Improvement of wetting and necking of nickel-based superalloys fabricated by sequential dual-laser powder bed fusion via particle-scale computational fluid dynamics

Abstract

The stability of additively manufactured products is mainly affected by their pore defects and surface quality and critical in their applications in various engineering fields. Based on this understanding, a three-dimensional high-fidelity particle-scale computational fluid dynamics (CFD) model for a sequential dual-laser powder bed fusion (SDL_PBF) process was developed in this paper. Using the model, the mechanism of improving the product quality of nickel-based superalloy GH4169 by dual laser sequential scanning strategies was particularly discussed. The effects of laser powers and offsets of sequential dual lasers on the molten pool wetting, pores, and necking were also specially studied, in which the process parameter window was determined through orthogonal experiments. The CFD simulations showed that, when the offsets of the sequential dual lasers are about 3.7 times of the laser radius, the wetting of the molten pool is the best in our test, because the molten pool flows around, resulting in a larger overlapping area. The SDL_PBF with a suitable rear laser source can eliminate the pores and the entrained air formed by the collapse of the recoil depression, which in turn is caused by the front laser. This is because the recoil depression generated by the rear laser can break down the pores caused by the incomplete melting of the front laser, so that the gas in the pores communicates with the air outside, and the liquid in the molten pool is replenished, thereby eliminating the pores and reducing the porosity of the product, which is consistent with the experimental results. In addition, the simulation results showed that the molten pool can flow stably and quickly due to the combined action of strong Marangoni force and steam recoil force as well as weak surface tension in the case of the SDL_PBF with appropriate process parameters, resulting in greatly improved surface quality. Therefore, this work can provide a way for improving multi-laser additive manufacturing of high-performance products. • A particle scale CFD model of SDL_PBF was developed for the first time. • The optimized process window was obtained through orthogonal experiment. • The mechanism of improving product quality was explored at mesoscopic scale.