Controlling the Deformation Mechanism in Disk Superalloys at Low and Intermediate Temperatures

The newly developed TMW disk superalloy exhibits better overall mechanical properties in the intended service temperature region (650-750 °C) than the most advanced cast & wrought disk alloy U720Li. Clarification of the underlying mechanisms is beneficial for designing advanced superalloys. Among the TMW alloys, TMW-4M3 has the best tensile strength and creep resistance. In this study, tensile tests of U720Li and TMW-4M3 were conducted at temperatures ranging from 25 °C to 750 °C. The deformation microstructures have been investigated by transmission electron microscopy (TEM). Dislocation activity, involving anti-phase boundary (APB), was the dominant mechanism in U720Li up to 725 °C. However, the transition of deformation mechanisms from dislocation pairs cutting to stacking fault (SF) shearing and deformation twinning was observed in TMW-4M3. A concise model related to the increased surface energy is put forward to describe the competing mechanisms. It is found that APB energy, SF energy (SFE), and volume fraction of tertiary γ ́ have important influence on the transition of deformation mechanisms. The controlling of deformation mechanism by alloy design is discussed.