Influence of yttrium implantation on growth stresses developed in FeO scales formed on pure iron at 800 degrees C.

In-situ internal stress determinations by X-ray diffraction have been perfo rmed during pure iron oxidation (p(O-2) = 2 x 10(-3) Pa, T = 800 degrees C. The compressive stress, initially present in a blank substrate, due to sur face preparation, is completely released at 400 degrees C. On yttrium impla nted iron no stress is initially present in the substrate. Under oxidising conditions, the in-situ compressive stress level determined in the FeO scal e during oxidation does not strongly depend on the presence of implanted yt trium. On blank and implanted specimens, the compressive stress changes fro m - 400 +/- 80 to - 150 +/- 100 MPa after 30 h oxidation. However, after co oling to room temperature. blank specimens show compressive residual stress es, while implanted samples show tensile residual stresses. Our results als o indicate that epitaxial relationships between the oxide scale and the sub strate can be a source of stress in an oxide scale. A way to lower compress ive stresses can be the use of yttrium ion implantation. (C) 1999 Elsevier Science S.A. All rights reserved.