Investigation of corrosion properties and vibration damping capacities of AISI 4140, 4340 and 5140 steels

Vibration analysis is an essential method for maintaining and monitoring industrial rotating machinery. For machines operating in harsh environmental conditions, studies that evaluate the effects of factors such as corrosion and wear on machine components are crucial. These studies help to increase machine reliability and durability, reduce maintenance and repair costs, maintain performance and efficiency, extend component life, manage environmental impacts, meet industrial quality and reliability standards, and promote technological innovations. The aim of this thesis is to investigate the relationship between dynamic behaviour and the corrosion mechanisms of corroded steels. The corrosion mechanisms and dynamic behaviours of AISI 4140, AISI 4340, and AISI 5140 steels, which are widely used in industry, were studied in 3.5% NaCl and 0.5 M H2SO4 environments at different exposure times (24 hours, 7 days, 15 days, and 30 days). Electrochemical Impedance Spectroscopy (EIS), Dynamic Electrochemical Impedance Spectroscopy (DEIS), Linear Polarisation (LPR), and Tafel Polarisation (TP) methods were used to determine the corrosion mechanisms of the steels. Experimental Modal Analysis (EMA) and Finite Element Methods (FEM) were employed to assess their dynamic behaviour. The surface morphologies of the steels after corrosion measurements were analysed using Scanning Electron Microscopy (SEM-EDS) and Optical Profilometry (OP) techniques. The damping capacities and natural frequencies of the steels, before corrosion and after exposure to 3.5% NaCl and 0.5 M H2SO4 for 24 hours, 7 days, 15 days, and 30 days, were determined using modal analysis. Based on the data, it was found that the natural frequencies of the steels corroded in both environments decreased, whereas the vibration damping capacities increased.