A ZnO piezoelectric coating material capable of exciting pure shear waves, and its preparation method and application

Abstract

The present invention discloses a ZnO piezoelectric coating material capable of exciting pure shear waves, a preparation method thereof, and an application thereof, belonging to the field of coating materials. The method comprises: using Zn as a target material, depositing ZnO as a ZnO piezoelectric functional layer on the surface of a substrate by magnetron sputtering; in the magnetron sputtering, the sputtering temperature is above 200°C, a mixed gas of argon and oxygen is introduced until the pressure in the cavity is 1.0-2.5 Pa, the sputtering power is 400-700 W, and the sputtering time is 3-6 hours; or, in the magnetron sputtering, the sputtering temperature is 50-200°C, a mixed gas of argon and oxygen is introduced until the pressure in the cavity is 1.0-2.5 Pa, the bias voltage is ‑100V-‑200V, the sputtering power is 400-700 W, and the sputtering time is 3-6 hours. The present invention adopts magnetron sputtering technology to deposit ZnO on the surface of the substrate as a ZnO piezoelectric functional layer. By adjusting the sputtering temperature or bias voltage during the magnetron sputtering process, a ZnO piezoelectric coating material that can excite ultrasonic pure shear waves is prepared, thereby realizing the measurement of subtle changes in the thickness of the workpiece.

Description

Technical Field

[0001] The present invention relates to the technical field of coating materials, and in particular to a ZnO piezoelectric coating material capable of exciting pure shear waves, a preparation method thereof, and applications thereof. Background Art

[0002] Ultrasonic nondestructive testing (NDT) is often used to detect internal defects in materials and devices or simply measure the thickness of workpieces. It offers real-time performance, high precision, excellent stability, and is nondestructive. This method, based on acoustic-elasticity theory, uses piezoelectric materials as the acoustic-to-electric conversion medium. The internal stress and overall thickness of the material are ultimately determined by processing and calculating the echo signal. Two common methods for ultrasonic measurement are ultrasonic probes and piezoelectric ceramics. The former requires the use of a coupling agent, which is complex to operate, exhibits large errors, and carries the risk of sample corrosion. The latter is subject to errors caused by the thickness of the glue. Furthermore, attaching the piezoelectric ceramic to the test piece can lead to corrosion of the substrate and ceramic cracking and falling. Compared to these two methods, piezoelectric thin films deposited on the workpiece surface using thin-film deposition technology offer superior structural stability. While there are potential errors in stress calculation, they can achieve long-term, rapid, and accurate measurements. During the inspection process, the excited signal is divided into two types: longitudinal and transverse waves, depending on the generation mechanism. Longitudinal waves offer advantages such as a distinct peak and sensitivity to axial variations. However, in actual thickness measurement, they are often more affected by material surface stress than by variations in the thickness itself, resulting in significant errors. While transverse waves propagate more slowly, they offer higher resolution and are unaffected by surface stress. Therefore, when measuring the thickness of thin samples, a measurement method that can exclusively generate transverse waves is a better choice.

[0003] According to relevant research statistics, the main materials of piezoelectric coatings that can simultaneously excite transverse waves and longitudinal waves are ZnO and AlN. Both of these material coatings have a hexagonal cubic structure in the lattice structure and have piezoelectric effect. The performance of ultrasonic excitation coatings depends entirely on the growth direction of the internal crystals. Among them, ZnO material has a high piezoelectric coefficient and a high electromechanical coupling coefficient K. 2The advantages of ZnO coatings are that they have good properties, and their structural characteristics are suitable for growth on a variety of substrate materials. At the same time, the temperature required for growth is relatively low, and the composition and growth morphology are easier to control. Therefore, most researchers choose ZnO as the target coating material. When the ZnO coating grows along the C-axis and the crystal quality is high, a longitudinal ultrasonic signal will be excited. The most basic condition for exciting a transverse ultrasonic signal is that the direction of the applied electric field should be perpendicular to the direction of sound wave propagation, which is closely related to the growth direction of the coating crystal. At present, there have been a lot of studies on the excitation of pure longitudinal waves or pure transverse waves in ZnO piezoelectric coatings. Among them, the preparation method used in the research related to the performance of ZnO mainly uses ZnO ceramic material RF target for RF sputtering. The ZnO coating deposited by this preparation method will stably generate regular crystals with C-axis orientation growth under different parameter conditions. The excited signal is also mainly a pure longitudinal wave signal. In a few cases, there is a structure with mixed longitudinal and transverse waves. Regarding coatings capable of stimulating pure shear-wave ultrasonic signals, some research has achieved a (110)-oriented crystal structure by growing tilted ZnO and ZnCoO coatings on SrTiO substrates, stimulating pure shear-wave signals. Others have used aluminum and molybdenum as electrode materials to achieve both pure shear-wave and pure longitudinal-wave excitation. While both methods achieve stable excitation of pure shear-wave signals, they are limited by the substrate and electrode materials.

[0004] Therefore, it is very necessary to explore the preparation method of more universal pure shear wave ultrasonic signal coating. Summary of the Invention

[0005] In view of the shortcomings of the above-mentioned prior art, one of the objects of the present invention is to provide a method for preparing a ZnO piezoelectric coating material that can excite pure shear waves. ZnO is deposited on the surface of a substrate as a ZnO piezoelectric functional layer by magnetron sputtering technology. By adjusting the sputtering temperature or bias voltage during the magnetron sputtering process, a ZnO piezoelectric coating material that can excite ultrasonic pure shear waves is prepared, thereby realizing the measurement of subtle changes in the thickness of the workpiece, avoiding complicated operations and the falling off of piezoelectric ceramic sheets, as well as the adverse effects of coupling agents and adhesives on the substrate, and achieving corrosion-free and high-precision online permanent measurement of the entire cycle.

[0006] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves, comprising:

[0008] Using Zn as a target, ZnO is deposited on the substrate surface by magnetron sputtering as a ZnO piezoelectric functional layer;

[0009] In the magnetron sputtering, the sputtering temperature is above 200° C., a mixed gas of argon and oxygen is introduced until the pressure in the chamber is 1.0-2.5 Pa, the sputtering power is 400-700 W, and the sputtering time is 3-6 hours;

[0010] Alternatively, in the magnetron sputtering, the sputtering temperature is 50-200° C., a mixed gas of argon and oxygen is introduced into the chamber until the pressure is 1.0-2.5 Pa, the bias voltage is -100 V to -200 V, the sputtering power is 400-700 W, and the sputtering time is 3-6 h.

[0011] The present invention uses magnetron sputtering technology to deposit ZnO on the surface of a substrate as a ZnO piezoelectric functional layer. In the prior art, the sputtering temperature for depositing ZnO is 50-200°C. Within this temperature range, the particles can have sufficient energy to migrate to the surface of the body and form a stable columnar Zn coating structure. However, after extensive research, the inventors found that as the temperature increases, when the sputtering temperature reaches above 200°C, the oxidation reaction can become more intense, causing the ZnO coating on the substrate surface to form a structure different from the normal columnar crystal structure. In addition, controlling the bias voltage of the substrate during the magnetron sputtering process to -100V to -200V can give the substrate a higher energy, thereby causing the ZnO coating on the substrate surface to form a structure different from the normal columnar crystal structure. Therefore, the present invention controls the sputtering temperature or bias voltage during the magnetron sputtering process to transform the growth direction of the ZnO coating from a single (002) single orientation growth to a (110) orientation growth, thereby preparing a ZnO piezoelectric coating material that can excite pure shear waves.

[0012] Preferably, the sputtering temperature is 210-250°C.

[0013] Preferably, the growth orientation of the ZnO piezoelectric functional layer on the substrate surface includes at least one of a (002) diffraction crystal plane, a (110) diffraction crystal plane, and a (100) diffraction crystal plane.

[0014] Preferably, the thickness of the ZnO piezoelectric functional layer is 5-20 μm.

[0015] Preferably, the target material has a diameter of 140-160 mm and a thickness of 4-8 mm.

[0016] Preferably, the preparation method of the ZnO piezoelectric coating material is: first depositing a ZnO piezoelectric functional layer on the surface of the substrate, then depositing a protective layer on the surface of the ZnO piezoelectric functional layer, and finally depositing an electrode layer on the surface of the protective layer.

[0017] Preferably, the preparation method comprises the following steps:

[0018] S1. Plasma etching of the substrate surface in an argon atmosphere at 100-250°C.

[0019] S2. After etching, using Zn as the target, the chamber temperature was adjusted to above 200°C, a mixture of argon and oxygen was introduced until the pressure in the chamber was 1.0-2.5 Pa, the RF power was turned on, the sputtering power was 400-700 W, and the sputtering time was 3-6 h to deposit a ZnO piezoelectric functional layer on the substrate surface;

[0020] Alternatively, after etching is completed, using Zn as a target, adjusting the chamber temperature to 50-200° C., introducing a mixture of argon and oxygen until the pressure in the chamber is 1.0-2.5 Pa, turning on the bias voltage to -100 V to -200 V, starting the RF power supply, setting the sputtering power to 400-700 W, and sputtering time to 3-6 hours, depositing a ZnO piezoelectric functional layer on the surface of the substrate;

[0021] S3. Depositing a protective layer on the surface of the ZnO piezoelectric functional layer under conditions of 1 to 2Pa and 0 to 80A;

[0022] S4. Depositing an electrode layer on the surface of the protective layer at 0.5-1.5 Pa, a bias voltage of 0-100 V, and a current of 0-80 A to obtain the ZnO piezoelectric coating material capable of exciting pure shear waves.

[0023] In the above technical solution, plasma etching is first used to remove oxides and contaminants on the surface of the substrate to improve the adhesion of the coating; then, by controlling the sputtering temperature or the bias voltage of the substrate during magnetron sputtering, the growth orientation of the ZnO piezoelectric coating is adjusted to prepare a ZnO piezoelectric functional layer that can excite pure shear waves; then, a protective layer and an electrode layer are deposited on the surface of the ZnO piezoelectric functional layer, which has better structural stability, forms protection for the piezoelectric functional layer, and can directly excite ultrasonic waves on the surface of the substrate (bolt).

[0024] Another object of the present invention is to provide a ZnO piezoelectric coating material that can excite pure shear waves and is prepared by the preparation method. The ZnO piezoelectric coating material includes a ZnO piezoelectric functional layer, a protective layer and an electrode layer.

[0025] Another object of the present invention is to provide an application of the ZnO piezoelectric coating material capable of exciting pure shear waves in defect detection and stress measurement.

[0026] Furthermore, by utilizing the method of the present invention to directly deposit the ZnO piezoelectric coating material on the surface of the bolt as an acoustic-to-electric conversion layer for exciting ultrasound, non-destructive testing technology can be realized.

[0027] Compared with the prior art, the present invention is beneficial in that:

[0028] The present invention uses radio frequency magnetron sputtering to prepare a ZnO piezoelectric functional layer on the surface of a substrate. By controlling the sputtering temperature or the substrate bias voltage within a certain range and adjusting the growth orientation of the ZnO coating, a ZnO piezoelectric coating that can excite ultrasonic pure shear waves is prepared. In addition, a protective layer and an electrode layer are deposited on the ZnO piezoelectric functional layer to prevent the coating from falling off the substrate surface, avoid sensor failure, and achieve convenient and fast measurement and long-term measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic top view of a device for preparing a ZnO piezoelectric coating material according to an embodiment of the present invention;

[0030] Figure 2 A schematic structural diagram of a ZnO piezoelectric coating material prepared according to an embodiment of the present invention;

[0031] Figure 3 The XRD patterns of the ZnO piezoelectric functional layers deposited in Examples 1 and 2 and Comparative Examples 1 and 2 are shown;

[0032] Figure 4 The XRD patterns of the ZnO piezoelectric functional layers deposited in Examples 3 to 5 and Comparative Examples 3 to 5 are shown;

[0033] Figure 5 Surface and cross-sectional morphologies of the ZnO piezoelectric functional layers deposited in Examples 1-2 and Comparative Examples 1-2;

[0034] Figure 6 Surface and cross-sectional morphologies of the ZnO piezoelectric functional layers deposited in Examples 3 to 5 and Comparative Examples 3 to 5;

[0035] Figure 7 Ultrasonic signals excited by the ZnO piezoelectric coating material prepared at different temperatures of the present invention;

[0036] Figure 8 Ultrasonic signals excited by the ZnO piezoelectric coating material prepared under different bias voltages of the present invention;

[0037] Among them, 1. Arc sputtering target; 2. Baffle; 3. Radio frequency magnetron sputtering (RF); 4. Etching source; 5. Sample; 6. Sample holder; 7. Rotary table; 8. Heater; 9. Exhaust port; 10. Bias power supply; 11. Furnace door; 12. Substrate; 13. ZnO piezoelectric functional layer; 14. SiO2 protective layer; 15. AgCr electrode layer. DETAILED DESCRIPTION

[0038] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] An embodiment of the present invention provides a method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves, comprising the following steps:

[0040] S1. Plasma etching of the substrate surface in an argon atmosphere at 100-250°C.

[0041] S2. After etching, using Zn as the target, the chamber temperature was adjusted to above 200°C, and a mixture of argon and oxygen was introduced into the chamber at a flow ratio of 3:1 to 1:3 until the pressure in the chamber reached 1.0 to 2.5 Pa. The RF power supply was turned on, the sputtering power was set at 400 to 700 W, and the sputtering time was 3 to 6 hours to deposit a ZnO piezoelectric functional layer on the substrate surface.

[0042] Alternatively, after etching is completed, using Zn as a target, adjusting the chamber temperature to 50-200° C., introducing a mixed gas of argon and oxygen with a flow ratio of argon to oxygen of 3:1-1:3 until the pressure in the chamber is 1.0-2.5 Pa, turning on the bias voltage to -100 V--200 V, starting the RF power supply, setting the sputtering power to 400-700 W, and sputtering time to 3-6 h, depositing a ZnO piezoelectric functional layer on the surface of the substrate;

[0043] S3. Depositing a protective layer on the surface of the ZnO piezoelectric functional layer under conditions of 1 to 2Pa and 0 to 80A;

[0044] S4. Depositing an AgCr electrode layer on the surface of the protective layer at 0.5-1.5 Pa, a bias voltage of 0-100 V, and a current of 0-80 A to obtain the ZnO piezoelectric coating material capable of exciting pure shear waves.

[0045] In the present invention, the substrate can be selected from stainless steel, aluminum, cemented carbide, high-speed steel, titanium, etc., which are suitable for ultrasonic testing. The diameter of the Zn target is 140-160 mm, and the thickness is 4-8 mm.

[0046] The present invention is further described below with reference to specific examples, which are not intended to be limiting of the present invention. In the following examples and comparative examples, the substrate is a stainless steel sheet, and the target is a pure Zn metal target with a purity of 99.99%.

[0047] Figure 1The figure shows a top-down schematic diagram of the apparatus used to prepare ZnO piezoelectric coating materials according to an embodiment of the present invention. The apparatus's vacuum chamber is enclosed by furnace walls and measures 600 x 600 x 600 mm. The vacuum chamber is equipped with an exhaust port 9, through which a vacuum pump evacuates the chamber. Heaters 8, with a heating power of 25 kilowatts, are located at the upper two corners of the vacuum chamber to improve heating efficiency. Etching sources 4 are located at the lower two corners of the chamber to remove impurities from the substrate surface and ensure a clean surface. An arc sputtering target 1, mounted on the furnace wall with its back facing the furnace door 11, serves as a source of high-energy particles for etching. A baffle 2 prevents the formation of the coating on the substrate. Two Zn targets used to deposit the functional layer are mounted on opposing furnace walls and connected to a radio frequency magnetron sputtering (RF) sputtering unit 3, enabling adjustable sputtering power. A sample 5 is placed on a sample holder 6, which is secured to a rotatable turntable 7. The sample holder 6 is connected to an external bias power supply 10 to ensure good electrical conductivity of the turntable 7, sample holder 6, and sample 5. This layout significantly increases the plasma density in the vacuum chamber, completely immersing the workpiece in the plasma. This significantly 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 improved coating uniformity. Furthermore, the rotatable turntable 7 and the installation of multiple Zn targets allow the preparation of multiple layers of different coatings in a single process operation, greatly improving preparation efficiency.

[0048] Example 1

[0049] This embodiment provides a method for preparing a ZnO piezoelectric coating material that can stably excite pure shear waves, comprising the following steps:

[0050] S1. Control the distance between the target and the substrate to about 70 mm, and at the target temperature, vacuum to 7*10 -3 Pa, introduce 50 sccm of argon (purity 99.99%), turn on the bias and arc power supply, and perform plasma etching on the substrate at -150 V, 50% duty cycle, gas pressure 1.0 Pa, and current 80 A to remove impurities attached to the substrate surface and improve the bonding strength between the film layer and the substrate;

[0051] S2. After etching, vacuum the chamber to 3*10 -3 Pa, control the position of the substrate to face the center of the target, introduce a mixed gas of argon (purity 99.99%) and oxygen (purity 99.99%) with a flow rate of 1:1 until the pressure in the chamber reaches 2.0 Pa, turn on the RF power supply, the sputtering power is 600 W, the sputtering time is 4 h, and ZnO is deposited on the surface of the substrate to obtain a ZnO piezoelectric functional layer;

[0052] S3. After the ZnO piezoelectric functional layer is prepared, a SiO2 protective layer is deposited on the surface of the ZnO piezoelectric functional layer at 1.0Pa and a current of 80A;

[0053] S4. An AgCr electrode layer was deposited on the protective layer at room temperature under no bias at 1.0 Pa. After the deposition, the layer was naturally cooled to room temperature to obtain a ZnO piezoelectric coating material capable of exciting ultrasonic pure shear waves.

[0054] Example 2

[0055] The preparation method of the ZnO piezoelectric coating material in this embodiment is basically the same as that in Example 1, except that in step S2, the temperature is 210°C.

[0056] Comparative Example 1

[0057] The preparation method of the ZnO piezoelectric coating material in this comparative example is basically the same as that in Example 1, except that in step S2, the temperature is 150°C.

[0058] Comparative Example 2

[0059] The preparation method of the ZnO piezoelectric coating material in this comparative example is basically the same as that in Example 1, except that in step S2, the temperature is 100°C.

[0060] Example 3

[0061] This embodiment provides a method for preparing a ZnO piezoelectric coating material that can stably excite pure shear waves, comprising the following steps:

[0062] S1. Control the distance between the target and the substrate to about 70 mm, and at the target temperature, vacuum to 7*10 -3 Pa, introduce 50 sccm of argon (purity 99.99%), turn on the bias and arc power supply, and perform plasma etching on the substrate at -150 V, 50% duty cycle, gas pressure 1.0 Pa, and current 80 A to remove impurities attached to the substrate surface and improve the bonding strength between the film layer and the substrate;

[0063] S2. After etching, vacuum the chamber to 3*10 -3 Pa, the position of the substrate was controlled to be opposite to the center of the target material, and a mixed gas of argon (purity 99.99%) and oxygen (purity 99.99%) was introduced with a flow rate of 1:1 until the pressure in the chamber reached 2.0 Pa. The bias voltage was turned on to -200 V with a duty cycle of 50%, and the RF power was turned on. The sputtering power was 600 W and the sputtering time was 4 hours. ZnO was deposited on the surface of the substrate to obtain a ZnO piezoelectric functional layer;

[0064] S3. After the ZnO piezoelectric functional layer is prepared, a SiO2 protective layer is deposited on the surface of the ZnO piezoelectric functional layer at 1.0Pa and a current of 80A;

[0065] S4. An AgCr electrode layer was deposited on the protective layer at room temperature under no bias at 1.0 Pa. After the deposition, the layer was naturally cooled to room temperature to obtain a ZnO piezoelectric coating material capable of exciting ultrasonic pure shear waves.

[0066] Example 4

[0067] The preparation method of the ZnO piezoelectric coating material in this embodiment is basically the same as that in Example 3, except that in step S2, the bias voltage is -150V.

[0068] Example 5

[0069] The preparation method of the ZnO piezoelectric coating material in this embodiment is basically the same as that in Example 3, except that in step S2, the bias voltage is -100V.

[0070] Comparative Example 3

[0071] The preparation method of the ZnO piezoelectric coating material in this comparative example is basically the same as that in Example 3, except that in step S2, the bias voltage is -75V.

[0072] Comparative Example 4

[0073] The preparation method of the ZnO piezoelectric coating material in this comparative example is basically the same as that in Example 3, except that in step S2, the bias voltage is -50V.

[0074] Comparative Example 5

[0075] The preparation method of the ZnO piezoelectric coating material in this comparative example is basically the same as that in Example 3, except that, in step S2, there is no bias voltage.

[0076] Figure 2 This is a schematic diagram of the structure of a ZnO piezoelectric coating material prepared according to an embodiment of the present invention. The ZnO piezoelectric coating material of the present invention sequentially comprises a substrate 12, a ZnO piezoelectric functional layer 13, a SiO2 protective layer 14, and an AgCr electrode layer 15. The composition gradient in the coating structure can further enhance structural stability and enable the deposition of thicker piezoelectric coatings.

[0077] Figure 3The XRD patterns of the ZnO piezoelectric functional layers deposited at different temperatures for Examples 1-2 and Comparative Examples 1-2 of the present invention are shown. For Comparative Examples 1 and 2, the sputtering temperatures are 100°C and 150°C, respectively, and the ZnO coatings exhibit only (002) and (004) diffraction peaks. For Examples 1 and 2, the sputtering temperatures are 250°C and 210°C, respectively, and in addition to the (002) diffraction peak, the ZnO coatings also exhibit (100) and (110) diffraction peaks. This indicates that the present invention can adjust the growth orientation of the ZnO coating on the substrate by adjusting the sputtering temperature, changing the growth direction of the ZnO coating from a single (002) orientation to a multi-orientation growth of (002), (100), and (110), thereby preparing a ZnO piezoelectric coating material capable of stimulating pure shear waves.

[0078] Figure 4 The XRD patterns of the ZnO piezoelectric functional layers deposited at different bias voltages in Examples 3 to 5 of the present invention and Comparative Examples 3 to 5 are shown. As can be seen from the figure, as the substrate bias voltage changes from 0 V to -200 V, the orientation of the ZnO coating on the substrate changes to multi-oriented growth, and the intensity of the (110) diffraction peak becomes increasingly stronger.

[0079] Figure 5 Surface and cross-sectional morphologies of the ZnO piezoelectric functional layers deposited at different temperatures in Examples 1-2 and Comparative Examples 1-2 of the present invention are shown. As can be seen from the figures, the surface morphology changes little as the temperature varies from 100°C to 250°C, and the deposition rate is similar. However, the cross-sectional morphology shows that after the temperature exceeds 200°C, a denser structure appears within a certain range close to the substrate.

[0080] Figure 6 Surface and cross-sectional morphologies of the ZnO piezoelectric functional layers deposited under different bias voltages in Examples 3 to 5 of the present invention and Comparative Examples 3 to 5 are shown. As can be seen from the figure, when the substrate bias voltage changes from 0 V to -200 V, the surface morphology of the coating changes significantly after the bias voltage exceeds -100 V, from the fine-grained unit cell morphology of the columnar crystal end face to a "scale-like" morphology, while the cross-sectional morphology changes from a regular columnar crystal structure to a denser structure.

[0081] Figure 7 Ultrasonic signals excited by ZnO piezoelectric coating materials prepared at different temperatures in the embodiments and comparative examples of the present invention; Figure 8 These are the ultrasonic signals excited by the ZnO piezoelectric coating materials prepared under different substrate bias voltages in the embodiments of the present invention and the comparative example. It can be clearly seen from the figure that with the increase of the sputtering temperature, the ultrasonic waveform excited by the coating changes from a pure longitudinal wave signal to a pure shear wave. Similarly, when the substrate bias voltage increases from 0V to -200V, the excited ultrasonic waveform changes from a pure longitudinal wave to a pure shear wave.

[0082] In summary, the present invention can adjust the growth orientation of the ZnO coating by controlling the sputtering temperature or the substrate bias voltage within a certain range, and prepare a ZnO piezoelectric coating that can excite ultrasonic pure shear waves; the piezoelectric coating material is directly deposited on the bolt surface as an acoustic-to-electric conversion layer for exciting ultrasound, which can realize non-destructive testing technology.

[0083] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves, characterized in that: include: Using Zn as a target, the substrate is positioned facing the center of the target, and ZnO is deposited on the substrate surface by magnetron sputtering as a ZnO piezoelectric functional layer. In the magnetron sputtering, the sputtering temperature is 210-250° C., a mixed gas of argon and oxygen is introduced until the pressure in the chamber is 1.0-2.5 Pa, the flow ratio of argon and oxygen is 1:1, the sputtering power is 400-700 W, and the sputtering time is 3-6 hours; Alternatively, in the magnetron sputtering, the sputtering temperature is 50~200°C, a mixed gas of argon and oxygen is introduced until the pressure in the chamber is 1.0~2.5 Pa, the flow ratio of argon and oxygen is 1:1, the bias voltage is -100V~-200V, the sputtering power is 400~700W, and the sputtering time is 3~6h.

2. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 1, characterized in that: The growth orientation of the ZnO piezoelectric functional layer on the surface of the substrate includes at least one of a (002) diffraction crystal plane, a (110) diffraction crystal plane, and a (100) diffraction crystal plane.

3. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 1, characterized in that: The thickness of the ZnO piezoelectric functional layer is 5-20 μm.

4. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 1, characterized in that: The target material has a diameter of 140-160 mm and a thickness of 4-8 mm.

5. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 1, characterized in that: First, a ZnO piezoelectric functional layer is deposited on the surface of the substrate, then a protective layer is deposited on the surface of the ZnO piezoelectric functional layer, and finally an electrode layer is deposited on the surface of the protective layer.

6. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 1, characterized in that: The following steps are involved: S1. Plasma etching of the substrate surface in an argon atmosphere at 100-250°C. S2. After etching, a Zn target was used, the chamber temperature was adjusted to 210-250°C, a mixture of argon and oxygen was introduced until the pressure in the chamber was 1.0-2.5 Pa, the RF power was turned on, the sputtering power was 400-700 W, the sputtering time was 3-6 h, and a ZnO piezoelectric functional layer was deposited on the substrate surface; Alternatively, after etching is completed, using Zn as a target, adjusting the chamber temperature to 50-200° C., introducing a mixture of argon and oxygen until the pressure in the chamber is 1.0-2.5 Pa, turning on the bias voltage to -100 V to -200 V, starting the RF power supply, setting the sputtering power to 400-700 W, and sputtering time to 3-6 hours, depositing a ZnO piezoelectric functional layer on the surface of the substrate; S3. Depositing a protective layer on the surface of the ZnO piezoelectric functional layer under conditions of 1 to 2Pa and 0 to 80A; S4. Depositing an electrode layer on the surface of the protective layer at 0.5-1.5 Pa, a bias voltage of 0-100 V, and a current of 0-80 A to obtain the ZnO piezoelectric coating material capable of exciting pure shear waves.

7. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 6, characterized in that: The protective layer is SiO2 or a high entropy alloy; the electrode layer includes at least one of Ti, Ag, and Ag-Cr.

8. The ZnO piezoelectric coating material capable of exciting pure shear waves prepared by the method according to any one of claims 1 to 7, characterized in that: The ZnO piezoelectric coating material includes a ZnO piezoelectric functional layer, a protective layer and an electrode layer.

9. Application of the ZnO piezoelectric coating material capable of exciting pure shear waves prepared by the method according to any one of claims 1 to 7 in defect detection and stress measurement.

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