Oxidation Behavior and Oxide Transformation of a Pt-Modified Aluminide Coating at Moderate High Temperature

• Main Authors: Yanyan Li, Shuai Li, Chao Zhang, Na Xu, Zebin Bao
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Crystals
• Subjects: Pt-modified aluminide coating; alumina scale; single crystal superalloy; microstructure; isothermal oxidation
• Online Access: https://www.mdpi.com/2073-4352/11/8/972

The oxidation performance of a single-phase Pt-modified aluminide coating was assessed in oxidation test at 980 °C in comparison with the single crystal superalloy. The results suggested that the Pt-modified aluminide coating exhibited superior oxidation resistance. During oxidation, the oxide scale formed on bare alloy changed constantly followed by the constitution of the multi-layer scale structure: An outer scale mainly consisted of Cr₂O₃ + NiCr₂O₄ + TiO₂ with scarce protection, and an internal scale mainly consisted of Al₂O₃. The thickness of the outer oxide scale increased with time, where the scale became looser and more porous. Meanwhile, the internal scale was discontinuous. Oxygen and nitrogen inwardly diffused into substrate, forming Ta₂O₅ and TiN particles. In contrast to the complex constitution of oxide scale, a uniform and continuous Al₂O₃ scale formed on Pt-modified aluminide-coated samples after oxidation at 980 °C for 1500 h, which showed no spallation and cracking. Interestingly, θ-Al₂O₃ and α-Al₂O₃ phases remained after such a long oxidation time. It is the relatively lower temperature and the presence of Pt retarded θ-α transformation. The degradation rate from β-NiAl to γ′-Ni₃Al was very slow in the coating. The various development of oxide scale on the coating and substrate was individually studied.