Patent Application
20080193782
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.
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.
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.
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.
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.
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.
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.
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.
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.
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° 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.
With respect to prior art the following disadvantages are summarized, in particular regarding the production of oxidic layers with reactive process:
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.
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.
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.
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° 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.
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.
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 F2, Cl2, Br2, J2, or halogen-containing compounds such as CF6 or the like.
The known CVD processes use halogen with which at undesirably high temperatures of approximately 1100° 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.
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
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.
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.
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.
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.
In the following the invention will be described in further detail by example and schematically with Figures. Therein depict:
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.
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.
Proceeding according to the invention, as depicted in
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
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
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.
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
The advantages of such dual pulsed cathode configuration and in particular one comprised of two arc evaporator sources are summarized as follows:
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° C., which, as a result, are nevertheless high temperature-resistant, preferably >800° 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.
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.
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 μm, preferably from 1.0 to 5.0 μm. 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.
The layer thickness of the intermediate layer 31 should be in the range of 0.05 to 5 μm, preferably 0.1 to 0.5 μm. 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.
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.
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.
As functional layer 32 with the desired hard material properties, now aluminum oxide layers (Al2O3), 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 (AlxMe1-x)yOz, 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 (AlxMe1-x)yOz which consequently forms (AlxCr1-x)yOz or (AlCr)yOz. 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)yNz or at most also (AlTi)yNz.
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.
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 Me1 to an Me2-oxide and/or from an Me1-nitride to an Me1-oxide and/or from an Me1-nitride to an Me2-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
The coatings introduced here, whether single layer or multilayer system should preferably have an R, value of not less than 2 μm and/or an Ra value of not less than 0.2 μm. 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 Ra 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 Im. By Rz 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. Rz 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.
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.
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.
1. Pretreatment (cleaning, etc.) of the workpieces (30) (substrates) as known to the person of skill in the art.
2. Placing the substrates into the holders intended for this purpose and transfer into the coating system.
3. Pumping the coating chamber 1 to a pressure of approximately 10−4 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 10−7 mbar attainable).
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:
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:
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.
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 (
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).
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:
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
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
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 (
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.
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)
Steps 1 to and including 5 analogous to Example 1.
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 μs negative, 4 μs positive).
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.
8. Coating with the functional layer 32
The bipolar pulsed high-power supply 16, as shown in
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.
Workpieces were coated with different coatings and under the same conditions subjected to a practical comparison test.
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 μm 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.
Results:
Invention:
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)yOz, and (AlZr)yOz show similarly low wear as known CVD layers of α-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 O2 to N2) 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 518/05 | Mar 2005 | CH | national |
| 1289/05 | Aug 2005 | CH | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CH06/00042 | 1/19/2006 | WO | 00 | 9/13/2007 |
