Packing Changes in Melting, Freezing, and Coalescence of Titanium Nanoparticles from Atomic Simulations

Abstract

Atomic simulations by using an embedded-atom-method potential were used to study changes of packing patterns in melting, freezing, and coalescence of titanium particles that contained tens to thousands of atoms. The packing evolution under dynamics processes leads to shape fluctuations. Small particles prefer icosahedron configurations. Large particles undergo hexagonal close-packed (HCP)-body-centered cubic (BCC) and BCC-melt transitions in a heating-cooling cycle. Calculations of specific heat are higher than those predicted from the classical Dulong-Petit law. Upon cooling, the hysteresis transition temperatures depend on the particle size and surface morphologies. The connection at room temperature results from contact and deformation between near facets of two particles. Complex facets exist after coalescence. A single-domain structure occurs for the coalescence of two relatively small particles. The occurrence accompanies the HCP-BCC transition, and the melting temperature is improved. In these large particles, coalescence particles consist of domains before melting.