Evolution of Σ3n CSL boundaries in Ni-Cr-Mo alloy during aging treatment

The evolution of Σ3n (n = 1,2,3) boundaries in a Ni-Cr-Mo alloy during an aging treatment at 600 °C was investigated based on electron backscatter diffraction (EBSD) measurements. Incoherent Σ3 (Σ3ic) and coherent Σ3 (Σ3c) boundaries were identified using the single-section trace analysis method. The results show that the Σ3n boundary distribution characteristics are changed and that a Pt2Mo-type Ni2(Cr,Mo) superlattice phase precipitates during the aging treatment. Through the analysis and comparison of the average grain diameters measured under the different conditions, the migration behaviors of both the Σ3ic boundaries and random high-angle boundaries (HABs) are found. The migration of the Σ3ic boundaries provides the probability of interaction between Σ3n boundaries. This interaction is responsible for some different types of triple junctions, the increase in Σ9 and Σ27 boundary fractions and interrupted connectivity of the network of random HABs. However, the Σ3c boundaries' consumption caused by the migration of random HABs and the difficulty of forming new Σ3c boundaries lead to the decreased fraction of Σ3c boundaries. The further discussion about the increase in the fraction of Σ3ic boundaries indicates that the generation mechanism of the Σ3ic boundaries during the aging treatment differs from the models applied to recrystallization and subsequent grain growth processes.