Molecular dynamics study of thermodynamic properties of nanoclusters for additive manufacturing

Abstract

4D printing is a new process that involves the use of 3D-printed objects and materials able to change shape over time. Therefore, a comprehensive understanding of 3D-printed objects is needed prior to developing 4D-printed ones. Selective laser melting (SLM) is a very promising 3D printing technique; however, because of the intense heat input, problems such as balling phenomena, deteriorated surface finish, tensile residual stress, and part distortion are still frequently observed in the SLM process. For such cases, micro-/nano-scale heat management becomes a key problem. Indeed, heat conduction during the SLM process is significantly affected by powder diameter and compactness. The thermodynamic behaviors of powder due to laser heating are considerably different from that of a solid bulk body. In this paper, molecular dynamics (MD) and empirical embedded atom computational methods are applied to study the thermodynamic properties of Ag nanoclusters, which are 2.1-6.9 nm in diameter during the heating and cooling process. We find that the melting point, heat of fusion, entropy of fusion, and surface energy are highly dependent on nanocluster size. Remarkably, we define the mesoscale regime where the properties of nanoclusters can be described in terms of macroscopic concepts with well-defined bulk and surface thermodynamic properties.