Internal oxidation with significant contribution of oxygen diffusion through the oxide phase

Internal oxidation kinetics of alloys is often controlled by the diffusion of oxygen through the metallic matrix. However high rates of internal oxidation of binary Ni–Al and Ni–Zr alloys can only be explained taking oxygen diffusion along the metal/oxide interfaces into account. In this work ternary Ni–Zr–Y alloys are investigated in H2/H2O atmospheres under isothermal conditions from 800 to 1000 °C. Internal oxidation rates for these ternary alloys are about three orders of magnitude higher than for binary Ni–Zr alloys. These extremely high rates are attributed to fast oxygen diffusion through the oxide phases which are forming during internal oxidation.

► Y and Zr are used as alloying elements.
► During internal oxidation yttria-stabilized zirconia (YSZ) is formed.
► This oxide phase leads to enhanced oxygen diffusion.