Method for rapidly developing large-fracture toughness amorphous thin film material

Abstract

The application discloses a method for rapidly developing amorphous thin film material with high fracture toughness, which comprises the following steps: depositing corresponding alloy elements on a substrate based on different element targets by using a physical vapor deposition co-sputtering method to obtain a sample library containing a plurality of amorphous thin films with different element compositions; performing potential test by using a Kelvin probe force microscope to characterize the surface potential distribution of each amorphous thin film in the sample library, and obtaining the surface potential difference of each amorphous thin film; calculating the surface electronic work function of each amorphous thin film by using the obtained surface potential difference; the composition of the amorphous thin film with the maximum electronic work function is the composition of the amorphous thin film with the maximum fracture toughness in the sample library, and the amorphous thin film material with high fracture toughness is developed according to the composition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mechanical property testing, and particularly relates to a method for rapidly developing amorphous thin film material with large fracture toughness. BACKGROUND

[0002] Amorphous alloy is a new type of metal material obtained by ultrafast cooling of high-temperature melt. Due to the disorder of micro-atomic structure, amorphous alloy exhibits many excellent mechanical properties, such as high elastic strain, high specific strength, high wear resistance and excellent impact self-sharpening. However, the problem of brittle fracture at room temperature has always restricted its practical application in structural engineering materials.

[0003] Among them, an important mechanical property closely related to the brittleness problem of amorphous alloy is fracture toughness. Generally, the material system with larger fracture toughness will exhibit excellent fatigue propagation resistance, which is crucial for the practical application of amorphous alloy materials. Therefore, the development of amorphous alloy system with large fracture toughness has become one of the difficulties and hotspots in the field. However, at present, only a few amorphous alloy composition systems have large fracture toughness, and it is urgent to speed up the development process of new amorphous alloy materials with large fracture toughness.

[0004] At present, most of the research on the fracture toughness of amorphous alloy is focused on bulk, because it has a larger volume and a size closer to practical application. However, the preparation of bulk amorphous alloy is usually more complex, and internal stress concentration may occur during testing, which may affect the test results of fracture toughness. In contrast, thin film amorphous alloy usually has a more uniform structure and fewer internal defects, which makes them very useful in studying the physical mechanism of fracture toughness. And thin film samples of different compositions can basically reflect the mechanical properties of their corresponding bulk samples. Therefore, the exploration of fracture toughness of amorphous thin film materials can provide unique advantages for the development of bulk amorphous alloy with large fracture toughness based on the research of glass forming ability.

[0005] In the past decades, researchers have proposed various experimental methods for calculating fracture toughness, such as nanoindentation, three-point bending, etc. However, these traditional experimental methods are based on the idea of trial and error, and can only characterize one component at a time, which is time-consuming and inefficient. Moreover, as the number of alloy elements increases with changes in alloy composition, these trial-and-error-based experimental methods greatly increase research costs. In recent years, high-throughput screening methods for amorphous fracture toughness have been proposed, such as the patent technology disclosed in the applicant's prior application CN116223760A, which uses physical vapor deposition co-sputtering to deposit multiple alloy elements on a substrate to obtain a high-throughput sample library. Each position on the surface of the high-throughput sample library is represented by the x and y coordinates. Multiple indentation test points are set on the surface of the high-throughput sample library, and nanoindentation tests are performed on them. The fracture toughness value is calculated from the results to screen for the composition with the maximum fracture toughness. Compared to previous methods, this patent technology can indeed reduce research costs, but if the screening range is too large, it is still time-consuming. For example, at 30 test points, to ensure test accuracy, 6 nanoindentations are pressed at each test point, which will take 40-45 minutes of test time, and 30 groups will require more than 20 hours, which is not easy to ensure continuous experiments. Therefore, in order to obtain alloy components with large fracture toughness more quickly, a more convenient screening indicator needs to be found.

[0006] For crystalline alloy materials, the electronic work function (EWF) shows a positive correlation with fracture toughness, i.e., the larger the work function, the greater the fracture toughness of the alloy system. The electronic work function refers to the minimum energy required to move an electron at the Fermi level from inside the metal to its surface without kinetic energy. Considering that the mechanical properties of materials are essentially determined by electronic behavior, which determines the strength of atomic bonds and ultimately determines the overall mechanical properties. For crystalline materials, the correlation between electronic behavior and mechanical properties of materials, including ductility and strength, has been theoretically studied using quantum mechanics and first-principles simulations. However, quantum theory is complex and difficult to practically apply to material characterization and design. Mohn et al. showed that the electronic work function can be used to detect electron density and distribution in systems of different scales, including nanostructures and even single molecules, which is crucial for a deep understanding of the physical, chemical, and mechanical properties of materials. Although the electronic work function reflects the electronic state of the material surface, it fundamentally controls the electron-nuclear interaction that determines the strength of atomic bonds and materials. Therefore, the electronic work function can be used to reflect the fracture toughness of materials. Considering that the electronic work function is not closely related to specific crystalline or amorphous structures, the electronic work function may be a potential screening indicator for fracture toughness.

[0007] There are many methods to measure the electron work function of materials, but they can be divided into two categories according to their measurement principles: one is direct measurement method, and the other is indirect measurement method. The direct measurement method is greatly affected by the sample surface morphology, measurement environment, measurement equipment and other factors. In contrast, the indirect measurement method can obtain the work function information of the sample as long as the work function of the probe tip is determined, and it is particularly suitable for smooth thin film materials. Specifically, it is realized by measuring the contact potential difference between the probe tip and the sample with a Kelvin microscope. When two different metals are in contact, the Fermi level will adjust due to the difference in Fermi level height or electron work function. Electrons will flow from the metal with a higher Fermi level to the metal with a lower Fermi level under the driving of the contact potential difference until the Fermi levels of the two phases are the same. If the two metals are connected to a parallel plate capacitor, the equal and opposite charges generated by the difference in electron work function will gather on the parallel plates. When an external voltage is applied to the capacitor, the charges on the parallel plates disappear when the external voltage is equal to the contact potential difference. This voltage is the potential difference between the two different metals, and if the electron work function of one of the metals is known, the electron work function of the other metal phase can be obtained. This method of measuring the electron work function through the potential difference is commonly known as the Kelvin method. Therefore, the Kelvin method can be used to realize the high-throughput characterization of the electron work function of the amorphous alloy thin film sample database with different chemical compositions. SUMMARY

[0008] The present application provides a method for rapidly developing amorphous thin film materials with high fracture toughness. Compared with the nanoindentation method for testing fracture toughness on a large area, the Kelvin measurement method is more time-saving and labor-saving. For example, for 30 test points, potential measurement is only needed for 3-5 minutes, and 30 groups are completed in about 2 hours, which is nearly 10 times more efficient than the nanoindentation method. Moreover, the potential measurement does not damage the sample surface, which further ensures the integrity of the sample surface and can be further tested for other properties.

[0009] A method for rapidly developing amorphous thin film materials with high fracture toughness, comprising:

[0010] A physical vapor deposition (PVD) co-sputtering method is used to deposit corresponding alloy elements on a substrate based on different element targets to obtain a sample library containing multiple amorphous thin films with different element compositions;

[0011] Kelvin probe force microscopy (KPFM) is used to perform potential testing to characterize the surface potential distribution of each amorphous thin film in the sample library, and obtain the surface potential difference of each amorphous thin film. The surface potential difference obtained is used to calculate the electron work function of the surface of each amorphous thin film;

[0012] The composition of the amorphous thin film with the largest electronic work function is the composition of the amorphous thin film with the largest fracture toughness in the sample library, and the amorphous thin film material with large fracture toughness is developed according to the composition.

[0013] The present application can determine the electronic work function information of the amorphous alloy thin film sample database by measuring the potential difference database of the amorphous alloy thin film sample database with different chemical compositions, screen out the amorphous alloy chemical composition with large electronic work function, that is, the amorphous alloy chemical composition with large fracture toughness, and further, the fracture toughness can be verified by the measurement method based on the nanoindentation energy conversion method.

[0014] The method for rapidly developing the amorphous thin film material with large fracture toughness can set multiple potential test points on the surface of the sample library, for example, including: dividing the surface of the sample library into multiple horizontal regions, dividing multiple sub-regions in any one or more horizontal regions, and selecting potential test points from each sub-region. By setting the sub-regions, the coordinate points on the surface of the sample library can be determined, so that the potential, alloy element content and subsequent fracture toughness value can be accurately corresponded. Each sub-region contains an amorphous thin film.

[0015] The surface potential distribution of each amorphous thin film of the sample library is characterized by the Kelvin probe force microscope for potential test, and the surface potential difference of each amorphous thin film can include: obtaining the potential difference distribution image of each amorphous thin film and the Kelvin probe, and obtaining the average potential difference between each amorphous thin film and the Kelvin probe through image processing as the surface potential difference.

[0016] The electronic work function can be obtained by the following formula:

[0017]

[0018] Wherein, And The work functions of the Kelvin probe and the amorphous thin film are respectively, e represents the electric charge, V CPD represents the surface potential difference.

[0019] The scanning range of the Kelvin probe force microscope for potential test in the method for rapidly developing the amorphous thin film material with large fracture toughness can be 50 microns, and the scanning rate can be 0.9 Hz.

[0020] The probe model used by the Kelvin probe force microscope in the method for rapidly developing the amorphous thin film material with large fracture toughness can be SCM-PIT-V2, and the needle tip radius can be 25 nm.

[0021] The roughness of the amorphous thin film in the method for rapidly developing the amorphous thin film material with large fracture toughness is preferably less than 5 nm, and the thickness can be 50 nm to 10 microns.

[0022] The method for rapidly developing the amorphous thin film material with high fracture toughness, the amorphous thin film can be a Zr-Co-Al ternary amorphous alloy thin film.

[0023] The method for rapidly developing the amorphous thin film material with high fracture toughness can perform the indentation test on each indentation test point by using the nanoindentation continuous stiffness method, obtain the fracture toughness value of each indentation test point based on the indentation test result by using the nanoindentation energy conversion formula, and further match and verify the surface potential distribution of the obtained thin film with the fracture toughness value.

[0024] Further, a plurality of indentation test points corresponding to the amorphous thin films respectively can be set on the surface of the sample library.

[0025] The indentation test result can be the sample elastic modulus and the load-displacement curve, and the irreversible energy, the total energy, the maximum indentation depth and the indentation depth after unloading can be obtained through the load-displacement curve.

[0026] When the indenter used in the nanoindentation continuous stiffness method is a diamond indenter, the fracture toughness value K c of each indentation test point obtained based on the indentation test result by using the nanoindentation energy conversion formula is:

[0027]

[0028] wherein, U i is the irreversible energy, U e is the reversible energy, U i + U e is the total energy, U p is the plastic energy, is the contact area, h m is the maximum indentation depth, h f is the indentation depth after unloading, E s is the elastic modulus of the amorphous thin film, V s is the Poisson's ratio of the amorphous thin film, E i is the elastic modulus of the indenter, V i is the Poisson's ratio of the indenter.

[0029] In an embodiment, the parameters of the indentation test can be: the indentation depth is 1 / 9 of the thickness of the alloy in the sample library, there is no fixed indentation rate, the indentation load is 0 Newton, and the holding time is 10 seconds.

[0030] The nanoindentation indenter used in the indentation test can be any one of a Berkovich indenter, a Vickers indenter and a Berkovich indenter.

[0031] In some embodiments, the method for rapidly developing large fracture toughness amorphous thin film material, the physical vapor deposition co-sputtering method based on different element targets on the substrate to deposit corresponding alloy elements to obtain a sample library containing a plurality of amorphous thin films with different element compositions can comprise: by adjusting the sputtering power and / or sputtering angle of different element targets, depositing elements with different atomic ratios on the substrate to obtain a sample library.

[0032] The substrate material of the method for rapidly developing large fracture toughness amorphous thin film material can be any one of single crystal silicon, quartz, and the like. The purpose of selecting the substrate material is to ensure that the prepared sample has smooth and flat properties, and meets the mechanical property test conditions.

[0033] The physical vapor deposition co-sputtering can be any one of magnetron sputtering, evaporation, ink printing, and the like, and is not limited thereto.

[0034] As a general inventive concept, the present application also provides a large fracture toughness Zr-Co-Al ternary amorphous alloy thin film material, which has a composition of Zr 33 Co 63 Al4.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] The present application sets multiple test points in the prepared amorphous thin film sample library, measures the potential difference of each test point using a Kelvin probe, further calculates the electron work function, and can obtain the fracture toughness of each indentation test point using the nano-continuous stiffness method and the nano-indentation energy conversion formula for verification. Based on the set test points, the electron work function of different regions (different amorphous thin films) in the sample library is one-to-one corresponding to the measured fracture toughness, so as to verify that the surface work function size obtained by testing can reflect the fracture toughness value, that is, a method for rapidly developing large fracture toughness amorphous thin film material can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A device structure schematic diagram of physical vapor deposition co-sputtering deposition sample library is provided for the specific embodiments of the present application;

[0038] Figure 2 A different element spatial distribution diagram of the thin film sample library prepared in the embodiments of the present application;

[0039] Figure 3 A distribution schematic diagram of 8 circular sub-regions on the sample library provided in the embodiments of the present application;

[0040] Figure 4A flowchart of a process for performing potential testing is provided for the embodiments of the present application.

[0041] Figure 5 A distribution map of surface potential difference of the sample library with respect to element composition is provided for the embodiments of the present application.

[0042] Figure 6 A distribution map of work function of the sample library with respect to element composition is provided for the embodiments of the present application.

[0043] Figure 7 A flowchart of a process for performing indentation testing is provided for the embodiments of the present application.

[0044] Figure 8 A distribution map of fracture toughness of the sample library with respect to element composition is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0045] The present application will be further described with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The operation methods not specified in the following embodiments are usually performed according to the conventional conditions or the conditions suggested by the manufacturers.

[0046] A method for rapidly developing a large fracture toughness amorphous thin film material, comprising the steps of:

[0047] 1) obtaining a substrate and at least two target materials capable of forming an alloy.

[0048] 2) using a physical vapor deposition co-sputtering technique to deposit alloy elements with different atomic ratios on the surface of the substrate, thereby forming a sample library, the surface elements of the sample library being arranged in a gradient, and each position on the sample surface being represented by horizontal and vertical coordinates.

[0049] In implementation, the composition gradient is arranged in terms of atomic percentage of different elements. Taking a zirconium-cobalt-aluminum ternary alloy as an example, the alloy composition is: Zr (33%-41%), Co (56%-63%), and Al (3%-4%). Among them, the percentage of each element is atomic percentage.

[0050] 3) Based on the horizontal and vertical coordinates of the surface of the sample library, a plurality of sub-regions are set, and the content of alloy elements corresponding to each sub-region is measured by energy dispersive spectroscopy.

[0051] 4) The above sample library is divided into a plurality of circular regions arranged according to element composition. Kelvin probe measurement is performed on each region to obtain the potential difference V CPD , and the electron work function is calculated by formula (1) introduced above, and the chemical composition with the maximum electron work function, i.e., the chemical composition with the maximum fracture toughness, is screened out.

[0052] 5) Nanoindentation test is performed on each region to obtain the load-displacement curve, elastic modulus of the corresponding region, and the fracture toughness is calculated according to the fracture toughness energy conversion formula (2)-(4) for verification.

[0053] Example 1

[0054] 1. Preparation of Zr-Co-Al ternary alloy sample library:

[0055] The sample library is synthesized by physical vapor deposition co-sputtering deposition, and pure zirconium (C target), cobalt (B target) and aluminum (A target) metals are used, wherein, as shown in Figure 1 , the pure zirconium (C target), cobalt (B target) and aluminum (A target) are respectively at an angle of 60 degrees with the substrate. By adjusting the sputtering power of each target, the A target is 50W, the B target is 70W, and the C target is 120W. The sputtering parameters provided by the embodiment of the present application are that the basic pressure in the chamber is less than 10 -5 Pa, the working pressure is 0.35 Pa, and the flow rate of argon is 30 standard cubic centimeters per minute (SCCM). The deposition is performed for 180 minutes.

[0056] The alloy element content of the indentation test points in the deposited sample library is measured by energy dispersive spectroscopy (EDS) analysis. In order to meet the premise of mechanical property test, atomic force microscopy (AFM) is used for measurement, and the roughness of the sample library is about 0.516 nanometers, and the thickness is about 900 nanometers. Figure 2 The chemical composition gradient coverage range chart of the sample library prepared in this embodiment is shown in Figure 2 , the zirconium is 33-41 at.%, the cobalt is 56-63 at.%, and the aluminum is 3-4 at.%.

[0057] The method for dividing circular sub-regions on the surface of the high-throughput sample library provided by the present application is: dividing the high-throughput sample library into 8 circular sub-regions with a diameter of 4 millimeters, and the center distance of 2 adjacent circular sub-regions is 10 millimeters. And taking the lowest sub-region as the coordinate origin, a coordinate system is established. As shown in Figure 3 .

[0058] 2. Kelvin probe measurement is performed, and the test principle is shown in Figure 4 .

[0059] 2.1. Before testing the sample, the probe work function value is measured first, and the gold standard sample with a known electron work function of 5.1ev is fixed on the sample stage first.

[0060] 2.2. The sample library surface is observed to be smooth and flat through the lens, and it is ensured that the probe can normally test.

[0061] 2.3, Adjust the test parameters, scan range 50 microns, scan rate 0.9HZ, the probe type used is SCM-PIT-V2, needle tip radius 25nm.

[0062] 2.4, The potential difference between the gold standard sample and the probe is 0.4V, and the electronic work function of the probe is calculated by the formula 5.5eV:

[0063] 2.5, Take out the standard sample, and then place the sample library obtained in step 1 on the AFM sample stage, so as to fix it on the test platform to avoid sample sliding during testing.

[0064] 2.6, The potential measurement of the sample library is carried out in accordance with the potential test parameters of the standard sample.

[0065] 2.7, As shown in Figure 4 , the potential distribution of a sub-region of the measured sample library is shown, and the average potential difference of each sub-region is summarized as shown in Table 1.

[0066] Table 1 Average potential difference (V) of different test points in sub-regions

[0067] Sub-region center coordinates Potential difference Sub-region center coordinates Potential difference (0,0) 0.741 (0,16) 0.972 (-6,8) 0.869 (12,16) 0.0807 (6,8) 0.131 (-6,24) 0.0507 (-12,16) 0.766 (6,24) 0.5955

[0068] 2.8, The corresponding electronic work function value is calculated by formula (1), as shown in Table 2.

[0069] Table 2 Electronic work function values (eV) of different sub-regions

[0070] Sub-region center coordinates Work function Sub-region center coordinates Work function (0,0) 4.759 (0,16) 4.528 (-6,8) 4.631 (12,16) 5.4193 (6,8) 5.369 (-6,24) 5.4493 (-12,16) 4.734 (6,24) 4.9045

[0071] 2.9, The surface potential difference of each sub-region is counted, and the surface potential distribution map of the sample library is obtained by integrating the data, as shown in Figure 5 , the height represents the size of the potential difference, the higher the height, the larger the potential difference. The corresponding electronic work function value is shown in Figure 6 .

[0072] 3, Perform fracture toughness testing, as shown in Figure 7 .

[0073] 3.1, Place the high-throughput sample library obtained in step 1 on the nanoindentation tester, so as to fix it on the test platform to avoid sample sliding during testing.

[0074] 3.2, The surface of the sample library is observed to be smooth and flat by the nanoindentation instrument, ensuring that the mechanical property test is carried out normally.

[0075] 3.3. Adjust the test parameters to a surface approach speed of 10 nm / s, a dwell time of 10 s, and a Poisson's ratio of 0.367. Using the continuous stiffness method, with a film thickness of 900 nm and a fixed indentation depth of 100 nm, perform an indentation test at each indentation test point and record the load-displacement curve for each indentation. The hardness was 5.5 GPa and the elastic modulus was 60 GPa.

[0076] 3.4、If Figure 7 Based on the load-displacement curve of the indentation shown, the fracture toughness at different indentation test points is calculated according to the fracture toughness energy conversion formula (2) based on the hardness and elastic modulus obtained in step 3.3. The fracture toughness of the three indentation test points in each sub-region is selected by comparing the elastic modulus obtained by nanoindentation with the reference value (the reference value of the elastic modulus of the ZrCoAl alloy component in this case is 50-80 GPa), determining the correct value of this data point, and then calculating the average value as the fracture toughness value of the region. The selection is shown in Table 3.

[0077] Table 3 Fracture toughness of different sub-regions (MPa*m 1 / 2 )

[0078] Sub-region center coordinates Fracture toughness Sub-region center coordinates Fracture toughness (0,0) 65.46906 (0,16) 54.11313 (-6,8) 58.84426 (12,16) 67.26393 (6,8) 70.28544 (-6,24) 77.96924 (-12,16) 61.60763 (6,24) 59.74915

[0079] 3.5. Count the fracture toughness values ​​of each sub-region and obtain the distribution diagram of the fracture toughness values ​​of the high sample library by integrating the data. The height represents the size of the fracture toughness. The higher the height, the better the fracture toughness. Figure 8 shown.

[0080] 4. Match the work function value and fracture toughness value of each test point to verify and determine the component with high fracture toughness.

[0081] The potential difference at the coordinate (-6,24) of the sample library is 0.0507V, and the work function is 5.4493eV, which is the highest work function. Figure 2 It can be seen that when the coordinates of the high-throughput sample library are (-6,24), the content of alloy elements is Zr 33 Co 63 Al4 (at.%),

[0082] The fracture toughness value at the coordinate (-6,24) of the sample library is 77.96924MPa*m 1 / 2 , the fracture toughness is the largest, from Figure 2 It can be seen that when the coordinates of the sample library are (-6,24), the content of alloy elements is Zr 33 Co 63 Al4 (at.%), the composition is the same as the composition at the highest electron work function selected above. Therefore, the alloy in this sample library is Zr33 Co 63 The electronic work function is highest and the fracture toughness is best when Al4(at.%) is 0.5. That is, the composition with the maximum work function can be found by measuring the potential difference of the sample by KPFM, so as to obtain the material with large fracture toughness, and the development is completed.

[0083] In addition, it should be understood that, after reading the above description of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application.

Claims

1. A method for rapidly developing amorphous thin film materials with high fracture toughness, characterized in that: include: A sample library containing multiple amorphous films with different elemental compositions is obtained by depositing corresponding alloy elements on a substrate using a physical vapor deposition co-sputtering method based on different elemental targets; The amorphous film is a Zr-Co-Al ternary amorphous alloy film; A Kelvin probe force microscope was used to perform potential testing to characterize the surface potential distribution of each amorphous film in the sample library, and the surface potential difference of each amorphous film was obtained. The obtained surface potential difference was used to calculate the electron work function of each amorphous film surface; the electron work function was calculated using the following formula: in, and are the work functions of the Kelvin probe and the amorphous film, respectively, e represents the charge, V CPD represents the surface potential difference; The composition of the amorphous film with the largest electron work function is the composition of the amorphous film with the largest fracture toughness in the sample library. Based on this composition, amorphous film materials with high fracture toughness are developed.

2. The method for rapidly developing amorphous thin film materials with high fracture toughness according to claim 1, characterized in that: The potential test is performed using a Kelvin probe force microscope to characterize the surface potential distribution of each amorphous film in the sample library, and obtaining the surface potential difference of each amorphous film includes: obtaining a potential difference distribution image between each amorphous film and the Kelvin probe, and obtaining the average potential difference between each amorphous film and the Kelvin probe through image processing as the surface potential difference.

3. The method for rapidly developing amorphous thin film materials with high fracture toughness according to claim 1, characterized in that: The parameters of the potential test using Kelvin probe force microscope are: scanning range 50 μm, scanning rate 0.9 Hz.

4. The method for rapidly developing amorphous thin film materials with high fracture toughness according to claim 1, characterized in that: The probe model used in the Kelvin probe force microscope is SCM-PIT-V2, with a tip radius of 25 nm.

5. The method for rapidly developing amorphous thin film materials with high fracture toughness according to claim 1, characterized in that: The roughness of the amorphous film is less than 5 nanometers and the thickness is 50 nanometers to 10 micrometers.

6. A Zr-Co-Al ternary amorphous alloy thin film material with high fracture toughness, characterized in that: In terms of atomic percentage, the composition of the high fracture toughness Zr-Co-Al ternary amorphous alloy film material is Zr 33 Co 63 Al4.

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