Metallurgical study of mechanical milling mechanism in eutectic nanopowders: The role of heterogeneities

A study of the addition of Pb-Sn nanoparticles, as heterogeneities, during the high-energy milling (HEM) process to achieve eutectic nucleation was carried out using chemical arguments, as well as X-ray powder diffraction and microscopy techniques. In addition to a change of energy source input, growth of eutectic alloys with the addition of Pb-Sn nano-heterogeneities promotes a more refined microstructure. The conventional melting/solidification method produced coarser microstructure than that of the high-energy milling process. To determine the mechanism responsible, eutectic nucleation in high-purity Pb-Sn mixtures, with and without the addition of Pb-Sn nano-heterogeneities, was studied. It was found that the addition of nano-heterogeneities exerts a positive effect on the nucleation process, while nucleation was not detected in the unmodified powder mixture. It was concluded that mixtures with the addition of nano-heterogeneities contain a large number of potent supersaturated nuclei that are susceptible to promote eutectic nucleation.