Improvement of Surface Properties of Pure Iron Modified by Novel Plasma Electrolytic Oxy-Carburising Technique

Abstract

Plasma electrolytic oxy-carburising of pure iron was carried out by using novel plasma electrolysis technique using dynamic electrolyte flow between substrate and electrolytes. The electrolytes contained glycerine and sodium carbonate as a carbon source and conductivity provider, respectively. This novel plasma electrolysis (PE) technique and nozlle setup can provide high wear and corrosion resistance due to the high diffusion rate of O and C into the metal surface, and subsequent quenching results in the formation of multi-phase combinations of carbo-oxides, including mixtures of (Fe)2-3O3-4, austenite, martensite, (Fe)xC and a nanocrystalline layer.  The samples were treated for 1–5 minutes at voltages varying from 200 to 350 V. Constituent phases, surface morphology and topography, elemental analysis, microstructure and mechanical property investigations were conducted by XRD, OM and SEM, EDS, profilometry and microhardness testing, respectively. Potentiodynamic polarization measurements were carried out to determine the corrosion resistance of the oxy-carburised samples. The new PE technique was found to provide a more controllable process and better surface properties than conventional PEs.. The optimum process parameter was assessed at 300 V. An oxy-carburized layer of 30μm thickness was obtained, which had a hardness of 820 HV over 5 minutes at 300 V. Compared to untreated pure iron (-0.68 V), a more positive corrosion potential (-0.57 V) was obtained for the oxy-carburized layers.