Intermediate Temperature Creep and Deformation Behaviors in IN718 Superalloys under Different Pre-Stretched Status

The solution annealed Inconel 718 alloy was pre-stretched at different status, followed by a two-stage aging treatment and then subjected to medium temperature creep to investigate the creep deformation behavior from the perspective of microstructural evolution. The experimental results indicated that the precipitate morphology and creep resistance of the alloy were slightly changed with the increase in pre-stretching from 0 to 1%. The samples without pre-stretching revealed relatively homogeneous distribution of precipitates and higher volume fraction of sigma 3 twin boundaries, resulting in higher creep life compared with the pre-stretched specimens. Furthermore, the creep life decreased by 33.5% as the pre-stretch amount increased to 4%, which could be explained by microtopography change. Specifically, pre-stretching induces precipitation behavior and defects in the alloy, which presented faster coarsening and a monotonous increase in the number of microvoids with increasing pre-stretching value. Microstructural analysis showed that the microvoids and microcracks arising from the delta phase at the grain boundary were responsible for the creep fracture of alloy, and the creep deformation mechanism was microtwinning and dislocation cutting through the gamma "phase, which were present irrespective of the pre-stretching amount.