L to U then cubed: X-ray tomography charts the secrets of tensile strength
17 Jun 2022
Scientists have ‘photographed’ how microscopic crystals in molten metal change shape as they cool, throwing new light on how stronger alloys might be made.
The University of Birmingham team, led by Dr Biao Cai at the school of metallurgy and minerals, used used high-speed synchrotron X-ray tomography to chart the changing crystal structures.
Their work demonstrates that, as aluminium-copper alloy cools, solidification begins with faceted dendrites, formed by basic units micrometres in size stacking in layers. Initially L-shaped these transform into U-shapes and then a hollowed out cube as they cool, while some stacked together to form beautiful dendrites.
The Birmingham have described how the research s breaking new ground in alloy research and paves the way for improving the tensile strength of alloys used in casting and welding.
Cai commented that the findings, published in Acta Materialia: “provide a real insight into what happens at a micro level when an alloy cools, and show the shape of the basic building blocks of crystals in molten alloys. Crystal shape determines the strength of the final alloy, and if we can make alloys with finer crystals, we can make stronger alloys.”
“The results are in direct contrast with the classical view of dendrite formation in cooling alloys, and open the door to developing new approaches that can predict and control the formation intermetallic crystals.”