Nucleated and continuous ordering inCu3Au

The early-stage ordering kinetics in ${\mathrm{Cu}}_3$Au has been investigated by in situ time-resolved x-ray scattering. At temperatures above the first-order transition point, $T_{\mathrm{tr}}$, short-range order fluctuations reeequilibrate in a few seconds after a quench from high temperature. At temperatures just below $T_{\mathrm{tr}}$ the fluctuations relax to a metastable state which then decays by relatively slow nucleation and growth. At lower temperatures, the time scales of the two processes become similar. The ordering becomes continuous well above the classical spinodal temperature.