Mechanism for the formation of titanium oxynitride (TiO2-xNx) on the surfaces of spherical Ti powder particles upon heat treatment in air at 500, 600, 700 and 800 degrees C was investigated. The results showed that the first at 500 degrees C a hexagonal closed packed (HCP) TiOx film was formed while aTiO(2) film was observed after annealing at 600 degrees C and eventually a TiO2-xNx layer coated the spherical Ti particles at 700 and 800 degrees C due to N diffusion within the TiO2 crystal lattice. The resulting surface structure was studied by means of x-ray diffraction (XRD) while the surface morphology of the powders was characterized using the scanning electron microscope (SEM) attached with energy dispersive x-ray spectroscopy (EDS) detector. The AFM images confirmed that when the N content increases (800 degrees C-heat treated sample) the powder loses its triangular grains (700 degrees C-annealed sample) to irregular shaped grains. (C) 2019 Elsevier B.V. All rights reserved.