The ligament-size effect to the coefficient of thermal expansion for nanoporous gold: A molecular dynamics simulation study

Nanoporous gold (NPG) is a latest class of nano-lightweight material, characterized by excellent strength and toughness stemming from its unique microstructures. Besides mechanical properties, some experiments have demonstrated a dimensional effect between the thermal properties, such as coefficient of thermal expansion (CTE), and NPG's ligament size. In this paper, molecular dynamics simulations are performed to probe the relationship between the CTE of NPG and microstructural factors such as ligament size, porosity and grain boundary. The results show that the CTE of NPG increases gradually approaching the bulk gold, as the ligament diameter increases from about 6.5 nm to 18.5 nm. The analytic approximation formulas to calculate the linear CTE of single crystal NPG have been constructed based on the surface effect which matches the simulation results fairly well. Additionally, upon investigating the impact of grain boundaries and porosity on CTE, it has been noted that the presence of grain boundaries and narrow ligaments in NPG will introduce extra defects, consequently leading to a decrease in CTE.