MORPHOLOGY AND GROWTH OF CREEP CAVITIES IN ALPHA-IRON

Electron fractography has been used to study the intergranular cavities formed in alpha-iron during slow tensile deformation at high temperatures. A minimum in ductility is observed at about 700° C: this coincides with conditions where grain-boundary sliding makes a maximum contribution to the overall deformation and where the morphology of the cavities tends to be dendritic and finely terraced. This is explained in terms of the gradient of chemical potential for vacancies which may develop at the cavity periphery during grain-boundary sliding. Under other testing conditions, planar growth is observed and the cavity surface is often faceted. © 1969 Chapman and Hall.