Hot Corrosion Behavior of Ti-6Al-4V Alloy and Its Surface CrN/Cr Coating

LI Rongzhi; DENG Gaping; CHENG Congqian; PU Jibin; CAO Tieshan; ZHAO Jie

doi:10.16490/j.cnki.issn.1001-3660.2025.14.003

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Surface Technology ›› 2025, Vol. 54 ›› Issue (14) : 26-36. DOI: 10.16490/j.cnki.issn.1001-3660.2025.14.003

Corrosion and Protection

Hot Corrosion Behavior of Ti-6Al-4V Alloy and Its Surface CrN/Cr Coating

LI Rongzhi^1,2, DENG Gaping¹, CHENG Congqian^1,*, PU Jibin^2,*, CAO Tieshan¹, ZHAO Jie¹

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Abstract

Corrosion damage of titanium alloy in marine environments has been widely concerned. The application of protective coatings is the key to enhance its comprehensive properties. To improve the hot corrosion resistance of titanium alloy in marine environments, in this study, the Multi-arc Ion Plating technique is used to deposit CrN single layers and CrN/Cr multilayer coatings on the surface of titanium alloy. The hot corrosion damage behavior of titanium alloy and its surface coating induced by NaCl is investigated by the surface and cross-sectional morphology and phase composition of samples are analyzed before and after hot corrosion at 500 ℃ for 60 h. The results show that the corrosion weight gain of titanium alloy is obvious, and the maximum weight gain is about 3.5 mg/cm² after corrosion for 30 h. The weight gain curve shows a trend of first increasing and then decreasing (caused by severe spallation of the corrosion layer on the surface, and the weight gain is less than the amount of spalling). Moreover, it is found that the α and β phases have different corrosion sensitivities, and the corrosion preferentially occurs at the β phase and the α/β interface. Compared with titanium alloy, the coating has a lower weight gain, and the corrosion resistance of the CrN coating is better. The corrosion of CrN coating mainly occurs in the large droplet inside the coating and the surrounding defects, forming corrosion holes, which further confirms the adverse effect of large droplets on the overall coating properties. It is worth noting that different from most nitride/metal multilayer coatings, the introduction of Cr layers reduces the corrosion resistance of the coating. After hot corrosion, the CrN/Cr coating appears interlayer corrosion cracking, and an oxide layer of about 2~3 μm is formed on the surface. The analysis reveals that the surface oxide layer is related to the upward diffusion of Cr elements in the coating rather than by direct oxidation of the coating surface entirely. Surface diffusion of Cr elements in this high temperature corrosive environment leads to the depletion of Cr layer elements inside the coating and the formation of holes, which destroys the internal structural integrity of the coating. As the corrosion process progresses, the corrosion inhomogeneity within the coating becomes more serious. Due to the difference in molar volume and thermal expansion coefficient between the corrosion product and the coating itself, internal stress is induced, which becomes one of the main reasons for the accelerated coating failure. Therefore, it can be concluded that the peeling of the CrN/Cr coating is related to the poor thermal and chemical stability of the Cr element in a high-temperature corrosive environment. Besides, the application of the coating improves the hardness and load bearing capacity of titanium alloy. Compared with the CrN coating, the mechanical properties of the CrN/Cr multilayer coating are better, and the improvement of its performance is related to the obstruction of the dislocation movement by the multilayer structure. So, the mechanical properties and corrosion resistance of the coating should be considered comprehensively during service in the marine environment.

Key words

titanium alloy / CrN coating / CrN/Cr coating / NaCl / hot corrosion / diffusion

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LI Rongzhi, DENG Gaping, CHENG Congqian, PU Jibin, CAO Tieshan, ZHAO Jie. Hot Corrosion Behavior of Ti-6Al-4V Alloy and Its Surface CrN/Cr Coating[J]. Surface Technology. 2025, 54(14): 26-36 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.14.003

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