Formation of fivefold deformation twins in an ultrafine-grained copper alloy processed by high-pressure torsion

Fivefold deformation twins (DTs) are formed in an ultrafine grain, with a size of ∼100 nm, of a Cu–16 at.% Al alloy processed by high-pressure torsion. Formation occurs through the sequential emission of partial dislocations from grain boundaries and other multiple twin boundaries. These observations confirm the emission of partial dislocations from multiple-fold nodes which can be attributed to increased twinnability via the introduction of Al atoms which lower the driving force for partial emission.