ABSTRACT Despite a large body of literature, mechanisms contributing to low temperature jerky flow remain controversial. Here, we report a cross-over from a smooth at room and liquid nitrogen temperatures to serrated plastic flow at 4.2 K in high-entropy CrMnFeCoNi alloy. Several complimentary investigations have been carried out to get a coherent physical picture of low temperature jerky flow in these alloys. Microstructural characterisations at 77 K and 4.2 K show that the number of Lomer-Cottrell (L-C) locks at 4.2 K is much higher than that at 77 K, inducing stronger barriers for dislocation glide at 4.2 K. A stability analysis shows that the jerky flow results from an interaction between dislocation inertial motion with L-C locks. The instability results from a competition between inertial and viscous time scales characterised by a Deborah number. A detailed nonlinear time series analysis of experimental serrated stress signals shows that jerky flow is chaotic characterised by the existence of a finite correlation dimension and a positive Lyapunov exponent. Further, the minimum degree of freedom required for the chaotic dynamics turns out to be four, consistent with four collective modes degrees of freedom used in our model equations. These results highlight the crucial ingredients for jerky flow at liquid helium temperatures.

中文翻译：

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极低温下高熵合金中急流的时空动力学

摘要 尽管有大量文献，导致低温急动流的机制仍然存在争议。在这里，我们报告了在高熵 CrMnFeCoNi 合金中从室温和液氮温度下的平滑过渡到 4.2 K 的锯齿状塑性流动。为了获得这些合金中低温急动流动的连贯物理图片，已经进行了一些补充研究。77 K 和 4.2 K 的微观结构特征表明，4.2 K 的 Lomer-Cottrell (LC) 锁的数量远高于 77 K 的数量，从而在 4.2 K 时产生更强的位错滑移障碍。稳定性分析表明，湍流位错惯性运动与 LC 锁之间相互作用的结果。这种不稳定性源于以德博拉数为特征的惯性和粘性时间尺度之间的竞争。实验锯齿应力信号的详细非线性时间序列分析表明，急流是混沌的，其特征是存在有限的相关维数和正的李雅普诺夫指数。此外，混沌动力学所需的最小自由度为 4，与我们模型方程中使用的四种集体模式自由度一致。这些结果突出了液氦温度下急动流动的关键因素。混沌动力学所需的最小自由度为 4，与我们模型方程中使用的四种集体模式自由度一致。这些结果突出了液氦温度下急动流动的关键因素。混沌动力学所需的最小自由度为 4，与我们模型方程中使用的四种集体模式自由度一致。这些结果突出了液氦温度下急动流动的关键因素。