In situ transmission electron microscopy observations of dislocation processes in δ′-strengthened aluminium-lithium alloys

Abstract Dislocation processes in δ′-strengthened aluminium-rich aluminium-lithium alloys have been studied by transmission electron microscopy; thin foils have been tensile tested in the transmission electron microscope and the configurations of the dislocations and their glide have been observed under full load. The average radii r of the δ′ precipitates and their volume fractions f have been varied independently: 5nm < r < 16 nm and 0.05 ≤ f ≤. 0.17. Two types of dislocation configuration have been found: firstly, pairs of dislocations; secondly, single unpaired dislocations. All dislocations had Burgers vectors of the type ½〈110〉. The abundance of these configurations varied with f; single dislocations were dominant if f was low, whereas high values of f favoured pairing. Cross-slip and double cross-slip were very frequent. If f was low, it led to uncoupling of the two dislocations, forming a pair.