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Samples of several Al-Cu alloys (AlCu 0,60 at %, AlCu 1,21 at %, AlCu 2,12 at %, AlCu 17,35 at %) were irradiated with a high-energy laser pulse (1013 WM-2, 150 ns) at ambient temperature in a vacuum of 10-4 bar. Under these conditions the sample surfaces reach vaporiza¬ tion temperature. The thin, molten surface layer (approx. 10 pm) re¬ solidifies very rapidly. The solidification microstructure of such layers was studied in the transmission electron microscope (TEM). It was found that the segregation microstructure consists of cellular dendrites, except for a very thin superficial layer of about 1 pm where the cells are replaced by small, spherical, incoherent precipitates (0 = 20 nm). In order to obtain information on the nature of these spherical preci¬ pitates, some samples were heat treated in situ in the TEM. It was ob¬ served that these small, spherical, incoherent precipitates transform into larger, coherent 0'-precipitates. During irradiation the samples are deformed due to plasma ignition at the surface. The dislocation structure characterising this deformation was studied in those parts of the sample that had not molten. Helical dislocations were found, generally distributed in bands. The alloy AlCu 2,12 % at was also irradiated at -195 °C. The microstructure of the resolidified layer is the same in the samples irradiated at -195 °C as in the samples irradiated at ambient temperature, but the dislocation density in the rest of the samples is much higher in the -195 °C samples.

Effets produits par l'irradiation d'alliages Al-Cu par un pulse laser(TEA-Co-2): étude par microscopie électronique à transmission