Design, microstructure, wear and corrosion behaviors of laser clad FeNiCoCrMo0.3Nbx hypoeutectic high entropy alloys coatings

Abstract

FeNiCoCrMo0.3Nbx (x = 0.15, 0.40 and 0.55 in molar ratio) hypoeutectic high entropy alloys (HEAs) coatings are prepared by laser cladding (LC) designed by binary eutectic composition strategy. Nbx HEAs coatings present FCC + Laves duplex. Under the joint action of various strengthening mechanisms, the average microhardness of Nb0.15, Nb0.40 and Nb0.55 coatings is as high as 480.5 ± 7, 510.2 ± 6 and 540.6 ± 5 HV0.2, respectively. The unique fluctuating oxide film of the HEAs coatings plays a role in reducing wear, with the specific wear rates of 0.37 × 10−4, 0.22 × 10−4 and 0.18 × 10−4 mm3/Nm for Nb0.15, Nb0.40, and Nb0.55 cladding layers, respectively. The Nbx HEAs coatings displayed excellent corrosion resistance in 0.5 M H2SO4 solution. For Nb0.15 and Nb0.40 HEAs coatings, the increase of Nb promotes the formation of passivation film and improves corrosion resistance. However, the higher dislocation density intensifies the chemical inhomogeneity of the alloy due to excessive addition of Nb, which is not conducive to the corrosion resistance of Nb0.55 HEAs coating. The Nb0.40 cladding layer exhibits better corrosion resistance, and the Icorr is only 1.24 ± 0.6 μA/cm2. Combined with Mott-Schottky (M-S) test, the carrier densities (ND) of three HEAs coatings are increased in the order of Nb0.40 (1.09 × 1021 cm−3) < Nb0.15 (1.83 × 1021 cm−3) < Nb0.55 (3.57 × 1021 cm−3), indicating that the strong protective passivation film is also a key factor to achieve better corrosion resistance.