The present study investigates the superelasticity properties of spark plasma sintered (SPS) nickel titanium shape memory alloy (NiTi SMA) with the influence of sintering temperature and particle size. The nanoindentation is conducted on the surface of the NiTi SMA at various loads such as 100, 300 and 500mN. The nanoindentation technique determines the quantitative results of elasto-plastic properties such as depth recovery in the form of superelasticity, stiffness, hardness and work recovery ratio from load–depth (P–h) data during loading and unloading of the indenter. Experimental findings show that the depth and work recovery ratio increases with the decrease of indentation load and particle size. In contrast, increasing the sintering temperature exhibited a better depth and work recovery due to the removal of pores which could enhance the reverse transformation. The contact stiffness is influenced by dp∕dh which leads to attain a maximum stiffness at the highest load (500mN) and particle size (45μm) along with the lowest sintering temperature (700^∘C). NiTi alloy exhibited a maximum hardness of 9.46GPa when subjected to indent at the lowest load and particle size sintered at 800^∘C. The present study reveals a better superelastic behavior in NiTi SMA by reducing the particle size and indentation load associated with the enhancement of sintering temperature.

中文翻译：

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粒度和烧结温度对纳米压痕镍钛形状记忆合金超弹性行为的影响

本研究研究了放电等离子烧结 (SPS) 镍钛形状记忆合金 (NiTi SMA) 的超弹性性能受烧结温度和粒度的影响。纳米压痕是在表面进行镍钛合金在各种负载下，例如 100、300 和 500mN。纳米压痕技术确定弹塑性性能的定量结果，例如以超弹性、刚度、硬度和载荷-深度的工作恢复率形式的深度恢复（磷–H) 压头加载和卸载期间的数据。实验结果表明，随着压痕载荷和粒度的减小，深度和工作恢复率增加。相比之下，提高烧结温度表现出更好的深度和功恢复，因为去除了可以增强逆转变的孔隙。接触刚度受以下因素影响dp∕dH这导致在最高负载下获得最大刚度（500mN) 和粒径 (45μm) 以及最低烧结温度 (700 ^∘ C)。NiTi合金的最大硬度为9.46GPa 在最低载荷下经受压痕时，在 800 ^∘ C 下烧结时的颗粒尺寸。本研究通过降低与烧结温度提高相关的颗粒尺寸和压痕载荷，揭示了 NiTi SMA 中更好的超弹性行为。