In situ transmission electron microscopy observations of dislocation processes in delta '-strengthened aluminium-lithium alloys

Dislocation processes in delta'-strengthened aluminium-rich aluminium-lithi um alloys have been studied by transmission electron microscopy; thin foils have been tensile tested in the transmission electron microscope and the c onfigurations of the dislocations and their glide have been observed under full load. The average radii r of the delta' precipitates and their volume fractions f have been varied independently: 5 nm < r < 16 nm and 0.05 less than or equal to f less than or equal to 0.17. Two types of dislocation con figuration have been found: firstly, pairs of dislocations; secondly, singl e unpaired dislocations. All dislocations had Burgers vectors of the type 1 /2[110]. The abundance of these configurations varied with f; single disloc ations were dominant if f was low, whereas high values off 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.