Strengthening mechanisms in multi-phase FeCoCrNiAl1.0 high-entropy alloy cladding layer

In order to study the strengthening mechanisms in the multi-phase (FCC + BCC) high-entropy alloy cladding layer, FeCoCrNiAl1.0 coating was fabricated by laser cladding technology. For comparison, single phase (FCC) FeCoCrNiAl0.3 coating, pure copper, and pure iron were also considered. XRD analysis, optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscope (TEM) were used to investigate the evolution of phases and microstructures in the materials. The hardness and tensile property of the materials were investigated using micro-hardness and small punch tests. It was found that Al element could promote the formation of BCC solid solutions. The solidification pattern of coatings changed from columnar to equiaxed crystals. The FeCoCrNiAl1.0 high-entropy alloy cladding layer (FCC + BCC) exhibited the best mechanical properties. Furthermore, the strengthening mechanisms in the multi-phase high-entropy alloy cladding layer were analyzed systematically. The rapid solidification in the laser cladding process resulted in the formation of fine grains that strengthened the material. In addition, the FCC and BCC lattice structures contain different slip directions and types of dislocation. The lattice distortions of the two crystal structures were determined by calculating the interplanar spacings and the interplanar angles. Under external load, the FCC and BCC phases in the multi-phase high-entropy alloy cladding layer experienced different degrees of displacements, which also played a role in strengthening the material.