Enhancing high-temperature oxidation resistance of nickel superalloy obtained by laser powder bed fusion via reactive electric spark treatment
(National University of Science and Technology MISIS, Leninsky pr. 4, Moscow 119049, Russia)
Abstract: The high-temperature oxidation resistance of the nickel superalloy prepared by the laser powder bed fusion (LPBF) has been significantly increased as a result of in-situ formation of a thermal barrier layer (α-Al2O3 + CaMoO4) during oxidative annealing of surface layers modified by electric spark treatment (EST). The reactive EST of the LPBF-built items based on nickel EP741NP alloy was carried out with low-melting Al-12%Si, Al-6%Ca-0.6%Si and Al-7%Ca-1%Mn electrodes. It was found that under EST done by Al-7%Ca-1%Mn electrode an intermetallic (β-NiAl + γ''''-Ni3Al) 15 μm-thick layer reinforced by spherical oxide (CaMe)O nanoparticles was formed. Formation of that structure increases the wear resistance of LPBF nickel superalloy by 4.5 times. Further oxidative annealing at 1000 °C leads to a formation of continuous two-layered coating with an inner layer of α-Al2O3 and an outer layer of CaMoO4, which together act as an effective barrier preventing the diffusion of oxygen into the bulk of the superalloy.
Key words: Ni-base superalloy; laser powder bed fusion (LPBF); reactive electric spark treatment (EST); low-melting electrode; oxidation resistance; thermal barrier layer