Influence of mean grain size and excess energy on the melting temperature of nanocrystalline aluminum

The influence of the mean grain size and excess energy on the melting temperature of nanocrystalline aluminum was investigated by means of molecular dynamics. It is shown that the smaller the mean grain size and the greater the excess energy caused by the presence of grain boundaries, the lower the melting temperature. Moreover, within the considered range of grain sizes from 2.5 to 10 nm, the difference in melting temperature from the melting temperature of a single crystal is inversely proportional to the mean grain size and decreases linearly with increasing excess energy. In the simulated polycrystal, melting occurred heterogeneously and began primarily from the grain boundaries, after which the melting front moved towards the rest of the volume. In a single crystal without any defects or free surfaces, melting in the model proceeded homogeneously, that is, immediately throughout the volume, and began at a temperature significantly higher than in the presence of grain boundaries. When studying recrystallization in nanocrystalline aluminum, it was found that it occurs more intensively as the temperature approaches the melting temperature, as well as with a smaller initial grain size, that is, at a higher density of grain boundaries. The most intense recrystallization occurred in the case of grain sizes below 4 nm.