Al-rich AlCrN coating layer fabricated 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, Cr and N as main components and having a formula (Al a Cr b ) x O y C z N q where a and b are the concentrations of aluminum and chromium, respectively, in atomic ratio, considering only Al and Cr 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 Cr; and y, z, and q are the concentrations of oxygen, carbon, and nitrogen, respectively, in atomic ratio, considering only Al, Cr, O, C, and N in calculating the elemental composition in the layer, where x+y+z+q=1, and 0.45≦x≦0.55, 0≦y≦0.25, 0≦z≦0.25, and the coating layer exhibits an fcc cubic phase of 90% or more and 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 AlCrN coating (hereinafter also simply referred to as an Al-rich AlCrN coating layer, Al-rich AlCrN layer, or Al-rich AlCrN 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 AlCrN layers of the present invention described above. [Background technology]

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

[0004] In this regard, the use of the term "main components Al, Cr, and N" in the Al-rich AlCrN layer means that, when considering all elements contained in the Al-rich AlCrN layer in order to determine the total elemental composition of the Al-rich AlCrN layer in atomic percentages, the sum of the content of Al, Cr, and N in the Al-rich AlCrN 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 AlCrN layer is equal to or preferably greater than 70 at% when only Al and Cr are considered for determining the chemical elemental composition in atomic percentages (i.e., Al[at%] / Cr[at%]>70 / 30).

[0006] technical level AlCrN coating layers having an Al content exceeding 70 at-% (relative to Cr) and exhibiting a cubic crystal structure and columnar microstructure are PVD-based Al coatings. 0.7 Cr 0.3 Since it is expected to exhibit superior wear protection compared to coatings with lower Al content, such as N coatings, it is subject to numerous studies and attempts, particularly in industrial PVD chambers, to obtain such materials.

[0007] Therefore, 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]

[0008] Objective of the present invention The object of the present invention is to provide an Al-rich AlCrN-based coating and a method for producing the same that overcomes or mitigates the shortcomings of the latest technology.

[0009] Al-rich AlCrN 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.

[0010] A further object of the present invention is to provide a flexible and reliable method for producing the Al-rich AlCrN-based coating of the present invention. [Means for solving the problem]

[0011] Description of the present invention The object of the present invention is to provide a method for producing Al-rich AlCrN coating layers and substrates coated with one or more of these Al-rich AlCrN coating layers, or a coating system comprising one or more of these Al-rich AlCrN coating layers, as described below and as described in the claims.

[0012] Specifically, the present invention comprises Al, Cr, and N as main components, and the formula (Al a Cr b ) x O y C z N q Regarding a coating layer having an elemental composition in atomic percentages for these elements as follows: (wherein a and b are the concentrations of aluminum and chromium in atomic ratios considering only Al and Cr in calculating the chemical elemental composition of the layer, respectively, where a+b=1, 0≠a>0.7, and 0≠b≧0.18 (more specifically, a is in the range of 0.7>a≦0.82), x is the sum of the concentrations of Al and Cr, and y, z, and q are the concentrations of oxygen, carbon, and nitrogen in atomic ratios considering only Al, Cr, O, C, and N in calculating the elemental composition of the layer, respectively, where x+y+z+q=1, 0.45≦x≦0.55, 0≦y≦0.25, and 0≦z≦0.25), ●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 GPa.

[0013] Depending on the application, a higher compressive stress may be more appropriate in such cases. For example, when required for coatings or parts of coatings in certain applications, a compressive stress between 4 and 6 GPa is preferable.

[0014] 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, which is used as a reactive gas, is introduced into the vacuum coating chamber, at least one arc evaporation source containing the target material, which operates as a cathode for evaporating the target material, is used, the target material consists of Al and Cr or contains Al and Cr as main components, and when considering only the contents of Al and Cr in atomic percentage in the target material, the ratio of Al[at%] / Cr[at%] in the target material exceeds 70 / 30 (i.e., Al[at%] / Cr[at%]>70 / 30), the method involves reactive deposition of aluminum chromium nitride as a result of the reaction between aluminum and chromium from the target material and nitrogen introduced into the coating chamber, the reactive deposition of aluminum chromium nitride is i. at a deposition temperature from 180°C to 600°C, preferably from 200°C to 500°C,[[ID=1s]] ii. at a nitrogen partial pressure from 0.1 Pa to 9 Pa, preferably from 0.2 Pa to 8 Pa, more preferably from 0.6 Pa to 7.5 Pa, iii. carried out using a bias voltage Ub within the range corresponding to -250V≦Ub≦-30V, preferably within the range corresponding to -200V≦Ub≦-40V.

[0015] Therefore, preferably, this method is carried out by using one or more arc evaporation sources described by Krassnitzer in PCT / EP2020 / 068828 (having international publication number WO2021 / 001536A1), which is incorporated herein by reference. In this way, for example, an arc current of 200 A can be applied to the target, and at the same time, a reactive PVD coating process can be implemented to achieve a certain discharge voltage, making it possible to produce an Al-rich AlCrN coating layer (having an Al content higher than 70 at% as described above).

[0016] The inventors have found that the above-mentioned ratio of Al and Cr combinations in the Al-rich AlCrN layer (meaning Al[at%] / Cr[at%]>70 / 30, preferably 82 / 18≧Al[at%] / Cr[at%]>70 / 30) makes a significant contribution to improving wear protection for tools and / or parts.

[0017] Furthermore, the present invention relates to a coating system comprising one or more Al-rich AlCrN coating layers of the present invention.

[0018] The above-described method of the present invention for producing the Al-rich AlCrN coating layer of the present invention can also be modified, for example, by using additional targets and / or 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 AlCrN coating layer of the present invention.

[0019] 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 AlCrN with an Al content of 70%, as such a material system attracts considerable attention within PVD hard coatings, and as a result improves the wear resistance of tools during cutting processes, for example.

[0020] The Al-rich AlCrN coating layer and / or coating system according to the present invention (i.e., including the Al-rich AlCrN coating layer according to the present invention) exhibits excellent mechanical properties and is expected to have a beneficial set of properties for providing excellent performance to tools and components exposed to a combination of wear and stress.

[0021] The above-mentioned (Al a Cr b ) x N y layer preferentially exhibits a face-centered cubic structure. Importantly, the present invention describes a method for manufacturing the Al-rich AlCrN coating of the present invention by a reactive physical vapor deposition (PVD) process by arc-discharging a metal AlCr target having more than 70 at% Al and simultaneously introducing N2 gas into the coating PVD chamber / device.

[0022] To provide a better understanding of the present invention, several examples, tables, and figures are used below to explain the present 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.

[0023] As described below, examples of the present invention of Al-rich AlTiN layers deposited in accordance with the present invention were carried out by using a cathode arc evaporation process at a process temperature of 400 °C (in this context, the term "process temperature" is used specifically to refer to the set temperature during the coating deposition process), and different values of nitrogen partial pressure from 0.2 Pa to 5 Pa. As the Al and Cr material sources, an AlCr target having an elemental composition of 80Al / 20Cr at% was used, and the target was operated as a cathode by applying an arc current of 120 A to 200 A or 100 A to 200 A, as well as different substrate bias voltages and pressures for each example.

[0024] Table 1 shows five examples of such deposition processes with detailed process parameters.

[0025] The properties of the Al-rich AlCrN-based coatings obtained by the processes shown in Examples 1 to 5 are shown in Figures 1 to 5. [Brief explanation of the drawing]

[0026] [Figure 1] (a) SEM cross-sectional image of an Al-rich AlCrN 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 AlCrN 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 AlCrN 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 AlCrN-based 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 AlCrN-based 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]

[0027] Figures 1(a), 2(a), 3(a), 4(a), and 5(a): SEM fracture cross-sectional images of monolithic coatings of Al-rich AlCrN-based materials 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.

[0028] Figures 1(b), 2(b), 3(b), 4(b), and 5(b): XRD patterns of as-deposited films from five examples of Al-rich AlCrN-based coatings deposited by a process having the parameters shown in Table 1.

[0029] [Table 1]

[0030] 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).

[0031] 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.

[0032] 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, hardness, and Al content.

[0033] 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.

[0034] The method of the present invention makes it possible to produce coating layers consisting of cubic AlCrN containing more than 70 at% Al or mainly (at least 90%) cubic AlCrN, with respect to the presence of different atoms of Al in the coating, having the full range of physical and chemical properties such as hardness, elastic modulus, and texture, but importantly, all these coatings are completely or at least 90% cubic and simultaneously contain more than 70 at% Al (when considering only Al and Cr).

[0035] The impressive possibility of producing such a broad Al-rich AlCrN coating layer having at least 90% cubic planes is achieved by the inventors by carrying out the method of the present invention, in particular, such that the following conditions are met: High nitrogen (N) ionization, meaning that more than 50% of the N species reaching the substrate for coating formation are double-charged, is achieved and maintained during the coating process, High implantation of metal species (aluminum and chromium) is achieved and maintained during the coating process so that high-energy metal ions with energies of 200 eV or more are available.

[0036] The above conditions in the method of the present invention are achieved by a suitable combination of process parameters that must be employed in a particular PVD coating apparatus in order to satisfy the two given conditions above.

[0037] Examples of process parameter combinations to achieve the above coating conditions are shown below: Group 1: For low bias voltage, -100V b Only voltages ≤ -40V, low voltages (0.1Pa to 1Pa), and simultaneously higher temperatures (350°C to 500°C) are suitable, Group 2: For higher bias voltages, -200V ≤ U b ​It can be used in a higher pressure range of ≤-100V (0.8Pa to 9Pa) and simultaneously in a higher temperature range (200℃ to 480℃).

[0038] Table 1 shows specific examples of Al-rich AlCrN-based coatings deposited by processes that satisfy the above conditions and have specific combinations of process parameters.

[0039] Examples 1 to 5 described herein used Oerlikon Balzers PVD coaters.

[0040] In Examples 1 and 2 of Table 1, it can be observed that the process parameters described correspond to appropriate combinations of coating parameters according to Group 2 described above, with the parameters T, source current, and pressure being the same (400°C, 200A, and 5Pa, respectively), except that the bias voltage is changed from -150V to -100V.

[0041] Figures 1(a, b) and 2(a, b) show the essential properties of the AlCrN coatings obtained by the processes shown in Examples 1 and 2, using the coating parameter combinations shown in Table 1. Specifically, in both examples, the obtained coatings were Al-rich (the coatings contained 73 and 75 at% Al, respectively), and although both coatings were cubic, they had different textures E and H.

[0042] On the other hand, Example 3 shown in Table 1 provides an example of process parameters corresponding to a suitable combination of coating parameters according to Group 1 described above. At a very low bias voltage of -40V, only low pressure values ​​may be suitable (for example, a pressure of only 0.2Pa is given here). Such low pressures allow for the minimization of collisions and, as reflected by the very high Al content (81 at%, see Figure 3(a)), allow for a higher level of ionization of the influent species while simultaneously maintaining a high influent flux of Al species, but surprisingly, still allows for the acquisition of a predominantly cubic phase (see Figure 3(b)).

[0043] Plasma properties, particularly the energies of nitrogen ionization and metal ions, can be measured using the Langmuir technique.

[0044] To produce the Al-rich AlCrN film of the present invention, the inventors used a reactive arc deposition process on a metal target having more than 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, Cr, and N.

[0045] b) General: The combination of pressure, source current, and bias voltage is selected to provide very high-energy species, thus increasing kinetic energy and thereby increasing the quench rate of incident ions on the thin film growth surface. At the same time, these process parameters were manipulated to suppress nucleation of the hexagonal phase on the growth surface. Furthermore, the nitrogen gas pressure is high enough to form stoichiometric AlCrN thin films.

[0046] 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-AlCrN to a higher concentration than 70 at.% (e.g., above 75 at.%).

[0047] Specifically, the present invention relates to a method for manufacturing a coated substrate, which includes depositing at least one coating layer onto the surface of the substrate. ● The at least one coating layer is synthesized inside a vacuum coating chamber by 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 is used, which includes the target material and acts as a cathode for evaporating the target material. The target material consists of Al and Cr, or contains Al and Cr as its main components, and considering only the content of Al and Cr in the target material by atomic percentage, the ratio of Al[at%] / Cr[at%] in the target material is greater than 70 / 30, preferably 70 / 30. <Al[at.%] / Cr[at.%]≦90 / 10であり、 The method involves reactive deposition of chromium aluminum nitride as a result of a reaction between aluminum and chromium from the target material and nitrogen contained in the coating chamber. The reactive deposition of aluminum chromium nitride is i. At a deposition temperature of 180°C to 600°C, preferably 200°C to 500°C, ii. At nitrogen partial pressures from 0.1 Pa to 9 Pa, preferably from 0.2 Pa to 8 Pa, and more preferably from 0.6 Pa to 7.5 Pa, iii. -250V ≤ U b Within the range corresponding to ≤-30V, preferably -200V ≤ U b Within the range corresponding to ≤-40V, the bias voltage U b It is done using iv. The coating layer that is formed is a. Al, Cr, and N are included individually or as the main component, and the formula (Al a Cr b ) x O y C z N q(In the formula, a and b are the concentrations of aluminum and chromium in atomic ratios considering only Al and Cr in calculating the chemical elemental composition in the layer, respectively, where a+b=1, 82≧a≧>0.7, 0≠b≧0.18, x is the sum of the concentrations of Al and Cr, and y, z, and q are the concentrations of oxygen, carbon, and nitrogen in atomic ratios considering only Al, Cr, O, C, and N in calculating the elemental composition in the layer, respectively, where x+y+z+q=1, and 0.45≦x≦0.55, 0≦y≦0.25, 0≦z≦0.25) The elemental composition of these elements in atomic percentages is as follows: b. Exhibits over 90% fcc cubic phase, c. A method in which the compressive stress is 2.5 GPa or more, preferably between 2.5 GPa and 6 GPa.

[0048] In the above method, The coating parameters are: i. During the deposition of at least one coating layer, high nitrogen ionization is achieved and maintained such that more than 50% of the nitrogen species reaching the substrate are double-charged. ii. The high implantation of metallic aluminum and chromium species is characterized by being selected so as to be made possible by achieving high-energy metallic ions of aluminum and chromium corresponding to values ​​of 200 eV or more.

[0049] In the above method, The coating parameters are simultaneously within the following range: i.-100V b Bias voltage U in the low bias voltage range of ≤-40V b , ii. Partial pressure of nitrogen in the low pressure range from 0.1 Pa to a maximum of 1 Pa, and iii. A combination of coating parameters is selected such that the process temperature is in the temperature range of 350°C to a maximum of 500°C. or The aforementioned coating parameters are simultaneously within the following range: i.-200V≦U b Bias voltage U in the high bias voltage range of ≤-100V​b , ii. A nitrogen partial pressure in the high-pressure range from 0.8 Pa to a maximum of 9 Pa, and iii. It is selected to be a combination of coating parameters at a process temperature in the temperature range from 200 °C to a maximum of 480 °C.

[0050] The arc evaporation source current is in the range from 120 A to a maximum of 200 A up to, the above method. A coated substrate comprising a coating system including at least one coating layer manufactured according to any of the above methods of the present invention, wherein the coating layer has a hardness higher than 30 GPa, for example between 30 GPa and 50 GPa, and a Young's modulus higher than 330 GPa, for example between 330 GPa and 400 GPa, and an aluminum content in the range between 72 at.% and 82 at.%, that is, 0.72 ≤ a ≤ 0.82, the coated substrate.

[0051] Other Generally, for layers and / or methods according to one or more of the following (combined) paragraphs, it is intended to optionally claim, when the time comes, whether it is independent of or additional to the protection of the patent claims existing from the beginning: A coating layer containing Al, Cr, and N as main components, having an elemental composition in atomic percentages for these elements according to the formula (AlaCrb)xOyCzNq (where a and b are the concentrations of aluminum and chromium, respectively, in atomic ratios considering only Al and Cr in the calculation of the chemical element composition in the layer, here, a + b = 1, and 0 + a > 0.7 and 0 + b > 0.2, x is the sum of the concentrations of Al and Cr, y is the concentrations of oxygen, carbon, and nitrogen, respectively, in atomic ratios considering only Al, Cr, O, C, and N in the calculation of the elemental composition in the layer, here, x + y + z + q = 1, and 0.45 < x < 0.55, 0 < y < 0.25, 0 < z < 0.25), presenting more than 90% fcc cubic phase, and being progressive in that the compressive stress is 2.5 GPa or more, preferably between 2.5 GPa and 6 GPa, the coating layer.

[0052] 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 used as a reactive gas is introduced into the vacuum coating chamber, and at least one arc evaporation source is used which contains a target material acting as a cathode for evaporating the target material, wherein the target material consists of Al and Cr, or contains Al and Cr as the main components, and considering only the content of Al and Cr in the target material in atomic percentages, the ratio of Al[at%] / Cr[at%] in the target material is greater than 70 / 30, and the method involves reactive deposition of aluminum chromium nitride as a result of a reaction between aluminum and chromium from the target material and nitrogen contained in the coating chamber, wherein the reactive deposition of aluminum chromium nitride is performed at -250V

Claims

1. A method for manufacturing a coated substrate, comprising depositing at least one coating layer onto the surface of the substrate, ● The at least one coating layer is synthesized inside a vacuum coating chamber by 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 is used, which includes the target material and acts as a cathode for evaporating the target material. The target material consists of Al and Cr, or contains Al and Cr as its main components, and considering only the content of Al and Cr in atomic percentages in the target material, the ratio of Al [at%] / Cr [at%] in the target material exceeds 70 / 30. The method involves reactive deposition of chromium aluminum nitride as a result of a reaction between aluminum and chromium from the target material and nitrogen contained in the coating chamber. The reactive deposition of aluminum chromium nitride is i. At deposition temperatures ranging from 350°C to 500°C, ii. At nitrogen partial pressures from 0.1 Pa to 1 Pa, iii. Within the range corresponding to -100V < U b ≤ -40V, the bias voltage U ｂ It is done using iv. The coating layer that is formed is a. Contains Al, Cr, and N individually or as the main component, and the formula (Al ａ Cr ｂ ) ｘ O ｙ C ｚ N ｑ (wherein a and b are the concentrations of aluminum and chromium in atomic ratios considering only Al and Cr in calculating the chemical elemental composition in the layer, respectively, where a + b = 1, and 0.82 ≥ a ≥ > 0.7 and 0 ≠ b ≥ 0.18, x is the sum of the concentrations of Al and Cr, and y, z, and q are the concentrations of oxygen, carbon, and nitrogen in atomic ratios considering only Al, Cr, O, C, and N in calculating the elemental composition in the layer, respectively, where x + y + z + q = 1, and 0.45 ≤ x ≤ 0.55, 0 ≤ y ≤ 0.25, and 0 ≤ z ≤ 0.25) The elemental composition has atomic percentages for these elements as follows: b. Exhibiting over 90% fcc cubic phase, c. The compressive stress is 2.5 GPa or more. The coating parameters are, i. During the deposition of the at least one coating layer, high nitrogen ionization is achieved and maintained such that more than 50% of the nitrogen species reaching the substrate are double-charged. ii. High implantation of metallic aluminum and chromium species is made possible by achieving high-energy metallic ions of aluminum and chromium corresponding to values ​​of 200 eV or higher. The method to be selected.

2. The method according to claim 1, characterized in that the arc evaporation source current is in the range of 100 A to a maximum of 200 A.

3. The method according to claim 1 or 2, wherein the coating layer exhibits a hardness higher than 30 GPa, a Young's modulus higher than 330 GPa, and an aluminum content between 70 at.% and 82 at.% (i.e., in the range of 0.70 ≤ a ≤ 0.82).

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