Laser directed energy deposition/milling hybrid additive manufacturing of thin-walled GH4169 alloy: Effect of processing strategy on its microstructure and mechanical properties

Laser directed energy deposition (LDED)/milling hybrid manufacturing process was utilized to produce thinwalled GH4169 parts for the first time. The impact of processing strategy, including varied milling rounds and building heights, on the printability, microstructure, and mechanical properties of the GH4169 parts were investigated. Increasing the number of milling rounds within a certain height along the build direction reduced the distance between adjacent hybrid-processed interfaces. Base on a comparative study of the thermal histories of LDED and LDED/milling processes, it was found that the microstructure at the hybrid-processed interfaces experienced less heat accumulation and fewer heating/cooling cycles. Therefore, GH4169 parts after milling exhibited a lower proportion of the Laves phase area with refined sizes and greater interdendritic Nb segregation than those produced by LDED alone. With increased milling rounds, the ultimate tensile strength and yield strength of the thin-walled GH4169 part fabricated using the hybrid process increased from 777.0 MPa to 823.0 MPa and from 506.0 MPa to 538.0 MPa, respectively, while the elongation decreased from 35.1% to 27.2%. These effects can be attributed to an increase in milling round within a constant forming distance, resulting in higher stiffness of the fabricated thin-walled GH4169 part. Finally, a thin-walled GH4169 blade with excellent dimensional accuracy and surface finish was successfully produced using the LDED/milling hybrid process, demonstrating the potential applicability of this process to nickel-based alloys.