Wear Properties of Gray Cast Iron Coated with Niobium Carbide Produced by Pack Process

Gray cast iron is used mainly due to its characteristics of low cost, high damping capacity and high machinability. These outstanding properties are due to the presence of free graphite and the high fluidity of the molten metal what allows the casting of complex parts with thin walls easily. Suitable coatings can increase their wear resistance, expanding its usability range. Niobium carbide, with its high hardness might be a good candidate for this purpose. In this work, samples of this  material with the composition 3.6% C - 2.1% Si - 0.43% Mn - 0.26% Cr - bal Fe were subjected to niobizing powder thermo-reactive diffusion treatment, using a coating mix composed of Ferro-niobium, NH₄Cl, Al₂O₃ at 1000 ⁰C during 5 hours. Layers with hardness of 2100 HV, typical for niobium carbides were obtained. Micro-adhesive wear tests demonstrated great increase in wear resistance obtained with this treatment.