Development of NiCrFeCoBX eutectic high entropy alloy coating by laser cladding: Investigation of microstructural, solidification, corrosion, and wear properties

Abstract

Developing protective coatings resistant to corrosion and wear has always been a challenge in various industries. In this work, we processed NiCrFeCoBx (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) high-entropy alloy by laser cladding on a GTD-111 superalloy. At B ≤ 0.3, the microstructure of the coating consisting of inter-dendritic FCC1 and FCC2 lamellae coupling was confirmed by XRD and SEM analysis. By increasing the value of B (B≥ 0.4), a coating with the phase structures of FCC1, FCC2, and MXBY was identified. The presence of Cr-rich borides (MXBY) was attributed to the enrichment of the eutectic composition with B and its segregation into interdendritic regions. With increasing B, more areas were created for inhomogeneous nucleation of dendrites from the melt, resulting in a finer eutectic structure with a higher volume fraction. The comparison between B0.1 and B0.6 samples showed that the hardness increased from 240 HV to 603 HV and the coefficient of friction decreased from 0.63 to 0.42. Raising the B value led to a drop in the corrosion current potential of the NiCrFeCoBX coating from −0.456 V to −0.895 V in a 3.5 % NaCl solution. Additionally, this shift altered the corrosion mechanism from pitting to intergranular corrosion. This was attributed to the high surface energy of the eutectic phase and the intensification of galvanic corrosion.