PNNL

Abstract

We report in situ atomic-scale visualization of the dynamical three-dimensional (3D) growth of NiO during initial oxidation of Ni-10at%Cr using environmental transmission electron microscopy (ETEM). Despite the thermodynamic preference for Cr2O3 formation, cubic NiO oxides nucleated and grew epitaxially as the dominating oxide phase on the Ni-Cr (100) surface during initial oxidation. The growth of NiO islands proceeds through step-by-step adatom mechanism in 3D, which is sustained by surface diffusion of Ni and O atoms. Although the shapes of oxide islands are controlled by strain energy between oxide and alloy substrate, local surface kinetic variations can lead to the change of surface planes of oxide islands. These results demonstrate that surface diffusion dominates initial oxidation of Ni-Cr in these test conditions.