TiN formed by laser gas alloying (LGA) of Ti-6Al-4V

A surface layer of titanium nitride is formed by locally melting Ti-6Al-4V alloy in nitrogen with a 1200 W continuous wave Nd:YAG laser. Optical light microscopy (OM) was performed to investigate the microstructure of the cross section and surface morphology of the coating. X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS), X-ray Photo Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) analyses were performed to determine the chemical composition, the structure and the stoichiometry of the formed nitride. The OM results showed, in the molten area of the sample, a dendritic microstructure of TN with alpha'-Ti and retained beta-Ti in the interdendritic region The XRD results showed that the coating consisted mainly of TiN and some AlN. XPS analyses determined that the nitride formed is near-stoichiometric TN. From AES and EDS analyses it was found that the dendrites contained large amounts of nitrogen and titanium. The interdendritic, on the other hand, region showed a low concentration of nitrogen but high concentrations of Al and V. It is therefore expected that AIN would be present in the interdendritic region and not in the dendrites.