Microstructure evolutions and deformation mechanisms of a Ni-based GH3536 Superalloy during loading at 293 K and 77 K

In this study, tensile tests and interrupted experiments at different true strain levels were performed at 293 K and 77 K to reveal the deformation mechanisms of GH3536 superalloy during loading. The microstructure evolutions of the alloy with strain at both temperature were studied via Transmission electron microscopy (TEM), and dislocation densities were calculated by X-ray diffraction (XRD) for quantifying the forest hardening contribution to the flow stress. Deformation twins were rarely observed in the GH3536 superalloy specimens deformed at 293 K, where deformation occurred solely by dislocation slip. While twinning was initially found at a strain of ∼7% at 77 K, and the corresponding stress at which twinning occurs is 808 ± 46 MPa. The twin volume fractions, their widths and spacings were determined by electron backscatter diffraction (EBSD), which is used to investigate the twin evolution of GH3536 alloy at 77 K. The deformation mechanisms of GH3536 alloy, as well as its twinning behaviors, depend on the competition between the maximum flow stress and critical stress for twinning. The maximum flow stress is large enough to activate twinning at cryogenic temperature, resulting in the transition of deformation mechanisms for GH3536 alloy as SLIP (dislocation slip) at 293 K and TWIP+SLIP (deformation twinning and dislocation slip) at 77 K, and the improved combination of ductility and strength at 77 K compared to 293 K is derived from additional deformation mode provided by twinning during the process of deformation.