Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes
Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes
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通过有序氧配合物增强高熵合金的强度和延展性
DOI：
10.1038/s41586-018-0685-y
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发表时间：
2018-11-22
期刊：
影响因子：
64.8
通讯作者：
Lu, Zhaoping
中科院分区：
文献类型：
--
作者：
Lei, Zhifeng;Liu, Xiongjun;Lu, Zhaoping
氧是地球上最丰富的元素之一，在金属材料中经常形成不需要的间隙杂质或陶瓷相(如氧化物颗粒)。即使氧掺杂增加了强度，它也会使金属变脆1-3。在这里，我们表明，氧可以采取有序氧络合物的形式，在氧化物粒子和频繁出现的随机间隙之间的一种状态。与传统的间隙强化4，5不同，这种有序间隙复合体在成分复杂的固溶体，即所谓的高熵合金(HEAs)6-10中，导致了前所未有的强度和塑性的提高。当掺杂含2.0原子%氧的TiZrHfNb HEA模型时，抗拉强度提高(48.5+/-1.8%)，延展性显著改善(95.2+/-8.1%)，从而打破了长期存在的强度-塑性权衡11。氧配合物是HEA中的有序纳米区域，其特征是(O，Zr，Ti)富原子络合物的形成，这种形成是由于HEA中一些替代基质元素之间存在化学短程有序化而促进的。据报道，碳可以通过降低层错能和增加晶格摩擦应力来同时提高面心立方HEAs12的强度和塑性。相反，本文描述的有序间隙复合体通过在变形过程中形成Frank-Read源(一种解释多个位错产生的机制)，将位错剪切模式从平面滑移转变为波状滑移，并促进双交叉滑移，从而促进位错增殖。这种有序的间隙络合物介导的应变硬化机制在含钛、锆和含Hf的合金中尤其有用，在这些合金中，由于间隙元素的脆化效应，间隙元素是非常不受欢迎的，并且在调整层错能和利用非热转变13不会导致性能改善的合金中。这些结果为深入了解间隙固溶体在金属材料中的作用和相关的有序化强化机制提供了依据。
Oxygen, one of the most abundant elements on Earth, often forms an undesired interstitial impurity or ceramic phase (such as an oxide particle) in metallic materials. Even when it adds strength, oxygen doping renders metals brittle1-3. Here we show that oxygen can take the form of ordered oxygen complexes, a state in between oxide particles and frequently occurring random interstitials. Unlike traditional interstitial strengthening4,5, such ordered interstitial complexes lead to unprecedented enhancement in both strength and ductility in compositionally complex solid solutions, the so-called high-entropy alloys (HEAs) 6-10. The tensile strength is enhanced (by 48.5 +/- 1.8 per cent) and ductility is substantially improved (by 95.2 +/- 8.1 per cent) when doping a model TiZrHfNb HEA with 2.0 atomic per cent oxygen, thus breaking the long-standing strength-ductility trade-off11. The oxygen complexes are ordered nanoscale regions within the HEA characterized by (O, Zr, Ti)-rich atomic complexes whose formation is promoted by the existence of chemical short-range ordering among some of the substitutional matrix elements in the HEAs. Carbon has been reported to improve strength and ductility simultaneously in face-centred cubic HEAs12, by lowering the stacking fault energy and increasing the lattice friction stress. By contrast, the ordered interstitial complexes described here change the dislocation shear mode from planar slip to wavy slip, and promote double cross-slip and thus dislocation multiplication through the formation of Frank-Read sources (a mechanism explaining the generation of multiple dislocations) during deformation. This ordered interstitial complex-mediated strain-hardening mechanism should be particularly useful in Ti-, Zr-and Hf-containing alloys, in which interstitial elements are highly undesirable owing to their embrittlement effects, and in alloys where tuning the stacking fault energy and exploiting athermal transformations13 do not lead to property enhancement. These results provide insight into the role of interstitial solid solutions and associated ordering strengthening mechanisms in metallic materials.