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<p>The functional degradation of NiTi shape memory alloys (SMAs) poses a significant risk to their reliability in cyclic applications. This study utilizes Berkovich nanoindentation to quantitatively assess the microscale deformation properties of NiTi alloy subjected to different regimes of preceding macroscopic cyclic loading. The nanoindentation responses, including reduced modulus and depth recovery ratio, were examined as a function of maximum load (500–10000&#xa0;μN) and loading rate (100–2000&#xa0;μN/s). Results indicate that prior cyclic loading substantially diminishes local reversibility, with the depth recovery ratio dropping from approximately 50% in the virgin condition to about 43–48% in the degraded states. Variations in loading rate produced negligible alterations in the microscale characteristics compared to the predominant effect of functional degradation from cyclic loading. A definitive correlation was found between this microscale recovery measure and the macroscopic residual strain from uniaxial cyclic loading, connecting the decrease in reversibility at both scales to the accumulation of dislocation-based barriers during cyclic loading. This study confirms nanoindentation as an effective diagnostic method for investigating the functional fatigue from cyclic loading while recognizing the interpretive differences resulting from the intricate, localized deformation conditions beneath the indenter.</p>

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Investigating the Small-Scale Deformation Characteristics of NiTi Shape Memory Alloy Under Cyclic Loadings Using Nanoindentation

  • 期刊论文

  • 发表日期：

    2026年3月24日

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  • Shan Gong,
  • Di Song

摘要

The functional degradation of NiTi shape memory alloys (SMAs) poses a significant risk to their reliability in cyclic applications. This study utilizes Berkovich nanoindentation to quantitatively assess the microscale deformation properties of NiTi alloy subjected to different regimes of preceding macroscopic cyclic loading. The nanoindentation responses, including reduced modulus and depth recovery ratio, were examined as a function of maximum load (500–10000 μN) and loading rate (100–2000 μN/s). Results indicate that prior cyclic loading substantially diminishes local reversibility, with the depth recovery ratio dropping from approximately 50% in the virgin condition to about 43–48% in the degraded states. Variations in loading rate produced negligible alterations in the microscale characteristics compared to the predominant effect of functional degradation from cyclic loading. A definitive correlation was found between this microscale recovery measure and the macroscopic residual strain from uniaxial cyclic loading, connecting the decrease in reversibility at both scales to the accumulation of dislocation-based barriers during cyclic loading. This study confirms nanoindentation as an effective diagnostic method for investigating the functional fatigue from cyclic loading while recognizing the interpretive differences resulting from the intricate, localized deformation conditions beneath the indenter.