The purpose of this paper is to ascertain the high cycle fatigue behavior of CoCrNi medium-entropy alloy (MEA) and the effect of chemical short-range ordering (CSRO) on the fatigue behavior of CoCrNi MEA.
Cyclic loading tests utilized a 10 kN SHIMADZU servo-hydraulic system under stress-controlled conditions (R = 0.1, 40 Hz, sinusoidal waveform). Post-test analyses integrated surface deformation mapping via electron backscatter diffraction and fracture morphology characterization using SEM (ZEISS). Subsurface damage mechanisms were investigated through transmission electron microscopy (FEI Talos F200X) at selected stress amplitudes.
High-CSRO conditions promote planar slip via constrained cross-slip and localized barrier rupture, while low-CSRO states enable stress-relieving wavy slip through enhanced cross-slip activity. Crucially, wavy slip morphology demonstrates superior fatigue resistance by delaying crack nucleation through stress homogenization and impeding crack propagation via synergistic serrated crack branching and deflection mechanisms. Through multiscale microstructural characterization, we reveal a microstructural pathway connecting CSRO modulation, slip mode transitions (planar to Wavy) and fatigue life optimization.
Through multiscale microstructural characterization, we reveal a microstructural pathway connecting CSRO modulation, slip mode transitions (planar to Wavy) and fatigue life optimization. These findings provide a mechanistic framework for designing fatigue-resistant MEAs through targeted CSRO engineering.
