Stacking fault energy in short-range ordered γ-phases of Ni-based superalloys

Abstract

Several aspects on the stacking fault energy (SFE) in short-range ordered γ-phase model alloys of new nickel based superalloys are discussed. Using transmission electron microscope weak beam observations and computer simulated images of dissociation widths, the SFE was determined as a function of temperature. The values for both alloys are close (31±4 mJ m−2 for the Re-containing alloy and 28±6 mJ m−2 for the Ru-containing alloy). In both cases, the dissociation widths remain quite constant up to 350°C and a slight decrease is observed at higher temperature. The deformation micromechanisms and the constancy of the SFE up to 750°C are analysed in connection with short-range order. The deformation at low temperature is characterised by dislocation pile ups, the influence on the dissociation widths of the internal stress due to such configuration is analysed. The calculation reveals a strong effect on the leading dislocation of the pile-up whose dissociation distance can be reduced at most by 50%.