Understanding the formation of twins and new grains (NGs) in B2 austenite NiTi alloys under shock loading is of significance and importance for its science insights and engineering applications. However, the formation of $\left\{112\right\}$ twin in austenite phase under shock loading is still controversial, and the NGs evolution under shock loading is unclear. {The EBSD characterizations and XRD analyses of the NiTi samples recovered from the shock experiments reveal that the main deformation modes include dislocations, twins, and new grains, etc. Similar phenomena are also obtained in our nonequilibrium molecular dynamics simulations (NEMD) for nanocrystalline NiTi (nc-NiTi) with limited-duration-pulse shock loading. Simulations confirmed that $\left\{112\right\}$ twins in austenite phase can be formed by successively gliding a displacement of $\frac{a}{3}$[111] on (${2}$11) plane.} It can occur in both shock compression and release stages, in addition, the grain boundaries (GBs) triple junction and the interaction of slip bands with different slip systems can serve as the nucleation of twins. Moreover, that the nanoscale rotational deformation (NRD) leads to the formation of NGs is found in our simulation of nc-NiTi, without experiencing the conventional disorder-recrystallization-grain refinement stages in the corresponding region. Related to shear stress $\tau$, the shock loading velocity U$_{\rm p}$ plays the key role in the formations of twins and NGs. {These early successes may hope to get some insights into the deformation mechanism of NiTi under shock loading.

中文翻译：

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冲击载荷下纳米晶NiTi的孪生和旋转变形

理解在冲击载荷下B2奥氏体NiTi合金中孪晶和新晶粒（NGs）的形成对于其科学见解和工程应用具有重要意义。但是，形成$\left\{112\right\}$在冲击载荷下奥氏体相孪晶仍然是有争议的，并且在冲击载荷下NGs的演化尚不清楚。{从冲击实验中回收的NiTi样品的EBSD表征和XRD分析表明，主要变形模式包括位错，孪晶和新晶粒等。在我们对纳米晶NiTi的非平衡分子动力学模拟（NEMD）中也获得了相似的现象。 （nc-NiTi），脉冲持续时间有限。模拟证实$\left\{112\right\}$ 可以通过连续滑动​​一个位移来形成奥氏体相孪晶 $\frac{\mathrm{一种}}{3}$[$ {2} $ 11）平面上的[111]。}它可以在冲击压缩阶段和释放阶段发生，此外，晶界（GB）三重结以及滑带与不同滑移系统的相互作用也可以作为双胞胎成核。此外，在我们对nc-NiTi的模拟中发现了纳米级旋转变形（NRD）导致NG的形成，而没有在相应区域中经历常规的无序重结晶晶粒细化阶段。与剪应力有关$\tau$，冲击载荷速度U $ _ {\ rm p} $在双胞胎和NG的形成中起关键作用。{这些早期的成功可能希望对冲击载荷下NiTi的变形机理有一些认识。