Evolution of grain boundary character distributions in a cold-deformed Nickel-based superalloy during electropulsing treatment

Abstract

The evolution of grain boundary character distribution in a cold-deformed nickel-based superalloy during the electropulsing treatment (EPT) was studied. The results revealed that both coherent Σ3 boundaries (Σ3c) and incoherent Σ3 boundaries (Σ3ic) were formed in the recrystallized structures mainly by growth accidents during EPT, while the fraction of Σ3ic boundaries became much lower at the higher EPT temperatures. Meanwhile, the fraction of Σ3 boundaries increased with the increasing EPT temperatures till 850 °C, and decreased again at 900 °C. In addition, the high mobility of grain boundary during EPT could promote the formation of stacking errors at some locations of high angle grain boundaries (HAGBs), and thus promoting the nucleation of annealing twins. With the increasing EPT time, the fraction of Σ3 boundaries increased slightly, and the unstable Σ3ic boundaries were transformed into stable Σ3c boundaries, in which intersecting migrating SRX fronts were easier to be extended. On the other hand, a lot of low-Σ CSL grain boundaries were formed in the pre-deformed alloy with the strain of 0.1 during EPT, which was mainly attributed to the development of large grain-clusters. As the strain was large enough, the energy supplied by electropulsing could enable the cold-rolled alloy to effectively utilize the stored energy on the formation of Σ3 boundaries. Besides that, the evolution of Σ9 and Σ27 boundaries was analyzed in detail as well as the corrosion resistance of the studied alloy after different treatments.