Intermetallic Al-based coatings such as Al–Ni, Al–Cr, and Al–Pt are widely used as bond coats and/or as oxidation protection of turbine blades. Investigations during earlier work indicated promising thermal stability and oxidation resistance of intermetallic Al2Au-based coatings. Hence, here we study in detail the microstructure and mechanical properties of unbalanced magnetron sputtered Al–Au films with AlAu at. % ratios of 1.85, 2.00, and 4.32. The film with an AlAu ratio of 2.00 has a single-phase Al2Au dense columnar structure in the as-deposited state and a hardness of 8GPa. With increasing Al and Au contents the morphology changes into a more equiaxed structure with additional Al, AlAu, and Au phases, respectively. During growth, excess Al of the film with an AlAu ratio of 4.32 forms lamellar nanosegregations (3nm thick) in the Al2Au domains. The simultaneous nucleation and growth of Al2Au, AlAu, and Au phases in the coatings with an AlAu ratio of 1.85, with their different growth mechanisms, leads to the formation of pores having an average size of 150nm. These Al- and Au-rich films, compared to Al2Au, have reduced hardnesses of 4 and 2GPa, respectively, due to the additional soft metallic phases and pores present. Our results show that within the Al–Au system the single-phase intermetallic Al2Au films exhibit the best structural and mechanical properties for protecting oxidation sensitive materials.

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