Corrosion resistant layers produced in vacuum titanizing process on a low carbon steel surface coated electrolytically with cobalt

摘要

Diffusion layers produced on low-carbon steel and iron surfaces by means of vacuum titanizing process have been studied. A new technological process combining a vacuum titanizing with a preliminary electrolytic deposition of cobalt has been proposed to increase the corrosion resistance of layers. As a result, diffusion duplex layers of a Ti+Co type on the low-carbon steel and iron surfaces have been obtained. The layers microstructure, their thickness, phase composition and concentration depth profiles of elements in the diffusion zone of these layers have been investigated. Microstructure studies of these layers were performed by metallographic microscopy, X-ray diffraction, and a SEM electron microscope with a BSE and an EDS spectrometer. In addition, the layers hardness and their corrosion resistance have been determined. Corrosion measurements were performed in 0.1 M H_2SO_4 by means of potentiodynamic polarization and electrochemical impedance tests. The highest corrosion resistance was observed for steel samples with the Ti+Co type duplex layers, which showed the least passive current density and the highest charge transfer resistance, whereas the titanized layers, and the steel without any layer, corroded actively.