COMPETITION BETWEEN STRESS GENERATION AND RELAXATION DURING OXIDATIONOF AN FE-CR-AL-Y ALLOY

The residual biaxial stress in Al2O3 scales formed during oxidation of Fe-22.O%Cr-4.8%Al-0.3%Y in the temperature range 1000-1300 degrees C have been measured using Cr3+ luminescence piezospectroscopy. The stre ss measurements together with substantial dimensional changes of the s pecimens show! that oxidation produces high compressive growth stresse s in the Al2O3 scale in addition to thermal-mismatch stresses that ari se during cooling from the oxidation temperature. The magnitude of the growth stress is determined by two opposing processes: stress generat ion, associated with lateral growth of the scale, and stress relaxatio n in both the metal and oxide. The scale lateral-growth strain continu ously increases concurrently with the scale thickening. Creep in the o xide is a major relaxation process when the scale is thin, while metal deformation becomes significant during the later stages of oxidation at higher temperatures.