Microstructural evolution and enhanced properties of multi-layer TiZrNbCrCo high entropy alloy coatings laser-clad onto Ti-6Al-4V alloy

In response to the issues of low hardness and inadequate wear resistance observed in Ti-6Al-4V alloy, this study employs a laser cladding technique to fabricate high-entropy alloy (HEA) coatings composed of TiZrNbCrCo on the alloy's surface. The investigation explores the effects of varying the number of cladding layers on elemental composition, and its influence on the phase constitution, microstructure, microhardness, as well as wear and electrochemical properties of high-entropy alloy coatings. Empirical thermophysical parameters were used to predict the phase composition of solid solution phases in high-entropy alloy coatings with different layer numbers. The findings indicate that coatings, regardless of the number of layers applied, share a consistent phase composition, featuring predominantly by a body-centered cubic (BCC) structured solid solution that encompasses Nb-rich dendrites and Co-rich interdendrites. With an increase in the number of cladding layers, the dilution rate decreases, resulting in the formation of interdendritic C14 type Laves phases enriched in Zr and Co. In the 3-layer HEA cladding, microstructure displays a refined dendritic structure, accompanied by an increased content of Co and Zr. Concurrently, Ti(Zr) precipitates, which contain a significantly lower concentration of beta stabilizers (Nb, Cr and Co), also begin to emerge. The average microhardness of the coatings reaches 747.7 HV0.1, approximately 2.33 times that of the substrate, leading to a reduction of wear volume by 68.6 % compared to the substrate. The optimal corrosion resistance is observed when the number of layers reaches two, exhibiting the lowest self-corrosion current (6.46 x 10-6 A cm-2), a larger open circuit potential (-0.286 V), and the lowest corrosion rate, indicating a significant enhancement in corrosion resistance.