M. Shengcheng, Beijing University of Technology, Beijing, China; X. Han, Institute of Microstructure and Property of Advanced Materials, Beijing, China; M. H. Wu, Edwards Lifesciences, Irvine, CA; Z. Zhang, Zhejiang University, Hangzhou, China; Y. Liu, University of Western Australia, Crawley, Australia
In this paper, low-cycle fatigue mechanisms of a pseudoelastic nanocrystalline NiTi shape memory alloy (SMA) thin films (fabricated by magnetron sputtering) under different mean strains were investigated at atomic scale directly. The uni-axial cyclic tensile tests with small amplitude of 0.25% are operated at three different states, i.e. austenite/elastic region, austenite and martensite coexisted region and martensite/elastic region. Mechanical results indicate that the cyclic deformation strain is mainly in the inhomogeneous deformation band when the sample cycling in the B2 + B19’ phase coexist status. Cyclic deformation in the B2 + B19’ phase showed cyclic hardening effect. The atomic mechanisms responsible for the above phenomena were elucidated directly from the atomic scale observation of the fatigue cycling processes in the HREM.
Summary: Low-cycle fatigue mechanisms of a pseudoelastic nanocrystalline NiTi shape memory alloy (SMA) thin films (fabricated by magnetron sputtering) under different mean strains were investigated at atomic scale directly.
