Developing methods for in-situ and real-time measurement of surface damage induced by cavitation using electrochemical techniques

• Applicant: Dr.-Ing. Morteza Abedini, Ph.D.
• Subject Area: Coating and Surface Technology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 529857700

Mechanical wear and electrochemical corrosion frequently act simultaneously and accelerate the damage evolution on technical surfaces. Complex interactions and often a synergistic behavior are observed, and the combined damage is denominated as tribocorrosion. Many components are affected, including biomedical implants, mining equipment, marine infrastructures, or valves. Tribocorrosion systems encompass various types including sliding wear-corrosion (contact of two moving bodies), slurry erosion-corrosion (impact of solid particles) and cavitation erosion-corrosion (collapse of bubbles). The latter one is the main subject of this project.Cavitation is the formation and collapse of bubbles in a fluid due to local changes in pressure. When bubbles collapse close to a solid surface, a high velocity water-jet and shock waves form. These induce stresses on the surface, and if occurring repeatedly may cause severe cavitation erosion. As cavitating fluids often are corrosive solutions, the occurrence of tribocorrosion is common. Electrochemical techniques are the only available approach for in-situ investigation of tribocorrosion. Various techniques have been used earlier to study the role of corrosion in tribocorrosion systems. However, each technique has its own limitations. For example, the damage in some cases (like slurry or cavitation erosion) occurs in a high rate, and it is not possible to study details using common methods of polarization tests and electrochemical impedance spectroscopy. High-speed techniques like chronoamperometry are suitable and generate large amounts of data but have not been applied extensively yet. In this research project, the effects and interrelations of erosion and corrosion of technical alloys under single bubble cavitation and ultrasonic cavitation will be studied on different time and length scales using various electrochemical techniques. High speed cameras will be used to reveal details of bubble collapse and correlate them with high time resolution electrochemical signals from chronoamperometry technique. Observing open circuit potential (OCP) and applying external anodic and cathodic potentials will reveal the influence of repassivation kinetics, nature of passive films and other effects of electrochemical behavior on erosion-corrosion damage. A relationship between the damage under single bubble collapse and ultrasonic cavitation (structure containing multiple, interacting bubbles), which is typically used to study material behavior, will be developed. The effect of galvanic coupling created between damaged and undamaged regions on the surface of samples will be clarified by changing the sample size. This project aims to complete the understanding of the synergy mechanisms of corrosion and erosion under cavitation damage of different passive alloys, providing a basis for the development of new (electro-/chemical) protective measures in the future.

• DFG Programme: Research Grants