Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off
Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off
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DOI：
10.1038/nature17981
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发表时间：
2016-06-09
期刊：
影响因子：
64.8
通讯作者：
Tasan, Cemal Cem
中科院分区：
文献类型：
--
作者：
Li, Zhiming;Pradeep, Konda Gokuldoss;Tasan, Cemal Cem
几千年来，金属一直是人类最基本的材料;然而，它们的使用受到生态和经济问题的影响。具有更高强度和延展性的合金可以通过减轻重量和提高能源效率来减轻这些担忧。然而，大多数用于增加强度的冶金机制导致延展性损失，这种效应被称为强度-延展性权衡（1，2）。在这里，我们提出了一个亚稳态工程策略，我们设计的纳米结构，散装高熵合金与多个组成等价的高熵相。最初提出高熵合金是为了通过熵最大化（3-6）从相稳定中受益。然而，在这里，最近的工作通过证明这种联系的弱点（7-11）放松了对高熵合金成分的严格限制，这一概念被推翻了。我们降低相稳定性以实现两个关键益处：由于双相微观结构导致的界面硬化（由高温相的热稳定性降低引起（12））;和相变诱导硬化（由室温相的机械稳定性降低引起（13））。这结合了两个世界中的最好的：由于先进钢（14，15）的相稳定性降低而导致的广泛硬化和高熵合金（3）的大规模固溶强化。在我们的相变诱导塑性辅助的双相高熵合金（TRIP-DP-HEA）中，这两个贡献分别导致增强的跨晶和晶间抗滑移性，并因此增加强度。此外，通过稳定相的位错硬化和亚稳相的相变诱导硬化实现的增加的应变硬化能力产生增加的延展性。这种强度和延展性的组合增加将TRIP-DP-HEA合金与其他最近开发的结构材料区分开来（16、17）。因此，这种亚稳性工程策略应该可以有效地指导高熵合金近乎无限的成分空间的设计。
Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off(1,2). Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization(3-6). Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection(7-11), the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase(12)); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase(13)). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels(14,15) and massive solid-solution strengthening of high-entropy alloys(3). In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials(16,17). This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys.