Investigations on the Diffusion of Platinum between CMSX-4 Superalloy and Platinum-Enriched Bond Coat

• Main Authors: Mingwen Bai, Ying Chen, Ping Xiao
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Coatings
• Subjects: bond coat; platinum; diffusion; thermodynamic; thermal barrier coatings
• Online Access: https://www.mdpi.com/2079-6412/11/4/441

The depletion of Pt in Pt-enriched bond coats due to inter-diffusion with superalloys has been a critical concern for the long-term oxidation resistance of thermal barrier coatings. This study investigated the diffusion behaviour of Pt between CMSX-4 superalloys and two commercial Pt-enriched bond coats comprising intermetallic γ′/γ-phase or β-phase, with the aim to understand the mechanism that leads to the depletion of Pt at high temperatures. The results demonstrated that the diffusion of Pt in superalloy disrupts its phase equilibrium, causes a significant lattice parameter misfit between the γ-phase and γ′-phase, and results in the formation of large γ′-grains with irregular shapes and random orientations. In addition, by using the Thermo-Calc software, Pt was found to have negative chemical interactions with both Al and Ta that stabilise Pt by decreasing its chemical activity. The depletion of Al due to the growth of Al₂O₃ scale during oxidation increases the activity of Pt and therefore accelerates the inwards depletion of Pt towards superalloys.