Role of Iridium in Hot Corrosion Resistance of Pt-Ir Modified Aluminide Coatings with Na₂SO₄-NaCl Salt at 1173 K

Abstract

Platinum-iridium films (Ir=0,32,46,83,100 at%) were deposited on the nickel-base single crystal superalloy TMS-82+ through magnetron sputtering. After annealing and aluminizing, the Pt-Ir modified aluminide coatings mainly consisted of PtAl₂ and β-(Ni,Pt,Ir)Al phases. Hot corrosion resistance of the different Pt-Ir modified aluminide coatings was evaluated through exposure at 1173 K with the Na₂SO₄+10 mass%NaCl salt coatings. The lowest mass gain (2.99×10⁻³ kg/m², after 100 h) was observed for the Pt-46Ir aluminide coating, which formed the dense and continuous protective Al₂O₃ scale on the surface. The effect of Ir on the corrosion resistance of Pt-Ir modified aluminide coatings was discussed from three aspects—phase transformation, protective scale formation and the role of a Pt-Ir enriched layer.