Atmospheric plasma spraying (APS) is one of the most efficient processes for the preparation of yttrium oxide (Y₂O₃) ceramic coatings. Changing the spraying process parameters can significantly improve the microstructure and enhance the coating properties. In this study, the combination of plasma-spraying process parameters (current, spraying distance, and argon (Ar) flow) was varied by Response Surface Methodology (RSM) with the help of Minitab 19 software. Applied to the design of experiments, improvement of errors, and prediction of microstructure property results, the optimization and validation of experimental parameters for attaining the desired microstructure of Y₂O₃ coatings, especially porosity, was achieved. Process parameters were optimized by RSM: current 613.64 A, Ar flow rate 46.92 L/min, spray distance 15.38 cm, and optimum porosity 1.8% after optimization. Electrochemical corrosion experiments and breakdown voltage experiments revealed that the corrosion resistance and dielectric properties increased significantly as the porosity of the coatings decreased. Therefore, by optimizing the plasma-spraying process parameters, the porosity of the coatings can be significantly reduced and the corrosion resistance and dielectric properties of Y₂O₃ coatings can be effectively improved.

In this work, FeCoCrNiMo_0.2 high-entropy alloy coatings were fabricated using the atmospheric plasma spraying technique. The dependence of the microstructure and wear property of the coatings on spraying power was explored. The results showed that with increasing spraying power, the streamlined structure of the coating was gradually disturbed, the content of the oxides in the coating was enhanced, and the distribution of oxides became relatively uniform. Meanwhile, the porosity in the coating was reduced due to the increased melting degree of feeding particles. As the spraying power increased from 25.5 to 45 kW, the micro-hardness of the coating was improved from 438 ± 15.27 to 558.73 ± 7.23 HV_0.2 and the wear loss of the coating decreased from 2.05 × 10⁻⁴ to 1.18 × 10⁻⁴ mm³/nm. The synergistic effect of the dispersive oxides and the reduced porosity could account for the enhanced micro-hardness by the second phase strengthening mechanisms. Subsequently, the wear resistance of the coating prepared at a high spraying power was improved due to the increased micro-hardness and the reduced crack behaviors. In addition, the broken oxides of metal elements, especially Cr oxides, during wearing led to the abrasive wear behavior, and the broken oxides could work as a lubricant to decrease the wear coefficient of the coating. Finally, the FeCoCrNiMo_0.2 coating prepared at a power of 45 kW had the best wear resistance.

The FeCrMoSi amorphous coatings were fabricated on the surface of a 304 stainless steel (SS) base material using atmospheric plasma spraying. A comprehensive investigation was carried out to evaluate the structure, morphology, adhesion to base material, hardness, hydrophobicity, interfacial contact resistance, and corrosion resistance of the coatings. The results show a remarkable hardness of 1180.1 HV, a strong bond strength of up to 64.3 N/mm², and excellent hydrophobicity with a water contact angle reaching 141.2°. Additionally, in an acidic environment with fluoride ions (0.5 M H₂SO₄ + 2 ppm HF, 80 °C), the FeCrMoSi amorphous coating demonstrated superior corrosion resistance compared with 304 SS while maintaining similar electroconductibility. Detailed analysis of the structural characteristics and corrosion resistance of FeCrMoSi amorphous coatings provided valuable insights into their mechanics. These promising results signify a bright future for FeCrMoSi amorphous coatings in various industrial sectors, including transportation, petroleum, and electric power industries.

In this study, the experimental design of response surface methodology was used to explore the interaction between spraying parameters to obtain an optimized process to reduce the porosity of the coating, and to prepare an excellent chromium oxide coating. The order of the single parameter affecting porosity is as follows: power > main gas > spraying distance > carrier gas flow. This study found that the spraying process with the lowest porosity of the chromium oxide coating is as follows: power of 625 W, stand-off distance of 105 mm, primary gas of 42.5 lpm, carrier gas flow of 5 lpm, and feed powder delivery rate of 35 g/min. The EDS results show that the Cr and O elements in the coating with the lowest porosity are uniformly distributed, while for the coating with the highest porosity, the elements are unevenly distributed to a certain extent, which is caused by the unevenness of the structure caused by the structure defects. The corrosion current density of chromium oxide coating VI (low porosity) is 4.34 × 10⁻⁶ A, whereas that of chromium oxide coating IV (high porosity) is 1.862 × 10⁻⁵ A. On the coating with the highest porosity, the corrosion activity is dominant, while the minimum porosity of coating is the smallest.

Ships and offshore equipment operating in marine environments often face issues such as seawater corrosion and biofouling, leading to significant economic losses. To address the corrosion problems of ships and offshore equipment, heavy-duty anticorrosive coatings are widely used for corrosion protection in marine environments due to their long-term effectiveness, cost-efficiency, and excellent applicability. In this study, silane coupling agent (KH-560) was employed to modify sodium silicate, and the modified sodium silicate was then incorporated as a reinforcing phase into polyurethane to ultimately prepare a modified sodium silicate/polyurethane coating. The feasibility of the modified sodium silicate/polyurethane coating was investigated by characterizing its conventional physicochemical properties, weather resistance, acid and alkali resistance, and salt spray corrosion resistance. Experimental results indicate that the silane coupling agent acts as a bridge between the organic and inorganic interfaces through the hydrolysis and condensation reactions of its bifunctional groups, forming an interfacial layer connected by hydrogen bonds and covalent bonds, thereby improving the compatibility between the organic resin and inorganic sodium silicate. Comprehensive performance analysis revealed that when the content of modified sodium silicate was 60 wt%, the coating hardness reached 4H. Additionally, electrochemical tests demonstrated that the coating exhibited higher impedance (9.62 × 10⁴ Ω/cm²) and lower corrosion current density (5.82 × 10⁻⁷ A/cm²). This study provides a theoretical and experimental basis for the development of high-performance anticorrosive coatings for marine applications.

In this study, Mo2NiB2 coatings were prepared by the laser cladding technique and the relationship between coating microstructure and corrosion resistance with cladding power was analyzed. The results showed that Mo2NiB2 was reactively generated in all coatings while Mo2FeB2 and (Fe, Ni) were also present in the coatings due to dilution of the substrate. There was a good metallurgical bond between the coating and the substrate. The white cermet phase and black Fe-rich phase alternated within the coatings. As observed from the surface, the ceramic phase spreads out in a flattened shape and the black Fe-rich phase was present in a large number of pores. Due to the overdilution of the substrate, the volume of the ceramic phase decreased at a power of 800 W and the Fe content within the coating increased. The corrosion resistance of the coatings increased as the laser power increased from 500 to 700 W. Then the corrosion resistance of the coatings decreased at 800 W due to the excess Fe content and the decrease in the relative content of Mo2NiB2 and (Fe, Ni). Mo2NiB2 coating prepared at 700 W has the best corrosion resistance.