INFLUENCE OF CERIA COATINGS ON GROWTH STRESSES DEVELOPED IN WUSTITE SCALES FORMED ON PURE IRON AT 800-DEGREES-C

In situ XRD stress determinations have been performed during oxidation of pure iron (p(O-2 = 2 x 10(-3) Pa, T = 800 degrees C)). The compres sive stress, initially present in the substrate due to surface prepara tion, is completely released at 400 degrees C. Under the test conditio ns, the in situ compressive-stress level determined in the FeO scale d uring oxidation is not strongly dependent upon the stress varies from -400 +/- 80 MPa to -150 +/- 100 MPa during 30 hr oxidation. The decrea se is quicker at the beginning of the test performed on blank specimen s. Epitaxial relationships between the wustite scale and iron (under l ow-pressure starting conditions) caused the in situ compressive stress in the oxide scale to be two times greater compared to the usual test conditions. This indicates that epitaxial relationships can be a sour ce of stress in an oxide scale that ceria coatings may lower compressi ve stresses.