Plastic Deformation through Dislocation Saturation in Ultrasmall Pt Nanocrystals and Its in Situ Atomistic Mechanisms.

The atomic-scale deformation dynamic behaviors of Pt nanocrystals with size of ∼18 nm were in situ investigated using our homemade device in a high-resolution transmission electron microscope. It was discovered that the plastic deformation of the nanosized single crystalline Pt commenced with dislocation "appreciation" first, then followed by a dislocation "saturation" phenomenon. The magnitude of strain plays a key role on dislocation behaviors. At the early to medium stage of deformation, the plastic deformation was controlled by the full dislocation activities accompanied by the formation of Lomer dislocation locks from reaction of full dislocations. When the strain increased to a significant level, stacking faults and extended dislocations as well as Lomer-Cottrell locks appeared. The Lomer-Cottrell locks can unlock through transferring into Lomer dislocation locks first, and then Lomer dislocation locks were destructed under high stresses. The very high density dislocations and the frequent dislocation reactions through Lomer dislocations and Lomer-Cottrell locks may lead to work hardening in nanosized Pt.