Development, Characterization, and Design Considerations of Ni_19.5Ti_50.5 Pd₂₅Pt₅ High-temperature Shape Memory Alloy Helical Actuators

Abstract

Shape memory alloys (SMAs) have been used in various applications since their discovery. However, their use as actuation devices in high-temperature environments has been limited due to the temperature constraints of commercially available materials. Recently, SMAs that produce good work characteristics at elevated temperatures have been developed at NASA’s Glenn Research Center. One such alloy, Ni19.5Ti50.5Pd25Pt 5, has shown repeatable strain recovery on the order of 2.5% in the presence of an externally applied stress at temperatures greater than 250°C. Based on these findings, potential applications for this alloy are being explored and further work is being done to assess the use of this alloy in various structural forms. In this article, the characterization of Ni 19.5Ti50.5Pd25Pt5 helical actuators is reported, including their mechanical responses and how variations in their responses correlate to changes in geometric parameters and training loads. Finally, implementation of previously published SMA spring design methodology in future SMA helical actuator development is considered through comparison of the observed and predicted responses.

Shape memory characteristics of Ti49.5Ni25Pd25Sc0.5 high-temperature shape memory alloy after severe plastic deformation

“…But very recently, additions of Pd and Pt have attracted extra attention compared with other alloying elements, since many favorable attributes of binary TiNi, such as high work output, ductility and workability, can be maintained to a reasonable extent in these ternary alloys [11][12][13][14][15]. In terms of transformation temperatures, TiNiPd alloys are capable of martensitic transformations up to 773 K (500°C).…”

In Situ Neutron Diffraction Studies of Increasing Tension Strains of Superelastic Nitinol

“…The effects of pre-strain or ''training'' has long been recognized in the shape-memory actuator field [9][10][11][12][13][14][15]. These references indicate that there are optimal combinations of thermomechanical processing with subsequent prestraining (straining over that of the application) that tends to stabilize the microstructures for either stress or strain cycling.…”

Role of B19′ martensite deformation in stabilizing two-way shape memory behavior in NiTi

“…It has been shown that the Young's modulus for NiTi alloys decreases with temperature reaching a significant minimum at about the start of the reverse transformation followed by a steep increase once the reverse transformation is completed. [44][45][46][47] The Ni 49.9 Ti 50.1 alloy studied here exhibits similar compliance characteristics that were measured using a dynamic technique 48 and would definitely provide a mechanism for reverse reorientation to occur with increasing temperature.…”