Analysis of Ordering Process in an Al-Li Alloy by a Newly Developed Method of Degree of Order Determination Using High-Resolution Transmission Electron Micrographs

Ordering processes of an Al-11.7 at. pct Li alloy in the early stage of aging have been investigated quantitatively by means of a newly proposed technique to determine the degree of order in a nanoscale area by using high-resolution transmission electron microscopy (TEM). After solid solution treatment at 833 K (560 °C) for 1.8 ks, the specimen was quenched into iced brine. The specimen exhibited congruent ordering. It was continuously heated at a rate of 0.17 Ks⁻¹ (0.17 °C s⁻¹). During heating to 673 K (400 °C), the reactions occurred in the following sequences: progress of the congruent ordering, partition of Li atoms around the antiphase domain boundaries, phase separation into Li-rich and Li-lean regions toward equilibria, and dissolution of δ′ phase.