Effects of Cr on twinning in Ni-based superalloys.

Micro-twinning is the major creep deformation mechanism in Ni-based superalloys at temperatures above 700 °C. Recent experiments suggest that superlattice stacking faults in γ′ phase may serve as precursors for twin formation. Segregation of alloy elements to these precursors may have a significant effect on the formation and extension of micro-twins. Using atomistic modeling, we investigated and explained the effects of Cr on these processes. Our results indicate that depending on the site preference of Cr in Ni 3 Al γ′ phase, two drastically different deformation behaviors can be expected. Occupying Al sites, Cr significantly accelerates deformation twinning. Cr on Ni sites, on the other hand, suppresses twin growth and slows down the high temperature deformation creep. These results help to rationalize the experimentally observed puzzling effects of alloy composition on creep resistance. [Display omitted] [ABSTRACT FROM AUTHOR]