近年来，研究人员打破传统的以单一主元为基础的合金设计理念，运用多种元素以等原子或近等原子比混合，成功制备出多种化学无序的“高熵合金”。这一类合金呈现出一系列优异的力学性能，在航天、国防等领域展示出广泛的应用前景。目前对高熵合金在不同服役环境，尤其是一些极端环境下的塑性流动行为及其背后的机理认识尚不充分，亟待开展进一步的相关工作。为此，本文针对CrMnFeCoNi高熵合金在不同极端条件下的塑性流动行为展开了研究，取得如下主要创新性进展：

（1）基于自主搭建的电化学系统，对高熵合金进行氢鼓泡原位生长观察，开展了充氢前后高熵合金的拉伸性能测试，并与传统合金进行对比，发现高熵合金在室温以及低温环境下均具备更优异的抗氢脆性能。运用SEM、TEM等显微电子观测技术，表征了各种材料充氢前后的断口形貌与微观变形结构，发现高熵合金主要以韧性断裂为主，而两种传统合金则存在一定程度的脆性断裂特征；微观变形结构方面，高熵合金形成更少的氢捕获点，抑制了氢在材料内部的富集，从而限制了氢脆机理的开动，使其具备更优异的抗氢脆性能。

（2）对高熵合金开展了在273 K、77 K与4.2 K温度下的准静态拉伸实验，发现其在4.2 K温度下出现显著的“锯齿状”塑性流动现象。运用TEM对不同温度下变形试样进行观察发现，“Lomer-Cottrell锁”对位错滑移的阻碍效应是造成材料塑性变形时应力集中的主要原因，而后续的位错滑移、变形孪晶、马氏体相变等过程则在一定程度上使材料内部发生应力松弛。结合热力学分析，证明上述过程的交替出现是造成材料在极低温下“锯齿状”塑性流动的主要原因。对4.2 K拉伸实验信号进行非线性动力学分析，证明了高熵合金在该极低温度下塑性变形时，位错群体行为具有混沌的动力学特征。

（3）基于CQ-4磁驱动斜波加载系统，实现了对高熵合金高达至30 GPa的准等熵加载；通过波形分析，首次获得了CrMnFeCoNi高熵合金的准等熵压缩曲线。通过设计动量陷阱装置，成功回收加载后的高熵合金薄片样品。通过XRD表征与EBSD观察，并未在加载后的样品中发现相变，从而证明该高熵合金具备稳定的晶体结构特征。不同加载压力样品的纳米压痕实验表明，加载后该合金的硬度显著提高。运用TEM技术对不同加载压力的样品进行观察，发现位错滑移与变形孪晶是高熵合金在准等熵加载下的主要塑性变形方式。

（4）运用压缩式挤压切削装置，对块体高熵合金进行大塑性变形处理，实现充分的晶粒细化；通过后续不同条件的退火工艺，实现了材料内部的部分再结晶。拉伸实验表明，经适当处理后的试样，其屈服强度大大提升，而均匀延伸率也得到不错的保留，这初步提升了材料的“强-韧”匹配性能。运用EBSD、TEM等显微电子技术，对不同预处理试样变形前后的微结构与组织进行观察，揭示了这些高熵合金的塑性变形机理。

In recent years, researchers have broken traditional concepts of alloy design, that they focused on mixing alloy elements in equiatomic or approximately equiatomic ratio instead of seeking for a single principle element. Accordingly, chemical disordered ‘high entropy alloy’ has been successfully prepared, which shows application prospect in fields of spaceflight and national defence. At present, plastic flow behaviors and the underlying mechanisms of high entropy alloys in different service environments, especially in some extreme ones, remain unclear and urgently need for further related research. Therefore, this work has studied the plastic flow behaviors of CrMnFeCoNi high entropy alloy under different extreme environments, and the main innovative developments are as follows:

1. Based on a self-designed electrochemical system, in-situ observation of growth of hydrogen bubble in high entropy alloy has been conducted, along with the tensile tests of high entropy and traditional alloys before and after hydrogen charging. The results indicate that high entropy alloy has better resistant to hydrogen embrittlement under both room and low temperatures. Based on SEM and TEM technologies, fracture morphologies and deformation microstructures for high entropy and traditional alloys have been characterized, which reveals ductile fracture for high entropy alloy while brittle fracture features exist in traditional alloys. With regard to deformation microstructure, less hydrogen trap sites were found in high entropy alloy, which inhibits the accumulation of hydrogen in materials and limits the hydrogen embrittlement mechanism, thus leading to its better resistance to hydrogen embrittlement.
2. Tensile tests of high entropy alloy at 273 K、77 K and 4.2 K have been conducted, which reveals a pronounced ‘serrated flow’ behavior when tensiled at 4.2 K. Ultizing TEM observation for the high entropy alloys tensiled at different temperatures, it is shown that the Lomer-Cottrell lock is the main reason that induces the stress concentration, while subsequently dislocation slip, deformation twinning and martensite transformation trigger the stress relaxation during the deformation of materials. Combined with thermodynamic analysis, it is proved that the alternating occurrence of the above process is the main reason for the ‘serrated flow’ behavior. By conduction nonlinear dynamic analysis on the tensile signals at 4.2 K, the collective behavior of dislocations is proved to be chaotic, during the high entropy alloy at this extremely low temperature.

(3) Based on a CQ-4 magnetic driven loading system, quasi isentropic compression of high entropy alloy up to 30 GPa has been conducted. By wave analysis, the isentrope of CrMnFeCoNi high entropy alloy was first obtained. Using a momentem trap device, the loaded specimens were succesfully reserved. After XRD characterize and EBSD observation, no phase transformation was found in the reserved specimens, indicating strong stability of crystal structure of this alloy. Nanoindentation experiments of samples with different loading pressures show that the hardness of the samples is significantly improved after loading. Using TEM observation, dislocation slip and deformation twinning is considered to be two main deformation mechanism for high entropy alloy under quasi isentropic compression.

(4) Based on a compression cutting extrusion machine, severe plastic deformation for high entropy alloy has been conducted, which produce a high degree of grain refinement. After anneal at different conditions, partial recrystallization has been produced in the material. Tensile tests indicate that, yield strength of the high entropy alloy after such treatment has largely increased, along with relatively good reservation of its uniform elongation, achieving the enhancement of strength-ductile matching properties. By EBSD and TEM technologies, the microstructures and organizations of high entropy alloy with different pretreatment were observed, revealing the corresponding plastic deformation mechanisms.