Molecular Dynamics Simulation of Fe-Based Metal Powder Oxidation during Laser Powder Bed Fusion

Abstract

Because the laser powder bed fusion process is generally completed in a confined space and in a very short time, it is difficult to study material oxidation during this process using traditional methods. To address this knowledge gap, in this work, we used molecular dynamics (MDs) based on a reaction force field (ReaxFF) to clarify the atomic-level interaction mechanism between metal atoms and oxygen molecules during laser powder bed fusion. The ReaxFF potential energy model has variable charges that can dynamically handle charge changes between atoms and the breaking and formation of chemical bonds that occur during oxidation reactions. We investigated the effects of laser power, scanning speed, region position, and oxygen concentration on powder oxidation. The results show that the laser power and scanning speed affected the oxidation degree by changing the energy input density, and the oxidation degree increased with the energy input density. Different forms of oxidation occurred near the melt channel due to the existence of a temperature gradient, and the degree of oxidation increased with the temperature. Atoms in the metal powder model underwent selective oxidation, which was related to the potential energy of their atomic position. A larger potential energy made it easier for iron atoms to overcome the energy barrier during the initial stage of oxidation, making them easier to oxidize.

Effect of Fe–O ReaxFF on Liquid Iron Oxide Properties Derived from Reactive Molecular Dynamics

“…In this context, reactive molecular dynamics (MD) simulations enabled by reactive force fields (ReaxFFs) have proven their ability to provide fundamental insights into the oxidation of gas, liquid, and solid fuels, predicting material properties and other physicochemical processes . For the specific case of iron, (reactive) molecular dynamics simulations have been used for various applications: to determine the material properties of pure liquid iron, the oxidation of nanoparticles and surfaces with oxygen, − the oxidation of Fe with CO 2 , and H 2 O, and also for the oxidation of alloys . In the study of Thijs et al reactive MD simulations were used to investigate the thermal and mass accommodation coefficients (TAC and MAC, respectively) for the combination of high-temperature iron­(-oxide) and air.…”

Additive manufacturing of Inconel-625: from powder production to bulk samples printing

“…Both experimental and modeling methods are useful for analyzing and optimizing powder generation during AM feedstock preparation (Wang and Zhou, 2022). Powder features such as particle size distribution (PSD), flow properties and packing density may be measured and analyzed by experimental methods (Azeem et al , 2019a).…”