Comparative tribological studies of ductile iron before and after vanadizing, niobizing, and combined vanadizing-niobizing

Ductile iron substrates underwent various pack cementation techniques, including vanadizing, niobizing, and a combined vanadizing-niobizing process at 950 °C for 4 h, resulting in the formation of dense and crack-free diffusional layers with thicknesses of about 18, 17.7, and 12.2 μm, respectively. X-ray diffraction analysis of the treated layers confirmed the formation of vanadium and niobium carbides in the vanadized and niobized layers, respectively, while the combined treated layers contained both vanadium and niobium carbides as well as complex carbides of vanadium and niobium. Microhardness measurements showed that the combined vanadized-niobized layer achieved the highest surface hardness, reaching approximately 3200 HV 0.1, whereas the hardness values for vanadized and niobized layers were 2600 and 2400 HV 0.1 , respectively. To investigate and compare the tribological behaviors of the aforementioned diffusion coatings and the ductile iron base material, ball-on-disk wear tests were performed under normal loads of 10 and 30 N. The results demonstrated a significantly lower wear rate for the combined vanadizing-niobizing treatment samples at all applied loads compared to those of both single-treated and untreated ductile iron. Notably, the combined treated material exhibited a negative wear rate under the normal load of 10 N due to the material transfer from the ZrO 2 balls to the harder layer containing NbVC 2 carbides.