Deformation-induced intergranular creep cavitation in alpha-iron

Abstract

The nature of cavitational damage accumulation has been analysed on the basis of quantitative measurement of the processes contributing to creep deformation in alpha-iron at 700°C. An assessment of the damage accumulation kinetics during steady state dislocation creep has demonstrated that the overall rate of increase in intergranular cavitation is directly related to the process facilitating grain boundary deformation. The rate at which cavities are nucleated has been related to the creep deformation rate, and observations on the cavity distribution together with -the effect of prior deformation at room temperature are interpreted in support of a mechanism in which cavity nucleation is promoted by slip impingement at selective grain boundary sites. Cavity stability may be achieved by local enhancement of the vacancy supersaturation brought about by grain boundary deformation which relaxes the associated stress concentration. Results favour a process in which subsequent cavity enlargement occurs predominantly by the collection of vacancies produced during the motion in the grain boundaries of dislocations which continue to join the boundaries from the lattice during the remaining creep life.