Evaluation of wave-like nucleation events in Al-4%Si alloys with addition of TiB2 particles by time-resolved and in-situ observation

Abstract

This paper proposes a technique for evaluating the nucleation sequence and grain refinement phenomena during solidification of a metallic alloy. Time-resolved and in-situ transmission imaging using a monochromatized X-ray in a synchrotron radiation facility, SPring-8, showed wave-like nucleation events, in which nucleation sequentially occurred along the temperature gradient, in an Al-4mass%Si alloy with addition of TiB2 (Al-3mass%Ti-1mass%B alloy). The position and time of nucleation events were measured to analyze the nucleation wave. The wave motion, which was calculated from the measured data, was used to evaluate the difference of nucleation temperature for each dendritic grain from the wave front. The standard deviation of the temperature difference in the Al-4mass%Si alloy with TiB2 particles was evaluated to be as small as 0.25 K. The addition of TiB2 reduced the standard deviation to more than one tenth. This study shows that the dispersion or the standard deviation is a representative figure for evaluating the potency of nuclei.