T.E.M. Statistical Characterization of Grain Boundaries in Polycrystalline NiO Scales Obtained by High Temperature Oxidation of Nickel

Abstract

This paper describes a statistical study carried out by T.E.M. on the geometrical features of more than 100 grain boundaries observed in polycrystalline nickel oxide scales. The data (orientation relationships, possible coincidence indices, grain boundary planes and their orientations in relation to the surface, etc.) were collected to give a statistical insight into the NiO scales which develop during oxidation of nickel at 1100°C. The results show 1. the growth of columnar outer oxide scale during oxidation, as well as the existence of an equiaxial zone close to the Ni/NiO interface. 2. a random distribution of grain boundary planes (with the exception that there is no {011} grain boundary plane). 3. a random distribution of the orientationsrelationships. That is, despite their low energy, special grain boundaries do not play any significant role during the growth of nickel oxide scales on nickel.