Dynamic recrystallization-induced temperature insensitivity of yield stress in single-crystal Al1.2CrFeCoNi micropillars
Dynamic recrystallization-induced temperature insensitivity of yield stress in single-crystal Al1.2CrFeCoNi micropillars
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DOI：
10.1007/s11431-020-1660-8
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发表时间：
2020-07-27
影响因子：
4.6
通讯作者：
Li XiaoYan
中科院分区：
文献类型：
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作者：
Huang RuiRui;Zhang Qian;Li XiaoYan
高熵合金是一类新型金属材料，在高温下表现出优异的机械性能。尽管引起了全世界的兴趣，但这些合金机械性能与温度相关的基本机制仍然知之甚少。在这里，我们通过使用微柱内部的原位压缩，系统地研究了具有三个取向（[100]、[110]和[111]）的Al1.2CrFeCoNi（包含体心立方相）和Al0.3CrFeCoNi（包含面心立方相）单晶微柱在300至675 K的温度下的力学行为和性能。扫描电子显微镜。结果表明，Al1.2CrFeCoNi微柱的屈服应力对温度变化不敏感，其流动应力和加工硬化率随着温度从300 K升高到550 K而略有增加，这与金属和合金中屈服/流动应力的典型温度依赖性不同。相比之下，Al0.3CrFeCoNi 微柱表现出典型的热软化。此外，发现Al1.2CrFeCoNi微柱在临界温度下表现出从均匀变形到局部变形的转变，而Al0.3CrFeCoNi微柱始终保持均匀且精细的滑移变形。详细的透射电子显微镜分析表明，动态再结晶（涉及位错缠结、位错单元结构和亚晶粒的形成）在所观察到的屈服应力的温度不敏感性和随温度升高而增加的 Al1.2CrFeCoNi 微柱中的流动应力（和加工硬化率）中起着关键作用，并且热激活的位错滑移导致 Al0.3CrFeCoNi 微柱的热软化。 Al1.2CrFeCoNi 和 Al0.3CrFeCoNi 之间的变形模式和机械性能的温度依赖性差异本质上源于位错活动和滑移系统的差异，因为两种合金采用不同的相。我们的研究结果为具有体心立方和面心立方相的高熵合金的机械性能和变形行为的温度依赖性提供了重要见解。
High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al1.2CrFeCoNi (comprising a body-centered cubic phase) and Al0.3CrFeCoNi (comprising a face-centered cubic phase) single-crystal micropillars with three orientations ([100], [110], and [111]) at temperatures varying from 300 to 675 K by usingin situcompression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al1.2CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to 550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast, Al0.3CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al1.2CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al0.3CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization (involving dislocation tangles, and formation of dislocation cell structures and sub-grains) plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress (and work hardening rate) with increasing temperature in the Al1.2CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al0.3CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al1.2CrFeCoNi and Al0.3CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.