Final thermomechanical treatment of thin NiTi filaments for textile applications by electric curent

Thin superelastic and shape memory NiTi wires are currently used to produce fabrics for various applications in medical, filtration and other technical textile fields. Since properties of NiTi textiles inherit functional properties from the NiTi filaments it is essential to be sure that kilometers of wires have exactly the required functional properties and it is very beneficial to be able to adjust them in the laboratory. Functional properties of NiTi filaments can be in a large extent controlled by the final heat treatment applied after final cold drawing. Conventionally, this is performed by straight annealing in long tubular electrical furnace by SMA providers.

An alternative heat treatment method by Joule heating will be presented in this work. It allows performing the heat treatment much faster on a compact device more appropriate for textile or smart materials laboratories. In addition to the convenience, one can easily adjust and modify the functional thermomechanical properties that might even be set as varying along the wire.

The recently developed method called Final Thermomechanical Treatment by Electric Current /FTMT-EC/ will be introduced. Results of in-situ electrical resistivity, X-ray and TEM investigations of the microstructures found in the heat treated NiTi microwires while developing the method will be discussed and a prototype of the compact device on which the FTMT-EC is carried out will be presented.