CRYSTALLIZATION KINETICS AND GLASS-FORMATION IN UNDERCOOLED FE-NI-P-B ALLOY MELTS

The glass-forming ability of Fe40Ni40P14B6 alloys has been investigated under the conditions of containerless solidification of small droplets during free fall in a drop tube. Glassy spheres in diameter up to 300 mum could be prepared provided the melt is overheated by 250 K above the liquidus temperature prior to solidification of the droplets. The critical cooling rate for glassy solidification is estimated to be 8000 K/s. Full temperature-time-transformation curves (TTT) are developed using current theories of nucleation and crystal growth. Under the assumptions of polymorphous crystallization and homogeneous nucleation, the TTT curves suggest critical cooling rates much lower than experimentally found. However, the results can be explained if it is assumed that primary crystallization of intermetallic Ni3P initiates solidification of the undercooled melt.