RAPID SOLIDIFICATION OF UNDERCOOLED EUTECTIC AND MONOTECTIC ALLOYS

Bulk samples of Co-34.2wt.%Sn eutectic alloy and Ni-5wt.%Ag monotectic alloy were undercooled by up to 244 and 313 K respectively The recale scence velocities were measured as a function of undercooling, and det ermine the upper limits of the actual crystal growth velocities. Theor etical calculations were also accomplished on the basis of the current eutectic and dendritic growth theories. A ''lamellar eutectic-anomalo us eutectic'' microstructural transition was observed for undercooling s of more than 57 K, which agrees qualitatively with Trivedi-Magnin-Ku rz's prediction that there is a maximum growth velocity for regular la mellar eutectic. In the highly undercooled monotectic alloy melt, liqu id Ag phase seemed to nucleate preferentially. The a-Ni phase grew den dritically and facilitated the formation of macrosegregation at the bo ttom and top of the sample through coalescence of Ag droplets.