The Nucleation and Growth of Cavities in Iron during Deformation at Elevated Temperatures

Abstract

A fractographic technique has been used in a quantitative study of intergranular cavities formed in alpha-iron during creep at 700°C. By studying the role of grain-boundary sliding and the effect of prestrain followed by creep under various conditions, an assessment was made of the factors that govern the kinetics of cavity nucleation and growth. During the early stages of creep cavity growth occurred in all three dimensions, being proportional in each to σ^1·5 t ^0·5, where σ is stress and t is time. As creep proceeded cavity growth continued solely by spreading in the boundary plane and the above dependence held for two dimensions only. Cavity nucleation occurred at an early stage but the number of cavities increased continuously with strain and was proportional to the square of the stress over a limited range.