Abstract
Chromium carbide, vanadium carbide, and chromium–vanadium mixture coatings were deposited on AISI D2 steel via the thermo-reactive deposition/diffusion (TRD) technique. The carbides were obtained from a salt bath composed of molten borax, ferro-chrome, ferro-vanadium, and aluminum at 1020 °C for 4 h. Analysis of the morphology and microstructure of the coatings was done via scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The hardness of the coatings was evaluated using nano-indentation, and the friction coefficient was determined via pin-on-disk (POD) testing. The electrochemical behavior was studied through potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The XRD results show evidence of the presence of V8C7 in the vanadium carbide coating and Cr23C6 and Cr7C3 in the chromium carbide coating. The hardness value for the vanadium–chromium carbide coating was 23 GPa, which was higher than the 6.70 ± 0.28 GPa for the uncoated steel. The wear and corrosion resistance obtained was higher for the niobium–chromium carbide coating, due to the nature of the ceramic carbide produced.
Highlights
AISI D2 steel is widely used in the manufacturing industry, especially in the development of dies, due to its high degree of hardness and wear resistance
Icorr for the results show that the coatings that grow in a salt bath with the highest concentration of vanadium exhibit lower corrosion resistance, contents exhibit the best protection against corrosion coatings that while grow the in acoatings salt bathwith withchromium the highest concentration of vanadium exhibit lower corrosion resistance, while the coatings with chromium contents exhibit the best protection against corrosion
Potentiodynamic polarization curves show better performance as a protective coating than those grown with greater chromium content in the salt bath treatment
Summary
AISI D2 steel is widely used in the manufacturing industry, especially in the development of dies, due to its high degree of hardness and wear resistance. The coatings are industrially produced using techniques such as physical vapor phase deposition (PVD) and chemical vapor deposition (CVD) [1,2]. An alternative for producing hard coatings with good wear resistance is the thermo-reactive deposition/diffusion (TRD) process [3], which is applied over substrates containing a higher percentage of carbon, up to 0.3% by weight [4]. Coatings produced using this process have good adhesion to the substrate, a low friction coefficient, and excellent thickness uniformity [4,5]. A bath of molten salts can be used, consisting of borax, Coatings 2019, 9, 215; doi:10.3390/coatings9040215 www.mdpi.com/journal/coatings
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