Atomic structures of interfacial solute gateways to θ′ precipitates in Al-Cu alloys

Many materials employed in critical structural applications depend upon metastable strengthening precipitates that transform or dissolve at elevated temperatures. Herein, aberration-corrected scanning transmission electron microscopy and first-principles calculations are used to accurately determine the atomic structure of the highly mobile, semi-coherent precipitate interfaces that control this process in the classic theta' (Al2Cu) precipitate in the Al-Cu system. Semi-coherent {110} interfaces are found to be composed of an array of unexpected misfit dislocations that are arranged in two different structural units. Dislocations accommodate nearly all of the misfit between the Al matrix and strengthening phase. Cu is observed to segregate to the compressed edge of the dislocation cores at specific sites in this interface. First-principles calculations revealed the energetic landscape that facilitates these sites to become entry and exit gateways of Cu atoms in this semi-coherent interface. This investigation reveals critical features within semi-coherent interfaces that determine the thermal stability of precipitation-hardened alloys. (C) 2021 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

This study accurately determines the atomic structure of semi-coherent precipitate interfaces using aberration-corrected scanning transmission electron microscopy and first-principles calculations, revealing critical features that determine the thermal stability of precipitation-hardened alloys.Unexpected misfit dislocations are found to be key in accommodating the misfit between the matrix and strengthening phase.