Effect of Ion‐Implanted Cerium on the Growth Rate of Chromia Scales on Ni‐Cr Alloys

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Abstract
The oxidation kinetics of Ni‐30 Cr and Ce‐implanted Ni‐30 Cr alloys are studied at low oxygen partial pressures in the temperature range 900–1100°C. The growth rate of scales on the Ce‐implanted alloys is slower by at least an order of magnitude. The growth rate decreases with increasing Ce concentration but is independent of the ambient oxygen partial pressure. Oxide scales on the Ce‐implanted alloys grow predominantly by inward oxygen diffusion. Microstructural characterization of the oxide scale shows segregation of Ce to oxide grain boundaries and the presence of second‐phase particles. These observations have led to a model in which Ce dopes into , in both the grain boundary and the lattice regions, consuming Cr interstitials through an equilibrium between and Cr interstitials. The consumption of Cr interstitials retards chromium transport to such an extent that inward oxygen diffusion via doubly ionized oxygen vacancies becomes the dominant mode of transport during oxide scale growth.

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