S. Mao, X. Han, Institute of Microstructure and Property of Advanced Materials, Beijing, China; P. Liu, Y. Liu, University of Western Australia, Crawley, Australia; M. Wu, Edwards Lifesciences, Irvine, CA; Z. Zhang, Zhejiang University, Hangzhou, China
Using our newly developed atomic-scale in situ tensile technique in high resolution electron microscope, we conducted atomic-scale tensile experiments in HREM for nanocrystalline TiNi thin films. The twinning, detwinning and fracture processes of the nanocrystalline NiTi structure were in situ monitored and recorded. The nucleation and propagation of martensitic variants were studied at the atomic scale directly. The front of the martensitic variants widens through consuming the neighboring parent zones but left a permanent parent phase region. A crack nucleation and growth path was observed at the atomic scale. The cracks nucleated at the tri-grain boundaries and advanced by inter- and intragranular fracture. Concentration of stress ahead of the crack was released by nucleation of martensite which increases the ductility of NiTi alloys.
Summary: Atomic-scale tensile experiments in HREM for nanocrystalline TiNi thin films were conducted in this study.
