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<p>This study investigates the thermomechanical behavior of Ni<sub>50.3</sub>Ti<sub>29.7</sub>H<sub>f20</sub> high-temperature shape memory alloys (HTSMAs), examining the effect of different aging treatments. Samples were produced via vacuum induction melting and extrusion, and aged at 500, 525, and 550&#xa0;°C for 3&#xa0;h. Material characterization involved differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and Vickers microhardness. Small punch testing (SPT) was employed to assess mechanical performance at 22 and 150&#xa0;°C. Results indicated that aging promoted the formation of nanoscale H-phase precipitates, with their maximum presence and intensity at 525&#xa0;°C. This correlated with the highest transformation temperatures and peak hardness values. SPT revealed temperature-dependent deformation behavior: Martensite-rich samples (22&#xa0;°C) demonstrated higher fracture resistance, more cycles before failure, and greater ductility compared to austenite-rich samples (150&#xa0;°C), which showed earlier degradation and brittle fracture. Cyclic SPT confirmed better loop stability and recoverability for martensitic samples. Aging at 525&#xa0;°C optimizes the balance of transformation temperature, hardness, and mechanical resilience for HTSMA applications, contributing to the validation of SPT as an efficient characterization method for these alloys.</p>

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Characterizing the Thermomechanical Behavior of NiTiHf Shape Memory Alloys Using Small Punch Testing

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Alejandro Padilla-Gonzalez,
  • Andre Montagnoli,
  • Marcus L. Young,
  • Martin Abendroth,
  • Bjoern Kiefer

摘要

This study investigates the thermomechanical behavior of Ni50.3Ti29.7Hf20 high-temperature shape memory alloys (HTSMAs), examining the effect of different aging treatments. Samples were produced via vacuum induction melting and extrusion, and aged at 500, 525, and 550 °C for 3 h. Material characterization involved differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and Vickers microhardness. Small punch testing (SPT) was employed to assess mechanical performance at 22 and 150 °C. Results indicated that aging promoted the formation of nanoscale H-phase precipitates, with their maximum presence and intensity at 525 °C. This correlated with the highest transformation temperatures and peak hardness values. SPT revealed temperature-dependent deformation behavior: Martensite-rich samples (22 °C) demonstrated higher fracture resistance, more cycles before failure, and greater ductility compared to austenite-rich samples (150 °C), which showed earlier degradation and brittle fracture. Cyclic SPT confirmed better loop stability and recoverability for martensitic samples. Aging at 525 °C optimizes the balance of transformation temperature, hardness, and mechanical resilience for HTSMA applications, contributing to the validation of SPT as an efficient characterization method for these alloys.