Impact of thermal cycling on the evolution of grain, precipitate and dislocation structure in Al, 0.5% Cu, 1% Si thin films

Abstract

Thermal cycles have been performed both outside and inside a transmission electron microscope (TEM) in order to analyze the evolution of the microstructure of Al, 0.5% Cu, 1% Si thin films deposited onto oxidized Si substrates. It is shown that grain growth and dislocation activity start almost simultaneously and cooperate throughout the plastic regime of the stress–temperature curve to generate bamboo-type grains with low dislocation density. Si precipitates serve as anchoring points for dislocations and grain boundaries. Thermal cycling and diffusion cause the growth of these precipitates and a diminution of their number. Diffusion also proves to play an important role regarding plastic relaxation at the Al/SiO x interface and at the grain boundaries where an intense hillock and whisker formation has been observed in scanning electron microscope (SEM). The stress–temperature evolution is discussed in light of these observations.