Kinetic Study of Niobium Carbide Coating Formation on AISI L۲ 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 L۲ steel. The coating was formed in five different composition of borax (Na۲B۴O۷), boric acid (B۲O۳), and ferro-niobium. For all of the five compositions of molten bath, niobium carbide coating treatment was carried out at ۱۱۷۳ K, ۱۲۷۳ K, and ۱۳۷۳ K for ۲, ۴ and ۸ hours. The thickness of coating ranged between ۳.۶ ± ۰.۱ µm to ۳۳.۶ ± ۰.۵ 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 ۱۰ 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 ۱۲۲.۵ kJ/mol. A practical formula to estimate the coating thickness in these molten baths has been suggested.

Keywords:

Surfaces , Niobium Carbide , thermo , Reactive Diffusion , Kinetic