Oxide scale formation and microstructural degradation of conventional, Pt- and Pt/Ir-modified NiAl diffusion coatings during thermocyclic exposure at 1100 °C

•Slurry deposition of Pt- and Pt/Ir-layers leads to homogenous modified aluminide coatings after aluminisation.•Conventional NiAl coatings degrade faster than their Pt- and Pt/Ir-modified counterparts during thermocyclic exposure.•Pt addition to NiAl coatings enhances the resistance against oxide scale spallation during thermocyclic exposure.•Ir addition to NiAl coatings slows down the interdiffusion and particularly obstructs Ni-enrichment in the coating. The microstructural degradation of Pt- and Pt/Ir-modified NiAl coatings during thermocyclic exposure at 1100 °C was investigated. Detailed microstructural investigation revealed the different beneficial effects of Pt and Ir. Platinum was found to be active in the healing mechanism of the oxide scale, whereas Ir incorporation provided an obstruction to interdiffusion. Oxidized surface morphologies exhibited the formation of a dense alumina scale on top of the PtAl coating, whereas Al-depletion in the NiAl coating was accelerated due to scale spallation and interfacial void formation. Additionally, Pt inward- and Ni outward diffusion was substantially reduced in the Ir-containing coatings.