La faible masse volumique et les bonnes propriétés mécaniques des alliages d’aluminium en font des matériaux de structure de choix dans l’industrie aéronautique. Ils présentent une microstructure polyphasée qui crée des discontinuités électrochimiques et une sensibilité accrue à la corrosion. Un système de revêtements protecteurs composé de chromate Cr(+VI) est traditionnellement formé à la surface de ces alliages. Néanmoins, les directives environnementales REACH imposent leur remplacement en raison de la cancérogénicité des chromates. L'objectif des travaux a été le développement d'un nouveau traitement constitué d’une Oxydation Anodique Sulfurique (OAS) et d’un colmatage aux sels de sulfate de chrome et de fluorozirconate (Cr3+ / ZrF62-). L’étude du procédé électrochimique d’OAS a permis de faire le lien entre la microstructure des alliages et la morphologie poreuse de la couche anodique développée à leur surface. Le traitement de colmatage Cr3+ / ZrF62- est réalisé par simple immersion dans la solution. Il est démontré que le colmatage est le fait d’une alcalinisation locale de la surface de la couche anodique qui mène à la précipitation des sels de Cr3+ et ZrF62-. Ces derniers forment un film de colmatage de 300 nm d’épaisseur très recouvrant des pores nanométriques. Le colmatage des couches anodiques permet d’améliorer considérablement la tenue à la corrosion des alliages anodisés en formant une barrière supplémentaire contre les agents corrosifs et en cicatrisant les départs de corrosion. Le traitement développé permet à la fois d’atteindre les performances des traitements aux Cr(+VI) sur une large gamme d’alliages et de satisfaire aux exigences environnementales / Aluminium alloys are very used in the aircraft industry as structural materials because of their low density and their good mechanical properties. They have a polyphase microstructure that is causing electrochemical discontinuities and increasing sensitivity to corrosion. A system of protective coatings containing chromate Cr(+VI) is traditionally formed at the surface of these alloys. However, the REACH environmental guidelines impose Cr(+VI) surface treatments replacement because of chromate carcinogenicity. The aim of the thesis work has been the development of a new surface treatment constituted of a sulfuric acid anodizing (SAA) and a sulfate chromium and fluorozirconate salts sealing (Cr3+/ ZrF62-). The study of the SAA electrochemical process linked the alloys microstructure and the anodic layer porous morphology developed at their surface. The Cr3+ / ZrF62- sealing treatment is realized by a simple immersion of the anodized alloy in the solution. It is demonstrated that the sealing is caused by a local alkalinization of the anodized coating surface that leads to the precipitation of the Cr3+ and ZrF62- salts. These ones are forming a sealing film of about 300 nm thick, very covering of the nanometric pores. The anodic layers sealing greatly improves the corrosion resistance of the anodized alloys by forming an additional barrier against corrosive agents and by healing the corrosion initiation. The developed treatment allows both to achieve Cr(+VI) treatments performance over a wide range of alloys and to satisfy the environmental requirements.

The contributions of nonlinear absorption processes to laser-induced damage of three selected groups of transparent dielectrics were investigated. The studied materials were irradiated and non-irradiated fused silica, doped and undoped fluorozirconate glass and cubic zirconia stabilized with yttria. The laser-induced damage thresholds, prebreakdown transmission, and nonlinear absorption processes were studied for several specimens of each group. Experimental measurements were performed at wavelengths of 1064 nm and 532 nm using nanosecond and picosecond Nd:YAG laser pulses. In the irradiated fused silica and fluorozirconate glasses, we found that there is a correlation between the damage thresholds at wavelength λ and the linear absorption of the studied specimens at λ/2. In other words, the laser-induced breakdown is related to the probability of all possible two-photon transitions. The results are found to be in excellent agreement with a proposed two-photon-initiated electron avalanche breakdown model. In this model, the initial "seed" electrons for the formation of an avalanche are produced by two-photon excitations of E' centers and metallic impurity levels which are located within the bandgaps of irradiated Si02 and fluorozirconate glasses, respectively. Once the initial electrons are liberated in the conduction band, a highly absorbing plasma is formed by avalanche impact ionization. The resultant heating causes optical damage. In cubic zirconia, we present direct experimental evidence that significant energy is deposited in the samples at wavelength 532 nm prior to electron avalanche formation. The mechanism is found to be due to formation of color centers (F+ or F° centers) by the two-photon absorption process. The presence of these centers was directly shown by transmission measurements. The two-photon absorption (2PA) process was independently investigated and 2PA coefficients obtained. The accumulated effects of the induced centers on the nonlinear absorption measurements were also considered and the 2PA coefficients were measured using short pulses where this effect is negligible. At room temperature, the color centers slowly diffuse out of the irradiated region. The density of these centers was monitored as a function of time. The initial distribution of the centers was assumed to have a Gaussian profile. For this model the diffusion equation was solved exactly and the diffusion constant obtained.