Strengthening mechanism in two-phase FeCoCrNiMnAl high entropy alloy coating

The two-phase FeCoCrNiMnAl high entropy alloy cladding layer was produced by laser cladding method, and its strengthening mechanism was studied. Using XRD, EDS, TEM and EBSD analyses, the phase and microstructural evolutions, dislocation density and distribution, and degree of lattice distortion were investigated. Nano-indentation and tensile tests were employed to study the hardness and tensile properties of the cladding layer, respectively. The results show that Al element, due to its large atomic radius, promoted the formation of BCC solid solution in the cladding layer and significantly refined the grains. Diffraction peak shift, change lattice constant change, interplanar spacing and crystal plane included angle calculations indicate that all the phases in the FeCoCrNiMn and FeCoCrNiMnAl cladding layers experienced serious lattice distortions. Dislocations in the FeCoCrNiMnAl coating mainly accumulated and moved in the softer FCC phase, increasing the material's resistance to plastic deformation. The combined effects of grain size, lattice distortion, dislocation density and dual-phase interaction significantly increased the plastic deformation resistance (i.e., tensile strength, yield strength and microhardness) of the FeCoCrNiMnAl coating compared to the FeCoCrNiMn coating, but also reduced the elastoplasticity.