New regime of homogeneous flow in the deformation map of metallic glasses: elevated temperature nanoindentation experiments and mechanistic modeling
New regime of homogeneous flow in the deformation map of metallic glasses: elevated temperature nanoindentation experiments and mechanistic modeling
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DOI：
10.1016/j.actamat.2004.09.005
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发表时间：
2004-12-01
期刊：
影响因子：
9.4
通讯作者：
Nieh, TG
中科院分区：
文献类型：
--
作者：
Schuh, CA;Lund, AC;Nieh, TG
通过对非晶合金Pd40Ni40P20和Mg65Cu25Gd10的纳米压痕实验，研究了非晶合金的塑性变形特征。使用定制的实验装置，纳米压痕实验已经进行了超过四十年的压痕应变速率和从环境温度到玻璃化转变，允许快速评估的广泛的变形图，只有小体积的实验材料。在低速率和低温度下，由于单个剪切带的离散操作，观察到不均匀或锯齿状流动。可以确定两种不同的均质流状态。第一，预期，制度的均匀流对应于在高温和低速率的粘性变形的发病，并很好地描述了现有的机械模型。第二均匀制度发生在高变形率甚至远低于玻璃化转变，并出现时，变形率超过剪切带成核的特征速率，动力学迫使应变分布。通过扩展现有的玻璃变形模型，探讨剪切带成核动力学，这第二个政权定量合理化和剪切带成核的自然频率从数据中提取。从这个分析的临界半径的剪切带，因为它从成核过渡到传播估计是在亚微米范围内。(C)2004 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
The character of plastic deformation in metallic glasses is investigated through instrumented nanoindentation experiments on amorphous Pd40Ni40P20 and Mg65Cu25Gd10. Using a customized experimental apparatus, nanoindentation experiments have been conducted over four decades of indentation strain rate and from ambient temperature up to the glass transition, allowing rapid evaluation of an extensive deformation map with only small volumes of experimental material. At low rates and temperatures, inhomogeneous or serrated flow is observed, owing to the discrete operation of individual shear bands. Two distinct regimes of homogeneous flow can be identified. The first, expected, regime of homogeneous flow corresponds to the onset of viscous deformation at high temperatures and low rates, and is well described by existing mechanistic models. The second homogeneous regime occurs at high deformation rates even well below the glass transition, and arises when deformation rates exceed the characteristic rate for shear band nucleation, kinetically forcing strain distribution. By extending an existing model for glass deformation to explore shear band nucleation kinetics, this second regime is quantitatively rationalized and the natural frequency for shear band nucleation is extracted from the data. From this analysis the critical radius of a shear band as it transitions from nucleation to propagation is estimated to be in the submicron range. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.