Kinetics of niobium carbide reinforced composite coating produced in situ

Niobium carbide (NbC) coatings on gray cast iron (Fe) (HT300) substrate were prepared by in situ synthesis at 1070, 1100, or 1130 °C for 15, 30, 45, or 60 min. The microstructure, elemental distributions, and phases of the coatings were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffraction. The kinetics of NbC coating growth by in situ synthesis was examined by measuring the depth of the NbC layer as a function of time and temperature. The results showed that the surface coating consists of NbC and α-Fe phases. The average grain size of NbC on the top surface of the coating was approximately 400 nm. The estimated growth rate constant varied from1.84 × 10−9 cm2/s to2.57 × 10−9 cm2/s, and activation energy of the NbC layer was calculated as 86.01 kJ/mol.