The Loss of Coherency of θ′ Precipitates in an Aluminium-Copper Alloy

The mechanism of loss of coherency of θ′ plates in an Al-4% Cu alloy has been studied by a high voltage transmission electron microscopy using a tiltable specimen heating stage. The θ′ plates lose coherency by the nucleation of misfit dislocations at the periphery of the plates. Burgers vectors of the misfit dislocations are identified by a contrast experiment as an a〈100〉 type lying on the flat faces of θ′. Irradiation of high voltage electrons promotes the formation of misfit dislocations at relatively low temperatures. Loss of coherency of θ′ occurs also in the unirradiated area at high temperatures.