Microstructural characterization and oxidation performance of solution-annealed and precipitation hardened wire-arc additively manufactured Inconel 718 superalloys

This research work investigated the effects of standard solution-annealed (SA) treatment on microstructure and chemical characteristics Inconel 718 (IN718) superalloys fabricated using tungsten inert gas welding based wire-arc additive manufacturing (WAAM) process. A commercial wrought IN718 product was also studied for comparison. It observed that WAAM parts developed highly-textured large columnar austenite (γ) grains along build-up direction due to epitaxy high thermal dissipation rate. The micro-segregation Nb produced an inhomogeneous γ-matrix precipitating non-hardening laves phases as a result constitutional undercooling, energy input slow cooling rate After solution treatment, SA sample remained be solid-solution formed delta (δ) plates with undissolved residual in Nb-enriched regions. These deprived precipitation beneficial hardening γ″ γ′ particles during treatment. high-temperature oxidation study SA-treated samples obeyed parabolic law which independent temperatures. mechanisms formation oxide scale were found temperature dependent. At 800 °C, only thin continuous layer Cr2O3 externally at air-alloy interface. multi-layer external air-scale interface, inner Nb-rich complex Ti0.67Nb1.33O4 scale-alloy interface internal sub-scale Al2O3 900–1000 °C. Due lattice diffusivity Mn+2 Ti+4 cations through scale, TiO2 MnCr2O4 outermost part 1000 reaction process growth alloys mainly dominated by outward diffusion Cr+3 activation energies range 250–290 kJ/mol (chromia) forming Ni-based superalloys.