Evolution of annealing twins in Inconel 625 alloy during tensile loading

Abstract

In situ electron backscatter diffraction (EBSD) has been demonstrated as a powerful tool for tracking the microstructural evolution of alloys; however, it has not yet been applied to analyse the evolution of annealing twin boundaries (TBs) during loading. In this study, we investigated the evolution of annealing TBs and their interaction with dislocations in Inconel 625 alloy under room-temperature uniaxial tension using in situ EBSD and ex situ transmission electron microscopy (TEM) techniques, which provided experimental evidence and detailed insights into the interaction between TBs and dislocations during plastic deformation. The results showed that annealing TBs remained stable during the initial deformation period (strain of 5%). With increasing strain, high-angle grain boundaries (HAGBs) changed to low-angle grain boundaries (LAGBs), the fraction of TBs decreased, and the TBs reacted with dislocations. As a result, the TBs gradually lost coherence and transformed into random HAGBs, which then partially transformed into LAGBs. The tensile yield strength of 348 MPa, ultimate tensile strength of 634 MPa, and elongation of 50.7% of the Inconel 625 alloy were attributable to the reaction of grain boundaries and pre-existing annealing TBs with dislocations as well as to the formation of stacking faults and deformation nano-twins during tensile loading. In addition, the deformation of the Inconel 625 alloy was mainly caused by dislocation slip during the initial deformation period, whereas deformation twinning occurred in the later period.