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).
展开▼
机译：从根本上说，材料流动应力在变形率超过典型值〜10 3 s -1 时呈指数增长，从而导致脆性破坏。这种行为的起源是由于位错运动引起的，由于声子相互作用的拖曳力，在较高的应变速率下导致了非阿累尼乌斯变形。在这里，我们发现，当微观结构的长度稳定在极细的尺寸（纳米尺度范围）时，这种假设就不会出现。这种对应变率不敏感的特性归因于独特的微观结构，该结构改变了平均位错速度和行进距离，从而防止/延迟了与声子的位错相互作用，直到应变率高于已知系统。因此即使在极端条件下也可以实现恒定的流应力响应。以前，由于其微结构的热和机械不稳定性，这些极限载荷条件在纳米晶体材料中是无法实现的。因此，从未在任何其他材料中观察到这些异常。最终，独特的稳定性使高温强度保持在熔点的80％（〜1356 K）。
展开▼
