Origin of subsurface voids in additively manufactured Ni-base alloy IN625 induced by oxidation

Journal article, 2026

Additively manufactured (AM) high-temperature alloys often develop subsurface porosity during oxidation at high temperatures. These voids in the surface-near region can oxidize and cause intergranular oxidation attack. The origin of the oxidation-induced porosity has been studied in AM as well as in the conventionally manufactured (CM) alloy IN625. The alloy specimens were exposed in air, Ar-4%H2-2%H2O, and Cr/Cr2O3 Rhines pack (RP) for up to 1000 h at 900 and 1000 °C. The alloys were also welded with pure nickel to simulate interdiffusion, i.e., Cr loss without oxidation. The diffusion couples were annealed in vacuum for up to 1000 h at 900 and 1000 °C. The CM specimens did not form significant micron-scale subsurface voids while the AM specimens developed extensive subsurface porosity (4–7 vol%) in the oxidation experiments and very limited porosity (less than 1 vol%) in the interdiffusion couples. No voids developed in the RP exposures. Vacancy injection was demonstrated to be the primary trigger of the subsurface porosity in AM.