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 on the oxidation behaviour of chromium has been studied. Emphasis was placed on the initial stages of oxidation during rapid heating to 900 degrees C by exposing samples to intermediate temperatures and withdrawing them for analysis. Characterization of the surface layers was carried out with two X-ray techniques at glancing angles. Glancing angle X-ray diffraction (GAXRD) at various angles was used to obtain structural and texture information as a function of depth. X-ray absorption spectroscopy at the yttrium K-edge enabled information to be gained on the local structure around this element. The short-range structure of two yttrium-rich oxides, Y2O3 and YCrO4, was observed. The latter is believed to represent the structure around yttrium segregated to the oxide grain boundaries. It is thought that this segregation in the chromia scales can cause many, if not all, of the reported beneficial reactive element effects. The Y2O3, present as particles, is expected to play only an indirect role by forming a source of yttrium, which slowly segregates to the grain boundaries. The possible effects of the grain boundary segregation of yttrium on the oxidation behaviour of the material and the oxide scale properties are discussed. Copyright (C) 1996 Elsevier Science Ltd.