Abstract
Preexisting twin boundaries (TBs) and deformation twinning have been reported to significantly improve the strength and ductility of nanocrystalline and ultrafine-grained face-centered cubic (FCC) metals and alloys by interaction between gliding dislocations and TBs. Here, we prepared nanocrystalline Cu-30% Zn alloy with an average size of 80nm and characterized TB-dislocation interactions by high resolution transmission electron microscopy. Our observations show that the TBs with one or multiple (111) atomic layer steps were formed either by Shockley partial dislocations slipping along TBs or by reversible reaction between unit dislocations and TBs with the help of sessile Frank partial dislocation dissociation. Moreover, dislocation accumulation at the end of twin lamellae form an asymmetric tilt grain boundary in the matrix and prevent twin propagation. Our findings provide insight into understanding TB migration and strengthening mechanisms in highly twinned FCC metals and alloys.
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