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<p>Ni content has a significant effect on martensitic transformation behaviour and tensile mechanical properties of Ni-rich NiTi shape memory alloys. In this study, the effect of grain size on sensitivity of tensile mechanical properties to Ni content of nanocrystalline NiTi alloys was investigated. Two NiTi alloys with nominal compositions of Ni-49.6 at %Ti and Ni-48.8 at %Ti were cold drawn into 21%−72% deformations, followed by annealing at 350 − 450 ºC. Nanocrystalline NiTi alloys were acquired when cold drawing strain was larger than 62% after annealing and average grain size that smaller than 20&#xa0;nm was acquired when annealed at 350 ºC. The results of tensile mechanical properties suggest that sensitivity of upper plateau stress to Ni content decreased with the decreasing grain size. When grain size was smaller than 20&#xa0;nm, the upper plateau stress of samples with different Ni content were close, which may be attributed to the Ni concentration at grain boundaries. When cold drawing strain was smaller than 52%, the sensitivity of stress hysteresis to Ni content of 350 ºC annealed samples decreased, which is attributed to the high-density dislocations in grains.</p> <!--Query ID="Q1" Text="Kindly note that Fig. 9 and Graphical Abstract figure are same. Please check and confirm." Resolved="yes"--> Graphical Abstract <p></p>

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Grain Size Effect on Sensitivity of Pseudoelasticity to Ni Content of Nanocrystalline NiTi Alloys

  • 期刊论文

  • 发表日期：

    2025年7月7日

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  • Penghui Li,
  • Xiaobin Shi,
  • Ping Liu

摘要

Ni content has a significant effect on martensitic transformation behaviour and tensile mechanical properties of Ni-rich NiTi shape memory alloys. In this study, the effect of grain size on sensitivity of tensile mechanical properties to Ni content of nanocrystalline NiTi alloys was investigated. Two NiTi alloys with nominal compositions of Ni-49.6 at %Ti and Ni-48.8 at %Ti were cold drawn into 21%−72% deformations, followed by annealing at 350 − 450 ºC. Nanocrystalline NiTi alloys were acquired when cold drawing strain was larger than 62% after annealing and average grain size that smaller than 20 nm was acquired when annealed at 350 ºC. The results of tensile mechanical properties suggest that sensitivity of upper plateau stress to Ni content decreased with the decreasing grain size. When grain size was smaller than 20 nm, the upper plateau stress of samples with different Ni content were close, which may be attributed to the Ni concentration at grain boundaries. When cold drawing strain was smaller than 52%, the sensitivity of stress hysteresis to Ni content of 350 ºC annealed samples decreased, which is attributed to the high-density dislocations in grains.

Graphical Abstract