Revealing the temperature-dependent cyclic plasticity and failure mechanisms in GH4169 nickel-based superalloy

The low-cycle fatigue behavior and associated microstructural evolution of GH4169 nickel-based superalloy were systematically investigated at elevated temperatures. The macroscopic cyclic results show a relatively stable cyclic response, with neither significant cyclic hardening/softening nor an obvious Bauschinger effect. However, the fatigue resistance degrades substantially at temperatures above approximately 650 °C. Microstructural characterization reveals that cyclic strain localization originates at high-angle grain boundaries and progressively penetrates into grain interiors. Concurrently, the frequency of low-angle grain boundaries increases continuously, while twin boundaries gradually deteriorate during cyclic deformation. Elevated temperature further promotes δ phase coarsening and the formation of precipitate-depleted zones. TEM analysis reveals that cyclic plasticity is dominated by dislocation rearrangement and dislocation-precipitate interactions. Fatigue cracks preferentially nucleate at free surfaces and grain-boundary regions, and then propagate mainly along high-angle grain boundaries. By contrast, twin boundaries effectively impede crack growth by inducing crack deflection.