Annealing effects on the microstructure of electrodeposited Cu/Ag multilayered nanocomposites

摘要

TEM was used to investigate the annealing effects on the microstructure of two electrodeposited Cu/Ag multilayered nanocomposites with bi-layer thickness values of 110nm and 330 nm, respectively, as well as electrodeposited pure copper. It was found that silver layers limited the lateral growth of columnar copper grains and possibly acted as sites for nucleation of new copper grains in the as-deposited composites. The refinement of copper grains in this condition is one reason for the much higher strength of these materials in comparison to pure copper. Annealing at 100 deg C did not change the microstructure significantly. After annealing at 150 deg C, recrystallization occurred in all samples. The degree of recrystallization was dependent on the extent of internal stresses. Recrystallization was complete in the 110nm bi-layer thick composite, which had the highest internal stresses owning to its large Cu/Ag interfacial area. The recrystallization and growth of coper grains can be one reason for the drastic drop of the composites yield strength after annealing at 150 deg C.