Microstructure Evolution of Zr/Re Co-modified PtAl Coatings During Isothermal Oxidation

Abstract:

The Zr/Re co-modified PtAl coating was fabricated by electroplating Pt vacuum diffusion annealing and composite electroplating Ni-Zr/Re layer+arc ion plating Al layer vacuum diffusion annealing. The isothermal oxidation experiment was carried out at 1100 ℃ for 200 h. The phase composition and microstructure of the as-annealed coating and the oxidized coating were characterized by SEM, XRD and EPMA, and the distribution law of the modified elements and the evolution law of the coating microstructure during oxidation were investigated. The results show that the Re-rich precipitates dispersed in the coating aggregate and grow during oxidation and form volatile oxide Re₂O₇. The Zr solid-solved in the coating co-precipitates with the Ta element diffused into the coating from the substrate alloy, and some Zr enters the Al₂O₃ scale to form Zr-rich oxides, reducing the growth rate of the Al₂O₃ scale. In addition, with the mutual diffusion of elements between the coating and the substrate, the β phase in the coating undergoes martensitic transformation. The precipitates in the mutual diffusion zone change from plate-like to particle-like, and the coexistence relationship of Cr-rich precipitates and Re, Cr and W-rich precipitates is found in the secondary reaction zone of the coating.