Surface carburization of aluminum alloys by excimer laser

The excimer laser cementation process reported is developed to enhance the mechanical and chemical properties of aluminum alloys. It would be interest ing to use aluminum alloys in the automotive industry widely because of the ir low density, corrosion resistance and good workability. The motor weight can be reduced by replacing usual materials such as iron-steel by light al loys treated to increase their wear resistance. Ceramic materials generally exhibit great strength, resistance to wear and oxidation. The use of laser beams allows surface treatment to be located at the parts strongly exposed to wear and friction. The surface undergoes a transformation leading to an increase in hardness without changing the dimensions of the piece, thus av oiding post machining after treatment. The laser process is especially suit able for environment protection as there is no pollution by chemical solven t or emanation. An excimer laser beam is focused onto the alloy surface in a cell containing I bar methane or propylene gas. A vapor plasma expands fr om the surface and a shockwave dissociates and ionizes the ambient gas. It is assumed that nitrogen or/and carbon from the plasma in contact with the surface penetrates into the depth. Thus, it is necessary to work with a suf ficient laser fluence to create the plasma, but this fluence must be limite d to prevent laser-induced surface roughness. The carbon concentration prof iles are determined from Rutherford backscattering spectroscopy (RBS) and s canning electron microscopy (SEM). Crystalline quality is evidenced by graz ing incidence X-ray diffraction (GIXD) technique. Transmission electron mic roscopy (TEM) gives the in-depth microstructure. The polycrystalline cement ed layer obtained is several micrometers thick and composed of a pure compo sition (columnar microstructure) top layer (200-500-nm thick) standing on a diffusion layer (grains). Fretting test measurements exhibit an improvemen t of the surface mechanical behavior for some experimental conditions. (C) 2001 Elsevier Science B.V. All rights reserved.