AlScN piezoelectric coating materials with high mechanical properties and high temperature resistance, their preparation methods and applications

Abstract

This invention provides a method for preparing an AlScN piezoelectric coating material with high mechanical properties and high temperature resistance. The method includes: using an alloy target composed of Al and Sc, forming an AlScN piezoelectric functional layer on a substrate surface via magnetron sputtering; and controlling the volume ratio of argon to nitrogen, temperature, sputtering power, deposition pressure, and target-substrate distance during magnetron sputtering to allow the AlScN piezoelectric functional layer to grow in multiple orientations during deposition. The AlScN piezoelectric coating material obtained by this invention exhibits excellent mechanical properties, temperature resistance, and corrosion resistance. When deposited on a substrate, this coating material can simultaneously generate longitudinal waves, longitudinal and transverse waves, and transverse waves to achieve defect detection and stress measurement in steel plates, welds, and steel pipes in various media. Furthermore, it exhibits long-term stable service capability under high temperature and harsh operating conditions without the need for a protective layer, meeting long-term usage requirements, facilitating mass production, and possessing promising prospects for promotion and application.

Description

Technical Field

[0001] This invention belongs to the field of coating materials technology, specifically relating to an AlScN piezoelectric coating material with high mechanical properties and high temperature resistance, and its preparation method, as well as the application of an AlScN piezoelectric coating material with the above-mentioned high mechanical properties and high temperature resistance in ultrasonic testing. Background Technology

[0002] Ultrasonic testing, with its advantages of convenience, speed, and non-harmful operation, has become one of the most important methods for inspecting and testing special equipment. Ultrasonic sensors are widely used in defect detection, stress measurement, thickness measurement, and bolt axial force measurement. Taking bolt stress measurement as an example, based on the principle of acoustoelasticity, the propagation speed of ultrasound in a bolt is related to the bolt stress. By observing the propagation time of ultrasound in the bolt, the propagation speed can be determined. A functional relationship between the ultrasound propagation time and the bolt axial stress can be established, and the correlation coefficient in the functional relationship can be obtained through calibration experiments. Therefore, by measuring the propagation time of ultrasound in the bolt, the bolt stress value can be quantitatively measured, thereby judging the health condition of the bolt connection. Ultrasonic testing of preload has advantages such as high accuracy, good real-time performance, and strong penetration. Thin films with piezoelectric effect are simple to prepare, highly stable, and widely applicable, making them very suitable for preload testing. Currently, patch-type ultrasonic stress testing methods have been used for many years, but because piezoelectric wafers are generally bonded to bolts with epoxy resin or adhesives, they are prone to detachment. Furthermore, the thickness of the adhesive layer cannot be measured, significantly affecting the testing accuracy.

[0003] However, existing ultrasonic sensors are mainly suitable for ambient temperature environments (<100℃). With the increasing demand for high-parameterization in high-temperature and high-pressure special equipment, ultrasonic detection under high-temperature conditions is gaining attention, necessitating the development of high-temperature resistant ultrasonic sensors. The main challenges in developing ultrasonic sensors for high-temperature conditions include: the Curie temperature limitation of piezoelectric wafers. Traditional PZT materials have low Curie temperatures, making them unsuitable for use as high-temperature probes. Furthermore, high-temperature piezoelectric films are prone to cracking and detachment from the substrate under repeated high and low temperature conditions and long-term use. Improving the bonding force between the piezoelectric film and the substrate material is crucial for stable sensor operation. Simultaneously, matching and backing materials prepared using polymers are not heat-resistant. The development of high-temperature and corrosion-resistant ultrasonic sensors for use in special equipment, where operating temperatures can reach up to 400℃, requires the selection and development of environmentally suitable sensor components and their assembly processes with the substrate.

[0004] Currently, the main piezoelectric materials that can be used to excite ultrasound are ZnO and AlN. Both of these materials have a hexagonal wurtzite structure, and their piezoelectric performance depends entirely on their crystal orientation without polarization. Compared to ZnO and AlN piezoelectric materials, Sc-doped AlN has superior piezoelectric performance and a larger piezoelectric coupling coefficient. However, Sc doping leads to a significant increase in stress in the AlN coating, which can easily cause cracking, peeling, and other issues, resulting in piezoelectric coating failure.

[0005] Based on this, a piezoelectric coating material is provided that simultaneously possesses high mechanical properties, high temperature resistance, high corrosion resistance, strong adhesion to the substrate, and the ability to generate different ultrasonic waves according to application requirements. This material is not only of great significance for achieving high-precision and high-efficiency measurement of bolt preload, as well as defect detection and stress measurement of substrates such as steel plates, welds, and steel pipes, but also prevents the piezoelectric coating from peeling off, avoids corrosion of the steel substrate and bolt materials caused by the use of coupling agents, and extends the service life of equipment. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing an AlScN piezoelectric coating material with high mechanical properties, high temperature resistance, high corrosion resistance, stronger adhesion to the substrate, and the ability to generate different ultrasonic waves.

[0007] The second objective of this invention is to provide an AlScN piezoelectric coating material with high mechanical properties, high temperature resistance, high corrosion resistance, stronger adhesion to the substrate, and the ability to generate different ultrasonic waves.

[0008] A third objective of this invention is to provide an application of a high-mechanical-performance AlScN piezoelectric coating material in measuring substrate preload.

[0009] One of the technical solutions adopted to achieve the objective of this invention is: to provide a method for preparing an AlScN piezoelectric coating material with high mechanical properties, comprising: using an alloy target composed of Al and Sc, and forming an AlScN piezoelectric functional layer on the substrate surface by magnetron sputtering;

[0010] In the magnetron sputtering process, the temperature is 100–250°C, a mixed gas of argon and nitrogen with a volume ratio of 3:1 to 1:3 is introduced, the sputtering power is 700–900W, the deposition pressure is P = 0.4–3.0Pa, the target-substrate distance is d = 40–80mm, and the deposition time is 3–10h.

[0011] In the above preparation method, an AlScN piezoelectric functional layer is prepared by radio frequency magnetron sputtering. The sputtering temperature is controlled at 100–250°C. Increasing the temperature allows the particles to have higher energy, ensuring that the particles have sufficient energy to migrate to the surface of the substrate and deposit the AlScN coating. Controlling the volume ratio of argon and nitrogen allows control of the atomic percentage of Al, Sc, and N particles in the vacuum chamber, which can adjust the collision probability between particles and the growth orientation of the coating. Using a sputtering power of 700–900 W allows adjustment of the energy level of the particles and control of the coating thickness. Controlling the deposition gas pressure (pressure after the reaction gas is introduced into the vacuum chamber) P = 0.4–3.0 Pa and the target-substrate distance (vertical distance between the target and the substrate) d = 40–80 mm allows adjustment of the mean free path of Al, Sc, and N particles, enabling the preparation of AlScN coatings with various orientations within this deposition range. Under the above preparation conditions, AlScN piezoelectric functional layers with high hardness, high wear resistance, high corrosion resistance, and strong bonding ability with the substrate can be prepared.

[0012] Preferably, the temperature of the magnetron sputtering is 150–250°C.

[0013] Furthermore, before the magnetron sputtering, a vacuum process is performed to ensure that the vacuum level does not exceed 7 × 10⁻⁶. -3 Pa.

[0014] Further, the alloy target material is composed of 60 wt.% to 90 wt.% Al and 10 wt.% to 40 wt.% Sc. Preferably, the alloy target material is composed of 70 wt.% Al and 30 wt.% Sc.

[0015] Furthermore, the alloy target has a diameter of 140–160 mm and a thickness of 4–8 mm. In this invention, there is a certain correlation between the target diameter, thickness, and magnetron sputtering power. This application uses a larger diameter target in conjunction with higher sputtering power, enabling the simultaneous preparation of more samples during coating deposition, resulting in higher deposition efficiency, easier mass production, and easier widespread application.

[0016] Furthermore, the growth orientation of the AlScN piezoelectric functional layer on the substrate surface includes (002) diffraction planes and / or (103) diffraction planes.

[0017] Research has shown that, in this invention, by adjusting the deposition parameters during the magnetron sputtering process, including the deposition gas pressure and the target-substrate distance, the AlScN piezoelectric functional layer can exhibit multiple growth orientations on the substrate surface, which can excite various ultrasonic wave patterns. Therefore, AlScN piezoelectric coating materials capable of exciting different ultrasonic waves can be prepared according to detection requirements.

[0018] Preferably, when the deposition pressure P = 0.4 Pa and the target-substrate distance is 55 mm, the coating exhibits a (103) diffraction crystal plane.

[0019] Preferably, when the deposition pressure P = 0.6 Pa and the target-substrate distance is 55 mm ≤ d ≤ 60 mm, the coating exhibits a preferred growth of (002) diffraction crystal planes. The cross-sectional morphology of the AlScN piezoelectric functional layer prepared under these conditions is a columnar crystal structure perpendicular to the substrate, exhibiting higher hardness and wear resistance.

[0020] Correspondingly, except for the special conditions mentioned above, for example, in the magnetron sputtering, when the target-substrate distance is 55mm≤d≤60mm, the deposition gas pressure is controlled to be P≠0.6Pa and P≠0.4Pa; or when P=0.6Pa, the target-substrate distance is controlled to be 40mm≤d<55mm or 60mm<d≤80mm, the AlScN piezoelectric functional layer can exhibit multi-oriented growth on the substrate surface.

[0021] Preferably, in the magnetron sputtering, the temperature is 100–250°C, a mixture of argon and nitrogen in a volume ratio of 1:1 is introduced, the sputtering power is 700–900 W, the deposition pressure is P = 1.0–2.0 Pa, the target-substrate distance is d = 50–70 mm, and the deposition time is 3–10 h. In this case, the AlScN piezoelectric functional layer exhibits typical multi-oriented growth on the substrate surface, including (002) crystal planes and (103) diffraction crystal planes.

[0022] Under the above conditions, the AlScN piezoelectric coating material prepared by this invention can emit a combined longitudinal and transverse wave when excited. Numerous studies have shown that when using a combined transverse and longitudinal wave method to detect stress, besides constants related to the material's properties and geometry, only the flight time of the longitudinal and transverse waves and the initial temperature under bolt unloaded conditions need to be measured. Then, by simultaneously solving an eighth-order polynomial, the real-time bolt load can be obtained without calibrating the original stress. This method reduces the number of compensation factors, simplifies the detection steps, reduces errors in the conversion calculation between ultrasonic signals and stress, and improves measurement accuracy.

[0023] Furthermore, the thickness of the AlScN piezoelectric functional layer is 5–20 μm. AlScN piezoelectric functional layers prepared using conventional methods often suffer from cracking and peeling due to the increased stress caused by Sc doping in the AlN coating. Excessive coating thickness can easily lead to failure. Therefore, the thickness of the AlScN piezoelectric functional layer needs strict control (typically less than 5 μm). In contrast, this invention optimizes various parameters in the preparation method, improving both the hardness and wear resistance of the AlScN piezoelectric functional layer itself, while also significantly enhancing the adhesion between the coating and the substrate. This meets the requirements for preparing thicker AlScN piezoelectric functional layers, resulting in superior ultrasonic excitation performance and enabling the excited ultrasonic waves to have a larger amplitude.

[0024] Furthermore, the preparation method includes: first depositing a bonding layer on the substrate surface, then preparing an AlScN piezoelectric functional layer on the bonding layer surface, and finally preparing an electrode layer on the AlScN piezoelectric functional layer surface. The bonding layer increases the adhesion between the substrate and the coating, preventing cracking and peeling of the coating during long-term use. The electrode layer provides an external electrode for the bolt, allowing a stable voltage to be applied across the bolt, which can then generate ultrasonic waves. The bonding layer is made of Cr, and the electrode layer can be made of Cr, Ti, Ag, or Ag-Cr.

[0025] Preferably, the preparation method of the present invention may include the following steps:

[0026] S1. Plasma etching is performed on the substrate surface at 100–250°C in an argon atmosphere.

[0027] S2. A Cr bonding layer is deposited on the surface of the substrate after plasma etching at 0.5-1 Pa and 50-250 V;

[0028] S3. An AlScN piezoelectric functional layer is formed by magnetron sputtering of an alloy target composed of Al and Sc onto the surface of the Cr bonding layer.

[0029] S4. On the surface of the AlScN piezoelectric functional layer, under the conditions of vacuum degree of 0.25 to 1 Pa, bias voltage of 0 to 100 V and current of 0 to 80 A, an electrode layer is deposited. The electrode layer material is selected from one of Cr, Ti, Ag, and Ag-Cr, thus completing the preparation of the AlScN piezoelectric coating material.

[0030] The technical solution adopted to achieve the second objective of this invention is to provide an AlScN piezoelectric coating material prepared by the preparation method described in the first objective of this invention.

[0031] The AlScN piezoelectric coating material consists of a bonding layer, an AlScN piezoelectric functional layer, and an electrode layer. The AlScN piezoelectric coating material obtained by this invention possesses excellent mechanical properties, temperature resistance, and corrosion resistance, and can meet the requirements for long-term use in harsh working conditions and high-temperature environments without the need for a protective layer.

[0032] Furthermore, the AlScN piezoelectric functional layer has a hardness greater than 15 GPa, a bonding strength with the substrate greater than 10 MPa, and an operating temperature range of -196 to 700℃.

[0033] The technical solution adopted to achieve the third objective of this invention is: to provide an application of the high mechanical properties AlScN piezoelectric coating material as described in the second objective of this invention, wherein the AlScN piezoelectric coating material excites various ultrasonic waves for use in bolt preload detection, or for defect detection and stress measurement of steel plates, welds, and steel pipes.

[0034] In some preferred embodiments, the AlScN piezoelectric coating material substrate is a smart bolt. According to the preparation method provided by this invention, a bonding layer, an AlScN piezoelectric functional layer, and an electrode layer are sequentially deposited on the surface of the smart bolt. Based on the specific requirements of bolt preload measurement, relevant parameters in the AlScN piezoelectric coating material preparation method are specifically adjusted so that the smart bolt with the piezoelectric coating material on its surface can generate different waveforms (longitudinal waves, transverse waves, or both). These features simplify the bolt preload calculation steps, improve measurement accuracy, and the piezoelectric coating of the smart bolt has advantages such as high mechanical properties, good temperature resistance, and stronger adhesion to the bolt substrate, which can broaden its operating temperature range and extend the service life of the smart bolt.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) This invention provides a method for preparing an AlScN piezoelectric coating with high mechanical properties and high temperature resistance. The AlScN piezoelectric coating is prepared using radio frequency magnetron sputtering. By adjusting different gas pressures and the distance between the target and the substrate, piezoelectric coating materials that can simultaneously generate different waveforms can be obtained, enabling precise measurement of bolt preload. Furthermore, the AlScN piezoelectric coating prepared by this invention also possesses high hardness, high wear resistance, and high corrosion resistance, eliminating the need for additional protective layer deposition. The preparation process is simple and efficient. Moreover, the equipment required for this piezoelectric coating preparation method is similar to existing industrial equipment, making industrial mass production easily achievable and achieving high processing efficiency, which can significantly reduce manufacturers' production costs.

[0037] (2) The AlScN piezoelectric coating material prepared by this invention uses AlScN coating with high piezoelectric coefficient, high electromechanical coupling coefficient and low epitaxial growth temperature, making it applicable to various substrate materials with large sound attenuation coefficients. The AlScN piezoelectric coating material has a hardness greater than 15 GPa, a bonding strength with the substrate greater than 10 MPa, and an operating temperature range of -196 to 700℃. It also has high wear resistance and corrosion resistance, which can ensure that the piezoelectric coating can work stably on the surface of various alloy bolts for a long time, reduce the possibility of failure, and meet the application and testing requirements under harsh working conditions.

[0038] (3) The present invention deposits an AlScN coating material with high mechanical strength, high temperature resistance and high wear resistance on the substrate surface. The AlScN coating material serves as an acoustic-electric conversion layer for exciting ultrasound, enabling non-destructive testing technology. In addition, the AlScN coating material can simultaneously emit longitudinal and transverse waves under ultrasonic excitation, enabling high-precision (error less than 5%) and high-efficiency measurement of the preload of smart bolts. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall structure of the apparatus for preparing AlScN piezoelectric coating materials according to an embodiment of the present invention;

[0040] Figure 2 The XRD patterns of AlScN piezoelectric functional layers deposited under different gas pressure conditions in Examples 1-5 of this invention are shown.

[0041] Figure 3 The images show the surface and cross-sectional morphology of the AlScN piezoelectric coatings obtained under different deposition distance conditions in Examples 2, 14, and 15 of this invention.

[0042] Figure 4 The figures show the hardness data of AlScN piezoelectric functional layers obtained under different air pressure conditions in Examples 1, 2, and 5 of this invention, obtained through nanohardness tests; where (a) represents hardness and elastic modulus; and (b) represents H / E and H. 3 / E 2 ;

[0043] Figure 5 The image shows an SEM image of the AlScN piezoelectric functional layer prepared under a deposition pressure of 0.6 Pa in Example 2 of this invention, obtained by tribological testing.

[0044] Figure 6 The waveforms of different ultrasonic waves generated by the AlScN piezoelectric functional layers obtained under different air pressure conditions in Examples 1-5 of the present invention are shown.

[0045] Figure 7The ultrasonic waveforms of AlScN piezoelectric coatings obtained under different deposition time conditions in Examples 2, 11, and 13 of this invention are shown.

[0046] Figure 8 The XRD patterns and ultrasonic waveforms of AlScN piezoelectric functional layers obtained in Example 2 of this invention under a deposition pressure of 0.6 Pa and annealed at 600 °C for different times are shown; where (a) is the XRD pattern and (b) is the ultrasonic waveform.

[0047] Figure 9 The images show the morphology of AlScN piezoelectric functional layers obtained in Example 2 of this invention under a deposition pressure of 0.6 Pa after annealing at 600°C for different times.

[0048] Figure 10 The ultrasonic waveform of the smart bolt was prepared under the conditions of deposition pressure of 0.6 Pa, deposition distance of 60 mm, and deposition time of 7 h as an application example of the present invention.

[0049] Among them, 1-RF magnetron sputtering (RF); 2-Al-Sc alloy target; 3-bolt sample; 4-etching source; 5-sample holder; 6-workpiece holder; 7-heater; 8-exhaust port; 9-furnace door. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0052] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0053] The main parameters involved in the preparation of the AlScN piezoelectric functional layer in various embodiments of the present invention are shown in Table 1 below.

[0054] Table 1

[0055]

[0056] Figure 1The apparatus shown is the device used in this invention. The vacuum chamber of the apparatus is enclosed by the furnace wall, and the dimensions of the vacuum chamber are 400x400x400mm. The vacuum chamber is equipped with an evacuation port 8, through which the vacuum pump unit evacuates the vacuum chamber. The upper two corners of the vacuum chamber are heaters 7, with a heating power of 25 kW, improving heating efficiency; the lower two corners of the vacuum chamber are etching sources 4, which can remove impurities from the substrate surface, ensuring the cleanliness of the substrate surface. The Al-Sc alloy target 2 is mounted on the furnace wall and connected to the radio frequency magnetron sputtering (RF) unit 1, allowing adjustment of the sputtering power. The back of the Al-Sc alloy target 2 faces the furnace door 9, and its front is the sample 3, which is placed on a sample holder 5, which is mounted on a workpiece holder 6. This layout significantly increases the plasma density in the vacuum chamber, completely immersing the workpiece in the plasma. This greatly improves the coating deposition rate, hardness, and adhesion. Due to the optimized target structure, the magnetic field distribution is more uniform, resulting in uniform etching of the magnetron sputtering target surface and improving the uniformity of the coating.

[0057] Example 1

[0058] The AlScN piezoelectric functional layer was prepared on stainless steel and Si substrates. The specific preparation method is as follows:

[0059] The substrate surface is pretreated to remove impurities. The vacuum chamber temperature is adjusted to 150℃, and a vacuum of 3×10⁻⁶ is applied. -3 Pa, using an Al-Sc alloy target (composed of 70 wt.% Al and 30 wt.% Sc), with the substrate surface aligned with the center of the target and the target-substrate distance adjusted to 55 mm, deposited an AlScN piezoelectric functional layer on the substrate surface using magnetron sputtering.

[0060] During the magnetron sputtering process, a mixture of argon (99.99% purity) and nitrogen (99.99% purity) in a 1:1 flow ratio is introduced until the gas pressure (deposition pressure) in the cavity is 0.4 Pa. The radio frequency power supply is turned on, the sputtering power is 900 W, and the sputtering time is 5 h, thus depositing an AlScN piezoelectric functional layer on the substrate surface.

[0061] Examples 2-5

[0062] The difference between Examples 2-5 and Example 1 is that the gas pressure inside the cavity is adjusted to 0.6 Pa, 1.0 Pa, 1.5 Pa and 2.0 Pa respectively, while the other conditions remain unchanged, and an AlScN piezoelectric functional layer is deposited on the substrate surface.

[0063] Example 6

[0064] The difference between Example 6 and Example 1 is that the temperature of the vacuum chamber is adjusted to 250°C and the gas pressure inside the chamber is 3.0 Pa, while the other conditions remain unchanged, and an AlScN piezoelectric functional layer is deposited on the substrate surface.

[0065] Examples 7 and 8

[0066] The difference between Examples 7 and 8 and Example 1 is that the vacuum chamber temperature is adjusted to 100°C, the gas pressure inside the chamber is adjusted to 2.0 Pa, and the flow ratio of argon (99.99% purity) and nitrogen (99.99% purity) is adjusted to a mixed gas of 3:1 and 1:3 respectively, while the other conditions remain unchanged, and an AlScN piezoelectric functional layer is deposited on the substrate surface.

[0067] Example 9

[0068] The difference between Example 9 and Example 2 is that the target-substrate distance is adjusted to 50 mm, while other conditions remain unchanged, and an AlScN piezoelectric functional layer is deposited on the substrate surface.

[0069] Example 10

[0070] The difference between Example 10 and Example 1 is that the vacuum chamber temperature was adjusted to 250°C, the gas pressure inside the chamber was adjusted to 2.2 Pa, the target-substrate distance was adjusted to 55 mm, the sputtering power was adjusted to 750 W, and the sputtering time was 10 h, while the other conditions remained unchanged, and an AlScN piezoelectric functional layer was deposited on the substrate surface.

[0071] Example 11

[0072] The difference between Example 11 and Example 2 is that the vacuum level is adjusted to 5×10. -3 Pa, the sputtering time was adjusted to 9h, and all other conditions remained unchanged, to deposit an AlScN piezoelectric functional layer on the substrate surface.

[0073] Example 12

[0074] The difference between Example 12 and Example 2 is that the vacuum chamber temperature is adjusted to 100°C and the vacuum level is adjusted to 4×10⁻⁶. - 3 Pa, with the sputtering time adjusted to 7h, and other conditions remaining unchanged, an AlScN piezoelectric functional layer was deposited on the substrate surface.

[0075] Example 13

[0076] The difference between Example 13 and Example 2 is that the vacuum level is adjusted to 7×10. -3 Pa, with the sputtering time adjusted to 3h, and other conditions remaining unchanged, an AlScN piezoelectric functional layer was deposited on the substrate surface.

[0077] Examples 14 and 15

[0078] The difference between Examples 14 and 15 and Example 2 is that the vacuum level is adjusted to 4 × 10⁻⁶. -3Pa, the target-substrate distance was adjusted to 60 mm and 70 mm, the sputtering time was adjusted to 5 h and 9 h, and the other conditions remained unchanged, and an AlScN piezoelectric functional layer was deposited on the substrate surface.

[0079] Performance testing

[0080] (I) XRD pattern of the coating

[0081] Figure 2 The XRD patterns of AlScN piezoelectric functional layers deposited under different gas pressure conditions in Examples 1-5 of this invention are shown. As can be seen from the figures, when the deposition pressure is 0.4 Pa, the film does not show a (002) diffraction peak, only a (103) diffraction peak, and does not exhibit c-axis preferred orientation growth. This is because the low deposition pressure results in a large mean free path of the particles, leading to higher particle energy. The film surface is bombarded by high-energy Al, Sc, and N particles, damaging the surface structure and altering its growth orientation, resulting in a (103) growth orientation. As the deposition pressure increases to 0.6 Pa, a (002) diffraction peak appears in the XRD pattern of the film, indicating a high c-axis preferred growth orientation. This is because under this deposition pressure, the particles' energy is optimally used for migration and rearrangement, resulting in the most significant c-axis preferred orientation growth of the film. As the sputtering pressure further increases from 1.0 Pa to 2.0 Pa, the grain size on the film surface gradually decreases, and the film shows diffraction peaks of (002) and (103). This is because the lower mean free path results in lower energy of the particles, which causes the grain size of the particles to gradually decrease, resulting in a gradual increase in the intensity of the (002) diffraction peak and a gradual decrease in the intensity of the (103) diffraction peak.

[0082] (II) Surface morphology diagram of the coating

[0083] Figure 3The figures show screenshots of the surface and morphology of the AlScN coatings prepared in Examples 2, 14, and 15 at different target-substrate distances. As can be seen, different target-substrate distances have a significant impact on the surface morphology of the AlScN film. When the deposition pressure is 55 mm, the film exhibits a relatively clear grain size and distinct grain boundaries. As the target-substrate distance increases to 60 mm, the grain size on the film surface increases. This is because, with the increase in target-substrate distance, the deposited grains merge and grow into larger grains. With further increases in target-substrate distance, the kinetic energy of the particles is insufficient to deposit at greater distances, resulting in clustered growth. As the deposition process continues, the number of atoms deposited on the substrate surface increases, and the gaps between clusters are filled, resulting in a "wavy" growth morphology on the film surface. The cross-sectional morphology of the film shows that there are no cracks or fissures between the film and the substrate, indicating good adhesion. When the target-substrate distance is 55 mm, the film exhibits obvious columnar crystal growth. When the target-substrate distance is 70 mm, the columnar crystal structure becomes less obvious, which is due to the growth of its clusters.

[0084] (III) Hardness and wear resistance testing

[0085] Figure 4 The figures show the hardness data of the AlScN piezoelectric functional layers obtained in Examples 1, 2, and 5 of this invention under different air pressure conditions, obtained through nanohardness testing. As can be seen from the figures, the AlScN coatings obtained in Examples 1, 2, and 5 all exhibit high hardness, exceeding 15 GPa. Furthermore, compared to Examples 1 and 5, the AlScN piezoelectric functional layer obtained in Example 2 under an air pressure of 0.6 Pa exhibits significantly higher hardness, reaching 20 GPa.

[0086] Furthermore, Figure 5 The SEM images and elemental composition changes of the AlScN piezoelectric functional layers prepared under deposition gas pressures of 0.4 Pa-2.0 Pa in Examples 1-5 of this invention were obtained by line scanning after a tribological test (loading a 50g Cu-Zn alloy ball for 30 min). The images show that the tribological test did not cause significant wear to the AlScN piezoelectric functional layers prepared in Examples 1-5. Furthermore, the AlScN coating prepared in Example 2 showed the narrowest wear track, indicating that all coatings prepared in Examples 1-5 have good wear resistance, with the AlScN coating prepared in Example 2 exhibiting even stronger wear resistance. In addition, the bonding strength between the AlScN piezoelectric functional layer and the substrate was tested. The test results show that the bonding strength between the AlScN piezoelectric functional layer and the substrate prepared in each embodiment of this invention exceeds 10 MPa.

[0087] (iv) Excitation performance test

[0088] Electrodes were prepared by depositing electrode layers (including Cr, Ag, Ti, Ag-Cr, etc.) on the surface of the AlScN piezoelectric functional layers obtained in Examples 1-5 or by spot coating with silver paste, and the excitation performance was tested.

[0089] Figure 6 The figures show the waveforms of different ultrasonic waves generated by the AlScN piezoelectric functional layers obtained under different gas pressures in Examples 1-5 of this invention. As can be seen from the figures, when the deposition gas pressure is 0.4 Pa, the waveform is mainly a transverse wave (SW); when the deposition gas pressure is 0.6 Pa, the waveform is mainly a longitudinal wave (LW); and when the deposition gas pressure is 1.0–2.0 Pa, a mixed transverse and longitudinal waveform is observed. These various waveforms can meet the requirements for defect detection and stress measurement of steel plates, welds, and steel pipes in solid, liquid, and gaseous media.

[0090] Figure 7 The figures show the ultrasonic waveforms excited by the AlScN piezoelectric coatings obtained under different deposition time conditions in Examples 2, 11, and 13 of this invention. As can be seen from the figures, the increase in deposition time does not change the ultrasonic signal excited by the film. The films all excited ultrasonic longitudinal wave signals, and the amplitude of the ultrasonic signal gradually increases with the increase of deposition time. This is related to the structure of the film being a (002) diffraction crystal plane. Films with (002) diffraction crystal planes can excited ultrasonic longitudinal waves, and the intensity of the (002) diffraction peak gradually increases with the increase of deposition time. Therefore, the ultrasonic signal excited by the prepared AlScN film also gradually increases.

[0091] (V) High Temperature Resistance Test

[0092] Figure 8 The images show the XRD patterns and ultrasonic waveforms of AlScN piezoelectric functional layers obtained in Example 2 of this invention under a deposition pressure of 0.6 Pa, after annealing at 600°C for different times. It is clear from the images that 600°C does not affect the orientation or ultrasonic signal of the samples.

[0093] Figure 9 The figures show the morphology of AlScN piezoelectric functional layers obtained in Example 2 of this invention under a deposition pressure of 0.6 Pa after annealing at 600°C for different times. It can be clearly seen from the figures that 600°C does not damage the surface morphology of the samples.

[0094] The above experimental results show that the AlScN piezoelectric functional layer prepared by the present invention can be used for a long time at high temperatures and can meet the usage requirements in the working temperature range of -196 to 700℃.

[0095] Application examples

[0096] This application example uses a 50mm long high-temperature alloy bolt as the substrate, and deposits an AlScN piezoelectric coating material on its surface to achieve the fabrication of a smart bolt with high mechanical and high-temperature resistance properties that can elicit different ultrasonic waves. The fabrication method of this smart bolt includes the following steps:

[0097] Step 1: Control the distance between the target and the substrate to 40–80 mm, and evacuate to 3 × 10⁻⁶ mm at 100–150 °C. -3 ~7×10 -3 Pa, 50 sccm of argon gas (purity 99.99%) is introduced, the bias voltage and arc power supply are turned on, and plasma etching is performed on the substrate under the conditions of -150V, duty cycle 80%, gas pressure 0.5Pa and current 70A to remove impurities attached to the substrate surface and improve the adhesion between the film and the substrate.

[0098] Step 2: After etching, a bonding layer Cr is prepared on the bolt substrate under the conditions of 0.5-1 Pa and bias voltage of 50-250 V. This can eliminate internal stress and increase the bonding force between the coating and the substrate. The thickness of the bonding layer is about 500 nm.

[0099] Step 3: After the bonding layer is prepared, vacuum is applied at 100–150°C to a temperature of 3 × 10⁻⁶. -3 ~7×10 -3 Pa, with the control bolt positioned directly above the center of the target, a mixture of argon (99.99% purity) and nitrogen (99.99% purity) is introduced, with the argon to nitrogen flow rate ratio between 3:1 and 1:3, until the gas pressure inside the cavity is 0.4 Pa to 3 Pa. The radio frequency power supply is then turned on, and the sputtering power is 700 to 900 W for 3 to 10 hours, forming an AlScN piezoelectric functional layer.

[0100] Step 4: After the AlScN piezoelectric functional layer is prepared, an electrode layer is deposited under the conditions of 0.25-1 Pa, 0-100 V bias voltage, and 0-80 A current. The electrode layer is selected from Ag, Ag-Cr, and Ti. After preparation, it is naturally cooled to room temperature. A smart bolt with high mechanical and high temperature resistance and capable of exciting different ultrasonic waves can be obtained on the substrate surface.

[0101] Figure 10 As an application example of the present invention, the ultrasonic waves generated by the smart bolt prepared under the conditions of deposition gas pressure of 0.6 Pa, target-substrate distance of 60 mm, and deposition time of 7 h are mainly ultrasonic longitudinal waves (LW).

[0102] The above application example only uses high-temperature alloy bolt substrate as an example. The preparation method of this AlScN piezoelectric coating material is also applicable to substrates such as stainless steel, aluminum, cemented carbide, and titanium, and is not limited here.

[0103] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. The application of an AlScN piezoelectric coating material with high mechanical properties and high temperature resistance, characterized in that, The AlScN piezoelectric coating material serves as an acoustic-electric conversion layer for exciting ultrasound. Under ultrasonic excitation, it simultaneously emits longitudinal and transverse waves, which can be used for bolt preload detection, or for defect detection and stress measurement of steel plates, welds, and steel pipes. The AlScN piezoelectric coating material consists of a bonding layer, an AlScN piezoelectric functional layer, and an electrode layer; The AlScN piezoelectric functional layer is formed by depositing an alloy target composed of Al and Sc on the surface of the bonding layer through magnetron sputtering. In the magnetron sputtering, the temperature is 100~250℃, a mixed gas of argon and nitrogen with a volume ratio of 1:1 is introduced, the sputtering power is 700~900W, the deposition pressure P is 1.0~2.0Pa, the target-substrate distance d is 50~70mm, and the deposition time is 3~10h.

2. The application according to claim 1, characterized in that, The alloy target material is composed of 60 wt.%~90 wt.% Al and 10 wt.%~40 wt.% Sc.

3. The application according to claim 1, characterized in that, The alloy target has a diameter of 140-160 mm and a thickness of 4-8 mm.

4. The application according to claim 1, characterized in that, The AlScN piezoelectric functional layer exhibits multi-orientation growth on the substrate surface with (002) and (103) diffraction crystal planes.

5. The application according to claim 1, characterized in that, The thickness of the AlScN piezoelectric functional layer is 5~20μm.

6. The application according to claim 1, characterized in that, The preparation method of the AlScN piezoelectric coating material includes: first depositing a bonding layer on the surface of a substrate, then depositing an AlScN piezoelectric functional layer on the surface of the bonding layer, and finally depositing an electrode layer on the surface of the AlScN piezoelectric functional layer.

7. The application according to claim 6, characterized in that, The preparation method of the AlScN piezoelectric coating material includes the following steps: S1. Plasma etching is performed on the substrate surface at 100~250℃ in an argon atmosphere. S2. A Cr bonding layer is deposited on the surface of the substrate after plasma etching at 0.5~1 Pa and 50~250 V; S3. An AlScN piezoelectric functional layer is formed by magnetron sputtering of an alloy target composed of Al and Sc onto the surface of the Cr bonding layer. S4. On the surface of the AlScN piezoelectric functional layer, under the conditions of vacuum degree of 0.25~1 Pa, bias voltage of 0~100V and current of 0~80A, an electrode layer is deposited, thus completing the preparation of the AlScN piezoelectric coating material.

8. The application according to claim 1, characterized in that, The hardness of the AlScN piezoelectric functional layer is 15~20GPa, the bonding strength between it and the substrate is greater than 10MPa, and the working temperature range is -196~700℃.

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