Coated tool having a coating including a boride-containing diffusion barrier layer

Abstract

A coated tool comprising a coated surface, the coated surface comprising a substrate (1) having a surface on which a coating (2) is deposited, the substrate being made of a material comprising cobalt, the coating comprising at least one boron-containing layer (20), the at least one boron-containing layer (20) comprising Al, the boron contained in the layer being present as a boride, whereby the boron-containing layer (20) can form an additional layer for providing a diffusion barrier layer effect, particularly for inhibiting the diffusion of cobalt from the substrate surface into the coating when the coated tool or coated surface is exposed to temperatures in the range of about 600°C to 1200°C.

Description

[Background technology]

[0001] A wide range of industrial processes are carried out under harsh conditions, e.g., high temperatures. Demanding efficiency improvements greatly increase this criticality. One approach to protect industrial tools in such operating conditions is to isolate them from the harsh environment by applying thin coatings on the tool's surface. Among the coating methods, physical vapor deposition (PVD) techniques have attracted much attention in both academia and industry and have achieved great success.

[0002] Nevertheless, even today, high temperatures can affect coatings applied to tool surfaces and the tool surfaces covered by the coatings (i.e., the substrate surfaces covered by the coatings).

[0003] A well-known example is coated cemented carbide cutting tools. During the use of the tools, especially in the case of tools made of or containing cemented carbide, it may happen that the tool surface is exposed to high temperatures, which leads to a diffusion outflow of cobalt into the coating. Furthermore, already during deposition, if this proceeds with high temperatures and powerful plasma treatments, a diffusion outflow of cobalt into the substrate surface may occur.

[0004] Problems solved by the present invention Even with the use of coatings, in certain applications, such as cutting materials containing Ti, it is unavoidable that the substrate, such as the cutting edge of the cutting tool, is exposed to high temperatures, and therefore there is a need for coatings that can help avoid damage to the substrate surface in operations involving exposure to high temperatures.

[0005] In the context of the present invention, the term "high temperature" is used in particular to refer to temperatures in the range of 600 to 1200°C.

[0006] Objective of the invention A primary objective of the present invention is to provide a coating that helps inhibit the diffusion of elements from the substrate surface into the coating when the coated substrate surface is exposed to high temperatures, a problem that can occur normally. 1. When forming a coating on a coated substrate, for example, ion bombardment can cause the substrate surface to heat up during deposition of the coating. 2. During use of the coated substrate, for example due to direct exposure of the surface of the coated substrate to high temperatures (for example if the coated substrate is a component used in a turbine part where high temperatures are generated) or due to indirect exposure of the coated substrate to high temperatures (for example when high temperatures are generated by frictional contact between a coated tool and a workpiece during machining operations). Summary of the Invention

[0007] Description of the invention The object of the present invention is achieved by providing a coated substrate comprising a substrate 1 comprising cobalt (Co) and a coating 2 deposited on a surface of the substrate, the coating further comprising aluminium and comprising at least one boron-containing layer 20 in which the boron is present as a boride, the at least one boron-containing layer 20 being deposited directly on the surface of the Co-containing substrate 1 (see FIG. 3 a).

[0008] The present inventors have surprisingly found that the boride constituting the boron-containing layer 20 has the property of inhibiting the diffusion of cobalt from the Co-containing substrate 1 into the coating 2 .

[0009] This surprising effect is particularly useful when performing machining operations with tools made from Co-containing materials, for example when tools made from cemented carbide are used, to avoid damage to the substrate and to the coating.

[0010] The present inventors have determined that the mechanism that suppresses the diffusion process operates at the interface between the substrate surface and the coating.

[0011] The present inventors have found that the layer 21 containing Co (FIG. 3) containing Al-Co and B-Co intermetallic phases is superior to the layer 21 containing Al-Co and B-Co intermetallic phases in at least the following two cases: b It was confirmed that the formation of 1. The coating process is carried out in such a way that the substrate surface becomes hot during coating deposition (e.g., caused by ion bombardment); and 2. If the coated substrate is exposed to high temperatures during use.

[0012] Thus, the formation of Al-Co and B-Co intermetallic phases at the interface between the substrate 1 and the coating 2 could suppress the diffusion of cobalt from the Co-containing workpiece into the coating.

[0013] Furthermore, the inventors have observed an additional beneficial effect when the coated substrate of the invention is exposed to high temperatures in an oxygen-containing atmosphere: this additional effect is the formation of an aluminum oxide-containing layer 22 (Al-O-containing layer 22) on top of the boron-containing layer 20 (see FIG. 3b). This Al-O-containing layer 22 prevents atmospheric oxygen from diffusing into the coating, improving the chemical stability of the coating at high temperatures, even when the coated tool is exposed to an oxygen-containing atmosphere.

[0014] Borides and their excellent properties are well known. be In the present invention, boride coatings, which are very promising coating materials, can be used in applications exposed to high temperatures in oxygen-containing atmospheres, as the coated tools of the present invention provide higher thermal stability while inhibiting the diffusion of Co by forming intermetallic compounds at the coating-substrate interface.

[0015] For example, when using a boron-containing layer 20 composed of AlWB2, a layer 21 may be formed that contains the following types of Al-Co and / or B-Co intermetallic phases (e.g., AlCo, Al2Co5, Co2B and / or Co3B). These intermetallic phases are present at the interface between the substrate and layer 20, allowing the remainder of the coating (e.g., layer 20) to remain intact.

[0016] Moreover, a major weak point of boride coatings is their poor oxidation resistance.

[0017] So, by applying an Al-boride coating, for example AlWB2, a protective Al-O layer can be formed, which can suppress the inward diffusion of O2 from the atmosphere into the coating.

[0018] In this way it was further possible to achieve that the coating material itself can suppress diffusion even in contact with the workpiece, particularly when the workpiece contains fast diffusing elements such as cobalt.

[0019] The coating of the present invention is particularly useful for protecting tools having substrates that contain cobalt.

[0020] Thus, according to a preferred embodiment of the present invention, the coating of the present invention comprises a layer 20 containing a boride having the property of inhibiting the diffusion of cobalt (hereinafter also referred to in the context of the present invention as a diffusion barrier layer), which is deposited directly on the substrate.

[0021] Further description of the invention The present invention will now be described in more detail with reference to some embodiments and figures. [Brief description of the drawings]

[0022] Figure caption:

[0023] [Figure 1]SEM-EDX elemental mapping showing the out-diffusion of Co from the substrate (a cemented carbide tool with Co binder) throughout the coating (a TiSiN coating with Co islands formed by out-diffusion of Co from the cemented carbide substrate) after annealing at 1100 °C for 1 h. [Diagram 2] 13 is a SEM cross-sectional image of the coated cemented carbide, where the Co-depleted areas can be clearly seen. [Diagram 3] An embodiment of a coated substrate of the present invention before (FIG. 3a) and after (FIG. 3b) exposure to high temperatures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The following descriptions and examples should not be construed as limiting the invention.

[0025] Figure 1 shows the SEM / EDX elemental mapping of cobalt (Co) achieved on a cross-section of a coated cemented carbide substrate after annealing at 1100 °C for 60 min. A scanning electron microscope (SEM) was used for this analysis. The elemental mapping was performed using an energy dispersive X-ray spectrometer (EDX) detector in the SEM. One can observe the Co binder in the cemented carbide substrate (here the cutting tool) and the Co islands dispersed in the TiSiN coating. The Co islands in the TiSiN coating were not present before annealing. Therefore, we conclude that the Co islands in the TiSiN coating were formed as a result of Co diffusion throughout the coating during annealing.

[0026] The diffusion outflow depicted in this annealing experiment illustrates a diffusion process that can take place during deposition as well as during use of the coated substrate, as explained above. Co diffusion changes the chemical composition of the coating and its properties. As a result, Co diffusion outflow weakens the coating-tool interface, affecting the coating properties and shortening the lifetime of the coated tool.

[0027] Figure 2 shows an example of such an interface in a cross-sectional SEM image. The image shows the formation of voids at the interface between the substrate surface and the coating, which is initiated by the diffusion outflow of Co. Furthermore, an accumulation of Co is observed in the initial part of the coating. Thus, the deterioration of the mechanical properties is evident.

[0028] As mentioned above, the diffusion process can occur or be initiated during the deposition process and during the operation of the coated substrate. During deposition, typical substrate temperatures in PVD processes are between 300 ° C and 600 ° C, i.e. lower than the temperature range of 600 ° C to 1200 ° C defined as relevant for diffusion. However, the deposition process is characterized not only by the condensation of neutral elements on the surface, but also by the simultaneous irradiation of high-energy ions. This leads to a very high "temperature" on the top surface of the substrate, which leads to a high mobility of Co atoms for diffusion. In other cases, during the operation of the coated substrate, the surface of the coated tool in contact with the workpiece (e.g. the cutting edge of the cutting tool) can become very hot, for example exceeding 1000 ° C in the machining of Ti alloys. In such conditions, the diffusion of Co also begins.

[0029] A primary object of the present invention is to provide a coating that inhibits the diffusion of Co from the substrate material into the coating at high temperatures.

[0030] Another object of the present invention is to provide a coating that has better mechanical properties in terms of hardness and Young's modulus both at room temperature and at elevated temperatures.

[0031] Binary and ternary Al-B compounds exhibit very attractive properties, such as high hardness of over 50 GPa, making them promising candidates for wear-resistant coatings to protect cutting tools and components in harsh environments.

[0032] The composition of Al-B based coatings by PVD is more or less determined by the composition of the target used for sputtering or cathodic arc evaporation.

[0033] According to a preferred embodiment of the invention, the coating or at least parts of the coating are produced by a PVD (Physical Vapour Deposition) sputtering technique, preferably a non-reactive PVD sputtering technique, i.e. using only non-reactive gases, e.g. argon, as process gas.

[0034] According to a further preferred embodiment of the present invention, the coating or at least a part of the coating (for producing the coated tool of the present invention) is deposited using a PVD (Physical Vapour Deposition) cathodic arc evaporation technique, preferably a non-reactive PVD cathodic arc evaporation technique, i.e. no process gas or only a non-reactive gas, e.g. argon, is used as process gas.

[0035] Depending on the parameters of these processes (composition and preparation of the target, evaporation process, reactive and noble gas background atmosphere, substrate bias, etc.), Al-B based coatings may contain, in addition to elemental components, different Al-B phases according to the corresponding phase diagrams.

[0036] An important contribution of the present invention is also to prevent oxygen diffusion towards the substrate / coating interface and towards the substrate, which initiates the diffusion outflow of Co through the coating. Since Al-B based coatings inherently contain Al which reacts with oxygen, it forms at the surface of the coating and in areas where oxygen can diffuse into Al-O which acts as a diffusion barrier.

[0037] On the other hand, Co diffusion is also reduced in regions where this mechanism does not exist due to the absence of oxygen: here, high temperatures initiate the formation of Al-Co and B-Co intermetallic phases that inhibit the diffusion of elemental Co.

[0038] The present invention specifically relates to a coating system comprising at least one diffusion barrier layer, wherein at least one diffusion transition layer is - a layer of AlB2 or a layer containing AlB2, or - a layer of AlWB2 or a layer containing AlWB2, or - a layer of AlB2 and AlWB2 or a layer containing AlB2 and AlWB2, or - a layer of AlN and AlB2 or a layer containing AlN and AlB2, or - a layer of AlN and AlWB2 or a layer containing AlN and AlWB2, or a layer of or containing a transition metal boride (TM boride), where TM is one or more transition metals selected from 3d, 4d and 5d elements, said layer further comprising Al.

[0039] At the transition region between the cobalt-containing substrate and the boride-containing layer, a gradient layer containing Al and W is added to improve adhesion and inhibit the diffusion of cobalt to the substrate surface during the deposition process.

[0040] The coatings of the present invention may be deposited to exhibit monolithic or layered coating architectures that include one or more of the diffusion barrier layers described above.

[0041] The coatings of the present invention may be used to coat cemented carbide tools in a variety of applications where the coated tools are exposed to high temperatures, such as cutting Ti-Al compounds.

[0042] The coating of the present invention may be used to coat cemented carbide tools in a variety of applications where the coated tool is exposed to high temperatures, preferably cutting Ni-based, Co-based or Ni-Co-based superalloys.

[0043] The presence of Al in these layers is preferred because Al can be important to achieve the inhibition of the diffusion outflow of Co into the coating. The presence of boride compounds in these layers is because they can play a decisive role in providing superior properties such as excellent hardness, especially hardness above 35 GPa, which is a very important property in various operations, for example in various cutting tool applications.

[0044] Preventing the diffusion of Co into the coating ensures that the unique properties of the coating of the present invention are maintained even during high temperature applications.

[0045] Binary and ternary borides in the context of the present invention may be synthesized, for example, by non-reactive physical vapor deposition (PVD) sputtering techniques using simply Ar as the process gas. To synthesize a binary boride, a binary boride target is sputtered in an Ar atmosphere, and co-sputtering two binary boride targets, e.g. WB2 and AlB2, synthesizes a ternary boride spanning a wide range of chemical compositions, in this case WAlB2. In combinatorial synthesis such as the latter, the chemical composition of the synthesized coating may be adjusted based on the power applied to each binary boride target and the change in its sputtering rate. The range of process gas pressure required to obtain a stable process is 0.3-0.9 Pa. The stability of the process may be ensured by adjusting the pressure of the process gas to the above range. The substrate temperature is 400-600 °C, and the required mobility is ensured when low bias voltage values ​​from the floating voltage to 50 V are used. This setup provides good crystal structure while at the same time ensuring that the residual stress levels in the boride coating do not cause the coating to spall.

[0046] To deposit the intermediate / gradient layer between the substrate surface and the boride, an Al-W target containing preferably more than 20 at.% W is utilized.

[0047] In the above examples, deposition by sputtering was described. Of course, it is also possible to deposit Al-B based coatings by cathodic arc evaporation. In this process, a target containing Al-B or Al-BW is used as the cathode.

[0048] The most important aspects of the present invention can be summarized as follows. a coated tool having a coated surface, the coated surface comprising a substrate surface that is part of the coated tool and a coating deposited on the substrate surface, the substrate surface being made from a material comprising cobalt and / or nickel, the coating having at least one boride-comprising layer, the at least one boride-comprising layer being made from a boride or made from a material comprising a boride, the at least one boride-comprising layer being a diffusion barrier layer that stops diffusion of cobalt and / or nickel from the substrate surface into the coating when the coated tool or the coated surface is exposed to a temperature in the range of about 600-1200°C.

[0049] The diffusion barrier layer is preferably made from: -AlB2 or -AlWB2 or -AlB2 and AlWB2 or -TM borides, where TM is one or more transition metals selected from the following groups 3d, 4d and 5d elements, and the layer further comprises Al.

[0050] In a particularly preferred embodiment of the invention, said diffusion barrier layer is an AlWB2 layer.

[0051] In a further preferred embodiment of the invention, the substrate surface is made of cemented carbide or made of any other material containing cemented carbide or containing cobalt.

[0052] In one more preferred embodiment of the invention, the substrate surface is made of a nickel alloy or made of a carbide of a material containing nickel or made of any other material containing nickel.

[0053] In one more preferred embodiment of the invention, the coating comprises, in addition to the diffusion barrier layer, a layer comprising Al and W, which is preferably not a boride layer.

[0054] In one more preferred embodiment of the invention, the layer described above, which comprises Al and W but which is preferably not a boride layer, is a metallic layer Al-W layer deposited as an intermediate layer (or interlayer) between the substrate and the diffusion barrier layer.

[0055] In one more preferred embodiment of the invention, said intermediate layer is a gradient layer.

[0056] The invention further relates to the use of a coated tool according to any of the above-mentioned embodiments or combinations thereof, wherein the coated tool or the coated surface is exposed to a temperature in the range of about 600-1200°C.

[0057] The invention further relates to the use of a coated tool according to any of the above-mentioned embodiments or combinations thereof, in which the substrate of the coated tool is a hard metal and a diamond layer is deposited on the diffusion barrier layer, in such a case the hard metal substrate does not need to be subjected to a pre-treatment to remove cobalt prior to the deposition of the diamond layer.

[0058] The invention further relates to a method for coating a coated tool according to any one of claims 1 to 7, characterized in that the coating is sputtered using PVD, in particular non-reactive PVS (Physical Vapour Deposition).

[0059] In one preferred embodiment of the invention in the above-mentioned method, Ar is used as the process gas.

[0060] In one more preferred embodiment of the invention in the above-mentioned method, at least one binary boride target is sputtered, in particular for the synthesis of binary borides, preferably for the simultaneous sputtering of two binary boride targets, for example WB2 and AlB2.

[0061] In one more preferred embodiment of the invention in the above mentioned method, a pressure range of 0.3-0.9 Pa is used during sputtering.

[0062] In one more preferred embodiment of the invention in the above mentioned method a temperature range of 400-600° C. is used during sputtering.

[0063] In one more preferred embodiment of the invention in the above mentioned method, bias values ​​of less than 50 V are used during sputtering.

[0064] In one preferred embodiment of the present invention in the above-mentioned method for depositing an Al-W intermediate layer, a target containing more than 20 at.% W is used.

[0065] All the above-described embodiments of the coated tool according to the invention may be used for machining superalloy materials.

[0066] The diffusion boride layer in the context of the present invention may also be used as a diffusion barrier layer to prevent the diffusion of other elements other than cobalt and nickel.

Claims

1. 1. A coated tool comprising a coated surface, The coated surface comprises a substrate (1) having a surface on which a coating (2) is deposited, The substrate (1) contains cobalt, said coating (2) comprising at least one boron-containing layer (20) which is a diffusion barrier layer for preventing diffusion of cobalt from a substrate surface into said coating, said at least one boron-containing layer (20) comprising Al, said boron contained in said layer being present as a boride, whereby said boron-containing layer (20) forms a first further layer (21) when said coated tool or said coated surface is exposed to a temperature in the range of 600° C. to 1200° C., the coating (2) comprises a first further layer (21) formed between the substrate (1) and the at least one boron-containing layer (20), the first further layer (21) comprising an Al—Co intermetallic phase and a B—Co intermetallic phase, tool.

2. The coated tool of claim 1 , wherein the boron-containing layer (20) comprises: -AlB ２ or -AlWB ２ or -AlB ２ and AlW.B. ２ or -TM borides, where TM is one or more transition metals selected from the following groups 3d, 4d and 5d elements:

3. 3. Coated tool according to claim 1 or 2, characterized in that the coating (2) comprises a second further layer (22) formed on the at least one boron-containing layer (20), the second further layer (22) comprising Al-O.

4. A coated tool according to any one of claims 1 to 3, characterized in that the substrate surface is made from or comprises a hard metal.

5. Coated tool according to any one of claims 1 to 4, characterized in that the substrate of the coated tool is a hard metal.

6. A method for coating a coated tool according to any one of claims 1 to 4, said method comprising the steps of: 1) depositing the at least one boron-containing layer (20) directly onto the surface of the Co-containing substrate; 2) forming said first further layer (21) comprising Al-Co and B-Co intermetallic phases by exposing said substrate surface to an elevated temperature during coating deposition or by exposing said coated surface to an elevated temperature, said elevated temperature being in the range of 600°C to 1200°C.

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