PHASE SELECTION PROCESSES IN UNDERCOOLED NI-V MELTS

An electromagnetic levitation technique was applied to undercool bulk melts of Ni100-xVx in the composition range 41 < x < 73. The alloys we re undercooled up to 330 K. Time resolved measurements of the rapid te mperature rise during recalescence were used to investigate phase sele ction processes as well as the crystal growth behavior as a function o f undercooling. The experimental results are analysed by means of theo ries of nucleation and dendrite growth. A metastable phase diagram is developed which predicts the primary crystallization of competing alph a (fcc), beta (bcc) and sigma intermetallic phases as a function of bo th composition and undercooling. The application of this metastable ph ase diagram to rapid quenching processes is verified by its comparison with results obtained from investigations of splat quenched Ni-V samp les.