Preparation of FeCoNiCrMo high entropy alloy coatings by laser cladding on Ti6Al4V surface: Evolution of columnar - equiaxed crystal transition and longitudinal comparison of mechanical properties

High entropy alloys (HEAs), as multi-principal element alloys, have demonstrated significant potential and advantages in surface protection applications. In this study, FeCoNiCrMo single-track coatings were fabricated on the surface of Ti6Al4V using different laser energy densities (Led = 80, 90, 100, 110 and 120 J/mm 2 ). The control of heat input during the overlaying process has a substantial impact on the formation of the microstructure, which directly affects the mechanical properties of the material. In this work, a COMSOL numerical model was employed to obtain the solidification parameters of the FeCoNiCrMo single-track layer cross-section. Microstructural characterization was used to explore the relationship between solidification parameters and grain growth. The results revealed that high temperature gradients and low solidification rates tend to favor the formation of columnar grains, whereas the opposite conditions promote the development of equiaxed grains. Increasing the laser energy density facilitates the transformation from columnar to equiaxed grains, with only 57.12% of the columnar grains remaining at a laser energy density of 120 J/mm 2 . Additionally, the mechanical properties of the equiaxed grain region were superior to those of the columnar grain region. Specifically, the wear scar width and depth in the equiaxed grain region were only 91.30% and 71.76% of those in the columnar grain region, respectively. The wear mechanisms in the equiaxed grain region were identified as plowing wear, while the mechanisms at columnar crystal region was adhesive wear.