A novel La micro-alloying approach for microstructure and high-temperature performance improvement of LPBF-fabricated GH4169 superalloy

GH4169 superalloy is widely used in aero-engine components at 650°C due to its excellent high-temperature mechanical properties. LPBF offers unparalleled freedom in fabricating complex components. However, the intrinsic rapid solidification of LPBF often leads to detrimental phases, which have adverse effects on high-temperature performances of GH4169. This work employs a 0.14 wt% La micro-alloying strategy to investigate its effects on the microstructure and high-temperature properties of LPBFed-GH4169. Based on microstructure characterization and theoretical analyses (DFT and thermodynamic simulation), it is found that La increases the diffusion energy barrier for Nb, transforming δ phases at GBs from acicular to granular/short-rod like morphologies while promoting intragranular δ phases precipitation. Concurrently, La increases γ″/γ′ phases density, and improves γ″ stability by reducing γ/γ″ interfacial energy. These modifications suppress intergranular crack initiation/propagation, impede continuous dislocations movement to promote their uniform distribution. Therefore, the stress rupture life and elongation of 0.14La alloy reach 46.6 ± 2.4 h and 6.2 ± 0.05%, together with an UTS of 1165 MPa and a ductility of 25.5% at 650°C. All of them are much higher than those of La-free counterparts. This work establishes the specific role of trace La in concurrently regulating δ morphology and γ″/γ′ stability in GH4169. The combined experimental and theoretical analysis further clarifies the multi-scale strengthening mechanisms responsible for the simultaneous improvement in high-temperature strength, ductility, and stress-rupture resistance at 650°C.