Proton Exchange Membrane Fuel Cell(PEMFC) provide an innovative solution for mitigating the global energy crisis and addressing environmental challenges. In PEMFC, bipolar plates have attracted much attention as key components. Among them, metal bipolar plates have attracted much attention due to their low cost, easy material acquisition, excellent conductivity and ease of mechanical processing. However, metal bipolar plates still face challenges in terms of durability and conductivity. To address these issues, surface modified coatings are commonly used to treat metal bipolar plates. In this work, the research progress on surface modified coatings for metal bipolar plates in recent years was reviewed, which included multiple aspects such as material design, deposition processes and coating properties. On this basis, the influence of different coatings on the surface modification effect of metal bipolar plates was analyzed based on test results such as conductivity, corrosion resistance, film substrate bonding strength and hydrophobicity. Meanwhile, the future research trends of various types of modified coatings were discussed. These research results provided useful guidance and inspiration for improving the performance of metal bipolar plates and further promoting the development of PEMFC surface modification technology.

In order to improve the surface erosion resistance of titanium alloy substrate and study the effect of Cr based multilayer film on the fatigue mechanical properties of titanium alloy substrate, three kinds of Cr-CrN-Cr-CrAlN multilayer film with different thickness(3.99,6.85,9.62 μm) were deposited on the surface of TC4 titanium alloy by vacuum cathodic arc deposition technology. The axial tensile performance and axial high low cycle fatigue performance of TC4 titanium alloy substrate and the film specimens at room temperature were studied and compared mainly through tensile tests and axial loading fatigue tests. Results showed that the thicknesses of Cr-CrN-Cr-CrAlN multilayer film prepared on the surface of TC4 titanium alloy were approximately 3.99, 6.85 and 9.62 μm, respectively. Moreover, the corresponding hardnesses were 2 455, 3 024 and 3 578 HV, and the adhesion forces of film-substrate were 12.4, 15.2 and 20.1 N, respectively. After coated with multiple layers, the tensile yield strength, tensile strength and elastic modulus of TC4 titanium alloy were improved, while the elongation at break was reduced. The multilayer film with 6.85 μm decreased the axial high cycle fatigue limit of TC4 titanium alloy by 4.15%, and the film had little effect on the high cycle fatigue performance. Besides, the effect of film on the low cycle fatigue performance was significant, with a decrease of approximately 21.04% in fatigue strength corresponding to a lifespan of 50 000 cycles.

The adhesion and friction performance of tetrahedral amorphous carbon film(ta-C film) deposited on the surface of hard alloy affect its application effect in cutting tools and wear-resistant components. In this work, ta-C thin film was prepared based on high power pulse magnetron sputtering technology(HiPIMS), and the modification of ta-C thin film was studied through adjusting C₂H₂ flow rate. The thickness of the film was observed by SEM, the structure of the film was studied through Raman and XPS, the hardness of the film was characterized through nanoindentation, the adhesion of the film was analyzed by nanoscratches, and the wear resistance of the film was tested through friction and wear tests. Results showed that the introduction of C₂H₂ gas could effectively improve the structure, hardness, adhesion and wear resistance of ta-C film. Changing the C₂H₂ flow rate could regulate the performance of ta-C film. As the C₂H₂ flow rate gradually increased, the various properties of the film showed a trend of first increasing and then decreasing. When the flow rate of C₂H₂ was 15 cm³/min, the various properties of the film reached excellent results. Specifically, the as-obtained ta-C film had the thickness of 655.9 nm, the hardness of 43.633 GPa and the adhesion force of 19.2 N. Besides, the content of sp³ bond was 70.19%, and the surface of ta-C film was uniform and dense with good performance.

For investigating the influence and mechanism of bias voltage on the composition structure, mechanical properties and tribological properties of TiAlSiN coatings prepared by high-power pulsed magnetron sputtering(HiPIMS), TiAlSiN coatings were deposited on YG8 hardness alloy and N-type single crystal (111) Si by HiPIMS technology with regulating substrate bias voltage (0～－200 V).The microstructure,composition characterization and performance testing of TiAlSiN coatings were carried out by scanning electron microscopy (SEM),X-ray diffraction (XRD), electron probe microscopy (EPMA), X-ray photoelectron spectroscopy (XPS), ultra depth of field microscopy, white light interferometry, nanoindentation, scratch and reciprocating friction and wear testing machines.Results showed that in terms of HiPIMS discharge behavior, an increase in bias voltage could increase the HiPIMS ignition voltage, but the impact on the discharge voltage and current during the platform stage was not significant.The relative changes in elemental composition of TiAlSiN coatings prepared under different bias conditions were relatively small.As the bias voltage increased, the TiAlSiN coating changed from hcp-(Ti, Al)N＋fcc-(Ti, Al) N to fcc-(Ti, Al)N.In addition, as the bias voltage increased, the cross-sectional structure of the coating transformed from a loose columnar crystal structure to a dense stacked structure without obvious defects, with surface nodular defects disappearing and grain size gradually decreasing.In terms of mechanical properties, with the increase of bias voltage, the hardness and adhesion of TiAlSiN coating exhibited an upward trend.The coating prepared at－200 V achieved optimal performance, with a maximum hardness of 26.19 GPa and a maximum H/E* of 0.099 5.When the bonding force reached a maximum of 19.63 N,the coating had the lowest wear rate,which was 9×10－15 μm3/(N·m).Based on the above analysis, the microstructure and properties of the coating could be controlled by changing the substrate bias voltage during HiPIMS process, which also improved the toughness of the coating and enhanced the adhesion and tribological properties of the coating significantly.

The Cr coating deposited by PVD method is difficult to apply on a large scale due to its poor corrosion resistance.The use of composite multilayer coating structure design can interrupt the growth of penetrating columnar crystals, reduce porosity and improve the corrosion resistance of PVD deposited Cr coatings.In this work,Cr/CrCN multilayer coatings were deposited on the surface of 316L stainless steel substrate by high-power pulsed magnetron sputtering (HiPIMS) coupled with synchronous pulse bias technology.The morphology, composition and microstructure of the coating were characterized using SEM,XRD,EDS and Raman.The corrosion resistance of Cr/CrCN multilayer coatings prepared under four different methane flow rates (5, 15, 25, 35 sccm) was studied by electrochemical and acid salt spray tests.Results showed that the introduction of CrCN intermediate layer effectively interrupted the penetrating growth of columnar crystals, and the coating exhibited a dense and flat surface morphology.All four Cr/CrCN multilayer coatings had a good protective effect on the substrate, and the corrosion current density of the coating modified samples decreased compared to the substrate.After 48 h of acidic salt spray corrosion, the surface of the multi-layer coating prepared with a methane flow rate of 25 sccm did not show obvious pitting corrosion,demonstrating the best corrosion resistance performance.In general, the Cr/CrCN multilayer coatings prepared by HiPIMS could effectively improve the corrosion resistance of 316L stainless steel, which provided reference for the optimization design and industrial application of corrosion resistance of PVD Cr plated coatings.