Research Projects

Corrosion and cavitation-erosion are major challenges for metallic ship structures like propellers, rudders, and hulls in marine environments. Chloride ions accelerate corrosion in seawater, while water movement and bubble collapse increase cavitation-erosion on propellers. Nickel-Aluminium-Bronze (NAB) alloys are widely used materials for propellers due to their cost-effective casting process and good corrosion resistance. However, NAB alloys remain susceptible to cavitation-erosion. Enhancing the corrosion and cavitation-erosion resistance of propellers can be achieved through surface modification with appropriate coatings. Ti6Al4V alloy is known for its excellent corrosion resistance in marine environments, and coatings of Ti6Al4V on NAB alloys can be applied using various thermal methods, such as thermal spray coating. However, the high temperatures involved in these methods can introduce defects, which accelerate material degradation. These issues can be mitigated by using cold spray techniques, which develop coatings with strong mechanical bonds without melting, avoiding phase changes and residual stresses. Cold spray technology is widely used in aerospace and military applications and is also effective for surface repair. While cold spraying Ti6Al4V is a promising alternative, challenges remain in achieving a dense coating and enhanced wear resistance. However, cold-sprayed Ti6Al4V coatings show improved wear resistance, and post-coating heat treatment can further enhance coating density and wear resistance, and, consequently, corrosion and cavitation-erosion resistance. This project primarily focuses on optimizing and developing cold spray Ti6Al4V coatings on NAB alloy to protect ship propellers from cavitation-erosion and corrosion, with the aim of enhancing propeller performance and lifespan. To the best of the PI’s knowledge, this is likely the first attempt to use cold spray techniques to apply Ti6Al4V alloy coatings on NAB alloys to improve both corrosion and cavitation-erosion resistance of NAB alloys. In this project, Ti6Al4V alloy powder will be used to coat a Naval-grade NAB (C95800) alloy via high-pressure cold spray technology (PCS-100). Nitrogen gas will be employed to accelerate the powder particles. Optimal cold spray parameters, including particle velocity and temperature, will be established. The coated NAB alloy will undergo heat treatment in an argon atmosphere at 750–1050 °C. Electrochemical corrosion and cavitation-erosion tests on both coated and uncoated NAB alloys will be conducted in simulated seawater. The corroded and eroded samples will be characterized using different characterization techniques to understand the corrosion and erosion performance of coated NAB alloys for naval applications. Overall, this project will create robust applied knowledge that could support the commercialization of these coatings for marine and related applications.