AVS2001 Session EL+SE+TF-FrM: Laser Processing of Surfaces

Friday, November 2, 2001 8:20 AM in Room 131

Friday Morning

Start	Invited?	Item
8:20 AM	Invited	EL+SE+TF-FrM-1 Laser Creation of 3D Micro- and Nano-objects: Processing, Properties and Applications M.J. Stuke, M. Koch (Max-Planck-Institut f. Biophys. Chemie, Germany); A. Moore (University of the Pacific); K. Mueller (Max-Planck-Institut f. Biophys. Chemie, Germany); G. Padeletti (CNR Monterotondo); K. Williams (Max-Planck-Institut f. Biophys. Chemie, Germany); G. Fuhr (Humboldt University, Germany) Recent results obtained by VUV laser ablation of organic fibers and by laser direct write of 3D microelectrode structures will be described with special emphasis on: (1) creation of a cage on a tip for touch-free trapping, handling and transfer of NEUTRAL objects in solution. Video sequences will give direct evidence for the new possibilities (2) ultraprecise machining of spider fibers, an ultrastrong material.
9:00 AM		EL+SE+TF-FrM-3 Excimer Laser Surface Treatment for Aluminum Carbide Growth F. Fariaut (GREMI, France) The excimer laser process reported is developed to enhance the mechanical and chemical properties of aluminum alloys. It would be interesting to use aluminum alloys in the automotive industry widely because of their low density, corrosion resistance and good workability. The motor weight can be reduced by replacing usual materials such as iron-steel by light alloys 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 avoiding no remachining after treatment. The laser process is especially suitable for environment protection as there is no pollution by chemical solvent or emanation. An excimer laser beam is focused onto the alloy surface in a cell containing 1 bar propylene gas. A vapor plasma expands from the surface and shock wave dissociates and ionizes the ambient gas. It is assumed that carbon from plasma in contact with the surface penetrates in depth. Thus it is necessary to work with a sufficient laser fluence to create the plasma, but this fluence must be limited to prevent laser-induced surface roughness. The carbon concentration profiles are determined from RBS and SEM coupled to EDX analysis. Crystalline quality is evidenced by XRD technique. TEM gives the in-depth microstructure. Fretting coefficient measurements exhibit a lowering for some experimental conditions. The polycrystalline cemented layer obtained is several micrometers thick and composed of a pure composition (columnar microstructure) top layer (200-500nm thick) standing on a diffusion layer (grains). This layer allows a significant decrease in the fretting coefficient.
9:20 AM		EL+SE+TF-FrM-4 Laser Surface Treatment for Corrosion Prevention C. Georges, N. Semmar, C. Boulmer-Leborgne (GREMI, France); C. Perrin, D. Simon (CERI, France) The materials used in electrical contact applications are constitued of a copper alloy (brass or bronze) covered with nickel coating (diffusion barrier) and with a gold coating. There are some porosities in the nickel and gold layers which induced corrosion of the underlying layers. To modify structure of gold coating, some laser surface treatments have been undertaken. An excimer laser is used as the photon absorption coefficient is larger in UV range and because the laser beam homogeneity is available for a surface treatment. The purpose of this surface treatment is to suppress the porosities of the gold layer which are responsible of the corrosion pits and to smooth the surface as the roughness bothers a correct electrical contact. The effects of the laser treatment are studied according to different surface parameters (roughness and composition of the substrate, thickness and composition of the gold coating). The laser beam parameter influence on surface melting is simulated by numerical code. Tests of corrosion are carried out in the humid synthetic air containing low contents of pollutants (NO2, SO2 and Cl2). The technique used to control these effects are : optical microscopy, SEM, grazing X-rays and ESCA. One dimension heat conduction is resolved to simulate the temperature time evolution and the melted depth as a function of the laser parameters (laser fluence, pulse time duration). This modelling helps to the understanding of mechanisms for laser interaction with the connector surface and will allows to determine the laser type to use for this appication.
9:40 AM		EL+SE+TF-FrM-5 Laser Processing Opportunities with a High Average Power Free Electron Laser H.F. Dylla, S.V. Benson, J. Boyce, G. Biallas, D. Douglas, G.R. Neil, R. Evans, A. Grippo, J. Guebeli, K. Jordan (Jefferson Lab); M.J. Kelley (Jefferson Lab and College of William and Mary); R. Li, L. Merminga, J. Preble, M. Shinn, T. Siggins, R.W. Walker, G.P. Williams, B. Yunn (Jefferson Lab) A kilowatt class free electron laser has been operational at Jefferson Lab since 1999. The associated user facility laboratories are being used for laser-materials studies that take advantage of the FEL's high average power, broad tunability and sub-picosecond pulse structure. The presently operating FEL delivers kilowatt level powers over the mid-infrared (3-7 microns). Recently, the device has extended operation through the visible (at the 100 watt level) and the UV (at the 10 watt level) through harmonic generation. A major upgrade is currently under way that will increase the power level in the IR to 10 kW and extend kilowatt operation through 300 nm in the UV. FEL users involved in materials processing have demonstrated unique applications involving: pulsed laser deposition, laser nitriding, laser production of carbon nanotubes, laser ablation and laser micromachining.-This work supported by the Office of Naval Research, the Commonwealth of Virginia, DOE Contract DE-AC05-84ER40150, and the Laser Processing Consortium.