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首页> 外文期刊>Philosophical Magazine Letters >Implications from pre-straining experiments on emerging kink-based models for anomalous flow in Ll2 alloys
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Implications from pre-straining experiments on emerging kink-based models for anomalous flow in Ll2 alloys

机译：预应变实验对新兴的基于扭结的Ll2合金异常流动模型的影响

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We re-examine an experiment on the transient behaviour of NisAl which demonstrates that the anomalous flow stress is thermally reversible in the small-strain yielding regime. Further, we discuss the phenomenon within emerging kink-based models for the flow-stress anomaly in an effort to highlight critical aspects of these models which need further attention. Specimens from a Ni-22-9 at.% Al single crystal, having an orientation near (001), were pre-strained at 873 K and additionally strained at 300 K. The flow properties of this crystal were compared to those from a crystal strained at 300 K alone. Both crystals were examined using transmission electron microscopy. In the small-strain flow regime, the flow stress anomaly is reversible. Pre-straining at a higher temperature before room-temperature deformation shows little memory of the pre-straining during the yield transient, even though TEM observations show that many Kear-Wilsdorf locks are retained in the substructure. Microscopic examination also reveals the presence of a second dislocation structure, characteristic of the low-temperature deformation, in selected regions of thin foils from the pre-strained sample. This observation demands that some part of the substructure recovers extremely rapidly, if not instantly upon changing temperature and (or) unloading. We suggest that future models must consider the full behaviour of all dislocation loop characters and character junctions in accomplishing the thermally reversible transition from the elastic regime, through the microstrain regime, to flow.
机译：我们重新检查了NisAl瞬态行为的实验，该实验表明，在小应变屈服状态下，异常流动应力是热可逆的。此外，我们在新兴的基于扭结的模型中讨论了流动应力异常的现象，以突出这些模型的关键方面，需要进一步关注。来自Ni-22-9 at。％Al单晶的，取向接近（001）的样品在873 K下预应变，另外在300 K下应变。将该晶体的流动特性与晶体的流动特性进行了比较。仅在300 K时就紧张。使用透射电子显微镜检查两种晶体。在小应变流态下，流应力异常是可逆的。即使TEM观察表明许多Kear-Wilsdorf锁保留在子结构中，在室温变形之前在较高温度下进行预应变也不会在屈服瞬变期间对预应变进行记忆。显微镜检查还揭示了在预应变样品的薄片的选定区域中存在第二位错结构，该位错结构是低温变形的特征。该观察结果要求，即使在温度变化和（或）卸载后不是立即恢复，子结构的某些部分也会恢复得非常快。我们建议，将来的模型在完成从弹性状态到微应变状态到流动的热可逆转变时，必须考虑所有位错环字符和字符结的完整行为。

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