Microstructure and kinetics study on tantalum carbide coating produced on gray cast iron in situ

• TaC coating was produced by in situ synthesis and combined casting–heat treatment.
• TaC coating thickness depends upon the treatment time and temperature.
• From the surface to the substrate, the TaC particles gradually increased at 1155 °C.
• Thermodynamics, kinetics and atomic diffusion of coating formation were analyzed.
• The Q with the value of 388.68 kJ/mol indicated that TaC coating does not scatter easily.

Tantalum carbide (TaC) coatings were produced in this study on gray cast iron samples by a combination of casting and heat treatment at 1115–1155 °C. The microstructure and growth kinetics of TaC coatings were investigated. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were conducted to analyze macrostructure and the thickness of layer, microstructure, and phase composition. Results show that TaC coating thickness ranges from 14.4 ± 1.59 to 354.3 ± 2.89 μm depending upon the treatment time and temperature. The presence of Ta, TaC, α-Fe, G (graphite), and Fe3C phases on the iron matrix surface was detected. From the surface to the substrate, the TaC particles gradually increased from 100–300 nm to 1–2 μm at 1155 °C for different times. The kinetics of TaC coating in situ showed a parabolic relationship between carbide layer thickness and treatment time, and the activation energy for the process was 388.68 kJ/mol.