FAILURE OF OXIDE SCALES

The importance of the mechanical stability of oxide scales in the corr osion resistance of metallic components operating at high temperature is discussed. The mechanisms of scale fracture due to stresses generat ed during growth, applied directly or by thermal cycling, are describe d. Methods of measuring these mechanical properties in situ have been described and measurements of their fracture toughness produced. The i nfluence of defects in the scale on fracture behaviour is discussed, t ogether with methods whereby the effect of small irregular-shaped defe cts can be quantitatively assessed. Finally, the influence of strain r ate on scale fracture is summarized, and by comparing the yield and fr acture behaviour of surface scales it is suggested that the mechanical behaviour of these scales over a wide range of operating conditions c an be predicted.