Enhancing NiTi Shape-Memory Effect Properties Via Warm Working Process
An innovative Warm-Working process was suggested for coping with challenge of having high Af, high yield strength and low permanent set altogether [1]. Such process is expected to create internal sub-grain structure through polygonization, contrary to partial annealing taking place during hot-working.
In the current work, two lots of NiTi alloy rod (processed from the same ingot) were tested. The lots differ by the area-reduction methods: traditional hot-working and the suggested Warm-Working method. The results show superiority of the warm-worked SMA in terms of yield strength and permanent set. Additional properties, such as transformation temperatures without loading (Bend-Free Recovery tests) or under stress (Constant Load-Deflection tests), and actuation stress applied by the pre-strained material during heating, will be presented. Suitable post-working heat treatment leads to optimization of the desired properties. The microstructure of both materials is characterized by TEM.
References:
[1] R. Padan , Y. Khoptiar, I. Gutman, J. Flomenblit and D. Gorni, " Effect of Pre-Stressing on Transformation Temperature (Af) of Shape Memory NiTi Alloys", IMEC 15 proceedings (2012).