Surface nitridation of transition metals by pulsed laser irradiation in gaseous nitrogen

Abstract

Surface nitridation of transition metals Ti, Mo and Ta is realized by the laser gaseous nitriding (LGN) method. By repeated pulsed laser irradiation of these pure metals in a nitrogen atmosphere, nitride layers are formed as a result of a laser-enhanced nitridation reaction. Nitrogen is found to be well-distributed in the nitride layers, and the δ-TiN, γ-Mo 2N and TaN phases are identified respectively. It is also found that the formed nitride layers have a much denser microstructure than the microstructure of the original materials. Nitrogen activation and surface melting by laser pulses greatly enhance the reaction between the molten surface and activated nitrogen. Consecutive surface heating and melting are responsible for the efficient incorporation of nitrogen in the metal lattices. Despite the non-equilibrium characteristics of pulsed laser interaction with metals, the nitridation process also depends on the thermochemical parameters of the Me-N (Me: metal) systems.