Al-rich AlTiN coating layer manufactured from a metal target by PVD

Abstract

The present invention relates to a coating layer and a method for producing the same, the coating layer containing Al, Ti and N as main components and having a formula (Al a Ti b ) x N y where a and b are the concentrations of aluminum and titanium, respectively, in atomic ratios where only Al and Ti are considered in calculating the chemical elemental composition in the layer, where a+b=1 and 0≠a≧0.7 and 0≠b≧0.2, x is the concentration of Al plus the concentration of Ti, and y is the concentration of nitrogen, in atomic ratios where only Al, Ti, and N are considered in calculating the elemental composition in the layer, where x+y=1 and 0.45≦x≦0.55), and the coating layer exhibits an fcc cubic phase of 90% or more and has a compressive stress of 2.5 GPa or more, preferably between 2.5 GPa and 6 GPa.

Description

[Technical Field]

[0001] The present invention relates to an Al-rich AlTiN coating (hereinafter also simply referred to as an Al-rich AlTiN coating layer, Al-rich AlTiN layer, or Al-rich AlTiN film) manufactured by a physical vapor deposition (PVD) process from a metal target, and a method for manufacturing the same.

[0002] The present invention further relates to a coating system comprising, or containing, one or more of the Al-rich AlTiN layers of the present invention described above. [Background technology]

[0003] The Al-rich AlTiN coating layer according to the present invention should be understood as a coating layer composed of aluminum (Al), titanium (Ti), and nitrogen (N), or as a coating layer mainly composed of aluminum (Al), titanium (Ti), and nitrogen (N).

[0004] In this regard, the use of the term "main components Al, Ti, and N" in the Al-rich AlTiN layer means that, when considering all elements contained in the Al-rich AlTiN layer in order to determine the total elemental composition of the Al-rich AlTiN layer in atomic percentages, the sum of the content of Al, Ti, and N in the Al-rich AlTiN layer as atomic percentage concentrations is greater than 50 at% (i.e., a value between 50 at% and 100 at%), preferably greater than 75 at% (i.e., a value between 75 at% and 100 at%), and more preferably 80 at% or more (i.e., a value between 80 at% and 100 at%).

[0005] In this context, the term "Al-rich" is specifically used to indicate that the aluminum (Al) content in the corresponding Al-rich AlTiN layer is equal to or preferably greater than 70 at% when only Al and Ti are considered for determining the chemical elemental composition in atomic percentages (i.e., Al[at%] / Ti[at%] ≥ 70 / 30).

[0006] technical level AlTiN coating layers exhibiting cubic and columnar microstructures and having an Al content exceeding 75 at.-% (relative to Ti) are known to be synthesized by the LP-CVD process. These types of coatings are PVD-based Al 0.67 Ti 0.33 It is known to exhibit superior wear protection compared to coatings with lower Al content, such as N coatings.

[0007] Historically, it has been well known that AlTiN layers with a metastable cubic (B1 crystal structure) phase of up to 70 at.-% Al can be fabricated using PVD methods such as arc deposition and reactive magnetron sputtering.

[0008] Furthermore, some publications propose possible methods to raise the metastable solubility limit of Al above 70 at.%. However, all of these methods proposed so far have several drawbacks. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Objective of the present invention The object of the present invention is to provide an Al-rich AlTiN coating and a method for producing the same that overcomes or mitigates the shortcomings of the latest technology.

[0010] Al-rich AlTiN coatings should preferably exhibit a cubic phase, high hardness, appropriate compressive stress, and a coating microstructure, which, when applied to cutting tools, preferably enable the achievement of high wear resistance and improved cutting performance.

[0011] A further object of the present invention is to provide a flexible and reliable method for producing the Al-rich AlTiN coating of the present invention. [Means for solving the problem]

[0012] Description of the present invention The object of the present invention is achieved by providing a method for producing an Al-rich coating layer for coating a substrate, as described herein and also in claims 1 to 5. Furthermore, the object of the present invention is achieved by producing an Al-rich AlTiN coating layer as described herein and also in claims 6 to 10, and a substrate coated with the coating layer of the present invention.

[0013] The present invention specifically relates to a coating layer containing only Al, Ti, and N, or containing Al, Ti, and N as the main components, wherein the chemical elemental composition in atomic percentages in the coating layer, considering only these elements, is given by formula (Al a Ti b ) x N y Given by the equation, a and b are the concentrations of aluminum and titanium in atomic ratios considering only Al and Ti in calculating the elemental composition of the layer, respectively, where a+b=1 and 0≠a≧0.7 and 0≠b≧0.2, x is the sum of the concentrations of Al and Ti, and y is the concentration of nitrogen in atomic ratios considering only Al, Ti, and N in calculating the elemental composition of the layer, where x+y=1 and 0.45≦x≦0.55. ●The coating layer is ○90% or more fcc cubic phase, and ○ Exhibits a compressive stress of 2.5 GPa or higher, preferably between 2.5 GPa and 6 Pa.

[0014] In some applications requiring fairly high compressive stress, the compressive stress may preferably be between 4 and 6 Pa. Furthermore, the present invention specifically relates to a method for producing the coating layer described in claim 1 on the surface of a substrate. ● The coating layer is synthesized inside a vacuum coating chamber using reactive PVD cathode arc evaporation technology. Nitrogen gas, used as a reactive gas, is introduced into the vacuum coating chamber. At least one arc evaporation source containing a target material operating as a cathode for evaporating the target material is used. The target material consists of Al and Ti or contains Al and Ti as main components. Considering only the contents of Al and Ti in atomic percentage in the target material, the ratio of Al[at%] / Ti[at%] in the target material is 70 / 30 or more, that is, Al[at%] / Ti[at%] ≧ 70 / 30, preferably 70 / 30 ≦ Al[at%] / Ti[at%] ≦ 90 / 10. The method involves reactive deposition of titanium aluminum nitride as a result of the reaction between aluminum and titanium from the target material, with nitrogen introduced into the coating chamber as a reactive gas. The reactive deposition of titanium aluminum nitride is i. at a deposition temperature below 360°C, preferably as low as possible, for example, between 150°C and 250°C. ii. at a nitrogen partial pressure below 3 Pa, preferably below 2 Pa, more preferably below 1.5 Pa, in all cases higher than 0.05 Pa, preferably in the range between 0.1 Pa and 1.3 Pa, more preferably in the range between 0.1 Pa and 0.9 Pa, at a nitrogen partial pressure sufficient to form a stoichiometric nitride compound. iii. within the range corresponding to -250V ≦ U b ≦ -30V, preferably within the range corresponding to -200V ≦ U b ≦ -40V, more preferably within the range corresponding to -200V ≦ U b ≦ -60V, with a bias voltage U b used to carry out the process.

[0015] The inventors have found that when the low pressure within the proposed range is combined with other process parameters within the proposed range, particularly in combination with a particularly low process temperature (also referred to as the deposition temperature or substrate temperature during the coating process), the formation of the cubic phase fcc becomes possible for high Al concentrations (Al [at.%] / Ti [at.%] ≥ 70 / 30), but the arc discharge may become unstable. Therefore, the inventors propose to stabilize the arc discharge by using an improved magnetic field in the arc source. Such an improved magnetic field enables the achievement of a higher discharge voltage when a low nitrogen partial pressure is used, resulting in a stable process. Furthermore, by using a low nitrogen partial pressure in this way, the inventors have achieved the production of an Al-rich aluminum titanium nitride coating layer according to the invention, which exhibits a very small amount of droplets and results in a very smooth surface of the coating layer of the invention.

[0016] According to a preferred embodiment of the method according to the invention described above, the arc evaporation source is operated by generating an arc discharge at a discharge voltage exceeding 30 V, particularly between 30 V and 50 V, which was possible even with a low nitrogen partial pressure. Usually, when a low nitrogen partial pressure is used, the discharge voltage decreases.

[0017] A further advantage achieved by using a discharge voltage exceeding 30 V was that the surface of the target material (e.g., one or more AlTi targets) that is nitrided or partially nitrided as a result of the reaction between the target material and nitrogen present on the target surface during the coating process could be evaporated.

[0018] Furthermore, the inventors suggest that the dissipated power (which causes a heat load) should remain in the vicinity of the target surface and not dissipate into the substrate to be coated in order to reduce the heat load in the substrate to be coated. In this way, the process temperature can be kept low.

[0019] In this regard, preferably, this method is carried out by using one or more arc evaporation sources of the type described by Krassnitzer in the document PCT / EP2020 / 068828 (having international publication number WO2021 / 001536A1), which is incorporated herein by reference. In this way, it is possible to carry out a reactive PVD coating process such that an arc current of, for example, 200A can be applied to the target, and at the same time a discharge voltage of more than 30V (e.g., between 30V and 50V) can be achieved in the arc discharge, while maintaining a contribution of less than 20% of the power that would result in substrate heating (in this context, substrate heating should be understood as the thermal load on the substrate being coated), thereby producing an Al-rich AlTiN coating layer (having an Al content higher than 75 at% as described above). In many cases, the preferred power supply current of 200A or substantially 200A should not be understood as a limitation of the invention in each case. The source current may vary depending on the chemical elemental composition of the arc source and the target used. This can be in the range of 120A to 200A.

[0020] A coating layer with Al > 75% that grows in a cubic crystal structure (or grows to at least 90% in a cubic crystal structure) and has high hardness (for example, ((Al 76 Ti 33 )N and (Al 90 Ti 10 AlTiN having a coating layer having a chemical elemental composition in the range between ) and N is preferably manufactured according to the present invention by using low temperatures during the coating process (i.e., low process temperatures during the coating process), low gas pressure to achieve high energy input from ions (in this context, low gas pressure refers in particular to low nitrogen partial pressure, preferably only nitrogen gas is introduced into the coating chamber as process gas and reactive gas during the coating process), and a high negative bias voltage.

[0021] The inventors have found that the above-mentioned ratios of Al and Ti in the Al-rich AlTiN layer, which mean Al[at%] / Ti[at%]≧70 / 30, preferably Al[at%] / Ti[at%]>70 / 30, and more preferably 90 / 10≧Al[at%] / Ti[at%]≧80 / 20, make a significant contribution to improving wear protection for tools and / or components.

[0022] Furthermore, the present invention relates to a coating system comprising one or more Al-rich AlTiN coating layers of the present invention.

[0023] The above-described method of the present invention for producing the Al-rich AlTiN coating layer of the present invention can also be modified, for example, by using further targets and / or further reactive gas flows, to produce different coating systems, such as multilayer and / or gradient coating systems, or to produce other types of coating layers to be combined with the Al-rich AlTiN coating layer of the present invention.

[0024] Furthermore, reactive PVD coating processes using a metal target and simultaneously introducing N2 gas into the coating PVD chamber / apparatus are crucial for hard PVD coatings with complex coating architectures / designs, such as nanolayers and / or multilayer portions of the coating or the entire coating. PVD coating solutions for hard coatings on tools and / or components. Preferably, this coating solution should have a combination of desired coating properties such as microstructure, texture, modulus, hardness, and stress, and general (less limited) coating properties such as a thickness not limited to less than 50 nm, and the orientation of a single crystal grain or very limited low residual compressive stress. Specifically, this coating solution must also be able to improve the properties of AlTiN with an Al content of less than 70%, as such material systems attract considerable attention within PVD hard coatings, and as a result improve the wear resistance of tools during cutting processes, for example.

[0025] The Al-rich AlTiN coating layer and / or coating system according to the present invention (i.e., including the Al-rich AlTiN coating layer according to the present invention) is expected to exhibit excellent mechanical properties and possess a beneficial set of properties for providing superior performance to tools and parts subjected to wear and stress accumulation.

[0026] The above-mentioned (Al a Ti b ) x N y The layers preferentially exhibit a face-centered cubic structure. Importantly, the present invention describes a method for producing the Al-rich AlTiN coating of the present invention by a reactive physical vapor deposition (PVD) process by arc-discharging a metallic AlTi target having more than 70 at.% and less than 100 at.% (preferably between 75 at% and 90 at%) of Al and simultaneously introducing N2 (nitrogen) gas into a coating PVD chamber / apparatus.

[0027] To provide a better understanding of the present invention, several examples, tables, and figures are used below to illustrate the invention in more detail. However, these examples, tables, and figures should not be understood as limitations of the present invention, but only as specific examples and / or preferred embodiments of the present invention.

[0028] As described below, embodiments of the present invention of Al-rich AlTiN layers deposited according to the present invention were carried out by using a cathode arc evaporation process at a process temperature of 200°C (in this context, the term "process temperature" is used to refer specifically to the set temperature during the coating deposition process) and a low nitrogen partial pressure of less than 1.5 Pa. An AlTi target having an elemental composition of 80Al / 20Ti at% was used as the Al and Ti material source, and the target was operated as a cathode by applying an arc current of 200A and different substrate bias voltages and pressures for each embodiment.

[0029] Table 1 shows five examples of such deposition processes with detailed process parameters.

[0030] The properties of the Al-rich AlTiN coatings obtained by the processes shown in Examples 1 to 5 are shown in Figures 1 to 5. [Brief explanation of the drawing]

[0031] [Figure 1] (a) SEM cross-sectional image of an Al-rich AlTiN coating film deposited according to Example 1 of the present invention, and (b) pattern of the film as deposited. [Figure 2] (a) SEM cross-sectional image of an Al-rich AlTiN coating film deposited according to Example 2 of the present invention, and (b) pattern of the film as deposited. [Figure 3] (a) SEM cross-sectional image of an Al-rich AlTiN coating film deposited according to Example 3 of the present invention, and (b) pattern of the film as deposited. [Figure 4] (a) SEM cross-sectional image of an Al-rich AlTiN coating film deposited according to Example 4 of the present invention, and (b) pattern of the film as deposited. [Figure 5] (a) SEM cross-sectional image of an Al-rich AlTiN coating film deposited according to Example 5 of the present invention, and (b) pattern of the film as deposited. [Modes for carrying out the invention]

[0032] Figures 1(a), 2(a), 3(a), 4(a), and 5(a): SEM fracture cross-sectional images of Al-rich AlTiN monolithic coatings deposited in five examples of processes having the parameters shown in Table 1, including Young's modulus (E), hardness (H), and Al content measured in the deposited film.

[0033] Figures 1(b), 2(b), 3(b), 4(b), and 5(b): XRD patterns of as-deposited films from five examples of Al-rich AlTiN coatings deposited by a process having the parameters shown in Table 1.

[0034] [Table 1]

[0035] The membrane structure was analyzed by X-ray diffraction (XRD) using a PANalytical X'Pert Pro MPD diffractometer equipped with a CuKa radiation source. Diffraction patterns were collected using Bragg-Brentano geometry. Microscopic images of the membrane fracture cross-section were obtained using a FEGSEM Quanta F 200 Scanning Electron Microscope (SEM).

[0036] The hardness and indentation modulus of the as-deposited sample were determined using an Ultra-Micro-Indentation System equipped with a Berkovich diamond tip. The test procedure included a vertical load of 10 mN. Hardness values ​​were evaluated according to the Oliver and Pharr method. This allowed the inventors to ensure an indentation depth of less than 10% of the coating thickness to minimize substrate interference.

[0037] Figures 1(a), 2(a), 3(a), 4(a), and 5(a) show SEM micrographs of the fractured cross-sections of the films of Examples 1 to 5, as well as their coating properties: elastic modulus (Young's modulus), hardness, and Al content.

[0038] Figures 1(b), 2(b), 3(b), 4(b), and 5(b) show the XRD patterns of the as-deposited films of Examples 1-5, and these XRD patterns suggest a face-centered cubic structure for all coatings. These figures, in particular, show the changes in microstructure and the presence of small amounts of wurtzite phase when the coating layers of the present invention are treated with various process parameters, as shown in Table 1.

[0039] To produce the Al-rich AlTiN-based film of the present invention, the inventors used a reactive arc deposition process on a metal target having a minimum of 70 at% Al, and the combination of deposition parameters of the present invention was selected based on the following understanding: a) Target: The arc discharge current, magnetic field distribution, and intensity are selected to form a desired plasma state of film-forming species consisting of single and multiple charged ions of Al, Ti, and N.

[0040] b) On the substrate: The bias voltage is high enough to increase the kinetic energy, thereby increasing the quench rate of incident ions on the thin film growth surface. At the same time, the substrate temperature is low enough to freeze the mobility of adsorbed atoms on the growth surface.

[0041] c) General: The nitrogen gas pressure is operated within a desired window low enough to reduce the aggregation of nitrogen ions, thereby suppressing hexagonal phase nucleation enabled by the gas ion-induced limiting effect on the growth surface, while the nitrogen gas pressure is high enough to form a stoichiometric AlTiN thin film.

[0042] By optimizing the above process levels of arc deposition, thermodynamically favorable hexagonal phase nucleation was suppressed on the growth surface, thereby increasing the metastable solubility of Al in c-AlTiN to a higher concentration than 75 at.% (e.g., 80 at.%).

[0043] others Generally, it is intended that, at the time of writing, one or more (combined) paragraphs of the following layers and / or methods may be claimed to be independent of or additional to the protection of the original claims: A coating layer comprising Al, Ti, and N as the main components, and having the formula (Al a Ti b ) x N yA coating layer having an elemental composition of atomic percentages for these elements as follows (wherein a and b are the concentrations of aluminum and titanium in atomic ratios considering only Al and Ti in calculating the chemical elemental composition of the layer, respectively, where a+b=1 and 0≠a≧0.7 and 0≠b≧0.2, x is the sum of the concentrations of Al and Ti, and y is the concentration of nitrogen in atomic ratios considering only Al, Ti and N in calculating the elemental composition of the layer, where x+y=1 and 0.45≦x≦0.55), and being progressive in that the coating layer exhibits a fcc cubic phase of 90% or more and has a compressive stress of 2.5 GPa or more, preferably between 2.5 GPa and 6 GPa.

[0044] A method for producing the coating layer described in the above paragraph on the surface of a substrate, which is progressive in that the coating layer is synthesized inside a vacuum coating chamber by using reactive PVD cathode arc evaporation technology, wherein nitrogen gas is introduced into the vacuum coating chamber to be used as a reactive gas, and at least one arc evaporation source is used which contains a target material that acts as a cathode for evaporating the target material, wherein the target material consists of Al and Ti, or contains Al and Ti as the main components, and considering only the content of Al and Ti in atomic percentages in the target material, The method is characterized in that the Al[at%] / Ti[at%] ratio is 70 / 30 or greater, and the method involves reactive deposition of titanium aluminum nitride as a result of a reaction between aluminum and titanium from the target material and nitrogen contained in the coating chamber, wherein the reactive deposition of titanium aluminum nitride is carried out at a deposition temperature of less than 360°C with a bias voltage Ub in the range corresponding to -250V≦Ub≦-30V, preferably in the range corresponding to -200V≦Ub≦-40V, more preferably in the range corresponding to -200V≦Ub≦-60V, with a nitrogen partial pressure of less than 3 Pa, preferably less than 2 Pa, more preferably less than 1.5 Pa.

[0045] In particular, the method described in the previous section, wherein the arc evaporation source is operated by generating an arc discharge with a discharge voltage exceeding 30V.

[0046] The method according to the preceding paragraph, characterized in that the arc discharge is generated such that it contributes less than 20% of the power resulting in heating of the substrate.

Claims

1. A method for manufacturing a coated substrate, comprising depositing at least one coating layer onto the surface of the substrate, The process involves synthesizing the at least one coating layer inside a vacuum coating chamber by using reactive PVD cathode arc evaporation technology. Introducing nitrogen gas, which is used as a reactive gas, into the vacuum coating chamber, The method involves using at least one arc evaporation source containing the target material, which acts as a cathode for evaporating the target material using a source current in the range of 120A to 200A, wherein the target material consists of Al and Ti, or contains Al and Ti as the main components, and the ratio of Al [at%] / Ti [at%] in the target material is greater than 70 / 30. This includes depositing titanium aluminum nitride as a result of a reaction between aluminum and titanium from the target material and nitrogen from the nitrogen gas contained in the coating chamber, wherein, The reactive deposition of aluminum titanium nitride is - At a deposition temperature within the range of 150°C to 250°C, - At a nitrogen partial pressure within the range of 0.1 Pa to 0.9 Pa, -250V ≤ U ｂ Within a range corresponding to ≤-30V, the bias voltage U in the substrate ｂ It is done using The coating layer that is formed is - Contains Al, Ti, and N as individual components or as the main components, and has the elemental composition of these elements in atomic percentages according to the formula (Al a Ti b) x N y (wherein a and b are the concentrations of aluminum and titanium in atomic ratios considering only Al and Ti in calculating the chemical elemental composition of the layer, respectively, where a + b = 1 and 0 ≠ a ≥ 0.7 and 0 ≠ b ≥ 0.2, x is the sum of the concentrations of Al and Ti, and y is the concentration of nitrogen in atomic ratios considering only Al, Ti, and N in calculating the elemental composition of the coating layer, where x + y = 1 and 0.45 ≤ x ≤ 0.55), ・Exhibits over 90% fcc cubic phase, A method that exhibits a compressive stress of 2.5 GPa or higher.

2. The method according to claim 1, wherein only nitrogen gas is introduced into the coating chamber as a process gas and reactive gas during the coating process.

3. The method according to claim 1 or 2, characterized in that the arc evaporation source is operated by generating an arc discharge at a discharge voltage exceeding 30V.

4. The method according to claim 3, characterized in that the arc evaporation source is operated by generating an arc discharge at a discharge voltage between 30V and 50V.

5. The method according to any one of claims 1 to 4, characterized in that the arc discharge is generated such that it contributes less than 20% of the power that results in a thermal load on the substrate.

6. The following process parameters within the following range: The target material having an Al[at%] / Ti[at%] ratio within the range of 80 / 20 ≤ Al[at%] / Ti[at%] ≤ 90 / 10, The deposition temperature is in the range of 180°C to 220°C. The bias voltage in the range of -90V to -160V The method according to any one of claims 1 to 5, characterized in that the following is used.

7. The method according to claim 6, wherein the bias voltage is in the range of -100V to -150V.

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