Mechanical Properties and σ-Phase Precipitation in FeCoCrNiMox (x = 0, 0.4, 0.5, 0.8, 1.3) High-Entropy Alloys: Insights from First-Principles Study

High-entropy alloys (HEAs) have garnered significant global interest due to their outstanding properties. This study investigates the structural stability and mechanical properties of FeCoCrNiMox (x = 0, 0.4, 0.5, 0.8, 1.3) HEAs using a first-principles approach coupled with the special quasi-random structure (SQS) method. Of the alloys examined, all except FeCoCrNiMo1.3 were found to be thermodynamically and dynamically stable. Elasticity calculations revealed that molybdenum improves the ductility and anisotropy of the alloys, though with a slight decrease in strength and stiffness, as confirmed by electronic structure analysis. Defect-free FeCoCrNiMo0.5 HEAs coatings were then prepared using laser cladding and characterized for their microstructure and hardness. The coating exhibited a transition from columnar crystals at the bottom to equiaxed crystals at the surface, forming a honeycomb-like structure. Inside the crystal cells, high-density dislocations and σ-phase were observed. Elasticity calculations of the σ-phase confirmed its high hardness, low ductility, and classification as a brittle, hard phase.