Investigation of coating surface of AISI 4140 steel with graphite reinforced vanadium carbide powders

In this study, graphite powder added to VC (Vanadium Carbide) and VC powder at different (1,2,3,4,5% wt% C) ratios using TIG (Tungsten Inert Gaz) welding method on the AISI 4140 steel surface, which is preferred as the substrate, was used. The surface properties were improved by coating with VC-C). Elemental analyzes in the coating region were analyzed by energy dispersive spectroscopy (EDS). X-Ray diffraction (XRD) analysis was used to determine the phase structures formed in the coating region. In order to determine the microhardness values of the samples, measurements were made from the coating surface to the substrate. In addition, the friction coefficients and wear rates of the coated surfaces were determined by performing abrasion tests on the coated samples. Intense eutectic and dendritic structures were observed in the microstructure images obtained from the coating region. Dendritic structures were formed in cellular, round and lath-like forms. In the EDS results, especially dark gray pebble-like structures V and C are dense elements, while in the eutectic region V, C and Fe are dense. In XRD analysis results, it was determined that VC, α-Fe, FeV, Fe7C3, Fe3C phases were formed in the V and C element-rich carbide phases in the primary dendritic region and the interdendritic regions. According to the microhardness measurement results, an increase in the microhardness values in the coating region was determined depending on the added C ratio. In the measurement results obtained, the lowest hardness value was measured as N2 (1% C-reinforced) 318 HV0.5 sample in the substrate region, while the highest hardness value was measured as N6 (5% C-reinforced) 1295 HV0.5. With these results, it was determined that the hardness of the coating layer increased approximately 3-4 times than the hardness of the substrate. In the light of all the data, it can be said that increasing C ratio in VC-C coating contributes significantly to the increase of coating hardness. In the coating thickness results depending on the energy input, 932 μm coating thickness was obtained in the N3 sample with an energy input of 720 J/mm, while a coating thickness of 2000 µm was obtained in the N6 sample with an energy input of 1296 J/mm. Depending on the coating thickness results, it is thought that the energy input has a significant effect on the coating thickness. The lowest friction coefficient of 150 m after abrasion was found in the N6 sample with 0.2, while the highest was determined in the N1 sample with 0.6. At 300 m, the friction coefficients were found to be 0.5 in the N1 sample and 0.15 in the N6 sample. In the light of these results, it was determined that the wear volume decreased depending on the C ratio. In the SEM results taken from the worn surfaces, it was observed that micro scratches, debris and cavities were formed on the wear surfaces. In the light of the data obtained, the microhardness of the coatings increased with the addition of C, and accordingly, the wear resistance increased. The coating surfaces exhibited a metallurgically smooth structure and no pore formation was observed.