Reasons for the superior mechanical properties of medium-entropy CrCoNi compared to high-entropy CrMnFeCoNi
Reasons for the superior mechanical properties of medium-entropy CrCoNi compared to high-entropy CrMnFeCoNi
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DOI：
10.1016/j.actamat.2017.02.036
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发表时间：
2017-04-15
期刊：
影响因子：
9.4
通讯作者：
George, E. P.
中科院分区：
文献类型：
--
作者：
Laplanche, G.;Kostka, A.;George, E. P.
中熵合金CrCoNi的拉伸性能明显优于高熵合金crmnnfeconi。为了了解其优越的变形机制，在液氮温度（77 K）和室温（293 K）下对CrCoNi进行了拉伸试验，并在不同应变下进行了中断。透射电镜显微组织分析表明，在塑性初期，1/2 < 110 >位错在011平面上解离成1/6 < 112 >的肖克利部分发生滑动变形，与CrMnFeCoNi的行为相似。部分分离的测量结果显示，层错能为22 +/- 4 mJ m(-2)，比CrMnFeCoNi低25%。随着应变的增加，纳米孪晶作为CrCoNi的附加变形机制出现。晶粒尺寸为16 μ m的CrCoNi的临界剪切应力为260 +/- 30 MPa，与温度无关，与相似晶粒尺寸的CrMnFeCoNi相当。CrCoNi的屈服强度和加工硬化率均高于crmnnfeconi。因此，在CrCoNi中，孪生应力较早（在较低应变下）达到。这反过来又导致了更大的应变范围，纳米孪晶可以提供高、稳定的加工硬化，与高熵CrMnFeCoNi相比，中等熵CrCoNi具有优越的机械性能（极限强度、延展性和韧性）。(C) 2017材料学报Elsevier Ltd.出版。
The tensile properties of CrCoNi, a medium-entropy alloy, have been shown to be significantly better than those of CrMnFeCoNi, a high-entropy alloy. To understand the deformation mechanisms responsible for its superiority, tensile tests were performed on CrCoNi at liquid nitrogen temperature (77 K) and room temperature (293 K) and interrupted at different strains. Microstructural analyses by transmission electron microscopy showed that, during the early stage of plasticity, deformation occurs by the glide of 1/2 < 110 > dislocations dissociated into 1/6 < 112 > Shockley partials on 011) planes, similar to the behavior of CrMnFeCoNi. Measurements of the partial separations yielded a stacking fault energy of 22 +/- 4 mJ m(-2), which is similar to 25% lower than that of CrMnFeCoNi. With increasing strain, nanotwinning appears as an additional deformation mechanism in CrCoNi. The critical resolved shear stress for twinning in CrCoNi with 16 mu m grain size is 260 +/- 30 MPa, roughly independent of temperature, and comparable to that of CrMnFeCoNi having similar grain size. However, the yield strength and work hardening rate of CrCoNi are higher than those of CrMnFeCoNi. Consequently, the twinning stress is reached earlier (at lower strains) in CrCoNi. This in turn results in an extended strain range where nanotwinning can provide high, steady work hardening, leading to the superior mechanical properties (ultimate strength, ductility, and toughness) of medium-entropy CrCoNi compared to high-entropy CrMnFeCoNi. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.