Increasing the Surface Hardness of Cast Iron by Electrodeposition of Borides in Molten Salts

In this paper the electrodeposition of boron on the surface of cast iron as a coating is applied to increase the hardness and protect the substrate against abrasive wear. The boron containing coating was synthesized by electrodeposition process from a NaCl-KCl (1:1 mol)-10 w%NaF-10w% KBF molten salt. The effect of electrolysis parameters (temperature and time) on the hardness is presented; the current density varied in the range −37 – −4.5 mA/cm , allowing perfect coverage of and respect for dimensions. The electrochemical process was carried out at different temperatures (750°C-900°C) and for different periods of time (5-10 hours). Depending on the current density and duration of electrolysis, the deposits consist of FeB or Fe B. Microhardness measurements across the boride layer indicated very high hardness values (between 1600 and 2100 HV0.05). The structure of the boride layer is linked to its boron content and thermal history: as-deposited coatings present very small grain sizes and can be considered as nearly amorphous.