Due to the metastable state in the as-sputtered Ni-3Cr-20Al and Ni-10Cr-11Al-8Ti nanocrystalline coatings, gamma' phase precipitation will occur during oxidation and then produce a gamma and gamma' two-phase microstructure. In this paper, as-sputtered Ni-3Cr-20Al and Ni-10Cr-11Al-8Ti nanocrystalline coatings were initially oxidized at 1000 degreesC in air for 200 h and 90 min, respectively in order to produce a two-phase microstructure in these two coatings. And then the formed oxide scales were removed. The oxide formation on the Ni-3Cr-20Al and Ni-10Cr-11Al-8Ti coating surface with a gamma and gamma' two-phase microstructure has been examined after 200 It oxidation at 1000 degreesC in air. Compared with the as-sputtered coating, the oxide formation on the Ni-10Cr-11Al-8Ti two-phase coating surface was not altered, both TiO2 dispersions on Al2O3 scales were formed. Whereas the oxide dispersions on AI,03 scale formed on the Ni-3Cr-20Al coating has changed from NiAl2O4 on the as-sputtered single phase coating to NiO on two-phase coating surface. The formation mechanism is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.