Inverse growth transport in thermal chromia scales on Fe–15Cr steels in oxygen and in water vapour and its effect on scale adhesion

Chromia scales of near equivalent thickness were thermally grown on Fe–15Cr steels in 16 O 2 followed by 18 O 2 and in H 2 16 O followed by H 2 18 O. SIMS oxygen isotope profiles showed that oxidation in oxygen proceeded by outward chromium transport, whereas oxidation in H 2 O involved inward transport of hydroxide species. Adhesion measurements using room temperature tensile testing could quantify adhesion energy: 20 J m −2 for O 2 -grown scales and 80 J m −2 for scales formed in H 2 O, a result of this mass transport inversion.