Microstructure and mechanical properties of GH4169 thin-walled parts fabricated by ultrasonic vibration assisted laser directed energy deposition/milling hybrid process

Abstract

Ultrasonic vibration (UV) was employed for the first time to assist laser directed energy deposition/milling hybrid process (LMHP) in fabricating GH4169 thin-walled parts. The effects of building strategy, including UV-assistance, milling rounds, and building heights, on the thermal history, printability, microstructure, and mechanical properties of the fabricated thin-walled parts were systematically investigated. The thermal history analysis revealed that the UV-assistance resulted in a reduction in the average temperature of the laser scanning area, an increase in pore defects, and compromised surface finish due to an enlarged molten pool and enhanced heat transfer. Moreover, the thin-walled parts exhibited refined grain structure, equiaxed crystallization, homogenized element distribution, decreased proportion of the Laves phase, and increased strength with UV-assistance. Notably, the grain size was significantly reduced from a millimetre scale to 86.2 μm, while the average yield strength increased from 489.1 MPa to 523.6 MPa and the average ultimate tensile strength increased from 747.1 MPa to 830.4 MPa. Furthermore, introducing more hybrid-processed interfaces within a certain distance allowed for further grain refinement, enhanced strength, and decreased elongation in the GH4169 thin-walled part. This work is anticipated to provide a comprehensive understanding of the thin-walled parts fabricated by UV-assisted LMHP with high surface quality and superior mechanical properties.