Multi-layer coating

Abstract

The present invention relates to a method for coating a substrate, a coating system for implementing the method, and a coated body. In a first method step (62), the substrate (40) is pretreated by an ion etching process. In a second method step (64), a first coating layer (56a) having a thickness of 0.1 μm to 6 μm is deposited on the substrate by a PVD process. To achieve a particularly high-quality and durable coating (50), the surface of the first coating layer (56a) is treated by an ion etching process in a third method step (66), and an additional coating layer (56b) having a thickness of 0.1 μm to 6 μm is deposited on the first coating layer (56a) by a PVD process in a fourth method step (68). The coated body includes at least two coating layers (56a, 56b, 56c, 56d) having a thickness of 0.1 μm to 6 μm on a substrate (40), with an interface region formed by ion etching disposed between the coating layers (56a, 56b, 56c, 56d).

Description

[Technical Field]

[0001] The present invention relates to a method for coating a substrate, a coating system for carrying out the method, and a coated body. [Background technology]

[0002] It is known to provide a surface coating on a body or part of a body in order to improve its properties, and in particular in the case of tools, to provide a coating of hard material on functional surfaces.

[0003] One class of known methods for applying hard material coatings is the PVD (physical vapor deposition) technique, which includes, for example, cathode sputtering and arc sputtering, in which a coating consisting of a sputtered target material is deposited on a substrate.

[0004] In this context, it is known to pretreat the substrate before applying the coating, in order to achieve particularly good coating adhesion. Apart from chemical and mechanical pretreatment steps, ion etching steps, in which ions are accelerated towards the substrate by an accelerating voltage, thereby producing an etching effect on the substrate surface, are suitable for pretreatment of, for example, hard metal or steel substrates.

[0005] WO 2009 / 132822 A2 describes an apparatus and method for pretreating and coating a body by magnetron sputtering. The apparatus includes a vacuum chamber with metal chamber walls and magnetrons with sputtering targets disposed therein. At least one of the magnetrons is provided for operation by high-power pulsed magnetron sputtering (HPPMS, also known as HIPIMS). Electrical pulses are supplied to the HPPMS magnetron, which has a capacitive element connected to the sputtering target by a switching element. In this method, the body to be coated is placed in the vacuum chamber of the apparatus, and a plasma is generated during operation of the HPPMS magnetron. In the etching step, a negative bias voltage is applied to the body, and the body is etched by bombardment with metal ions. The bias voltage is then continuously lowered so that material sputtered from the sputtering target forms a layer deposit on the body.

[0006] DE 10 2006 019 000 A1 describes an apparatus and method for plasma-enhanced deposition of hard material coatings, particularly for producing titanium aluminum nitride (titanium-aluminum-nitride) layers. A substrate support rotatable about a central axis is arranged in a vacuum chamber. At least one evaporation source and at least one hollow cathode are arranged radially outward of the substrate support. The line between the hollow cathode and the associated anode is offset by 15° to 70° from the line between the evaporation source's target and the central axis in a plane perpendicular to the central axis. The arc discharge of the hollow cathode is maintained parallel to the central axis and the evaporation of target material from the evaporation source. A target with a 1:1 Ti:Al ratio is used to produce titanium aluminum nitride coatings with a Ti:Al ratio of 50:50 to 40:60 in a reactive nitrogen atmosphere. EP 2042261 A2 describes a method for producing a coated cutting tool, which includes providing a substrate and depositing a cathodic arc vapor deposition (PVD) coating of nitride, oxide, boride, carbide, carbonitride, carboxynitride, or combinations thereof on the substrate. During deposition, the coating is subjected to one or more ion etching steps. The cutting tool has an increased lifespan due to the PVD coating having improved smoothness due to a reduced number of surface defects. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication WO2009 / 132822A2 [Patent Document 2] German Patent Application Publication DE102006019000A1 [Patent Document 3] European Patent Application Publication EP2042261A2 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to specify a coated body, a method for coating a substrate, and a coating system for carrying out said method, which makes it possible to achieve particularly high quality and durable coatings. [Means for solving the problem]

[0009] This object is achieved by the method according to claim 1, 8 Coating system related to Mu The dependent claims present advantageous embodiments of the invention.

[0010] It has been shown that coatings applied by PVD methods can have different properties depending on the coating thickness. In particular, longer coating durations and thicker coating thicknesses have often been shown to promote, for example, coating roughness and residual stress. Therefore, the basic concept of the present invention is not to continuously produce a coating, but rather to interrupt the growth of the coating one or more times and then resume it in a targeted manner.

[0011] The method according to the invention initially provides, in a first method step, the pretreatment of a substrate by an ion etching process, in which ions, e.g., gas or preferably metal ions, are generated and accelerated towards the substrate surface by a bias voltage. Due to the impinging ions, an etching effect is produced over the entire irradiation time, which may involve activation of the substrate surface, removal of surface material, and implantation of ions.

[0012] In the second step of the method according to the present invention, a first coating layer having a thickness of 0.1 μm to 6 μm is deposited on the substrate by a PVD process. The coating method can be magnetron sputtering. Used The coating procedure is carried out for a selected coating period such that a first coating layer is deposited on the substrate surface.

[0013] According to the present invention, the application of the coating in the second step is interrupted by a third method step, which is a separate etching step. In the third method step, according to the present invention, the surface of the previously produced first coating layer is treated by an ion etching process. The ion etching process of the third method step can preferably be of the same type as the first method step. The method parameters used, in particular the etching duration and bias voltage, can be selected to be the same or different from each other.

[0014] The layer growth is first interrupted in the third method step by using an etching process. Depending on the intensity of the etching step, a more or less significant amount of layer material may be removed. Furthermore, the etching process causes surface nucleation by introducing microdefects.

[0015] In a subsequent fourth method step according to the invention, a further coating layer having a thickness of 0.1 μm to 6 μm is deposited by PVD Cathode sputteringThe process deposits the first coating layer or its surface formed by the previous etching step. Preferably, the fourth method step uses the same type of coating method as the second method step. In both steps, individual or all method parameters can be selected to be the same or different from each other.

[0016] The method according to the invention therefore comprises a series of steps: coat, etch, coat, which may also be called a "repeat start" procedure.

[0017] Surprisingly, it has been found that a repeat-start procedure, i.e., interrupting the coating process with ion etching followed by continued coating, results in structural changes in multilayer coatings compared to single-layer coatings applied at once without the formation of a coating interrupted by an intermediate etching step. The microstructure generated during the formation of the coating can be at least partially interrupted by the intermediate etching step, such that the subsequent coating step cannot seamlessly continue the previous growth but rather new growth nuclei are formed. A continuous coating process can, under certain circumstances, coarsen the coating morphology in the growth direction; this effect can be reduced or even completely reversed by the intermediate etching step. In this way, it is possible to achieve a coating morphology in which the layer structure of an additional coating layer applied after the intermediate etching step is finer than that at least at the start, i.e., at the surface of the previous coating layer adjacent to the interface region to the previous coating layer.

[0018] In particular, it can affect the residual stress of the resulting coating. Residual stress in a coating can increase as the coating duration and thickness increase. It has been shown that when coating is interrupted and restarted within a repeat-start procedure, the residual stress in multilayer coatings does not increase to the same extent as in single-layer coatings. As a result, using the repeat-start method, when the coating time is long and the coating thickness is high, results in coatings with lower overall residual stress. Coatings with lower residual stress have more favorable ductility properties and better adhesion to substrates.

[0019] Overall, it has been shown that interrupting growth one or more times can produce layers with a reduced number of defects and therefore a higher density and less porosity (fewer small holes). On the one hand, this allows for a smoother layer surface. On the other hand, denser layers have important advantages in terms of chemical resistance, since a denser structure means fewer diffusion paths through which atmospheric oxygen can undesirably diffuse during use, leading to coating failure, for example.

[0020] As will be clear to those skilled in the art, it is possible to modify the above sequence of the first to fourth steps, for example by subdividing the coating or etching step into several substeps with different coating or etching parameters, or by temporarily inserted method steps including other processing means such as thermal treatments (annealing) or chemical treatments (oxidation, carburization, etc.), etc. However, the basic pattern, i.e. the sequence of the first to fourth steps, always remains the same.

[0021] While the advantages of the repeat start procedure are already apparent after one application, multiple applications can show particular advantages. For example, following the fourth method step, the surface of the top coating layer may be treated by an ion etching process, after which an additional coating layer may be applied by PVD. Cathode sputteringThe process may deposit onto an underlying coating layer. This may be repeated one or more times to produce, for example, at least three or four coating layers. The total number of repetitions of the repeat-start sequence may be selected according to the type and desired thickness, such that, for example, 2 to 50 coating layers are formed, preferably 3 to 20, and more preferably 3 to 10 or 3 to 5 coating layers are formed.

[0022] In principle, the advantages of interrupting and subsequently continuing the coating growth can also be utilized if individual or all method steps are carried out in separate processing or coating systems, so that they are spatially and / or temporally separated from one another, for example, at separate locations, after intermediate storage, etc. However, it is particularly efficient to apply the method steps in the same coating system, in particular in the same vacuum chamber. Preferably, the application of two or more of the above-mentioned method steps is carried out without interrupting the vacuum, e.g., the application of a repeat start step (second method step—coating, third method step—ion etching, fourth method step—coating), particularly preferably the first to fourth steps.

[0023] Preferably, two or more or all of the method steps can be performed in the same vacuum chamber of the coating system and / or using the same electrodes (e.g., cathodes and / or electrical connections to the substrate or holder), and simply the means for changing the power supply and / or pressure or atmosphere can be switched on and off to perform different method steps without modifying the equipment. However, various magnetron cathodes (e.g., HIPIMS cathodes and DC cathodes) can also be located, for example, in the same vacuum chamber and operated differently in the method steps or switched off in individual method steps. Similarly, cathodes with different targets can be used. In this way, different process parameters can be achieved in consecutive method steps purely by external control, without having to reconfigure the system equipment or interrupt the vacuum between method steps.

[0024] Similar to the temporally interleaved etching steps, the coating steps may be the same or different from one another, for example, in terms of application duration and / or process parameters such as pressure, atmospheric composition, target material, voltage / power, etc.

[0025] Preferably, a negative bias voltage is applied during the coating step, i.e., the second and fourth method steps, and, if applicable, during the PV D-Ma The bias voltage is applied to the substrate during the additional method step in which the coating layer is produced by magnetron sputtering and during the etching step or steps. 2 and 4 Step 1 of the method 3 The method step (2) is higher. Ion etching is performed at a higher bias voltage because a higher bias voltage accelerates the ions of the plasma more strongly onto the substrate. As a result, the operating modes of coating and etching can be switched by changing the bias voltage.

[0026] According to a preferred embodiment of the present invention, in addition to the second and fourth method steps, additional coating steps may optionally be carried out to produce respective coating layers having thicknesses of 0.1 μm to 6 μm, preferably 0.5 μm to 5 μm, more preferably 1 μm to 4 μm. Particularly preferably, the thicknesses of at least two successive coating layers differ from each other by less than + / - 50%, more preferably less than + / - 25%, and particularly preferably less than + / - 15% (in each case compared to the thinner coating layer). More preferably, this applies to all coating layers produced in the repeat-start process.

[0027] By the method according to the present invention , total thickness is 12 μm or more coating is formed.

[0028] Due to such a thick coating, Particular advantages of the method according to the invention occurs. The total thickness (overall thickness) is , most The thickness can be as large as 30 μm. The continuous formation of single-layer coatings of such thickness by PVD coating methods often results in poor structure and / or high residual stresses, such that the coating is no longer usable for many applications, for example, due to insufficient coating adhesion and / or excessive roughness. Surprisingly, these disadvantages can be avoided by subdividing the thick coating into, for example, two or more, preferably three or more coating layers.

[0029] For at least one, preferably all, method steps (i.e., the second, fourth, and / or one or more additional method steps) in which the coating is applied. , small a cathode sputtering method in which at least one target of at least one magnetron cathode is sputtered; , messenger It is used.

[0030] In this method, for example, DC, AC, or pulsed voltages can be applied to the cathode, but the HIPIMS method is particularly preferred. This is a type of method also known as "high power pulse magnetron sputtering," in which the magnetron cathode is supplied with power in the form of very short but very high energy pulses, so that a high ion density can be achieved in the coating particles in front of the magnetron cathode. During the pulse, for example, 60 W / cm (per cathode relative to the target surface area of ​​each cathode) can be achieved. 2 More than 100W / cm 2 More than 200 W / cm is particularly preferable. 2 ~2,300W / cm 2 High peak powers of 1000 kJ / cm are characteristic of the HIPIMS method. Furthermore, the duty cycle, i.e., the ratio between pulse duration and pulse interval, is usually less than 0.5, i.e., the pulse interval is longer than the pulse duration. An apparatus and method for operating magnetron cathodes by HIPIMS is disclosed, for example, by the applicant in WO 2009 / 132822 A2. The HIPIMS coating method is understood to mean that preferably, one, several, or all cathodes in the vacuum chamber of the coating system are operated with high-power pulses according to the HIPIMS method, and if necessary, it is possible to simultaneously operate additional cathodes in DC mode.

[0031] The pulse duration preferably used in the HIPIMS method can be, for example, 5 to 200 μs. The HIPIMS pulse can be generated at a frequency of, for example, 100 to 10,000 Hz, particularly preferably 2,000 to 6,000 Hz.

[0032] In one or more coating steps, a bias voltage is preferably applied to the substrate, in particular a negative bias voltage, so that positively charged ions are accelerated toward the substrate surface. In particular, when magnetron sputtering is used, for example, with a DC voltage, a pulsed DC voltage, or a HIPIMS pulse at at least one magnetron cathode, the bias voltage can be a constant or pulsed DC voltage. The pulsed DC voltage is preferably pulsed in a unipolar manner. The pulse frequency can be in the MF (medium frequency) range, for example, 50 kHz to 3 MHz, preferably 100 kHz to 1 MHz, particularly preferably 150 to 500 kHz.

[0033] However, according to a preferred embodiment, the HIPIMS coating method is carried out by applying a pulsed bias voltage to the substrate. Preferably, in this case, the bias pulses can be synchronized in time with the HIPIMS pulses applied to the cathodes. "Synchronized" should be understood to mean that the pulses of bias voltage (bias pulses) are applied at the same frequency as the HIPIMS pulses at one or more cathodes, or that the frequencies are integer multiples of each other. In the case of multiple HIPIMS cathodes that are controlled so that the HIPIMS pulses are applied sequentially rather than simultaneously, the pulse frequency of the bias pulses preferably corresponds to at least the HIPIMS pulse frequency multiplied by the number of HIPIMS cathodes.

[0034] In this connection, the HIPIMS pulse and the bias pulse may be synchronized in time so that they have the same duration and start at the same time. However, preferably, the duration may be different and / or a lead or delay (offset) of the bias pulse with respect to the associated HIPIMS pulse may be specified. Particularly preferably, the synchronization is such that the bias pulse occurs with a delay (offset) of, for example, 5 μs or more, preferably 20-50 μs or more, relative to the assigned HIPIMS pulse. Furthermore, the synchronization is preferably such that the bias pulse in each case has a delay time after the assigned HIPIMS pulse, for example, 5 μs or more, preferably 10 μs or more.

[0035] It has been shown that when a HIPIMS pulse is applied, different types of ions, particularly metal and gas ions, are generated at different times. Gas ions are often observed in large numbers early in the HIPIMS pulse, while the generation of high densities of metal ions can be observed with a time delay. By delaying the bias pulse relative to the HIPIMS pulse in a targeted manner, it is possible to accelerate preferably metal ions and, to a lesser extent, gas ions toward the substrate with the applied bias voltage. The injection of gas ions into the forming coating has been shown to significantly contribute to the increase in residual stress within the coating. By temporally synchronizing the bias pulse with the cathode pulse so that the bias pulse voltage is applied during a time interval rich in metal ions, a coating with low residual stress can be obtained.

[0036] The composition of the coating or each coating layer can take into account various components. On the one hand, these include one or more target materials that are released by sputtering. On the other hand, the components can be supplied in gaseous form. In particular, the coating can take place in a reactive coating process by supplying reactive gases containing, for example, nitrogen, oxygen and / or carbon.

[0037] Preferably, the coating is a hard material coating. Each coating layer can be composed of a material system containing, for example, one or more metallic elements, or preferably at least one metallic element and at least one non-metallic element. It can be composed, in particular, of one or more metallic elements and one or more non-metallic elements. Binary, ternary, and quaternary hard materials, i.e., those containing two, three, or four different metallic elements, are preferred. In this context, compositions in which the metallic element or elements are selected from the group including Al, Si, B, and elements of groups 4 to 6 of the IUPAC Periodic Table (1988) are preferred. (In this context, for simplicity, the semimetallic elements Si and B are considered metallic elements.) Particularly preferably, Ti is included in the composition as one of the metallic elements. The non-metallic elements can be selected, for example, from the group including C, N, and O, preferably from the group including C and N, with N being particularly preferred as the only non-metallic element.

[0038] In the following examples, the coating compositions are referred to directly as compounds or phases, or as material systems. In this context, material systems are identified by a list of the elements contained therein, each separated from the other by a dash (-), with metallic elements listed first, followed by non-metallic elements. Metallic and non-metallic elements are preferably named in each case in the order of their proportions (atomic percentages). The names of material systems may correspond to the compounds, but this is not always the case. For example, the material system Ti-C comprises or consists entirely of the hard material compound TiC, while the material system Ti-B comprises or consists entirely of the hard material compound TiB2. Preferred material systems include, for example, Al-Ti-N, Ti-B, Ti-Si-N, Al-Ti-Si-N, Ti-CN, Al-Ti-Cr-Si-N, or Ti-Al-CN. Metals, such as Al, Ti, Si, and / or Cr, are preferably provided in solid form as components of one or more cathode targets.

[0039] In a preferred embodiment, at least one coating layer, preferably several or all coating layers, is Al X -Ti 1-X -N, more preferably x≧0.4 or x≧0.5, particularly preferably 0.55≦x≦0.65. The portion x of Al is preferably at most 70%.

[0040] At least two, preferably more or all coating layers of the coating formed during the coating step may have the same elements, i.e., the same material system and, if applicable, the same relative proportions of the elements involved, or alternatively, the coating layers may be assigned different compositions.

[0041] The ion etching process in the first, third, and / or additional method steps may preferably be carried out by igniting a plasma by the cathode and applying a relatively high accelerating voltage (bias voltage) to the substrate. The plasma may, for example, be composed primarily of gas ions. Alternatively, the cathode may be operated with HIPIMS pulses to generate a plasma containing a large amount of metal ions. The bias voltage may preferably be a constant DC voltage or a unipolar or bipolar (MF-) pulsed DC voltage in a unipolar or bipolar manner.

[0042] As will be described below based on exemplary embodiments, the ion etching process may include multiple substeps, such as an etching substep in which a plasma is generated and a bias voltage is applied for a first period, in the form of a DC voltage pulsed in a bipolar manner at a medium frequency, e.g., 50 kHz to 1 MHz, with a pulse height of, e.g., 100 V to 1,000 V, preferably 300 V to 800 V; and an additional etching substep in which, after the plasma is generated, a bias voltage is applied for a second period, in the form of a DC voltage in the range of, e.g., −50 V to −400 V, preferably −100 V to −300 V. The second period is preferably longer than the first period, more preferably at least twice as long. For example, the first period may be 5 to 30 minutes, and the second period may be 30 to 200 minutes, preferably 40 to 150 minutes.

[0043] The two etching substeps differ in their effect on the substrate due to the use of electrical edge effects, particularly in the presence of a DC bias. Etching with an FM pulsed bias voltage produces a substantially uniform effect on the entire surface of the substrate. In the case of etching with a DC bias, the edges, i.e., especially the cutting edges, are primarily etched.

[0044] The parameters of the ion etching process in the first method step in which the substrate is etched may correspond to the parameters of the etching process in the third method step (and, if applicable, in any additional method steps in which additional intermediate etchings are performed). Alternatively, different parameters can be used. For example, the substrate may be etched longer in the first method step than the relevant surface of the coating layer is etched in the subsequent intermediate etching steps. Even more preferably, for example, a lower bias voltage may be applied in the first method step than in the other etching steps. The total amount of material removed in the intermediate etching steps preferably corresponds to less than 20%, more preferably less than 10%, more preferably less than 5%, and particularly preferably less than 2% of the thickness of the relevant coating layer.

[0045] The method according to the invention is particularly suitable for manufacturing tools, in particular tools with at least one cutting edge, such as drills, milling cutters or indexable inserts (throw-away inserts).

[0046] The coated substrate can be made of various materials, for example steel (HSS). Preferably, it is a hard metal, in particular a WC / Co sintered material. Similarly, the method according to the invention can also be applied to other types of substrate materials, for example cBN substrates or ceramic substrates.

[0047] According to a second aspect, the present invention relates to a coating system for carrying out the method of the present invention. The system comprises a vacuum chamber and a device for placing a substrate in the vacuum chamber, e.g., a substrate holder, preferably for rotating the substrate, particularly preferably for planetary rotation. A means for generating plasma is provided in the vacuum chamber, preferably a magnetron cathode connected to a suitable power supply. Furthermore, a means for generating a bias voltage on the substrate is provided, preferably a power supply attached to the substrate. Both power supplies may be attached to an opposing electrode (counter electrode), e.g., the chamber wall, or a separate anode.

[0048] According to the present invention, the coating system includes control means for controlling the coating system to automatically carry out the method according to the present invention. The control means may, for example, include a programmable computer having an operating program defining the method steps according to the present invention. In particular, the means for generating plasma and / or the means for generating a bias voltage can preferably be controlled by the control means. The programming preferably includes at least one loop for repeating the programmed method steps to realize the above-mentioned repeat start method.

[0049] In a third aspect, in addition to the method of the present invention, the present invention also relates to a coated body, preferably produced by the method of the present invention. The coated body of the present invention comprises a substrate and at least one coating applied thereto. The coating comprises at least two coating layers, each having a thickness of 0.1 μm to 6 μm. An interface region formed by ion etching is disposed between the at least two coating layers. In the interface region, the coating layers directly adjacent to each other have different layer morphologies due to a visible structural change, i.e., the interruption in layer growth.

[0050] The coating may preferably comprise two or more coating layers of 0.1 μm to 6 μm each, in each case arranged between them an interface region formed by ion etching.

[0051] Ko The coating morphology, when viewed in a direction of increasing distance from the substrate, is such that the first and subsequent second coating layers are separated from each other by an interface region, and the structure of the second coating layer adjacent the interface region is finer than the structure of the first coating layer adjacent the interface region. Thus, the interface region is preferably characterized by a change in coating morphology from coarser to finer morphology.

[0052] The morphology can be evaluated in a manner known to those skilled in the art, for example based on the structural zone model by Thornton (Thornton, J., 1974. The influence of apparatus geometry and deposition conditions on the structure and topography of thick sputtered coatings. Journal of Vacuum Science and Technology, Vol. 11, pp. 666-670).

[0053] Preferably, the overall coating has lower residual stress compared to a coating of the same thickness deposited under otherwise identical conditions continuously, i.e., without interruption, and without the formation of an interfacial region by ion etching.

[0054] In the following, exemplary embodiments are explained in more detail with reference to the drawings. [Brief explanation of the drawings]

[0055] [Figure 1] 1 is a schematic diagram of a coating system viewed from above. [Figure 2] 2 is a perspective schematic view of a portion of the coating system of FIG. 1. [Figure 3] 1 shows an embodiment of a coated body in the form of an indexable insert (throwaway tip). [Figure 4] 4 is a schematic cross-sectional view of the coating of the coated body of FIG. 3 with multiple coating layers. [Figure 5] 1 is a flow chart of an exemplary embodiment of a coating process. [Figure 6] 1 is a graph showing the progression of various electrical variables over time during a coating step. [Figure 7a] 10 is a photograph of carrot grinding of a coating according to an exemplary embodiment; [Figure 7b] Photographs of carrot grinding of coatings made by the reference method. [Figure 7c] 1 is an SEM image of a coating on a substrate. [Figure 7d] FIG. 7c is an enlarged view of a portion of the SEM photograph of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0056] 1 and 2 show a PVD coating system 10 including a vacuum chamber 12. The interior 20 of the vacuum chamber 12 can be evacuated via a vent 14 to create a vacuum. A process gas, preferably a noble gas or a mixture of various noble gases, e.g., argon and / or krypton, can be supplied via an inlet 16. A reactive gas, such as nitrogen, can be supplied via an inlet 18. In an alternative embodiment, inlets 16 and 18 can be replaced with a common inlet for the process gas and the non-flammable reactive gas.

[0057] Four magnetron cathodes 22a, 22b, 22c, and 22d, each having a plate-shaped sputter target 24a, 24b, 24c, and 24d, are disposed inside 20 of vacuum chamber 12. Figure 2 shows two magnetron cathodes 22a and 22b for a better overview.

[0058] The magnetron cathodes 22a, 22b, 22c, 22d are oriented so that their sputter targets 24a, 24b, 24c, 24d are directed toward the center of the vacuum chamber 12. There is a rotatable substrate table 30 on which are disposed a plurality of rotatable substrate plates 32 having substrate holders 34. In the illustrated example, indexable inserts 40 (throw-away tips) are loaded as substrates.

[0059] The substrate holder 34 is an upright rod-shaped holder on which an indexable insert 40 is positioned. The indexable insert 40 is electrically connected to the substrate table 30 via the substrate holder 34 and the substrate plate 32. Figure 2 shows only the substrate holder 34 of one substrate plate 32 for a better overview.

[0060] The indexable insert 40 is shown in Figure 3. It includes a rake face 42 and a flank face 44. In the orientation shown in Figure 2, the flank face 44 is positioned parallel to the sputter targets 24a, 24b, 24c, and 24d of the magnetron cathodes 22a, 22b, 22c, and 22d. The edge between the faces 42 and 44 is intended for use as a cutting edge during machining. The indexable insert 40 is made of WC / Co sintered hard metal.

[0061] The indexable insert 40 is only one example of a substrate to be coated. Alternatively, components or tools of different shapes can be loaded into the substrate holder 34 of the appropriate shape in each case.

[0062] The magnetron cathodes 24 a , 24 b , 24 c , 24 d are connected to respective controllable power supplies 26 a , 26 b , 26 c , 26 d , which allow a voltage to be applied to the conductive walls of the vacuum chamber 12 .

[0063] Attached to the substrate table 30 is a controllable bias power supply 36 that can apply a voltage to the substrate table 30 , substrate holder 34 , and substrate 40 relative to the walls of the vacuum chamber 12 .

[0064] In this case, power supplies 26a, 26b, 26c, 26d, and 36 are each shown merely schematically as controllable voltage supplies. They may be conventional DC power supplies, pulsed power supplies, and / or HIPIMS power supplies. In the illustrated example, power supplies 26a, 26b, 26c, and 26d are controlled to switch between DC and HIPIMS modes of operation. In an alternative embodiment, each dedicated DC and HIPIMS cathode may be located inside vacuum chamber 12 and connected to a dedicated DC and HIPIMS power supply, which can be activated or deactivated as needed during operation by central control unit 36.

[0065] The power supplies 26a, 26b, 26c, 26d, 36 and the pumps (not shown) for the inlets and outlets 14, 16, 18, respectively, are attached to a central control unit 36 ​​of the system 10. The central control unit 36 ​​can be programmed such that all parameters of the pre-treatment and coating methods performed inside 20 of the vacuum chamber 12 are controlled by the control unit 36.

[0066] In the following, a coating process sequence programmed in the central control unit 36 ​​will be described by way of example.

[0067] Example: Thick PVD hard coating

[0068] To coat a substrate such as the indexable insert 40, a particularly thick hard material coating of more than 10 μm must be applied, which typically would not be suitable for machining applications with sufficient coating adhesion.

[0069] 5 shows a schematic diagram of the coating process sequence automatically defined by the programming of the central control unit 36. Titanium plates are provided with aluminum plugs as sputter targets 24a, 24b, 24c, and 24d in the system 10. In a preparation step 60, a substrate 40 is loaded inside the system 10, and the vacuum chamber 12 is evacuated to a pressure of 350 mPa and heated.

[0070] Subsequently, the surface 54 of the hard metal material 52 of the substrate 40 is etched in a first etching step 62. In the example, the first etching step 62 is a combined etching step with first and second etching sub-steps, whereby the substrate surface is cleaned and etched by gas ions.

[0071] In the first etching substep, ion etching is performed, and a plasma is first ignited by the magnetron cathodes 22a, 22b, 22c, 22d.

[0072] Therefore, the bias power supply 36 is operated such that a bias voltage of −650 V is applied to the substrate 40, pulsed at a medium frequency (240 kHz) in a bipolar manner relative to the chamber walls. In this manner, the gas ions of the plasma are accelerated onto the surface 54 of the substrate 40.

[0073] The first etching substep is applied for approximately 15 minutes, resulting in a low etching removal rate of 0.1 μm / h. In the second etching substep, ion etching is again performed, and the plasma is again initially ignited by the magnetron cathodes 22a, 22b, 22c, and 22d.

[0074] The bias power supply 36 was operated with an argon / krypton mixture as the process gas for a treatment time of 60 minutes, so that the substrate 40 was subjected to a constant DC bias voltage of negative value -200V.

[0075] The etching removal rate in the second etching substep is about 0.5 μm / h. Without interrupting the vacuum, the etching step 62 is followed by a coating step 64, in which the power supplies 26 a, 26 b, 26 c, and 26 d of the magnetron cathodes 22 a, 22 b, 22 c, and 22 d are driven with short high-voltage pulses to operate in HIPIMS mode. Each of the four magnetron cathodes 22 a, 22 b, 22 c, and 22 d is supplied with a peak power of about 100 kW during the coating step 64.

[0076] The bias voltage power supply 36 is driven to apply a pulsed bias voltage, for example, from −50 to −150 V, and the bias pulse is synchronized with the power pulse of the magnetron cathodes 22 a, 22 b, 22 c, and 22 d, with an offset in the bias voltage so that the bias pulse begins with a slight time delay relative to the HIPIMS pulse.

[0077] During a coating time of approximately 100 minutes, nitrogen is supplied as a reactive gas in addition to argon / krypton as process gas.

[0078] 6 shows example time curves of various electrical variables during the coating step 64: voltage 80 (solid line), cathode current 82 (dotted line), cathode peak power 84 (dashed line), bias voltage 86 (dashed line), and bias current 88 (dashed line) of magnetron cathodes 24a, 24b, 24c, 24d. As can be clearly seen, voltage 80 is applied to magnetron cathodes 24a, 24b, 24c, 24d in a pulse 90, while bias voltage 86 is applied in a temporally subsequent bias pulse 92.

[0079] 4 shows a schematic structure of the coating 50 on the hard metal substrate material 52. A first coating layer 56a is produced therein in a coating step 64. The coating rate is about 2 μm / h, so that at the end of the coating step 64 a thickness of the first coating layer 56a of about 3 μm is produced.

[0080] The material system of the first coating layer 56a is Al-Ti-N. An Al share x (among the metallic elements) of about 60% is achieved.

[0081] By delaying the bias pulse 92 relative to the HIPIMS pulse 90, fewer gas ions are implanted into the coating layer 56a, thereby producing less residual stress.

[0082] An intermediate etching step 66 follows the coating step 64. In the example shown, the intermediate etching step 66 is performed using the same parameters as the first etching step 62, i.e., using two successive etching sub-steps. As already mentioned, it is alternatively possible to perform the etching steps 62, 66 using different parameters, in particular the intermediate etching step being of shorter duration than the first etching step 62.

[0083] Because the etched coating layer 56a is harder than the substrate surface etched in the first etching step 62, the amount of material removed in the intermediate etching step 66 is significantly less than the value shown above for the first etching step 62.

[0084] This is followed by an additional coating step 68. In this example, coating step 68 corresponds in terms of all parameters used to the previous coating step 64. In the example shown, coating step 68 is performed for the same duration as the previous coating step 64. Alternatively, different coating steps can be performed using different parameters, such that different coating layers are produced, e.g., with respect to thickness, structure and / or composition.

[0085] In the present example, the coating / intermediate etching / coating cycle, controlled by the programming of the central control unit 36 ​​in the form of a loop, is repeated until a total of four coating layers 56a, 56b, 56c, 56d have been deposited one on top of the other, in each case with intermediate etching of the underlying surface (FIG. 4), after which the substrate 40 is cooled in the next step 70.

[0086] By interrupting layer growth at each point with intermediate etching steps 66, there is no continued growth of crystallites, but rather the formation of new crystallization nuclei, after the subsequent coating step 68 is initiated again. Although coating steps 64, 68 are each performed using identical parameters in the above example, the resulting coating 50 has a structure with recognizably distinct coating layers 56a, 56b, 56c, 56d.

[0087] Figure 7a shows carrot grinding on surface 44 of coated body 40. The interface regions between coating layers 56a, 56b, 56c, and 56d and formed by intermediate etching steps can be seen as rings. In contrast, Figure 7b shows the coating produced continuously after carrot grinding without such rings.

[0088] FIG. 7c is an SEM photograph of substrate material 52 having coating layers 56a, 56b, 56c, and 56d formed thereon. The interfacial regions are indicated by white frames. The respective changes in coating morphology are difficult to discern at the magnification shown, but become more apparent upon viewing at higher magnification (FIG. 7d). FIGS. 7c and 7d, the latter more clearly showing, show that the coating morphology changes from a coarser structure to a substantially finer structure, at least in the first interfacial region as viewed from the substrate surface. In Thornton's structural zone model, this corresponds to the change from structural zone 1 to structural zone T.

[0089] The surface of the coating 50 has been proven to be smooth, dense and nearly pore-free, making the tool 40 coated therewith highly resistant to a variety of applications, particularly machining purposes.

[0090] Coating 50 has a total thickness (total thickness) of about 12 μm. A reference coating using the same parameters but applied sequentially exhibits very high coating residual stress and poor adhesion to substrate material 52, while coating 50 of the same thickness has a compressive stress of about 1.4 Gpa and good coating adhesion.

[0091] Other possible embodiments can be gleaned from the following table, which identifies the coating material, total coating thickness, number of coating layers, as well as the type of coated tool, its application, and the workpiece material to be machined with said tool for various examples.

[0092] In the examples, for simplicity, coating layers each having at least substantially the same thickness are assumed, i.e., for example, a coating layer having four coating layers each 3 μm thick, with a total coating thickness of 12 μm.

[0093] TIFF0007621342000001.tif141152

[0094] TIFF0007621342000002.tif235152

[0095] TIFF0007621342000003.tif240152

[0096] TIFF0007621342000004.tif244152

[0097] While exemplary embodiments of this method are presented above by way of example only, those skilled in the art will recognize that the principles are applicable to a variety of material systems, layer structures, coating types, and coating parameters, and to a wide variety of applications. While the advantages have been presented for a particularly thick coating 50, they may also be advantageous for thin coatings, such as coatings formed from three coating layers of 0.2 μm each, with a total thickness of less than 1 μm on a very fine drill (microdrill).

[0098] The PVD coating system 10, and in particular the assembly of magnetron cathodes 22a, 22b, 22c, and 22d therein, as well as its electrical circuitry, should be considered merely exemplary. Alternatively, a different number of magnetron cathodes can be provided inside the vacuum chamber 12. The different cathodes can be connected to different types of power supplies, for example, a pure DC power supply. As shown, the power supply can be connected to the chamber wall, or alternatively, a separate anode can be provided that is electrically isolated from the chamber wall. In particular, in the case of DC magnetron cathode operation, it is preferable to connect the magnetron cathode to this type of anode.

Claims

1. A method for coating a substrate (40), comprising the steps of: The substrate (40) is a tool having at least one cutting edge; In a first method step (62), the substrate is pretreated by an ion etching process carried out as a first etching sub-step with a unipolar or bipolar medium frequency pulsed DC bias voltage and a second etching sub-step with a constant DC bias voltage, In a second method step (64), a first coating layer (56a) having a thickness of 0.1 μm to 6 μm is deposited on the substrate (40) by a HIPIMS PVD cathode sputtering process using HIPIMS pulses applied to the cathodes (24a, 24b, 24c, 24d) while a DC bias voltage is applied to the substrate with bias pulses synchronized in time with the HIPIMS pulses; In a third method step (66), the surface of the first coating layer (56a) is treated by an ion etching process, In a fourth method step (68), a second coating layer (56b) having a thickness of 0.1 μm to 6 μm is deposited on the first coating layer (56a) by the HIPIMS PVD cathodic sputtering process; repeating said third method step (66) and said fourth method step (68) one or more times to deposit one or more additional coating layers (56c, 56d) having a thickness of 0.1 μm to 6 μm by said HIPIMS PVD cathodic sputtering process; one or more of the coating layers (56a, 56b, 56c, 56d) comprises at least a composition selected from the group including Al-Ti-N, Ti-B, Ti-Si-N, Al-Ti-Si-N, Ti-C-N, Ti-Al-C-N, Al-Ti-Cr-Si-N; The coating layers (56a, 56b, 56c, 56d) stacked one on top of the other have a total thickness of 12 μm to 30 μm; A method for coating a substrate.

2. an interface region is formed between the first coating layer (56a) and a second coating layer (56b) thereon; the structure of the second coating layer (56b) adjacent the interface region is finer than the structure of the first coating layer (56a) adjacent the interface region; 2. The method of claim 1 .

3. One or more times following the fourth method step: First, the surface of the top coating layer (56b, 56a) is treated by an ion etching process; Thereafter, additional coating layers (56c, 56d) are deposited on the underlying coating layers (56b, 56a) by the HIPIMS PVD cathodic sputtering process.

3. The method according to claim 1 or 2.

4. At least the second, third and fourth method steps (64, 66, 68) are performed without interrupting the vacuum.

4. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

5. a bias voltage is applied to the substrate for each of the second, third and fourth method steps; the bias voltage is higher in the third method step than in the second and fourth method steps; 5. A method according to any one of claims 1 to 4.

6. Metal ions are generated during the ion etching process and accelerated towards the substrate by a bias voltage.

6. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

7. The coating layers (56a, 56b, 56c, 56d) are formed from the same element.

7. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

8. A coating system for carrying out the method according to any one of claims 1 to 7, comprising: A vacuum chamber (12); an apparatus (30, 32, 34) for placing a substrate (40) within said vacuum chamber (12); means (24a, 24b, 24c, 24d) for generating a plasma within said vacuum chamber (12); a means (36) for generating a pulsed DC bias voltage on said substrate (40); control means (36) for controlling the coating system (10) to automatically carry out said method; 1. A coating system comprising:

Images