Corrosion evaluation of laser gas nitrided Ti-6Al-4V alloy

Laser surface melting of Ti-6Al-4V alloy under a pure nitrogen environment of 30 lit/min gas flow rate was carried out with 200-600 mJ laser beams produced by a Nd-YAG pulsed laser. The Laser frequency and the pulse duration time were fixed at 10 Hz and 200 µs, respectively. The microstructure and corrosion behavior of the nitrided samples were examined, using scanning electron microscope, X-ray diffraction (XRD), and anodic polarization tests in 2M HCl solution. The microstructures consisted mainly of a thin continuous layer of titanium nitride followed by nearly perpendicular dendrites, and below this, a mixture of small dendrites and large needles with a random orientation. The dendritic structure was the TiN phase, and the needle phase and the phase of the matrix between the dendrites were nitrogen–enriched. An improvement in corrosion behavior, associated with the presence of a good TiN coating, was observed. Also, the improved pitting corrosion resistance was obtained due to the microstructural changes after laser treatment