Microstructure, wear and corrosion behavior of high-entropy alloy coatings: The concentration of Mo element and the dual effect of σ-CrMo phase

Abstract

In this work, LaB6/FeCoNiCrMoX (X = 0, 0.3, 0.6 and 1) high-entropy alloys coatings with different Mo contents were prepared on the Ti6Al4V substrate by laser cladding technology. The effect of Mo content on the microstructure, microhardness, friction and wear, and electrochemical properties were investigated. The results indicated that the increase of Mo element enhanced the lattice distortion effect, and σ-CrMo phase is generated at X = 0.6 and 1. Benefiting from the strength of σ-CrMo phase, the mechanical properties of the coating have been significantly improved. At X = 1, the microhardness of Mo1.0 coating was the highest (987 HV0.3), and compared to the Mo0 coating, the wear volume of Mo0.3, Mo0.6, and Mo1.0 were lower, with values of 5.01, 1.47, and 0.54 μm3, respectively. The appropriate content of Mo element significantly improved the corrosion resistance of the coating. The corrosion current density of Mo0, Mo0.3, Mo0.6, and Mo1.0 coatings were 2.045 × 10−5, 8.873 × 10−6, 1.641 × 10−6, 2.164 × 10−6, 1.641 × 10−6 A·cm−2, respectively. As the Mo content increased, the thickness of the passivation film increased, reaching the maximum value (6.915 nm) at X = 0.6. However, excessive Mo (X = 1.0) content led to crack initiation, disrupting the stability of the passivation film, and the thickness of the passivation film actually decreases (4.162 nm). The research in this work provided a theoretical basis for the composition design of high entropy alloys regarding Mo content.