Numerical Simulation of Rapid Nitriding of Aluminum via Pulsed Laser

To better understand the mechanisms of pulsed laser-assisted synthesis of metal nitride, a numerical model was proposed to simulate the process of laser nitriding of aluminum. The model incorporated various multiphysical processes in the laser nitriding process, including heating, melting and vaporization of aluminum, formation of plasma plume, shielding of laser energy, ionization of nitrogen gas, and the transport of nitrogen in the chemically active state N* (N atoms and N+ ions) inside the aluminum. The simulated results are in good agreement with the existing experimental results in terms of laser intensity, laser impulse, N+ lifetime in plume, and nitrogen diffusion depth in aluminum. The model can well simulate the laser shielding process by plume and the nitriding process of aluminum. Characteristics of the plume expansion, plasma formation, nitrogen ionization, and diffusion were investigated systematically by the developed model. Investigations on the effects of key operating conditions show that the impact of laser wavelength is negligible, while the full-width at half-maximum (FWHM), nitrogen gas pressure, and laser intensity have a significant impact on the laser nitriding process of aluminum. The larger FWHM and larger laser intensity yield a layer with a higher N* concentration and greater thickness. The higher nitrogen gas pressure leads to an increase in N* concentration at the same position.