Effects of laser irradiation on the mechanical response of polycrystalline titanium

The effects of laser treatment on the mechanical response of polycrystalline titanium (99.99%) have been investigated using the laser gas nitriding technique. Samples were subjected to irradiation by a 532 nm pulsed Nd:YAG laser for 100-400 shots. Laser pulses of energy 370 mJ with 10 Hz repetition rate were used to irradiate the surface of specimens and to activate the reaction between the irradiated surface and nitrogen. The effects of multiple laser pulses on the microstructure, yield stress (YS), ultimate tensile stress (UTS) and microhardness of the specimens were examined. Characterization of both the unirradiated and the irradiated specimens was carried out using a scanning electron microscope, an x-ray diffractometer and an energy dispersive x-ray spectrometer. The results show that irradiation of the specimens resulted in the growth of grains in the beginning and then their segregation as the number of laser shots was increased. An incorporation of nitrogen ions into the surface is also observed. The microhardness was found to increase with increasing laser shots, whereas changes in YS and UTS with laser shots were found to be anomalous.