Pipe diffusion ripening of Si precipitates in Al-0.5%Cu-1%Si thin films
Résumé
Al-0.5%Cu-1%Si thin films deposited onto oxidized Si substrates were subjected to both wafer curvature and in situ transmission electron microscopy (TEM) thermal cycling experiments between room temperature and 450°C. The evolution of precipitates was monitored during cycling. Chemical analysis revealed that the precipitates are pure Si. Their average size increased from 80 nm in the as-deposited state to 300 nm after thermal cycling. Si precipitates serve as anchoring points for dislocations and grain boundaries. Direct evidence for pipe-diffusion ripening was found in the vicinity of a dissolving precipitate. Real-time measurement of the radius of the precipitate allowed us to estimate the coefficient of pipe diffusion of Si in Al at this temperature. As expected, this coefficient is several orders of magnitude larger than the volume diffusion coefficient. The impact of precipitate ripening on the mechanical behaviour of these alloyed Al films will also be discussed.
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