The atomic force microscope (AFM) has been used to observe and characterize for the first time surface steps and grooves on the faces of Cr2O3 grains formed as an oxide scale on Ni-30Cr and Ni-30Cr-0.5Y alloys during high temperature oxidation. The very high spatial resolution of the AFM is required to characterize these features. We propose that these surface features, whose dimensions are in the range of nanometers and tens of nanometers, may be interpreted as evidence of highly localized plastic deformation of the oxide scale. The size and spacing of the steps and grooves are consistent with models of plastic deformation based on slip bands derived from dislocation climb or dislocation glide. Mechanical twinning and the models for stress-driven surface instability are also possibly responsible for some surface features. The addition of yttrium to the alloy seemed to enable enhanced plastic deformation of the scale. The strain corresponding to the observed features, estimated by simple models, could relax a significant part of oxide growth and thermal stresses.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Materials Research|
|State||Published - Mar 1997|
Bibliographical noteFunding Information:
This work was supported by a grant from the U.S. Department of Energy under Contract No. DE-FG02- 88ER45337. The authors are grateful to Professor James H. Stout for his constructive comments, to Dr. Susie Yang for her assistance and advice on the verification of high-resolution AFM images, and to Hongtao Zhu and Qi Wang for their assistance in the oxide scale orientation measurements by x-ray diffraction. The authors would also like to thank The Oak Ridge National Laboratory for providing the cast Ni–30Cr and Ni–30Cr–0.5Y alloys.