Uniting tensile ductility with ultrahigh strength via composition undulation
Uniting tensile ductility with ultrahigh strength via composition undulation
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通过成分波动将拉伸延展性与超高强度结合起来
DOI：
10.1038/s41586-022-04459-w
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发表时间：
2022-04-14
期刊：
影响因子：
64.8
通讯作者：
Sun, Jun
中科院分区：
文献类型：
--
作者：
Li, Heng;Zong, Hongxiang;Sun, Jun
具有纳米晶粒的金属具有接近2千兆帕斯卡的超高强度。然而，这种极端的晶界强化导致几乎所有拉伸延展性的丧失，即使金属具有面心立方结构——所有晶体结构中最具延展性的结构（1-3）。在这里，我们证明了纳米晶镍钴固溶体虽然仍然是面心立方单相，但其抗拉强度约为2.3千兆帕斯卡，延展性约为16%。这种不寻常的抗拉强度和延展性的组合是通过高浓度固溶体中的成分波动来实现的。这种波动使得层错能和晶格应变在空间上随长度尺度在1到10纳米范围内变化，从而使位错的运动受到显著影响。尽管纳米晶粒内部的空间非常有限，但位错的运动变得缓慢，促进了它们的相互作用、联锁和积累。这增加了流变应力，同时促进了位错的储存，从而增加了应变硬化，从而提高了塑性。同时，沿位错线的节段脱陷激活体积小，从而提高应变率敏感性，这也稳定了拉伸流动。因此，抵抗位错扩展的起伏景观提供了一种在高流动应力下保持拉伸延展性的强化机制。
Metals with nanocrystalline grains have ultrahigh strengths approaching two gigapascals. However, such extreme grain-boundary strengthening results in the loss of almost all tensile ductility, even when the metal has a face-centred-cubic structure-the most ductile of all crystal structures(1-3). Here we demonstrate that nanocrystalline nickel-cobalt solid solutions, although still a face-centred-cubic single phase, show tensile strengths of about 2.3 gigapascals with a respectable ductility of about 16 per cent elongation to failure. This unusual combination of tensile strength and ductility is achieved by compositional undulation in a highly concentrated solid solution. The undulation renders the stacking fault energy and the lattice strains spatially varying over length scales in the range of one to ten nanometres, such that the motion of dislocations is thus significantly affected. The motion of dislocations becomes sluggish, promoting their interaction, interlocking and accumulation, despite the severely limited space inside the nanocrystalline grains. As a result, the flow stress is increased, and the dislocation storage is promoted at the same time, which increases the strain hardening and hence the ductility. Meanwhile, the segment detrapping along the dislocation line entails a small activation volume and hence an increased strain-rate sensitivity, which also stabilizes the tensile flow. As such, an undulating landscape resisting dislocation propagation provides a strengthening mechanism that preserves tensile ductility at high flow stresses.