U.S. patent application number 14/131716 was filed with the patent office on 2014-06-26 for sulfur containing alpha-alumina coated cutting tool.
This patent application is currently assigned to WALTER AG. The applicant listed for this patent is WALTER AG. Invention is credited to Sakari Ruppi, Dirk Stiens.
Application Number | 20140173996 14/131716 |
Document ID | / |
Family ID | 46970250 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140173996 |
Kind Code |
A1 |
Stiens; Dirk ; et
al. |
June 26, 2014 |
Sulfur Containing Alpha-Alumina Coated Cutting Tool
Abstract
Cutting tool insert has a substrate and a coating of one or more
refractory layers of which at least one layer is an
.alpha.-Al.sub.2O.sub.3 layer having thickness of 1 to 25 .mu.m,
sulphur content of more than 100 ppm analysed by Secondary Ion Mass
Spectroscopy (SIMS), and texture coefficient TC (0 0 12)>4 for
the (0 0 12) growth direction. The at least one
.alpha.-Al.sub.2O.sub.3 layer is deposited by chemical vapour
deposition (CVD) using reaction gases comprising H.sub.2, CO.sub.2,
AlCl.sub.3 and X, with X being H.sub.2S, SO.sub.2, SF.sub.6, or
combinations thereof, and optional additions of N.sub.2 and Ar. The
amount of X is at least 1.0 vol-% of the total volume of gases in
the reaction chamber. The volume ratio of CO.sub.2 and X in the
reaction chamber lies within the range of
1.ltoreq.CO.sub.2/X.ltoreq.7 during deposition of the at least one
.alpha.-Al.sub.2O.sub.3 layer.
Inventors: |
Stiens; Dirk; (Reutlingen,
DE) ; Ruppi; Sakari; (Tubingen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WALTER AG |
Tubingen |
|
DE |
|
|
Assignee: |
WALTER AG
Tubingen
DE
|
Family ID: |
46970250 |
Appl. No.: |
14/131716 |
Filed: |
September 17, 2012 |
PCT Filed: |
September 17, 2012 |
PCT NO: |
PCT/EP2012/068207 |
371 Date: |
January 9, 2014 |
Current U.S.
Class: |
51/309 |
Current CPC
Class: |
C23C 30/005 20130101;
C23C 16/403 20130101; C23C 16/52 20130101; B24D 3/34 20130101 |
Class at
Publication: |
51/309 |
International
Class: |
B24D 3/34 20060101
B24D003/34 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2011 |
EP |
11181640.1 |
Claims
1. A cutting tool insert consisting of: a substrate of cemented
carbide, cermet, ceramics, steel or a superhard material; and a
coating with a total thickness of 5 to 40 .mu.m, the coating
consisting of one or more refractory layers of which at least one
layer is an .alpha.-Al.sub.2O.sub.3 layer having a thickness of 1
to 25 .mu.m, wherein the at least one .alpha.-Al.sub.2O.sub.3 layer
has a sulphur content of more than 100 ppm analysed by Secondary
Ion Mass Spectroscopy (SIMS) and the at least one
.alpha.-Al.sub.2O.sub.3 layer has a texture coefficient TC (0 0
12)>4 for the (0 0 12) growth direction, the TC (0 0 12) being
defined as follows: TC ( 0 0 12 ) = I ( 0 0 12 ) I 0 ( 0 0 12 ) [ 1
n n - 1 n I ( hkl ) I 0 ( hkl ) ] - 1 ##EQU00002## (hkl)=measured
intensity of the (hkl) reflection I.sub.0 (hkl)=standard intensity
of the standard powder diffraction data according to JCPDF-card no.
42-1468 n=number of reflections used in the calculation, whereby
the (hkl) reflections used are: (012), (104), (110), (113), (116),
(300) and (0 0 12).
2. The cutting tool insert of claim 1 wherein the at least one
.alpha.-Al.sub.2O.sub.3 layer has a sulphur content of more than
120 ppm analysed by SIMS.
3. The cutting tool insert of claim 1, wherein the coating
comprises, in addition to the at least one .alpha.-Al.sub.2O.sub.3
layer, one or more refractory layers consisting of carbide,
nitride, carbonitride, oxycarbonitride or borocarbonitride of one
or more of Ti, Zr, V and Hf, or combinations thereof deposited
using CVD or MT-CVD, having a thickness of from 0.5 to 20
.mu.m.
4. The cutting tool insert of claim 1, wherein a) the uppermost
layer of the coating is the .alpha.-Al.sub.2O.sub.3 layer or b) the
uppermost layer of the coating is a layer of carbide, nitride,
carbonitride or oxycarbnitride of one or more of Ti, Zr, V and Hf,
or combinations thereof, having a thickness of from 0.5 to 3 .mu.m
and being deposited atop of the .alpha.-Al.sub.2O.sub.3 layer or c)
surface areas of the cutting tool insert comprise the
.alpha.-Al.sub.2O.sub.3 layer as the uppermost layer whereas the
remaining surface areas of the cutting tool insert comprise as the
uppermost layer a layer of carbide, nitride, carbonitride or
oxycarbnitride of one or more of Ti, Zr, V and Hf, or combinations
thereof, having a thickness of from 0.5 to 3 .mu.m and being
deposited atop of the .alpha.-Al.sub.2O.sub.3 layer.
5. The cutting tool insert of claim 1 wherein the substrate
consists of cemented carbide optionally 0.3-10 wt-% cubic carbides
of the metals from groups IVb, Vb and VIb of the periodic table and
balance WC.
6. The cutting tool insert of claim 1 wherein the substrate
consists of cemented carbide comprising a binder phase enriched
surface zone having a thickness of 5 to 30 .mu.m from the substrate
surface, the binder phase enriched surface zone having a Co content
that is at least 1.5 times higher than in the core of the substrate
and having a content of cubic carbides that is less than 0.5 times
the content of cubic carbides in the core of the substrate.
7. The cutting tool insert of claim 1 wherein the at least one
.alpha.-Al.sub.2O.sub.3 layer has a texture coefficient TC (0 0
12)>5, for the (0 0 12) growth direction.
8. A method of manufacturing a cutting tool insert of claim 1,
comprising: depositing said at least one .alpha.-Al.sub.2O.sub.3
layer by chemical vapour deposition (CVD), wherein the reaction gas
of the CVD process comprises H.sub.2, CO.sub.2, AlCl.sub.3 and X,
with X being H.sub.2S, SO.sub.2, SF.sub.6, or combinations thereof,
and optional additions of N.sub.2 and Ar, wherein the X is present
in the reaction gas mixture in an amount of at least 1.0 vol-% of
the total volume of gases in the CVD reaction chamber, and wherein
the volume ratio of CO.sub.2 and X in the CVD reaction chamber lies
within the range of 1.ltoreq.CO.sub.2/X.ltoreq.7 during deposition
of the at least one .alpha.-Al.sub.2O.sub.3 layer.
9. The method of claim 8, wherein the volume proportion of the
component X or the combination of components X is present in the
reaction gas mixture during deposition of the at least one
.alpha.-Al.sub.2O.sub.3 layer in an amount of at least 1.2 vol-% of
the total volume of gases in the CVD reaction chamber.
10. The method of claim 8, wherein the volume ratio of CO.sub.2 and
X in the CVD reaction chamber lies within the range of
2.ltoreq.CO.sub.2/X.ltoreq.6 during deposition of the at least one
.alpha.-Al.sub.2O.sub.3 layer.
11. The method of any of claim 8, wherein the volume ratio of
CO.sub.2/AlCl.sub.3 in the CVD reaction chamber is equal or smaller
than 1.5 and/or the volume ratio of AlCl.sub.3/HCl in the CVD
reaction chamber is equal or smaller than 1, during deposition of
the at least one .alpha.-Al.sub.2O.sub.3 layer.
12. The method of claim 8, wherein the CVD process during
deposition of the at least one .alpha.-Al.sub.2O.sub.3 layer is
conducted at a temperature in the range of 850 to 1050.degree. C.
and/or the CVD process during deposition of the at least one
.alpha.-Al.sub.2O.sub.3 layer is conducted at a reaction gas
pressure in the range 50 to 120 mbar.
13. The method of claim 8, wherein the component X in the CVD
process is H.sub.2S or SO.sub.2 or a combination of H.sub.2S and
SO.sub.2, whereby, if the component X in the CVD process is a
combination of H.sub.2S and SO.sub.2, the volume proportion of
SO.sub.2 does not exceed 20% of the volume amount of H.sub.2S.
14. The method of any of claim 8, wherein the reaction gas of the
CVD process comprises additions of N.sub.2 and/or Ar in a volume
amount in the range of 4 to 20 vol % of the total volume of gases
in the CVD reaction chamber.
15. The cutting tool insert of claim 2 wherein at least one
.alpha.-Al.sub.2O.sub.3 layer has a sulphur content of more than
150 ppm analysed by SIMS.
16. The cutting tool insert of claim 7 wherein the at least one
.alpha.-Al.sub.2O.sub.3 layer has a texture coefficient TC (0 0
12)>6 for the (0 0 12) growth direction.
17. The method of claim 9, wherein the volume proportion of the
component X or the combination of components X is present in the
reaction gas mixture during deposition of the at least one
.alpha.-Al.sub.2O.sub.3 layer in an amount of at least 1.5 vol-% of
the total volume of gases in the CVD reaction chamber.
18. The method of claim 12, wherein the temperature is in the range
of 980 to 1050.degree. C.
19. The method of claim 12, wherein the temperature is in the range
of 1000 to 1020.degree. C.
20. The method of claim 12, wherein the reaction gas pressure is in
the range 50 to 150 mbar.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a cutting tool insert
consisting of a substrate of cemented carbide, cermet, ceramics,
steel or a superhard material such as cubic boron nitride (CBN) and
a hard coating consisting of one or more refractory layers of which
at least one layer is an .alpha.-Al.sub.2O.sub.3 layer containing
sulphur and having a specified growth orientation defined by the
texture coefficient, and a method of manufacturing the cutting tool
insert.
BACKGROUND OF THE INVENTION
[0002] The early approaches to deposit Al.sub.2O.sub.3 on a
substrate surface in a CVD process based on a
AlCl.sub.3/CO.sub.2/H.sub.2 reaction gas mixture had a very low
deposition rates in the order of about 0.2 .mu.m/h on flat
surfaces. Besides the fact that it was not possible to control the
phase content, this early Al.sub.2O.sub.3 deposition process also
suffered from a pronounced dog-bone-effect, i.e. the deposition
rate was higher on the edges than on the flat surfaces of the
substrate. U.S. Pat. No. 4,619,866 by Smith and Lindstom discloses
that dopants, such as H.sub.2S, could be used as a catalyst both to
enhance the overall deposition rate but also to suppress the
dog-bone effect. With the introduction of H.sub.2S as a catalyst
for the .alpha.-Al.sub.2O.sub.3 deposition process the deposition
rate increased by a factor of about five coinciding with a more or
less complete elimination of the dog-bone effect as compared to the
process without any H.sub.2S present
[0003] Several attempts have been made to deposit industrial alpha
and gamma alumina coatings onto cutting tools by CVD or PVD using
sulphur containing dopants. In EP-A-0 045 291 the addition of
0.02-0.3 vol-% of sulphur, selenium or tellurium containing gas,
preferably H.sub.2S, to the deposition gas in the CVD process has
been found to increase the growth rate and to improve the
uniformity of alumina coatings. EP-A-1 788 124 describes the
deposition of alpha alumina coatings having a defined crystal grain
boundary orientation wherein the deposition of the alumina is
performed by CVD adding from 0.25-0.6 vol-% of H.sub.2S to the
deposition gas. EP-A-1 683 893 describes the deposition of alpha
alumina coatings having a defined amount of .SIGMA.3 type grain
boundary length wherein the deposition of the alumina is performed
by CVD adding from 1.5-5 vol-% HCl and from 0.05-0.2 vol-% of
H.sub.2S to the deposition gas. The prior art literature does not
describe the actual sulphur content in the alpha alumina coatings.
Since H.sub.2S has only been used to enhance the growth rate and
prevent the dog-bone effect, there have been no attempts to use
higher amounts of sulfur-containing dopants or consider the sulfur
content in the .alpha.-Al.sub.2O.sub.3 coatings in general. One
reason for this is that, as disclosed in U.S. Pat. No. 4,619,866,
the effect of H.sub.2S on the growth rate on alumina was found to
be at maximum at a H.sub.2S concentration of 0.25 to 0.3 vol %.
Larger amounts of H.sub.2S than about 0.3 vol % were found to
result in strongly reduced growth rates"
OBJECT OF THE INVENTION
[0004] It is an object of the present invention is to provide a
coated cutting tool having an .alpha.-Al.sub.2O.sub.3 layer that
exhibits improved cutting properties, improved chipping resistance
and improved crater wear resistance as well as lower friction in
contact with the workpiece over the prior-art.
DESCRIPTION OF THE INVENTION
[0005] The present invention relates to a cutting tool insert
consisting of a substrate of cemented carbide, cermet, ceramics,
steel or a superhard material such as cubic boron nitride (CBN) and
a coating with a total thickness of 5 to 40 .mu.m, the coating
consisting of one or more refractory layers of which at least one
layer is an .alpha.-Al.sub.2O.sub.3 layer having a thickness of 1
to 25 .mu.m, wherein the at least one .alpha.-Al.sub.2O.sub.3 layer
having a sulphur content of more than 100 ppm analysed by Secondary
Ion Mass Spectroscopy (SIMS) and the at least one
.alpha.-Al.sub.2O.sub.3 layer having a texture coefficient TC (0 0
12)>4 for the (0 0 12) growth direction, the TC (0 0 12) being
defined as follows:
TC ( 0 0 12 ) = I ( 0 0 12 ) I 0 ( 0 0 12 ) [ 1 n n - 1 n I ( hkl )
I 0 ( hkl ) ] - 1 ##EQU00001## [0006] (hkl)=measured intensity of
the (hkl) reflection [0007] I.sub.0 (hkl)=standard intensity of the
standard powder diffraction data according to JCPDF-card no.
42-1468 [0008] n=number of reflections used in the calculation,
whereby the (hkl) reflections used are: (012), (104), (110), (113),
(116), (300) and (0 0 12).
[0009] It has surprisingly been found that improved cutting
properties, improved chipping resistance and improved crater wear
resistance of the cutting tool insert as well as lower friction in
contact with the workpiece can be achieved if the
.alpha.-Al.sub.2O.sub.3 layer has a high sulphur content of more
than 100 ppm analysed by Secondary Ion Mass Spectroscopy (SIMS) and
a texture coefficient TC (0 0 12)>4 for the (0 0 12) growth
direction.
[0010] In a preferred embodiment of the present invention the at
least one .alpha.-Al.sub.2O.sub.3 layer of the cutting tool insert
has a sulphur content of more than 120 ppm, preferably more than
150 ppm analysed by SIMS. It has been found that the cutting
properties of the inventive cutting tool can be further improved by
a higher sulphur content.
[0011] However, the sulphur content of the .alpha.-Al.sub.2O.sub.3
layer should not exceed 2000 ppm, since a larger sulphur content
may impair the properties of the cutting tool, such as grain
boundary strength, and, in addition, cause porosity.
[0012] In another preferred embodiment of the cutting tool insert
of the present invention the coating comprises, in addition to the
at least one .alpha.-Al.sub.2O.sub.3 layer, one or more refractory
layers consisting of carbide, nitride, carbonitride,
oxycarbonitride or borocarbonitride of one or more of Ti, Zr, V and
Hf, or combinations thereof deposited using CVD or MT-CVD, having a
thickness of from 0.5 to 20 .mu.m, preferably from 1 to 10
.mu.m.
[0013] Preferably, the coating comprises a first layer adjacent to
the substrate body of CVD deposited Ti(C,N), TiN, TiC or HfN, or
MT-CVD deposited Ti(C,N), Zr(C,N), Ti(B,C,N), or combinations
thereof. Most preferably, the first layer is if Ti(C,N).
[0014] In yet another preferred embodiment of the cutting tool
insert of the present invention
a) the uppermost layer of the coating is the
.alpha.-Al.sub.2O.sub.3 layer or b) the uppermost layer of the
coating is a layer of carbide, nitride, carbonitride or
oxycarbnitride of one or more of Ti, Zr, V and Hf, or combinations
thereof (herein called Ti top coating), having a thickness of from
0.5 to 3 .mu.m, preferably 0.5 to 1.5 .mu.m, being deposited atop
of the .alpha.-Al.sub.2O.sub.3 layer or c) surface areas of the
cutting tool insert, preferably the rake face of the cutting tool
insert, comprise the .alpha.-Al.sub.2O.sub.3 layer a) as the
uppermost layer whereas the remaining surface areas of the cutting
tool insert comprise as the uppermost layer a layer b) of carbide,
nitride, carbonitride or oxycarbnitride of one or more of Ti, Zr, V
and Hf, or combinations thereof, having a thickness of from 0.5 to
3 .mu.m, preferably 0.5 to 1.5 .mu.m, being deposited atop of the
.alpha.-Al.sub.2O.sub.3 layer.
[0015] The Ti top coating layer atop the .alpha.-Al.sub.2O.sub.3
layer can be provided as a wear indicator or as a layer of other
functions. Embodiments, where only parts of the surface areas of
the cutting tool insert, preferably the rake face of the cutting
tool insert, comprise the .alpha.-Al.sub.2O.sub.3 layer as the
uppermost layer whereas the remaining surface areas are covered
with the Ti top coating as the outermost layer, can be produced by
removing the deposited Ti top coating by way of blasting or any
other well known method.
[0016] In another preferred embodiment of the cutting tool insert
of the present invention the substrate consists of cemented
carbide, preferably of cemented carbide consisting of 4 to 12 wt-%
Co, optionally 0.3-10 wt-% cubic carbides of the metals from groups
IVb, Vb and VIb of the periodic table, preferably Ti, Nb, Ta or
combinations thereof, and balance WC.
[0017] For steel machining applications the cemented carbide
substrate preferably contains 7.0 to 9.0 wt-% cubic carbides of the
metals from groups IVb, Vb and VIb of the periodic table,
preferably Ti, Nb and Ta, and for cast iron machining applications
the cemented carbide substrate preferably contains 0.3 to 3.0 wt-%
cubic carbides of the metals from groups IVb, Vb and VIb of the
periodic table, preferably Ti, Nb and Ta.
[0018] In another preferred embodiment of the cutting tool insert
of the present invention the substrate consists of cemented carbide
comprising a binder phase enriched surface zone having a thickness
of 5 to 30 .mu.m, preferably 10 to 25 .mu.m, from the substrate
surface, the binder phase enriched surface zone having a Co content
that is at least 1.5 times higher than in the core of the substrate
and having a content of cubic carbides that is less than 0.5 times
the content of cubic carbides in the core of the substrate. The
thickness of the .alpha.-Al.sub.2O.sub.3 layer in this embodiment
is preferably about 4 to 12 .mu.m, most preferably 4 to 8
.mu.m.
[0019] Preferably, the binder phase enriched surface zone of the
cemented carbide body is essentially free from cubic carbides. The
binder enriched surface zone enhances toughness of the substrate
and widens the application range of the tool. Subtrates having a
binder enriched surface zone are particularly preferred for cutting
tool inserts for metal cutting operations in steel, whereas cutting
tool inserts for metal cutting operations in cast iron are
preferably produced without binder enriched surface zone.
[0020] In another preferred embodiment of the cutting tool insert
of the present invention the at least one .alpha.-Al.sub.2O.sub.3
layer has a texture coefficient TC (0 0 12)>5, more preferably a
texture coefficient TC (0 0 12)>6 for the (0 0 12) growth
direction.
[0021] The present invention further provides a method of
manufacturing a cutting tool insert as defined herein wherein said
at least one .alpha.-Al.sub.2O.sub.3 layer is deposited by chemical
vapour deposition (CVD) the reaction gas of the CVD process
comprising H.sub.2, CO.sub.2, AlCl.sub.3 and X, with X being
H.sub.2S, SO.sub.2, SF.sub.6, or combinations thereof, and optional
additions of N.sub.2 and Ar, wherein the X is present in the
reaction gas mixture in an amount of at least 1.0 vol-% of the
total volume of gases in the CVD reaction chamber and wherein the
volume ratio of CO.sub.2 and X in the CVD reaction chamber lies
within the range of 1.ltoreq.CO.sub.2/X.ltoreq.7 during deposition
of the at least one .alpha.-Al.sub.2O.sub.3 layer.
[0022] It has surprisingly been found that the inventive
.alpha.-Al.sub.2O.sub.3 coating can be controlled by particular
deposition conditions. The inventive kind of high sulphur content
and the texture coefficient TC(0 0 12)>4 of the
.alpha.-Al.sub.2O.sub.3 coating can be achieved by the control of
the volume portion of the sulfur containing dopant X in the
reaction gas mixture of the total volume of gases in the CVD
reaction chamber in an amount of at least 1.0 vol-%, preferably at
least 1.2 vol %, and, at the same time, by control of the volume
ratio of CO.sub.2 and X in the CVD deposition reaction. Cutting
tests and friction tests have clearly confirmed the beneficial
effects of high sulfur content in the .alpha.-Al.sub.2O.sub.3
layer.
[0023] If the amount X is less than 1.0 vol-% of the total volume
of gases in the CVD reaction chamber the sulphur content and the
texture coefficient TC(0 0 12) that can be achieved in the
.alpha.-Al.sub.2O.sub.3 coating will not be sufficiently high.
[0024] It has been found that the introduction of a high amount of
sulphur containing dopant X alone will not lead to a high sulphur
content and the desired texture coefficient TC(0 0 12) in the
coating. The inventors have found that the ratio of sulfur
containing dopant X to CO.sub.2 during CVD strongly affects the
sulfur content and the texture coefficient TC(0 0 12) in the
deposited .alpha.-Al.sub.2O.sub.3 layer. Studies by the inventors
have confirmed that deposition of .alpha.-Al.sub.2O.sub.3 with a
high sulfur content and the texture coefficient TC(0 0 12) is
difficult if too high CO.sub.2/X ratios during deposition are used.
It was surprising that the control of the CO.sub.2/X ratio in the
CVD deposition process of .alpha.-Al.sub.2O.sub.3 is the most
important factor to obtain a high sulfur content and the desired
texture coefficient TC(0 0 12) in the .alpha.-Al.sub.2O.sub.3 layer
and, surprisingly and most importantly, that certain ratios
resulted exclusively in high amounts of sulfur with good
reproducibly. Thus, the present invention provides for a new a
method to control the sulfur content and the texture coefficient
TC(0 0 12) of .alpha.-Al.sub.2O.sub.3 deposited by CVD.
[0025] In a preferred embodiment of the method of the present
invention the volume proportion of the component X or the
combination of components X is present in the reaction gas mixture
during deposition of the at least one .alpha.-Al.sub.2O.sub.3 layer
in an amount of at least 1.2 vol-%, preferably at least 1.5 vol-%
of the total volume of gases in the CVD reaction chamber. In
another embodiment the volume proportion of the component X or the
combination of components X lies within the range of 2.0 to 3.0
vol-%.
[0026] It has surprisingly been found that the sulphur content and
the texture coefficient TC(0 0 12) of the .alpha.-Al.sub.2O.sub.3
layer can be further improved by higher X content in the reaction
gas mixture during deposition of the .alpha.-Al.sub.2O.sub.3 layer
resulting in improved cutting properties, improved chipping
resistance and improved crater wear resistance of the cutting tool
insert. However, a too high content of X, for example above 5.0
vol-%, should be avoided due to the danger of handling the sulphur
sources. For example, the preferred sulphur source, H.sub.2S, is a
flammable and extremely hazardous gas.
[0027] In another preferred embodiment of the method of the present
invention the volume ratio of CO.sub.2 and X in the CVD reaction
chamber lies within the range of 1.ltoreq.CO.sub.2/X.ltoreq.6
during deposition of the at least one .alpha.-Al.sub.2O.sub.3
layer. When the deposition is carried out within this range of
CO.sub.2/X, both a sufficient amount of sulphur of >100 ppm in
the alumina layer together with a strong preferred growth of
alumina along the (0 0 12) direction, resulting in a relatively
high texture coefficient TC(0 0 12) for the .alpha.-Al.sub.2O.sub.3
layer, can be obtained.
[0028] In yet another preferred embodiment of the method of the
present invention the volume ratio of CO.sub.2/AlCl.sub.3 in the
CVD reaction chamber is equal or smaller than 1.5 and/or the volume
ratio of AlCl.sub.3/HCl in the CVD reaction chamber is equal or
smaller than 1, during deposition of the at least one
.alpha.-Al.sub.2O.sub.3 layer. If the ratio of CO.sub.2/AlCl.sub.3
is too high (>1.5) and/or if the ratio of AlCl.sub.3/HCl is too
high (>1.0), corresponding to too low amounts of HCl, this will
enhance growth along the (0 1 2) direction and, consequently, will
lead to a lower TC(0 0 12) in the resuiting alumina coating.
[0029] The CVD process of the present invention during deposition
of the at least one .alpha.-Al.sub.2O.sub.3 layer is suitably
conducted at a temperature in the range of 850 to 1050.degree. C.,
preferably 980 to 1050.degree. C., most preferably 1000 to
1020.degree. C. If the temperature of the CVD process is too low,
the growth rate would be too low, and f the temperature of the CVD
process is too high, gas-phase nucleation and non-uniform growth
will occur.
[0030] The reaction gas pressure range where the CVD process of the
present invention is conducted during deposition of the at least
one .alpha.-Al.sub.2O.sub.3 layer is preferably from 50 to 120
mbar, more preferably from 50 to 100 mbar.
[0031] In yet another preferred embodiment of the method of the
present invention the component X in the CVD process is H.sub.2S or
SO.sub.2 or a combination of H.sub.2S and SO.sub.2, whereby, if the
component X in the CVD process is a combination of H.sub.2S and
SO.sub.2, the volume proportion of SO.sub.2 does not exceed 20% of
the volume amount of H.sub.2S. If too much SO.sub.2 is used the
coating uniformity can be reduced due to the so-called dog-bone
effect.
[0032] In yet another preferred embodiment of the method of the
present invention the reaction gas of the CVD process comprises
additions of N.sub.2 and/or Ar in a volume amount in the range of 4
to 20 vol %, preferably 10-15 vol %, of the total volume of gases
in the CVD reaction chamber.
[0033] As will be shown in the examples below, the coatings of the
invention exhibit an excellent chipping resistance in a high-speed
intermittent cutting and enhanced crater wear resistance in
continuous turning over the prior-art coatings.
Methods
Secondary Ion Mass Spectroscopy (SIMS)
[0034] The measurement of sulphur in the alumina coatings has been
done by Secondary Ion Mass Spectroscopy (SIMS) on a Cameca ims3f
spectrometer. The quantitative determination of the sulphur
concentration in a sample was done relative to the known aluminum
concentration in the sample. For the determination of the
sensitivity (relative ion yield) for sulphur relative to aluminum
the reference glas SRM 610 of the National Institute of Standards
and Technology (NIST) was used. The sulphur concentration in SRM
610 is 575 .mu.g/g, and the relative accuracy of the measurements
is about .+-.20%.
[0035] The sample surface was sputtered with negative oxygen ions
having an energy of 14.5 keV. The primary ion current was about 30
nA, and the diameter of the focussed primary ion beam at the sample
surface was about 30-40 .mu.m. The generated positive secondary
ions were accelerated to an energy of 4.5 keV and measured with a
mass spectrometer at a mass resolution of m/.DELTA.m=1800 using a
secondary ion multiplier in counting modus (for.sup.32S) and with a
Faraday cup (for .sup.27Al), respectively. The starting energy of
the detected secondary ions was 55.+-.20 eV to lower molecular
interferences and increase the measurement accuracy (energy
filtering). As the measurement results the average of six equal
measurement cycles was calculated. The integration times per cycle
were 25 sec for.sup.32S and 3 sec for.sup.27Al, respectively. For
each sample the measurements have been repeated 5 times.
TC(0 0 12) X-Ray Diffraction Measurements
[0036] X-ray diffraction measurements were done on a diffraktometer
XRD3003PTS of GE Sensing and Inspection Technologies using Cu
K.sub..alpha.-radiation. The X-ray tube was run at 40 kV and 40 mA
focussed to a point. A parallel beam optic using a polycapillary
collimating lens with a measuring aperture of fixed size was used
on the primary side whereby the irradiated area of the sample was
selected to avoid a spill over of the X-ray beam over the coated
face of the sample. On the secondary side a Soller slit with a
divergence of 0.4.degree. and a 0.25 mm thick Ni K.sub..beta.
filter were used. .theta.-2.theta. scans within the angle range of
20.degree.<2.theta.<100.degree. with increments of
0.25.degree. have been conducted. The measurements were done on a
flat face of the coated insert, preferably on the flank face. The
measurements were done directly on the alumina layer as the
outermost layer. Any layer present in the coating above the alumina
layer to be measured, if any, is removed by a method that does not
substantially influence the XRD measurement results, e.g. etching.
For the calculation of the texture coefficient TC(0 0 12) peak
height intensities were used. Background subtraction and a
parabolic peakfit with 5 measuring points were applied to the XRD
raw data. No further corrections such as K.sub..alpha.2 stripping
or thin film correction were made.
CVD Coatings
[0037] All CVD coatings were prepared in a radial flow reactor,
type Bernex BPX 325S.
EXAMPLES
Example 1
.alpha.-Al.sub.2O.sub.3 Coatings
[0038] Cemented carbide substrates for cutting inserts with a
composition of 6.0 wt % Co and balance WC (hardness about 1600 HV)
were coated with a Ti(C,N) layer by applying MT-CVD using 0.6 vol %
CH.sub.3CN, 3.8 vol % TiCl.sub.4, 20 vol % N.sub.2 and balance
H.sub.2. The thickness of the Ti(C,N) MT-CVD layer was about 5
.mu.m.
[0039] Onto this Ti(C,N) layer of separate substrate samples
different layers consisting of about 8 .mu.m
.alpha.-Al.sub.2O.sub.3 were deposited. The coating parameters are
given in Table 1, and the texture coefficients, TC(0 0 12),
measured by X-ray diffraction, and the sulphur concentrations in
the .alpha.-Al.sub.2O.sub.3 coatings, measured by SIMS, are given
in Table 2.
[0040] The deposition of .alpha.-Al.sub.2O.sub.3 was started by
depositing a 0.05 .mu.m to about 1 .mu.m, preferably 0.5 .mu.m to
about 1 .mu.m, thick bonding layer on top of the MTCVD layer from
the system H.sub.2--N.sub.2--CO--TiCl.sub.4--AlCl.sub.3 at a
pressure of 50 to 100 mbar. For the preparation of the bonding
layer the MTCVD layer was treated with a gas mixture of 3 vol %
TiCl.sub.4, 0.5 vol % AlCl.sub.3, 4.5 vol % CO, 30 vol % N.sub.2
and balance H.sub.2 for about 30 min at a temperature of about
1000.degree. C. The deposition was followed by a purge of 10 min
using H.sub.2 before starting the next step.
[0041] .alpha.-Al.sub.2O.sub.3 was nucleated on the (Ti,Al)(C,N,O)
bonding layer by treating said layer with a gas mixture of 4 vol %
CO.sub.2, 9 vol % CO, 25 vol % N.sub.2, balance H.sub.2 for 5-10
min at a temperature from about 750 to 1050.degree. C., preferably
at about 980 to 1020.degree. C. and most preferably at 1000 to
1020.degree. C. (P=80 to 100 mbar). The oxidation was followed by a
purge of 10 min using Ar.
[0042] The alumina deposition was started with by introducing a gas
mixture of AlCl.sub.3, CO.sub.2, Ar.sub.2, N.sub.2 HCl and H.sub.2,
in the volume amounts as indicated in table 1, without precursor X
for about 10 min at a temperature of about 1000.degree. C. These
precursors were shunted in simultaneously except HCl. HCl flow was
shunted into the reactor 2 min after the start (8 min before X was
introduced).
TABLE-US-00001 TABLE 1 .alpha.-Al.sub.2O.sub.3 coatings H.sub.2S
SO.sub.2 CO.sub.2 AlCl.sub.3 Ar.sub.2 N.sub.2 HCl H.sub.2 Pressure
CO.sub.2/X Coating [vol %] [vol %] [vol %] [vol %] [vol %] [vol %]
[vol %] [vol %] [mbar] ratio 1a 0.5 -- 5.0 3.4 5.0 10.0 3.4 bal. 80
10 1b 0.5 -- 2.5 3.2 5.0 10.0 3.3 bal. 80 5 2a 1.0 -- 8.0 5.4 5.0
10.0 5.4 bal. 80 8 2b X 1.0 -- 4.0 2.7 5.0 10.0 2.7 bal. 80 4 3a
1.8 -- 14.4 9.6 5.0 10.0 9.6 bal. 80 8 3b X 1.8 -- 9.0 6.0 5.0 10.0
6.0 bal. 80 5 3c X 1.8 -- 3.6 2.4 5.0 10.0 2.4 bal. 80 2 4a 2.4 --
21.6 14.4 5.0 10.0 14.4 bal. 80 9 4b X 2.4 -- 2.4 1.6 5.0 10.0 1.6
bal. 80 1 5 0.4 0.1 4.0 2.7 5.0 10.0 2.7 bal. 80 8 6 0.9 0.1 16.0
10.5 5.0 10.0 11.0 bal. 80 16 7 X 0.9 0.1 4.0 4.7 5.0 10.0 7.2 bal.
80 4 8 1.5 0.3 15.0 10.0 5.0 10.0 12.0 bal. 80 8.3 9 X 1.5 0.3 7.5
5.0 5.0 10.0 5.0 bal. 80 4.2 10 X 1.5 0.3 2.0 1.4 5.0 10.0 1.4 bal.
80 1.1 11 2.0 0.4 20.0 2.0 5.0 10.0 2.0 bal. 80 8.4 12 X 2.0 0.4
3.0 2.0 5.0 10.0 2.0 bal. 80 1.3 X = invention
TABLE-US-00002 TABLE 2 .alpha.-Al.sub.2O.sub.3 coatings Sulphur
Coating TC(0 0 12) [ppm] 1a -- 15 1b 2.2 30 2a 2.6 40 2b X 4.8 101
3a 3.8 60 3b X 4.1 108 3c X 5.9 220 4a 3.2 80 4b X 6.8 390 5 4.2 51
6 0.8 32 7 X 5.7 102 8 3.8 40 9 X 6.1 119 10 X 6.7 222 11 2.3 72 12
X 6.9 385 X = invention
[0043] The inserts with coatings 4a and 4b were tested for friction
coefficient using the pin-on-disc method. The coating 4a showed a
friction coefficient of 0.56, whereas the coatings 4b and 12 showed
a lower friction coefficient of 0.42 and 0.39, respectively. Thus,
a high sulphur content in the alpha alumina coatings has been
identified to be friction reducing.
Example 2
Edge Toughness Tests
[0044] The samples 1a to 4b of Example 1 were tested with respect
to edge toughness (chipping resistance) in longitudinal turning of
cast iron (GG25) using the following cutting parameters:
Work piece: GG25; cylindrical bar Insert type: SNUN Cutting speed:
v.sub.c=400 m/min Feed (f)=0.4 mm/rev Depth of cut: a.sub.p=2.0 mm
Remarks: dry turning
[0045] The inserts were inspected after 2 and 4 minutes of cutting.
As shown in Table 3, compared to the coating of the prior art, the
edge toughness of the samples was considerably enhanced when the
coating was produced according to this invention.
TABLE-US-00003 TABLE 3 Edge Toughness Flaking of the edge line (%)
Flaking of the edge line (%) Coating after 2 minutes after 4
minutes 1a 22 34 1b 18 32 2a 18 41 2b 12 32 3a 19 29 3b X 2 8 3c X
0 4 4a 18 33 4b X 0 3 X = invention
Example 3
Turning Tests
[0046] The samples 6, 8, 10 and 12 of Example 1 were tested in
carbon steel (C45) without coolant using the following cutting
parameters:
Work piece: C45 Insert type: WNMG080412-NM4 Cutting speed:
v.sub.c=280 m/min Feed (f)=0.32 mm/rev Depth of cut: a.sub.p=2.5 mm
Remarks: dry turning
[0047] The end of tool life criterion was flank wear >0.3 mm.
Three edges of each variant were tested.
TABLE-US-00004 TABLE 4 Turning Test results Coating Tool Life (min)
6 13.2 8 15.5 10 X 21.3 12 X 32.2 X = invention
* * * * *