Nitridation of titanium surface by the irradiation of YAG laser pulses in N2/O2 gas mixture and liquid nitrogen

Surface nitridation of a titanium target by the irradiation of YAG laser pulses in liquid nitrogen is reported, in comparison with that in pure N2 gas and the gas mixture of N2 and O2. The atomic composition, the morphology, the color, and the roughness of the irradiated surface were examined. In the gas-phase treatment, the titanium target surface was nitrided with increasing the partial pressure of N2. The surface treated in pure N2 gas had a silver color and the highest N atom concentration. The surface color changed from silver to yellow or brown with the increase in the partial pressure of O2. The depth of the nitrided layer was estimated to be several hundreds of nanometers. In contrast, the surface irradiated in liquid nitrogen had a white yellow color, and the nitrided layer was concentrated within several nanometers from the top of the surface