Nucleation and Dendritic Growth in Undercooled Melts

ABSTRACTTechniques of containerless processing are applied to undercool and solidify metals and alloys. These techniques allow direct measurements of both the undercooling and the crystal growth velocity. Experimental results are presented for studies of nucleation of metastable crystalline phases and quasicrystals. Measurements of the dendrite growth velocity as a function of undercooling are exemplified for dilute Ni-based alloys and intermetallics. The results are analysed within current theories of rapid crystal growth. Their consequences on the formation of grain refined microstructures are highlighted. In addition, recent experiments on the undercooling of magnetic alloys are discussed revealing the existence of long-range magnetic ordering in an undercooled melt.