Anomalous mechanical behavior of nanocrystalline binary alloys under extreme conditions.
Anomalous mechanical behavior of nanocrystalline binary alloys under extreme conditions.
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DOI：
10.1038/s41467-018-05027-5
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发表时间：
2018-07-12
影响因子：
16.6
通讯作者：
Solanki KN
中科院分区：
文献类型：
--
作者：
Turnage SA;Rajagopalan M;Darling KA;Garg P;Kale C;Bazehhour BG;Adlakha I;Hornbuckle BC;Williams CL;Peralta P;Solanki KN
从根本上讲，材料流动应力在变形率通常超过~103 s−1 时呈指数增加，导致脆性破坏。这种行为的起源源于位错运动，由于声子相互作用的阻力，在较高应变率下引起非阿累尼乌斯变形。在这里，我们发现当微观结构长度稳定在极细的尺寸（纳米级状态）时，这种假设就不会出现。这种发散的应变率不敏感行为归因于独特的微观结构，它改变了平均位错速度和行进距离，防止/延迟位错与声子的相互作用，直到比已知系统中观察到的应变率更高；因此即使在极端条件下也能实现恒定的流动应力响应。此前，由于纳米晶材料微观结构的热和机械不稳定性，这些极端负载条件是无法实现的。因此，从未在任何其他材料中观察到这些异常现象。最后，独特的稳定性使高温强度保持在熔点 (~1356 K) 的 80%。由于位错阻力，以非常高的速率变形的金属会经历流动应力的快速增加。在这里，作者稳定了纳米晶体微观结构，以抑制位错速度并限制阻力效应，在更高的应变率和温度下保留低应变率变形机制。
Fundamentally, material flow stress increases exponentially at deformation rates exceeding, typically, ~103 s−1, resulting in brittle failure. The origin of such behavior derives from the dislocation motion causing non-Arrhenius deformation at higher strain rates due to drag forces from phonon interactions. Here, we discover that this assumption is prevented from manifesting when microstructural length is stabilized at an extremely fine size (nanoscale regime). This divergent strain-rate-insensitive behavior is attributed to a unique microstructure that alters the average dislocation velocity, and distance traveled, preventing/delaying dislocation interaction with phonons until higher strain rates than observed in known systems; thus enabling constant flow-stress response even at extreme conditions. Previously, these extreme loading conditions were unattainable in nanocrystalline materials due to thermal and mechanical instability of their microstructures; thus, these anomalies have never been observed in any other material. Finally, the unique stability leads to high-temperature strength maintained up to 80% of the melting point (~1356 K). Metals deformed at very high rates experience a rapid increase in flow stress due to dislocation drag. Here, the authors stabilise a nanocrystalline microstructure to suppress dislocation velocity and limit drag effects, conserving low strain-rate deformation mechanisms up to higher strain rates and temperatures.
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