U.S. patent application number 11/808404 was filed with the patent office on 2007-12-27 for coated cutting tool insert.
This patent application is currently assigned to SANDVIK INTELLECTUAL PROPERTY AB. Invention is credited to Gunilla Andersson, Katarina Dahl, Anders Karlsson, Jan Kjellgren, Peter Littecke.
Application Number | 20070298282 11/808404 |
Document ID | / |
Family ID | 38873898 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070298282 |
Kind Code |
A1 |
Andersson; Gunilla ; et
al. |
December 27, 2007 |
Coated cutting tool insert
Abstract
A CVD-coated cutting tool insert with improved toughness
properties having the ability to withstand high temperatures
without sacrificing edge line security is disclosed. The insert
coating comprises a TiC.sub.xN.sub.y-layer with a low tensile
stress level of 50-500 MPa and an .alpha.-Al.sub.2O.sub.3-layer
with a high surface smoothness with a mean Ra<0.12 .mu.m as
measured by AFM-technique, obtained by subjecting the coating to an
intensive wet blasting operation.
Inventors: |
Andersson; Gunilla;
(Sollentuna, SE) ; Karlsson; Anders; (Stockholm,
SE) ; Dahl; Katarina; (Sandviken, SE) ;
Kjellgren; Jan; (Kista, SE) ; Littecke; Peter;
(Huddinge, SE) |
Correspondence
Address: |
DRINKER BIDDLE & REATH (DC)
1500 K STREET, N.W.
SUITE 1100
WASHINGTON
DC
20005-1209
US
|
Assignee: |
SANDVIK INTELLECTUAL PROPERTY
AB
|
Family ID: |
38873898 |
Appl. No.: |
11/808404 |
Filed: |
June 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/SE06/00736 |
Jun 16, 2006 |
|
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11808404 |
Jun 8, 2007 |
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Current U.S.
Class: |
428/698 |
Current CPC
Class: |
B24C 7/0007 20130101;
C23C 16/56 20130101; Y10T 428/265 20150115; Y10T 428/24975
20150115; Y10T 407/27 20150115; C23C 16/36 20130101; C23C 16/403
20130101; C23C 30/005 20130101; B24C 1/10 20130101 |
Class at
Publication: |
428/698 |
International
Class: |
B32B 9/00 20060101
B32B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2005 |
SE |
0501410-5 |
Dec 15, 2006 |
SE |
0602723-9 |
Claims
1. A coated cutting tool insert of cemented carbide comprising: a
body of generally polygonal or round shape having at least one rake
face and at least one clearance face; and a coating on the body,
wherein said insert is at least partly coated with the coating,
wherein said body has a composition including 4.4-6.6 wt-% Co,
4-8.5 wt-% cubic carbides, balance WC, a CW-ratio in the range
0.78-0.92 and has a surface zone of a thickness of 10 to 40 .mu.m,
depleted from the cubic carbides TiC, TaC and/or NbC, wherein said
coating is 10-25 .mu.m thick and includes at least one layer of
TiC.sub.xN.sub.y, where x.gtoreq.0, y.gtoreq.0 and x+y=1 and an
.alpha.-Al.sub.2O.sub.3-layer, the .alpha.-Al.sub.2O.sub.3-layer
being the outer layer at least on the rake face, and wherein: (i)
on said at least one rake face: the TiC.sub.xN.sub.y-layer has a
thickness of from 3 .mu.m to 15 .mu.m and a tensile stress level of
50-500 MPa, and the .alpha.-Al.sub.2O.sub.3-layer has a thickness
of from 3 .mu.m to 12 .mu.m, is the outermost layer with an
XRD-diffraction intensity ratio I(012)/I(024).gtoreq.1.3, and has a
mean Ra value MRa<0.12 .mu.m at least in the chip contact zone
on the rake face, and on said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a tensile stress in the range 500-700
MPa, and the .alpha.-Al.sub.2O.sub.3-layer has an XRD-diffraction
intensity ratio I(012)/I(024)<1.5, or (ii) on said at least one
rake face and said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a thickness of from 3 .mu.m to 15 .mu.m
and a tensile stress level of 50-500 MPa, the
.alpha.-Al.sub.2O.sub.3-layer has a thickness of from 3 .mu.m to 12
.mu.m, has an XRD-diffraction intensity ratio
I(012)/I(024).gtoreq.1.3, and is the outermost layer on the rake
face with a mean Ra value MRa<0.12 .mu.m at least in the chip
contact zone on the rake face, and the outermost layer on said
clearance face consists of a colored heat resistant paint or a
colored PVD-layer.
2. The coated cutting tool insert according to claim 1, comprising
a 0.2-2 .mu.m TiC.sub.xN.sub.yO.sub.z bonding layer between the
TiC.sub.xN.sub.y-layer and the Al.sub.2O.sub.3-layer, wherein
x.gtoreq.0, z>0 and y.gtoreq.0 for the TiC.sub.xN.sub.yO.sub.z
bonding layer.
3. The coated cutting tool insert according to claim 1, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 104-direction
with a texture coefficient TC(104)>1.5.
4. The coated cutting tool insert according to claim 3, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 104-direction
with a texture coefficient TC(104)>2.0.
5. The coated cutting tool insert according to claim 4, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 104-direction
with a texture coefficient TC(104)>2.5.
6. The coated cutting tool insert according to claim 1, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 012-direction
with a texture coefficient TC(01 2)>1.3.
7. The coated cutting tool insert according to claim 6, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 012-direction
with a texture coefficient TC(01 2)>1.5.
8. The coated cutting tool insert according to claim 1, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 110-direction
with a texture coefficient TC(110)>1.5.
9. The coated cutting tool insert according to claim 1, wherein the
coating includes additional layers composed of metal nitrides
and/or carbides and/or oxides with the metal elements selected from
Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and Al to a total layer thickness
of <5 .mu.m.
10. The coated cutting tool insert according to claim 1, wherein
said surface zone depleted from cubic carbides has a thickness of
from 15 .mu.m to 35 .mu.m.
11. The coated cutting tool insert according to claim 10, wherein
said surface zone depleted from cubic carbides has a thickness of
from 20 .mu.m.
12. The coated cutting tool insert according to claim 10, wherein
said surface zone depleted from cubic carbides has a thickness to
30 .mu.m.
13. The coated cutting tool insert according to claim 12, wherein
said surface zone depleted from cubic carbides has a thickness to
25 .mu.m.
14. The coated cutting tool insert according to claim 1, wherein
the composition of said body includes 5.0-6.0 wt-% Co.
15. The coated cutting tool insert according to claim 14, wherein
the composition of said body includes 5.0-5.8 wt-% Co.
16. The coated cutting tool insert according to claim 1, wherein
the at least one layer of TiC.sub.xN.sub.y is TiC.sub.xN.sub.y
deposited by MTCVD.
17. The coated cutting tool insert according to claim 1, wherein
the TiC.sub.xN.sub.y-layer has a thickness from 4 .mu.m.
18. The coated cutting tool insert according to claim 17, wherein
the TiC.sub.xN.sub.y-layer has a thickness from 5 .mu.m.
19. The coated cutting tool insert according to claim 18, wherein
the TiC.sub.xN.sub.y-layer has a thickness from 6 .mu.m.
20. The coated cutting tool insert according to claim 1, wherein
the TiC.sub.xN.sub.y-layer has a thickness to 13 .mu.m.
21. The coated cutting tool insert according to claim 20, wherein
the TiC.sub.xN.sub.y-layer has a thickness to 10 .mu.m.
22. The coated cutting tool insert according to claim 1, wherein
the TiC.sub.xN.sub.y-layer has a tensile stress level of 50-450
MPa.
23. The coated cutting tool insert according to claim 1, wherein
the .alpha.-Al.sub.2O.sub.3-layer has a thickness from 3.5
.mu.m.
24. The coated cutting tool insert according to claim 23, wherein
the .alpha.-Al.sub.2O.sub.3-layer has a thickness from 4 .mu.m.
25. The coated cutting tool insert according to claim 1, wherein
the .alpha.-Al.sub.2O.sub.3-layer has a thickness to 11 .mu.m.
26. The coated cutting tool insert according to claim 25, wherein
the .alpha.-Al.sub.2O.sub.3-layer has a thickness to 10 .mu.m.
27. The coated cutting tool according to claim 1, wherein the
.alpha.-Al.sub.2O.sub.3-layer on said at least one rake face has an
XRD-diffraction intensity ratio I(012)/I(024).gtoreq.1.5.
28. The coated cutting tool insert according to claim 1, wherein
the .alpha.-Al.sub.2O.sub.3-layer has a mean Ra value
MRa.ltoreq.0.10 .mu.m.
29. The coated cutting tool insert according to claim 1, wherein
the .alpha.-Al.sub.2O.sub.3-layer on said at least one clearance
face is covered with a TiN, TiC.sub.xN.sub.y, ZrC.sub.xN.sub.y or
TiC layer giving the insert a different color on that face.
30. The coated cutting tool insert according to claim 29, wherein
the TiN, TiC.sub.xN.sub.y, ZrC.sub.xN.sub.y or TiC layer has a
thickness of 0.1-2 .mu.m.
31. A coated cutting tool insert of cemented carbide comprising: a
body of generally polygonal or round shape having at least one rake
face and at least one clearance face; and a coating on the body,
wherein said insert is at least partly coated with the coating,
wherein said body has a composition including 4.4-6.6 wt-% Co,
4-8.5 wt-% cubic carbides, balance WC, a CW-ratio in the range
0.78-0.92 and has a surface zone of a thickness of 10 to 40 .mu.m,
depleted from the cubic carbides TiC, TaC and/or NbC, wherein said
coating is 10-25 .mu.m thick and includes at least one layer of
TiC.sub.xN.sub.y, where x.gtoreq.0, y.gtoreq.0 and x+y=1 and an
.alpha.-Al.sub.2O.sub.3-layer, the .alpha.-Al.sub.2O.sub.3-layer
being the outer layer at least on the rake face, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 104-direction
with a texture coefficient TC(104)>1.5, and wherein: (i) on said
at least one rake face: the TiC.sub.xN.sub.y-layer has a thickness
of from 3 .mu.m to 15 .mu.m and a tensile stress level of 50-500
MPa, and the .alpha.-Al.sub.2O.sub.3-layer has a thickness of from
3 .mu.m to 12 .mu.m, is the outermost layer with an XRD-diffraction
intensity ratio I(012)/I(024).gtoreq.1.3, and has a mean Ra value
MRa<0.12 .mu.m at least in the chip contact zone on the rake
face, and on said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a tensile stress in the range 500-700
MPa, and the .alpha.-Al.sub.2O.sub.3-layer has an XRD-diffraction
intensity ratio I(012)/I(024)<1.5, or (ii) on said at least one
rake face and said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a thickness of from 3 .mu.m to 15 .mu.m
and a tensile stress level of 50-500 MPa, the
.alpha.-Al.sub.2O.sub.3-layer has a thickness of from 3 .mu.m to 12
.mu.m, has an XRD-diffraction intensity ratio
I(012)/I(024).gtoreq.1.3, and is the outermost layer on the rake
face with a mean Ra value MRa<0.12 .mu.m at least in the chip
contact zone on the rake face, and the outermost layer on said
clearance face consists of a colored heat resistant paint or a
colored PVD-layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part patent
application under 37 C.F.R. .sctn. 1.53(b), of pending prior
International Application No. PCT/SE2006/000736, having a filing
date of Jun. 16, 2006, which claims priority to Swedish Patent
Application No. 0501410-5 filed Jun. 17, 2005, of pending prior
U.S. application Ser. No. 11/454,127, having a filing date of Jun.
16, 2006, which also claims priority to Swedish Patent Application
No. 0501410-5 filed Jun. 17, 2005, and this application also claims
priority to Swedish Patent Application No. 0602723-9 filed Dec. 15,
2006; the content of each of these applications is incorporated by
reference herein.
FIELD
[0002] The present disclosure relates to a high performance coated
cutting tool insert particularly useful for turning in low alloyed
steel, carbon steel and tough hardened steels in the area from
finishing to roughing in wet and dry conditions at high cutting
speed, having the ability to withstand high temperatures without
sacrificing edge security. The insert is based on WC, cubic
carbides and a Co-binder phase with a cobalt enriched surface zone
giving the cutting insert an excellent resistance to plastic
deformation and a high toughness performance. Furthermore, the
coating comprises a number of wear resistance layers which have
been subjected to a surface post treatment giving the tool insert a
surprisingly improved cutting performance.
BACKGROUND
[0003] In the discussion of the background that follows, reference
is made to certain structures and/or methods. However, the
following references should not be construed as an admission that
these structures and/or methods constitute prior art. Applicant
expressly reserves the right to demonstrate that such structures
and/or methods do not qualify as prior art.
[0004] The majority of today's cutting tools are based on a
cemented carbide insert coated with several hard layers like TiC,
TiC.sub.xN.sub.y, TiN, TiC.sub.xN.sub.yO.sub.z and Al.sub.2O.sub.3.
The sequence and the thickness of the individual layers are
carefully chosen to suit different cutting application areas and
work-piece materials. The most frequent employed coating techniques
are Chemical Vapor Deposition (CVD) and Physical Vapor Deposition
(PVD). CVD-coated inserts in particular have a tremendous advantage
in terms of flank and crater wear resistance over uncoated
inserts.
[0005] The CVD technique is conducted at a rather high temperature
range, 950-1050.degree. C. Due to this high deposition temperature
and to a mismatch in the coefficients of thermal expansion between
the deposited coating materials and the cemented carbide tool
insert, CVD can lead to coatings with cooling cracks and high
tensile stresses (sometimes up to 1000 MPa). The high tensile
stresses can under some cutting conditions be a disadvantage as it
may cause the cooling cracks to propagate further into the cemented
carbide body and cause breakage of the cutting edge.
[0006] In the metal cutting industry there is a constant striving
to increase the cutting condition envelope, i.e., the ability to
withstand higher cutting speeds without sacrificing the ability to
resist fracture or chipping during interrupted cutting at low
speeds.
[0007] Important improvements in the application envelope have been
achieved by combining inserts with a binder phase enriched surface
zone and optimized, thicker coatings.
[0008] However, with an increasing coating thickness, the positive
effect on wear resistance is out-balanced by an increasing negative
effect in the form of an increased risk of coating delamination and
reduced toughness making the cutting tool less reliable. This
applies in particular to softer work piece materials such as low
carbon steels and stainless steels and when the coating thickness
exceeds 5-10 .mu.m. Further, thick coatings generally have a more
uneven surface, a negative feature when cutting smearing materials
like low carbon steels and stainless steel. A remedy can be to
apply a post smoothing operation of the coating by brushing or by
wet blasting as disclosed in several patents, e.g., EP 0 298 729,
EP 1 306 150 and EP 0 736 615. In U.S. Pat. No. 5,861,210 the
purpose has, e.g., been to achieve a smooth cutting edge and to
expose the Al.sub.2O.sub.3 as the outermost layer on the rake face
leaving the TiN on the clearance side to be used as a wear
detection layer. A coating with high resistance to flaking is
obtained.
[0009] Every post treatment technique that exposes a surface, e.g.,
a coating surface to a mechanical impact as, e.g., wet or dry
blasting will have some influence on the surface finish and the
stress state (a) of the coating.
[0010] An intense blasting impact may lower the tensile stresses in
a CVD-coating, but often this will be at the expense of lost
coating surface finish by the creation of ditches along the cooling
cracks or it can even lead to delamination of the coating.
[0011] A very intensive treatment may even lead to a big change in
the stress state, e.g., from highly tensile to highly compressive
as disclosed in EP-A-1 311 712, in which a dry blasting technique
is used.
SUMMARY
[0012] It has now surprisingly been found that a cutting tool
insert having a combination of a certain cemented carbide substrate
composition and a certain coating structure and thickness, and
being post treated by wet-blasting under controlled conditions
obtains excellent cutting properties over a broader range of
applications than prior art cutting tool inserts.
[0013] The cobalt binder phase is highly alloyed with W. The
content of W in the binder phase can be expressed as the CW-ratio:
CW-ratio=M.sub.s/(wt-%Co*0.0161) wherein M.sub.s=measured
saturation magnetization in hAm.sup.2/kg and wt-% Co is the cobalt
content in the cemented carbide. A low CW-ratio corresponds to a
high W-content in the Co binder phase. The employed post treatment
will give the coating a favorable tensile stress level, the
Al.sub.2O.sub.3-layer a certain important crystallographic feature
and a top surface with an excellent surface finish.
[0014] The mentioned combination with the blasting technique
effectively expands the limitations of what coating thickness that
can be applied without performance penalty. As a result of the
invention application areas of unsurpassed width is now possible.
The significant improvements achieved with respect to toughness
behavior and coating adhesion was surprising.
[0015] To significantly change the stress state of a coating by
blasting, the blasting media, e.g., Al.sub.2O.sub.3 grits have to
strike the coating surface with a high impulse. The impact force
can be controlled by, e.g., the blasting pulp pressure (wet
blasting), the distance between blasting nozzle and coating
surface, grain size of the blasting media, the concentration of the
blasting media and the impact angle of the blasting jet.
[0016] It is an object of the present invention to provide
CVD-coated tool inserts with improved toughness properties having
the ability to withstand high temperatures without sacrificing edge
security or toughness.
[0017] An exemplary embodiment of a coated cutting tool insert of
cemented carbide comprises a body of generally polygonal or round
shape having at least one rake face and at least one clearance
face, and a coating on the body, wherein said insert is at least
partly coated with the coating, wherein said body has a composition
including 4.4-6.6 wt-% Co, 4-8.5 wt-% cubic carbides, balance WC, a
CW-ratio in the range 0.78-0.92 and has a surface zone of a
thickness of 10 to 40 .mu.m, depleted from the cubic carbides TiC,
TaC and/or NbC, wherein said coating is 10-25 .mu.m thick and
includes at least one layer of TiC.sub.xN.sub.y, where x.gtoreq.0,
y.gtoreq.0 and x+y=1 and an .alpha.-Al.sub.2O.sub.3-layer, the
.alpha.-Al.sub.2O.sub.3-layer being the outer layer at least on the
rake face, and wherein: [0018] (i) on said at least one rake face:
the TiC.sub.xN.sub.y-layer has a thickness of from 3 .mu.m to 15
.mu.m and a tensile stress level of 50-500 MPa, and the
.alpha.-Al.sub.2O.sub.3-layer has a thickness of from 3 .mu.m to 12
.mu.m, is the outermost layer with an XRD-diffraction intensity
ratio I(012)/I(024).gtoreq.1.3, and has a mean Ra value MRa<0.12
.mu.m at least in the chip contact zone on the rake face, and on
said at least one clearance face: the TiC.sub.xN.sub.y-layer has a
tensile stress in the range 500-700 MPa, and the
.alpha.-Al.sub.2O.sub.3-layer has an XRD-diffraction intensity
ratio I(01 2)/I(024)<1.5, or [0019] (ii) on said at least one
rake face and said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a thickness of from 3 .mu.m to 15 .mu.m
and a tensile stress level of 50-500 MPa, the
.alpha.-Al.sub.2O.sub.3-layer has a thickness of from 3 .mu.m to 12
.mu.m, has an XRD-diffraction intensity ratio
I(012)/I(024).gtoreq.1.3, and is the outermost layer on the rake
face with a mean Ra value MRa<0.12 .mu.m at least in the chip
contact zone on the rake face, and the outermost layer on said
clearance face consists of a colored heat resistant paint or a
colored PVD-layer.
[0020] An additional exemplary embodiment of a coated cutting tool
insert of cemented carbide comprises a body of generally polygonal
or round shape having at least one rake face and at least one
clearance face, and a coating on the body, wherein said insert is
at least partly coated with the coating, wherein said body has a
composition including 4.4-6.6 wt-% Co, 4-8.5 wt-% cubic carbides,
balance WC, a CW-ratio in the range 0.78-0.92 and has a surface
zone of a thickness of 10 to 40 .mu.m, depleted from the cubic
carbides TiC, TaC and/or NbC, wherein said coating is 10-25 .mu.m
thick and includes at least one layer of TiC.sub.xN.sub.y, where
x.gtoreq.0, y.gtoreq.0 and x+y=1 and an
.alpha.-Al.sub.2O.sub.3-layer, the .alpha.-Al.sub.2O.sub.3-layer
being the outer layer at least on the rake face, wherein the
.alpha.-Al.sub.2O.sub.3-layer has a texture in the 104-direction
with a texture coefficient TC(104)>1.5, and wherein: [0021] (i)
on said at least one rake face: the TiC.sub.xN.sub.y-layer has a
thickness of from 3 .mu.m to 15 .mu.m and a tensile stress level of
50-500 MPa, and the .alpha.-Al.sub.2O.sub.3-layer has a thickness
of from 3 .mu.m to 12 .mu.m, is the outermost layer with an
XRD-diffraction intensity ratio I(012)/I(024).gtoreq.1.3, and has a
mean Ra value MRa<0.12 .mu.m at least in the chip contact zone
on the rake face, and on said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a tensile stress in the range 500-700
MPa, and the (.alpha.-Al.sub.2O.sub.3-layer has an XRD-diffraction
intensity ratio I(012)/I(024)<1.5, or [0022] (ii) on said at
least one rake face and said at least one clearance face: the
TiC.sub.xN.sub.y-layer has a thickness of from 3 .mu.m to 15 .mu.m
and a tensile stress level of 50-500 MPa, the
.alpha.-Al.sub.2O.sub.3-layer has a thickness of from 3 .mu.m to 12
.mu.m, has an XRD-diffraction intensity ratio
I(012)/I(024).gtoreq.1.3, and is the outermost layer on the rake
face with a mean Ra value MRa<0.12 .mu.m at least in the chip
contact zone on the rake face, and the outermost layer on said
clearance face consists of a colored heat resistant paint or a
colored PVD-layer.
[0023] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWING
[0024] The following detailed description can be read in connection
with the accompanying drawings in which like numerals designate
like elements and in which:
[0025] FIG. 1 shows a goniometer set-up for the evaluation of
residual stress by X-ray measurements in which: [0026] E=Euler
1/4-cradle [0027] S=sample [0028] I=incident X-ray beam [0029]
D=diffracted X-ray beam [0030] .theta.=diffraction angle [0031]
.omega.=.theta. [0032] .psi.=tilt angle along the Euler 1/4-cradle
[0033] .phi.=rotation angle around the sample axis.
DETAILED DESCRIPTION
[0034] The present disclosure thus relates generally to coated
cutting tool inserts. In exemplary embodiments, the coated cutting
tool inserts comprise a body of generally polygonal or round shape
having at least one rake face and at least one clearance face,
comprising a coating and a carbide substrate. The body has a
composition of 4.4-6.6, preferably 5.0-6.0, most preferably
5.0-5.8, wt-% Co, 4-8.5 wt-% cubic carbides, balance WC, preferably
85-91 wt-% WC, most preferably 87-90 wt-% WC, preferably having an
average grain size of 1-4 .mu.m, a CW-ratio in the range 0.78-0.92
and a surface zone depleted from the cubic carbides TiC, TaC and/or
NbC.
[0035] Said surface zone depleted from cubic carbides has a
thickness of from 10 .mu.m, alternatively from 15 .mu.m, or
alternatively from 20 .mu.m, to 40 .mu.m, alternatively to 35
.mu.m, alternatively to 30 .mu.m, or alternatively to 25 .mu.m.
[0036] The coating comprises at least one TiC.sub.xN.sub.y-layer
and one well-crystalline layer of 100 % .alpha.-Al.sub.2O.sub.3.
One such .alpha.-Al.sub.2O.sub.3-layer is the outermost visible
layer on the rake face and along the cutting edge line and the
layer can be intensively wet blasted with a sufficiently high
energy to create tensile stress relaxation in both the
Al.sub.2O.sub.3-- and the TiC.sub.xN.sub.y-layers. The
Al.sub.2O.sub.3 outermost layer has a very smooth surface at least
in the chip contact zone on the rake face.
[0037] It has surprisingly been discovered that a significant
improved toughness performance can be achieved if a coated cutting
tool insert with a generally polygonal or round shape having at
least one rake face and at least one clearance face, said insert
being at least partly coated, produced to possess the following
features: [0038] a penultimate TiC.sub.xN.sub.y-layer with a
thickness of from 3 .mu.m, preferably from 4 .mu.m, more preferably
from 5 .mu.m, most preferably from 6 .mu.m to 15 .mu.m, preferably
to 13 .mu.m, most preferably to 10 .mu.m, where x.gtoreq.0,
y.gtoreq.0 and x+y=1, preferably produced by MTCVD, with tensile
stresses of 50-500 MPa, preferably 50-450 MPa, most preferably
50-400 MPa, and [0039] an outer .alpha.-Al.sub.2O.sub.3-layer with
a thickness of from 3 .mu.m, preferably from 3.5, most preferably
from 4 .mu.m to 12 .mu.m, preferably to 11 .mu.m, most preferably
to 10 .mu.m, being the outermost layer on the rake face and along
the edge line having a mean roughness Ra<0.12 .mu.m,
preferably.ltoreq.0.10 .mu.m, at least in the chip contact zone of
the rake face, measured over an area of 10 .mu.m.times.10 .mu.m by
Atomic Force Microscopy (AFM) and an XRD-diffraction intensity
(peak height minus background) ratio of I(012)/I(024).gtoreq.1.3,
preferably .gtoreq.1.5.
[0040] Preferably there is a thin 0.2-2 .mu.m bonding layer of
TiC.sub.xN.sub.yO.sub.z, x.gtoreq.0, z.gtoreq.0 and y.gtoreq.0
between the TiC.sub.xN.sub.y-layer and the
.alpha.-Al.sub.2O.sub.3-layer. The total thickness of the two
layers is .ltoreq.25 .mu.m.
[0041] Also according to exemplary embodiments of the present
disclosure, additional layers can be incorporated into the coating
structure between the substrate and the layers, composed of metal
nitrides and/or carbides and/or oxides with the metal elements
selected from Ti, Nb, Hf, V, Ta, Mo, Zr, Cr, W and Al to a total
coating thickness of <5 .mu.m.
[0042] It is preferred to have some tensile stresses left in the
TiC.sub.xN.sub.y-layer since it was found that such induced
compressive stresses were not as stable with respect to temperature
increase, which occurs in a cutting operation, as compared to if
the coating has some tensile stresses still present. It was also
found, that if compressive stresses were to be induced by blasting,
a very high blasting impact force was required and under such
conditions flaking of the coating frequently occurred along the
cutting edge.
[0043] The residual stress, .sigma., of the inner
TiC.sub.xN.sub.y-layer is determined by XRD measurements using the
well known sin.sup.2.psi. method as described by I. C. Noyan, J. B.
Cohen, Residual Stress Measurement by Diffraction and
Interpretation, Springer-Verlag, N.Y., 1987 (pp 117-130). The
measurements are performed using CuK.sub..alpha.-radiation on the
TiC.sub.xN.sub.y (422) reflection with a goniometer setup as shown
in FIG. 1. The measurements are carried out on an as flat surface
as possible. It is recommended to use the side-inclination
technique (.psi.-geometry) with six to eleven .psi.-angles,
equidistant within a sin.sup.2.psi.-range of 0 to 0.5
(.psi.=45.degree.). An equidistant distribution of .phi.-angles
within a .phi.-sector of 90.degree. is also preferred. To confirm a
biaxial stress state the sample shall be rotated for
.phi.=0.degree. and 90.degree. while tilted in .psi.. It is
recommended to investigate possible presence of shear stresses and
therefore both negative and positive .psi.-angles shall be
measured. In the case of an Euler 1/4-cradle this is accomplished
by measuring the sample also at .phi.=180.degree. and 270.degree.
for the different .psi.-angles. The sin.sup.2.psi. method is used
to evaluate the residual stress preferably using some commercially
available software such as DIFFRAC.sup.Plus Stress32 v. 1.04 from
Bruker AXS with the constants Young's modulus, E=480 GPa and
Poisson's ratio, .nu.=0.20 in case of a MTCVD Ti(C,N)-layer and
locating the reflection using the Pseudo-Voigt-Fit function. In the
case of the following parameters are used: E-modulus=480 GPa and
Poisson's ratio .nu.=0.20. In case of a biaxial stress state the
tensile stress is calculated as the average of the obtained biaxial
stresses.
[0044] For the .alpha.-Al.sub.2O.sub.3 it is in general not
possible to use the sin.sup.2.psi. technique since the required
high 2.theta. angle XRD-reflections are often too weak. However, a
useful alternative measure has been found which relates the state
of the .alpha.-Al.sub.2O.sub.3 to cutting performance.
[0045] For an .alpha.-Al.sub.2O.sub.3 powder the diffraction
intensity ratio I(012)/I(024) is close to 1.5. Powder Diffraction
File JCPDS No 43-1484 states the intensities I.sub.0(012)=72 and
I.sub.0(024)=48. For tensile stressed (with .sigma. about >350
MPa) CVD .alpha.-Al.sub.2O.sub.3-layers on cemented carbide, the
intensity ratio I(012)/I(024) is surprisingly significantly less
than the expected value 1.5, most often <1. This may be due to
some disorder in the crystal lattice caused by the tensile
stresses. It has been found that when such a layer is stress
released by, e.g., an intense blasting operation or if it has been
completely removed from the substrate and powdered, the ratio
I(012)/I(024) becomes closer, equal or even higher than 1.5. The
higher the applied blasting force the higher the ratio will be.
Thus, this intensity ratio can be used as an important state
feature of an .alpha.-Al.sub.2O.sub.3-layer.
[0046] According to exemplary embodiments of the present
disclosure, a cutting tool insert is provided with a CVD-coating
comprising a penultimate TiC.sub.xN.sub.y-layer and an outer
.alpha.-Al.sub.2O.sub.3-layer. The Al.sub.2O.sub.3 can be produced
according to patent EP 603 144 giving the Al.sub.2O.sub.3-layer a
crystallographic texture in 012-direction with a texture
coefficient TC(012)>1.3, preferably >1.5 or produced
according to U.S. Pat. Nos. 5,851,687 and 5,702,808 giving a
texture in the 110-direction with texture coefficient
TC(110)>1.5. However, in an alternative embodiment the
Al.sub.2O.sub.3 is produced according to patent EP 738 336 giving
the Al.sub.2O.sub.3-layer a crystallographic texture in the
104-direction with a texture coefficient TC(104)>1.5, preferably
>2.0, most preferably >2.5. In order to obtain a high surface
smoothness and low tensile stress level the coating is subjected to
a wet blasting operation with a slurry consisting of F150 grits
(FEPA-standard) of Al.sub.2O.sub.3 in water at an air pressure of
2.2-2.6 bar for about 10-20 sec/insert. The spray guns are placed
approximately 100 mm from the inserts with a 90.degree. spray
angle. The insert has a different color on the clearance side than
on the black rake face. An outermost thin 0.1-2 .mu.m coloring
layer of TiN (yellow), TiC.sub.xN.sub.y (grey or bronze),
ZrC.sub.xN.sub.y (reddish or bronze), where x.gtoreq.0, y.gtoreq.0
and x+y=1 or TiC (grey) is preferably deposited. The inserts are
then blasted removing the top layer exposing the black
Al.sub.2O.sub.3-layer. The coating on the rake face will have the
low desired tensile stress 50-500 MPa while the clearance side will
have high tensile stresses in the range 500-700 MPa, the tensile
stress on the rake face being lower than the tensile stress on the
clearance face, dependent on the choice of coating and the
coefficient of Thermal Expansion (CTE) of the used cemented carbide
insert. In another exemplary embodiment, the coated insert is
blasted both on the rake face and the clearance side and a colored,
heat resistant paint is sprayed on the clearance side or a colored
PVD layer is deposited there in order to obtain a possibility to
identify a used cutting edge.
EXAMPLE 1
[0047] The following samples were made: [0048] A) Cemented carbide
cutting inserts with the composition 5.5 wt-% Co, 2.9 wt-% TaC, 0.5
wt-% NbC, 1.9 wt-% TiC, 0.4 wt-% TiN, balance WC, having an average
grain size of about 2 .mu.m, with a surface zone, 18 .mu.m thick,
depleted from cubic carbides.
[0049] The saturation magnetization, M.sub.s, was measured to be
0.077 hAm.sup.2/kg giving a CW-ratio of 0.87. The inserts were
coated with a 0.5 .mu.m thick layer of TiN using conventional
CVD-technique at 930.degree. C. followed by a 7 .mu.m
TiC.sub.xN.sub.y-layer employing the MTCVD-technique using
TiCl.sub.4, H.sub.2, N.sub.2 and CH.sub.3CN as process gases at a
temperature of 885.degree. C. In subsequent process steps during
the same coating cycle a layer of TiC.sub.xO.sub.z about 0.5 .mu.m
thick was deposited at 1000.degree. C. using TiCl.sub.4, CO and
H.sub.2, and then the Al.sub.2O.sub.3-process was stared up by
flushing the reactor with a mixture of 2 % CO.sub.2, 3.2 % HCl and
94.8 % N.sub.2 for 2 min before a 7 .mu.m thick layer of
.alpha.-Al.sub.2O.sub.3 was deposited. On top was a thin approx.
0.5 .mu.m TiN layer deposited.
[0050] The process conditions during the deposition steps were as
below: TABLE-US-00001 TiN TiC.sub.xN.sub.y TiC.sub.xO.sub.z
Al.sub.2O.sub.3-start Al.sub.2O.sub.3 Step 1 and 6 2 3 4 5
TiCl.sub.4 1.5% 1.4% 2% N.sub.2 38% 38% balance CO.sub.2 2% 4% CO
6% AlCl.sub.3 3.2% H.sub.2S 0.3% HCl 3.2% 3.2% H.sub.2 balance
balance balance -- balance CH.sub.3CN -- 0.6% Pressure 160 mbar 60
mbar 60 mbar 60 mbar 70 mbar Temp. 930.degree. C. 885.degree. C.
1000.degree. C. 1000.degree. C. 1000.degree. C. Time 30 min 4.5 h
20 min 2 min 7 h
[0051] Additional inserts were: [0052] B) Cemented carbide cutting
inserts of the same type as in A) differing only in
TiC.sub.xN.sub.y- and .alpha.-Al.sub.2O.sub.3-layer thickness,
being 6 .mu.m and 9 .mu.m thick respectively, were manufactured
using the same processing conditions except for the
TiC.sub.xN.sub.y and Al.sub.2O.sub.3 depositing times being 4 h and
10 h, respectively.
[0053] XRD-analysis of the deposited Al.sub.2O.sub.3-layer of the
inserts according to A) and B) showed that it consisted only of the
a-phase with a texture coefficient TC(104)=2.6 defined as below: TC
.function. ( 104 ) = I .function. ( 104 ) I 0 .function. ( 104 )
.times. { 1 n .times. I .function. ( hkl ) I 0 .function. ( hkl ) }
- 1 ##EQU1## where: [0054] I(hkl)=measured intensity of the (hkl)
reflection [0055] I.sub.0(hkl)=standard intensity of Powder
Diffraction File JCPDS No 43-1484. [0056] n=number of reflections
used in the calculation [0057] (hkl) reflections used are: (012),
(104), (110), (113), (024), (116).
[0058] The coated inserts according to A) and B) were post treated
by the earlier mentioned blasting method, blasting the rake face of
the inserts, using a blasting pressure of 2.4 bar and an exposure
time of 20 seconds.
[0059] The smoothness of the coating surface expressed as a well
known roughness value Ra was measured by AFM on an equipment from
Surface Imaging System AG (SIS). The roughness was measured on ten
randomly selected plane surface areas (10 .mu.m.times.10 .mu.m) in
the chip contact zone on rake face. The resulting mean value from
these ten Ra values, MRa, was 0.11 .mu.m.
[0060] X-ray Diffraction Analysis using a Bragg-Brentano
diffractometer, Siemens D5000, was used to determine the
I(012)/I(024)-ratio using Cu K.alpha.-radiation.
[0061] The obtained I(012)/I(024)-ratio on the clearance side was
about 1.2. A corresponding measurement on the rake face showed that
the obtained I(012)/I(024)-ratio was about 2.1.
[0062] The residual stress was determined using .psi.-geometry on
an X-ray diffractometer Bruker D8 Discover-GADDS equipped with
laser-video positioning, Euler 1/4-cradle, rotating anode as X-ray
source (CuK.sub..alpha.-radiation) and an area detector (Hi-star).
A collimator of size 0.5 mm was used to focus the beam. The
analysis was performed on the TiC.sub.xN.sub.y (422) reflection
using the goniometer settings 2.theta.=126.degree.,
.omega.=63.degree. and .phi.=0.degree., 90.degree., 180.degree.,
270.degree.. Eight .psi. tilts between 0.degree. and 70.degree.
were performed for each .phi.-angle. The sin.sup.2.psi. method was
used to evaluate the residual stress using the software
DIFFRAC.sup.Plus Stress32 v.1.04 from Bruker AXS with the constants
Young's modulus, E=480 GPa and Poisson's ratio, .nu.=0.20 and
locating the reflection using the Pseudo-Voigt-Fit function. A
biaxial stress state was confirmed and the average value was used
as the residual stress value. Measurements were carried out both on
the rake face and the clearance side. The obtained tensile stress
on the clearance side was about 630 MPa for the inserts according
to A) and B). A corresponding measurement on the rake face showed
that a tensile stress of about 370 MPa was obtained for the inserts
according to A) and a tensile stress of about 380 MPa was obtained
for the inserts according to B).
EXAMPLE 2
[0063] Inserts A) and B) from Example 1 were tested and compared
with commercially available, nonblasted inserts (high performance
inserts in the P15 area) with respect to toughness in a
longitudinal turning operation with interrupted cuts.
[0064] Material: Carbon steel SS1312.
[0065] Cutting data: [0066] Cutting speed=150 m/min [0067] Depth of
cut=1.5 mm [0068] Feed=Starting with 0.15 mm and gradually
increased by 0.08 mm/min until breakage of the edge. [0069] 10
edges of each variant were tested [0070] Inserts style:
CNMG120408-PM
[0071] Results: TABLE-US-00002 Average feed at breakage (mm/rev)
Commercially 0.206 available inserts A) 0.282 B) 0.240
EXAMPLE 3
[0072] Inserts A) from Example 1 were tested and compared with the
same commercially available inserts as in Example 2 with respect to
resistance to gross plastic deformation in a facing operation of
SS2541. [0073] Cutting data: [0074] Cutting speed=200 m/min [0075]
Feed=0.35 mm/rev. [0076] Depth of cut=2 mm [0077] Tool life
criteria: flank wear >=0.5 mm [0078] Insert style:
CNMG120408-PM
[0079] Results: TABLE-US-00003 Number of machining cycles needed to
reach tool life Commercially 59.5 available inserts A) 64
EXAMPLE 4
[0080] Inserts A) and B) from Example 1 were tested and compared
with the same commercially available inserts as in Example 2 with
respect to resistance to gross plastic deformation in a facing
operation of SS2541. The test comprised two different insert sizes,
represented by two different insert styles: CNMG160612-PR (cutting
edge length=16 mm) and CNMG190612-PR (cutting edge length=19 mm).
[0081] Cutting data: [0082] Cutting speed=220 m/min [0083]
Feed=0.35 mm/rev. [0084] Depth of cut=3 mm [0085] Tool life
criteria: flank wear >=0.5 mm
[0086] Results: TABLE-US-00004 Number of machining cycles needed to
reach tool life CNMG160612-PR CNMG190612-PR Commercially 36 50
available inserts A) 52 72 B) 51 77
[0087] Although described in connection with preferred embodiments
thereof, it will be appreciated by those skilled in the art that
additions, deletions, modifications, and substitutions not
specifically described may be made without department from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *