The effect of varying metastable epsilon-HCP phase in the metastable Fe 50 Mn 30 Co 10 Cr 10 alloy on low-cycle fatigue behavior is systematically investigated using strain-controlled low-cycle fatigue tests conducted at total strain amplitudes of 0.3% and 0.9%. A pronounced increase in fatigue life with increasing initial HCP volume fraction is observed. At 0.3% strain amplitude, the fatigue life increases from approximately 30,000 cycles of 60% HCP volume fraction to approximately 46,000 cycles for the 80% HCP volume fraction. Similarly, in a 0.9% strain amplitude test condition, HCP-rich microstructure provides significantly higher fatigue life, approximately 15,000 cycles, compared to FCC dominant microstructures reported in the literature. Detailed electron channelling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) reveal direct evidence of a continuous, hierarchical bidirectional FCC <-> HCP phase transformation during cyclic loading. The transformation proceeds via displacive mechanisms mediated by Shockley partial dislocations and preserves a well-defined crystallographic orientation relationship between transformed phases. Phasepartitioned kernel average misorientation (KAM), geometrically necessary dislocation (GND), and Schmid factor analyses demonstrate that epsilon-HCP-rich microstructures promote distributed slip activation and reduced strain localisation, even at high strain amplitudes. The combined effect of reversible phase transformation, favourable crystallographic orientation, and hierarchical lamellar architecture spanning from the micron to nanometer length scales enables efficient cyclic strain accommodation and delays fatigue damage accumulation. The present findings establish initial phase fraction as a critical microstructural design parameter and provide new insights into transformation-assisted cyclic plasticity for the fatigue-resistant design of metastable high-entropy alloys.
Laser Powder Bed Fusion (LPBF) enables fabrication of complex metallic components with high geometrical flexibility and material efficiency. However, poor surface integrity, residual stress, and process-induced defects significantly limit the fatigue performance of as-built parts. A plausible solution is optimization of LPBF process factors through the process-structure–property (PSP) framework. In the present work, a physics-based PSP framework is developed to correlate LPBF process parameters with the fatigue life of AlSi10Mg. A pulsed LPBF thermal model is first established to predict transient temperature distribution and melt pool geometry considering temperature-dependent material properties and heat loss mechanisms. The predicted melt pool morphology is then employed to model lack-of-fusion (LOF) porosity, surface topography, and the corresponding micro-V-notch angles. The thermal history is also used to predict residual stress through an incremental elastoplastic formulation. The combined effects of defect size, surface notch geometry, and residual stress are subsequently incorporated into a defect-driven and surface-driven fatigue life prediction approach, which is calibrated by experiments for various laser power and volumetric energy densities. It was found that within 54 datasets over 18 process conditions, 78% of predictions fall within a scatter factor of 2 around the 1:1 correlation line, indicating reasonable agreement between predicted and experimental fatigue lives. Moreover, the framework successfully captures the experimentally observed fatigue trends with LPBF process parameters and can serve as a guideline for fatigue modelling of other LPBF-manufactured materials.
