Microstructural evidence for short-circuit oxygen diffusion paths in the oxidation of a dilute Ni-Cr alloy

C. K. Kim, L. W. Hobbs

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

A comparative study of high-temperature oxidation of Ni containing 1 at.% Cr and pure Ni was carried out. Instead of the conventional kinetics study using thermogravimetry, a microlithographic marker experiment was designed. Observation of the markers using cross-sectional TEM and SEM has revealed striking differences in the scale morphology, microstructures, and oxidation mechanisms between pure Ni and the Cr-doped Ni substrates. In particular, the results suggest that a small addition of Cr promotes significant inward transport of oxygen. Marker experiments revealed that NiO grown on pure Ni is wholly attributable to outward-cation diffusion. In contrast, NiO grown on Ni-1 at. % Cr exhibited formation of a substantial inner layer having a submicron grain size, established by the markers to have formed from oxygen ingress. For pure Ni, voids were observed to be distributed only within oxide grains. In contrast, for Ni containing 1 at. % Cr, elongated pores formed extensively along oxide-grain boundaries. Formation of new fine-grain oxide in these pores was observed to have sometimes completely resealed the void. It is, therefore, proposed that the transport of oxygen in the case of oxide scale grown on Ni-1 at. % Cr occurs via voids (pores) formed by vacancy coalescence at the grain boundaries.

Original languageEnglish
Pages (from-to)247-265
Number of pages19
JournalOxidation of Metals
Volume45
Issue number3-4
DOIs
StatePublished - 1996 Jan 1

Keywords

  • Ni and Ni-1 at.% Cr oxidation
  • Photolithographic marker
  • Short-circuit diffusion path

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