Effect of ultrasonic excitation on the process of L-PBFAM

Abstract

Abstract Laser-Powder bed fusion additive manufacturing (L-PBFAM) is a layer-by-layer metal manufacturing technique that allows unlimited freedom of design with no increase in manufacturing complexity. Currently, parts made through L-PBFAM need to be heat treated and annealed to prevent residual stress, anisotropy, low ductility, and low fatigue life inherent to the process. This paper demonstrates that the adoption ultrasonic excitation to the L-PBFAM process is able to alleviate some of the aforementioned problems. To determine the effects of ultrasonic excitation on the solidification process and microstructure formation, a phase field simulation model incorporating the effect of ultrasonic cavitation in the melt pool was created. Finite Element Method simulation in ANSYS was used to determine the initial macro thermal condition of the melt pool, while the phase field was used to simulate the nucleation and grain growth within the melt pool under ultrasonic excitation based on thermodynamic theory. Robust Design of Experiment (DOE), guided by insights on the L-PBFAM process, was conducted to determine the contributions of different process parameters on the grain size and configuration. The simulated grain structure showed close correlation to optical micrographs of fabricated 304 L Stainless Steel L-PBFAM samples. The ultrasonic excitation is shown to have a significant effect on the microstructure and the cooling rate of the melt pool is found to be the key process optimization parameter affecting the grain morphology.