In Situ Monitoring of Solid-Liquid Interface of Aluminum Alloy Using High-Temperature Ultrasonic Sensor

Abstract

A high temperature ultrasonic sensor with a titanium buffer rod has been applied to the in situ monitoring of the solid-liquid interface of an aluminum alloy (Al-12.6%Si) during unidirectional solidification at 700°C. The ultrasonic sensor consists of a conventional piezoelectric transducer, a titanium buffer rod as an acoustic waveguide and a cooling system. Its length is approximately 300 mm. This ultrasonic sensor, because of the unique characteristics of titanium, provides not only good acoustic coupling to molten aluminum but also high-corrosion resistance. Pulse echo measurements in the molten aluminum alloy are performed using the sensor at 2.25 MHz. A clear reflected echo from a stable solid-liquid interface of the aluminum alloy has been successfully monitored. In addition, the reflected echo from the growing interface during unidirectional solidification has also been monitored. The growth rate of the interface was determined to be 0.12 mm/s from the monitored echo.

Integrated High-Temperature Longitudinal, Shear, and Plate Acoustic-Wave Transducers

“…Various efforts have been devoted to developing L-wave HTUTs of large bandwidth and high efficiency, [4][5][6][7][8][9] which are supplied by several companies. However, it is understood that S-waves may be advantageous over L-waves for the NDT&C of materials, because liquid and gas media do not support S-waves.…”

“…[1][2][3] Often NDT&C must be performed at elevated temperatures; thus, high-temperature (HT) ultrasonic transducers (UTs) are in demand. [4][5][6][7][8][9][10] For their applications to smart structures and materials, there is also a critical need for integrated in situ sensors for local and global damage detection and assessment. However, according to our knowledge, although there are a few HT longitudinal (L) wave ultrasonic probes are commercially available, there are no ultrasonic shear (S) probes, longitudinal and shear (L&S) probes, or plate acoustic-wave (PAW) transducers that operate at temperatures up to around 350 C. The purpose of this investigation is to demonstrate the fabrication and performance of integrated HT S-probes, L&S-probes, and PAW transducers directly onto desired structures or materials for NDT&C applications.…”

Ultrasonic Sensing: Fundamentals and its Applications to Nondestructive Evaluation

“…These spurious echoes deteriorate the signal to noise ratio (SNR) because of their possible interference with desired signals to be measured. To overcome such difficulty, tapered and clad buffer rods are developed for various applications in materials evaluations and monitoring [26,27,28,29,30,31]. Figure 11 shows the exterior of one of the developed buffer rod sensors, consisting of a tapered clad buffer rod, a cooling pipe and a conventional ultrasonic transducer (UT).…”

“…Using the buffer rod sensor, an attempt has been made to monitor a solid-liquid interface of aluminium alloy during unidirectional solidification at 700 • C [31]. A solid-liquid interface of aluminium alloy is produced using a directional solidification furnace and then the interface behaviour is monitored during heating and cooling as shown in Fig.…”

“…Recently, an ultrasonic [31] method has been applied to internal temperature monitoring [32]. The principle of the method is based on temperature dependence of ultrasonic velocity in materials.…”