Improved Spallation Resistance of the Oxide Scale by Hf/Y Co-doping in Ni-Based Superalloy at High Temperature

Ni-based superalloys added with comparably higher concentrations of single-doped Hf and co-doped Hf/Y are prepared by vacuum induction melting (VIM). The oxidation properties up to 300 h at 900 °C, 1000 °C, and 1100 °C are investigated. The undoped alloy exhibited a minimum oxidation rate at 900 °C and 1000 °C. The co-doped alloy showed a higher oxidation rate; however, it possesses better scale adhesion, and no spallation occurs. Hf-doped alloy showed a lower oxidation rate and better scale adhesion at 900 °C and 1000 °C, but exhibited a shorter lifetime at 1100 °C. The spallation of the Hf-doped alloy is attributed to the precipitation of the HfO 2 in and beneath the oxide scale. The spallation in the undoped alloy is accredited to the thermal expansion mismatch between the growing oxide scale and superalloy substrate. Incorporating two reactive elements (REs) in alloy minimized the precipitation of RE oxide in the oxide scale, diminished internal oxidation in the alloy, and decreased oxide scale spallation.