Yanan Fu

Real-Time Observation on Evolution of Droplets Morphology Affected by Electric Current Pulse in Al-Bi Immiscible Alloy

The evolution of Bi-rich droplets morphology in a solidifying Al-Bi immiscible alloy was directly observed using a synchrotron microradiography technique. The electric current pulse (ECP) was applied to control the solidification process of Al-Bi immiscible alloy. It was found that the electromagnetic pinch force and Marangoni force induced by ECP and temperature gradient, respectively, can significantly affect the distribution of Bi-rich droplets. The electromagnetic pinch force drove the droplets from the center to side; meanwhile, the Marangoni force lifted the droplets from the bottom to the top. As a result, the droplets finally distributed with a manner of “inverted triangle.”

In situ study on growth behavior of Cu6Sn5 during solidification with an applied DC in RE-doped Sn–Cu solder alloys

The growth behavior of Cu6Sn5 intermetallic compounds in rare earth (RE)-doped Sn–Cu solder alloys with an applied direct current (DC) has been in situ investigated using synchrotron radiation imaging technology. The morphological evolutions of Cu6Sn5 with various shapes of I-like, Y-like and bird-like are directly observed. After doping RE, the number of I-like and bird-like Cu6Sn5 is decreased, but the number of Y-like Cu6Sn5 is increased. The morphologies of Cu6Sn5 are more uniform and the mean lengths of Cu6Sn5 of different shapes are reduced in RE-doped alloys compared with that in RE-free alloys, which is attributed to the adsorption effect of RE. The growth orientation of Y-like Cu6Sn5 is changed after La is doped. Additionally, with an applied DC, the nucleation rate of Cu6Sn5 is increased and the growth rate is markedly enhanced resulting in the refinement of Cu6Sn5. Furthermore, the mechanisms of refinement caused by RE and DC are specifically discussed.

The void nucleation mechanism within lead phase during spallation of leaded brass

Abstract The incipient spall behaviours of Cu-34%Zn-3%Pb leaded brass samples with annealed and cryogenic-treated conditions were loaded using one-stage light gas gun experiments. The effect of Pb-phase on dynamic damage nucleation in leaded brass specimens was investigated by means of optical microscopy, scanning electron microscopy and x-ray computer tomography. It was found that the voids of incipient spall were mainly nucleated in the interior of the lead (no tensile stress would be produced within lead according to the impact theory) instead of nucleated at the phase interface as expected by quasi-static damage fracture theory. A nucleation model is proposed in the present work that is the asymmetry high compression zones in the centre of the lead-phase were formed by the rarefaction wave convergence effects of matrix/quasi-spherical lead interface, which caused adiabatic temperature rise that exceeded melting point of lead due to severe plastic deformation, finally led to local melting and void nucleation. In addition, the spall strength and damage rate increased with the increase in the Pb-phase number.

In Situ Study on the Evolution of Dendrite Morphology Affected by Electric Field in Sn‐Bi Alloy

With high energy, high brilliance and eminent collimation, synchrotron X-ray imaging enables in situ observation of dendrite growth during the solidification of Sn-Bi alloy under an applied electric field such as direct current (DC) and electric current pulse (ECP). In present study, the application of DC leads to the suppression of dendrite growth and the degeneration of the secondary and higher order dendrites. Due to the induced Joule heat, the sharp dendrite tips are modified to be round or flat. By applying ECP to the sample during the whole solidification process, a significant grain refinement is observed.

In Situ Visualization on Crystal Growth of Sn-Bi Alloy under Electric Field

The dendritic growth of solidifying Sn-Bi alloy under electric field is in situ observed by a synchrotron radiation X-ray imaging technique. The electric field in this paper includes direct current (DC) and electric current pulse (ECP). The dendritic growth suppressing, dendrite floating and rotating, dendrite refinement and remelting affected by electric field have been in situ observed. The influence of electric field on dendrite morphology and growth behavior is investigated and the mechanisms underlying these phenomena were discussed in terms of the electricity-to-heat effect and electrohydrodynamics.