Solidification Velocities in Deeply Undercooled Silver

Abstract

We measure the solidification velocity of pure Ag as a function of undercooling temperature from the melting point ($T_m=1235\mathrm{K}$) to $0.6T_m$ using ultrafast, pump-probe laser experiments. The thickness of the liquid layer, while it solidifies, is measured using optical third harmonic generation. We show that velocity reaches a maximum value at $0.85T_m$, and then remains nearly constant with additional undercooling. These results contradict simple collision-limited models, but they are in good agreement with molecular dynamics simulations presented here, which show that the crystallization velocity depends weakly on temperature from $0.85T_m$ to less than $\approx 0.1T_m$.