Multiple Memory Shape Memory Alloys

Abstract

Until now, shape memory alloys (SMAs) have been largely limited to “remembering” a single memory. In other words, monolithic components only possess a single set of functional properties. The current work describes how theorized change to local chemical composition induced through laser processing enables controlled augmentation of transformation temperatures. Proof of concept was demonstrated by locally embedding multiple shape memories into a monolithic NiTi component. This novel technique overcomes traditional fabrication challenges and promises to enhance SMA functionality and facilitate novel applications through producing a new class of smart materials; namely multiple memory materials (MMMs).

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…As such, a good agreement between the thermal analysis and the microstructural characterization by X-ray diffraction was obtained. The existence of martensite in the processed region was explained based on preferential volatilization of Ni in the FZ [232]. In fact, Ni depletion increases the transformation temperatures [2].…”

“…So, the austenitic base material at room temperature prior to laser processing, experienced an increase in its transformation temperatures that allowed for martensite to be stable at room temperature, replacing austenite as the equilibrium phase. From [232] significant contributions can then be retrieved for understanding the implications of similar laser welding of NiTi joints. Namely, on how a material that is fully austenitic at room temperature can present, at room temperature, martensite in the FZ after welding; this may also justify the increase of transformation temperatures observed in this region when compared to the base material.…”

Thermomechanical fatigue of post-weld heat treated NiTi shape memory alloy wires

“…These limitations can be overcome with metallurgical bonding, which has a number of advantages that include high strength connections to control systems [6], and reduction of cost by joining NiTi with less expensive materials [7][8][9]. The counterpoint to these advantages are the difficulties that can be encountered during joining of NiTi, which include solidification cracking, formation of brittle intermetallics and oxides, and degradation of the material properties [10,11].…”

Design, processing, and characterization of nickel titanium micro-actuators for medical implants

“…The objective of decreasing the atmosphere pressure is to increase partial vaporization effects of the NiTi alloy, as functional properties may change due to higher vapor pressure of Ni at lower temperatures, compared to Ti. 11 Hence, the tendency of Ni vaporization in a NiTi melting pool is higher than that of Ti. Small changes in the Ni to Ti ratio cause significant changes in the phase transformation temperature of an NiTi alloy.…”

“…Results of different scientific publications [10][11][12][13][14] show opportunities to change the functional properties of SMA by using exactly adjusted laser parameters. Adapting this knowledge to the application of guidable CI electrodes offers the chance to realize a passive activation, i.e., that the martensitic transformation should be induced by using natural body heat.…”