Solidification from undercooled melts

Techniques of containerless processing are applied to undercool and solidify metals and alloys. These techniques allow direct measurements of both the undercooling and the cn stal growth velocity. Experimental results are presented for studies of nucleation of quasicrystalline and metastable crystalline phases. Measurements of dendrite growth velocity as a function of undercooling are presented for dilute Ni-B and CoSi alloys. The results an analysed within current theories of rapid crystal growth. The consequences of solute trapping on the formation of metastable supersaturated solutions are demonstrated. In analogy to the process of solute trapping, disorder trapping is investigated occurring during rapid solidification of deeply undercooled alloys of intermetallics. In addition, studies of crystal growth in undercooled semiconductors are presented. Finally, undercooling and its importance in the formation of grain-refined microstructures is highlighted. A new model is presented to explain the grain-refinement process in undercooled melts by the fragmentation of primarily formed dendrites. Recent investigations on magnetic ordering in undercooled melts of Co-Pd alloys are shortly introduced. (C) 1997 Elsevier Science S.A.