Dendritic solidification of undercooled Ni-based melts

Abstract

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. <br>For aquantitative 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 material.</br> <p>Acknowledgements:</p> <p>This work is financially supported by ESA under the MAP-project "NEQUISOL - Non-Equilibrium Solidification, Modelling for Microstructure Engineering of Industrial Alloys" and by DFG under the project No. He 1601/13.</p>