Investigation of corrosion behaviour of carbon steel coated by pulsed plasma electrolytic boronising technique in 3·5 wt-%NaCl aqueous solution

Abstract

Boride coatings were synthesised on AISI H13 steel using pulsed plasma electrolytic boronising technique in a modified aqueous solution of borax. Hard and strongly adherent coatings with various desirable properties were obtained by applying different frequencies and duty cycles during the treatment. The analytical characteristics of the coating were assessed using X-ray diffraction and scanning electron microscopy techniques. The thickness of boride layers was increased by increasing frequencies. The corrosion performances of these coatings were investigated by a potentiodynamic polarisation test and ac impedance spectroscopy. Equivalent circuits have been proposed to represent the boride phases, oxide film and electrolyte systems examined. The general corrosion resistance of the produced coatings has been found to increase with the frequency.