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MM: Metall- und Materialphysik

MM 35: Growth

MM 35.5: Vortrag

Donnerstag, 30. März 2006, 15:45–16:00, IFW B

Dendritic Solidification of undercooled Ni-based alloy melts — •Sven Reutzel^1,2, Peter K. Galenko², and Dieter M. Herlach² — ¹Ruhr-University, Institute of Experimental Physics IV, 44780 Bochum — ²German Aerospace Center (DLR), Institute of Space Simulation, 51170 Cologne

Morphology and size of dendritic microstructures sensitively depend on the solidification conditions, in particular on the crystallisation dynamics of the melt. Depending on the velocity with which a dendrite propagates into the undercooled melt a great spectrum of non-equilibrium phenomena can occur. For instance, if the velocity comes of comparable order with the atomic diffusive speed (1 - 10 m/s) solute trapping leads to the formation of supersaturated solutions and disorder trapping in intermetallic alloys produces disordered superlattice structures with completely different mechanical properties as the ordered counterparts. Also, as investigated in the present work grain refined alloys are solidified from the undercooled melt.

For a quantitative description of non-equilibrium solidification processes the growth velocity of the propagating dendrites in undercooled Ni and selected Ni-based alloy melts is experimentally determined as a function of undercooling on electromagnetically levitated drops. High accuracy measurements are realised even at small growth/undercooling values by applying a high speed camera technique, which allows for direct observation of morphology and dynamics of the solidification front. The analysis will be important to investigate and understand the development of various microstructures in as solidified materials.