Controlling macroscopic segregation of the directed energy deposited Cu-Fe alloy by laser oscillation

To achieve macro-segregation control and obtain a finer grain structure, oscillating laser directed energy deposition (OL-DED) was applied for the first time in the manufacturing of Cu-Fe immiscible alloys. Compared to the L-DED process, the oscillating laser did not affect the microscopic components, but it could regulate the segregation morphology. As the oscillation frequency (f) increases, the morphology of the gamma-Fe segregated phase gradually transformed from "crescent" to "column" and discrete "bulk". Moreover, the oscillating laser helped to reduce the grain size of each phase in the Cu-Fe alloy. When f increased to 200 Hz, the grain size of the Cu and Fe phases reached their minimum values, measuring 4.4 mu m and 7.2 mu m, respectively, which represented reductions of 52.2% and 66.7% compared to the absence of oscillation. Furthermore, at 300 Hz, the segregation morphology transforms into discrete "block-like" structures with higher thermal resistivity and heat accumulation, leading to grain coarsening. Due to the grain refinement effect induced by the oscillating laser, the OL-DED fabricated Cu-Fe alloy exhibited superior tensile properties compared to the L-DED samples, achieving the highest yield strength and tensile strength at 200 Hz, measuring 345 MPa and 418 MPa, respectively. Finally, the study successfully established a correlation between the melt flow state and the macro-segregation morphology of the Fe phase based on the Reynolds model derived from the melt stirring theory, and the evolution mechanism of the grain structure was discussed based on the solidification theory.