Some substructural aspects of high-temperature creep in metals

Abstract Some recent data obtained by investigating dislocation substructure formed in high-temperature creep of several metals are summarized, and some substructural aspects of both steady-state and primary creep are discussed on the basis of the data analysis. It is found that similar densities of dislocations unbound in sub-boundaries (free dislocations), ρ, exist in various metals in steady-state creep at the same value of the ratio of applied stress to elastic modulus. In steady state the mean subgrain diameter is proportional to the reciprocal of the square root of the total dislocation density ρc=ρ+ρSB ρSB being the density of dislocations forming sub-boundaries. Recovery in steady-state creep most probably takes place almost exclusively by annihilation of free dislocations and not by the entry of these dislocations into the sub-boundaries. The total dislocation density was found to increase in the course of primary creep. Most of the dislocations generated go to build the sub-boundaries as the density ρ decreases unless steady state is reached. As the internal stress increases with the strain in primary stage, the main contribution to it most probably follows from subgrain boundaries.