Sound velocity during solidification in binary eutectic systems

• Published in: Journal of applied physics 2017-12, Vol.122 (22)
• Main Authors: Yoshioka, Hideaki, Kyoden, Tomoaki, Hachiga, Tadashi
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5001893

We applied an ultrasound technique to an advanced material process by investigating the behavior of sound velocity during solidification of binary alloy melts over a wide range of temperatures and compositions. To gain a basic understanding of the relationship between the sound velocity and phase change in binary eutectic systems, the sound velocity was measured in Pb-Sn and Bi-Sn alloys by the pulse transmission method. Based on the measurement results, we established a link between the sound velocity variation and the complex solidification process, including the initial appearance of undercooling and eutectic reaction. During solidification, alloys usually pass through a transient mushy state between the liquid and solid phases. Since the solid fraction is uniquely related to the sound velocity, we demonstrate that it is possible to identify the solid fraction in the mushy state using the sound velocity. At the eutectic point, a sudden change was observed in relation to the eutectic reaction, in which the sound velocity exhibited an abrupt transition under isothermal conditions. This sudden change in the sound velocity was evident even when the initial composition was below the maximum solid-solution limit, such as when the solute distribution coefficient was relatively large. This result suggests that the presence of a eutectic in the final solidified texture can be predicted using our sound velocity measurement system. Finally, we present a novel sound velocity phase diagram that provides a real-time state determination system using ultrasound during solidification process, such as casting.