Molecular dynamics study of the formation of the nanocrystalline structure in nickel nanoparticles during rapid cooling from the melt

Abstract

The formation of a nanocrystalline structure in nickel nanoparticles during their rapid cooling from the molten state was studied using the molecular dynamics method. The influence of the cooling rate in the range from 5∙1010 to 5∙1012 K/s and particle diameter from 1.5 to 11 nm on the features of the resulting structure, the amount of stored energy, and the temperature of the onset of crystallization were considered. At a rate above 1013 K/s, crystallization did not have time to occur in the model used; at a rate from 1012 K/s to 5∙1012 K/s, a nickel particle crystallized with the formation of a nanocrystalline structure. With a decrease in the cooling rate, a decrease in the density of defects and the number of grains in the final structure of particles was observed. It is also shown that the crystallization temperature during rapid cooling is inversely proportional to the particle diameter and increases with decreasing cooling rate. The melting of a nanocrystalline particle, due to the high content of grain boundaries and other defects, occurs at lower temperatures compared to a single-crystal particle.