Atomic scale melting/solidification behavior and structural evolutions of AlCoCrFeNi high-entropy alloy in selective laser melting process

Abstract

Comprehension of the evolutions and phenomena that occur on the atomic scale can become a bridge toward a greater understanding of the properties of materials on the macro scale. In this study, molecular dynamics simulations were performed to investigate nano-structural evolutions in the SLM process of the near-equiatomic AlCoCrFeNi high-entropy alloy. Fifteen simulation systems were designed by altering laser power (400–800 eV/ps), scanning speed (0.2–2.0 Å/ps), and hatch spacing (5 and 10 nm) as the process variables for addressing their effects on the structure at the atomic scale. The results showed that the effect of parameters on the atomic displacement is decreased from laser power to scanning speed and hatch spacing, respectively. It was also indicated that the HCP stripes form due to the extreme cooling rates experienced in the process. Furthermore, the reduction of the hatch space can improve the surface quality by spreading the atoms accumulated in the fusion boundary of the previous laser track. These results indicate that controlling volumetric energy density (VED) by lowering laser power and scanning speed as much as possible, is beneficial to obtain the optimum crystal structure of the manufactured parts in this process. Although decreasing the hatch space has no considerable effect on the crystal structure, it can help to achieve a good surface finish which is essential in the SLM industry.

Keywords

• SLM
• Molecular dynamics
• Simulation
• HEA
• Powder bed fusion (PBF)
• Nano-structure