Functional performances of diamond like elements in NiTiHf based alloys for high temperature actuation

In the field of high-temperature shape memory alloys (HTSMA), Ni-Ti-Hf system has been extensively investigated to achieve higher transformation temperatures than standard binary NiTi. The addition of a fourth element has been demonstrated to be a valid approach for improving key issues of these functional materials.

Ni-Ti-Hf-Nb quaternary alloys were recently explored and emerged as particularly promising for a sustainable development of HTSMA components, due to superior mechanical properties and ductility of these alloys compared to those of the ternary Ni-Ti-Hf system.

In this work, a selected composition was subjected to cold rolling for processing thin sheets. Laser cutting was firstly explored on such alloy to realize diamond-like elements for demonstrating their actuation performances at high temperature under constant load. Differential scanning calorimetry and strain recovery testing were carried out for the determination of the transformation temperatures and the recoverable strain upon thermal cycling at varying the applied load. These results are finalized to demonstrate the opportunities of designing advanced shape memory-based actuators operating at temperatures above 100-150°C.