In this study, B 4 C-Ni and B 4 C-TiB 2 -TiC-Ni composite coatings were thermally sprayed on the surface of 4130 steel substrate by high velocity oxy-fuel (HVOF) torch. Before HVOF process, the B 4 C-Ni and B 4 C-TiB 2 -TiC-Ni composite powders were prepared by mechanical alloying (MA) and spray drying processes. In order to study the oxidation behavior of coatings, thermo-gravimetric analysis (TGA) was done at three temperatures of 500, 700 and 900 ? C for 35 h. Structural evolution of powder particles and coatings was investigated by X-ray diffractometry (XRD). The microstructure of coatings was studied by scanning electron microscopy (SEM). It was found that during TGA experiments of B 4 C-Ni coating, spallation was occurred at all temperatures, indicating the formation of non-protective oxide scale on the surface of this coating. First oxidation and then with increasing time, spallation were the predominant processes at 700 and 900 ? C. No spallation was seen in TGA experiments of B 4 C-TiB 2 -TiC-Ni coating. Formation of the protective oxide scale on the surface of this coating decreased the oxidation rate with increasing time. Keywords Mechanical alloying, HVOF process, B 4 C-TiB 2 -TiC-Ni coatings, Oxidation kinetics
