Atomistic insights of inconel 690 L-DED process with varying beam diameters

Abstract

Controlling laser beam diameter in laser-directed energy deposition (L-DED) offers an effective means to tailor microstructural evolution in high-chromium nickel-based alloys (Inconel 690). However, conventional simulations and in-situ characterization remain limited in resolving localized melting and solidification at relevant spatial and temporal scales. To address this, a molecular dynamics (MD) model is developed that incorporates the effect of laser movement by applying a directional temperature gradient within semi-elliptical meltpool domains of varying sizes. The model captures meltpool formation, grain evolution, and element segregation at the atomic scale. Simulations reveal that Cr tends to segregate at grain boundaries due to local energy minimization, and grain morphology transitions from equiaxed to columnar structures depending on the interplay between cooling rate and thermal gradient. Small meltpools predominantly exhibit equiaxed grains, while large meltpools favor columnar growth near the bottom and equiaxed grains at the top. Experimental validation was performed using a pre-placed powder L-DED method, with EBSD characterization confirming trends consistent with MD predictions in terms of grain morphology and distribution. Finally, potential applications of the variable-beam-diameter L-DED strategy are proposed. This study provides new atomic-scale insights into how beam diameter influences solidification behavior and microstructure formation, advancing the design of high-performance L-DED processes.