We have a diverse portfolio of projects investigating aspects of growth phenomena in metallic systems undercooled by electromagnetic levitation and flux melting techniques. Our expertise research into the formation of feather grains in DC cast aluminium, the production of ultra-hard materials by the control of microstructure on the nanoscale, non-equilibrium effects during the solidification of ordered intermetallics, the effects of flow on solidification, dendritic stability at high growth velocities and transitions to ‘dendritic seaweed’ and fractal morphologies.
Facilities for studying the solidification of metals far from equilibrium include;
High vacuum levitation/fluxing furnace
This furnace isolates the melt from its container in order to prevent nucleation. In the absence of a solid container to act as seed on which new solid can start to grow, it is possible to cool the metal several hundred degrees below its melting point while keeping it in the liquid state (undercooling). When solidification is initiated a bright growth front propagates across the sample (recalescence) from the point of nucleation as latent heat is rapidly evolved from the growing solid. The progress of this solidification front can be filmed at high frame rate (up to 40,000 fps) to image the solidification process as it occurs. The highest velocity yet recorded is 160 m/s in high purity Cu undercooled by 330 K.
6m high vacuum drop-tube
During drop-tube processing several grams of metal is melted in an alumina crucible, which has a number of small (0.2-0.5 mm) holes laser drilled into its base. When the metal is fully molten the crucible is pressurised to 2-5 times atmospheric pressure, producing a fine spray of droplets, which solidify in flight. Very high cooling rates are achieved, ranging from a few hundred K/s for droplets of 0.5mm in diameter, to > 40,000 K/s for droplets < 75 μm in diameter. In addition, as the droplets are in free fall they experience significantly reduced gravity, eliminating flow in the melt. See below to watch a video of the melt spray.
a video of the melt spray