Excimer laser surface treatment of aluminum alloy in nitrogen

The excimer laser nitriding process reported is developed to enhance the me chanical and chemical properties of aluminum alloys. An excimer laser beam is focused onto the alloy surface in a cell containing 1-bar nitrogen gas. A vapor plasma expands from the surface and a shock wave dissociates and io nizes nitrogen. It is assumed that nitrogen from plasma in contact with the surface penetrates to some depth. Thus it is necessary to work with a suff icient laser fluence to create the plasma, but this fluence must be limited to prevent laser-induced surface roughness. The nitrogen-concentration pro files are determined from Rutherford backscattering spectroscopy and scanni ng electron microscopy coupled to energy-dispersive X-ray analysis. Crystal line quality is evidenced by an X-ray diffraction technique. Transmission e lectron microscopy gives the in-depth. microstructure. Fretting coefficient measurements exhibit a lowering for some experimental conditions. The poly crystalline nitride layer obtained is several micrometers thick and compose d of a pure AIN (columnar microstructure) top layer (200-500 nm thick) stan ding on an AIN (grains) in alloy diffusion layer. From the heat conduction equation calculation it is shown that a 308-nm laser wavelength would be be tter to increase the nitride thickness, as it corresponds to a weaker refle ctance R value for aluminum.