In-situ observations and acoustic measurements upon fragmentation of free-floating intermetallics under ultrasonic cavitation in water

Abhinav Priyadarshi; Mohammad Khavari; Shazamin Bin Shahrani; Tungky Subroto; Lukman A Yusuf; Marcello Conte; Paul Prentice; Koulis Pericleous; Dmitry Eskin; Iakovos Tzanakis

doi:10.1016/j.ultsonch.2021.105820

In-situ observations and acoustic measurements upon fragmentation of free-floating intermetallics under ultrasonic cavitation in water

Ultrason Sonochem. 2021 Dec:80:105820. doi: 10.1016/j.ultsonch.2021.105820. Epub 2021 Nov 2.

Authors

Affiliations

¹ Faculty of Technology, Design and Environment, Oxford Brookes University, Oxford OX33 1HX, UK. Electronic address: abhinav.priyadarshi-2018@brookes.ac.uk.
² Faculty of Technology, Design and Environment, Oxford Brookes University, Oxford OX33 1HX, UK.
³ Brunel Centre for Advance Solidification Technology (BCAST), Brunel University London, Uxbridge UB8 3PH, UK.
⁴ Cavitation Laboratory, School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK.
⁵ Anton Paar TriTec SA, Vernets 6, 2035 Corcelles, Switzerland.
⁶ Computational Science and Engineering Group (CSEG), Department of Mathematics, University of Greenwich, London SE10 9LS, UK.
⁷ Brunel Centre for Advance Solidification Technology (BCAST), Brunel University London, Uxbridge UB8 3PH, UK; Tomsk State University, Tomsk 634050, Russia.
⁸ Faculty of Technology, Design and Environment, Oxford Brookes University, Oxford OX33 1HX, UK; Department of Materials, University of Oxford, Oxford OX1 3PH, UK.

Abstract

Grain refinement in alloys is a well-known effect of ultrasonic melt processing. Fragmentation of primary crystals by cavitation-induced action in liquid metals is considered as one of the main driving mechanisms for producing finer and equiaxed grain structures. However, in-situ observations of the fragmentation process are generally complex and difficult to follow in opaque liquid metals, especially for the free-floating crystals. In the present study, we develop a transparent test rig to observe in real time the fragmentation potential of free-floating primary Al₃Zr particles under ultrasonic excitation in water (an established analogue medium to liquid aluminium for cavitation studies). An effective treatment domain was identified and fragmentation time determined using acoustic pressure field mapping. For the first time, real-time high-speed imaging captured the dynamic interaction of shock waves from the collapsing bubbles with floating intermetallic particles that led to their fragmentation. The breakage sequence as well as the cavitation erosion pattern were studied by means of post-treatment microscopic characterisation of the fragments. Fragment size distribution and crack patterns on the fractured surface were then analysed and quantified. Application of ultrasound is shown to rapidly (<10 s) reduce intermetallic size (from 5 mm down to 10 μm), thereby increasing the number of potential nucleation sites for the grain refinement of aluminium alloys during melt treatment.

Keywords: Fragmentation time; Free-floating; Grain refinement; High-speed imaging; Primary intermetallic crystal.