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% KBF4 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/cm², 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 Fe₂B. 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.