Molecular Dynamics Simulation of Dislocation Evolution Mechanism of Nickel-Based Superalloys under Ultra-Low Temperature Fatigue

This study elucidates the dislocation evolution mechanism of nickel-based superalloys under ultra-low-temperature fatigue conditions. Using molecular dynamics simulations with LAMMPS and post-processing via OVITO, we analyze fatigue behavior across varying temperatures, focusing on shear strain distribution, atomic structure evolution, dislocation dynamics, and fatigue hysteresis. The findings reveal that shear strain concentration in fatigue crack regions peaks at 127 K, followed by 77 K, and is lowest at 177 K. Atomic structure analysis shows a temperature-dependent evolution of FCC and non-FCC atoms, highlighting complex dislocation slip and phase transformation mechanisms. The dominant dislocation type across all temperatures is 1/6 < 112 > (Shockley), with its density decreasing and then increasing as temperature rises. At 77 K, 1/2 < 110 > (Perfect) dislocations form pentagonal loops, signifying constrained mobility and increasing dislocation accumulation. At 177 K, stabilized dislocation density suggests recovery and recrystallization effects. Hysteresis loop analysis indicates significant temperature-dependent variations in fatigue limits and energy dissipation. The highest tensile fatigue limit occurs at 77 K, while the maximum compressive limit is at 127 K. The smallest hysteresis loop area at 177 K signifies reduced energy dissipation capacity. This study provides novel insights into ultra-low-temperature fatigue mechanisms of nickel-based superalloys, offering guidance for their application in extreme environments.