Effect of solidification behaviors on microstructures and properties of high-entropy alloys coatings by laser melting deposition

Laser melting deposition is commonly used to prepare high-entropy alloy (HEAs) coatings. Laser melting deposition with coaxial powder feeding (CPF) and laser melting deposition with powder pre-placed (PPP) lead to differences in the melting and solidification behaviors in non-equilibrium solidification conditions due to the differences in forming principles and energy input. In this paper, the solidification behaviors, microstructures, mechanical properties and strengthening mechanisms of FeCoCrNiAl0.5 high-entropy alloys coatings prepared by CPF and PPP were studied. The results demonstrated that the solidification path, crystal orientation, and average grain size of CPF and PPP HEAs coatings were significantly influenced by the temperature gradient (G) and solidification rate (R). The distinct microstructures between CPF and PPP HEAs coatings resulted in differences in their mechanical properties. Notably, the PPP HEAs coating, characterized by a higher G × R value, exhibited a combination of both FCC and BCC phases, along with a larger kernel average misorientation (0.4592) and a smaller average grain size (41.12 μm). Consequently, in non-equilibrium solidification conditions, the PPP HEAs coating displayed enhanced grain boundary strengthening, dislocation strengthening, BCC hard phase strengthening, and solid solution strengthening effects compared to the CPF HEAs coating. This led to a higher average microhardness (100 HV) and a lower friction coefficient (0.27) for the PPP HEAs coating in comparison to the CPF HEAs coating.