KINETIC STUDY OF NIOBIUM CARBIDE COATING FORMATION ON AISI L2 STEEL USING THERMO-REACTIVE DEPOSITION TECHNIQUE

In the present study, thermo-reactive deposition method (trd) in a molten bath was used to form niobium carbide coating on aisi l2 steel. the coating was formed in five different composition of borax (na2b4o7), boric acid (b2o3), and ferro-niobium. for all of the five compositions of molten bath, niobium carbide coating treatment was carried out at 1173 k, 1273 k, and 1373 k for 2, 4 and 8 hours. the thickness of coating ranged between 3.6 ± 0.1 µm to 33.6 ± 0.5 µm depending on the bath composition, treatment time, and temperature. kinetic study of the formation of nbc coating demonstrated that for the molten baths containing 10 wt.% ferro-niobium or more, growth of the coating is under the controled of by diffusion. for such molten baths, the activation energy of the process was estimated to be 122.5 kj/mol. a practical formula to estimate the coating thickness in these molten baths has been suggested.