Nonbasal Slip Systems Enable a Strong and Ductile Hexagonal-Close-Packed High-Entropy Phase
Nonbasal Slip Systems Enable a Strong and Ductile Hexagonal-Close-Packed High-Entropy Phase
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非基底滑移系统可实现坚固且延展的六方密堆积高熵相
DOI：
10.1103/physrevlett.122.075502
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发表时间：
2019-02-22
影响因子：
8.6
通讯作者：
Yang, Wei
中科院分区：
文献类型：
--
作者：
Bu, Yeqiang;Li, Ziming;Yang, Wei
被称为位错的线性缺陷决定了晶体金属合金的强度、可成形性和韧性。对于由一种或两种普遍的基体元素组成的传统金属材料，如钢或铝合金，相关的变形机制是很好理解的。在最近发展起来的含有多个主元素的高熵合金中，位错与力学行为之间的关系还不太清楚。特别是具有六方密堆积（hcp）结构的HEAs由于其滑移系统的数量不足而可能遭受固有脆性。在这里，我们报告了一种新的高熵相与hcp结构的令人惊讶的高成形性。通过原位拉伸试验和透射电子显微镜的死后表征，我们发现双相HEA（Fe 50 Mn 30 Co 10 Cr 10，at. %）激活三种类型的位错，即，< a >，< c >和< c + a >。具体来说，非基底< c + a >位错占据了类似于31%的高线分数，允许频繁的双交叉滑动，这解释了这种高熵相的高变形性。hcp结构具有1.616的c/a比，即，低于理想值1.633。这种结构参数的适度变化促进了非基底< c + a >滑移，这表明具有hcp结构的韧性HEAs可以通过将c + a比转移到非基底滑移系统被激活的区域来设计。这种简单的合金设计原理特别适用于HEAs，因为它们的特征性大量固溶体含量容易允许将hcp相的c/a比调节到促进非基底滑移活化的状态。
Linear defects, referred to as dislocations, determine the strength, formability, and toughness of crystalline metallic alloys. The associated deformation mechanisms arc well understood for traditional metallic materials consisting of one or two prevalent matrix elements such as steels or aluminum alloys. In the recently developed high-entropy alloys (HEAs) containing multiple principal elements, the relationship between dislocations and the mechanical behavior is less understood. Particularly HEAs with a hexagonal close-packed (hcp) structure can suffer from intrinsic brittleness due to their insufficient number of slip systems. Here we report on the surprisingly high formability of a novel high-entropy phase with hcp structure. Through in situ tensile testing and postmortem characterization by transmission electron microscopy we reveal that the hcp phase in a dual-phase HEA (Fe50Mn30Co10Cr10, at. %) activates three types of dislocations, i.e., < a >, < c >, and < c + a >. Specifically, nonbasal < c + a > dislocations occupy a high line fraction of similar to 31% allowing for frequent double cross slip which explains the high deformability of this high-entropy phase. The hcp structure has a c/a ratio of 1.616, i.e., below the ideal value of 1.633. This modest change in the structure parameters promotes nonbasal < c + a > slip, suggesting that ductile HEAs with hcp structure can be designed by shifting the c + a ratio into regimes where nonbasal slip systems arc activated. This simple alloy design principle is particularly suited for HEAs due to their characteristic massive solid solution content which readily allows tuning the c/a ratio of hcp phases into regimes promoting nonbasal slip activation.