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Segregation of Neodymium in Chromia Grain-Boundaries during High-Temperature Oxidation of Neodymium Oxide-Coated Chromia-Forming Alloys

Research paper by S. Chevalier, G. Bonnet, K. Przybylski, J. C. Colson, J. P. Larpin

Indexed on: 01 Dec '00Published on: 01 Dec '00Published in: Oxidation of Metals



Abstract

The influence of MOCVD reactive-element-oxide (REO) coatings (Nd2O3) onhigh-temperature, chromia-forming alloy oxidation was investigated. REOcoatings decreased steel oxidation rates and greatly enhanced oxide scaleadherence. Uncoated and coated F17Ti samples were oxidized over thetemperature range 700–1050°C in air at atmospheric pressure. SIMSexperiments were performed on oxidized-coated samples in order to determinethe RE distribution through the oxide scale. Nd was distributed across theoxide layers with a higher concentration in the outer part of thescale. Transmission-electron microscopy (TEM) investigations were performedto more precisely locate the RE through the scale. Transverse crosssections, prepared on oxidized Nd2O3-coatedFe–30Cr (model system), showed that Nd, associated with Cr and O,segregated at chromia grain boundaries. It is thought that this is the maincause of the beneficial effects usually ascribed to the RE inchromia-forming alloys. The effect of chromia grain-boundary segregation onchromia growth mechanism and its influence on the reactive-element effect(REE) are discussed.