Phase transformations in Al-Cu thin films: Precipitation and copper redistribution

The (micro-)structural changes occurring in thin Al-Cu films of about 500 n m thickness and containing up to 1 at% Cu have been investigated. In partic ular, the copper distribution and the precipitation behaviour have been stu died in situ during thermal cycling between 323 and 773 K. After slow cooli ng, large second-phase particles are observed which are mostly located at g rain boundary triple points; the shape and size depend on the copper concen tration. The average distance between these particles is about 16 mum, whic h is larger than the average grain size of approximately 1 IJ-m No second-p hase particles have been observed within the aluminium grains. After coolin g, a relatively large amount of copper (about 0.2 at%) as compared with bul k Al-Cu (0.001 at%) is not contained in second-phase particles. Most Likely , this copper has segregated at grain boundaries, interfaces and dislocatio ns. The temperature at which Al2Cu starts to form in the thin films is well below the copper solvus for bulk material. (C) 2001 Acta Materialia Inc. P ublished by Elsevier Science Ltd. All rights reserved.