摘要:
为了进一步探索间隙C原子对CoCrNi基中熵合金的应变率效应和温度效应的影响，系统地研究了由FCC基体和三级层级沉淀微观结构组成的CoCrNiSi0.3C0.048中熵合金在宽温域宽应变率范围内的压缩力学行为、微结构演化过程以及变形机理。/t/n℃下，其真应力-真应变曲线上观察到了锯齿流变现象，而且随着应变的增大，锯齿的振幅逐渐减小，直至消失。此外，其准静态下流动应力随温度的变化曲线上出现了反常应力峰（第三型应变时效现象），在高应变率下，第三型应变时效引起的反常应力峰消失。通过微观结构的表征分析，推测其准静态下出现第三型应变时效现象的主要原因可能是由于间隙C原子的存在，在塑性变形的不断进行和发展过程中，产生了一系列由致密位错胞、微带、层错、位错簇和变形孪晶等组成的类似于非均质结构的混合结构。这些混合结构加剧了间隙原子与移动位错之间的相互作用，进而钉扎位错，出现动态应变时效现象。在动态情况下并未出现第三型应变时效的原因可能是溶质原子的运动相较于位错的运动速度较慢，无法及时钉扎位错。另外，大量的纳米级SiC沉淀的析出弱化了动态加载下间隙原子的“钉扎”作用。
Abstract:
In order to further explore the influence of interstitial C atom on the strain rate effect and temperature effect of CoCrNi-based medium-entropy alloy, the compression mechanical behavior, microstructure evolution and deformation mechanism of CoCrNiSi0.3C0.048 medium-entropy alloy were systematically studied at a wide temperature and strain rate range./t/nThe investigated alloy is composed of FCC matrix and three-level precipitate microstructure, i.e. the primary Cr23C6 carbides (2 - 10 μm), the secondary SiC precipitates (200 - 500 nm), and the tertiary SiC precipitates (~50 nm). The results show that the serrated flow phenomenon is observed on the true stress-strain curve of the alloy at 400 ℃, and the amplitude of the serrations decreases gradually with the increase of strain until it disappears. In addition, the abnormal stress peak (the 3rd-type strain aging phenomenon) appears on the curve of the quasi-static flow stress with temperature, but at high strain rate, the abnormal stress peak disappears. Through the characterization and analysis of the deformed microstructure, it is speculated that the main reason for the phenomenon of 3rd-type strain aging under quasi-static conditions may be ac ascribe to the existence of interstitial C atoms. During the process of continuous plastic deformation and development, a series of mixed structures similar to heterogeneous structures are generated, which are composed of dense dislocation cells, micro bands, stack faults, dislocation clusters and deformation twins. These mixed structures intensify the interaction between interstitial atoms and moving dislocation, and then pin the dislocation, which results in dynamic strain aging phenomenon occurs. The reason why the 3rd-type strain aging does not appear under dynamic conditions may be that the movement of solute atoms is slower than that of the dislocation. The dislocation cannot be pinned in time. In addition, the precipitation of a large number of nanoscale SiC precipitates weakens the "pinning" effect of interstitial atoms under dynamic loading.
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