Synchrotron radiographic studies of ultrasonic melt processing of metal matrix nano composites

Abstract

Fast synchrotron radiography was used to investigate ultrasonic cavitation bubble formation and their dynamics during liquid metal processing of Al-Cu metal matrix nano composites (MMNC) in comparison with conventional alloys. The experimental observations showed enhanced cavitation potential in MMNC melts, due to the presence of Al 2 O 3 nano particles which believed to be acting as heterogeneous nuclei for bubble formation. Quantitative image analysis demonstrates that the addition of nano particles increases melt agitation partially, while introducing higher flow velocity variations across the melt. This suggests that the presence of nano particles may substantially alter propensity for ultrasonic treatment effects during solidification processing of MMNCs. Highlights• Fast X-ray imaging of ultrasound cavitation in Al-Cu metal matrix nano composite melts.• Nano particles significantly enhance the ultrasonic cavitation bubble formation potential.• Higher flow velocity variation across the melt with increased cavitation activity was found from the experimental observations.

Ultrasonic processing of molten and solidifying aluminium alloys: Overview and outlook

“…The development of in-situ characterisation using highintensity X-ray produced in synchrotron enables direct observations of cavitation bubbles in liquid metals [16,25,26] (Fig. 7) and their interaction with inclusions [27]. At the same time, new generation cavitometers are able to measure acoustic spectrum (see Fig.…”

Synchrotron quantification of ultrasound cavitation and bubble dynamics in Al–10Cu melts

“…Cavitation is a multi-scale and multi-physics phenomenon [7,9,10,36,37]. It includes many elementary processes such as bubble nucleation, growth, collapse, travelling/movement, and so on.…”

Advanced Metal Matrix Nanocomposites

“…There are many challenges; one is that liquid metals are usually optically opaque and the majority of metal alloys require relatively high temperature (above a few hundred degrees Celsius) to maintain liquidus structure; special techniques, such as X-ray imaging, are needed to "see" through the liquid metals. In addition, in situ observation requires imaging with nanoscale resolution and extremely high speed (up to on the order of 10 5 frames per second [119]) to be able to capture both activities of nanoparticle clusters and cavitation bubbles (with radii from a few to a few hundreds of micrometers [114,120]). According to the Minnaert equation [121], the critical radius of a cavitation bubble in liquid aluminum is around 60-70 µm when the acoustic pressure is sufficiently high [114].…”

“…According to the Minnaert equation [121], the critical radius of a cavitation bubble in liquid aluminum is around 60-70 µm when the acoustic pressure is sufficiently high [114]. Nevertheless, there are some in situ imaging experiments focused on the observation of cavitation bubble dynamics in molten metal with and without the presence of nanoparticles [120]. The influence of nanoparticles on the molten metal and cavitation bubbles can then be revealed through comparisons.…”

“…As shown in Figure 16, references [114,118,120] show the experimental setup of ultrasonic processing of molten nanocomposite system mainly consists of a furnace, crucible, and an ultrasonic probe (integrated with an ultrasound processer) generating adequate processing power inside the melt [122]. This work demonstrated that the number density of cavitation bubbles was increased two-fold when the nanoparticles were presented in the molten metal [120], implying that the introduction of nanoparticles provided a large number of heterogeneous nuclei for cavitation bubbles. It is then reasonable to hypothesize that the collapses of those cavitation bubbles may strongly impact the nearby clustered nanoparticles.…”