Enhancing high-temperature oxidation resistance of nickel superalloy obtained by laser powder bed fusion via reactive electric spark treatment

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.