Tension–compression asymmetry and underlying microstructural mechanisms in high-temperature stress relaxation of a DZ411 nickel-based superalloy

The high-temperature stress relaxation behavior of directionally solidified DZ411 superalloy was investigated using miniature specimens under constant total strain at 800–980 °C, with a focus on tension–compression asymmetry at 980 °C. The relaxation degree generally increases with temperature but exhibits a non‑monotonic drop at 980 °C, attributed to γ′ rafting strengthening. Under identical initial strain (2%), compression relaxes more completely than tension, which shows higher residual stress. Apparent stress exponents are 13.4 (tension) and 9.9 (compression). Microstructural observations reveal transverse γ′ rafts with 3D dislocation tangles and cross‑slip under tension, versus axial rafts with planar slip and interfacial pile‑ups under compression. These differences in rafting orientation alter γ‑matrix channel connectivity and dislocation motion modes, providing the mechanistic origin of the macroscopic tension–compression asymmetry in stress relaxation.