In-situ TEM observation of fracture in nanocrystalline Ni synthesized by electrodeposition

The microprocess of fracture in the nanocrystalline Ni (nc-Ni) with grain size of 20-30 nm synthesized by electrodeposition was investigated by in-situ tensile test in TEM. The results show that many dislocations were emitted from the crack tip and the grain boundaries near the crack. The dislocations traveled through the grain, and most of them annihilated in the opposite grain boundaries. The grain boundaries in nc-Ni can act as sources and sinks for dislocations. Some dislocations might pile up in the front of the crack tip and a very small dislocation free zone formed between crack tip and the pile-up dislocations. Nano-crack might initiate at the crack tip that made the main crack propagated continuously. Nano-crack might also initiate in the front of the crack and then connected with the main crack that made the main crack propagated discontinuously. A thin ribbon zone might form during the fracture in which the microcracks initiated. The connection of cracks in the ribbon resulted in the Zig-Zag crack propagation.