temperature in the furnace was set at 880.degree. C. As
raw-material gases, 2.1 vol % of TiCl.sub.4, 0.3 vol % of
CH.sub.3CN, and 15 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 65 hPa. Accordingly, an MT-TiCN layer of 3 .mu.m
in thickness was formed.
[0181] Then, the temperature in the furnace was set at 950.degree.
C. As raw-material gases, 2 vol % of TiCl.sub.4, 0.01 vol % of
BCl.sub.3, and 13 vol % of N.sub.2 were used. A residual content of
H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 50 hPA. Accordingly, a TiBN layer with a
thickness of approximately 1 .mu.m was formed. After this, CO gas
was introduced in the furnace to thereby oxidize the surface of the
TiBN layer.
[0182] Subsequently, an outer layer with a thickness of 2.5 .mu.m
was formed under the conditions of the temperature in the furnace,
the pressure, and the contents of the raw-material gases shown in
Table 10 below.
TABLE-US-00010 TABLE 10 temperature in furnace pressure AlCl.sub.3
ZrCl.sub.4 CO.sub.2 HCl H.sub.2 (.degree. C.) (hPa) (vol %) (vol %)
H.sub.2S (vol %) (vol %) (vol %) (vol %) Example 37 986 64 1.49 0.4
0.13 .+-. 0.0005 variation/20 s 2.9 1.7 residual 38 1010 77 1.30
0.6 0.02 .+-. 0.06 variation/1.5 min 2.9 1.7 residual 39 977 55
0.74 0.5 0.08 .+-. 0.04 variation/25 s 4.1 2.4 residual 40 986 64
1.02 0.3 0.10 .+-. 0.03 variation/45 s 4.6 2.8 residual 41 1010 95
1.77 0.4 0.13 .+-. 0.02 variation/10 s 2.0 2.1 residual 42 967 73
1.67 0.5 0.02 .+-. 0.11 variation/4.5 min 3.3 2.2 residual
Commparative 15 995 55 2.0 0.2 0.25 .+-. 0.02 variation/10 s 2.2
3.0 residual Example 16 978 66 4.7 0.4 0.4 2.4 2.6 residual 17 965
78 5.5 0.25 0.5 4.4 1.5 residual 18 1015 54 4.7 0.45 0.7 4.3 2.0
residual
[0183] Next, the temperature in the furnace was set at 900.degree.
C. TiCl.sub.4 gas and N.sub.2 gas were used as raw-material gases
and H.sub.2 gas was used as a carrier gas to form a TiN layer with
a thickness of approximately of 0.4 .mu.m. Again, an outer layer
with a thickness of approximately 0.5 .mu.m was formed. The TiN
layer with a thickness of 0.5 .mu.m and the outer layer with a
thickness of 0.5 .mu.m were alternately laid on each other so that
four TiN layers and four outer layers alternated with each other.
Finally, a state indication layer of TiN with a thickness of
approximately 0.4 .mu.m was formed. In this way, respective
surface-coated cutting tools of the Examples and Comparative
Examples were prepared.
[0184] <Evaluation of Equivalent Peak Intensity of Outer
Layer>
[0185] For respective outer layers of the surface-coated cutting
tools of the Examples and Comparative Examples prepared in the
above-described manner, the x-ray diffraction intensity was
measured by a similar method to the x-ray diffraction method used
for Examples 22 to 36. The results are shown in the column "x-ray
intensity" in Table 11. The reflection plane providing a maximum
x-ray diffraction intensity is shown in the column "maximum peak"
in Table 11.
[0186] <Evaluation of Tangent Intersection Angle of Outer
Layer>
[0187] For the outer layer of the coating surface of the
surface-coated cutting tool of the Examples and Comparative
Examples each, a similar method to the method used for Examples 22
to 36 was used to calculate the ratio of .alpha.-aluminum oxide
crystal grains providing a tangent intersection angle of
100.degree. to 170.degree.. The results are shown in the column
"ratio of 100.degree.-170.degree." in Table 11.
TABLE-US-00011 TABLE 11 ratio of x-ray intensity maximum
100.degree.-170.degree. I(012) I(104) I(110) I(113) I(024) I(116)
I(124) I(030) PR(024) peak (%) Example 37 1011 117 665 356 526 147
130 203 1.64 012 75 38 895 117 819 417 513 103 128 370 1.47 012 64
39 1189 97 748 425 563 121 128 200 1.61 012 59 40 2496 130 854 605
930 211 145 107 1.79 012 98 41 1598 54 1033 454 591 81 97 363 1.37
012 66 42 2537 64 1403 612 914 124 149 354 1.48 012 55 Comparative
15 2356 72 1793 235 864 65 569 580 1.18 012 42 Example 16 856 2566
1147 766 866 272 228 161 1.40 104 45 17 880 94 899 339 481 96 153
212 1.43 110 48 18 780 77 694 349 863 100 134 595 2.23 024 30
[0188] <Cutting Test>
[0189] Respective surface-coated cutting tools of the Examples and
Comparative Examples were used to perform a steel machining test
under the following cutting conditions C and a cast-iron machining
test under the cutting conditions D to thereby evaluate the rake
face wear amount (mm) of the surface-coated cutting tool.
[0190] Cutting Test C [0191] Workpiece: SCM435 block material
[0192] Cutting Speed: 320 m/min [0193] Feed Rate: 0.25 mm/rev (wet
cutting) [0194] Cut: 1.5 mm [0195] Cut Length: 10 m
[0196] Cutting Test D [0197] Workpiece: FC250 block material [0198]
Cutting Speed: 260 m/min [0199] Feed Rate: 0.25 mm/rev (dry
cutting) [0200] Cut: 1.5 mm [0201] Cut Length: 12 m
[0202] Here, "flank face wear amount" was obtained by measuring the
width of wear of the surface-coated cutting tool before and after
the cutting test. The results are shown in Table 12. It is noted
that a surface-coated cutting tool with a smaller flank face wear
amount is superior in wear resistance of the surface-coated cutting
tool.
TABLE-US-00012 TABLE 12 wear resistance test (mm) workpiece steel
cast iron Example 37 0.101 0.112 38 0.114 0.123 39 0.115 0.119 40
0.097 0.102 41 0.113 0.117 42 0.123 0.119 Comparative 15 0.204
0.220 Example 16 0.191 0.208 17 0.126 0.136 18 0.208 0.229
[0203] It is apparent from the results shown in Table 12 that
respective surface-coated cutting tools of the Examples have
smaller flank face wear amounts than those of the Comparative
Examples. It is considered that, because respective surface-coated
cutting tools of the Comparative Examples have lower strength of
the outer layer, the outer layer peels off in the initial stage of
the cutting process and the wear of the flank face increases.
Therefore, respective surface-coated cutting tools of the Examples
are superior in wear resistance to those of the Comparative
Examples. The reason for the enhancement of the wear resistance is
considered as the enhanced strength of the outer layer.
[0204] It has been proved from the results above that the
surface-coated cutting tools of the Examples are superior in wear
resistance to the surface-coated cutting tools of the Comparative
Examples.
Examples 43-52, Comparative Examples 19-23
[0205] Examples and Comparative Examples were prepared by similar
manufacturing methods to each other except that respective outer
layers were formed under different conditions from each other.
First, for the base material, raw material powders of a cemented
carbide were mixed so that the contents of the composition were:
81.4 mass % of WC, 6.7 mass % of TiC, 1.4 mass % of TaC, 1.2 mass %
of NbC, 2.0 mass % of ZrC, 0.4 mass % of Cr.sub.3C.sub.2, and 6.9
mass % of Co.
[0206] Next, the raw material powders were press-formed and held in
a vacuum atmosphere at 1390.degree. C. for one hour to thereby
sinter the raw material powders of the cemented carbide. After
this, the press-formed body was removed from the furnace, and the
surface of the body was smooth-polished. Then, on the ridgeline of
the cutting edge, edge treatment was performed with an SiC brush so
that the amount of honing from the rake face side was 0.06 mm in
width. In this way, the base material in the shape of
CNMG120408N-GE (manufactured by Sumitomo Electric Hardmetal) was
prepared. In the surface of the base material thus prepared, a
.beta.-free layer of 10 .mu.m in thickness was formed.
[0207] Next, the base material was set in a CVD furnace, and the
known thermal CVD was used to form, from the base-material side, a
binder layer (TiN layer), an inner layer (MT-TiCN layer), an
alumina binder layer (TiCNO layer), an outer layer
(.alpha.-Al.sub.2O.sub.3), and a state indication layer (TiN layer)
in this order.
[0208] Specifically, the temperature in the furnace was first set
at 890.degree. C. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 1 .mu.m in thickness. Then, the
temperature in the furnace was set at 860.degree. C. As
raw-material gases, 2.2 vol % of TiCl.sub.4, 0.47 vol % of
CH.sub.3CN, and 25 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 70 hPa. Accordingly, an MT-TiCN layer of 10
.mu.m in thickness was formed.
[0209] Then, the temperature in the furnace ("temperature in
furnace" in Table 13) was set at the same temperature as the
temperature at which the outer layer was formed as described later
herein. As raw-material gases, 2.0 vol % of TiCl.sub.4, 0.2 vol %
of CH.sub.4, and 10 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 70 hPA. Accordingly, a TiCN binder layer was
formed. After this, the temperature in the furnace was maintained
and, as raw-material gases, 2.2 vol % of TiCl.sub.4, 0.2 vol % of
CH.sub.4, 10 vol % of N.sub.2, 1.2 vol % of CO, and 1.2 vol % of
CO.sub.2 were used. A residual content of H.sub.2 gas was
introduced as a carrier gas. The pressure in the furnace was set at
70 hPa. Accordingly, a TiCNO layer with a thickness of
approximately 1 .mu.m was formed.
[0210] Subsequently, an outer layer with a thickness of 4.5 .mu.m
was formed under the conditions of the temperature in the furnace,
the pressure, and the contents of the composition of the
raw-material gases shown in Table 13 below. Here, as to the volume
ratio of the raw-material gas "H.sub.2S" in Table 13, "0.14.+-.0.01
variation/35S" means that the volume ratio of the introduced
H.sub.2S is successively increased from 0.14 vol % to 0.15 vol %,
then successively decreased to 0.13 vol %, and thereafter further
increased successively to 0.14 vol %, this variation of the volume
ratio of H.sub.2S is made in one cycle of 35 seconds, and the cycle
is repeated to form the outer layer.
TABLE-US-00013 TABLE 13 temperature in furnace pressure AlCl.sub.3
CO.sub.2 HCl H.sub.2 (.degree. C.) (hPa) (vol %) H.sub.2S (vol %)
(vol %) (vol %) (vol %) Example 43 935 66 1.39 0.14 .+-. 0.01
variation/35 s 4.7 1.7 residual 44 917 74 1.31 0.12 .+-. 0.04
variation/15 s 4.6 1.9 residual 45 900 50 1.22 0.06 .+-. 0.07
variation/25 s 4.5 1.4 residual 46 913 74 1.06 0.13 .+-. 0.01
variation/40 s 4.7 2.8 residual 47 944 91 1.22 0.11 .+-. 0.03
variation/55 s 5.1 1.6 residual 48 892 34 0.89 0.06 .+-. 0.05
variation/45 s 4.9 4.1 residual 49 905 71 1.22 0.12 .+-. 0.03
variation/1.5 min 4.8 2.8 residual 50 939 58 1.31 0.10 .+-. 0.05
variation/4 min 4.8 3.6 residual 51 917 66 0.81 0.09 .+-. 0.04
variation/30 s 4.8 3.1 residual 52 935 74 1.06 0.02 .+-. 0.07
variation/3 min 4.3 4.2 residual Comparative 19 935 68 1.22 0.27
.+-. 0.10 variation/20 s 5.6 1.9 residual Example 20 1012 84 2.76
0.10 .+-. 0.02 variation/20 s 5.5 2.4 residual 21 940 95 1.65 0.13
2.8 1.1 residual 22 921 120 1.25 0.25 5.0 3.0 residual 23 1001 68
1.05 0.05 4.3 3.2 residual
[0211] Finally, at the same temperature as the temperature in the
furnace when the outer layer was formed, TiCl.sub.4 gas and N.sub.2
gas were used as raw-material gases and H.sub.2 gas was used as a
carrier gas to form a TiN layer of approximately 1.0 .mu.m in
thickness. In this way, respective surface-coated cutting tools of
the Examples and Comparative Examples were prepared.
[0212] <Evaluation of Equivalent Peak Intensity of Outer
Layer>
[0213] For respective outer layers of the surface-coated cutting
tools of the Examples and Comparative Examples prepared in the
above-described manner, a Cu K.alpha..sub.1 (wavelength
.lamda.=1.5405 A) x-ray source was used, and based on the
2.theta.-.theta. scan x-ray diffraction method, the x-ray
diffraction intensity was measured. The results are shown in the
column "x-ray intensity" in Table 14.
TABLE-US-00014 TABLE 14 ratio of R = 3 mm x-ray intensity or I(012)
I(104) I(110) I(113) I(024) I(116) I(124) I(030) PR(024) PR(110)
PR(012) more (%) Example 43 546 117 523 376 562 149 130 210 2.07
2.17 1.21 69 44 927 112 847 427 527 98 123 377 1.47 2.66 1.55 41 45
1255 102 789 448 593 127 134 210 1.61 2.41 2.04 58 46 932 100 324
281 790 232 46 12 3.01 1.39 2.13 86 47 856 125 884 624 964 210 142
101 2.38 2.46 1.27 73 48 762 785 543 503 564 97 115 404 1.59 1.72
1.29 55 49 1203 2013 1675 695 1069 92 122 376 1.54 2.71 1.04 43 50
1515 57 356 324 965 116 102 32 2.86 1.19 2.70 75 51 1740 20 543 467
652 120 101 339 1.71 1.60 2.74 64 52 1035 110 592 20 318 157 64 42
1.35 2.82 2.63 35 Comparative 19 934 171 952 409 447 174 229 286
1.28 4.63 0.28 27 Example 20 230 183 2042 526 632 74 178 291 1.17
2.81 1.47 10 21 4610 4518 259 572 135 443 576 52 0.16 0.34 3.22 26
22 1129 3397 1515 1009 942 354 296 207 1.20 2.16 0.86 14 23 1370
316 263 724 495 350 401 1093 1.02 0.61 1.70 5
[0214] Then, the equivalent peak intensity PR(hkl) of a (hid) plane
defined by the following formula was calculated. Based on this
PR(hkl), the x-ray peak intensities from the (024) plane, the (110)
plane, and the (012) plane of the outer layer were quantitatively
evaluated.
PR(024)={I(024)/I.sub.0(024)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
PR(110)={I(110)/I.sub.0(110)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
PR(012)={I(012)/I.sub.0(012)}/[.SIGMA.{I(hkl)/I.sub.0(hkl)}/8]
[0215] <Evaluation of Surface R of .alpha.-Aluminum Oxide
Crystal Grains>
[0216] Respective surface-coated cutting tools of the Examples and
Comparative
[0217] Examples were each cut along a plane including a normal to
the coating surface, and the resultant cross section was
mechanically polished and thereafter further ion-polished. For a
region of 20 .mu.m in length in the polished surface, an FE-SEM was
used to perform three-field measurement at a magnification of 10000
on .alpha.-aluminum oxide crystal grains located in the surface of
the outer layer. Accordingly, the radius (surface R) of an
inscribed circle abutting on a protrusion formed by an
.alpha.-aluminum oxide crystal grain located in the surface of the
outer layer was calculated. Then, the ratio of .alpha.-aluminum
oxide crystal grains with a surface R of 3 mm or more to the
.alpha.-aluminum oxide crystal grains in the region of 20 .mu.m in
length was determined. The results are shown in the column "ratio
of R=3 mm or more" in Table 14.
[0218] <Cutting Test>
[0219] Respective surface-coated cutting tools of the Examples and
Comparative Examples were used to perform a steel machining test
under the following cutting conditions A and thereby evaluate the
flank face wear amount (mm) of the surface-coated cutting tool.
Further, a cast-iron intermittent cutting test was performed under
cutting conditions B to thereby evaluate the number of times
(count) impact was applied before chipping or fracture occurred to
the surface-coated cutting tool.
[0220] Cutting Test A [0221] Workpiece: S45C round bar [0222]
Cutting Speed: 260 m/min [0223] Feed Rate: 0.4 mm/rev (wet cutting)
[0224] Cut: 2.0 mm [0225] Cutting Time: 12 minutes
[0226] Cutting Test B [0227] Workpiece: FC250 (round bar with four
grooves) [0228] Cutting Speed: 190 m/min [0229] Feed Rate: 0.25
mm/rev (wet cutting) [0230] Cut: 1.5 mm
[0231] Here, the width of wear of the flank face of the
surface-coated cutting tool was measured before and after the
cutting test and the obtained value representing the width of wear
is shown in the column "flank face wear amount" in Table 15. It is
noted that a surface-coated cutting tool with a smaller flank face
wear amount is superior in wear resistance of the surface-coated
cutting tool.
[0232] Further, the number of times impact was applied before
chipping or fracture occurred to the surface-coated cutting tool
while a cast iron was intermittently cut with the surface-coated
cutting tool is shown in the column "count of impact" in Table 15.
It is noted that as the count of impact is higher, fracture is less
likely to occur.
TABLE-US-00015 TABLE 15 life flank face count of wear amount impact
(mm) (count) Example 43 0.048 4892 44 0.077 4172 45 0.065 4802 46
0.037 6152 47 0.043 4892 48 0.067 4712 49 0.076 4712 50 0.04 5072
51 0.064 4802 52 0.081 3992 Comparative 19 0.139 3011 Example 20
0.157 2651 21 0.148 2741 22 0.155 2891 23 0.175 2621
[0233] It is apparent from the results shown in Table 15 that
respective surface-coated cutting tools of the Examples have
smaller flank face wear amounts and higher counts of impact than
those of the Comparative Examples. It is seen from this result that
respective surface-coated cutting tools of the Examples are
excellent in wear resistance and fracture resistance relative to
those of the Comparative Examples. The reason for the enhanced wear
resistance and fracture resistance is considered as the enhanced
strength of the outer layer and the enhanced adhesion resistance of
the coating. In contrast, it is considered that, because respective
surface-coated cutting tools of the Comparative Examples are
insufficient in terms of the strength of the outer layer, the outer
layer peels off in the initial stage of the cutting process and the
wear of the flank face increases or chipping or fracture
occurs.
Examples 53-57, Comparative Examples 24-27
[0234] Examples and Comparative Examples were prepared by similar
manufacturing methods to each other except that respective outer
layers were formed under different conditions from each other.
First, for the base material, raw material powders of a cemented
carbide were mixed so that the contents of the composition were:
74.4 mass % of WC, 7.5 mass % of TaC, 7.7 mass % of TiC, 0.3 mass %
of Cr.sub.3C.sub.2, and 10.8 mass % of Co.
[0235] Next, the raw material powders were press-formed and held in
a vacuum atmosphere at 1380.degree. C. for one and a half hours to
thereby sinter the raw material powders of the cemented carbide.
After this, the press-formed body was removed from the furnace, and
the surface of the body was smooth-polished. Then, on the ridgeline
of the cutting edge, edge treatment was performed with an SiC brush
so that the amount of honing from the rake face side was 0.03 mm in
width. In this way, the base material in the shape of SPGN120412
was prepared. In the surface of the base material thus prepared, no
.beta.-free layer was formed.
[0236] Next, the base material was set in a CVD furnace, and the
known thermal CVD was used to form, from the base-material side, a
binder layer (TiN layer), an inner layer (MT-TiCN layer), an
alumina binder layer (TiBN layer), an outer layer
(.alpha.-Al.sub.2O.sub.3), and a state indication layer
(alternating TiN layer/Al.sub.2O.sub.3 layer) in this order.
[0237] Specifically, the temperature in the furnace was first set
at 880.degree. C. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 0.5 .mu.m in thickness. Then, the
temperature in the furnace was kept at 840.degree. C. As
raw-material gases, 2.0 vol % of TiCl.sub.4, 0.4 vol % of
CH.sub.3CN, and 17 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 70 hPa. Accordingly, an MT-TiCN layer of 3 .mu.m
in thickness was formed.
[0238] Then, the temperature in the furnace ("temperature in
furnace" in Table 16) was set at the same temperature as the
temperature at which the outer layer was formed as described later
herein. As raw-material gases, 1.8 vol % of TiCl.sub.4, 0.02 vol %
of BCl.sub.3, and 15 vol % of N.sub.2 were used. A residual content
of H.sub.2 gas was introduced as a carrier gas. The pressure in the
furnace was set at 50 hPA. Accordingly, a TiBN layer with a
thickness of approximately 1 .mu.m was formed.
[0239] Subsequently, an outer layer of 2.0 .mu.m in thickness was
formed under the conditions of the temperature in the furnace, the
pressure, and the contents of the composition of the raw-material
gases shown in Table 16 below.
TABLE-US-00016 TABLE 16 temperature in furnace pressure AlCl.sub.3
ZrCl.sub.4 CO.sub.2 HCl H.sub.2 (.degree. C.) (hPa) (vol %) (vol %)
H.sub.2S (vol %) (vol %) (vol %) (vol %) Example 53 917 63 1.39
0.41 0.12 .+-. 0.005 variation/20 s 4.7 1.6 residual 54 939 74 1.22
0.59 0.03 .+-. 0.06 variation/1.5 min 4.7 1.6 residual 55 909 55
0.72 0.50 0.09 .+-. 0.04 variation/25 s 4.7 2.2 residual 56 917 63
0.97 0.32 0.11 .+-. 0.03 variation/45 s 5.2 2.6 residual 57 939 91
1.64 0.41 0.12 .+-. 0.02 variation/10 s 4.9 1.9 residual
Comparative 24 926 55 2.85 0.23 0.10 .+-. 0.02 variation/10 s 5.0
2.8 residual Example 25 910 64 4.28 0.41 0.54 5.2 2.4 residual 26
1010 75 5.00 0.28 0.45 4.5 1.4 residual 27 944 54 4.28 0.46 0.13
3.9 1.9 residual
[0240] Next, the temperature at which the outer layer was formed
was maintained. TiCl.sub.4 gas and N.sub.2 gas were used as
raw-material gases and H.sub.2 gas was used as a carrier gas to
form a TiN layer of approximately 0.4 .mu.m in thickness. Again, an
outer layer with a thickness of approximately 0.4 .mu.m was formed.
The TiN layer with a thickness of 0.4 .mu.m and the outer layer
with a thickness of 0.4 .mu.m were alternately laid on each other
so that five TiN layers and five outer layers alternated with each
other. Finally, a state indication layer of TiN with a thickness of
approximately 0.4 .mu.m was formed. In this way, respective
surface-coated cutting tools of the Examples and Comparative
Examples were prepared.
[0241] <Evaluation of Equivalent Peak Intensity of Outer
Layer>
[0242] For respective outer layers of the surface-coated cutting
tools of the Examples and Comparative Examples prepared in the
above-described manner, the x-ray diffraction method used for
Examples 43 to 52 was used to measure the x-ray diffraction
intensity. The results are shown in the column "x-ray intensity" in
Table 17. Further, analysis was conducted similarly to the method
for analysis used for Examples 43 to 52 to thereby calculate the
equivalent peak intensities PR(hkl) of the (024) plane, the (110)
plane, and the (012) plane. The values representing the intensities
are shown in the columns "PR(024)" and "PR(110)" and "PR(012)" in
Table 17.
[0243] <Evaluation of Surface R of .alpha.-Aluminum Oxide
Crystal Grains>
[0244] For the outer layer of the coating surface of the
surface-coated cutting tool in the Examples and Comparative
Examples each, a similar method to the method used for Examples 43
to 52 was used to thereby calculate the ratio of .alpha.-aluminum
oxide crystal grains with a surface R of 3 mm or more. The results
are shown in the column "ratio of R=3 mm or more" in Table 17.
TABLE-US-00017 TABLE 17 ratio of R = 3 mm x-ray intensity or I(012)
I(104) I(110) I(113) I(024) I(116) I(124) I(030) PR(024) PR(110)
PR(012) more (%) Example 53 535 143 351 408 597 176 157 238 2.255
1.493 1.214 54 54 972 116 358 446 551 101 127 394 1.839 1.344 1.945
35 55 573 146 456 637 844 181 192 300 2.482 1.509 1.011 83 56 698
158 876 629 951 238 174 136 2.351 2.437 1.036 60 57 783 55 292 575
754 90 111 457 2.444 1.065 1.523 75 Comparative 24 2000 97 1531 233
757 91 511 520 1.18 2.69 1.88 18 Example 25 885 2253 1118 813 793
417 382 329 1.23 1.94 0.82 26 26 268 123 209 392 186 126 189 253
1.06 1.34 0.92 4 27 599 110 215 377 281 133 166 618 1.13 0.97 1.45
13
[0245] <Cutting Test>
[0246] Respective surface-coated cutting tools of the Examples and
Comparative Examples were used to perform a cast iron machining
test under the following cutting conditions C and thereby evaluate
the flank face wear amount (mm) of the surface-coated cutting tool.
Further, a steel machining test was performed under the following
cutting conditions D to thereby evaluate the cut length (mm) before
fracture occurred to the surface-coated cutting tool.
[0247] Cutting Test C [0248] Workpiece: FC250 block material [0249]
Cutting Speed: 270 in/min [0250] Feed Rate: 0.35 mm/rev (dry
cutting) [0251] Cut: 1.5 mm [0252] Cut Length: 12 m
[0253] Cutting Test D [0254] Workpiece: four S50C plate materials
[0255] Cutting Speed: 150 m/min [0256] Feed Rate: 0.27 mm/rev (dry
cutting) [0257] Cut: 2.0 mm
[0258] Here, the flank face wear amount was obtained by measuring
the width of wear of the surface-coated cutting tool before and
after the cutting test. The results are shown in Table 18. It is
noted that a surface-coated cutting tool with a smaller flank face
wear amount is superior in wear resistance. "Cut Length" in Table
18 refers to the length of cut before chipping or fracture occurred
to the surface-coated cutting tool while steel machining was
continued with the surface-coated cutting tool. It is noted that as
the cut length is longer, fracture is less likely to occur.
TABLE-US-00018 TABLE 18 wear resistance test cut length before
fracture (mm) (mm) Example 53 0.111 1120 54 0.112 1230 55 0.095
1190 56 0.11 1020 57 0.099 1170 Comparative 24 0.28 440 Example 25
0.221 416 26 0.295 272 27 0.292 458
[0259] It is apparent from the results shown in Table 18 that
respective surface-coated cutting tools of the Examples have
smaller flank face wear amounts and fracture is less likely to
occur relative to those of the Comparative Examples. Thus, it is
seen that respective surface-coated cutting tools of the Examples
are excellent in wear resistance and fracture resistance relative
to those of the Comparative Examples. The reason for the enhanced
wear resistance and fracture resistance of the surface-coated
cutting tool of each Example is considered as the enhanced strength
of the outer layer. In contrast, it is considered that, because the
surface-coated cutting tool of each Comparative Example has weak
strength and adherence of the outer layer, the outer layer peels
off in the initial stage of the cutting process and wear of the
flank face increases or fracture occurs.
[0260] It has been proved from the results above that the
surface-coated cutting tools of the Examples are superior in wear
resistance relative to the surface-coated cutting tools of the
Comparative Examples.
[0261] While the embodiments and examples of the present invention
have heretofore been described, it is originally intended to
appropriately combine the features of the above-described
embodiments and examples each.
[0262] It should be construed that the embodiments and examples
disclosed herein are 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.
* * * * *