Two-phase PtAl 2 +β-(Ni,Pt)Al and single-phase β-(Ni,Pt)Al coatings were fabricated on DD5 Ni-based superalloy and pure Ni substrates. A coating/pure Ni substrate system was studied to determine the diffusion behaviour of Pt in the Ni–Al–Pt ternary system. The evolutions of morphology, phases and component concentration during thermal cycles were analysed. It was found that there is a phase shift from PtAl 2 to β* in the two-phase coating, and Kirkendall porosity was observed in the single-phase coating. Our results further indicated that there are two different diffusion paths of Pt in the Ni–Al–Pt system.