Diffusional growth of creep voids

Abstract

The development of the theory of diffusional growth of creep voids is reviewed. It is pointed out that the process of growth can be considered as the removal of atoms from the surface of the voids and the plating of these as an even layer along those grain boundaries which are normal to the stress axis. The plating process jacks apart the two hemispheres of the void on either side of the boundary and the significance of this is explored. Plating also leads to overall creep strain and this is an important deformation mode; it is a form of diffusional creep which has been termed ‘Hull–Rimmer creep’ and its magnitude and kinetics have been determined. It is suggested that a suitable array of precipitate particles prevents the formation of a plated layer of even thickness and this inhibits void growth. The active nucleation sites for voids are considered to be precipitate particles in sliding grain boundaries. It is usually not feasible to completely remove all inclusions from materials and the most effective means of avoiding high-temperature creep embrittlement is to arrange to have copious intergranular precipitates in the microstructure of the alloy. These precipitates may suppress grain-boundary sliding and hence minimize void nucleation. As an added safeguard the diffusional growth of any void which did form would be inhibited by the presence of the precipitates.