Interdiffusion behavior of Pt-diffused γ + γ′ coatings on Ni-based superalloys

Platinum-diffused γ + γʹ coatings (~ 20 at.% Al, ~ 22 at.% Pt) were synthesized on René 142 and René N5 Ni-based superalloys by electroplating the substrates with ~ 7 μm of Pt, followed by an annealing treatment in vacuum at 1175 °C. In order to study the compositional and microstructural evolution of these coatings at elevated temperatures, interdiffusion experiments were carried out on coated specimens in the temperature range of 900–1050 °C for various durations. Composition profiles of the alloying elements in the γ + γ′ coatings before and after diffusion experiments were determined by electron probe microanalysis. Although the change of the Al content in the coatings was minimal under these interdiffusion conditions, the decrease of the Pt content and increase of the diffusion depth of Pt into the substrate alloys were significant. A preliminary diffusion model was used to estimate the Pt penetration depth after diffusion.