Method for preparing a substrate coated with an intermediate layer and a diamond layer - Patents.com

Abstract

The present invention relates to a method for preparing a substrate coated with an intermediate layer and a diamond layer, the method comprising the steps of: (a) roughening the surface of a substrate with an etching solution; (b) coating the roughened surface of the substrate with an intermediate layer; (c) nucleating the surface of the intermediate layer; and (d) coating the nucleated surface of the intermediate layer with a diamond layer by a chemical vapor deposition (CVD) process, wherein the intermediate layer comprises aluminum oxide (Al2O3) and / or AlCrXN, where Al is aluminum, Cr is chromium, X is a semimetal, preferably silicon (Si) or boron (B), and N is nitrogen. The present invention further relates to a substrate provided with an intermediate layer and a diamond layer that can be obtained by the method.

Description

[Technical Field]

[0001] The present invention relates to a method for preparing a substrate coated with an intermediate layer and a diamond layer, as well as to a substrate coated with an intermediate layer and a diamond layer obtainable by said method. [Background technology]

[0002] Diamond-coated tools have high hardness, good wear resistance, a low coefficient of friction, good thermal conductivity, and a low coefficient of thermal expansion, which results in excellent cutting performance. Applying a diamond layer is generally performed by chemical vapor deposition (CVD). However, it is difficult to apply a diamond layer directly onto a certain substrate, and the resulting diamond layer may not adhere well to the substrate. Depositing a diamond layer on a cemented carbide is particularly difficult. A cemented carbide is a composite material comprising hard particles and a binder phase that binds the hard particles together, and the binder phase usually contains cobalt, nickel, or iron. When applying a diamond layer on a cemented carbide, the binder phase may adversely affect nucleation and diamond growth and promote the formation of non-diamond carbon materials, which may in turn reduce the quality of the diamond layer and its adhesion to the substrate.

[0003] Several methods are known in the art for improving the adhesion of a diamond layer to a substrate, particularly a hard metal. Essentially, the binder phase (most often cobalt) must be passivated. One method is to remove the binder phase from the near-surface region of the hard metal by etching prior to applying the diamond layer. However, removing the binder phase can lead to embrittlement and a decrease in fracture toughness, which can result in breakage. Another method is to deposit an intermediate layer on the surface of the hard metal, which has good adhesion to both the hard metal and the diamond layer. The intermediate layer can act as a diffusion barrier for the binder phase and compensate for the difference in thermal and / or mechanical stress between the substrate and the diamond layer.

[0004] DE 4434428 A1 discloses a composite material consisting of a body based on hard metal, cermet, ceramic or steel, on which an intermediate layer and a polycrystalline diamond layer are applied, the intermediate layer mainly comprising a tetrahedrally bonded amorphous carbon-containing layer.

[0005] EP 2558610 B1 discloses a method for forming a coating layer comprising an intermediate layer and a diamond layer using PVD. Si and C are present in the formed Si x C 1-x-y-z N y M z It is an essential component of the intermediate layer (0.4≦x≦0.6, 0≦y≦0.1, 0≦z≦0.2), and M is one or more elements selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Y, B, Al, and Ru.

[0006] WO 2018 / 112909 A1 provides a method for the pretreatment of cemented carbide prior to the application of a diamond coating, in which, following etching of the binder phase, the cemented carbide is coated with a coating comprising a base layer (diamond or cubic boron nitride), an intermediate layer, and a top layer (tetrahedral amorphous carbon film layer). The intermediate layer comprises a metal transition layer and a core layer made of a metal nitride, carbonate, or borate.

[0007] Chinese Patent Application Publication No. 114134504 A reports etching of tungsten carbide (WC) particles from a cemented carbide tool with Murakami's reagent and removal of the binder phase with an acidic solution (e.g., a mixture of sulfuric acid and hydrogen peroxide), followed by immersion of the cemented carbide tool in a mixed solution of copper sulfate and chromium sulfate. The cobalt present in the near-surface region of the cemented carbide tool is partially replaced, resulting in a cemented carbide tool with a copper-chromium layer covering the cobalt surface. The treated cemented carbide tool can then be subjected to nucleation in a diamond powder suspension before initiating CVD diamond growth.

[0008] US Patent No. 6,214,247 B1 relates to a method for removing part of the binder phase from the surface of a substrate (e.g., cemented carbide, cermet, or nitride) by means of an etching gas to form voids in the surface, wherein a coating comprising a material selected from the group consisting of TiC, TiN, TiCN, diamond, Al2O3, TiAlN, HfN, HfCN, HfC, ZrN, ZrC, ZrCN, Cr3C2, CrN, and CrCN is subsequently deposited in these voids to increase the wear resistance of the substrate (e.g., metal cutting inserts, dies, punches).

[0009] U.S. Patent Application Publication No. 2003 / 129456 A1 focuses on a cemented carbide containing a hard phase component including tungsten carbide and at least one selected from carbides, nitrides, and carbonitrides of metals from Groups 4a, 5a, and 6a of the periodic table. The cemented carbide can be coated with a layer including at least one of metal carbide, metal nitride, metal carbonitride, TiAlN, TiZrN, diamond-like carbon (DLC), diamond, and Al2O3, where the metal is selected from Groups 4a, 5a, and 6a of the periodic table.

[0010] EP 0503822 A2 relates to a hard material (e.g., cemented carbide) onto which an intermediate layer is applied using, for example, CVD, PVD, or sputtering. The intermediate layer is made of a material that can easily induce nucleation, such as silicon nitride, silicon carbide, or an Al2O3-containing material. The surface of the intermediate layer coated on the hard material is then roughened, for example, by scratching or etching. This increases nucleation during a subsequent coating step to apply a diamond and / or diamond-like carbon coating layer.

[0011] US Patent Application Publication No. 2013 / 164557 A1 discloses a substrate coated with an intermediate layer in a PVD process. The intermediate layer has a metal portion composed of more than 50 atomic % W and / or Cr. Prior to the PVD process, the substrate may be subjected to a blasting treatment (e.g., by sandblasting with hard material particles) to increase its roughness. After the PVD process, the applied intermediate layer may be roughened and subjected to a nucleation pretreatment with abrasive particles and / or diamond particles. Subsequently, a diamond layer is applied using CVD. Summary of the Invention [Problem to be solved by the invention]

[0012] It is an object of the present invention to provide a substrate coated with an intermediate layer and a diamond layer, wherein the intermediate layer significantly reduces the diffusion of atoms and / or ions present in the substrate through the intermediate layer when the diamond layer is applied. [Means for solving the problem]

[0013] This object is solved by the claimed (i) method for preparing a substrate coated with an intermediate layer and a diamond layer, and (ii) a substrate coated with an intermediate layer and a diamond layer obtainable by said method.

[0014] The present invention relates to a method for preparing a substrate coated with an intermediate layer and a diamond layer, the method comprising:

[0015] (a) roughening the surface of the substrate with an etching solution;

[0016] (b) coating the roughened surface of the substrate with an intermediate layer;

[0017] (c) nucleating the surface of the intermediate layer;

[0018] (e) coating the surface on which the intermediate layer was nucleated with a diamond layer by a chemical vapor deposition (CVD) process;

[0019] Including,

[0020] The intermediate layer comprises aluminum oxide (Al2O3) and / or AlCrXN, where Al is aluminum, Cr is chromium, X is a metalloid, preferably silicon (Si) or boron (B), and N is nitrogen.

[0021] The substrate used in the present invention can be selected from metals such as iron, molybdenum, tungsten, and their alloys (for example, tungsten carbide), cemented carbide, steel (for example, stainless steel, high-speed steel), silicon nitride, or their mixtures.Various tools can be used as substrates, such as cutting tools (inserts, shank tools), punching tools, wear parts such as knives, dies or molds.Therefore, the substrate coated with intermediate layer and diamond layer is further disclosed as a tool.

[0022] In the present invention, it has been found that the use of an intermediate layer comprising Al2O3 and / or AlCrXN, in particular Al2O3, AlCrSiN, AlCrBN, or mixtures thereof, provides an effective barrier to prevent the diffusion through the intermediate layer of atoms and / or ions present in the substrate, in particular in the binder phase of the cemented carbide, which may adversely affect nucleation and diamond growth during application of the diamond layer in a CVD process. 3 It may prevent the formation of hybridized carbon and instead promote the formation of non-diamond carbon materials, which significantly reduces the quality of the diamond layer.

[0023] In a preferred embodiment of the present invention, the substrate is a cemented carbide (also known as a carbide). The intermediate layer provides an excellent diffusion barrier against the binder phase present in the cemented carbide. Otherwise, the binder phase may adversely affect diamond growth at the interface, thus resulting in weak adhesion. The present invention allows a high-quality diamond layer to be deposited on the intermediate layer regardless of the grade of cemented carbide used as the substrate. Cemented carbide containing tungsten carbide as the hard phase and cobalt as the binder phase is particularly preferred for use as the substrate in the present invention. Various amounts of cobalt (e.g., 3 to 12 wt.%) can be included in the cemented carbide substrate. First, tungsten carbide has high hardness, and second, it exhibits excellent etching response (especially when using Murakami's reagent as the etchant), allowing the tungsten carbide surface to be well prepared for further processing.

[0024] Preferably, the intermediate layer is made of AlCrSiN, AlCrBN, or Al2O3, all of which have excellent high-temperature stability in the diamond growth range up to 1,100°C. Furthermore, the surface energies of AlCrSiN, AlCrBN, and Al2O3 allow for high nucleation densities when nucleation is performed, thereby allowing a closed diamond layer (i.e., preferably a uniform layer without holes or defects) to be deposited on the surface where the intermediate layer was nucleated. In addition, AlCrSiN, AlCrBN, and Al2O3 all exhibit good adhesion to the substrate and provide excellent resistance to stresses, such as thermal or mechanical stresses, which in turn is advantageous in terms of adhesion of the intermediate layer to the diamond layer. An intermediate layer containing AlCrBN not only provides better passivation of the binder phase than an intermediate layer containing AlCrSiN, but also has the advantage of minimizing internal stresses that can adversely affect adhesion due to the similarity of the crystal lattice of boron nitride (BN) to that of diamond.

[0025] Preferably, the Al2O3 used in the intermediate layer of the present invention is amorphous. The advantage of an amorphous Al2O3 layer is that it is denser and more compact than the crystalline structure of Al2O3, especially when deposited at low temperatures (e.g., below 300°C), and therefore even very thin layers can be deposited in a closed manner and without pores.

[0026] According to the present invention, the surface of the substrate is roughened by an etching solution. This results in a roughened surface that can allow deeper ingrowth of the intermediate layer, for example due to improved mechanical bonding. Furthermore, at least a portion of the binder phase present in the near-surface region of the substrate can be removed during etching, thereby increasing the distance from the remaining binder phase to the subsequently applied diamond layer. This in turn reduces the diffusion of binder phases such as cobalt during application of the diamond layer, thus reducing sp 3This promotes the formation of hybridized carbon, thereby improving adhesion. The substrate can be immersed in the etching solution to ensure uniform etching across the entire surface. Prior to the etching step, the surface of the substrate can be mechanically pretreated (e.g., by wet blasting, dry blasting, or drag finishing) and / or cleaned using typical cleaning solutions (e.g., by ultrasonic treatment) to remove undesirable materials such as grinding lubricants, oils, and residual contaminants, regardless of the type of substrate used (e.g., the grade of carbide when the substrate is a cemented carbide), to prepare the surface for the subsequent etching step. Preferably, the surface of the substrate is cleaned prior to etching. The etching solution is preferably applied as an etching solution, i.e., a solution of the etching solution in water, particularly demineralized water, with the concentration of the etching solution preferably being in the range of 50 to 95% by weight (based on the total weight of the solution). This allows for longer etching times without damaging the substrate surface, which in turn increases surface roughness and therefore adhesion to the subsequently applied intermediate layer. Preferably, the substrate surface is etched at 20-40°C for 30 seconds to 5 minutes. These conditions have been found to favorably prepare the substrate surface for the subsequent coating step, allowing for good adhesion to the intermediate layer.

[0027] In a preferred embodiment of the present invention, the surface of the substrate is etched with Murakami's reagent. Murakami's reagent is an excellent etchant, capable of sufficiently roughening the surface of the substrate, thereby significantly improving adhesion to a subsequently applied intermediate layer. Murakami's reagent can contain 1 part potassium ferricyanide III, 1 part potassium hydroxide, and 10 parts water (by weight). Sodium hydroxide can also be used instead of potassium hydroxide. In the present invention, it has been found that Murakami's reagent is particularly suitable for etching tungsten carbide (WC), resulting in a surface with high roughness, which enables good mechanical bonding and therefore good adhesion to a subsequently applied intermediate layer. Therefore, Murakami's reagent is particularly preferred as an etchant when tungsten carbide is included in the hard phase of the substrate. Preferably, etching the surface of the substrate with Murakami's reagent is carried out at a temperature in the range of 20 to 40°C for 30 seconds to 5 minutes. When these conditions are applied, adhesion of a subsequently applied intermediate layer to the surface of the substrate can be significantly improved. In a particularly preferred embodiment, the etching is carried out at 25° C. for 3 minutes.

[0028] More preferably, the etching of the present invention is carried out as a multi-stage etching process. Thus, according to a preferred embodiment of the present invention, etching with Murakami's reagent is followed by etching with an acid. Because Murakami's reagent is alkaline, the subsequent acid etching can remove components from the substrate that could not be etched and removed using Murakami's reagent. The combination of Murakami's reagent and acid surface treatment results in optimal preparation of the substrate surface for subsequent coating with an intermediate layer. On the one hand, the substrate surface can be significantly roughened, thereby improving its adhesion to the intermediate layer through mechanical bonding. The resulting surface roughness is such that a flat and uniform intermediate layer can be obtained when coating the substrate surface in a subsequent step. On the other hand, the binder phase can be sufficiently removed from the near-surface region of the substrate, which leads to a significant reduction in the diffusion of the binder phase when applying a diamond layer by a CVD process.

[0029] When a cemented carbide substrate is used in the present invention, the acid is preferably one that can act as an etchant for the cemented carbide's binder phase. Therefore, at least a portion of the binder phase present on the surface and in the near-surface region of the cemented carbide (e.g., due to a previous grinding process) can be removed during etching. Loss of binder phase from the near-surface region can reduce the diffusion of the remaining binder phase in deeper regions of the cemented carbide toward and through the subsequently applied intermediate layer, thereby enabling the deposition of a high-quality diamond layer. During the etching process, the surface can be cleaned, for example, with water, preferably demineralized water. Etching of the substrate surface with acid is preferably carried out at a temperature ranging from 20 to 40°C for 30 seconds to 5 minutes. It has been found that applying these conditions results in excellent adhesion of the subsequently applied intermediate layer to the substrate surface. Several acids are suitable for use in the present invention, such as nitric acid (or a solution thereof), sulfuric acid (or a solution thereof), or a solution of peroxysulfuric acid (also known as Caro's acid). For example, several acids can be used in the subsequent etching process. In the present invention, nitric acid is preferably used because it is easy to handle and allows for efficient etching. Furthermore, nitric acid exhibits good etching efficiency for commonly used binder phases, especially cobalt, making it particularly suitable when using cemented carbide as the substrate. Particularly effective etching can be achieved when using an aqueous nitric acid solution with a nitric acid concentration of 50-60 wt. % (based on the total weight of the solution). In a preferred embodiment, etching with nitric acid (57 wt. % solution) is carried out at 25°C for 60 seconds.

[0030] In the present invention, it is particularly preferred to etch the surface of the substrate in a two-step etching process using Murakami's reagent and an acid (preferably nitric acid). Preferably, etching with Murakami's reagent is carried out in the first step of the two-step etching process, and etching with acid is carried out in the second step. Particularly preferably, the surface of the substrate is etched with Murakami's reagent for 30 seconds to 5 minutes and with an acid, particularly nitric acid, for 30 seconds to 5 minutes at a temperature of 20 to 40°C. Preferably, an aqueous nitric acid solution is used, with a nitric acid concentration of 50 to 60% by weight (based on the total weight of the solution). Following this etching protocol, the substrate is well prepared for the coating process to apply an intermediate layer, ensuring good adhesion. After the two-step etching process, the roughness value R of the etched surface of the substrate is z R can be in the range of 0.1 to 2 μm. z can be calculated by averaging the five highest peaks and five deepest valleys within a given measurement length using the software of an optical microscope Keyence VHX-7000 (Keyence International, Belgium). Furthermore, the average roughness R of the etched surface of the substrate a can be in the range of 0.1 to 0.5 μm. In this application, the roughness values ​​were determined using an optical microscope Keyence VHX-7000 over a measurement length of 800 μm in accordance with DIN EN ISO 4287. It should be noted that the exact roughness value depends, among other things, on the roughness of the substrate surface obtained after grinding. When tungsten carbide (WC) with a binder phase (in particular cobalt) is used as the substrate, R z The value can be in the range of half the size of the WC particles (which can range from 0.2 μm to 5 μm, or even from less than 0.2 μm to more than 5 μm).

[0031] According to the present invention, a cleaning step of the substrate can be performed after the step of roughening the substrate surface with an etching solution. Cleaning can be performed using water. This helps remove residues of the etching solution and residues of the etched substrate (such as residues of the bonding phase when using a cemented carbide substrate). Preferably, the substrate surface is immersed in a water bath for, for example, up to 10 seconds or up to 20 seconds. Subsequent immersion in an ultrasonic bath filled with water for 1 to 5 minutes can result in a clean substrate surface free of any residue. To avoid any contamination by ions present in the water, demineralized or deionized water is preferably used to clean the substrate surface. Such ionic contamination can adversely affect subsequent coating steps, particularly the adhesion of the substrate surface to an intermediate layer that is subsequently applied. For example, cleaning can be considered sufficient when the conductivity of an ultrasonic bath filled with demineralized water is reduced to less than 1 μS / cm, as measured using a water purity tester HI98309 (Hannah Instruments, Graz, Austria).

[0032] Subsequently, the roughened surface of the substrate according to the present invention is coated with an intermediate layer. The intermediate layer can be coated on the surface of the substrate by various thin film deposition processes, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), or sol-gel process. Preferably, the surface of the substrate is coated by plasma-enhanced atomic layer deposition (PE-ALD) or physical vapor deposition (PVD), which can achieve excellent results. For example, a uniform intermediate layer can be formed that is preferably free of any holes or defects. The intermediate layer can comprise either a single layer or multiple layers, such as two, three, or more layers. The use of a multi-layer structure is advantageous in that a material with high bonding strength to the substrate can be selected as the inner layer, and a material with high bonding strength to diamond can be selected as the outer layer. For example, the intermediate layer can include two layers, one intermediate layer including Al2O3 and the other intermediate layer including AlCrXN, preferably AlCrSiN or AlCrBN.

[0033] In the present invention, the intermediate layer preferably has an average thickness in the range of 0.1 to 5 μm. Providing an average thickness of less than 0.1 μm does not significantly improve the bond strength and may even result in a layer with pinholes, while an intermediate layer with an average thickness of more than 5 μm adversely affects the bond strength and residual stress. The thickness values ​​of the layers (intermediate layer, diamond layer) given in this application were determined from scanning electron microscopy (SEM) images obtained from cross-sections of substrates coated with these layers. The average thickness values ​​were calculated from three single measurements.

[0034] In a preferred embodiment according to the present invention, the roughened surface of the substrate is coated with an intermediate layer of AlCrXN by arc PVD. The arc PVD process can utilize standard direct current (DC) arc deposition with an arc steering configuration using an electromagnetic field or a permanent magnetic field. For example, a multi-arc source configuration can be used by using two or three arcs. A bias voltage can be applied to the intermediate layer to generate an electric field to control the energy of the ions, allowing them to reach the substrate surface on which the intermediate layer is intended to be coated. Al a Cr b X c The target can be used to form an AlCrXN intermediate layer, where a is 50-80 atomic %, b is 20-50 atomic %, and c is 1-10 atomic %. The substrate temperature can be in the range of 400-500°C and can be maintained by one or more radiant heaters. The pressure during the coating process can be 5-10 -3 ~8·10 -2The pressure can be in the range of 1000 mbar. The use of an arc PVD process offers the advantage that the intermediate layer can be bombarded with ions during the coating process due to the conventionally applied substrate bias, leading to improved compressive strength of the intermediate layer. After applying the arc PVD process, the surface of the formed intermediate layer can exhibit spattering and increased roughness. Therefore, the surface of the intermediate layer can be smoothed by different surface finishing methods, such as wet or dry blasting, brushing, lapping, or by drag and stream finishing processes. In a preferred embodiment according to the present invention, the intermediate layer is smoothed by drag and stream finishing processes well known in the art. The coated substrate can be clamped to a rotating holder and then immersed in a dry abrasive medium while rotating. The abrasive medium can contain one or more abrasive particles, such as corundum particles, SiC particles, SiO2 particles, walnut shell particles, diamond particles, or a mixture of walnut shell particles and diamond particles. The particle diameter of the abrasive medium can typically range from 0.2 to 10 mm. This allows for the reduction or even complete elimination of droplets present on the surface of the intermediate layer formed during the arc PVD process, resulting in excellent preparation of the intermediate layer for subsequent steps of the method according to the invention. The resulting intermediate layer can have an average thickness in the range of 1 to 5 μm.

[0035] In a further preferred embodiment of the present invention, the roughened surface of the substrate is coated with an intermediate layer of Al2O3 by PE-ALD. This is a self-limiting film growth method characterized by alternate exposure of the growing film to chemical precursors, resulting in the sequential deposition of (sub)monolayers. Key advantages of PE-ALD include high film density, low impurity content, good stoichiometry, and excellent electronic properties. Furthermore, in PE-ALD, the chemical reaction during Al2O3 deposition can be initiated already at lower temperatures in the range of 30-300 °C, thus extending the temperature window toward lower temperatures. Plasmas containing O2, N2, NH3, H2, or mixtures thereof can be used. Trimethylaluminum (TMA) and oxygen (O2) can be employed as precursors for depositing Al2O3. The deposition can be performed at temperatures of 10 -1 This can be done at pressures in the range of ~5 mbar. Conversely, under vacuum, the reaction between TMA and oxygen is too slow to allow deposition within an economical period. High-frequency (13.56 MHz radio frequency (RF) or up to 60 MHz very-high frequency (VHF)) pulsed oxygen plasma can be employed. Ignition of the plasma only during the oxygen phase may be sufficient. Because oxygen does not react with TMA without excitation, time-consuming purging / pumping is not necessary. Instead, oxygen can be used directly as a purge gas. The resulting Al2O3 interlayer can have an average thickness in the range of 0.1–0.6 μm.

[0036] According to the invention, nucleation is carried out on the surface of the intermediate layer, which surface is the surface of the intermediate layer opposite to the surface of the intermediate layer facing the substrate. Nucleation on this surface of the intermediate layer allows for sp 3Several nucleation processes can be used to support the growth of hybrid carbon: (a) scratching the substrate, for example manually using diamond paste or industrially by sandblasting, (b) ultrasonic seeding with a mixture of a solvent (e.g., isopropyl alcohol or demineralized water) and particles of a hard material (e.g., diamond particles or particles of Al2O3, SiC, BC, etc.), (c) bias-enhanced nucleation (BEN), which applies a negative potential to accelerate charged species and bring them onto the substrate surface, (d) electrospray, or (e) dip coating.

[0037] In the present invention, 10 10 / cm 2 It is particularly preferred that a high nucleation density exceeding 1000 kJ / cm is achieved on the nucleation surface of the intermediate layer. The density can be determined by counting seeds in images obtained by scanning electron microscopy (SEM) using image processing software. This allows for low roughness and excellent uniformity (e.g., significant reduction or absence of holes and inhomogeneities) of the subsequently applied diamond layer. Furthermore, due to good adhesion, a closed diamond layer can be formed already in the early stages of growth. Such a high nucleation density can be obtained, for example, by the following procedure: Diamond particles of a defined particle size (e.g., 5-10 nm) can be colloidally dissolved in a solvent. It has been shown that using isopropyl alcohol or demineralized water as the solvent results in good nucleation efficiency. For substrates coated with the intermediate layer, nucleation can be carried out in an ultrasonic bath for 10 minutes up to several hours, depending on the diamond particle concentration (0.1-10 ct / liter) and the power of the ultrasonic device (100-1,000 W). Preferably, the nucleation time in the ultrasonic bath is 10-30 minutes. More preferably, the temperature in the ultrasonic bath can be in the range of 0° C. to 20° C. Using any of these parameters allows for effective nucleation.

[0038] According to the present invention, a diamond layer is subsequently coated on the surface where the intermediate layer was nucleated by the CVD process. The diamond layer according to the present invention is intended to refer to either a microcrystalline or nanocrystalline diamond layer, or a combination of both (e.g., as a multilayer or as a gradient layer). A hot-filament (HF-) CVD process can be used, as commonly known in the art. Alternatively, the device and method disclosed in WO 2018 / 064694 A1 can be used to carry out the CVD process of the present invention. The substrate containing the intermediate layer can then be placed in a deposition chamber. A process gas (hydrogen or a mixture of hydrogen and a carbon-containing gas (e.g., methane)) can be supplied to the flow passages of the gas activation element by a gas inlet. The walls of the gas activation element surrounding the flow passages can be heated, preferably to a temperature of at least 2,000°C, to thermally excite the process gas inside the flow passages. The cross-sectional area of ​​the flow passages is preferably 5 to 30 mm to increase the impingement excitation of the process gas with the walls. 2More preferably, the flow passages of the gas activation element are closed at both ends, for example, using closures, so that the gas activation element has no openings separate from the inlet and outlet openings. The ratio of the area of ​​the only outlet opening to the cross-sectional area of ​​the gas activation element is preferably 1:5 to 1:20, particularly 1:10, which further improves the excitation rate of the process gas. Because the number of openings is small and the flow passages are closed at both ends, the partial pressure within the flow passages inside the gas activation element can be significantly increased. As a result, the partial pressure can be increased to several times the pressure in the separation chamber. This allows the process gas to be further excited by impact excitation (e.g., collision-induced dissociation) in addition to thermal excitation. Therefore, preferably, a process gas containing hydrogen is activated by a combination of thermal activation and impact excitation. This results in an excitation rate of atomic hydrogen of 80% or more, whereas thermal excitation alone can only achieve an excitation rate of 30%. This high excitation rate can accelerate the diamond growth rate and result in a high-purity diamond layer. Furthermore, thanks to the high excitation rate and controlled flow of the process gas in the present invention, it is possible to increase the distance from the gas activation element to the substrate, thereby significantly improving the uniformity of the deposited diamond layer. In known hot filament CVD processes, the low excitation rate of the process gas introduced into the chamber in the background without local control requires a short distance (typically in the range of 5-10 mm) from the substrate to the gas activation element. Conversely, in the CVD process according to WO 2018 / 064694 A1, the relatively high excitation rate of the process gas allows for a greater distance between the gas activation element and the substrate surface. The distance is preferably in the range of 20-100 mm, particularly preferably in the range of 40-60 mm, which ensures a uniform temperature distribution on the substrate surface and, consequently, increases the uniformity of the deposited diamond layer. During deposition of the diamond layer on the substrate surface, the substrate temperature can be in the range of 750-950°C. In the present invention, the substrate temperature is preferably in the range of 750-850°C.The duration of the CVD process depends on the target thickness and is typically in the range of 10 to 20 hours. Additionally, the pressure in the deposition chamber can range from 1 to 40 mbar. Using either of these parameters helps to produce a uniform diamond layer.

[0039] Using the method according to the present invention, intermediate layers and diamond layers can be formed with little or no pinholes, thereby achieving good interlayer adhesion and good adhesion to the substrate surface.Furthermore, when applying the diamond layer, the diffusion of atoms from the substrate, for example from the bonding phase of the substrate, towards the diamond layer can be reduced or even avoided.The formation of layers with little or no pinholes can be ensured in the present invention by carefully selecting process parameters and optionally present cleaning steps to avoid dust, contamination or inclusions in the formed layer.

[0040] The invention further relates to a substrate coated with an intermediate layer and a diamond layer obtainable by the method of the invention, the intermediate layer being arranged between the substrate and the diamond layer.

[0041] According to a preferred embodiment of the present invention, the intermediate layer has an average thickness in the range of 1 to 5 μm, preferably 2 to 4 μm, and is made of AlCrSiN or AlCrBN. Furthermore, the intermediate layer can be almost or completely free of pinholes, can fully compensate for the difference in thermal and / or mechanical stress between the substrate and the diamond layer, and has excellent adhesion to both the substrate and the diamond layer. Furthermore, when the substrate is a cemented carbide, the intermediate layer can provide an excellent diffusion barrier to the cemented carbide's binder phase.

[0042] In an alternative preferred embodiment, the intermediate layer has an average thickness in the range of 0.1-0.6 μm, preferably 0.1-0.2 μm, and is made of aluminum oxide (Al2O3). Furthermore, the intermediate layer can be largely or completely free of pinholes, can adequately compensate for the difference in thermal and / or mechanical stress between the substrate and the diamond layer, and has excellent adhesion to both the substrate and the diamond layer. Furthermore, when the substrate is a cemented carbide, the intermediate layer can provide an excellent diffusion barrier to the cemented carbide's binder phase.

[0043] Preferably, the diamond layer according to the present invention comprises at least 95% by weight of sp 3 Hybridized carbon (i.e., diamond), more preferably at least 98 wt. % sp 3 Hybrid carbon, particularly preferably at least 99% by weight of sp 3 The diamond layer preferably contains hybridized carbon, which ensures good quality of the diamond layer and excellent adhesion to the intermediate layer. The average thickness of the diamond layer is preferably in the range of 0.1 μm to 300 μm. An average thickness of less than 0.1 μm is insufficient to provide significant improvements in performance such as wear resistance, while an average thickness of more than 300 μm cannot provide significant further improvements in properties.

[0044] Thanks to the diamond layer, the coated substrate according to the invention exhibits high hardness and high wear resistance, and therefore, excellent wear and fracture resistance can be achieved together with good adhesion and toughness, which in turn improves durability.

[0045] Preferably, in the present invention, the area fraction of the binder phase of the substrate present in the intermediate layer is less than 15%, more preferably less than 12%, and most preferably less than 8% of the total area of ​​the intermediate layer, as determined from a cross-section of the coated substrate by energy dispersive X-ray spectroscopy (EDX) analysis. Preferably, the substrate is a cemented carbide, and the binder phase contains or consists of cobalt. The area fraction can be determined by subjecting the substrate coated with the intermediate layer to a heat treatment at 900°C for 10 hours under an argon atmosphere (i.e., conditions typically applied during CVD processes), followed by preparing a cross-section of the coated substrate and generating an EDX image. The preferred temperature during the CVD process according to the present invention is in the range of 750-850°C, although it should be noted that using higher temperatures during heat treatment can facilitate evaluation of the diffusion characteristics of the intermediate layer. When the coated substrate is subjected to the heat treatment, no diamond layer is attached prior to EDX analysis. However, the area fraction can also be determined from a cross-section of a substrate coated with an intermediate layer and a diamond layer, in which case the heat treatment described above is replaced by a CVD process. When the CVD process is performed at a temperature of 850°C for 10 hours, the results obtained correspond to those obtained when a substrate coated with an intermediate layer (and without a diamond layer) is subjected to a heat treatment. Due to its low diffusion, the intermediate layer according to the present invention can act as an excellent diffusion barrier, significantly reducing or even completely preventing the diffusion of the binder phase in the cemented carbide toward and through the intermediate layer. Therefore, the adhesion of the diamond layer to the intermediate layer can be significantly improved. Therefore, a high-quality diamond layer can be deposited. It has been found that an intermediate layer made of AlCrSiN, AlCrBN, or Al2O3 results in particularly low diffusion of the binder phase, especially cobalt. Conversely, when using an intermediate layer different from the present invention, the area fraction of the binder phase present in the intermediate layer can be significantly higher, for example, more than 15% or even more than 20% of the total area of ​​the intermediate layer.This in turn can reduce adhesion and therefore hinder the quality of the diamond layer.

[0046] According to the invention, it is preferred that the roughness of the surface on which the intermediate layer is nucleated is in the same range as the surface of the etched substrate. Preferably, the roughness R of the surface on which the intermediate layer is nucleated is in the same range as the surface of the etched substrate. z is in the range of 0.1 to 2 μm, particularly preferably 0.2 to 2 μm, and is determined in accordance with DIN EN ISO 4287 using an optical microscope Keyence VHX-7000.

[0047] When tungsten carbide (WC) with a binder phase (especially cobalt) is used as the substrate, the roughness of the cemented carbide is preferably within half the size of the WC grains (which can range from 0.2 μm to 5 μm, or even from less than 0.2 μm to more than 5 μm). When an intermediate layer made of Al2O3 is applied, the surface can exhibit a roughness similar to that of the etched substrate due to the small average thickness of the Al2O3 layer (e.g., less than 0.2 μm). Conversely, when an intermediate layer made of AlCrSiN or AlCrBN is applied, a lower roughness is obtained compared to the surface of the underlying substrate due to the relatively high average thickness of the AlCrSiN or AlCrBN layer (e.g., 2 to 4 μm).

[0048] The invention is further explained below with reference to examples and figure descriptions. [Brief explanation of the drawings]

[0049] [Figure 1a] Figure 1a shows an SEM image (magnification: 10,000 times) of the ground surface of a cemented carbide substrate (taken at Tesca Mira, Tesca GmbH, Germany). Figure 1a shows a secondary electron (SE) image. As can be seen from the image, the cobalt binder phase of the substrate is exposed to the surface after grinding (i.e., prior to etching). [Figure 1b]Figure 1b shows an SEM image (magnification: 10,000 times) of the ground surface of the cemented carbide substrate (taken at Tescamira, Tesca GmbH, Germany). Figure 1b shows a backscattered electron (BSE) image. As can be seen, the cobalt binder phase of the substrate is exposed to the surface after grinding (i.e., prior to etching). [Figure 2a] Figure 2a shows an SEM image (taken with a Tescan Mira) of the surface of the cemented carbide substrate shown in Figures 1a-b after roughening using a two-step etching procedure (using Murakami's reagent and nitric acid). Figure 2b shows an SEM image. The magnification is 10,000 times. [Figure 2b] Figure 2b shows an SEM image (taken with a Tescan Mira) of the surface of the cemented carbide substrate shown in Figures 1a-1b after roughening using a two-step etching procedure (using Murakami's reagent and nitric acid). Figure 2b shows a BSE image. The magnification is 10,000 times. [Figure 3a] Figure 3a shows an SEM image (taken with a Tescan Mira) of the surface of the cemented carbide substrate shown in Figures 1a-b after roughening using a two-step etching procedure (using Murakami's reagent and nitric acid). Figure 3a shows an SEM image. The magnification is 20,000 times. [Figure 3b] Figure 3b shows an SEM image (taken with a Tescan Mira) of the surface of the cemented carbide substrate shown in Figures 1a-1b after roughening using a two-step etching procedure (using Murakami's reagent and nitric acid). Figure 3b shows a BSE image. The magnification is 20,000 times. [Figure 4] FIG. 4 shows an SEM image (taken on a Hitachi SU-8010 from Hitachi High-Tech Corporation, Japan) of the fracture edge of a substrate containing tungsten carbide as the hard phase and cobalt as the binder phase and coated with an Al2O3 layer (average thickness 0.2 μm). [Figure 5]FIG. 5 shows an SEM image (taken with a Hitachi SU-8010) of the fracture edge of a substrate containing tungsten carbide as the hard phase and cobalt as the binder phase, coated with an AlCrSiN layer (average thickness 4 μm) and a diamond layer (average thickness 6 μm). [Figure 6a] FIG. 6a shows the results of a scratch test carried out with a substrate containing tungsten carbide as the hard phase and cobalt as the binder phase, coated with an intermediate layer (Al 2 O 3 ) and a diamond layer. [Figure 6b] FIG. 6b shows the results of a scratch test carried out with a substrate containing tungsten carbide as the hard phase and cobalt as the binder phase, coated with an intermediate layer (AlCrSiN) and a diamond layer. [Figure 7a] Figure 7 a shows an EDX image of the cross section of a substrate coated with a reference interlayer, showing significant cobalt diffusion through the interlayer after heat-treating the coated substrate in a vacuum furnace (DSVF-3, Taeheung Chemical Co., Ltd., Korea) under an argon atmosphere at 900 °C for 10 h. aC:H:Si (average thickness 2 μm) was used as the interlayer. [Figure 7b] Figure 7 b shows an EDX image of the cross section of a substrate coated with a reference interlayer, showing significant cobalt diffusion through the interlayer after the coated substrate was heat treated at 900 °C for 10 h under argon atmosphere in a vacuum furnace (DSVF-3, Taeheung Chemical Co., Ltd., Korea) with a C:H:N (average thickness 1.5 μm) applied. [Figure 8] FIG. 8 shows an EDX image of a cross section of a substrate coated with an AlCrSiN intermediate layer (average thickness 4 μm) according to the present invention, showing relatively low cobalt diffusion after heat treating the coated substrate in a vacuum furnace (DSVF-3 from Taeheung Chemical Co., Ltd.) under an argon atmosphere at 900° C. for 10 hours. DETAILED DESCRIPTION OF THE INVENTION

[0050] Example

[0051] Example 1 - Preparation of a substrate coated with an intermediate layer and a diamond layer according to the present invention

[0052] Substrates with a diameter of 6 mm and a length of 50 mm, containing tungsten carbide (WC) as the hard phase and cobalt as the binder phase (the WC grain size was 0.7-1.2 μm and the cobalt (Co) content was 6-10 wt%), were cleaned by a standard cleaning process to remove lubricants and residual oil. A two-step etching process in an ultrasonic bath using Murakami's reagent followed by nitric acid (53 wt%) was applied to remove an average R, which was up to half the size of the WC grains after etching. z The surface of the substrate was roughened until a roughness value R was obtained. The surface of the substrate was etched using Murakami's reagent for 180 seconds at 25°C and nitric acid for 60 seconds at 25°C. The roughness profile of the substrate surface was then measured using an optical microscope Keyence VHX-7000 over a length of 800 μm in accordance with DIN EN ISO 4287. From the obtained roughness profile, the resulting roughness value R z and R a were calculated by Keyence software and reached amounts of 0.98 μm and 0.14 μm, respectively. Subsequently, the etched surface of the substrate was coated with amorphous Al2O3 and AlCrSiN as an intermediate layer.

[0053] (A) Amorphous Al2O3 as an intermediate layer

[0054] An amorphous aluminum oxide (Al2O3) layer was deposited on the roughened substrate surface by PE-ALD over a coating length of 30 mm. An Al2O3 layer with an average thickness of 0.2 μm was obtained, covering the entire surface area of ​​the substrate. -1An established PE-ALD process was applied using two precursors, trimethylaluminum (TMA) and oxygen (O), under a pre-vacuum in the pressure range of ~5 mbar. The oxygen plasma was ignited by radio frequency (13.56 MHz) at a process temperature below 100 °C. An SEM image of the fracture edge of the substrate coated with an AlO layer is shown in Figure 4.

[0055] Nucleation was then carried out on the surface of the Al2O3 layer in an ultrasonic bath filled with a diamond suspension (0.25 g suspended in 900 ml of isopropyl alcohol) at 0 °C and 300 W for 10 minutes. A nanocrystalline diamond layer with an average thickness of 6 μm was then coated onto the nucleated surface of the Al2O3 layer in a CVD process using the device described in WO 2018 / 064694 A1, using a process gas of 5.0 parts hydrogen and 3.5 parts methane. The process was carried out at temperatures ranging from 800 to 850 °C and a pressure of 10 mbar.

[0056] (B) AlCrSiN as an intermediate layer

[0057] Temperatures of 400 to 500°C and 5 to 10 -3 ~8·10 -2 An AlCrSiN layer was deposited on the surface of the roughened substrate by arc PVD at a pressure of 1000 mbar over a coating length of 35 mm. The AlCrSiN layer was composed of 60 at. % a, 30 at. % b, and 10 at. % c. a Cr b X c The resulting AlCrSiN layer had an average thickness of 4 μm and uniformly covered the entire surface area of ​​the substrate. The surface of the resulting intermediate layer was then smoothed by a drag and stream finishing process.

[0058] Nucleation was then carried out on the surface of the AlCrSiN layer in an ultrasonic bath filled with a diamond suspension (0.25 g dissolved in 900 ml of isopropyl alcohol) at 0 °C and 300 W for 10 minutes. A nanocrystalline diamond layer with an average grain size of 5-15 nm and an average thickness of 6 μm was then coated on the nucleated surface of the AlCrSiN layer in a CVD process using a device described in WO 2018 / 064694 A1, using a process gas of 5.0% hydrogen and 3.5% methane. The process was carried out at temperatures ranging from 800 to 850 °C and a pressure of 10 mbar. Figure 5 shows an SEM image of the fracture edge of a substrate coated with an AlCrSiN layer and a diamond layer.

[0059] Example 2 - Adhesion Test

[0060] Adhesion tests were carried out on substrates coated with the intermediate layer (Al2O3 or AlCrSiN) and diamond layer prepared in Example 1 by dry blasting with corundum particles (F90, 125-180 μm) at 3 bar. Both intermediate layers showed good adhesion to the substrate, with no delamination or damage to the intermediate layer occurring for up to 30 seconds for AlCrSiN and over 120 seconds for Al2O3.

[0061] Example 3 - Scratch Test

[0062] The substrates coated with the intermediate layer (Al2O3 or AlCrSiN) and diamond layer prepared in Example 1 were further subjected to scratch tests using an automated Revetest® scratch tester RST in accordance with ASTM C1624, ISO 20502 and ISO EN 1071. 3Scratch tests were performed using a scratch tester (Anton Paar, Austria). This scratch tester is widely used to characterize hard-coated materials with typical coating thicknesses exceeding 1 μm. The following parameters were used: a diamond Rockwell indenter with a 200 μm radius, progressive load scratch mode, scratch length of 2 mm, scratch loads of 0.5–60 N, and a loading rate of 300 N / min. The critical load (Lc) was 66 N for the substrate coated with Al2O3 as an intermediate layer (see Figure 6a) and 73 N for the substrate coated with AlCrSiN as an intermediate layer (see Figure 6b).

[0063] Example 4 - Diffusion of Cobalt Through the Interlayer

[0064] Energy dispersive X-ray spectroscopy (EDX) analysis was used to analyze the diffusion of cobalt, which exists as a binder phase in tungsten carbide substrates, through various interlayers. Substrates coated with different interlayers were heat-treated in a vacuum furnace (Daefun Chemical Co., Ltd., DSVF-3) under an argon atmosphere at 900°C for 10 hours. After the heat treatment, EDX analysis was performed on the cross-sections of the coated substrates. This was performed using a Hitachi SU8010 field-emission scanning electron microscope and a Horiba X-Max N50 EDX device (Horiba, Ltd., Japan). The cross-sections of the coated substrates were introduced into a vacuum chamber via a subchamber. The measurements were performed at room temperature (20–25°C), and the pressure in the vacuum chamber was 100°C. -4 ~10 -3 The voltage and current were in the range of 10 kV and 10 μA, respectively. Images were taken at 300,000 counts / image, 4 s processing time, 10 ms pixel dwell time, and 1024 channels. The EDX device was operated in cold mode, and a working distance of 15 mm was applied.

[0065] Substrates coated with an intermediate layer were prepared according to the preparation method disclosed in Example 1. The following systems are examples of various intermediate layers that were tested (average thickness and coating method are in parentheses): SiO2 (1 μm, PE-CVD), aC:H:Si (2 μm, PE-CVD), aC:H:N (1.5 μm, PE-CVD), AlTiN (1 μm, 2 μm, arc PVD), AlTiSiN (1 μm, 2 μm, arc PVD), AlCrN (1 μm, 2 μm, arc PVD), AlCrSiN (1 μm, 2 μm, 4 μm, arc PVD) using various targets with Si contents ranging from 1 to 10 atomic %, Al2O3 (0.2 μm, PE-ALD), Cr (1 μm, arc PVD), and Ti (1 μm, arc PVD).

[0066] EDX analysis confirmed significant cobalt diffusion from the substrate into most of the analyzed interlayers and through the interlayers toward the surface of the interlayer opposite the surface facing the substrate. The area fraction of cobalt present in the interlayers after heat treatment was calculated from cross-sectional EDX images using conventional image processing software. Exemplary EDX images of the cross sections of substrates coated with aC:H:Si interlayers (average thickness 2 μm) and aC:H:N interlayers (average thickness 1.5 μm) are shown in Figures 7a and 7b, respectively. The area fraction of cobalt present in the interlayers after heat treatment (relative to the total area of ​​the interlayer, respectively) was 19% for the aC:H:Si-coated substrates and 23% for the aC:H:N-coated substrates. Conversely, when a substrate was coated with an inventive intermediate layer composed of AlCrSiN or Al2O3, EDX analysis surprisingly revealed a significant reduction in the diffusion of cobalt into and through each of these two intermediate layers. An exemplary EDX image of a cross section of a substrate coated with an AlCrSiN intermediate layer (average thickness of 4 μm) is displayed in FIG. 8. The area fraction of cobalt present in the AlCrSiN layer after heat treatment was only 6% (relative to the total area of ​​the intermediate layer), confirming the excellent ability of the inventive intermediate layer to act as a cobalt passivation layer.

[0067] Example 5 - Performance testing of carbide tools coated with an intermediate layer and a diamond layer

[0068] According to the preparation method of Example 1, 10 mm diameter carbide router end mills containing tungsten carbide (WC) (1 μm-sized WC particles) as the hard metal and cobalt (Co) (Co content: 6 wt%) as the binder phase were coated with an intermediate layer and a nanocrystalline diamond layer (average thickness: 6 μm). An Al2O3 layer (average thickness: 0.2 μm) was applied by PE-ALD, and an AlCrSiN layer (average thickness: 4 μm) was applied by arc PVD. Furthermore, the carbide router end mills were wet-etched to remove the cobalt, and then coated with a diamond layer as a reference (i.e., no intermediate layer was applied). The average thickness of the nanocrystalline diamond layer was 6 μm for all prepared carbide router end mills. Wear was measured using the average wear width mark after machining a highly abrasive carbon fiber reinforced polymer (CFRP, type T700 carbon fiber with a tow size of 12k) with a 36 m milling path.

[0069] The results revealed significantly superior performance when using carbide router end mills coated with an intermediate layer and a diamond layer according to the present invention. When using Al2O3 and AlCrSiN as intermediate layers, average wear of only 118 μm and 65 μm was achieved. Conversely, wet etching the substrate and immediately applying the diamond layer resulted in significantly higher average wear of 174 μm.

Claims

1. (a) roughening the surface of the substrate with an etching solution; (b) coating the roughened surface of the substrate with an intermediate layer; (c) nucleating a surface of the intermediate layer; (d) coating the surface where the intermediate layer was nucleated with a diamond layer by a chemical vapor deposition (CVD) process; Including, The intermediate layer is made of aluminum oxide (Al ２ O ３ ) and / or AlCrXN, where Al is aluminum, Cr is chromium, X is a metalloid (preferably silicon (Si) or boron (B)), and N is nitrogen; A method for preparing a substrate coated with an intermediate layer and a diamond layer.

2. The method of claim 1 wherein the substrate is a cemented carbide.

3. The intermediate layer is made of AlCrSiN, AlCrBN or Al ２ O ３ 3. The method according to claim 1 or claim 2, comprising:

4. The Al ２ O ３ The method according to any one of claims 1 to 3, characterized in that the is amorphous.

5. The method according to any one of claims 1 to 4, characterized in that the surface of the substrate is etched using Murakami's reagent.

6. 6. The method of claim 5, wherein the surface of the substrate is etched in a two-stage etching process by etching with Murakami's reagent and acid, preferably nitric acid.

7. 7. The method of claim 6, wherein the surface of the substrate is etched with Murakami's reagent for 30 seconds to 5 minutes and with nitric acid for 30 seconds to 5 minutes at a temperature of 20°C to 40°C.

8. Method according to any one of claims 1 to 7, characterized in that the surface of the substrate is coated with an intermediate layer made of AlCrXN by arc physical vapor deposition (PVD).

9. The surface of the substrate is deposited with Al by plasma enhanced atomic layer deposition (PE-ALD). ２ O ３ 8. The method according to claim 1, wherein the coating is performed with an intermediate layer consisting of:

10. The method according to any one of claims 1 to 9, characterized in that in the CVD process, a process gas containing hydrogen is activated by a combination of thermal activation and impact excitation.

11. A substrate coated with an intermediate layer and a diamond layer, obtainable by the method according to any one of claims 1 to 10.

12. 12. The substrate of claim 11, wherein the intermediate layer has an average thickness in the range of 1 μm to 5 μm and is made of AlCrSiN or AlCrBN.

13. The intermediate layer has an average thickness in the range of 0.1 μm to 0.6 μm and is made of aluminum oxide (Al ２ O ３ 12. The substrate of claim 11, comprising:

14. 14. A substrate according to any one of claims 11 to 13, characterized in that the area fraction of the binder phase of the substrate present in the intermediate layer, as determined from a cross section of the coated substrate by energy dispersive X-ray spectroscopy (EDX) analysis according to the specification, is less than 15% relative to the total area of ​​the intermediate layer.

15. The surface on which the intermediate layer is nucleated has a roughness R in the range of 0.1 μm to 2 μm as specified in accordance with the specification. ｚ The substrate according to any one of claims 11 to 14, characterized in that it has

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