Grain boundary plasticity in nanocrystalline alloys: Transition to glassy behavior?

该项目的目标是在纳米尺度(10 Nm)的低端揭示纳米晶(NC)PdAu合金中共存变形模式的协同性和层次性。我们特别强调识别和量化不同的弹性和塑性应变承载变形机制的份额的演变。在集合论的精神下，我们已经能够确定晶界介导的变形机制对NC PdAu合金的总应变的贡献占主导地位。大量的证据表明，剪切变形(ST)是无序介质中的本征流动事件，应该是晶界上活跃的和主要的变形方式。事实上，我们发现ST主导着宏观变形行为。通过对NC Pd90Au10阻挡层高度标度的应力相关性研究，推导出材料应力应变率响应的标度关系，推测该粘塑性材料定律应具有普适性。这一建议的主要信任依赖于证实这一猜测。由于观察到的势垒高度缩放的应力依赖是各种无序介质的特征，因此似乎也可以直接研究一下，并弄清楚普遍的粘塑性材料反应是否占优势。

The goal of this project is to unravel the synergy and hierarchy of coexisting deformation modes in nanocrystalline (nc) PdAu-alloys at the low end of the nanoscale (< 10 nm). We put special emphasis on identifying and quantifying the evolution of shares of different elastic and plastic strain carrying deformation mechanisms. In the spirit of set theory, we have been able to identify that grain boundary mediated deformation mechanisms contribute in a dominant manner to overall strain in nc PdAu-alloys. We gathered ample evidence that shear tranformations (ST), the intrinsic flow event in disordered media, should be the active and dominant deformation mode in grain boundaries. In fact, we find that ST dominate the macroscopic deformation behavior. Based on a study of the stress dependence of the barrier height scaling in nc Pd90Au10, we could deduce a scaling relation for the stress strain-rate reponse of the material and conjecture that this viscoplastic material law should have universal character. The main trust of this proposal relies upon corroborating this conjecture. Since the observed stress dependence of barrier height scaling is a signature of quiet a variety of disorderd media, it seems straightforward to also look into nanglasses and figure out whether or not the universal viscoplastic material response prevails.