Abstract Iron boride coatings were developed on AISI H13 hot work tool steel using the electrochemical boriding method at temperatures of 850, 950, and 1050 °C for durations of 2, 4, and 6 h. The process was conducted at a current density of 200 mA/cm 2 , utilizing a powder mixture containing 22.5 wt.% ferroboron (Fe-B), 70 wt.% borax (Na 2 B 4 O 7 ), and 7.5 wt.% ammonium chloride (NH 4 Cl). The obtained coatings were examined using light microscopy (LM), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), and X-ray diffraction (XRD). Metallographic analysis revealed a distinct saw-tooth shaped interface between the boride layer and the underlying transition zone, which was consistent and uniform across the examined area. XRD results revealed the formation of a dual-phase boride layer (FeB/Fe 2 B) with traces of chromium and vanadium borides. The kinetics of the boriding process were evaluated using the classical parabolic growth law, demonstrating a parabolic relationship between boride layer thickness and treatment time. The activation energy required for boron diffusion throughout the boride layer was determined to be 168.4 kJ/mol. Additionally, the microhardness and wear rate were evaluated. The boride layer reached a thickness up to 252 µm and exhibited a microhardness of 1956 ± 67 HV 0.05 , representing an increase of over 300% compared to the quenched and tempered specimens, which had a microhardness of 543 ± 8 HV 0.05 . The findings demonstrated that the phase composition and thickness of the boride coatings are strongly influenced by the immersion time and processing temperature.
Mourad et al. (Mon,) studied this question.