Abstract
Objective: In this work, niobium carbide (NbC) coatings were deposited on substrates of the tool steels AISI H13 and AISI D2 using thermo-reactive deposition/diffusion (TRD) in order to analyze their behavior against corrosion in a saline environment. Materials and methods: The niobium carbides were obtained using salt baths composed of borax pentahydrate, aluminum and ferroniobium. This mixture was heated at 1050 °C for 4 hours. The chemical composition was determined by X-ray fluorescence (XRF). The coatings were morphologically characterized using scanning electron microscopy (SEM), the crystal structure was analyzed using X-ray diffraction (XRD), and the electrochemical behavior was studied using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results and discussion: The XRF analysis indicated that the coatings contained 87.476 wt% Nb and 51.943 wt% Nb for the D2-substrate and the H13-substrate, respectively. The SEM images revealed that the morphology of the surface of the coatings was homogeneous. The XRD analysis established that the coatings were polycrystalline, and the electrochemical tests established that the corrosion resistance increased slightly in the covered substrates with respect to the uncoated steels, with the best results being obtained in the layers of niobium carbide deposited on AISI D2 steel. Conclusions: The analysis of corrosion resistance revealed that the coatings prepared on D2 steel have a higher corrosion resistance because they have fewer surface imperfections, which causes the coating to exhibit a dielectric behavior.
Highlights
To reduce the effect of corrosion and wear on equipment exposed to chemically aggressive environments and subject to wear, the industry applies protective coatings on these elements
In this work, niobium carbide (NbC) coatings were deposited on substrates of the tool steels AISI H13 and AISI D2 using thermoreactive deposition/diffusion (TRD) in order to analyze their behavior against corrosion in a saline environment
The X-ray diffraction (XRD) analysis established that the coatings were polycrystalline, and the electrochemical tests established that the corrosion resistance increased slightly in the covered substrates with respect to the uncoated steels, with the best results being obtained in the layers of niobium carbide deposited on AISI D2 steel
Summary
To reduce the effect of corrosion and wear on equipment exposed to chemically aggressive environments and subject to wear, the industry applies protective coatings on these elements These coatings are hard layers of carbides, nitrides, borides and oxides. The use of carbide coatings on steels is due to their physical and chemical properties such as high surface hardness, excellent adhesion, and resistance to wear and corrosion [1]. Niobium carbide (NbC) is a chemically stable compound with a cubic crystalline structure; it melts at a high temperature and has a high hardness These properties make NbC potentially useful as a protective coating against corrosion. The aim of the present work is to analyze the corrosion resistance of niobium carbide coatings grown on AISI D2 and AISI H13 steels using a TRD system with electrochemical techniques
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