In this study, a NiCr/YSZ coating was applied to a γ-TiAl surface using multi-arc ion plating technology to enhance its high-temperature performance and explore the mechanisms of high-temperature oxidation and thermal corrosion. The thermal corrosion properties of the γ-TiAl matrix and NiCr/YSZ coating were investigated at 850 °C and 950 °C using a constant-temperature corrosion test in a 75% Na₂SO₄ + 25% NaCl mixture. The results indicate that after 100 h, the thermal corrosion weight gain of the coating samples was 70.1 mg/cm² at 850 °C and 118.2 mg/cm² at 950 °C. At these temperatures, sulfide formation on the surface increases, leading to a loose and porous surface. After 100 h of high-temperature corrosion at 850 °C, the primary oxidation product on the surface of the coating was tetragonal-ZrO₂. At 950 °C, Y₂O₃, which mainly acts as a stabilizer in YSZ, reacted with Na₂SO₄, resulting in the continuous consumption of Y₂O₃. This reaction caused a substantial amount of tetragonal-ZrO₂ to transform into monoclinic-ZrO₂, altering the volume of the ceramic layer, which induced internal stress, crack propagation, and minor spallation. A continuous and dense internal thermally grown oxide (TGO) layer effectively impeded the diffusion of molten salt substances and oxygen, thereby significantly improving the thermal corrosion resistance of the thermal barrier coating.

In order to enhance the bonding strength between coatings and substrates, argon glow plasma pretreatment with various times was conducted on tantalum substrates, followed by hafnium coating deposition. The coating, consisting of deposition and a diffusion layer with nanocrystalline grains of dimensions ranging from 10 to 20 nm, obtained on the substrate pretreated for 1 h, manifested the optimal structure, with a maximum thickness of approximately 14 μm and the best adhesion performance of approximately 9.5 N. The study found that the pretreatment led to grain refinement at a depth of approximately 150 nm and an increase in the crystal face spacing of substrate and high-energy defects. In addition, the crystal defects and lightly increased surface roughness enhanced the surface energy, while the Ta (200) and Ta (211) crystal faces, which had a lower combination energy and a more stable state with Hf atoms than the Ta (110) crystal face, were considerably increased on pretreated substrates with a decrease in the Ta (110) crystal face. Consequently, coating elements exhibited enhanced diffusion within the substrate, leading to the better formation of a gradient structure, which effectively improved the adhesion of coatings. Further, this study offers an efficacious approach to enhance coating adhesion and provides a deeper understanding of plasma pretreatment.

In this study, we have developed a water-based aluminum phosphate (WAP) coating consisting of a base layer and a surface layer. Graphene oxide (GO) was used to modify the base layer. Three different GO concentrations—0.5, 0.75, and 1 wt.%—were employed to assess their impact on the corrosion resistance of the coating and to explore the underlying mechanisms. The corrosion resistance mechanism was also examined. In the coating, GO combined with phosphate to form large blocks that effectively blocked the pores, and the porosity decreased with the increase in GO content. This led to an improvement in the substrate protection efficiency by over 10%. Impedance spectroscopy revealed that the main mechanism behind the enhanced corrosion resistance was the shielding effect of GO, which created a “maze effect” that improved the coating’s protective properties. However, an excessive amount of GO reduced the corrosion resistance of the coating. Overall, the WAP coating modified with 0.75 wt.% GO exhibited the best corrosion resistance.

Metal nitride coatings have been considered as a promising approach to improve the performance of metal bipolar plates for proton exchange membrane fuel cells (PEMFCs). In this study, NbN_x coatings with three different ratios of N₂/Ar (1:2, 1:1 and 3:1) were prepared on TC4 alloy substrates using the double glow plasma alloying technology. The NbN_x coatings are homogeneous and dense, and the phase of the coating transforms from hexagonal β-Nb₂N to δ′-NbN phase as the nitrogen content increases. All coatings demonstrate high protective efficiency, with the coating (N₂/Ar ratio of 3:1) displaying the lowest current density of 8.92 × 10⁻⁶ A/cm² at a working voltage of 0.6 V. The EIS results also show that this coating has the best corrosion resistance. Notably, it also presents the lowest interfacial contact resistance of 7.29 mΩ·cm² at 1.5 MPa and good hydrophobicity. More importantly, this study provides a new idea and method for corrosion-resistant coatings of metal bipolar plates for PEMFC applications.