On the Characteristic Features of Dislocations during Ratcheting-Creep Interaction

The present investigation systematically represents for the first time the density and role of characteristic dislocations in controlling ratcheting and ratcheting-creep behavior of A356 Al alloy. The dislocation characteristics were evaluated using the modified Williamson-Hall method from x-ray diffraction profile analysis. The obtained results indicated that the strain accumulation during ratcheting increased with an increase in both mean stress (sigma(m)) and stress amplitude (sigma(a)). The dislocation density of all the deformed specimens increased by at least three orders of magnitude compared to the specimen in as-received condition. Further, ratcheting was primarily controlled by significant variation of screw dislocations, and its quantitative fraction was inversely varied with applied sigma(m) and sigma(a). Ratcheted+crept specimens, on the other hand, showed the dominance of edge dislocations. The creep deformation followed by ratcheting was associated with work softening, with an inverse relationship between the quantity of edge dislocations and strain accumulation. This variation in quantity and nature of dislocations was due to the effects of the annihilation of dislocations and the type of loading in the respective phenomenon.

Automated summary

This study systematically investigates the density and role of characteristic dislocations in controlling ratcheting and ratcheting-creep behavior of A356 Al alloy for the first time. The results show that the accumulation of strains during ratcheting is related to both mean stress and stress amplitude, with screw dislocations playing a significant role in controlling ratcheting behavior. In contrast, edge dislocations dominate in ratcheted+crept specimens, which is associated with work softening and an inverse relationship between edge dislocation quantity and strain accumulation.