Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Preoxidation procedure of PM 2000 to generate in situ a smooth alumina scale

Preoxidation of PM 2000 leads to the formation of an outer a-alumina scale fine, dense and tightly adherent to the substrate. Surface roughness increases about one order of magnitude as a consequence of the formation of small oxide nodules, the density and size of which depend on the temperature of oxidation, exposure time and surface finishing. In general the number and size of the nodules increased with increasing temperature and/or exposure, i.e. scale thickness.

Possible procedures to suppress nodule formation during oxidation have been analysed. The oxide nodules formed during the first hour of exposure depend strongly on the temperature and the oxygen partial pressures. The samples exposed in vacuum during the first 90 sec formed a pure alumina layer, whereas the samples that were introduced into the air-filled furnace showed an iron-chromium-oxide mixed surface layer underneath that the alumina formed.

Mechanical polishing of the alumina-coated material may reduce the roughnes to about 30-40 nm. Further effort should be addressed to reduce this value to 20 nm that is required for bulk ceramics used for wearing parts

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