Modelling and experimental study into the laser assisted nitriding of Ti-6Al-4V alloy

Laser gas assisted processing offers advantages over commercial nitriding processes due to precise operation and local treatment. In the present study, laser gas assisted nitriding of Ti-6Al-4V alloy is considered. Temperature field is simulated using a nonconduction laser heating model, in which the phase change is accommodated. Temperature dependent nitrogen diffusion coefficient is used when computing the nitrogen concentration distribution in the substrate material. Thermal stresses due to temperature gradient are predicted in the solid region of the substrate material. Experimentation is carried out in an effort to nitride the Ti-6Al-4V alloy surface employing a pulsed Nd:YAG laser. Laser treated surfaces are examined using SEM, XRD, and XPS. It is found that the temperature gradient reduces sharply while the nitrogen concentration gradient reduces gradually inside the substrate material. The depth of the nitride layer almost matches the depth of the melt layer. It is observed from the experimental study that the nitride compound in the surface region of the substrate material is TiN and neither microcracks nor microvoids are observed in the nitrided region.