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

In-situ internal stress determinations by X-ray diffraction have been performed during pure iron oxidation (p(O2)=2×10−3 Pa, T=800°C). The compressive stress, initially present in a blank substrate, due to surface preparation, is completely released at 400°C. On yttrium implanted iron no stress is initially present in the substrate. Under oxidising conditions, the in-situ compressive stress level determined in the FeO scale during oxidation does not strongly depend on the presence of implanted yttrium. On blank and implanted specimens, the compressive stress changes from −400±80 to −150±100 MPa after 30 h oxidation. However, after cooling to room temperature, blank specimens show compressive residual stresses, while implanted samples show tensile residual stresses. Our results also indicate that epitaxial relationships between the oxide scale and the substrate can be a source of stress in an oxide scale. A way to lower compressive stresses can be the use of yttrium ion implantation.