【作者】 张娟；

【导师】 赵天龙； 赵士勇；

【作者基本信息】 西安电子科技大学 ， 电子信息（专业学位）， 2024， 硕士

【摘要】 超声无损检测技术由于成本低、速度快和用途广泛等优点,广泛应用于工业领域,其中如高温管道缺陷、核反应堆冷却液下成像等无损检测要在高温下进行,这要求超声换能器具有良好的耐温性、高灵敏度和宽带宽以提高检测效率。压电材料和聚合物构成的压电复合材料可以实现较高的机电耦合系数和可调节的声阻抗,是提高换能器性能的有效途径。但高温复合超声换能器的实现面临一些问题:聚合物的高热膨胀系数和低导热系数容易造成复合材料的变形和开裂,超声换能器的结构和各部件材料的选择受到高温的限制。诸多温度限制因素使得对高温复合超声换能器的研究相对有限,对高温复合超声换能器的设计和实现极具挑战性。本文针对目前的研究难点,对高温复合材料、高温复合超声换能器及其应用展开了系统的研究。主要研究内容如下:（1）BS-PT基高温压电复合材料的设计、制备与表征。本文引入1-3-2型复合结构来提升复合材料的机械强度与温度稳定性,选择0.36Bi Sc O₃-0.64Pb Ti O₃（BS-PT）陶瓷作为压电材料,高温环氧树脂作为聚合物,结合改进的W.A.Smith理论模型和PZFLex有限元仿真对1-3-2复合材料进行了设计。使用切割填充法制备了频率为6MHz的1-3-2高温复合材料并进行了电学与声学性能的表征。复合材料的声阻抗从30.05 MRayl降低到了21.52 MRayl。从常温到250℃,1-3-2高温复合材料表现出了良好的谐振特性,频率随温度升高有所下降,但机电耦合系数有很大的提升（从25℃时的0.524提高到250℃时的0.641）,明显优于BS-PT陶瓷（～0.500）。（2）BS-PT基高温压电复合超声换能器的设计、制备与表征。基于1-3-2高温复合材料设计了高温换能器结构,采用热膨胀系数较低的高温导电胶作为背衬同时引出电极,使压电元件为均匀的层状结构,避免了在高温下可能出现的局部高温和不均匀热形变,最后使用高温环氧树脂进行封装。通过PZFLex有限元仿真预测了换能器的性能。对制备得到的中心频率为6 MHz的1-3-2高温复合超声换能器进行了电学和声学性能表征,从常温到250℃,换能器结构并未发生损坏,各部件均无失效,可以正常工作。随着温度上升,1-3-2复合换能器频率逐渐下降,等效机电耦合系数逐渐提升（25℃时为0.593,250℃为0.655）,带宽也逐渐升高（25℃时为35.6%,250℃时为103.1%）,回波幅值在150℃以下保持在500 m V左右,从200℃开始显著下降。整个温度范围内,性能均较BS-PT换能器（～0.5,～30%,回波幅值为复合换能器的1/2）有很大提升。（3）BS-PT基高温压电复合超声换能器的应用研究。使用制备得到的1-3-2高温复合超声换能器进行了一系列高温应用实验。1-3-2高温复合超声换能器可以在250℃以下实现对台阶金属块的B-模式成像,与BS-PT换能器相比表现出更高的成像质量和更大的探测深度。在200℃下对一元硬币的C-模式成像依旧达到了很高的分辨率。通过多次回波法对25 mm厚的钢块进行了声速测试,得到了钢块在25℃到250℃内不同温度下的声速。利用测试得到的变温声速,在250℃下的不同温度对钢块内部直径为4 mm的圆孔形缺陷进行了深度检测,检测结果与理论值的最大相对误差不超过0.7%。证明了1-3-2高温复合超声换能器应用于高温无损检测的潜力。更多还原

【Abstract】 Ultrasonic non-destructive testing technology is widely used in industrial fields due to its advantages of low cost,high speed and wide range of applications.Among them,such as high-temperature pipeline defects and imaging in nuclear reactor coolant need to be carried out at high temperatures,which requires ultrasound transducers with good temperature resistance,high sensitivity and wide bandwidth to improve the detection efficiency.Piezoelectric composites composed of piezoelectric materials and polymers can achieve high electromechanical coupling coefficient and adjustable acoustic impedance,making it an efficient way to improve the performance of transducers.However,the realization of high-temperature composite ultrasonic transducers faces some problems:the high thermal expansion coefficient and low thermal conductivity of polymers tend to cause deformation and cracking of composites,and the ultrasonic transducer structure and the choice of materials for the various components are limited by the high temperature.Multiple temperature constraints have made the research of high-temperature composite ultrasonic transducers relatively limited as and the design and realization of high-temperature composite ultrasonic transducers very challenging.In this paper,a systematic research on BS-PT based high-temperature piezoelectric composites,high-temperature composite ultrasonic transducers and their applications has been carried out in view of the current research difficulties.Main research contents are as follows:（1）Design,fabrication and characterization of BS-PT based high-temperature piezoelectric composites.In this paper,a 1-3-2 type composite structure is introduced to enhance the mechanical strength and temperature stability of the composites,0.36Bi Sc O₃-0.64Pb Ti O₃（BS-PT）ceramics are selected as the piezoelectric material and high-temperature epoxy as the polymer.The 1-3-2 composites are designed with the combination of the modified W.A.Smith theoretical modelling and PZFLex finite element simulation.A batch of 1-3-2 high-temperature composites with a frequency of 6 MHz are prepared by dice and fill method and the electrical and acoustic properties are characterized.From room temperature to 250°C,the 1-3-2 high-temperature composites shows good resonance characteristics,with a decrease in frequency with increasing temperature,but a great improvement in the electromechanical coupling coefficient（from 0.524 at 25°C to 0.641 at250°C）,which is significantly better than that of the BS-PT material（～0.500）.（2）Design,fabrication and characterization of BS-PT based high-temperature piezoelectric composite ultrasonic transducers.Based on 1-3-2 high-temperature composites,the structure of high-temperature transducer is designed,and a high-temperature conductive adhesive with low coefficient of thermal expansion is used as the backing and to lead the electrodes at the same time,so that the piezoelectric element can achieve a uniform laminate structure,which avoids local high temperature and inhomogeneous thermal deformation,and finally,the high-temperature epoxy is used for the encapsulation.The performance of the transducers is predicted by PZFLex finite element simulation.And the electrical and acoustic properties of the 1-3-2 high-temperature composite ultrasonic transducers with a center frequency of 6 MHz are characterized.From room temperature to 250°C,the transducers can work normally without any failure.With temperature rises,the center frequency of the1-3-2 composite transducers gradually decreases,the equivalent electromechanical coupling coefficient gradually increases（0.593 at 25°C,0.655 at 250°C）,the bandwidth gradually increases（35.6%at 25°C,103.1%at 250°C）,and the echo amplitude is maintained at about500m V below 150°C and decreases significantly from 200°C,which achieve great improvement compared with those of BS-PT transducers（～0.5,～30%,echo amplitude reaches 1/2 that of the 1-3-2 composite transducers）over the entire temperature range.（3）Research on applications of BS-PT based high-temperature piezoelectric composite ultrasonic transducers.A series of high-temperature application experiments are conducted using the prepared 1-3-2 high-temperature composite ultrasound transducers.The 1-3-2high-temperature composite ultrasound transducer can realize B-mode imaging of a step metal block below 250°C,which shows higher imaging quality and greater depth of detection compared with that of BS-PT transducers.C-mode imaging of a dollar coin can still achieve high resolution at 200°C.The velocity of a 25 mm thick steel block is measured by the multiple echo method,and the velocity of the steel block is obtained at different temperatures from 25°C to 250°C.The depth of a circular hole-shaped defect with a diameter of 4 mm inside a steel block is detected at different temperatures up to 250°C,and the maximum relative error between the detection result and the theoretical value do not exceed 0.7%.The potential of the 1-3-2 high-temperature composite ultrasonic transducer for high-temperature non-destructive testing is demonstrated.更多还原