Improved yielding strength and fatigue-crack-growth resistance of non-equiatomic FeNiCoCr high-entropy alloy produced by laser powder-bed fusion

This study compares the tensile properties and fatigue-crack-growth (FCG) behavior of a non-equiatomic Fe-20Ni-20Co-20Cr (at. %) high-entropy alloy (HEA) fabricated by laser powder-bed fusion (LPBF) and conventional casting-and-thermomechanical routine. Tests were conducted on dog-bone-shaped single-edge-notched tensile (SENT) samples in accordance with ASTM E647 at frequencies of 1 Hz and 10 Hz. The LPBF samples exhibited approximately 20% higher ΔKth value and a 30~40% reduction in da/dN compared to their cast counterparts. Specifically, the microstructure in the LPBF sample consists of hierarchical cellular and columnar grains with dense dislocation-cell networks concentrated along low-angle cell walls. This multi-scale architecture promotes repeated crack deflection, microbranching, and enhanced plastic energy dissipation, thereby prolonging the effective crack path and decelerating crack growth. The findings demonstrate that intentionally engineered dislocation-cell networks via LPBF provide a viable microstructural design strategy for significantly enhancing fatigue resistance in multi-component Fe-based alloys.