Abstract
In this paper, the (CoCrFeNi)95Nb5 high-entropy alloy (HEA) coating with a thickness of 500 μm on Q235 steel substrate was fabricated by plasma spraying. The microscopic results showed that a new Laves phase is formed in the (CoCrFeNi)95Nb5 HEA coating compared to the HEA powder, and elemental segregation occurs between the dendrites and the interdendrites of the coating, while the interdendritic phase enriches with the Cr and Nb. The phase composition change and elemental segregation behavior were mainly due to the faster cooling rate of the plasma spraying technique. At the junction of the coating and the substrate, the HEA coating bonded well to the substrate; in addition, the width of transition zone was merely 2 μm. The microhardness of the (CoCrFeNi)95Nb5 HEA coating was 321 HV0.5, which is significantly higher than that of the substrate. In terms of corrosion resistance, the (CoCrFeNi)95Nb5 HEA coating has good corrosion resistance in NaCl solution. Although the corrosion form was pitting corrosion, the pitting potential of the (CoCrFeNi)95Nb5 HEA coating was significantly higher than that of other coatings, which was mainly because of the dense passivation film formed by Cr and Nb on the surface of the coating. Once the passivation film was destroyed by Cl−, the selective corrosion occurred on the surface of the (CoCrFeNi)95Nb5 HEA coating. In summary, the (CoCrFeNi)95Nb5 HEA coating prepared by plasma spraying technology can significantly improve the corrosion resistance and mechanical properties of the Q235 steel substrate.
Highlights
In the past decade, high-entropy alloys (HEAs), containing at least four principle elements in equimolar or near-equimolar ratios, have received more and more attention due to the remarkable comprehensive performance
The results show that the microhardness of the HEA coating, 310~325 HV0.5, is significantly higher prepared other processes in 3.5 wt.%
The mixed enthalpy of Nb and Cr is larger than the other three elements, indicating that Nb has a relatively weak binding force with Cr; the actual situation is that Nb and Cr are enriched in the interdendritic phase
Summary
High-entropy alloys (HEAs), containing at least four principle elements in equimolar or near-equimolar ratios, have received more and more attention due to the remarkable comprehensive performance. CoCrFeNi system HEAs, which possess the typical FCC solid solution structure, exhibit a remarkable combination of high ductility, cryogenic fracture toughness, corrosion resistance, and thermal stability Such FCC-typed HEAs have been proven to achieve high strength while maintaining sufficient ductility by means of precipitation strengthening mechanisms. Compared to conventional Ni-based superalloys and steel, high density (~8 g/cm3 ) and cost severely limit its engineer application This is caused by the expensive metal elements used, such as Co and Ni, for bulk CoCrFeNi system HEAs. At present, a recognized and effective solution is to develop high performance HEAs coatings on substrates of traditional materials, which could give full play to its performance advantages, and an increasing number of work on HEAs coating have been reported [8,9,10,11,12]. The phase formation and the corrosion behavior of the coatings were analyzed
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