Surface corrosion behavior of β-(Ni,Pt)Al coating: α-Al2O3 decohesion-induced failure mechanism

[Display omitted] •The α-Al2O3 at grain-boundary ridges of (Ni,Pt)Al coating is prone to cracking under short-term corrosion.•Cl plays a major role in α-Al2O3 embrittlement under tensile stress at grain-boundary ridges.•H ions in corrosion test further reduce the tensile strength of α-Al2O3, deepening the corrosion.•Pre-oxidation process for (Ni,Pt)Al coating effectively enhances α-Al2O3 integrity in corrosion test.•Oxide scale at grain-boundary ridges is more brittle after NaCl-corrosion rather than Na2SO4. In marine and gas turbine environments, impurities like hydrogen (H), sulfur (S) and chlorine (Cl) ions frequently impact continuity and integrity of the oxide scale of Pt-modified aluminide coating. This study systematically investigated the segregation behavior of these impurities using first-principles calculations, to reveal their weakening potency on both α-Al2O3 bulk and grain boundary (GB). The energetic properties, including separation work, surface energy and GB energy, are strongly associated with existing form of impurities. The interstitial S and Cl atoms are particularly intensive in reducing cohesion of α-Al2O3 in comparison with solute state. The single-atom S- and Cl-doping with S and Cl have similar effects on the embrittlement of α-Al2O3 bulk/GB, and the Cl-introduction exhibits extreme brittleness once the atomic concentration increases. Interestingly, single H-addition has no significant effect on the α-Al2O3 decohesion, while its weakening potency on α-Al2O3 is further enhanced upon contacting with S and Cl atoms. Therefore, we decomposed strengthening energy into mechanical contribution and chemical contribution, finding that the incorporation of H increases the chemical contribution to decohesion of α-Al2O3. This work, along with initial corrosion behavior of various (Ni,Pt)Al coatings, aims to deepen understanding of H, S and Cl on α-Al2O3 decohesion from multiple perspectives.