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Nitinol Fatigue Reviewed from Microstructural Perspective
Nitinol Devices & Components has an article available titled “Nitinol Fatigue: A Review of Microstructures and Mechanisms,” by Alan Pelton, in which the fundamental principles of Nitinol fatigue are reviewed from a microstructural perspective. Thermal and mechanical fatigue are discussed, with supporting data from DSC, TEM, and tensile testing. A transmission electron microscope photo shows that microstructure after 10 cycles consists of 75 nm grains with dislocations and subgrains and no apparent retained martensite, similar to the nonfatigued microstructures.
Microstructural analyses of thermally or mechanically fatigued Nitinol show remarkable similarities and are characterized by an increase in dislocation density with increasing number of cycles. Dislocation bands, which are thought to be due to the effects of moving martensite interfaces, align with the martensite lattice invariant plane. These microstructural effects...