Intriguing Challenges in the Development of High-Temperature Shape Memory Alloys

Shape memory alloys (SMAs) represent today a consolidated technology in a plethora of industrial applications for high work output actuators. However, there are still a few factors that restrict their widespread introduction. For instance, transformation temperatures are a limitation for use in devices operating at temperatures above 373K.

To overcome the inherent temperature limitation of NiTi SMAs, research on high-temperature SMAs (HTSMAs) has accelerated during the last decade. The transformation temperatures of NiTi are generally elevated by adding elements such as Au, Hf, Pd, Pt, and Zr. One of the major issues with using Au, Pd, or Pt is the prohibitive cost. NiTiHf(Zr) alloys have recently been developed for that purpose, making them a more affordable option. However, many challenging aspects must be considered to have a viable, robust, economic, and reliable solution.

First, tuning of the transformation temperatures and behavior through chemistry and processing is desirable. Results of our efforts pertaining the NiTiHf system will be presented in this context.

Another critical factor is the low workability of these alloys that is a serious problem and can represent a key barrier to the scale-up of a commercial production. Improvement of the cold workability of these alloys is crucial for manufacturing them into suitable sizes and shapes and for microstructure control.

In this work, preliminary evaluations about the effects of heat treatments, hot and cold working on functional properties will be discussed. In addition, the impact of this study on production and processing of future NiTiHf-based HTSMAs will be debated.