Micromechanical and microstructural investigation of steel corrosion layers of variable age developed under impressed current method, atmospheric or saline conditions

In this paper, we have gathered the conclusions of an experimental campaign dedicated to the microstructural characterization and the determination of the local elastic properties of various natural and artificial corrosion product layers. The results of micro-indentation testing and Raman spectroscopy coupled with a semi-quantitative analysis have been presented for the whole set of investigated materials, from early-age (2 weeks) corrosion products to 660 years-old massive corroded samples. An interpretation of the local Young's modulus and hardness values has been proposed by relying on a Gaussian mixture model. The relation between the observed morphologies of the corrosion products layers, their composition and the distribution of elastic modulus and indentation hardness has finally been discussed.