U.S. patent application number 11/908563 was filed with the patent office on 2008-08-14 for hard material layer.
Invention is credited to Wolfgang Kalss, Jurgen Ramm, Beno Widrig.
Application Number | 20080193782 11/908563 |
Document ID | / |
Family ID | 35149632 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080193782 |
Kind Code |
A1 |
Ramm; Jurgen ; et
al. |
August 14, 2008 |
Hard Material Layer
Abstract
A hard material layer is deposited on a workpiece as a
functional layer by an arc-PVD method. The layer is essentially an
electrically insulating oxide of at least one of the metals (Me) of
the transition metals of the sub-groups IV, V, VI of the periodic
table and Al, Si, Fe, Co, Ni, Co, or Y and the functional layer
(32) contains no noble gas or halogen.
Inventors: |
Ramm; Jurgen; (Maienfeld,
CH) ; Widrig; Beno; (Bad Ragaz, CH) ; Kalss;
Wolfgang; (Feldkirch, AT) |
Correspondence
Address: |
NOTARO AND MICHALOS
100 DUTCH HILL ROAD, SUITE 110
ORANGEBURG
NY
10962-2100
US
|
Family ID: |
35149632 |
Appl. No.: |
11/908563 |
Filed: |
January 19, 2006 |
PCT Filed: |
January 19, 2006 |
PCT NO: |
PCT/CH06/00042 |
371 Date: |
September 13, 2007 |
Current U.S.
Class: |
428/469 ;
204/192.38; 427/576 |
Current CPC
Class: |
C23C 14/024 20130101;
C23C 14/08 20130101; F05D 2230/313 20130101; H01J 37/34 20130101;
F01D 5/288 20130101; C23C 14/325 20130101; H01J 37/32055 20130101;
H01J 37/3444 20130101; C23C 14/081 20130101; C23C 14/0641 20130101;
C23C 14/083 20130101 |
Class at
Publication: |
428/469 ;
427/576 |
International
Class: |
B32B 15/01 20060101
B32B015/01; C23C 14/32 20060101 C23C014/32 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2005 |
CH |
518/05 |
Aug 3, 2005 |
CH |
1289/05 |
Claims
1. Hard material layers deposited on a workpiece (30) as Arc-PVD
functional layer (32) wherein this layer is formed substantially as
an electrically insulating oxide of at least one of the metals (Me)
from the transition metals of subgroups IV, V, VI of the periodic
system of elements and Al, Si, Fe, Co, Ni, Y, characterized in that
the functional layer (32) has a content of inert gas and/or of a
halogen of less than 2%.
2. Hard material layer as claimed in claim 1, characterized in that
the content of inert gas in the functional layer (32) is maximally
0.1%, preferably maximally 0.05%, and/or that of halogen maximally
0.5%, preferably maximally 0.1%, preferably comprises substantially
no inert gas and/or halogen.
3. Hard material layer as claimed in claim 1, characterized in that
the functional layer (32) has a thickness in the range from 0.5
.mu.m to 12 .mu.m, preferably 1.0 to 5 .mu.m.
4. Hard material layer as claimed in claim 1, characterized in that
the functional layer (32) is substantially an aluminum metal mixed
oxide of the form (Al.sub.xM.sub.1-x).sub.yO.sub.z wherein Me is
preferably one of the metals Al, Cr, Mo, Zr, Fe, Co, Ni, Y, singly
or also in mixtures thereof.
5. Hard material layer as claimed in claim 4, characterized in that
Me is the metal chromium and forms the form
(Al.sub.xCr.sub.1-x).sub.yO.sub.z.
6. Hard material layer as claimed in claim 5, characterized in that
the fraction of the metal chromium in the layer is 5 to 80 atom %,
preferably 10 to 60 atom %.
7. Hard material layer as claimed in claim 1, characterized in that
the functional layer (32) is substantially a stoichiometric
aluminum oxide layer of the form Al.sub.2O.sub.3.
8. Hard material layer as claimed in claim 1, characterized in that
the functional layer (32) forms the outermost layer or an
additional support layer, with at least one superjacent cover layer
(35), such as in particular a friction-reducing layer (35).
9. Hard material layer as claimed in claim 1, characterized in that
the functional layer (32) has a temperature resistance of greater
than 800.degree. C. and that it is chemically stable.
10. Workpiece with a hard material layer as claimed in claim 1,
characterized in that the workpiece (30) is a tool, a machine part,
preferably an indexable insert.
11. Workpiece as claimed in claim 10, characterized in that between
the functional layer (32) and the workpiece (30) a further layer
forming an intermediate layer (31) is disposed, and this layer
forms in particular an adhesion layer (31) and such adhesion layer
preferably comprises one of the metals of the subgroups IV, V and
VI of the periodic system of elements and/or Al, Si, Fe, Co, Ni, Y
or a mixture thereof.
12. Workpiece as claimed in claim 11, characterized in that the
metals of the intermediate layer (31) are compounds with N, C, O, B
or mixtures thereof, the compound with N being preferred.
13. Workpiece as claimed in claim 11, characterized in that the
layer thickness of the intermediate layer (31) is 0.05 to 5 .mu.m,
preferably is in the range of 0.1 to 0.5 .mu.m.
14. Workpiece as claimed in claim 10, characterized in that at
least one of the layers, in particular the functional layer (32)
and or the intermediate layer (31) is implemented as a progression
layer (34), such as from metallic over nitridic and/or from
nitridic to nitrooxidic and up to the oxide.
15. Workpiece as claimed in claim 10, characterized in that at
least one of the layers, in particular the functional layer (32),
is implemented as a multilayer system (33) with different material
composition, in which preferably several deposits (33) alternately
repeat with respect to their essential composition and that the
multilayer system (33) preferably comprises at least 3
deposits.
16. Workpiece as claimed in claim 15, characterized in that the
repeating layer sequence pairs of the layer system alternately
change the material composition, such as preferably from an
Me.sub.1 to an Me.sub.2-oxide and/or from an Me.sub.1-nitride to an
Me.sub.1-oxide and/or from an Me.sub.1-nitride to an
Me.sub.2-oxide.
17. Workpiece as claimed in claim 15, characterized in that the
repeating layer sequence pair of the layer system alternately
comprises the material composition of
(Al.sub.xCr.sub.1-x).sub.yN.sub.z and
(Al.sub.xCr.sub.1-x).sub.yO.sub.z and these preferably in
stoichiometric composition such as (Al.sub.xCr.sub.1-x)N and
(Al.sub.xCr.sub.1-x).sub.zO.sub.3.
18. Workpiece as claimed in claim 15, characterized in that the
repeating layer sequence pairs of the layer system comprise
alternately the material composition (AlZr).sub.xN.sub.y and
(AlZr).sub.xO.sub.y and these preferably in stoichiometric
composition such as (Al.sub.xZr.sub.1-x)N and
(Al.sub.xZr.sub.1-x).sub.2O.sub.3.
19. Workpiece as claimed in claim 15, characterized in that the
multilayer system (33) comprises at least 20 deposits, preferably
up to 500 deposits.
20. Workpiece as claimed in claim 15, characterized in that the
layer thickness of one deposit of the multilayer system (33) is in
the range of 0.01 to 0.5 .mu.m, preferably in the range of 0.02 to
0.1 .mu.m.
21. Method for coating a workpiece (3) in a vacuum process
installation (1) with a hard material layer (32) deposited as
functional layer, which is implemented as an electrically
insulating oxide of at least one of the metals (Me) of the
transition metals of the subgroups IV, V, VI of the periodic system
of elements and Al, Si, Fe, Co, Ni, Co, Y, and that the layer is
deposited with an arc evaporator source (5) operated with a DC
power supply (13), characterized in that a pulsed power supply (16,
16') is superimposed, wherein the target (5', 20) of the arc
evaporator source (5, 20) comprises one of the metals and the metal
vapor-deposited in this way is reacted to the oxide in an
oxygen-containing reactive gas atmosphere.
22. Method as claimed in claim 21, characterized in that in the
reactive gas atmosphere of the process chamber of the vacuum
installation (1) so small a quantity of inert gas and/or halogen
gas is supplied that in the deposited layer maximally 0.5% of such
gases, preferably substantially none of these gases, are
incorporated.
23. Method as claimed in claim 21, characterized in that two DC-fed
arc evaporator sources (5, 20) are operated, wherein additionally a
single pulsed power supply (16) is connected to the two sources (5,
20) and in this manner forms a dual pulse arc evaporator
configuration (5, 20).
24. Method as claimed in claim 21, characterized in that the
workpiece is substantially comprised of steel, an iron-, chromium-,
cobalt- or nickel-containing alloy of one or several metals, a hard
metal, a ceramic, a cermet, or cubic boron mononitride, wherein at
least one further layer is deposited by means of a PVD method and
one of the layers is an adhesion layer (31) which borders directly
on the workpiece (30), wherein the or at least one of the following
layers, the functional layer (32), is substantially comprised of
Al.sub.2O.sub.3 or (AlMe).sub.2O.sub.3, wherein Me comprises at
least one transition metal of the group IV, V or VI of the periodic
system of elements or silicon and at least the aluminum or aluminum
metal oxide layer is deposited with an arc evaporator (5, 20), in
which from at least one target (5', 20'), poisoned on the surface,
aluminum oxide, metal oxide or aluminum metal oxide is vaporized in
an oxygen-containing atmosphere.
25. Method as claimed in claim 21, characterized in that the
coating attains a roughness value R.sub.a of not less than 0.2
.mu.m.
26. Method as claimed in claim 21, characterized in that at least
one further layer is deposited which comprises substantially an
aluminum-free one or several metal oxides comprising oxide layer,
wherein the metal oxide comprises at least one transition metal of
group IV, V or VI of the periodic system of elements or silicon,
however preferably chromium or zirconium.
27. Method as claimed in claim 24, characterized in that the
adhesion layer (31) comprises at least one of the transition metals
of group IV, V or VI of the periodic system of elements and/or
aluminum or silicon.
28. Method as claimed in claim 24, characterized in that the
adhesion layer (31) comprises a hard layer which comprises a
nitride, carbide or boride, at least one of the transition metals
of group IV, V or VI of the periodic system of elements and/or
aluminum or silicon or a mixture of these compounds.
29. Method as claimed in claim 21, characterized in that the
functional layer (32) is deposited as hard material layer system
which comprises several deposits (33) of a nitride, carbide, boride
or oxide of at least one of the transition metals of group IV, V or
VI of the periodic system of elements and/or aluminum or silicon or
a mixture of these compounds, wherein at least directly succeeding
deposits differ by the stoichiometry of their metal or nonmetal
content.
30. Method as claimed in claim 29, characterized in that the
deposition of the hard material layer system (32) takes place with
one or several deposits (33) of aluminum chromoxide-containing
layers.
31. Method as claimed in claim 29, characterized in that
transitions between the individual deposits (33) of the hard
material layer system (32) with respect to the stoichiometry of
their metal or nonmetal content are increased or decreased smoothly
and continuously or stepwise.
32. Method as claimed in claim 29, characterized in that the layer
of the individual deposits of the hard material layer system (32)
is deposited with a thickness between 0.01 and 0.5 .mu.m,
preferably betwen 0.02 and 0.1 .mu.m.
33. Method as claimed in claim 30, characterized in that nitride-,
carbide- or boride-containing layers are deposited alternately with
aluminum chromoxide-containing layers.
34. Method as claimed in claim 24, characterized in that at least
one transition from the adhesion layer (31) to the aluminum
oxide-containing layer or to the hard material layer system (32) or
from the hard material layer system (32) or the aluminum
oxide-containing layer to the cover layer (35) with respect to the
stoichiometry of their metal or nonmetal content are increased or
decreased smoothly and continuously or stepwise.
35. Method as claimed in claim 21, characterized in that the
aluminum oxide-containing layer is substantially deposited as
(Al.sub.1-xCr.sub.x).sub.2O.sub.3, wherein 0.05<.times.<0.80,
however preferably 0.01<.times.<0.60.
36. Method as claimed in claim 21, characterized in that as
workpiece (30) a tool, in particular a cutting, forming or
injection molding tool is coated.
37. Method as claimed in claim 21, characterized in that as
workpiece (30) a part, in particular a part for an internal
combustion engine or a turbine, is coated.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The invention relates to a hard material layer deposited as
oxidic arc PVD functional layer (32) on a workpiece (30) according
to the preamble of claim 1 as well as to a method for coating a
workpiece with a hard material layer according to the preamble of
claim 21.
[0002] The operation of arc evaporator sources, also known as spark
cathodes, by feeding with electrical pulses has been known in prior
art for a relatively long time. With arc evaporator sources high
evaporation rates, and therewith high deposition rates, can be
achieved economically in coating. In addition, the structure of
such a source can technically be realized relatively simply. These
sources operate at currents typically in the range of approximately
100 A and more and at voltages of a few volts to a few tens of
volts, which can be realized with relatively cost-effective DC
power supplies. A significant disadvantage with these sources
comprises that in the proximity of the cathode spot very rapidly
proceeding melting occurs on the target surface, whereby drops are
formed, so-called droplets, which are hurled away as splatters and
subsequently condense on the workpiece and consequently have an
undesirable effect on the layer properties. For example, thereby
the layer structure becomes inhomogeneous and the surface roughness
becomes inferior. With high requirements made of the layer quality,
layers generated thusly, can often not be commercially applied.
Attempts have therefore already been made to reduce these problems
by operating the arc evaporator source in pure pulse operation of
the power supply. However, until now only marginal improvements in
the splatter formation could be achieved therewith.
[0003] The use of reactive gases for the deposition of compounds
from a metallic target in a reactive plasma was until now limited
to the production only of electrically conductive layers. In the
production of electrically nonconducting, thus dielectric layers,
such as for example of oxides using oxygen as the reactive gas, the
problem of splatter formation is intensified. The re-coating of the
target surfaces of the arc evaporator and of the counterelectrodes,
such as the anodes and also other parts of the vacuum process
installation, with a non-conducting layer leads to entirely
unstable conditions and even to the quenching of the arc. In this
case the latter would have to be repeatedly newly ignited or it
would thereby become entirely impossible to conduct the
process.
[0004] EP 0 666 335 B1 proposes for the deposition of purely
metallic materials with an arc evaporator to superimpose onto the
DC current a pulsing current in order to be able to lower hereby
the DC base current for the reduction of the splatter formation.
Pulse currents up to 5000 A are herein necessary, which are to be
generated with capacitor discharges at relatively low pulse
frequencies in the range of 100 Hz to 50 kHz. This approach is
proposed to prevent the droplet formation in the non-reactive
evaporation of purely metallic targets with an arc evaporator
source. A solution for the deposition of non-conducting dielectric
layers is not stated in this document.
[0005] In the reactive coating by means of arc evaporator source
there is a lack of reactivity and process stability, especially in
the production of insulating layers. In contrast to other PVD
processes (for example sputtering), insulating layers can currently
only be produced by means of arc evaporation with electrically
conducting targets. Working with high frequency, such as is the
case during sputtering, has so far failed due to the lacking
technique of being able to operate high-power supplies with high
frequencies. Working with pulsed power supplies appears to be an
option. However, in this case the spark, as stated, must be ignited
repeatedly or the pulse frequency must be selected so large that
the spark is not extinguished. This appears to function to some
degree in applications for special materials, such as graphite, as
described in DE 3901401. It should, however, be noted that graphite
is not an insulator, but rather is electrically conductive, even if
it is a poorer conductor than normal metals.
[0006] In oxidized target surfaces a renewed igniting with
mechanical contact and by means of DC supplies is not possible. The
actual problem in reactive arc evaporation are the coatings with
insulating layers on the target and the anode, or on the coating
chamber connected as the anode. In the course of their formation,
these insulating coatings increase the burn voltage of the spark
discharge, lead to increased splatters and sparkovers, an unstable
process, which ends in an interruption of the spark discharge.
Entailed therein is a coating of the target with island growth,
which decreases the conducting surface. A highly diluted reactive
gas (for example argon/oxygen mixture) can delay the accretion on
the target, however it cannot solve the fundamental problem of
process instability. While the proposal according to U.S. Pat. No.
5,103,766 of alternately operating the cathode and the anode with
renewed ignition each time results in process stability, it does
however lead to increased splatters.
[0007] The resolution via a pulsed power supply as is possible for
example in reactive sputtering, cannot be applied in classic spark
evaporation. The reason lies therein that a glow discharge has a
"longer life" than a spark when the power supply is interrupted. In
order to circumvent the problem of the coating of the target with
an insulating layer, in reactive processes for the production of
insulating layers either the reactive gas inlet is locally
separated from the target (in that case the reactivity of the
process is only ensured if the temperature on the substrate also
permits an oxidation reaction) or a separation between splatters
and ionized fraction is carried out (so-called filtered arc) and
after the filtering the reactive gas is added to the ionized
vapor.
[0008] There is further the wish for additional reduction or
scaling capability of the thermal loading of the substrates and the
ability to conduct low-temperature processes in cathodic spark
coating.
[0009] In WO 03018862 the pulse operation of plasma sources is
described as a feasible path for reducing the thermal loading on
the substrate. However, the reasons offered there apply to the
field of sputter processes. No reference is established to spark
evaporation.
[0010] In the application field of hard material coatings there has
in particular been for a long time the need to be able to produce
oxidic hard materials with appropriate hardness, adhesive strength
and under control according to the desired tribological properties.
Herein aluminum oxides, in particular aluminum chromoxides, could
play an important role. Prior art in the field of PVD (Physical
Vapor Deposition) deals herein most often only with the production
of gamma and alpha aluminum oxide. The method most frequently
mentioned is dual magnetron sputtering, which in this application
entails great disadvantages with respect to process reliability and
costs. Japanese patents concentrate more on layer systems in
connection with the tools and cite, for example, the arc ion
plating process as the production method. There is the general wish
to be able to deposit alpha aluminum oxide. However, in current PVD
methods, substrate temperatures of approximately 700.degree. C. or
more are required in order to obtain this structure. Some users
elegantly attempt to avoid these high temperatures through
nucleation layers (oxidation of TiAlN, Al--Cr--O system). However,
this does not necessarily make the process less expensive and
faster. Until now it also did not appear possible to be able to
produce satisfactorily alpha aluminum oxide layers by means of arc
evaporation.
[0011] With respect to prior art the following disadvantages are
summarized, in particular regarding the production of oxidic layers
with reactive process: [0012] 1. Stable conduction of the process
is not possible for the deposition of insulating layers, if there
is no spatial separation between arc evaporator cathode or anode of
the arc discharge and the substrate region with reactive gas
inlet.
[0013] 2. There is no fundamental solution of the problematic of
splatters: conglomerates (splatters) are not fully through-reacted,
wherein metallic components occur in the layer, increased roughness
of the layer surface is generated and the constancy of the layer
composition and the stoichiometry is disturbed. [0014] 3.
Insufficient possibilities for realizing low-temperature processes,
since insufficiently the thermal loading of the substrate is too
high for the production of oxides with high-temperature phases.
[0015] 4. The production of flat graduated intermediate layers for
insulating layers has so far not been possible by means of arc
evaporation.
[0016] In contrast to sputtering, coating by means of cathodic
spark is substantially a evaporation process. It is supposed that
in the transition between hot cathode spot and its margin parts are
entrained which are not of atomic size. These conglomerates impinge
as such onto the substrate and result in rough layers, and it has
not been possible fully to react-through the splatters. Avoidance
or fragmentation of these splatters was so far not successful,
especially not for reactive coating processes. In these, on the
cathode of the arc evaporator source, for example in oxygen
atmosphere, additionally a thin oxide layer forms, which tends to
increased splatter formation.
SUMMARY OF THE INVENTION
[0017] The present invention addresses the problem of eliminating
the listed disadvantages of prior art. The problem addressed is in
particular to deposit economically layers with better properties
with at least one arc evaporator source, such that the reactivity
in the process is increased through better ionization of the
vaporized material, and of the reactive gas involved in the process
is increased. In this reactive process the size and frequency of
the splatters is to be significantly reduced, in particular in
reactive processes for the production of insulating layers.
Further, better process control is to be made possible, such as the
control of the evaporation rates, increase of the layer quality,
settability of the layer properties, improvement of homogeneity of
the reaction, as well as the reduction of surface roughness of the
deposited layer. These improvements are in particular also of
importance in the production of graduated layers and/or alloys. The
process stability in reactive processes for the production of
insulating layers is to be generally increased.
[0018] In particular, an arc evaporation process is to be made
possible which permits the economic deposition of oxidic hard
material layers, aluminum oxide and/or aluminum chromoxide layers
which preferably have substantially alpha and/or gamma structure.
Moreover, a low-temperature process should be realized, preferably
below 700.degree. C., also at high economy of process. Furthermore
the expenditure for the device and in particular for the power
supply for pulsed operation should be kept low. Said tasks may
occur singly as well as also combined with one another, depending
on the particular required application area.
[0019] The problem is solved according to the invention through a
hard material layer applied with an arc evaporation PVD method
according to claim 1 and by proceeding according to a method as
claimed in claim 21 for the production of such a layer on a
workpiece. The dependent claims define further advantageous
embodiments.
[0020] The problem is solved according to the invention thereby
that a hard material layer is deposited as arc PVD functional layer
onto a workpiece, this layer substantially being formed as an
electrically insulating oxide, comprised of at least one of the
metals (Me) Al, Cr, Fe, Ni, Co, Zr, Mo, Y and the functional layer
comprises a content of inert gases and/or halogens of less than 2%.
The content of inert gases is preferably less than 0.1%, in
particular less than 0.05% or even better is zero and/or the
content of halogens is less than 0.5%, in particular less than
0.1%, or even better is zero. These gases should be incorporated
into the layer to as small an extent as possible and the arc
evaporation process should therefore exclusively take place with
pure reactive gas or a pure reactive gas mixture without inert gas
component, such as He, Ne, Ar, or halogen gases, such as F.sub.2,
Cl.sub.2, Br.sub.2, J.sub.2, or halogen-containing compounds such
as CF.sub.6 or the like.
[0021] The known CVD processes use halogen with which at
undesirably high temperatures of approximately 1100.degree. C. a
layer is deposited. Even under reactive process conditions, the
known sputter processes are operated with a high proportion of
inert gas, such as with argon. The content of such gases in the
layer should be below said values or preferably be zero. The pulse
arc evaporation process according to the invention also permits
sufficing without such process gases.
[0022] The preceding patent application with the application number
CH00518/05 shows essentially already an approach to a solution. A
first solution is specified which is especially well suited for
completely reacted target surfaces and has a marked reduction of
splatter formation compared to DC-operated arc evaporator targets.
This application proposes superimposing a high-current pulse onto
the DC feed of an arc evaporator source with a pulsed power supply,
as is shown schematically in FIG. 2. A further reduction of the
splatters and their size at higher economy is attained through the
approach according to the succeeding patent application CH 01289/05
which claims priority of CH 00518/05 and represents a further
development. In this application a vacuum process installation for
the surface working of workpieces with at least one arc evaporator
source is provided comprising a first electrode connected to a DC
power supply, a second electrode disposed separated from the arc
evaporator source being provided and that the two electrodes are
connected to a single pulsed power supply. Between the two
electrodes, consequently an additional discharge gap is operated
with only a single pulsed power supply which makes possible an
especially high ionization of the involved materials at very good
controllability of the process.
[0023] The second electrode can herein be a further arc evaporator
source, a workpiece holder or the workpiece itself, whereby in this
case the second electrode can also be implemented as an evaporation
crucible forming the anode of a low-voltage arc evaporator.
[0024] An especially preferred embodiment comprises that both
electrodes are the cathodes of one arc evaporator source each and
that each of these arc evaporator sources by itself is connected
directly to a DC power supply for the purpose of maintaining a
holding current and wherein the two cathodes are connected to a
single pulsed power supply such that the arcs, or the arc
discharges, of the two sources are not extinguished in operation.
In this configuration, consequently, only one pulsed power supply
is required since this supply is interconnected directly between
the two cathodes of the arc evaporators. Apart from the high degree
of ionization and the good controllability of the process, high
efficiency of the configuration also results. Between these two
electrodes and the pulse discharge gap additionally generated
thereby, compared to this discharge gap, a bipolar pulse forms
electrically from negative and positive components, whereby the
entire period duration of this fed AC voltage can be utilized for
the process. In fact, no unused pulse pauses are generated and the
negative as well as also the positive pulses without interruption
contribute overall to the process. The deposition rate can thereby
be additionally increased without having to employ additional
expensive pulsed power supplies. This configuration with two arc
evaporator sources is especially suited for the deposition of
layers from a metallic target utilizing reactive gas. With this
configuration it becomes even possible to omit entirely supporting
inert gases, such as argon, and it is possible to work with pure
reactive gas, even unexpectedly with pure oxygen. Through the high
degree of ionization attainable therewith of the vaporized material
as well as also of the reactive gas, such as for example oxygen,
nonconducting layers with high quality are generated which nearly
reach the quality of the bulk material. The process runs very
stably and herein the splatter formation is, unexpectedly, also
reduced or entirely avoided. However, said advantages can also be
attained by using other sources as the second electrode, such as,
for example, a bias electrode or a low-voltage arc evaporator
crucible, although said advantageous effects are not attained to
the same degree as in the implementation of the configuration with
two arc evaporators.
[0025] The present application claims priority of the two cited
preceding applications CH 00518/05 and 01289/05 which substantially
disclose a first approach to a solution for the present problem
formation of the deposition of electrically nonconducting oxidic
layers. The invention introduced in the present patent application
represents a further development regarding the conduction of the
process and the application. These two applications are
consequently an integrating component of the present
application.
[0026] The various features of novelty which characterize the
invention are pointed out with particularity in the claims annexed
to and forming a part of this disclosure and are entirely based on
the Switzerland priority application no. 518/05, filed Mar. 24,
2005, and Switzerland priority application no. 1289/05, filed Aug.
3, 2005.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In the following the invention will be described in further
detail by example and schematically with Figures. Therein
depict:
[0028] FIG. 1 schematically an illustration of an arc evaporator
coating installation, such as corresponds to prior art,
[0029] FIG. 2 a first configuration according to the invention with
a DC-fed arc evaporator source in operation with superimposed
high-current pulse,
[0030] FIG. 3 a second configuration with two DC-fed arc evaporator
sources and high-power pulsed supply connected between them
according to the invention, a dual pulse arc evaporator
configuration,
[0031] FIG. 4 a cross section through a deposited layer as a
multilayer according to the invention,
[0032] FIG. 5 an enlarged cross section of the layer according to
FIG. 4.
[0033] FIG. 1 shows a vacuum process installation which depicts a
configuration known from prior art for operating an arc evaporator
source 5 with a DC power supply 13. The installation 1 is equipped
with a pump system 2 for setting up the required vacuum in the
chamber of the vacuum process installation 1. The pump system 2
permits the operation of the coating installation at
pressures<10.sup.-1 mbar and also ensures the operation with the
typical reactive gases, such as O.sub.2, N.sub.2, SiH.sub.4,
hydrocarbons, etc. The reactive gases are introduced via a gas
inlet 11 into the chamber 1 and here distributed accordingly. It is
additionally possible to introduce additional reactive gases
through further gas inlets or also inert gases, such as argon, as
is necessary, for example, for etching processes or for the
deposition of nonreactive layers in order to use the gases singly
and/or in mixtures. The workpiece holder 3 located in the
installation serves for receiving and for electrical contacting of
the workpiece, not shown here, which are conventionally fabricated
of metallic materials, and for the deposition of hard material
layers using such processes. A bias power supply 4 is electrically
connected with the workpiece holder 3 for applying a substrate
voltage or a bias voltage to the workpieces. The bias power supply
4 can be a DC, an AC or a bipolar or a unipolar pulse substrate
power supply. Via a process gas inlet (11) an inert or a reactive
gas can be introduced in order to set and to control process
pressure and gas composition in the treatment chamber.
[0034] Component parts of the arc evaporator source 5 are a target
5' with cooling plate placed behind it, and an ignition finger 7,
which is disposed in the peripheral region of the target surface,
as well as an anode encompassing the target. A switch 14 permits
selecting between a floating operation of the anode 6 of the
positive pole of the power supply 13 and operation with defined
zero or ground potential. When igniting the arc of the arc
evaporator source 5 a brief contact is established of the ignition
finger 7 with the cathode and the former is subsequently withdrawn
whereby a spark is ignited. The ignition finger 7 is for this
purpose connected via a current limiter resistor to anode
potential.
[0035] The vacuum process installation 1 can additionally
optionally, should the conduction of the process require such, be
equipped with an additional plasma source 9. In this case the
plasma source 9 is implemented as a source for generating a
low-voltage arc with a hot cathode. The hot cathode is, for
example, formed as a filament disposed in a small ionization
chamber, in which with a gas inlet 8 a working gas, such as for
example argon, is introduced for the generation of a low-voltage
arc discharge which extends into the main chamber of the vacuum
process installation 1. An anode 15 for developing the low-voltage
arc discharge is located at an appropriate position in the chamber
of the vacuum process installation 1 and is operated, in known
manner, with a DC power supply between cathode and plasma source 9
and anode 15. If required, additional coils 10, 10' can be
provided, such as for example Helmholtz-like configurations which
are placed about the vacuum process installation 1 for the magnetic
focusing or guiding of the low-voltage arc plasma.
[0036] Proceeding according to the invention, as depicted in FIG.
2, the arc evaporator source 5 is operated being fed additionally
with a pulsed high-power supply 16'. This pulsed power supply 16'
is advantageously directly superimposed onto the DC power supply.
It is understood that for their protection the two supplies must be
operated electrically decoupled with respect to each other. This
can be carried out in conventional manner with filters, such as
with inductors, such as is familiar to a person of skill in the
art. With this configuration it is already possible according to
the invention to deposit layers exclusively with pure reactive gas
or reactive gas mixtures, such as oxides, nitrides, etc., without
undesirable support gas components, such as for example argon in
PVD sputter processes or halogens of the precursors in CVD
processes. It is, in particular, possible to generate therewith the
pure, electrically nonconducting oxides, which are very difficult
to obtain economically, in the desired crystalline form and to
deposit them as layers. This reactive pulsed arc evaporation method
is herewith denoted as RPAE method.
[0037] In a further improved and preferred embodiment of a vacuum
process configuration, apart from a first arc evaporator source 5,
a second arc evaporator source 20 is provided with the second
target electrode 20', as is shown in FIG. 3. Both arc evaporator
sources 5, 20 are operated with one DC power supply 13 and 13'
each, such that the DC power supplies ensure with a base current
the maintenance of the arc discharge. The DC power supplies 13, 13'
correspond to prior art and can be realized cost-effectively. The
two electrodes 5', 20', which form the cathode of the two arc
evaporator sources 5, 20, are connected according to the present
invention to a single pulsed power supply 16, which is capable of
outputting to the two electrodes 5', 20' high pulse currents with
defined form and edge slope of the pulses. In the depicted
configuration according to FIG. 3 the anodes 6 of the two arc
evaporator sources 5, 20 are referred to the electrical potential
of the ground of the process installation 1. This is herewith also
denoted as Dual Pulsed Arc Evaporation (DPAE).
[0038] It is possible to operate the spark discharges with
reference to ground or also floatingly. In the preferred case of
floating operation, the first DC power supply 13 is connected with
its negative pole to the cathode 5' of the first arc evaporator
source 5 and its positive pole with the opposing anode of the
second arc evaporator source 20. The second arc evaporator source
20 is operated analogously and the second power supply 13' is
connected to the positive pole of the anode of the first arc
evaporator source 5. This opposing operation of the anodes of the
arc evaporator sources leads to better ionization of the materials
in the process. However, the ground-free operation, or the floating
operation, of the arc evaporator source 5, 20 can also take place
without using the opposing anode feed. In addition, it is possible
to provide a switch 14, as shown in FIG. 1, in order to be able to
change over optionally between floating and ground-tied
operation.
[0039] The supply for this "Dual Pulsed Mode" must be able to cover
different impedance ranges and yet not be "hard" in the voltage.
This means that the supply must supply high current, yet, in spite
of it, be largely operable voltage-stably. An application of an
example of such a supply was filed under the No. CH 518/05 parallel
with the same date as said patent application No. CH 1289/05.
[0040] The first and preferred application field of this invention
is that of cathodic spark evaporation with two pulsed arc
evaporator sources (5, 20) as is depicted in FIG. 3. For these
applications the impedances are at intervals of approximately 0.01
.OMEGA. to 1 .OMEGA.. It should be noted here that usually the
impedances of the sources, between which "dual pulsing" is carried
out are different. The reason may be that these are comprised of
different materials or alloys, that the magnetic field of the
sources is different or that the material erosion of the sources is
at a different state. The "Dual Pulsed Mode" now permits a balance
via the setting of the pulse width such that both sources draw the
same current. This leads consequently to different voltages at the
sources. The supply can, of course, also be loaded asymmetrically
with respect to the current if such appears desirable for the
process conduction, which is the case, for example, for graduated
layers of different materials. The voltage stability of a supply is
increasingly more difficult to realize the lower the impedance of
the particular plasma. The capability of change-over switching or
the controlled active tracking of a supply to different output
impedances is of therefore of special advantage if the full range
of its power is to be utilized, thus for example in the range of
500 V/100 A to 50 V/1000 A or as it is realized in the parallel
application No. CH 518/05.
[0041] The advantages of such dual pulsed cathode configuration and
in particular one comprised of two arc evaporator sources are
summarized as follows: [0042] 1. Increased electron emission at
steep pulses results in higher current (also substrate current) and
increased ionization of the vaporized material and of the reactive
gas. [0043] 2. The increased electron density contributes also to a
fast discharge of the substrate surface in the production of
insulating layers, i.e. relatively short charge-reversal times on
the substrate (or also only pulse pauses of the bias voltage) are
sufficient in order to discharge the insulating layer which is
forming. [0044] 3. The bipolar operation between the two cathodic
arc evaporator sources permits a quasi-100% pulse pause ratio (duty
cycle), while the pulsing of a source along always necessarily
requires a pause and therefore the efficiency is not so high.
[0045] 4. The dual pulsed operation of two cathode spark sources,
which are opposite to one another, immerses the substrate region
into a dense plasma and increases the reactivity in this region
even of the reactive gas. This is also reflected in the increase of
the substrate current. [0046] 5. In reactive processes under oxygen
atmosphere in pulsed operation still higher electron emission
values can be attained, and it appears that a melting of the spark
region, as is the case in classic evaporation of metallic targets,
can be largely avoided. Working in purely oxidic reactive mode
without further foreign or support gases is now readily possible.
To be able to attain said advantageous process properties in said
different possible embodiments of the invention, the pulsed power
supply 16, 16' must satisfy different conditions. In bipolar pulse
presentation it should be possible to carry out the process at a
frequency which is in the range of 10 Hz to 500 kHz. Due to the
ionization conditions, herein the maintainable edge slopes of the
pulses is important. The magnitudes of the leading edges
U2/(t2-t1), U1/(t6-t5), as well as also of the trailing edges
U2/(t4-t3) and U1/(t8-t7) should have a slope in the range of 0.02
V/ns to 2 V/ns and this at least in open-circuit operation, thus
without load, however preferably also under load. It is understood
that the edge slope has an effect in operation, depending on the
corresponding magnitude of the load or the connected impedance of
the corresponding settings. The pulse widths in bipolar
presentation for t4 to t1 and t8 to t5 are advantageously >1
.mu.S, the pauses t5 to t4 and t9 to t8 can advantageously be
essentially 0, however, under certain conditions, they can also be
.gtoreq.0 .mu.s. If the pulse pauses are >0, this operation is
referred to as time-gapped and through, for example, variable time
shift of the pulse gap widths the specific and purposeful
introduction of energy into a plasma and its stabilization can be
set. It is especially advantageous if the pulsed power supply is
laid out such that a pulse option up to 500 A at 1000 V voltage is
possible, wherein herein the pulse/pause ratio (duty cycle) must be
appropriately taken into consideration or must be adapted for the
laid out possible power of the supply. Apart from the edge slope of
the pulse voltage it is necessary to observe that the pulsed power
supply (16) is capable of handling a current rise to 500 A in at
least 1 .mu.s.
[0047] With the operation introduced here of arc evaporator sources
with DC feed and superimposed high-current pulsed feed (RPAE, DPAE)
it is possible to deposit with high quality starting from one or
several metal targets with reactive gas atmosphere corresponding
metal compounds onto a workpiece 30. This is in particular suited
for the generation of purely oxidic layers, since the method does
not require additional support gases, such as inert gases,
customarily argon. The plasma discharge of the arc evaporator 5, 20
can thus, for example and preferably, take place in pure oxygen
atmosphere at desired working pressure without the discharge being
unstable, is prevented or yields unusable results, as too high a
splatter formation or poor layer properties. It is also not
necessary to use, as is the case in CVD methods, halogen compounds.
This permits, first, to produce economically wear-resistant oxidic
hard material layers of high quality at low process temperatures,
preferably below 500.degree. C., which, as a result, are
nevertheless high temperature-resistant, preferably >800.degree.
C. and which are chemically highly stable, such as, for example,
have high resistance to oxidation. Furthermore, to attain a stable
layer system the diffusion of oxygen with the oxidation entailed
therein in the deeper layer system and/or on the workpiece should
as much as possible be avoided.
[0048] It is now readily possible to produce oxidic layers in pure
oxygen as reactive gas from the transition metals of the subgroups
IV, V, VI of the periodic system of elements and Al, Si, Fe, Co,
Ni, Y, with Al, Cr, Mo, Zr as well as Fe, Co, Ni, Y being
preferred. The functional layer 32 is to contain as the oxide one
or several of these metals, no inert gas and/or halogen, such as
Cl, however at least less than 0.1% or better less than 0.05% inert
gas and less than 0.5% or better less than 0.1% halogen in order to
attain the desired layer quality.
[0049] Such functional layers 32 or multiple layer system 33
(multilayer) should, in particular, as hard material layer have a
thickness in the range of 0.5 to 12 .mu.m, preferably from 1.0 to
5.0 .mu.m. The functional layer can be deposited directly onto the
workpiece 30 which is a tool, a machine part, preferably a cutting
tool, such as an indexable insert. Between this layer and the
workpiece 30 at least one further layer or a layer system can also
be deposited, in particular for the formation of an intermediate
layer 31, which forms in particular an adhesion layer and comprises
preferably one of the metals of the subgroups lVa, Va and Vla of
the periodic system of elements and/or Al or Si or a mixture of
these. Good adhesive properties are achieved with compounds of
these metals with N, C, O, B or mixtures thereof, the compound
comprising N being preferred.
[0050] The layer thickness of the intermediate layer 31 should be
in the range of 0.05 to 5 .mu.m, preferably 0.1 to 0.5 .mu.m. At
least one of the functional layers 32 and/or of the intermediate
layer 31 can advantageously be implemented as a progression layer
34, whereby a better transition of the properties of the particular
layers is brought about. The progression can be from metallic over
nitridic to nitrooxidic and up to the pure oxide. Thus a
progression region 34 is formed where the materials of the abutting
layers, or, if no intermediate layer is present, the workpiece
material, are mixed into one another.
[0051] On the functional layer 32 a further layer or a layer system
35 can be deposited as cover layer, should this be required. A
cover layer 35 can be deposited as additional friction-reducing
layer for further improvement of the tribological behavior of the
coated workpiece 30.
[0052] Depending on the requirements, one or more layers of said
layers or layer systems can be developed as progression layers 34
in the region where they border on one another or within individual
layers concentration gradients of any type can be generated. In the
present invention this is simply possible through the controlled
introduction of the reactive gases into the vacuum process
installation 1 for setting the particular types of gas necessary
for this purpose and of the gas quantities for the reactive arc
plasma process.
[0053] As functional layer 32 with the desired hard material
properties, now aluminum oxide layers (Al.sub.2O.sub.3), layers can
now readily be produced which even have substantially
stoichiometric composition. Especially advantageous hard material
layers as functional layer 32 are substantially comprised of an
(Al.sub.xMe.sub.1-x).sub.yO.sub.z, where Me is preferably one of
the metals Cr, Fe, Ni, Co, Zr, Mo, Y singly or also in mixtures,
settable depending on the desired proportions x, y and z of the
involved substances. Further is especially preferred chromium as
the metal Me in the metal mixed oxide of the
(Al.sub.xMe.sub.1-x).sub.yO.sub.z which consequently forms
(Al.sub.xCr.sub.1-x).sub.yO.sub.z or (AlCr).sub.yO.sub.z. Herein
the proportion 1-x of the metal chromium in the layer should be 5
to 80 atom %, preferably 10 to 60 atom %. Well suited as hard
material functional layer 32 is also a metal nitride, in particular
the aluminum chromium nitride (AlCr).sub.yN.sub.z or at most also
(AlTi).sub.yN.sub.z.
[0054] Through the intentional capability of process conduction it
is now also possible in the case of aluminum and aluminum
chromoxides to be able to attain the especially desired alpha
and/or gamma structure.
[0055] Due to said simple settability of the layer conditions with
their composition via the control of the supply of the reactive
gases and due to the stable process condition, it is for the first
time possible to produce multilayer systems (multilayer) 33 with
any number of layers and any composition and even with
progressions. Several layers can herein be generated of different
materials or, and this appears often to be of advantage, with the
alternating identical materials as a type of sandwich. For
functional hard material layers 32, a layer system with repeated
layer sequence pairs 33, in which the material composition changes
periodically, is advantageous. Especially a structure from Me.sub.1
to an Me.sub.2-oxide and/or from an Me.sub.1-nitride to an
Me.sub.1-oxide and/or from an Me.sub.1-nitride to an Me.sub.2-oxide
yields excellent results with respect to endurance and less
fissuring of the functional layer or of this layer system. An
example of a functional layer 32 as a multilayer 33 is shown in
FIG. 4 and in enlarged cross section in FIG. 5. Shown is a
preferred material pairing of alternating aluminum chromium nitride
(AlCr).sub.xN.sub.y with aluminum chromoxide (AlCr).sub.xO.sub.y
produced with the method according to the invention, preferably in
stoichiometric material composition. The layer packet in this
example comprises 42 layer pairs with alternating materials, as
stated above. The entire layer thickness of this functional layer
32 as multilayer system 33 is approximately 4.1 .mu.m, the
thickness of a layer pair, thus two deposits, being 98 nm. Further
preferred material pairings are alternating aluminum zirconium
nitride (AlZr).sub.xN.sub.y with aluminum zirconium oxide
(AlZr).sub.xO.sub.y produced with the method according to the
invention, preferably in stoichiometric material composition. For
hard material layers as functional layer 32 it is of advantage if
the multilayer system 33 includes at least 20 deposits, preferably
up to 500 deposits. The thickness per deposit should be in the
range from 0.01 to 0.5 .mu.m, preferably in the range from 0.2 to
0.1 .mu.m. In the region of the individual bordering deposits of
the layers progressions 34 are also evident, which ensure for good
behavior of the transitions. In the example according to FIG. 4 as
an example a cover layer 35 is also deposit as a friction-reducing
layer over the functional layer 32, 33. The cover layer is
comprised of titanium nitride and is approximately 0.83 .mu.m
thick. Under the functional layer as an example additionally an
intermediate layer 31 is disposed as adhesion layer which is
approximately 1.31 .mu.m thick and has been deposited as an
Al--Cr--N intermediate layer with RPAE onto the workpiece 30.
[0056] The coatings introduced here, whether single layer or
multilayer system should preferably have an R, value of not less
than 2 .mu.m and/or an R.sub.a value of not less than 0.2 .mu.m.
These values are in each instance measured directly on the surface
before a potential after-treatment of the surface, such as
brushing, blasting, polishing, etc. Thus, the values represent a
purely process-dependent surface roughness. By R.sub.a value is
understood the mean rough value according to DIN 4768. This is the
arithmetic mean of all deviations of the roughness profile R from
the center line within the total measuring path I.sub.m. By R.sub.z
is understood the mean roughness depth according to DIN 4768. This
is the mean value of the individual roughness depths of five
successive individual measuring paths le in the roughness profile.
R.sub.z depends only on the distance of the highest peaks to the
deepest valleys. By forming the mean value the effect of an
individual peak (valley) is reduced and the mean width of the band,
in which the R profile is included, is calculated. The introduced
coating according to the invention is especially suited for
workpieces such as cutting, forming, injection molding or punching
and stamping tools, however, very specifically for indexable
inserts.
[0057] In the following a typical sequence of a substrate treatment
in a reactive pulse arc evaporation coating process is described
using the present invention. Apart from the coating process proper,
in which the invention is realized, the other process steps will
also be described, which involve the pretreatment and posttreatment
of the workpieces. All of these steps allow wide variations, some
can also be omitted under certain conditions, shortened or extended
or be combined differently. In a first step the workpieces are
customarily subjected to wet-chemical cleaning, which, depending on
the material and prior history, is carried out in different
manner.
Example 1
[0058] Description of a typical process sequence for the production
of an Al--Cr--O layer 32 (as well as of an Al--Cr--N/Al--Cr--O
multilayer 33) and Al--Cr--N intermediate layer 31 by means of RPAE
(reactive pulse arc evaporation) for coating workpieces 30, such as
cutting tools, preferably indexable inserts.
[0059] 1. Pretreatment (cleaning, etc.) of the workpieces (30)
(substrates) as known to the person of skill in the art.
[0060] 2. Placing the substrates into the holders intended for this
purpose and transfer into the coating system.
[0061] 3. Pumping the coating chamber 1 to a pressure of
approximately 10.sup.-4 mbar by means of a pump system as known to
the person of skill in the art (forepumps/diffusion pump,
forepumps/turbomolecular pump, final pressure approximately
10.sup.-7 mbar attainable).
[0062] 4. Starting the substrate pretreatment in vacuo with a
heating step in an argon-hydrogen plasma or another known plasma
treatment. Without restrictions, this pretreatment can be carried
out with the following parameters: Plasma of a low-voltage arc
discharge with approximately 100 A discharge current, up to 200 A,
to 400 A, the substrates are preferably connected as anode for this
low-voltage arc discharge: [0063] Argon flow 50 sccm [0064]
Hydrogen flow 300 sccm [0065] Substrate temperature 500.degree. C.
(partially through plasma heating, partially through radiative
heating) [0066] Process time 45 min [0067] It is preferred that
during this step a supply is connected between substrate 30 and
ground or another reference potential, which can act on the
substrates with DC (preferably positive) or DC pulsed (unipolar,
bipolar) or as IF (intermediate frequency) or RF (high
frequency).
[0068] 5. As the next process step etching is started. For this
purpose the low-voltage arc is operated between the filament and
the auxiliary anode. A DC, pulsed DC, IF or RF supply is connected
between substrates and ground and the substrates are preferably
acted upon with negative voltage. In the pulsed and IF, RF supplies
positive voltage is also impressed on the substrates. The supplies
4 can be operated unipolarly or bipolarly. The typical, however not
exclusive, process parameters during this step are: [0069] Argon
flow 60 sccm [0070] Discharge current low-voltage arc 150 A [0071]
Substrate temperature 500.degree. C. (partially through plasma
heating, partially through radiative heating) [0072] Process time
30 min [0073] To ensure the stability of the low-voltage arc
discharge during the production of insulating layers, the work is
either carried out with a hot, conductive auxiliary anode 15, or a
pulsed high-power supply is connected between auxiliary anode and
ground.
[0074] 6. Start of coating with the intermediate layer 31
(approximately 15 min) CrN intermediate layer 300 nm by means of
spark evaporation (source current 140 A, Ar 80 sccm, N2 1200 sccm,
with bias of -80 V or of -100 V down to -60 V or 40 V,
respectively. [0075] The coating can take place with and without
low-voltage arc.
[0076] 7. Transition to the functional layer 32 (approximately 5
min) In the transition to the functional layer proper, onto the
spark sources are additionally superposed unipolar DC pulses of a
second power supply connected in parallel, which can be operated
with 50 kHz (FIG. 2). An Al target is additionally operated in the
same manner in order to produce AlCr as a layer. In the example
work took place with 10 ps pulse/10 ps pause and in the pulsed
currents up to 150 A generated. Oxygen at 200 sccm was subsequently
let in.
[0077] 8. Driving back of the AlCrN coating After the oxygen gas
flow has been stabilized, the AlCrN coating is brought down. For
this purpose the N2 gas flow is reduced. This ramp takes place over
approximately 10 min. The Ar flow is subsequently reduced to zero
(unless work is carried out with low-voltage arc).
[0078] 9. Coating with functional layer 32 The coating of the
substrates with the functional layer proper takes place in pure
reactive gas (in this case oxygen). The most important process
parameters are: [0079] Oxygen flow 400 sccm [0080] Substrate
temperature 500.degree. C. [0081] DC source current 60 A [0082]
Onto the DC source current a pulsed DC current (unipolar) of 150 A
is superimposed with a pulse frequency of 50 kHz and a pulse
characteristic of 10 ps pulse/10 .mu.s pause. Process pressure in
the coating chamber 9.times.10.sup.-2 mbar. The bias at the
substrates is reduced to -40 V. Since aluminum oxide layers are
insulating layers, a bias supply is utilized, which is operated
either DC pulsed or as IF (50 kHz-350 kHz). [0083] The coating can
also be carried out simultaneously with the low-voltage arc. In
this case a higher reactivity is attained. The simultaneous use of
the low-voltage arc during the coating has furthermore the
advantage that the DC component in the sources can be reduced. At
higher arc current, it can be further reduced. [0084] The coating
process conducted in this way is stable even over several hours.
The target 5, 5' is covered with a thin smooth oxide layer.
However, no insulating islands are formed, although the target
surface changes through the oxygen, which is also reflected in the
increase of the burn voltage. The target surface remains
significantly smoother. The spark runs quieter and divides into
several smaller sparks. The number of splatters is significantly
reduced.
[0085] The described process is a fundamental preferred version
since it keeps the requirements made of the pulsed power supply
low. The DC supply supplies the minimum or holding current for the
spark and the pulsed high-power supply 16, 16' serves for avoiding
the splatters and ensures the process. One feasibility of
generating multilayer systems 33, thus multiple layers 33, for the
above layer example comprises that the oxygen flow during the layer
deposition is decreased or even switched off entirely, while the
nitrogen flow is added. This can take place periodically as well as
aperiodically, with layers of exclusive or mixed oxygen-nitrogen
concentration. In this way multilayers 33 are produced such as are
shown in FIG. 4, and enlarged in FIG. 5, by example in cross
section. In many cases this functional layer 32 forms the
termination of the coating to the outside, without a further layer
following thereon.
[0086] Depending on the application and requirement, wear
properties can be "topped" with one or several cover layers 35. The
example of the AlCrN/AlCrO multilayer already described above with
a TiN top layer is also shown in FIG. 4. The at least one cover
layer 35 can in this case be, for example, a friction-reducing
layer, wherein in this case the hard material layer 32, or the
functional layer or the multiple layer serves as support layer for
the friction-reducing layer 35.
[0087] If there is the wish to produce multilayer functional layers
33 or multilayer intermediate layers with especially thin
oxide-containing layer thickness, in a preferred process variant
this can also take place thereby that the operation of the
oxide-forming target under oxygen flow takes place just until the
target exhibits first poisoning signs (voltage rise, most often
after a few minutes) and then switching again to, for example,
nitrogen flow. The process variant is especially simple and can be
realized with the existing prior art (FIG. 1) thus without target
pulse operation. However, this does not permit a free adaptation of
the layer thickness to the particular requirements.
[0088] The implementation of said example in dual pulsed operation
with two or more arc evaporator sources yields, in addition,
advantages with respect to the conduction of the process and
economy.
Example 2
[0089] Coating of workpieces 30, such as cutting tools, preferably
indexable inserts, with an Al--Cr--O hard material layer system 32
and Cr--N intermediate layer 31 by means of DPAE (Dual Pulsed Arc
Evaporator)
[0090] Steps 1 to and including 5 analogous to Example 1.
[0091] 6. Starting the coating with the intermediate layer
(approximately 15 min) AlCrN intermediate layer 300 nm by means of
spark evaporation (target material AlCr (50%, 50%), source current
180 A, N2 800 sccm, with bipolar bias of -180 V (36 .mu.s negative,
4 .mu.s positive). [0092] The coating can take place with and
without low-voltage arc. [0093] Up to this point the method follows
prior art such as is shown for example in FIG. 1.
[0094] 7. Transition to functional layer 32 (approximately 5 min)
In the transition to the functional layer 32 proper, the nitrogen
is ramped down from 800 sccm to approximately 600 sccm and
subsequently an oxygen flow of 400 sccm is switched on. The
nitrogen flow is now switched off.
[0095] 8. Coating with the functional layer 32
[0096] The bipolar pulsed high-power supply 16, as shown in FIG. 3,
between both arc evaporator cathodes 5, 20 is now taken into
operation. In the described process work took place with a positive
or negative time mean value of the current of approximately 50 A.
The pulse durations were each 10 .mu.s for the positive as well as
negative voltage range with 10 ps pauses each in between at a
voltage of 160 V. The peak value of the current through the bipolar
pulsed power supply 16 depends on the particular pulse form. The
difference of DC current through the particular arc evaporator
cathode 5, 20 and peak value of the bipolarly pulsed current must
not fall below the so-called holding current of the arc evaporator
cathode 5, 20, since otherwise the arc (spark) is extinguished.
[0097] During the first 10 minutes of the coating the bias is
ramped from -180 V to '60 V. The typical coating rates for double
rotating workpieces 30 are between 3 .mu.m/hr and 6 .mu.m/hr.
[0098] The coating of the workpieces 30 with the functional layer
32 proper thus takes place in pure reactive gas (in this example
oxygen). The most important process parameters are once again
summarized: [0099] Oxygen flow 400 sccm [0100] Workpiece
temperature 500.degree. C. [0101] DC source current 180 A, for the
Al as well as also for the Cr source. [0102] The bipolarly pulsed
DC current between the two cathodes has a frequency of 25 kHz.
[0103] Process pressure approximately 9.times.10.sup.-3 mbar.
[0104] As already stated, the coating can also take place
simultaneously with the operation of the low-voltage arc. In this
case a further increase of the reactivity especially in the
proximity of the workpiece is attained. In addition, the
simultaneous utilization of the low-voltage arc during the coating
has also the advantage that the DC component at the sources can be
reduced. With higher arc current, this can be further reduced. The
coating process conducted in this way is stable even over several
hours. Targets 5', 20' of the arc evaporators 5, 20 are covered
with thin, smooth oxide layer. This is desirable and is also the
precondition for a largely splatter-free and stable process. The
covering is manifested in an increase of the voltage at the
target.
[0105] Workpieces were coated with different coatings and under the
same conditions subjected to a practical comparison test.
[0106] Test conditions for the rotation tests: As the measure for
these tests known TiAlN layers and known alpha aluminum oxide
layers deposited by means of CVD are used. In all test layers a
layer thickness of 4 .mu.m was tested. As test material were used
stainless steel (1.1192). As rotation cycles were selected 1, 2 and
4 min each. The cutting rate was 350 m/min, advance 0.3 mm/rev.
Engagement depth 2 mm. The conditions were selected such that short
test times are attainable at high temperatures on the cutting edge
of the workpiece. The wear on the end flank and the chipping edge
as well as the surface roughness of the worked steel were tested,
and the length of time was determined before a certain increased
roughness occurred. As the quantitative measure for wear, this
service time was determined.
[0107] Results: [0108] a) CVD layer alpha aluminum oxide (prior
art) [0109] layer thickness d=4 .mu.m [0110] The tool survived the
4-minute test. However, after the test in the SEM there was no
longer any layer material on the chipping edge. [0111] b) TiAlN
layer (prior art), d=4 .mu.m This layer showed already after less
than 2 min initial signs of destructions and supplied a rough
surface on the workpiece.
[0112] Invention: [0113] c) AlCrN intermediate layer, d=0.4 .mu.m
[0114] AlCrN/AlCrO multilayer, d=3.6 .mu.m [0115] TiN top layer,
d=0.8 .mu.m [0116] Endurance 4 min [0117] d) AlCrN intermediate
layer, d=0.4 .mu.m [0118] AlCrN/AlCrO multilayer, d=3.6 .mu.m 3 min
40 s [0119] e) AlCrN intermediate layer, d=0.3 .mu.m [0120] AlCrO
single layer, d=2.9 .mu.m [0121] TiN top layer, d=0.9 .mu.m 4 min
[0122] f) AlCrN intermediate layer, d=0.35 .mu.m [0123] AlCrO
single layer, d=3.5 .mu.m 3 min 20 s [0124] g) ZrN intermediate
layer, d=0.3 .mu.m [0125] ZrN/AlCrO multilayer, d=3.8 .mu.m [0126]
ZrN top layer, d=0.5 .mu.m 3 min 10 s [0127] h) ZrN intermediate
layer, d=0.2 .mu.m [0128] ZrO/AlCrO multilayer, d=6.4 .mu.m [0129]
ZrN top layer, d=0.8 .mu.m 4 min [0130] i) AlCrN intermediate
layer, d=0.5 .mu.m [0131] AlCrO/alpha alumina multilayer, d=8.2
.mu.m 4 min [0132] k) (Ti, AlCrN) intermediate layer, d=0.4 .mu.m
[0133] AlCrO/TiAlCrN multilayer, d=4.5 .mu.m 3 min 50 s
[0134] Layers of or multilayers comprising oxidic layers of the
stated materials show markedly less wear at high cutting rates.
Conducting layers (TiAlN) according to prior art at high cutting
rates are markedly inferior to the oxide systems according to the
invention. Systems according to the present invention of
(AlCr).sub.yO.sub.z, and (AlZr).sub.yO.sub.z show similarly low
wear as known CVD layers of .alpha.-aluminum oxide, however without
its disadvantage of high temperature loading or loading through
aggressive chemicals of the workpiece during the coating process.
The conduction of the process, furthermore, can be carried out
substantially simpler, for example through changing-over of gases
or controlled change of the gas components (for example O.sub.2 to
N.sub.2) and/or changing-over from one target, or changing of the
components of the target feed under control, to the other, while in
CVD processes intermediate flushing as well as adaptation of the
temperature level for individual layers of a multilayer layer
system are necessary.
* * * * *