Achieving Equiaxed Grain Microstructure and Isotropic Properties in Titanium Thin-Walled Components by Laser-Directed Energy Deposition

Abstract

Laser-directed energy deposition (L-DED) has emerged as a crucial innovation in aerospace manufacturing, particularly to produce titanium thin-walled components. However, achieving fine equiaxed grains with isotropic properties at the component level remains a significant challenge. This study investigated the application of a new metastable β titanium alloy with Fe addition (Ti-3Al-6Fe-6V-2Zr, wt%), focusing on optimizing 8 axis robot-based trajectory planning, combined with parameter adjustments, to achieve a homogeneous microstructure and isotropic properties at the component level. In the optimized trajectory plan, the grain size progressively decreased from the bottom (74.3 µm) to the top (63.7 µm) of the thin-walled blade, while the aspect ratio remained relatively constant at approximately 1.6. The equiaxed grain structure of the as-built part further demonstrated that the optimized trajectory planning strategy achieved a yield strength (Rp0.2) of 966±1 MPa and elongations of 26.3±1.1% in the horizontal direction, as well as 970±3 MPa and elongations of 26.1±0.7% in the vertical direction. The mechanical property anisotropy was reduced to less than 5% across all positions in the blade. This study demonstrated the importance of integrating titanium alloy design with trajectory planning to achieve isotropic mechanical properties in thin-walled components.

Keywords: Laser-directed energy deposition, thin-walled components, titanium alloys, isotropic mechanical properties, trajectory planning