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In situ observation of ultrasonic cavitation-induced fragmentation of the primary crystals formed in Al alloys

Wang, Feng; Tzanakis, Iakovos; Eskin, Dmitry; Mi, Jiawei; Connolley, Thomas

Authors

Feng Wang

Iakovos Tzanakis

Dmitry Eskin

Thomas Connolley



Abstract

The cavitation-induced fragmentation of primary crystals formed in Al alloys were investigated for the first time by high-speed imaging using a novel experimental approach. Three representative primary crystal types, Al3Ti, Si and Al3V with different morphologies and mechanical properties were first extracted by deep etching of the corresponding Al alloys and then subjected to ultrasonic cavitation processing in distilled water. The dynamic interaction between the cavitation bubbles and primary crystals was imaged in situ and in real time. Based on the recorded image sequences, the fragmentation mechanisms of primary crystals were studied. It was found that there are three major mechanisms by which the primary crystals were fragmented by cavitation bubbles. The first one was a slow process via fatigue-type failure. A cyclic pressure exerted by stationary pulsating bubbles caused the propagation of a crack pre-existing in the primary crystal to a critical length which led to fragmentation. The second mechanism was a sudden process due to the collapse of bubbles in a passing cavitation cloud. The pressure produced upon the collapse of the cloud promoted rapid monotonic crack growth and fast fracture in the primary crystals. The third observed mechanism was normal bending fracture as a result of the high pressure arising from the collapse of a bubble cloud and the crack formation at the branch connection points of dendritic primary crystals. The fragmentation of dendrite branches due to the interaction between two freely moving dendritic primary crystals was also observed. A simplified fracture analysis of the observed phenomena was performed. The specific fragmentation mechanism for the primary crystals depended on their morphology and mechanical properties.

Journal Article Type Article
Publication Date Nov 1, 2017
Journal Ultrasonics Sonochemistry
Print ISSN 1350-4177
Electronic ISSN 1873-2828
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 39
Pages 66-76
APA6 Citation Wang, F., Tzanakis, I., Eskin, D., Mi, J., & Connolley, T. (2017). In situ observation of ultrasonic cavitation-induced fragmentation of the primary crystals formed in Al alloys. Ultrasonics Sonochemistry, 39, 66-76. https://doi.org/10.1016/j.ultsonch.2017.03.057
DOI https://doi.org/10.1016/j.ultsonch.2017.03.057
Keywords Acoustics and Ultrasonics; Chemical Engineering (miscellaneous); Radiology Nuclear Medicine and imaging
Publisher URL https://www.sciencedirect.com/science/article/pii/S1350417717301657
Copyright Statement © 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
Additional Information This article is maintained by: Elsevier; Article Title: In situ observation of ultrasonic cavitation-induced fragmentation of the primary crystals formed in Al alloys; Journal Title: Ultrasonics Sonochemistry; CrossRef DOI link to publisher maintained version: http://dx.doi.org/10.1016/j.ultsonch.2017.03.057; Content Type: article; Copyright: © 2017 The Author(s). Published by Elsevier B.V.

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Copyright Statement
© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).





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