Elastic energy and interactions between twin boundaries in nanotwinned gold

Nanotwinned metals exhibit a surprising combination of ultrahigh strength and high ductility. We have performed atomistic simulations in gold to study interactions between coherent twin boundaries (CTBs) and between incoherent twin boundaries (ITBs) for two extreme cases: with close surfaces and without any surface, in order to simulate a relaxed or a constrained system. The estimated displacement fields give the extension of interactions between twin boundaries which are 6 atomic planes for the CTB and in the range of 30–42 atomic planes for the Σ3{112} ITB in the relaxed system. The displacement field in the constrained system is, to a very good approximation, the difference of the displacement field in the relaxed system and a homogeneous quantity which depends on the excess volumes. The elastic strain introduced by the twin boundaries in the constrained system and the associated elastic energy γexcess are deduced from the excess volumes. Our study highlights how the mechanical behaviour (e.g. the yield strength) of samples with TBs separated by distances less than a critical distance whose order of magnitude is (103−105)δTB≈(0.5−360)nm can be affected.