Joule Heating as an Alternative to Conventional Heat Treatment of NiTi

An alternative annealing method of thin SMA wires by using the Joule heating /FTMT-EC – Final TermoMechanical Treatment by Electric Current/ is a powerful tool both for basic research of the recovery processes taking place during shape setting of SMA alloys and as well as for giving special thermo-mechanical and fatigue properties to SMA wires for engineering applications. Applications of the method will be presented in two examples. First, a treatment using very short pulse (~ms) high-temperature annealing mode developed with the aim to precisely adjust the microstructure of thin NiTi fibers in relation to the desired thermo-mechanical response will be discussed. Secondly, the medium-long pulse (~s) low temperature heating mode /LTSS/ is applied with the aim to create special microstructures in which the wire exhibits unconventional very stable thermo-mechanical functional properties and possibly improved fatigue properties.