Oxidation in Water Vapor of Inconel 625 Fabricated by Additive Manufacturing

The high-temperature oxidation characteristics of Inconel 625 superalloy fabricated by additive manufacturing were studied at 900 and 1000 °C in a mixture of dry air and 12%vol water vapor. At 900 °C, oxidation in water vapor was slightly faster than oxidation in air ( kp wv 900 = 3.4 × 10 −3 mg 2 cm −4 h −1 and kp a900 = 2.9 × 10 −3 mg 2 cm −4 h −1 ). At 1000 °C, oxidation in air ( kp a1000 = 74 × 10 −3 mg 2 cm −4 h −1 ) occurred faster than oxidation in water vapor ( kp wv1000 = 45 × 10 −3 mg 2 cm −4 h −1 ) although for the early oxidation up to ~ 14 h the opposite behavior was observed. Features like crack and pore formation accounted for increasing the ionic mobility through the oxide and the oxidation rate in water vapor at this temperature. Chromia Cr 2 O 3 was the main oxide found on the surface of the alloy, but intergranular oxidation zones having Ti- and Al-rich oxides were also formed below the metal-oxide interface. Evidence of localized CrO 2 (OH) 2 volatilization was also found.