Elastic strain around needle-shaped particles embedded in Al matrix

Precise measurements of strain fields around precipitates embedded in a crystalline matrix were performed, and simple but accurate models were deduced from the observations. The measurements were carried out in an aged aluminum alloy containing needle-shaped particles. The displacement and strain fields around rod-shaped and lath-shaped particles were obtained from high-resolution electron micrographs using geometric phase analysis. The measurements reveal that strain field of a rod-shaped particle is well described by the classical Eshelby analytical elastic solution. For the more complex case of lath precipitates, it is shown that the strain field in the matrix can be simply approximated by a dislocations dipole. The methods developed are generally applicable to the characterization of strain in nano-structured materials, including those with complex or unknown structures.