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Deformation behaviour in the Nickel-base superalloy 625 has been studied by tensile testing at four temperatures: 295, 223, 173 and 77 K. The microstructure has been investigated using TEM, FIB-SEM, EBSD and ECCI techniques. Deformation in the alloy turns out to be a competitive course of events between at least two deformation mechanisms, namely dislocation slip and deformation twinning. Slip is the predominant deformation mechanism at higher temperatures. While at 77 K, deformation induced twinning gives an extra degree of freedom as one of the main deformation mechanisms, i.e., the material shows a twin induced plasticity, TWIP, behaviour. Ab initio calculations indicate that the influence of cryogenic/sub-zero temperatures on the stacking fault energy of this alloy can be limited and therefore the formation of deformation twins cannot be determined solely by the stacking fault energy. The results implies that critical strain and strain hardening rate influences the deformation twinning onset and twinning rate., QC 20240703

Deformation twinning behaviors have been studied in high Ni alloys, Alloy 28 or Sanicro 28 and Alloy 625 at RT and at cryogenic temperature. The microstructures were evaluated using SEM-EBSD. Some constitutive approach has also been used in the discussion on the deformation twinning in high Ni-alloys. The results show that deformation twinning can occur in high Ni alloys depending on the chemical composition, strain range and stress conditions. TWIP can occur in the Ni based superalloy Alloy 625 at cryogenic temperature, which increases both strength and ductility. This is the first report of this phenomena for this alloy. Deformation twinning in high Ni alloys occurs heterogeneously in the material, depending on crystallographic parameters such as grain orientation and Schmid factor. Formation of deformation twins can lead to high texture in the material, which will contribute to the increase of strength. The mechanisms for the formation of deformation twins in high Ni alloys have been discussed.