氏名　Dikky Burhan
学位の種類　博士（工学）
学位記番号　博甲第350号
学位授与の日付　平成17年09月30日
学位論文題目　Study on In Situ Evaluation of Molten Metals Using High Temperature Ultrasonic Waveguide Sensors　（高温超音波導波棒センサーによる溶解金属のその場評価に関する研究）
論文審査委員
　主査　助教授　井原　郁夫
　副査　教授　福澤　康
　副査　教授　古口　日出男
　副査　教授　鎌土　重晴
　副査　助教授　南口　誠

• 論文目次
• 論文要旨

［平成17（2005）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Contents

Abstract　p.i
Contents　p.ii

Chapter 1　INTRODUCTION　p.1
　1.1　Techniques for Molten Metal Evaluations　p.2
　1.1.1 Off-line Techniques　p.2
　1.1.2 On-line Techniques　p.4
　1.2　Ultrasonic Techniques for High Temperature Evaluations　p.7
　1.2.1 Non-Contact Techniques　p.7
　1.2.1.1 Laser Generated Ultrasound　p.7
　1.2.1.2 Electromagnetic Transducers （EMATs）　p.7
　1.2.2 Contact Techniques　p.9
　1.2.2.1 High Temperature Piezoelectric Trnsducers　p.9
　1.2.2.2 Ultrasonic Waveguide　p.9
　1.3　Literature Study and Related Works　p.10
　1.4　Scope of the Pressent Work　p.15
　1.5　References　p.18

Chapter 2　PRELIMINARY INVESTIGATION ON ULTRASONIC IN SITU EVALUATIONS OF MOLTEN METAL　p.21
　2.1　Introduction　p.22
　2.2　Basic Theory of Ultrasonic Non-Destructive Evaluation　p.23
　2.2.1 Principle of Ultrasonic Pulse-Echo Measurements　p.23
　2.2.2 Acoustic Impedance　p.25
　2.2.3 Transmission/Reflection Coefficients　p.27
　2.3　Steel Waveguide Sensor　p.28
　2.3.1 Waveguide Material　p.30
　2.3.2 Cooling Evaluation　p.30
　2.3.3 Numerical Simulation of Wave Propagation Characteristics　p.32
　2.3.4 Thermal Sprayed Cladding　p.38
　2.4　Experiments in Molten Mg　p.41
　2.4.1 Investigation of Chemical Reaction in Molten Mg　p.41
　2.4.1.1 Microstructure Evaluation　p.41
　2.4.1.2 Oxide Reduction　p.48
　2.4.1.3 Eutectic Reaction　p.48
　2.4.2 Ultrasonic Pulse-Echo Measurement in Molten Mg　p.50
　2.5　Experiments in in Molten Al　p.50
　2.5.1 Focussing Ability Evaluation　p.50
　2.5.2 Alumina Particle Detection　p.54
　2.6　Conclusion　p.54
　2.7　References　p.57

Chapter 3　PULSE-ECHO MEASUREMENTS OF ALUMINUM DURING MELTING AND SOLIDIFICATION　p.60
　3.1　Introduction　p.61
　3.2　Transmission/Reflection Coefficients of Ti in Molten Al　p.62
　3.3　Chemical Reactions of Ti in Molten Al　p.62
　3.3.1 Ti in Molten Al Alloy　p.64
　3.3.2 Ti in High Purity Al　p.75
　3.4　temperature Distribution of Ti Waveguide　p.79
　3.4.1 Temperature Distribution of a Preheated Rod　p.79
　3.4.2 Air Cooling Effect during Measurements　p.81
　3.4.3 Change of Temperature Distribution during Cooling　p.86
　3.5　Pulse-Echo Measurements using Ti Waveguide Sensor　p.86
　3.5.1 Ti Waveguide Sensor　p.86
　3.5.2 Ultrasonic Coupling of Ti in Molten Al　p.89
　3.5.3 Changes of Reflected Echoes during Melting and Solidification　p.92
　3.6　Ultrasonic Velocity Measurements　p.95
　3.6.1 Velocity of Al and Al Alloy　p.95
　3.6.2 Velocity of Steel and Ti　p.96
　3.6.3 Errors in the Velocity Measurements　p.100
　3.7　Ultrasonic Amplitude Measurements　p.101
　3.7.1 Prode End Echo Amplitude　p.101
　3.7.2 Surface and Backside of Steel Reflector Echo Amplitude　p.103
　3.8　Long Time Measurements in Molten Al Alloy　p.104
　3.9　Conclusion　p.112
　3.10 References　p.113

Chapter 4　IN SITU OBSERVATION OF SOLID/LIQUID INTERFACE OF ALUMINUM　p.115
　4.1　Introduction　p.116
　4.2　Ti Clad Tapered Waveguide Sensor　p.119
　4.2.1 Microstructure of Ti Thermal Sprayed Cladding　p.122
　4.2.2 Taper and Cladding Effect　p.122
　4.3　Pulse-Echo Measurements of Solid/Liquid Interface　p.125
　4.3.1 Interface of Al-Si Alloy　p.125
　4.3.1.1 Fixed Interface　p.125
　4.3.1.2 Interface during Heating and Cooling　p.128
　4.3.1.3 Variations in the Ampltude and Location of the Interface　p.130
　4.4.2 Interface of High Purity Al　p.133
　4.4.2.1 Interface during Cooling　p.133
　4.4.2.2 Variations in the Amplitude and Location of the Interface　p.133
　4.5　Periodic Oscilatory Phenomena of the Interface Echo　p.135
　4.5.1 Noise Reduction Process　p.136
　4.5.2 Amplitude of Reflected Echo in a Continuous Movement　p.139
　4.5.3 Periodic Fluctuations of Al Alloy Interface　p.141
　4.5.4 Periodic Fluctuations of Pure Al Interface　p.145
　4.6　Study on Future Waveguide Material for Molten Al Measurement　p.148
　4.6.1 Nband Mo Waveguide Sensor　p.152
　4.6.3 Pulse-Echo Measurements using Nb and Mo Waveguides　p.154
　4.7　Conclusion　p.160
　4.8　References　p.164

Chapter 5　GENERAL CONCLUSIONS AND FUTURE PROSPECTS　p.167
　5.1　General conclusions　p.168
　5.2　Prospects of Future Research　p.171
Acknowledgements　p.176
List of Publications　p.178

　There are growing demands for in situ evaluation of molten metals. Techniques for such in situ evaluations are needed not only to make basic researches on molten metals but also to realize on-line monitoring of molten metal processes in industries because of the necessity for the quality control and optimization in metal production line. In this work, in situ evaluation techniques of molten metal using ultrasonic waveguide sensors are studied. The sensors mainly consist of a piezoelectric ultrasonic transducer （UT）, an air cooling system and a buffer rod as an acoustic waveguide.
Chapter 1 reviews the literature study and related works on in situ evaluation techniques of molten metal and ultrasonic techniques for high temperature measurements. The scope of the present study is addressed.
　In chapter 2, a preliminary investigation on ultrasonic in situ evaluations of molten metals using a high temperature ultrasonic waveguide sensor is presented.
The fundamental of ultrasonic non-destructive evaluation （NDE） is given to refresh the essential of the experiments. In this preliminary stage, a clad tapered stainless steel is used for the waveguide material for measurements in molten Mg and Al. The performance of the sensor such as the wave propagation characteristic, cooling efficiency and chemical reactions in molten Mg has been evaluated experimentally. The numerical simulation using finite difference method is used to predict the characteristics of the spurious echoes that are strongly depended on the geometrical shape of the waveguide such as tapering angle. It is found that the air cooling used here effectively prevents the temperature increase of the UT end. In order to improve the ultrasonic wave guidance ability of the sensor, the stainless steel thermal sprayed cladding is deposited on the tapered surface of the steel waveguide. The result of chemical reaction investigation suggests that Si is the easiest element to react with molten Mg, owing to the possibility of intermetallic compound formation such Mg2Si. Based on such preliminary investigation, ultrasonic pulse-echo measurements in molten Mg at 700oC and molten Al at 800oC have been performed. Reflected echoes from steel reflectors immersed in molten Mg and Al are clearly observed using the sensor. In addition, the focusing ability of an acoustic lens fabricated at the top of the waveguide in molten Al has been evaluated. An attempt to detect 160 μm alumina （Al2O3） particles suspended in molten Al has been made. Backscattered echoes from the particles are clearly observed at the focal regionof the acoustic lens. The waveguide sensor might be useful for on-line cleanliness evaluation of molten metals.
　In chapter 3, pulse-echo measurements of Al during melting and solidification are presented. Titanium （Ti） has been chosen as the waveguide material because it is expected that Ti has a high transmission coefficient, chemical reaction resistance and ultrasonic coupling in molten Al. A steel reflector （S45C） is assembled at the probe end so that an accurate ultrasonic pulse-echo measurement can be made easily. It is found that the formation of an intermediate layer produced by the chemical reaction between Al and Ti inhibits further chemical reaction of Ti with the Al alloy and the Si element stabilizes the intermediate layer. It is also found from a finite element analysis that the air cooling does not significantly affect the temperature distribution of the Ti waveguide in molten Al. Pulse-echo measurements using the sensor in temperature range from 200 to 800oC have been performed at 5 MHz and the variations of the ultrasonic velocity of the Al alloy as a function of temperature have been determined. The velocity shows a rapid and significant change from 3900 to 5600 m/s near the eutectic point. The variations in the amplitude of the reflected echoes around the eutectic point have been examined. In addition, it is found that the chemical reaction between the sensor and Al alloy degrades the signal to noise ration of the measured echoes for a long time of immersion. The ultrasonic reflection technique used here might be useful to evaluate the solidification phenomena as well as material properties at elevated temperature.
　In chapter 4, in situ observations of a solid/liquid interface of Al are presented. A Ti thermal sprayed cladding is deposited on the tapered surface of Ti waveguide in order to ensure proper wave guidance. Pulse-echo measurements of a solid/liquid interface of Al have been performed at 2.25 MHz. Clear reflected echoes from the interface of Al alloy and high purity Al undergoing a directional solidification have been observed. From these echoes, the location and growth rate of the interface during melting and solidification have been determined. Oscillatory phenomena of the amplitude of the interface echo during the growing process have been observed. It seems that the periodic fluctuations of the amplitude are related to the surface configuration of the interface.
　General conclusions and future prospects of the research are summarized in chapter 5. It is shown that the ultrasonic technique has the potential to be a powerful diagnostic tool for the in situ observation of molten metals.