Formation of niobium carbide coating on AISI L2 steel using thermo-reactive diffusion (TRD) technique

In this study, a thin layer of niobium carbide was thermochemically formed on AISI L2 tool steel substrates using the thermo-reactive diffusion (TRD) method. Five different compositions of salt bath were selected and for each composition the treatment was performed at three different temperatures (900, 1000, 1100 ºC) for three different times (two, four, eight hours). The morphology of the coating was characterized through optical and scanning electron microscopy (SEM), and the crystalline structure was studied through X-ray diffraction (XRD). The reaction layer of niobium carbide formed was uniform all over the surface and had a smooth interface with the substrate. The thickness of the coating varied from 3.6 to 33 ?m depending on the chemical composition of the salt bath, process time and temperature. The chemical composition was evaluated via Energy-dispersive X-ray Spectroscopy (EDS) and the atomic distribution map of the coating and substrate was prepared. The hardness value of the coated samples was 2450±50 HV 0.05 which was much higher than the hardness of the uncoated sample (280 HV). Corrosion properties of NbC coated samples in 3% NaCl solution were studied and the results showed that coated samples had better corrosion resistance in comparison to the uncoated steel. (AU) Copyright © 2018 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved