In this study, an Nd:YAG laser was used to carry out laser surface remelting treatment on FeCrNiMnMo x (x = 0, 0.5, 1) alloys. A study was conducted on the potential impact of Mo on the microstructure and corrosion resistance of the laser-remelted layer. According to the research results, FeCrNiMnMo x alloys were more effective in refining the dendrites, compared with the matrix, whereas the FeCrNiMn alloys' remelted layer exhibited an almost single face-centered cubic (FCC) structure. In comparison, FeCrNiMnMo 0.5 and FeCrNiMnMo 1 alloys' remelted layer displayed the FCC and σ phase. In addition, the dendrite crystals' microstructure can be clearly refined by Mo alloying. Mo is effective in improving the corrosion resistance of the FeCrNiMnMo x alloys' remelted layer in 3.5% NaCl solution. The pitting resistance of Mo-containing-remelted layers is significantly higher, compared with Mo-free alloy's remelted layer, and the FeCrNiMnMo 0.5remelted layer shows the most satisfactory corrosion resistance. As revealed by X-ray photoelectron spectroscopy analyses, the addition of molybdenum promotes the generation of Cr 2 O 3 and enhances the corrosion resistance of the remelted layer.

Four FeCrNiMnMo x (x=0, 0.1, 0.3, 0.5, in molar ratio) high-entropy alloys (HEAs) were synthesized by vacuum arc melting to explore the potential impact of Mo on the microstructure, mechanical properties, and passivation and electrochemical behaviors in 0.5 M H 2 SO 4 solution. The results display that the FeCrNiMn alloy exhibits a single face-centered cubic (FCC) structure while the microstructures of the FeCrNiMnMo 0.1 , FeCrNiMnMo 0.3 , and FeCrNiMnMo 0.5 alloys consist of the FCC and σ phase. The appear of the σ phase ascribed to the addition of Mo enhances the hardness and yield strength with the sacrifice of plasticity. The FeCrNiMnMo x HEAs achieve the maximum hardness of 414 HV 0.2 and the highest compressive yield strength of 830 MPa when x=0.5, but compressive fracture strain is lowered to 10.8%. X-ray photoelectron spectroscopy (XPS) and electrochemical analysis show that the passivation film in FeCrNiMnMo x alloy mainly consists of chromium oxides and molybdenum oxides. Mo has a beneficial effect on the corrosion resistance of the FeCrNiMnMo x HEAs in a 0.5 M H 2 SO 4 solution by increasing the corrosion potential (E corr ) and decreasing the corrosion current density (I corr ) and passivation current density (I pass ). The FeCrNiMnMo 0.1 alloy shows the best corrosion resistance, mainly due to its passivation film consisting of a large proportion of chromium oxide (Cr 2 O 3 ). More Mo additions promote the formation of the precipitate of σ phase and the matrix regions depleted Cr and Mo elements adverse to the resistance to preferential localized corrosion.

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TiN coatings were successfully prepared by closed field unbalanced magnetron sputtering (CFUBMS) in this study. The microstructure, composition, phase structure, hardness and adhesion of TiN coating were investigated by SEM, EDS, XRD, and nanoindentation/scratch techniques, respectively. Emphatically, the oxidation behaviors of TiN coating were analyzed and discussed at 550, 600 and 650°C, respectively. Results showed that TiN coatings are golden with loose pyramidal structure, and the phases in TiN coating are mostly TiN and a small amount of Ti. The hardness, elastic modulus and bonding strength of TiN coating are about 23 GPa, 288 GPa and 35 N, respectively. The isothermal oxidation tests in a thermal analyzer at 550°C and 650°C for 19 h suggested that TiN coating has better oxidation resistance at 550°C because it was approximately intact at 550°C. However, the oxidation experiments in a muffle furnace at 600°C and 650°C for only 10 h indicated that TiN coatings were slightly oxidized. Therefore, above 600°C, TiN coating will fail due to the formation of the brittle rutile TiO2 as the oxidation time increases.