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Elementary Deformation and Damage Mechanisms During Fatigue of Pseudoelastic NiTi Microstents
Author(s) -
Frotscher Matthias,
Wu Sangni,
Simon Tobias,
Somsen Christoph,
Dlouhy Antonin,
Eggeler Gunther
Publication year - 2011
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201180001
Subject(s) - materials science , nickel titanium , martensite , softening , foil method , transmission electron microscopy , dislocation , deformation (meteorology) , composite material , cyclic stress , focused ion beam , stress (linguistics) , shape memory alloy , metallurgy , microstructure , structural engineering , ion , nanotechnology , linguistics , physics , philosophy , quantum mechanics , engineering
In the present study, we investigate the fatigue behavior of Nickel Titanium (NiTi) microstents at 22 °C (room temperature) and 37 °C up to 30 × 10 6 load cycles. We briefly describe our test procedure, which applies displacement‐controlled pull–pull fatigue cycling between displacements corresponding to apparent strains of 5 and 7.5%. The response of the microstents to mechanical loading indicates cyclic softening during 30 × 10 4 cycles. Subsequently, the maximum load remains constant throughout the remainder of the test. We use transmission electron microscopy (TEM) to clarify the microstructural reasons for cyclic softening. A focused ion beam (FIB) technique is used to take out thin foil specimens from critical microstent locations. Our TEM results show that the dislocation density increases during cycling. We also find that microstructural regions with stabilized stress‐induced B19′ martensite can be detected.