ZnO piezoelectric coating material capable of exciting pure transverse waves as well as preparation method and application of ZnO piezoelectric coating material

Abstract

The invention discloses a ZnO piezoelectric coating material capable of exciting pure transverse waves as well as a preparation method and application of the ZnO piezoelectric coating material, and belongs to the field of coating materials. The method comprises the following steps: by taking Zn as a target material, depositing ZnO on the surface of a substrate through magnetron sputtering to serve as a ZnO piezoelectric functional layer; during magnetron sputtering, the sputtering temperature is 200 DEG C or above, mixed gas of argon and oxygen is introduced till the air pressure in a cavity ranges from 1.0 Pa to 2.5 Pa, the sputtering power ranges from 400 W to 700 W, and the sputtering time ranges from 3 h to 6 h; or in the magnetron sputtering, the sputtering temperature ranges from 50 DEG C to 200 DEG C, mixed gas of argon and oxygen is introduced till the air pressure in the cavity ranges from 1.0 Pa to 2.5 Pa, the bias voltage ranges from-100 V to-200 V, the sputtering power ranges from 400 W to 700 W, and the sputtering time ranges from 3 h to 6 h. According to the method, ZnO is deposited on the surface of a substrate by adopting a magnetron sputtering technology to serve as a ZnO piezoelectric functional layer, and a ZnO piezoelectric coating material capable of exciting ultrasonic pure transverse waves is prepared by adjusting the sputtering temperature or bias voltage in the magnetron sputtering process, so that the measurement of fine change of the thickness of a workpiece is realized.

Description

Technical Field

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

[0002] Ultrasonic signal nondestructive testing is often used to check the internal defects of materials and devices or simply measure the thickness of workpieces. It has the characteristics of good real-time performance, high precision, good stability and non-destructiveness. This method is based on the theory of acoustic elasticity, using piezoelectric materials as the acoustic-electric conversion medium, and finally determining the internal stress and overall thickness data of the material by processing and calculating the echo signal. There are two commonly used methods for ultrasonic measurement: ultrasonic probe and piezoelectric ceramic sheet. The former needs to be used with a coupling agent, which is complicated to operate, has large errors and the risk of corroding the sample. The latter is affected by the error caused by the thickness of the glue. In addition, the method of attaching piezoelectric ceramic sheets to the tested piece may corrode the substrate and the ceramic sheet may break and fall off. Compared with the above two methods, the piezoelectric film deposited on the surface of the workpiece using thin film deposition technology has a higher advantage in structural stability. Although there are errors caused by the calculation of stress values, it can achieve long-term, fast and accurate measurements. During the detection process, the excited signals are divided into two types: longitudinal waves and transverse waves according to the different generation principles. The longitudinal wave signal has the advantages of obvious wave crest and sensitivity to axial changes, but in contrast, in actual thickness measurement experiments, the influence of material surface stress is greater than the influence of material thickness changes, resulting in large errors. Although the transverse wave signal has a slower propagation speed, it has the advantages of higher resolution and is not affected by surface stress. Therefore, when measuring the thickness of thinner samples, a measurement method that can only excite transverse waves would be 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 the ultrasonic excitation coating depends entirely on the growth direction of the internal crystal. 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 also 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 radio frequency target material for radio frequency sputtering. The ZnO coating deposited by this preparation method will stably generate regular crystals with C-axis orientation growth under different parameter conditions, and the excited signal is mainly pure longitudinal wave signal. In a few cases, there is a structure with mixed longitudinal and transverse waves. In terms of coatings that can excite pure shear wave ultrasonic signals, some related studies have achieved a crystal structure grown in the (110) direction by growing tilted ZnO and ZnCoO coatings on SrTiO substrates, thus exciting pure shear wave signals. There are also two excitation methods, pure shear wave signals and pure longitudinal wave signals, using aluminum and molybdenum as electrode materials. Although the above two methods can stably excite pure shear wave signals, they are subject to the constraints of substrate materials 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 deficiencies in the above 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, and a ZnO piezoelectric coating material that can excite ultrasonic pure shear waves is prepared by adjusting the sputtering temperature or bias voltage during the magnetron sputtering process, thereby realizing the measurement of subtle changes in the thickness of the workpiece, avoiding complicated operations and the falling off of piezoelectric ceramic sheets and 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 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 material, 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 h;

[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--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 the 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, it can be ensured that the particles have sufficient energy to migrate to the surface of the body and generate a stable columnar crystal Zn coating structure. However, the inventor has found through extensive research that as the temperature increases, when the sputtering temperature reaches above 200°C, the oxidation reaction can be made more intense, so that the ZnO coating on the surface of the substrate generates a structure different from the normal columnar crystal. In addition, controlling the bias voltage of the substrate during magnetron sputtering to -100V~-200V can make the substrate have higher energy, so that the ZnO coating on the surface of the substrate generates a structure different from the normal columnar crystal; therefore, the present invention controls the sputtering temperature or bias voltage during magnetron sputtering, so that the growth direction of the ZnO coating is converted 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 is performed on the substrate surface in an argon environment at 100-250°C;

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

[0020] Or, after etching, using Zn as a target, adjusting the chamber temperature to 50-200° C., introducing a mixed gas of argon and oxygen until the pressure in the chamber is 1.0-2.5 Pa, turning on the bias voltage, the bias voltage is -100 V to -200 V, starting the RF power supply, the sputtering power is 400-700 W, the sputtering time is 3-6 h, and 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 the conditions of 1 ~ 2Pa and 0 ~ 80A;

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

[0023] In the above technical scheme, plasma etching is first used to remove oxides and contaminants on the surface of the substrate to improve the adhesion of the coating; then, the growth orientation of the ZnO piezoelectric coating is adjusted by controlling the sputtering temperature or the bias voltage of the substrate during magnetron sputtering to prepare a ZnO piezoelectric functional layer that can excite pure shear waves; and 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, and by controlling the sputtering temperature or the substrate bias voltage within a certain range, the growth orientation of the ZnO coating is adjusted to prepare a ZnO piezoelectric coating that can excite ultrasonic pure shear waves; in addition, a protective layer and an electrode layer are deposited on the ZnO piezoelectric functional layer, which can prevent the coating from falling off the substrate surface, avoid sensor failure, and achieve convenient and fast measurement and long-period measurement. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 A schematic diagram of the structure 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 1-2 and Comparative Examples 1-2;

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

[0033] Figure 5 The surface and cross-sectional morphology of the ZnO piezoelectric functional layer deposited in Examples 1-2 and Comparative Examples 1-2;

[0034] Figure 6 Surface and cross-sectional morphology images 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. rotating 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 solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The 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 is performed on the substrate surface in an argon environment at 100-250°C;

[0041] S2. After etching, Zn is used as a target, the chamber temperature is adjusted to above 200°C, a mixed gas of argon and oxygen is introduced, the flow ratio of argon and oxygen is 3:1~1:3, the pressure in the chamber is 1.0~2.5Pa, the RF power is turned on, the sputtering power is 400~700W, the sputtering time is 3~6h, and a ZnO piezoelectric functional layer is deposited on the surface of the substrate;

[0042] Or, after etching, 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 and oxygen of 3:1-1:3, until the pressure in the chamber is 1.0-2.5 Pa, turning on the bias, the bias is -100 V to -200 V, starting the RF power supply, the sputtering power is 400-700 W, the sputtering time is 3-6 h, and 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 the conditions of 1 ~ 2Pa and 0 ~ 80A;

[0044] S4. Depositing an AgCr electrode layer on the surface of the protective layer at 0.5-1.5 Pa, 0-100 V bias, and 0-80 A current 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, hard alloy, high-speed steel, titanium and other substrates 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 in conjunction with specific examples, but is 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 material is a pure Zn metal target with a purity of 99.99%.

[0047] Figure 1The figure shows a schematic top view of the device used to prepare the ZnO piezoelectric coating material according to the embodiment of the present invention. The vacuum chamber of the device is surrounded by the furnace wall, and the size of the vacuum chamber is 600*600*600 mm. The vacuum chamber is provided with an exhaust port 9, and the vacuum pumping unit evacuates the vacuum chamber through the exhaust port 9. The upper two corners of the vacuum chamber are heaters 8 with a heating power of 25 kilowatts, which are used to improve the heating efficiency; the lower two corners of the vacuum chamber are etching sources 4, which can remove impurities on the surface of the substrate and ensure the cleanliness of the substrate surface; the arc sputtering target 1 is installed on the furnace wall and faces the furnace door 11, as an emission source for etching high-energy particles. Since a baffle 2 is provided, it will not affect the formation of the coating on the substrate. Two Zn targets for depositing the functional layer are respectively installed on two opposite furnace walls, connected to the radio frequency magnetron sputtering (RF) 3, and the sputtering power can be adjusted. The sample 5 is placed on the sample holder 6, and the sample holder 6 is fixed on the rotatable rotating table 7. The sample holder 6 is connected to an external bias power supply 10 to ensure that the rotating table 7, the sample holder 6 and the sample 5 have good conductivity. This layout greatly increases the plasma density in the vacuum chamber, and the workpiece is completely immersed in the plasma. The deposition rate, hardness and adhesion of the coating are greatly improved. Since the target structure is optimized, the magnetic field distribution is more uniform, the magnetron sputtering target surface is etched evenly, and the uniformity of the coating is improved. At the same time, the rotating table 7 that can rotate and the installation of multiple Zn targets can prepare multiple layers of different coatings in one process operation, greatly improving the 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 vacuum to 7*10 -3 Pa, introduce 50sccm of argon (purity 99.99%), turn on the bias and arc power supply, and perform plasma etching on the substrate at -150V, 50% duty cycle, 1.0Pa, and 80A 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 sample to 3*10 at 250℃. -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%), the flow rate of argon and oxygen is 1:1, until the pressure in the chamber is 2.0Pa, turn on the RF power supply, the sputtering power is 600W, the sputtering time is 4h, 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. A AgCr electrode layer is deposited on the surface of the protective layer at 1.0 Pa, without bias, and at room temperature. After the preparation is completed, it is naturally cooled to room temperature to obtain a ZnO piezoelectric coating material that can excite 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 Embodiment 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 of this comparative example is basically the same as that of 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 of this comparative example is basically the same as that of 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 vacuum to 7*10 -3 Pa, introduce 50sccm of argon (purity 99.99%), turn on the bias and arc power supply, and perform plasma etching on the substrate at -150V, 50% duty cycle, 1.0Pa, and 80A 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 sample to 3*10 at 150℃. -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%), the flow rate of argon and oxygen is 1:1, until the pressure in the chamber is 2.0Pa, turn on the bias, the bias is -200V, the duty cycle is 50%, and turn on the RF power supply, the sputtering power is 600W, the sputtering time is 4h, and ZnO is 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. A AgCr electrode layer is deposited on the surface of the protective layer at 1.0 Pa, without bias, and at room temperature. After the preparation is completed, it is naturally cooled to room temperature to obtain a ZnO piezoelectric coating material that can excite 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 Embodiment 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 Embodiment 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 of this comparative example is basically the same as that of 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 of this comparative example is basically the same as that of 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 of this comparative example is basically the same as that of Example 3, except that, in step S2, there is no bias voltage.

[0076] Figure 2 The schematic diagram of the structure of the ZnO piezoelectric coating material prepared in the embodiment of the present invention is that 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 exists in the coating structure, which can better increase the stability of the structure and deposit a thicker piezoelectric coating.

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

[0078] Figure 4 The XRD spectra 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 as follows; it can be seen from the figure that 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 larger and larger.

[0079] Figure 5 The surface and cross-sectional morphology images of the ZnO piezoelectric functional layer deposited at different temperatures in Examples 1-2 of the present invention and Comparative Examples 1-2 are shown in the figure. It can be seen from the figure that the surface morphology does not change much during the temperature change from 100°C to 250°C, and the deposition rate is also similar. However, the cross-sectional morphology image shows that after the temperature exceeds 200°C, a more compact 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; it can be seen from the figure that in the process of substrate bias changing from 0 V to -200 V, when the bias voltage exceeds -100 V, the surface morphology of the coating changes significantly, 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 The ultrasonic signals excited by the ZnO piezoelectric coating materials prepared at different temperatures in the embodiments of the present invention and the comparative examples; Figure 8 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 examples are as follows: as the sputtering temperature increases, 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 0 V to -200 V, 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, so as to realize non-destructive testing technology.

[0083] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present 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 material, ZnO is deposited on the substrate surface by magnetron sputtering as a ZnO piezoelectric functional layer; 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 h; 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--200 V, the sputtering power is 400-700 W, and the sputtering time is 3-6 h.

2. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 1, characterized in that: The sputtering temperature is 210-250°C.

3. 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.

4. 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.

5. 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.

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

7. 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 is performed on the substrate surface in an argon environment at 100-250°C; S2. After etching, Zn is used as a target, the chamber temperature is adjusted to above 200°C, a mixed gas of argon and oxygen is introduced until the pressure in the chamber is 1.0~2.5Pa, the RF power is turned on, the sputtering power is 400~700W, the sputtering time is 3~6h, and a ZnO piezoelectric functional layer is deposited on the surface of the substrate; Or, after etching, using Zn as a target, adjusting the chamber temperature to 50-200° C., introducing a mixed gas of argon and oxygen until the pressure in the chamber is 1.0-2.5 Pa, turning on the bias voltage, the bias voltage is -100 V to -200 V, starting the RF power supply, the sputtering power is 400-700 W, the sputtering time is 3-6 h, and 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 the conditions of 1 ~ 2Pa and 0 ~ 80A; S4. Depositing an electrode layer on the surface of the protective layer at 0.5-1.5 Pa, 0-100 V bias, and 0-80 A current to obtain the ZnO piezoelectric coating material capable of exciting pure shear waves.

8. The method for preparing a ZnO piezoelectric coating material capable of exciting pure shear waves according to claim 7, 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.

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

10. 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 8 in defect detection and stress measurement.

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