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United States Patent Application |
20120015148
|
Kind Code
|
A1
|
Ruppi; Sakari
|
January 19, 2012
|
Alumina layer with enhanced texture
Abstract
The present invention relates to a coated cutting tool insert comprising
a substrate and a coating to be used in metal machining. The hard and
wear resistant coating exhibits an excellent adhesion to the substrate
covering all functional parts thereof. The coating is composed of one or
more refractory layers of which at least one layer is
.alpha.-Al.sub.2O.sub.3 showing a strong growth texture along
<001>. The .alpha.-Al.sub.2O.sub.3 layer has a thickness ranging
from 1 to 20 .mu.m and is composed of columnar grains with a length/width
ratio of 2 to 15. The layer is characterised by a strong (006)
diffraction peak, measured using XRD, and by low intensity of (012),
(104), (113) (024) and (116) diffraction peaks. The <001>textured
.alpha.-Al.sub.2O.sub.3 layers is deposited in a temperature range of
750-1000.degree. C. The texture is controlled by a specific nucleation
procedure combined with the use of sulphur- and fluorine containing
dopants.
Inventors: |
Ruppi; Sakari; (Fagersta, SE)
|
Assignee: |
SECO TOOLS AB
Fagersta
SE
|
Serial No.:
|
135339 |
Series Code:
|
13
|
Filed:
|
July 1, 2011 |
Current U.S. Class: |
428/148; 423/625 |
Class at Publication: |
428/148; 423/625 |
International Class: |
B32B 5/16 20060101 B32B005/16; C01F 7/02 20060101 C01F007/02 |
Foreign Application Data
Date | Code | Application Number |
Sep 27, 2005 | SE | 0502115-9 |
Claims
1. A cutting tool insert comprising a substrate at least partially coated
with a coating having a total thickness of from about 5 to about 40
comprising one or more refractory layers of which at least one layer of
which is an .alpha.-alumina layer wherein said .alpha.-alumina layer
comprises columnar .alpha.-Al.sub.2O.sub.3 grains with a <001>
growth direction with texture coefficients a) TC(006)>1.4, preferably
>3.0 and most preferably >4.0. the texture coefficient TC(hkl)
being defined as TC ( hkl ) = I ( hkil ) I 0 ( hkil
) { 1 n I ( hkil ) I 0 ( hkil ) } - 1
##EQU00002## wherein I(hkl)=measured intensity of the (hkl) reflection
I.sub.0(hkl)=standard intensity according to JCPDS card no 46-1212
n=number of reflections used in the calculation (hkl) reflections used
are: (012), (104), (110), (006), (113) and (116).
2. Cutting tool insert according to claim 1, wherein said at least one
layer is an as deposited layer of .alpha.-alumina.
3. Cutting tool insert according to claim 1, wherein said alumina
columnar grains have a length/width ratio from about 2 to about 15.
4. Cutting tool insert according to claim 1, wherein said substrate
comprises cemented carbide with a binder phase enriched surface zone, CBN
or sintered CBN alloy.
5. Cutting tool insert according to claim 1, wherein the coating
comprises a first layer adjacent the body of CVD Ti(C,N), CVD TiN, CVD
TiC, MTCVD Ti(C,N), MTCVD Zr(C,N), MTCVD Ti(B,C.N), CVD HfN or
combinations thereof preferably of Ti(C,N) having a thickness of from 1
to 20 .mu.m, and said .alpha.-Al.sub.2O.sub.3 layer adjacent said first
layer having a thickness of from about 1 to about 40 .mu.m, preferably
from about 1 to about 20 .mu.m, most preferably from about 1 to about 10
.mu.m.
6. Cutting tool insert according to claim 1, wherein the
.alpha.-Al.sub.2O.sub.3 layer is the uppermost layer.
7. Cutting tool insert according to claim 1, wherein a layer of carbide,
nitride, carbonitride or carboxynitride of one or more of Ti, Zr and Hf,
having a thickness of from about 0.5 to 3 .mu.m, preferably from about
0.5 to about 1.5 .mu.m atop the .alpha.-Al.sub.2O.sub.3 layer.
8. Cutting tool insert according to claim 1, wherein a layer of carbide,
nitride, carbonitride or carboxynitride of one or more of Ti, Zr and Hf,
having a thickness of from about 1 to 20 .mu.m, preferably 2 to 8 .mu.m
atop the .alpha.-Al.sub.2O.sub.3 layer.
9. Cutting tool insert according to claim 1, wherein a layer of
.kappa.-Al.sub.2O.sub.3 or .gamma.-Al.sub.2O.sub.3 atop the
.alpha.-Al.sub.2O.sub.3 with a thickness of from 0.5 to 10 .mu.m,
preferably from 1 to 5 .mu.m.
10. Cutting tool insert according to claim 1, wherein a layer of TiN
between the substrate and said first layer with a thickness of <3
.mu.m, preferably 0.5-2 .mu.m.
11. Cutting tool insert according to claim 1, wherein said coating has a
total thickness of from about 5 to about 25 .mu.m.
12. Cutting tool insert according to claim 1, wherein said alumina
columnar grains have a length/width ratio from about 5 to about 10.
13. Cutting tool insert according to claim 1, wherein said first layer
adjacent the body having a thickness of from 1 to 10 .mu.m.
14. Cutting tool insert according to claim 1, wherein said
.alpha.-Al.sub.2O.sub.3 layer adjacent said first layer has a thickness
of from about 1 to about 20 .mu.m.
15. Cutting tool insert according to claim 1, wherein said
.alpha.-Al.sub.2O.sub.3 layer adjacent said first layer has a thickness
of from about 1 to about 10 .mu.m.
16. A cutting tool insert comprising a substrate at least partially
coated with a coating having a total thickness of from about 5 to about
40 .mu.m, preferably 5-25 .mu.m comprising one or more refractory layers
of which at least one layer of which is an .alpha.-alumina layer wherein
said .alpha.-alumina layer comprises columnar .alpha.-Al.sub.2O.sub.3
grains with a <001> growth direction with texture coefficients a)
TC(006)>1.4, preferably >3.0 and most preferably >4.0. the
texture coefficient TC(hkl) being defined as TC ( hkl ) = I
( hkil ) I 0 ( hkil ) { 1 n I ( hkil ) I 0
( hkil ) } - 1 ##EQU00003## wherein I(hkl)=measured
intensity of the (hid) reflection I.sub.0(hkl)=standard intensity
according to JCPDS card no 46-1212 n=number of reflections used in the
calculation (hkl) reflections used are: (012), (104), (110), (006), (113)
and (116), and wherein said .alpha.-alumina layer is formed by
controlling both the nucleation and growth of .alpha.-alumina using
sulphur-containing and at least one fluorine-containing precursor.
17. Cutting tool insert according to claim 16, wherein said at least one
sulphur-containing precursor is selected from the group consisting of
H.sub.2S, SF.sub.6, SO.sub.2, SF.sub.6 and mixtures thereof.
18. A method of making an .alpha.-Al.sub.2O.sub.3 layer on a substrate,
comprising the steps of: nucleating said alumina in a temperature range
of from about 750 to about 1000.degree. C., and controlling both the
nucleation and growth of .alpha.-alumina using sulphur-containing and at
least one fluorine-containing precursor.
19. Method according to claim 18, wherein said at least one
sulphur-containing precursor is selected from the group consisting of
H.sub.2S, SF.sub.6, SO.sub.2, SF.sub.6 and mixtures thereof.
20. Method according to claim 18, wherein said at least one
sulphur-containing precursor comprises a mixture of H.sub.2S and
SF.sub.6.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from Swedish application No. SE
0502115-9 filed Sep. 27, 2005 which is hereby incorporated by reference
in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a coated cutting tool insert
designed to be used in metal machining. The coating exhibits an excellent
adhesion to the substrate covering all functional parts thereof. The
coating is composed of one or more refractory layers of which at least
one is an .alpha.-Al.sub.2O.sub.3 layer strongly textured in the
<001> direction.
BACKGROUND OF THE INVENTION
[0003] Techniques to deposit .alpha.-Al.sub.2O.sub.3 and
.kappa.-Al.sub.2O.sub.3 layers with nucleation control have been
introduced on an industrial scale only recently, and it has clearly been
shown that .alpha.-Al.sub.2O.sub.3 is the preferred phase in most metal
cutting applications. According to the definition used in the
International Tables of Crystallography, .alpha.-Al.sub.2O.sub.3 belongs
to the trigonal crystal system and has a rhombohedrally centred hexagonal
lattice, the space group symbol being R3 c. The crystal structure of
.alpha.-Al.sub.2O.sub.3 is often described as being composed of oxygen
ions (A, B) in an approximate hcp (hexagonal close-packed) arrangement (
. . . ABAB . . . ) with the aluminium anions occupying two thirds of the
octahedral interstices. The aluminium cations can take three different
vacancy positions in the oxygen lattice with the stacking sequence of . .
. .alpha..beta..gamma..alpha..beta..gamma. . . . . These are usually
referred to as c.sup..alpha., c.sup..beta. and c.sup..gamma.. The unit
cell of .alpha.-Al.sub.2O.sub.3 comprises six layers of O and Al can be
described in the following way: Ac.sup..alpha.Bc.sup.62
Ac.sup..gamma.Bc.sup..alpha.Ac.sup..beta.Bc.sup..gamma.. The JPDS card,
defined hereinbelow, uses the hexagonal system and, consequently, four
axes (hkil) are used where i=-(h+k). Often, the index i is omitted as
done also in this case.
[0004] It has been known in the art to use nucleation control in order to
obtain various growth textures. As described in a recent publication (S.
Ruppi, "Deposition, microstructure and properties of texture-controlled
CVD .alpha.-Al.sub.2O.sub.3 coatings," Int. J. Refractory Metals & Hard
Materials 23(2005) pp.306-315) manipulation of the nucleation surfaces
can be used to obtain the growth textures <012>, <104> or
<003>. The commonly observed diffraction peaks from
.alpha.-Al.sub.2O.sub.3 are (012), (104), (110), (113) and (116). However
the diffraction peak (006), which is an indication of the <001>
texture, is always missing, as indicated by its absence in XRD-patterns
obtained from textured .alpha.-Al.sub.2O.sub.3 layers using known
methods.
[0005] Prior to the present invention, texture has been controlled by
modifying the chemistry of the nucleation surface. This approach,
however, does not provide complete nucleation control. When the
nucleation control is not complete, at least a portion of the produced
.alpha.-Al.sub.2O.sub.3 layers are formed via .kappa.-Al.sub.2O.sub.3
.fwdarw..alpha.-Al.sub.2O.sub.3 phase transformation. These kinds of
.alpha.-Al.sub.2O.sub.3 layers are composed of larger grains with
transformation cracks. They exhibit much lower mechanical strength and
ductility than textured .alpha.-Al.sub.2O.sub.3 layers composed of
.alpha.-Al.sub.2O.sub.3 formed from 100% or near 100% nucleation.
Consequently, there is a need to develop techniques to more precisely
control the nucleation step and growth texture of
.alpha.-Al.sub.2O.sub.3.
[0006] The control of the .alpha.-Al.sub.2O.sub.3 polymorph in industrial
scale was achieved in the beginning of the 1990s with commercial products
based on U.S. Pat. No. 5,137,774. Later modifications of this patent have
been used to deposit .alpha.-Al.sub.2O.sub.3 with preferred textures. In
U.S. Pat. No. 5,654,035 an alumina layer textured in the <012>
direction and in U.S. Pat. No. 5,980,988 in the <110>direction are
disclosed. In U.S. Pat. No. 5,863,640 a preferred growth either along
<012>, or <104> or <110> is disclosed. U.S. Pat. No.
6,333,103 describes a modified method to control the nucleation and
growth of .alpha.-Al.sub.2O.sub.3 along the <10(10)> direction.
U.S. Pat. No. 6,869,668 describes a method to obtain a strong <300>
texture in .alpha.-Al.sub.2O.sub.3 using a texture modifying agent
(ZrCl.sub.4). The prior-art processes discussed above all use deposition
temperatures of about 1000.degree. C.
[0007] US 2004/0028951A1 describes a technique to achieve a pronounced
<012> texture. The commercial success of this kind of product
demonstrates the importance to refine the CVD process of
.alpha.-Al.sub.2O.sub.3 towards fully controlled textures.
OBJECTS AND SUMMARY OF THE INVENTION
[0008] It is an object of the present invention is to provide an alumina
layer providing improved physical properties to a cutting tool insert.
[0009] It is another object of the invention to provide an alumina layer,
as above, wherein the physical properties of the coated insert can be
tailored through control of the nucleation and growth of an
.alpha.-Al.sub.2O.sub.3 phase in the coating.
[0010] These objects are achieved by a cutting tool insert comprising a
substrate at least partially coated with a coating having a total
thickness of from about 5 to about 40 .mu.m, preferably 5-25 .mu.m
comprising one or more refractory layers of which at least one layer of
which is an .alpha.-alumina layer wherein said .alpha.-alumina layer
comprises columnar .alpha.-Al.sub.2O.sub.3 grains with a <001>
growth direction.
[0011] The objects of the invention are also achieved by a method of
making an .alpha.-Al.sub.2O.sub.3 layer on a substrate which comprises
the steps of nucleating said alumina in a temperature range of from about
750 to about 1000.degree. C., and controlling both the nucleation and
growth of .alpha.-alumina using sulphur-containing and at least one
fluorine-containing precursor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a fuller understanding of the invention, the following detailed
description should be read in conjunction with the drawings, wherein:
[0013] FIG. 1a shows SEM-image of a typical surface morphology of the
layer according to this invention in 15000.times.;
[0014] FIG 1b shows the same layer in cross-section in 15000.times.; and
FIG.2 shows an XRD pattern of an .alpha.-Al.sub.2O.sub.3-layer according
to this invention for 2.theta.=20-70.degree..
DETAILED DESCRIPTION OF THE INVENTION
[0015] According to the present invention there is provided a coated
cutting tool insert comprising a substrate and a coating to be used in
metal machining. It has been surprisingly found that a <001>
texture can be deposited in a controlled way. It is characterised in the
XRD pattern by a strong (006) peak. The alumina layer with strong
<001> texture outperforms prior art coatings with random or other
controlled textures. Further, increased toughness can be obtained.
[0016] The substrate comprises a hard material such as cemented carbide,
cermets, ceramics, high speed steel or a superhard material such as cubic
boron nitride (CBN) or diamond preferably cemented carbide or CBN. With
CBN is herein meant a cutting tool material containing at least 40 vol-%
CBN. In a preferred embodiment the substrate is a cemented carbide with a
binder phase enriched surface zone.
[0017] It has been experimentally confirmed that .alpha.-Al.sub.2O.sub.3
can be nucleated, for example, on Ti.sub.2O.sub.3 surfaces, bonding
layers of (Ti,Al)(C,O) or by controlling the oxidation potential using
CO/CO.sub.2 mixtures. The idea in all these approaches is that nucleation
must not take place on the surfaces of TiC, TiN, Ti(C,N) or Ti(C,O,N)
with fcc (face centered cubic) or in general on phases with cubic
structure, otherwise .kappa.-Al.sub.2O.sub.3 is obtained.
[0018] Further, it has been noticed that enhanced performance can be
obtained through optimising the texture of .alpha.-Al.sub.2O.sub.3. It is
thus possible to enhance tool performance by tailoring the
.alpha.-Al.sub.2O.sub.3 texture for different metal cutting applications
and work piece materials.
[0019] The hard and wear resistant coating exhibits an excellent adhesion
to the substrate covering all functional parts thereof. It is composed of
one or more refractory layers of which at least one layer is a strongly
textured .alpha.-Al.sub.2O.sub.3 deposited on a bonding layer of
(Ti,Al)(C,O,N) with increasing aluminium content towards the outer
surface. The .alpha.-Al.sub.2O.sub.3 layer is 1-45 .mu.m composed of
columnar grains with a strong <001> texture. The length/width ratio
of the alumina grains is from 2 to 15, preferably >5. The layer is
characterised by a strong (006) diffraction peak, measured using XRD, and
by low intensity of (012), (104), (113), (024) and (116) diffraction
peaks. The texture coefficients (TC) for the
.alpha.-Al.sub.2O.sub.3-layer is determined as follows:
TC ( hkl ) = I ( hkil ) I 0 ( hkil ) { 1 n
I ( hkil ) I 0 ( hkil ) } - 1 ##EQU00001##
[0020] where
[0021] I(hkl)=intensity of the (hid) reflection
[0022] I.sub.0(hkl)=standard intensity according to JCPDS card no 46-1212
[0023] n=number of reflections used in the calculation
[0024] The (hkl) reflections used are: (012), (104), (110), (600), (113)
and (116). The (024) reflection, which is the second-order reflection of
(012), is omitted from the calculations.
[0025] The texture of the alumina layer is defined as follows:
[0026] TC(006)>1.4, preferably >3.0 and most preferably >4.0.
This is a manifestation of a strong <001> texture. The texture
coefficients for (012), (104), (113), (024) and (116) diffraction peaks
are less than 0.5, preferably less than 0.2 and most preferably less than
0.1.
[0027] More particularly, the coating comprises a first layer adjacent the
substrate of CVD Ti(C,N), CVD TiN, CVD TiC, MTCVD Ti(C,N), MTCVD Zr(C,N),
MTCVD Ti(B,C,N), CVD HfN or combinations thereof preferably of Ti(C,N)
having a thickness of from 1 to 20 preferably from 1 to 10 .mu.m.
Preferably there is an intermediate layer of TiN between the substrate
and said first layer with a thickness of <3 .mu.m, preferably 0.5-2
.mu.m.
[0028] In one embodiment the .alpha.-Al.sub.2O.sub.3 layer is the
uppermost layer. In another embodiment there is a layer of carbide,
nitride, carbonitride or carboxynitride of one or more of Ti, Zr and Hf,
having a thickness of from about 0.5 to 3 .mu.m, preferably 0.5 to 1.5
.mu.m atop the .alpha.-Al.sub.2O.sub.3 layer. Alternatively this layer
has a thickness of from about 1 to 20 .mu.m, preferably 2 to 8 .mu.m.
[0029] In yet another embodiment the coating includes a layer of
.kappa.-Al.sub.2O.sub.3 and/or .gamma.-Al.sub.2O.sub.3 preferably atop
the .alpha.-Al.sub.2O.sub.3 with a thickness of from 0.5 to 10,
preferably from 1 to 5 .mu.m.
[0030] The present invention also relates to a refined method to produce
textured .alpha.-Al.sub.2O.sub.3 layers in a temperature range of
950-1000.degree. C., preferably at 1000.degree. C. with a controlled
<001> texture. The .alpha.-Al.sub.2O.sub.3 layer is deposited on a
bonding layer of (Ti,Al)(C,O,N) with increasing aluminium content towards
the outer surface. On to this layer a Ti(C,O) layer is deposited with
controlled O-content. A very thin titanium oxide nucleation layer is
obtained in the similar way as used in ALD (Atomic Layer Deposition). The
procedure is as follows: (i) exposure of a first precursor TiCl.sub.4,
preferably together with AlC.sub.3, (ii) purge (N.sub.2), (iii) exposure
of the second precursor (H.sub.2O), (iv) purge (N.sub.2). The duration of
the steps (i) and (iii) is 1-5 min, preferably 2 min each and the steps
(ii) and (iv) 2-10 min, preferably 5 min each. The deposition of the
.alpha.-Al.sub.2O.sub.3 is started with a relatively long 30-120 min,
preferably 60 min, nucleation step without sulphur- or fluorine
containing compounds. .alpha.-Al.sub.2O.sub.3 is grown to its desired
thickness using sulphur-containing compounds H.sub.2S, or SO.sub.2,
preferably H.sub.2S, optionally together with fluorine-containing
compounds SF.sub.6 or HF, preferably SF.sub.6.
[0031] It has been found, quite unexpectedly, that <001> texture
could be obtained by careful control of the ratio of sulphur containing
dopants to CO.sub.2/CO. When .alpha.-Al.sub.2O.sub.3 is nucleated
correctly, followed by a deposition process using relatively low amounts
of these dopants (0.5-1.2%) together with a CO+CO.sub.2 gas mixture where
CO=0.5-2.times.CO.sub.2, a strong <001> growth texture can be
obtained in a controlled way. The correct ratios depend on the type of
deposition equipment, flow rate etc. An important difference compared
with the prior-art is that the texture is controlled, in addition to the
nucleation procedure, also during the growth of .alpha.-Al.sub.2O.sub.3
itself. The described texture is thereby obtained when both the
nucleation and growth are controlled correctly. The lack of control of
both nucleation and growth is a possible explanation for the fact that
the <001> texture [(006) diffraction peak)] has heretofore been
unknown.
[0032] The following is a detailed description of a preferred sequence of
nucleation steps. [0033] 1. Depositing a bonding layer 0.1-1 .mu.m
thick in a gas mixture of 2-3% TiCl.sub.4 and AlCl.sub.3 increasing from
0.5 to 6%, 3-10% CO, 1-3% CO.sub.2, 0.2-1.0% CH.sub.3CN, 0.2-1.0%, 2-10%
N2 and balance H2 at about 750-1000.degree. C., preferably at 800.degree.
C. and at a pressure of 50-200 mbar. [0034] 2. Purging by N.sub.2 for 5
min. [0035] 3. Treating the bonding layer in a gas mixture of 5-15%
TiCl.sub.4 and 5-20% CO, 0.5-3% CO.sub.2 and 10-20% Ar in hydrogen for
5-15, preferably 10, minutes min at 950-1000.degree. C., preferably at
1000.degree. C. and at a pressure of 50-200 mbar. [0036] 4. Purging by
N.sub.2 for 5 min. [0037] 5. Treating the bonding layer in a gas mixture
of 8-15% TiCl.sub.4 and 0.5-2% AlCl.sub.3 in hydrogen for 5-15 min at
about 950 to about 1000.degree. C., preferably at about 1000.degree. C.
and at a pressure of from about 50 to about 200 mbar. [0038] 6. Treating
in a gas mixture of 0.05 to 0.5% H.sub.2O, preferably 0.01%, balance
H.sub.2. [0039] 7. Purging by N.sub.2 for 5 min. [0040] 8. Nucleation of
the alumina layer at a temperature of 950-1000.degree. C. with desired
thickness according to known technique or depositing an alumina layer at
950-1000.degree. C. without any catalysing precursors. [0041] 9.
Deposition of the alumina layer at a temperature of 950-1000.degree. C.
to the desired thickness at 950-1000.degree. C. at deposition pressures
50-200 mbar using 0.01-0.05% H.sub.2S or SO.sub.2, preferably H.sub.2S
and 0.01-0.02% SF.sub.6 or HF, preferably SF.sub.6 as catalysing agents.
CO.sub.2 1.0-4.5% is used as the oxygen donor together with CO,
maintaining CO=2.times.CO.sub.2.
EXAMPLE 1
[0042] Cemented carbide cutting inserts with a composition of 5.9% Co and
balance WC (hardness about 1600 HV) were coated with a layer of MTCVD
Ti(C,N). The thickness of the MTCVD layer was about 2 .mu.m. On to this
layer an .alpha.-Al.sub.2O.sub.3 layer consisting of about 10 .mu.m.
.alpha.-Al.sub.2O.sub.3 was deposited according to this invention
referred to as Coating a). The detailed process data is given below:
[0043] Step 1:Bonding layer 1
TABLE-US-00001
Gas mixture TiCl.sub.4 = 2.8%
CH.sub.3CN = 0.7%
AlCl.sub.3 = increasing
from 0.8 to 5.4%
CO = 8.8%
CO.sub.2 = 2.2%
N.sub.2 . . . = 5%
Balance: H.sub.2
Duration 40 min
Temperature 1000.degree. C.
Pressure 100 mbar
[0044] Step 2: N.sub.2 purge
[0045] Step 3:Bonding layer 2
TABLE-US-00002
Gas mixture TiCl.sub.4 = 8%
CO = 12%
CO.sub.2 = 1.2%
Ar . . . = 5%
Balance: H.sub.2
Duration 2-10 min
Temperature 1000.degree. C.
Pressure 100 mbar
[0046] Step 3: (optional ALD steps): a)TiCl.sub.4 treatment b)
N.sub.2-purge c) H.sub.2O treatment d) N.sub.2-purge
TABLE-US-00003
a) TiCl.sub.4 = 9%
AlCl.sub.3 = 1%
H.sub.2 = balance
5 min . . .
c) H.sub.2O = 0.1%
H.sub.2 = balance
2 min . . .
b, d) N.sub.2 = 100%
5 min
Temperature 1000.degree. C.
Pressure 50 mbar
[0047] Step 4: Nucleation step
TABLE-US-00004
Gas mixture AlCl.sub.3 = 1.2%
HCl . . . = 2.0%
CO.sub.2 = 1.0-1.5%
CO = 0.5-2.4%
Balance H.sub.2
Duration 60 min
Temperature 1000.degree. C.
Pressure 50 mbar
[0048] Step 5: Deposition
TABLE-US-00005
Gas mixture AlCl.sub.3 = 2.8%
HCl = 3%
CO.sub.2 = 1.8-2.5%
CO = 0.9-.5%
H.sub.2S = 0.05-1.0%
Balance: H.sub.2
Duration 630 min
Temperature 1000.degree. C.
Pressure 70 mbar
EXAMPLE 2
[0049] Coating a) was studied using X-ray diffraction. The texture
coefficients of the .alpha.-Al.sub.2O.sub.3 layers were determined and
are presented in Table 1. A SEM micrograph of Coating a) in top view with
<001> texture is shown in FIG. 1a and in cross section in FIG. 1b.
The .alpha.-Al.sub.2O.sub.3 layer was composed of columnar grains. The
X-Ray diffraction pattern is shown in FIG. 2.
TABLE-US-00006
TABLE 1
hkl Coating a)
012 0.01
104 0.06
110 0.01
006 5.91
113 0.00
116 0.02
EXAMPLE 3
[0050] For reference Coatings b) and c) with <012> and <104>
textures were deposited according to the prior-art (coating thickness
about 10 .mu.m). The coatings were studied using X-ray diffraction. The
texture coefficients of the .alpha.-Al.sub.2O.sub.3 layers were
determined and are presented in Table 2.
TABLE-US-00007
TABLE 2
hkl Coating a), invention Coating b) Coating c)
012 0.03 5.15 0.16
104 0.06 0.13 4.27
110 0.01 0.10 0.08
600 5.88 0.00 0.09
113 0.00 0.18 0.66
116 0.02 0.44 0.74
EXAMPLE 4
[0051] Coating a), b) and c) deposited on Co-enriched substrates were
tested with respect to toughness in longitudinal turning with interrupted
cuts.
Work piece: Cylindrical slotted bar
Material: SS1672
[0052] Insert type: CNMG120408-M3 Cutting speed: 140 m/min Feed: 0.1,
0.125, 0.16, 0.20, 0.25, 0.315, 0.4, 0.5, 0.63, 0.8 mm/rev gradually
increased after 10 mm length of cut
Depth of cut: 2.5 mm
[0053] Remarks: dry turning
[0054] Tool life criteria: Gradually increased feed until edge breakage.
10 edges of each variant were tested.
[0055] The inserts were inspected after 2 and 4 minutes of cutting. As
clear from Table 3 the edge toughness was considerably enhanced when the
layer was produced according to this invention.
TABLE-US-00008
TABLE 3
Mean feed at
Experimental coating breakage (mm/rev)
Coating a (006), 0.50
according to the invention
Coating b (012) 0.22
Coating c (104) 0.36
[0056] The test results show (Table 3) that the coating according to the
invention (Coating a) exhibited clearly better toughness behaviour than
the prior-art (Coatings b and c).
EXAMPLE 5
[0057] The coatings a), b) and c) were tested with respect to edge
chipping in longitudinal turning in cast iron.
[0058] Work piece: Cylindrical bar
[0059] Material: SS0130
[0060] Insert type: SNUN
[0061] Cutting speed: 400 m/min
[0062] Feed: 0.4 mm/rev
[0063] Depth of cut: 2.0 mm
[0064] Remarks: dry turning
[0065] The inserts were inspected after 2 and 4 minutes of cutting. As
clear from Table 4 the edge toughness of the prior art product was
considerably enhanced when the coating was produced according to this
invention.
TABLE-US-00009
TABLE 4
Flaking of the Flaking of the
edge line (%) edge line (%)
after 2 minutes after 6 minutes
Coating a (Invention) 0 5
Coating b 0 18
Coating c 5 10
EXAMPLE 6
[0066] Cubic boron nitride (CBN) insert containing about 90% of
polycrystalline CBN (PCBN) were coated according to this invention and
according to prior art Coating b). The coated CBN was compared with
uncoated CBN insert in cutting of steel containing ferrite. It is known
that B has a high affinity to ferrite and diffusion wear occurs at high
cutting speeds.
[0067] Work piece: Cylindrical bar
[0068] Material: SS0130
[0069] Insert type: SNUN
[0070] Cutting speed: 800 m/min
[0071] Feed: 0.4 mm/rev
[0072] Depth of cut: 2.5 mm
[0073] Remarks: dry turning
TABLE-US-00010
TABLE 5
Life time (min)
Coated CBN, Invention 23
Coated CBN, prior art, 14
012 texture
Uncoated CBN 9
[0074] As is evident from Table 5 the coating according to this invention
is superior to the prior art.
EXAMPLE 7
[0075] The hardness and Young's modulus of the coatings a)-c) together
with .kappa.-Al.sub.2O.sub.3 and older prior-art .alpha.-Al.sub.2O.sub.3
were measured using nanoindentation. The results are shown in Table 6.
TABLE-US-00011
TABLE 6
Hardness Young's
(GPa) Modulus (GPa)
Coating a 28.92 444.42
Coating b 27.31 419.53
Coating c 28.81 441.17
Prior-art .alpha.-Al.sub.2O.sub.3 (no texture) 25.79 385.45
.kappa.-Al.sub.2O.sub.3 23.64 339.51
[0076] Coating c) according to the invention shows the highest values of
hardness and modulus, closely followed by coating c).
* * * * *