STUDY OF THE INITIAL-STAGES OF OXIDATION OF YTTRIUM-IMPLANTED CHROMIUM USING X-RAY-DIFFRACTION AND ABSORPTION-SPECTROSCOPY

The beneficial effect of the addition of yttrium by ion implantation o n the oxidation behaviour of chromium has been studied. Emphasis was p laced on the initial stages of oxidation during rapid heating to 900 d egrees C by exposing samples to intermediate temperatures and withdraw ing them for analysis. Characterization of the surface layers was carr ied out with two X-ray techniques at glancing angles. Glancing angle X -ray diffraction (GAXRD) at various angles was used to obtain structur al and texture information as a function of depth. X-ray absorption sp ectroscopy at the yttrium K-edge enabled information to be gained on t he local structure around this element. The short-range structure of t wo yttrium-rich oxides, Y2O3 and YCrO4, was observed. The latter is be lieved to represent the structure around yttrium segregated to the oxi de grain boundaries. It is thought that this segregation in the chromi a scales can cause many, if not all, of the reported beneficial reacti ve element effects. The Y2O3, present as particles, is expected to pla y only an indirect role by forming a source of yttrium, which slowly s egregates to the grain boundaries. The possible effects of the grain b oundary segregation of yttrium on the oxidation behaviour of the mater ial and the oxide scale properties are discussed. Copyright (C) 1996 E lsevier Science Ltd.