Laser-direct energy deposition of the high γ′ LW 4280 Ni-based superalloy

This study investigates the structure-properties relationships of LW 4280 processed using laser direct energy deposition. The alloy exhibited a typical dendritic microstructure in the as-deposited condition, with a significant microsegregation of alloying elements. Fine γ′ precipitates were present in the dendrite cores, while the interdendritic regions showed relatively coarser γ′ precipitates and Ta, Hf, and W-based carbides. The γ′ precipitates were enriched in Al, and Ta, whereas the γ matrix was rich in Cr, Co, W, Re and Mo. The application of a two-step sub-solvus heat treatment to the as-deposited specimens resulted in the growth of Ta, Hf, and W-based carbides, the formation of Cr-based carbides, and a bimodal distribution of roughly 49 % γ′ precipitates. Despite heat treatments, chemical variations persisted between dendrite cores and interdendritic regions. The difference in lattice parameters between the γ phase and γ′ precipitates was used to determine the lattice mismatch in both the as-deposited and heat-treated specimens. The heat treatment increased the hardness from 434 ± 15 HV 0.1 to 495 ± 17 HV 0.1 . Heat-treated specimens also exhibited excellent thermophysical and mechanical properties at both room temperature and elevated temperatures. Stress rupture tests at elevated temperatures revealed an outstanding rupture life, including 1084 h at 788 °C/448 MPa, 119 h at 871 °C/276 MPa, 458 h at 927 °C/179 MPa, and 93 h at 982 °C/138 MPa. Axial fatigue tests were conducted at 982 °C under stress amplitudes of 168, 134, and 121 MPa, resulting in fatigue lives of 3.5E+ 06, 1.0E+ 07, and 1.13E+ 07 cycles, respectively. • Crack-free, dense LW 4280 specimens were fabricated using laser–direct energy deposition. • A slower cooling rate resulted in the formation of γ′ precipitates during deposition. • Heat treatment resulted in the growth of γ′ precipitates and the carbides. • Heat-treated LW 4280 showed excellent mechanical properties at low and high temperatures.