The Structure of Thin Oxide Films Formed on Nickel Crystals

Abstract

A study was made of the structural details of thin oxide films formed on the (100), (111), (110), and (311) of nickel. Oxidation temperatures ranged from 400° to 600°C, and the oxide films produced were between 25 and 500Aå thick. An x‐ray technique was utilized to measure the average strain in the films, the mosaic spread, the thickness, and the epitaxial relationships between oxide and metal. The oxide films on all crystal planes studied were observed to contain large numbers of short circuit diffusion paths. A change in the extent of these diffusion paths in the oxide on a given crystal plane produced a corresponding change in the oxidation rate. Furthermore, there was a variation in the extent and efficiency of the short circuit diffusion paths as a function of crystallographic orientation of the substrate, and this variation correlated directly with the marked oxidation rate anisotropy exhibited by nickel.

Effects of crystallographic orientation on the early stages of oxidation in nickel and chromium

“…The data consistently show a trend indicating that as the underlying crystallographic orientation deviates away from the reference direction of <111> the oxidation rate increases. The results obtained here for oxidation of Ni at 700°C are generally in agreement with single crystal studies that consistently show more rapid oxidation on (001) faces than on (111) faces [3][4][5][6][7][8]. In addition, the relationship (111) < (011) < (001) was observed for oxidation of single crystal Ni at 500 and 600°C [4] and for corrosion of Ni-based superalloys at low acid concentrations where a passivating film forms [17,18].…”

“…The dependence of oxidation rate on crystallographic orientation has also been suggested for Fe and Cr [9][10][11][12][13][14]. In oxidation studies on Ni single crystals, more rapid oxidation is consistently observed on (001) faces than on (111) faces [3][4][5][6][7][8]. In those studies, where oxidation occurs for up to hundreds of hours, the character of the grain boundaries that form in the oxide is responsible for the observed differences in oxidation rate.…”

“…Although many studies of oxidation neglect the effects of the underlying microstructure (e.g., grain size, grain boundary character, and crystallographic orientation), surface orientation has been shown to impact the rate of oxidation in both Ni and Cu alloys [1][2][3][4][5][6][7][8]. The dependence of oxidation rate on crystallographic orientation has also been suggested for Fe and Cr [9][10][11][12][13][14].…”

“…Oxides grown on (111) surfaces tend to form fewer grain boundaries because the epitaxial growth relationship (i.e., (111) Ni ||(111) NiO ) has only two variants in oxide alignment. However, oxides grown on the (001) face, which also have an epitaxial relationship (i.e., (001) Ni ||(111) NiO ), form more grain boundaries because there are four oxide alignments possible [3,5,6]. A higher concentration of grain boundaries, which are known to exhibit higher diffusivities than the bulk [15], is responsible for the observed differences in oxidation rate.…”

“…While the (111) and (001) faces have been studied extensively, the (011) has received considerably less attention. In general, the (011) face is found to form an oxide that is polycrystalline and contains many more high diffusivity paths (e.g., high-angle grain boundaries and dislocations) than do the oxides on (001) and (111) faces [3,6]. In addition, oxidation of the (011) surface has been shown to be most sensitive to effects of surface contamination [6].…”