Solidification microstructures and solid-state parallels: Recent developments, future directions

https://hal.archives-ouvertes.fr/hal-00457075/document

In situ and real-time 3-D microtomography investigation of dendritic solidification in an Al-10 wt.% Cu alloy

Recent improvements in detectors combined with the eminent brightness and collimation offered with modern synchrotron sources open the way forin situ X-radiographic investigations of solidification fundamentals and phenomena in real alloys at resolutions approaching regular video microscopy. Here, the authors present observations on dendrite fragmentation from columnar fronts in Al-Cu and subsequent transport phenomena. From directional solidification experiments it has been found that the tendency for crystal fragments to detach by remelting of branch roots in the mush dendrite network strongly depends upon the relative buoyant and settling motions of crystal fragments and mush liquid, respectively. At the copper concentrations studied (20 to 30 wt pct), primary aluminum dendrites are lighter than the melt and solidification experiments parallel and anti-parallel to gravity show significant differences in detachment tendency. The experimental results compare well with three different models proposed for fragmentation at different mush locations; however, the results also demonstrate that these models differ substantially both with respect to detachment frequency and the ability for detached fragments to cause eventual columnar to equiaxed transitions. Under particular conditions it has been found that crystal fragmentation could lead to an alternating mesoscale segregation.

Crystal fragmentation and columnar-to-equiaxed transitions in Al-Cu studied by synchrotron X-ray video microscopy

A synchrotron X-ray radiography study of dendrite fragmentation induced by a pulsed electromagnetic field in an Al–15Cu alloy

https://bura.brunel.ac.uk/bitstream/2438/15139/5/Fulltext.pdf

A synchrotron X-radiography study of the fragmentation and refinement of primary intermetallic particles in an Al-35 Cu alloy induced by ultrasonic melt processing

An improved synchrotron microradiography technique is being used to study dendrite growth and coarsening in Sn-13%Bi alloy in real time. The morphology of growing dendrites can be well resolved with reasonable image contrast. Dendrite arm remelting, coalescence, and fragmentation have been observed in a real alloy and in real time during solidification under controlled thermal gradients and cooling rates. This research opens a different window to the study of alloy solidification and enables unambiguous understanding of solidification processes in optically opaque, metallic alloys.

Real-time observation of dendrite coarsening in Sn-13%Bi alloy by synchrotron microradiography

Using synchrontron microradiography, temperature gradient zone melting (TGZM) was observed in Sn-13 wt pct Bi alloy in real time during directional solidification A significant amount of remelting was measured on the cold sides of the dendrite arms, whereas added solidification on the hot sides of the dendrite arms was observed during dendrite growth Kinetics of TGZM was measured based on the real-time observations TGZM had a significant effect on dendrite morphology during continuous cooling and holding within the solidification range The presence of tertiary dendrite arms enhanced the rate of TGZM Remelting also led to the disintegration of some secondary dendrite arms

Synchrotron microradiography of temperature gradient zone melting in directional solidification

A third generation synchrotron x-ray source and advanced imaging facilities were used to study dendritic solidification in metallic alloys in real time. A digital camera and a video camera with different time and spatial resolution were tested to capture growing dendrites during solidification of Sn-13 wt%Bi and Al-25 wt%Cu alloys. The captured digital images show that the morphology of the dendrites can be resolved with satisfactory resolution and contrast. The trade-off between spatial resolution and time resolution was discussed. The effect of beam characteristics such as intensity, parallelism and coherency on both spatial and time resolution was analysed, and potential improvements with higher image quality with reduced exposure time were also discussed.

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=854290

Real time observation of dendritic solidification in alloys by synchrotron microradiography

Dendrite coarsening in Sn-13 wt pct Bi alloy was observed in real time with high resolution synchrotron microradiography during continuous cooling and isothermal holding. Coarsening mechanisms such as dendrite remelting from tips toward roots and coalescence between neighboring branches were observed. Dendrite remelting was found to be dominant in the early stage of dendrite growth, whereas coalescence was dominant during isothermal coarsening. Rates of dendrite remelting and coalescence during continuous cooling and isothermal holding were measured from the captured images. The evolution of secondary dendrite arm spacing (DAS) was also measured from the real time observations. These results provided better understanding of dendrite coarsening during alloy solidification.

Real Time Synchrotron Microradiography of Dendrite Coarsening in Sn-13 Wt Pct Bi Alloy

A compact, convenient and economic design of a temperature gradient furnace for synchrotron microradiography is described. The thermal control of the furnace, in terms of cooling rate and temperature gradient, was achieved by programmable temperature controllers, and provided necessary thermal conditions for real time observations of dendritic solidification in real alloys. The experiments at the Advanced Photon Source (APS), Argonne National Laboratory (ANL) demonstrate that the design is well suited to the melting and solidification of alloys with liquidus temperatures up to intermediate ranges (≈650 °C), such as aluminium alloys. Real time observations with this furnace of dendritic solidification in Al–25 wt% Cu alloy by synchrotron microradiography show interesting and promising results.

/pdf/a-compact-design-of-a-temperature-gradient-furnace-for-1f88bn565h.pdf

H. D. Brody

Papers

Real-time observation of dendrite coarsening in Sn-13%Bi alloy by synchrotron microradiography

Synchrotron microradiography of temperature gradient zone melting in directional solidification

Real time observation of dendritic solidification in alloys by synchrotron microradiography

Real Time Synchrotron Microradiography of Dendrite Coarsening in Sn-13 Wt Pct Bi Alloy

A compact design of a temperature gradient furnace for synchrotron microradiography