Diffusion analysis across grain boundary in Al-3.7 mass%Cu alloy using analytical electron microscopy

An Al-3.7 mass%Cu alloy was subjected to aging treatment at selected temperatures in the range from 453 to 548 K. Diffusion coefficients of Cu in the alloy were then determined from Cu concentration profiles measured across the grain boundary. A high spatial resolution analytical electron microscope (AEM) capable of forming a 1 nm probe was used to measure the concentration profiles. As the aging temperature is lower, the diffusion coefficients tend to deviate from the values extrapolated from the higher annealing temperatures. It is suggested that this deviation is due to the presence of quenched-in excess vacancies. The concentration profiles were also measured for the boundaries having different misorientation angles. It is shown that the concentration profiles are essentially the same regardless of the misorientation angles and of the boundary characters except for the misorientation angles smaller than a few degrees.