"Characterization Of Thermo-Mechanically Processed High Temperature Shape Memory Wires"

High temperature shape memory alloys (HTSMAs) are becoming of more interest to the automotive, defense, and aerospace industries due to the need for elevated actuation temperatures above 100 °C. HTSMAs are currently being developed for some applications in the form of either a rod/wire or a spring. The transformation temperatures of the material can be tuned with the addition of alloying elements such as Hf, Pt, Pd, or Zr. While these elements can increase the transformation temperatures, two issues of commercialization arise: 1) The cost of elements such as Pt and Pd is prohibitive and 2) The processability of elements such as Hf and Zr is currently difficult. For commercialization, it is critical that the HTSMA is cost effective and thermo-mechanically processable and exhibits high work output capability and dimensional stability. In this study, two Ni-rich HTSMAs, NiTiZr_{20­ ­­}and NiTiHf₂₀ (at.%) were thermo-mechanically processed via hot rolling and wire drawing (<500 µm in diameter). Both of the alloys show promise, however, previous studies have shown difficulty in processing the wire below a diameter of 1 mm. Characterization of the materials actuation temperature was performed via differential scanning calorimetry (DSC), while the microstructural evolution of the material was characterized through scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and orientation imaging microscopy (OIM). Synchrotron radiation x-ray diffraction (SR-XRD) was performed to evaluate the number of phases, texture, and phase/strain evolution as a function of temperature.