Achieving strength–ductility synergy and enhanced intergranular corrosion resistance in the Inconel 625 alloy via twin boundary tailoring

The effects of twin boundaries (TBs) and grain sizes have a significant influence the mechanical properties and intergranular corrosion (IGC) resistances of low-to-medium stacking fault energy face-centered cubic (FCC) materials. The effect of the grain size on the yield strength and IGC weight loss of an alloy can be evaluated using the Hall–Petch relationship; however, a trade-off exists between the yield strength and the IGC resistance. In this study, the effects of different annealing TB proportions were investigated in terms of the mechanical properties and IGC resistance at the same grain size level to provide experimental evidence and detailed insights into the mechanisms by which annealing TBs impart their effects. A higher proportion of annealing TBs led to an excellent IGC resistance and strength–ductility synergy in the Inconel 625 alloy. This extra enhanced strength and ductility observed at 25 and 600 °C were attributed to the higher proportion of annealing TBs exhibiting a low grain boundary (GB) energy and an excellent thermal stability, which impede dislocation slip and enable dislocation accumulation. The excellent IGC resistance of the alloy was attributed to the connectivity of the random high-angle grain boundary network being interrupted by the Σ3 n -type triple junctions, which are connected by higher proportion and low-energy stable TBs (Σ3) and high-order TBs (Σ9 and Σ27) in the larger grain clusters. This indicates that tailoring TBs at the same grain size level could be an effective means to simultaneously enhance the mechanical properties and IGC resistances of Ni-based superalloys.