The hydrothermal method enables the production of high-quality piezoelectric materials. In this study, we propose to irradiate the reaction solutions with ultrasonic power during the hydrothermal method to obtain a shorter reaction time and a smooth film surface. A high-pressure reaction container for the ultrasonic transducer was newly developed, and the ultrasonically-assisted hydrothermal method was examined by using this container. The effect of ultrasonic assist on the synthesis of lead-zirconate-titanate (PZT) thin films and (K,Na)NbO3 powders was verified. Thicker PZT film, thickness around 10 µm, could be obtained in one process, and (K,Na)NbO3 powder was synthesized in half the previous reaction time.

Direct ultrasound irradiation is advantageous for increasing the efficiency of the hydrothermal method, which can be used to produce piezoelectric thin films and lead-free piezoelectric ceramics. To apply ultrasound directly to the process, transducer prototypes were developed regarding the boundary conditions of the hydrothermal method. LiNbO3 and PIC 181 were proven to be feasible materials for high-temperature-resistant transducers (≥200 • C). The resistance of the transducer's horn against a corrosive mineralizer was achieved by using Hastelloy C-22. The efficiency of the ultrasound-assisted hydrothermal method depends on the generated sound field.The impedance and the sound field measurements have shown that the sound field depends on the filling level and on the position and design of the transducer.

Recently, for the weight reduction of automotive bodies, steel sheets used in automobiles have been becoming thinner owing to the application of high-strength steels. Press forming of high-strength steels, however, has many problems. Wrinkle formation is one of the most serious problems in press forming, especially in the application of highstrength steels. The cause of wrinkle formation has not yet been completely understood, particularly in the case of bending flange wrinkles, which are common in automotive parts forming. There are, therefore, few well-known methods of satisfactorily preventing bending flange wrinkles. In order to prevent bending flange wrinkles, it is important to understand the effect of press conditions on wrinkle formation. In this study, cylindrical forming experiments simulating bending flange wrinkle formation in press forming of automotive body parts were conducted to clarify the forming limit for wrinkles, that is, the critical circumferential strain, which is the threshold of bending flange wrinkle formation. In addition, a new method of wrinkle suppression by die shoulder shape optimization was developed on the basis of the results of the above experiments. A die shoulder shape was designed such that the edge of the blank remains in contact with the die shoulder. The superiority of the developed design method was verified by forming experiments.

No abstract