Influence of Y Addition and Processing Route on Grain Boundary Character Distribution in Nickel Alloy 718

This work investigates how yttrium additions and distinct thermomechanical processing routes influence the grain boundary character distribution (GBCD) of alloy 718. Two Y-alloyed compositions (0.011 and 0.067 wt pct Y) were produced and compared with the standard alloy without yttrium. The materials were processed through two iterative cold-rolling routes followed by annealing, with total accumulated reductions of approximately 5 pct (low-strain route) and 36 pct (high-strain route). Electron backscatter diffraction (EBSD) analyses showed that yttrium markedly increases the fraction of low-Σ CSL boundaries after hot working, primarily by enhancing grain boundary mobility and promoting Σ3 twin formation. These effects lead to distinct microstructural evolutions during subsequent processing. In the Y-containing alloys, the low-strain route (2.5 pct per pass) effectively increased the fractions of Σ3, Σ9 and Σ27 boundaries. Connectivity analyses confirmed that the low-deformation route was the most efficient in disrupting random boundary networks in the Y-alloyed samples. In contrast, the higher-strain route (18 pct per pass) induced extensive recrystallization in all alloys, limiting the proliferation of CSL boundaries and driving Σ3 n fractions toward values typical of recrystallized microstructures. Overall, yttrium promotes an optimized GBCD in alloy 718 by increasing boundary mobility and twin formation, although excessive deformation or excessive Y additions may mitigate these benefits through recrystallization or Zener pinning.