Abstract Molecular dynamics simulations are performed to study the thermally induced martensitic phase transformation (B2-B19′) of NiTi free-standing nanoparticles. We successfully reproduce the experimental observations that the martensitic transformation temperature decreases with reducing particle size and the martensite may form self-accommodated herringbone morphology. It is found that a core-shell structure with shell thickness of 0.3 nm (approximately equal to one unit cell) exists in NiTi nanoparticles and the B2-B19′ transformation is dominated by the core region. In addition, three detwinning manners are observed in the reverse martensitic phase transformation (B19′-B2) process. It is concluded that the suppression of B2-B19′ transformation in NiTi nanoparticles is due to the lack of nucleation sites and the size dependent martensitic morphology originates from the constraints of surface shell.

中文翻译：

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NiTi纳米颗粒对热致马氏体相变的尺寸影响

摘要 进行分子动力学模拟以研究 NiTi 独立式纳米粒子的热致马氏体相变 (B2-B19')。我们成功地再现了实验观察结果，即马氏体转变温度随着粒径的减小而降低，并且马氏体可能形成自调节的人字形形态。发现NiTi纳米颗粒中存在壳厚度为0.3 nm（约等于一个晶胞）的核壳结构，并且B2-B19'转变以核区为主。此外，在逆马氏体相变（B19'-B2）过程中观察到三种解孪方式。