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An in-line, highly sensitive refractive index (RI) sensor based on a tapered multicore fiber (MCF) structure sandwiched between two single-mode fibers is proposed and demonstrated. The fiber tapering technique was employed to fabricate in-line interferometers based on the multicore fiber. The waist diameter is one of the dominant factors of the intercore coupling. The tapered MCF interferometer is highly sensitive to the surrounding refractive index with a maximum sensitivity of 9194.6 nm/RIU in the RI range of 1.4264 to 1.4278 when the waist diameter is 9 µm. The enhancement of the evanescent field by graphene coating is proved to be able to improve the RI sensitivity further. A graphene-coated MCF interferometer with waist diameter of 9 µm offers the maximum sensitivity of 12617.6 nm/RIU in the RI range of 1.4144 to 1.4159. The experimental data have good agreement with the simulated results.

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High-entropy alloy (HEA) coatings of CoCrFeNiTiAlx (x = 0, 0.5, 1, 1.5, 2) were prepared on the surface of AISI1045 steel by laser cladding. The effects of the Al content on the microstructure, composition, phase constitution, and wear and corrosion resistance of the coatings were investigated. The results showed that when increasing the Al element content from 0 to 0.5, the phase constitution of the CoCrFeNiTiAlx coating changed from a single Face-centered cubic (FCC) phase to Body-centered cubic 1 (BCC1) and Body-centered cubic 2 (BCC2) phases, with a small amount of Laves phase, which obviously improved the friction and corrosion resistance of the coating. With further enhancing of the Al content, the amount of BCC1 phase increased, while the BCC2 phase and the Laves phase decreased. The CoCrFeNiTiAl2 HEA coating transformed into a single BCC1 phase, with retrogressive wear and corrosion resistance. It was found that the Al0.5 alloy coating exhibits excellent wear resistance, high hardness, and corrosion resistance in a 3.5 wt.% NaCl solution. Furthermore, the effect of the Al content on the microstructure, phase, and the relating properties of the CoCrFeNiTiAlx HEA coatings is also discussed.

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