The velocity of solidification of highly undercooled nickel

At large undercoolings (τ;10 pctT _M, present theories relating solidification velocity to degree of undercooling do not agree well with reported experimental data for the solidification velocity of nickel as a function of undercooling. The present work shows that this discrepancy is due to two factors. First, the majority of previously reported results overestimate the solidification velocity of nickel at large undercoolings. Second, the scatter in experimental data is so large that a functional relationship between undercooling and velocity is not evident. In this study, the solidification velocity of undercooled nickel was measured using a linear array of 38 photodiodes. The results indicate that the velocity of the thermal field generated by the solid/liquid interface approaches a maximum velocity of 20 m s⁻¹ atΔT} ≈ 10 pctT _M (173 K) and men remains constant with increasing undercooling. This suggests that the velocity of the solid/liquid interface, at undercoolings greater than 10 pctT _M, could be limited by attachment kinetics at the interface. GABRIEL CARRO, formerly Research Associate, Department of Applied and Engineering Sciences, Vanderbilt University